Pros and Cons of home shop CNC

[Jasonb]

Prompted by some comments on my James Coombes thread I thought I would start another for general discussions about the use of CNC machines in the home workshop.

The point raised was about how long it takes to machine a part compared to castings . This can have several different answers.

If the casting is readily available and assuming no hard spots, defects such as being undersize or having bosses that don't line up with hole positions then generally machining the casting would take less time as you may simply need to flatten the top & bottom and drill/tap a few holes if we take a typical sole plate or bed casting as an example. But if a lot of fettling and reworking is required then time differences will start to reduce

On the other hand if you are making something to your own design or replicating an old long out of production model then using the CNC to cut from solid will quite probably be quicker than making your own patterns, having castings done if you don't have your own facilities and then there is the actual machining to be added on so in this case the CNC is likely to come out the quickest. Though for those that do want to use castings the CNC is just as happy machining wooden, plastic or even metal patterns and can be quicker than traditional woodworking methods as well as very accurate.

It was then questioned how machining a part on the CNC compared to a built up fabrication. This is another where there is no easy answer as each part will be different and depending on what the user has to hand in the way of materials and machines will dictate what is best for them to produce the part in question. Some parts will be better suited to cutting from solid, others better built up with manually machined parts but a lot of the time a combination of the two works out to be the best option using the CNC for things that it is best at like cutting curved components for the fabrication, the lathe to do round parts and maybe the manual mill for simple flat, square and rectangular bits.

The CNC's ability to cut quite complex shapes from solid can also be an advantage where a specific material is required. For example it is easy to silver solder a steel fabrication together but what if you want that crankcase to be aluminium or cylinder head in iron both of which are not so easy to join. So the CNC will be faster than manually carving the part from solid.

I'm probably in a bit of a unique situation, I was originally approached a few years ago asking if I would like a KX-1 size mill. After giving it some thought I said now based on what I had seen at a couple of shows where the guys demonstrating their CNC machines seemed to take an age to perform the simplest of 2D operations that I could have done in a fraction of the time on a manual machine. I also did not fancy having to learn "G-Code" that I had heard about and it all seemed quite daunting.

Moving on a couple more years I was again asked if I would like a CNC, this time the larger KX-3, this one being a customer return. by this time I'd seen a bit of CAM in use and was more proficient at CAD so decided to take up the offer, after all it was only going to cost me a Mach licence and reconditioned PC so no great loss if I did not like it.

Most will have seen my Darkside thread about my journey into CNC and having used it now for a couple of years I'm glad I accepted the offer. Although I still enjoy using the manual machines the CNC is really just another tool and I tend to use it for the things it excels at and don't have any intension of going over to a fully CNC workshop though it does seem to work for others.

To be continued

[Jasonb]

Carrying on with the time question there are also some other factors that should be considered.

At the moment you can't just go out and buy or download the code that the CNC needs to produce a part let alone a whole model. So you need to produce a 2D or more often these days a 3D model of the required part, not really an additional time addition for me as I was designing or redrawing existing designs to be built on the manual machines before I got the CNC. However if you are used to working from others plans then you will need to draw these up in CAD which depending on how proficient you are will add time to the overall picture.

But that is not all, once you have your part drawn you need to tell the CNC how to machine it, some may choose to do this by writing out the G-code themselves which depending on teh complexity of the part could be a few lines or thousands. However I think anyone venturing down the CNC route these days will opt to use some form of CAM which simplifies the production of the G-code. This is the way I have done it from the start and with all the items I have produced have not written a single line of G-code so don't let the thought of it put you off like it did for me.

Even with CAM you do still need to have an understanding of milling as the CAM although it may have some presets for various cutters and materials will need to have these tweaked to suit the users individual machine and the cutters you actually have.

Which brings us nicely onto another variable that has a big effect on how long a job may take on the CNC, which is the capability of the various machines. In the home workshop machines are likely to fall into three catagories. Gantry type router, converted manual or purpose made machine.

The gantry machines often fitted with small DC motors at the smaller end of the scale through routers to spindle motors at the top of the range. These can often be the cheapest option into CNC but are often of fairly lightweight construction so are not that efficient at cutting metal particularly steel or iron. If you do want to cut metal with these particularly the entry level ones then very light cuts are needed which means the cutter has to make many passes so the run time can become very long.

Converted machines suit quite a few particularly if you are able to build them up yourself. Being based on manual mills they will have the rigidity to cut all metals. Their biggest downfall is likely to be maximum spindle speed which will have an effect on feed rates for a given chip load. For example the majority of manual mills are likely to have a spindle that can run up to around 2000rrpm, maybe not too bad if you just want to profile a piece of sheet to a fancy shape with HSS tools but when it comes to using smaller diameter tools to machine complex three dimensional curved surfaces then these slow feed rates will see the converted machine needing to be run for a long time to complete a part. Though there are some benchtop mills on the market now with spindle speeds of 5000rpm which would be ideal for conversion and using carbide tooling

Purpose design machines are going to be the fasted option be that a new machine or an old one with updated software, drivers etc. These will generally be solidly built with spindle speeds of 5-10Krpm which allows faster feed rates and would reduce machining times to 20-40% of a typical converted manual mill.

Whatever type of mill CNC is being used in the home workshop it is unlikely to be able to perform like a commercial machining centre due to a combination of rigidity and power so metal removal rates will be less than they can manage. Comparing like for like size machines a CNC one is likely to be able to remove metal faster than a manual one not least because you can't physically wind the handles fast enough but also the tool is always on the move even at corners or other changes of direction. For example if you manually machine out a rectangular pocket you are likely to slow down your hand feed as you approach each corner watching the DRO readout, lock one axis , unlock the other and then go through the same again for the next side. The CNC will move constantly from one instant change of direction to the other and there is no risk of it overrunning which is all too easy on the manual machine. The added bonus is that you don't end up with the tool rubbing as it slows into to the corners which wears the tool.

Enough for now, hopefully a few others with CNC will chip in or if you don't have one feel free to ask any questions.

M

[Jo]

Lots of words there JB  

In the beginning: Some stuff for model engines was originally made with castings, some stuff would be a difficult casting (like a table with the fancy bits that chill) and they can be made up in layers. Some members make some amazing stuff by twiddling the handles on their manual machines (Crueby, gbritnell, Ramon to name a few). All models have other bits that are made using a lathe or milling machine manually.

And then the world changed... We gained CNC  We now have members like Vixen building really complex model engines using their stable of CNC milling machines  And others like Jason using his to make models which would previously been done by more traditional means. I can't recall anyone showing off their CNC lathe (I know Vixen was looking in to it). I assume these models also require bits made by traditional hand milling/turning


So what are the good points, the bad points and the ugly points of CNC? This is a comparison with other more traditional techniques for making a one off model for a hobby not as a business.

I know that Vixen claims his CNC can be very Artistic  and applies features to his parts to keep him on his toes.

I am going to claim price is an Ugly point 

Jo

[Jasonb]

I'm sure I have seen Vixen's Emco based CNC lathe in action in a number of his posts

[vtsteam]

I have a fairly eclectic view since I both cast and have some cnc facilities, but have never bought a casting. And that view is, I do what is pleasurable to me. I do love to cast metal, and I do love to make patterns, so I don't account the time involved as getting in the way of what I want to accomplish.

I can't say I enjoy CNC milling, but then I don't really enjoy hand milling much either. That's just personal. I do love working with the lathe, and I am quite certain I don't want to convert my lathe to CNC, because that would (for me) take the fun out of it and the challenge.

Because I have no call for production, repetition with the lathe isn't generally needed. I imagine if I were into production, all would be different.

I will say (and it takes a reversal of a former "attitude" on my part) that I did enjoy making my first pattern using a 3D printer this fall, BUT, I still did a lot of hand work with that, including filling sanding and painting. AND, I have no wish to eliminatethe extra time they involve either. Those are tasks that I put into every pattern, and I actually like them, and the final result.

What I liked about the 3D printed pattern was being able to make a relatively thin pattern with a hollow torroidal shape -- which would have been very difficult to execute in wood. I would never however want to stop making wooden patterns that are easier conventional shapes. I am through long practice, very fast at making and finishing a pattern, as well as casting. I can make a simple pattern, fill, sand, paint and have cast it in about 4 hours when I'm really interested. And I like all aspects of that. A small 3D printed pattern takes much longer -- at least the first one I tried did, but its complexity made it advantageous.

So, conclusion? Uh well frankly I like both oranges and apples, and I don't think one will ever replace the other for me because they are different. I do particularly enjoy manual skills, and do not want a computer to do things for me in general, but I also appreciate the option to do some complex things with assistance from CNC, as long as it doesn't take over as a substitute for my actually physically making things.

As for my opinion of others work in CNC. I absolutely enjoy seeing good work, by whatever method, and have been truly amazed at some of the models I've seen here. I know how much work, programming, foresight, research, skill, goes into making those models, and I honor them no less than I do pure manual works.

To me it's all about each person finding the niche they enjoy the most, and I'm frankly glad we're all a bunch of individuals with different joys in what we do. I am nowhere near as skillful as many people here, and yet I see that here, we all seem to appreciate the full range of abilities, experience, and personal interests we express in the works we show here.

[Kim]

Well said, Steve!  I tend to agree with what you said there.

I also like what Jason said - CNC is a tool, and if you have it, it's a great way to do some things.  Some people (like Williy) like to use files and hand saws for as much of his work as possible.  For me, that wouldn't be fun.  While I have those tools, and I use them from time to time, I don't do all may shaping with files and hand saws.  CNC is no different.  If you have the tool there are many great ways it can be used!  It is, however, a tool that requires a steep learning curve.

My closest brush with CNC is a 3D printer.  Has a lot of the similar up front CAD and gcode issues of CNC, and has a pretty steep learning curve for it to become useful.  But it's great for some things.  Plus, (and this is the most important part, which ties in with what Steve said) I'm having a lot of fun learning it and using it!

Maybe someday, I'll get into CNC.  But for now, I'm happily enjoying working with the manual machines that I have now.

Interesting discussion. 

Beyond Steve's point about it being all about fun (which it is) I'm fascinated to hear the thoughts of people on when CNC is the right tool for the job.  Maybe it will convince me that I have to get into CNC next. 

Kim

[Dave Otto]

I really enjoy the whole CNC process, CAD, CAM, and running parts. I got into CNC about 24 years ago by purchasing a kit and converting my Bridgeport clone mill. This was a stepper based kit and only 2 axis. I taught myself to run it and also how to use a really early version of BobCAD. I ran this way for around 10 years and made lots of parts with that setup. I always dreamed of having a full 3 axis machine so I started planning, buying parts and fabricating new hardware. Attached are some pictures of my control setup. I was able to purchase a second hand Elrod quill drive unit that bolted right up to my machine. Part of the upgrade was to ditch the noisy slow stepper motors and replace them with servo motors.

I guess the one con that I can think of is this is my only mill so everything I do, I have to do it on the CNC. But you do get used to using the jog control for quick jobs or entering a few lines of G code.

Yes and you can machine castings using the CNC, My Pacific, Essex and now KyKo engines are all done on my CNC mill.

I don’t have a lot of need for a CNC lathe in my home shop. I do have access to one at work and have used it to make a few engine parts, but they could have also been done on my manual at home.

Dave

[Woodguy]

One point to note in favor of home shop cnc. Taking as an example the MEM corliss cylinder block. While I drilled and tapped every hole manually, preferring to "feel" the operations, All the positioning was done rapidly and accurately by cnc.


I got into cnc because I wanted power feeds on all axes of my SX3 mill. By the time one adds up the cost, it wasn't a lot more to cnc convert the thing.  I still use the mill manually but I push a button - no crank turning.

[Mike R]

I fall into the “conversion” camp, with both a mill and a lathe.
The mill came first about 12 years ago.  I'd had a 3-in-1 lathe and mill/drill and wanted something more so I bought a large “bench top” mill and converted it right away to cnc.  It was partly for the challenge of doing it, partly cause I wanted a cnc mill and couldn't afford the single shot cost of a commercial mill. Back then a Tormach 1100 being the comparable size I wanted was over $20000 delivered in local bucks. In the end I had an all in conversion cost of ~ $4000 so that much was a success.  I've subsequently probably put another $1000 or so on incremental improvements and add-ons (but I don't keep track on purpose).
Later on I picked up a small Emco Compact 5 CNC lathe, and while its controls worked, they were too antiquated to work with newer software (tape drive for programs) so I updated its control system to be the same as the mills (only need to learn 1 control system).
I learned a great deal doing the conversion, and have become very familiar with various pros and cons of different aspects of small / hobby CNC machines.
I will say up front – doing a conversion of a machine can be a significant project in its own right, especially for larger machines and if you have no prior experience or mentor.
Honestly I enjoy doing it so much I'd convert more machines, except for the cost and lack of space!
As far as usefulness – I had (still have) the goal of making a 1/6 scale 9 cylinder radial. Lots of interesting geometry and repetitive operations that I thought CNC would be great for (and is!).
For the mill, I kept the quill and still use it to hand feed drills when I don't want the CNC doing it as I haven't a clue to the correct feed rate.  And its nice to use it to position things (bolt circles) for tapping by hand.
As I learn, I'm becoming more pragmatic and some things I just do manually as opposed to setting up a program.  One issue is having access to a decent CAD / CAM program.  That is where there's lots of time savings to be had as an amateur that doesn't use it frequently.  I'm sure that if I used it more I'd learn more tricks to be faster in programming but for now I'm pretty slow.  Also, not to turn this thread into a what software to use discussion but I'm leaning towards buying Alibre Workshop bundle (Alibre Atom and MeshCam) at the moment as a way of escaping from Fusion360 ever dwindling free offering. It looks like the 3-axis CAM (Meshcam) is really easy – so hopefully that makes it easier to get off the PC and hop into the shop to make stuff.
I won't go into the gory details of the conversions here, but I can create a thread if anyone's interested.
Mill is a clone of the Rong-Fu 12Z  travels 24”X ,9”Y , 18”Z after conversion.
Control system is MESA 7i76E card and LinuxCNC V2.8
Lathe – Emco Compact 5
Control is also the MESA 7i76E and LinuxCNC V2.8

 
So getting back to Pros and Cons:
Pros
 

• built in DRO when using manually, easy to return to know positions (don't need to count the handle turns!)
• Can program up curves and other difficult or impossible to manually machine shapes
• Make repetitive tasks easier / more reliable (added 4th axis for gear cutting)
• can help improve surface finish by having a very steady and appropriate feed rate.
• Can pretty much do everything a manual machine can – except provide tactile feedback to the user.

Cons
 

• Faster and more efficient breakage of end mills
• Faster conversion of bar stock to scrap metal
• Giant rabbit hole to get sucked into learning about everything cnc (feed rates, machine rigidity, steppers vs servos, control systems, CAM, CAD, spindle speeds, VFDs, 4th axis, etc.)
• no tactile feedback – need to learn feeds and speeds to keep scrap / tool breakage low.
• No avantage to CNC for many one off, relatively straight forward operations (though “conversational” programming at the mill can help speed up things)

[mikemill]

I have enjoyed being a model engineer for over 50 years, I bought my X3 CNC mill eleven years ago and enjoyed using it ever since.
I now build G3 model railway engines (can’t fit any more 5inG engines in the house)

Using CNC allows me to buld models that would cost many thousands for a few hundred, the whole process of researching the prototype, drawing the parts, machining them and final assembly is a joy.

Yes, the initial cost of a CNC mill is high but you will get your money back many times over by creating models that are not commercially available and just sheer enjoyment, after all that why we peruse the hobby.

Mike

[Alex]

I've seen MikeR's work, and workshop, and it's great. As is his work.

I've been CNC'd at home (mills, lathe(s)) since 2010 or 2011. All LinuxCNC based; even my KX1.

I don't understand why more people don't CNC mill. I do have 1 manual mill still (a Centec 2B) that I use sometimes, but honestly, I use one of my CNCs more, even if manually milling or drilling. For instance, drilling 0.025" holes in steel/Bronze last night, did it on one of my CNCs, with one of those spring-loaded sensitive drilling things, because it could easily get the spindle revs way up.

I'm not sure about lathes though - you generally need lots of accuracy, so right now, my last CNC lathe is used with steppers removed.

I have used my larger mill as a lathe - I think it was published in an article in Model Engineer regarding the making of bronze bells a while ago. Tools held in a vice on the table. Turned a headlight reflector in the same way.

For CAD, QCad, 2.5D. It works (very well) for what I want to do - take existing plans, assumes bar stock, and machines them. Last major job was locomotive coupling and connecting rods, CNC the outline, then CNC the thickness reduction and fluiting of rods. I've made chain links in QCad, with a "rotate" manually added, and these little links made without tool-changes. (again, written up in Model Engineer a while ago now)

I do have Alibre Atom3D, and Meshcam, but it's tied tightly to Windows, and my last Windows machine went into storage years ago. Now it's QCad, CamBam, running on a Mac M1, and even FreeCAD, running when I want to use it (but QCad is the "go-to" as it's faster to use for what I do). CamBam runs in a virtual machine, and it's pretty transparent in operation. 

I'm not against 3D CAD; lots of my well-paid-employment revolved (and still does as a contractor) around 3D rendering and writing of 3D rendering code. I use what I find the easiest and quickest for my workshop jobs - whatever you use is fine. (if you want to talk about Quaternions, scene-graph traversal, avatar-object collision vector detection code, GLSL shaders, etc, etc... sure! but Model Engineering is more fun)

Pros and Cons? I don't think there's any cons!

[Alex]

Mike;

Cons: No avantage to CNC for many one off, relatively straight forward operations (though “conversational” programming at the mill can help speed up things)

One place where prototypes were made had zero CNC mills. The workshop was about the size of 2 basketball courts, one of the machines was huge - well over a story tall. CNC allowed the machinists to do mundane operations quickly (e.g. conversational programming, as you mentioned) and accurately (e.g. placing and boring for push-fit ball races) and the machinists there could not believe that I'd still own a manual milling machine! That was the eye-opener for me.

For LinuxCNC, there is a package, called "Features" by Fern or something like that, which is great for conversational milling, and maybe turning, but I did have Andy Pug's Lathe Macros on my little Unimat SL now owned by another club member, and on my Sherline lathe (when I put the steppers back on after getting used to how it cuts by hand)


 

[Jasonb]

Lots of interesting posts.

Jo, Price can be considered a con but will depend on where you decide to enter the market be it a 3040 gantry for a few hundred quid to a plug and play hobby CNC like wabeco or Sieg. may not be much more than the combined cost of several mills and lathes that some people have in their workshops.

Alex mentions No advantage for many one off jobs is a con, agree that for straightforward parts there is not much difference but that is far outweighed by the pros of what a CNC can do for more complex one off jobs. For example I've spent several weeks of workshop time manually carving crankcases out of blocks of aluminium that the CNC can easily do in a day and most of that time I don't even need to be stood in front of the machine.

I've mentioned the learning curve which I suppose is a con but most going into CNC are likely to already be using CAD and if the same provider has a CAM package then it will be easier to find your way about.

For me the pros are the 3D ability as quite a few things I make need that rather than just using it to cut out a bit of plate or drill a pattern of holes, There were several engines that I fancied doing but had put off due to the complexity of manually machining some of the parts that I have now made since getting the CNC so to me that is a big Pro.

Finish was mentioned in one of the posts, the constant speed of feed certainly helps with this as does the ability to climb mill which usually gives a better surface finish. You can just use climb to do a final finish pass or two around a contour or I tend to use it for almost everything as the machine sounds happier cutting that way. So that's another pro. Also linked to that is you can machine in both directions if you want so no time wasted cranking the table back to the opposite end of the job to start another pass.

Linked to the above is that a CNC mill is in effect a mill with power feed on all three axis which most of us don't have so if you have a lumpy casting that needs boring and can't easily be held on the lathe you can get a nice constant feed of your boring head, pro again.

I'll list a few more later but have an appointment with a mug of tea right now.

[Jo]

Jo, Price can be considered a con but will depend on where you decide to enter the market be it a 3040 gantry for a few hundred quid to a plug and play hobby CNC like wabeco or Sieg. may not be much more than the combined cost of several mills and lathes that some people have in their workshops.

As you say equivalent to the combined costs of everything else Great if you acquire a bargain machine.

I recall how long it took to learn CAD. I assume CAM would be a simpler step. I still think of CNC as a separate hobby combining playing with computers  with making lots of swarf.


For me its a bit like knitting: I started learning to knit by hand. In my late teens I brought a knitting machine. Yes there was the "programming" but having made possibly 20 or so jumpers on the machine I just found it boring. Knocking out jumpers did nothing for me. Years later all I do is hand knitting and I threw the knitting machine in the skip. The challenge for me is the hand skill, I also by commercial knitted jumpers from the shops - It is cheaper to buy a commercial jumper than to buy wool to knit one.

Jo

[Hugh Currin]

In the late 1990s I adapted our (wife and I) touring bicycles to use small 22cc gas motors for power assist. (Worked great for mountain tours) Doing that I remade the fan side cover of the motor for better mounting options. This cover has a spiral shape that involves 6 or 8 different arcs. I did these on a rotary table. This "job" was the last push I needed to convert my mill to CNC. The mill is a 1960a SuperMax Mill from Taiwan, a Bridgeport copy. I converted X and Y starting in 2000 and the quill Z a few years later. Ball screws and stepper motors which are still in use. It uses a, vintage 2000, breakout board and Gecko stepper drives. That board is still in use but now connected using a Mesa 5I25 card. Many computers have cycled though. Control software has always been LinuxCNC (well back to when it was EMC). Back when it took me a week, 10 hours a day, to get EMC installed and working. Ah, the good old days.

I found the idea of a CNC lathe appealing. However, converting my 14" lathe to CNC was daunting. So, I found a Sherline lathe to convert and see how a CNC lathe fit my shop. Well, I found a great buy on a complete Sherline shop so ended up with a lot more equipment than just the lathe. I did convert the Sherline lathe and thought it promising. In 2017 we decided to take on full time RV life. I couldn't conceive of not having a shop so build the Sherline equipment into a traveling CNC mill/lathe combo machine. These used Sherline supplied conversion parts. It uses a Gecko 540 driver system from a parallel port. Again using LinuxCNC, which by 2018 was very easy to install and configure.

For various reasons the Traveling Sherline Show did not work out well. Chip all over the campsite was a big problem. But also it took maybe an hour to get it out and set it up. It worked fine but wasn't optimum in this use.

We now have a house in Prescott with the large machines set up. However we only spend a couple of months a year there. But we have a winter spot at an RV "Resort" in Arizona. So we can now have a permanent shed for a small machine shop and rock shop. I've been setting up the machines for a couple of years now. The mill is a Precision Mathews PM728 with PMs CNC conversion kit installed. The lathe is a PM1022 which I converted to CNC. Both use steppers and Gecko drivers. Both also use Mesa cards in the computers. I'm nearly set up enough to start building another model engine. As things go that will likely take us into March when we need to prepare for major summer travels. Yep, CNCs can take up a lot of time and energy. But just setting up a new shop takes a lot of energy and time.

My baseline is the knee mill and 14" lathe I've had since 1985. Compared to those I didn't get along well with the Shreline. For me Sherlines are too light. It could be me because I know many here use them with great success. But for machine tools mass is important. The winter shop bench mill and lathe look to have great promise. They need considerably lighter cuts than the larger machines and I'm still learning this. But I think they will work well for model sized projects. The machine has a dramatic effect on how long it takes to cut a part.

The machines are documented at www.currin.us if anyone is interested. However the bench top machines aren't there yet.

This is already long so I'll leave it here for now. I'd be glad to address any questions with my slanted propoganda and skewed truth.

Thanks if you made it this far. Have a great day in the shop.

[Vixen]

For me its a bit like knitting: I started learning to knit by hand. In my late teens I brought a knitting machine. Yes there was the "programming" but having made possibly 20 or so jumpers on the machine I just found it boring. Knocking out jumpers did nothing for me. Years later all I do is hand knitting and I threw the knitting machine in the skip. The challenge for me is the hand skill, I also by commercial knitted jumpers from the shops - It is cheaper to buy a commercial jumper than to buy wool to knit one.

Jo

Hello Jo,

Do you remember you knitted me a Fowler Ploughing Engine jumper on that knitting machine. But my, that was a long, long time ago.

Mmmmm!! Jo in her late teens 



Thanks again

Mike

[Jo]

I do 

My latest speciality is hand knitted socks: I could do some with ploughing engines round them 

Jo

[Jo]

Mmmmm!! Jo in her late teens 

Its been down hill since then   

Jo

[gbritnell]

 Actually I think having a CNC mill is very beneficial, if, you can afford one that will do what you need, if, you are familiar with a solid modeling program to make parts, if, you are somewhat tech literate to understand the functionality of the machine itself and it's connection with the computer, if, you can afford all the tooling (end mill holders, collets, cutters etc.) You think making fixtures to hold parts for manual machining is a pain well a CNC mill will only cut a part in the Z direction (I know it moves in X and Y also) just like manual machining so if the part has details on the sides or bottom then you have to use a fixture or tooling setup to do those sides. It's not just pop the part into the machine and wait for the finished product to come out. Some CNC mills don't have automatic tool changers so at the end of a cutting cycle the operator has to manually change the tools.

 Now don't take the preceding paragraph as me being against having or using a CNC mill. On the contrary! I would love to have one but do I really need one? No. To make one of two engines or models per year certainly doesn't justify having a CNC mill. Lord knows I spend enough time on the computer making 3d models for my 3d printer and 2d drawings for everything I make.

 Most of the long time members on the forum know me and my work. The one model I made (T-5 transmission) took hours and hours of manual machining and hand work to complete the housings alone. I would have relished having a CNC mill to do the work but after the parts were made how long would it have been before it was put to use again. I do a lot more machining on my manual lathe and mill in the course of day than I would on a CNC machine.

[Alyn Foundry]

After running with my old Gal for nigh on 40 years now. I find manual machining almost second nature. I rarely need to measure when roughing, I know my machine so well. As Jo has pointed out there’s nothing interesting about watching a machine doing the work that you could do.

However, Jason has provided me with several patterns made using the CNC process. They have been absolutely perfect in every way. I now have a different view on the use of CNC/CAD where just a one off is required.

In my opinion a casting provides the end user with the means to make something that works with minimal wastage. The profile remains a constant particularly in the area of marketing “ true to scale “ models.

Needless to say at my age I won’t be going over to what Jason refers to as the Dark side but I can see its virtues. Attached a couple of photos of some of Jason’s CNC/CAD patterns that he made last year. Along with the machined castings.

   Graham.

[Jasonb]

For me its a bit like knitting: I started learning to knit by hand. In my late teens I brought a knitting machine. Yes there was the "programming" but having made possibly 20 or so jumpers on the machine I just found it boring. Knocking out jumpers did nothing for me. Years later all I do is hand knitting and I threw the knitting machine in the skip. The challenge for me is the hand skill, I also by commercial knitted jumpers from the shops - It is cheaper to buy a commercial jumper than to buy wool to knit one.

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

CNC embroidery machine  I don't think I could justify one of those (yet).

Jo

Strange Jo only a couple of days ago you seemed interested in CNC embroidery yet now you don't seen to want to let a machine do some of the work

[Jasonb]

Actually I think having a CNC mill is very beneficial, if, you can afford one that will do what you need, if, you are familiar with a solid modeling program to make parts, if, you are somewhat tech literate to understand the functionality of the machine itself and it's connection with the computer, if, you can afford all the tooling (end mill holders, collets, cutters etc.) You think making fixtures to hold parts for manual machining is a pain well a CNC mill will only cut a part in the Z direction (I know it moves in X and Y also) just like manual machining so if the part has details on the sides or bottom then you have to use a fixture or tooling setup to do those sides. It's not just pop the part into the machine and wait for the finished product to come out. Some CNC mills don't have automatic tool changers so at the end of a cutting cycle the operator has to manually change the tools.

I suppose it depends on the CNC but I had an R8 spindle manual mill before getting the CNC which is also R8 so did not have to buy anything in the way of tooling and was able to start making parts with the tooling and HSS cutters that I had. I've since added some Carbide cutters t make better use of the higher spindle speed  better clear the swarf and a smaller ER16 collet holder better clear the swarf so that need not be a con.

There is no more need for fixturing between an manual mill and 3 axis CNC as both really only cut in Z as you say. When I do use fixture plates I can use the 3D part to pick up the location of tapped holes for holding the part down or can cut nesting jaws to hold odd shaped work for second ops so may be even a pro rather than a con.

Quiet a few here seem to have a 4th axis added so on smaller parts you can hold a bit of stock in the 4th axis chuck and have it index the part round in 90deg steps so you can get at it from all 4 sides to do all the roughing and then round again for finishing and maybe round again to add holes etc and not once have you had to disturb the hold of the work so it will be in the exact same place for every operation, I'd say that is a pro. Interestingly I have been swapping a few e-mails with someone who wants to make a 1/3rd scale Galloway but as castings are hard to get he intends to make from solid with his Tormach, the bed casting will be done using the 4th axis so all areas can be reached and no need for excessively long cutters to get at the deeper recesses. Or you could go the whole hog and get a little desktop Pocket NC machine the gives you 5-axis all in the single set up

I doubt many with home machines have autochangers, some will have quick change others just get on fine with changing tools as needed which is no different to changing tools on a manual mill so neither a pro or con. Same for needing to be there to change tools you have to do that on the manual mill as well but the big advantage of the CNC is you don't have to be there while it is cutting like you do with  a manual machine so can be making another part on another machine or doing something completely different got to be a pro again.

[Jasonb]

One issue is having access to a decent CAD / CAM program.  That is where there's lots of time savings to be had as an amateur that doesn't use it frequently.  I'm sure that if I used it more I'd learn more tricks to be faster in programming but for now I'm pretty slow.  Also, not to turn this thread into a what software to use discussion but I'm leaning towards buying Alibre Workshop bundle (Alibre Atom and MeshCam) at the moment as a way of escaping from Fusion360 ever dwindling free offering. It looks like the 3-axis CAM (Meshcam) is really easy – so hopefully that makes it easier to get off the PC and hop into the shop to make stuff.

I did get a trial of Meshcam with a view to getting it to run alongside my Alibre Pro but found it quite basic and lacking many features that F360 has. It is more aimed at the "maker" with a gantry type machine working in various materials and only the occasional but of metal. It's limited if you want to do 3D work as it does not have much in the way of finishing path options except parallel and I recently read of someone using to to make a part out of some round stock and they said Meshcam only works with square or rectangular stock (sheet on a gantry machine) so there was a lot of air cutting which made for a very extended run time. F360 will happily accept square, rectangular, or round stock and you can also model the stock if it's an odd shape for example if the part is L shaped you can save time by sawing out most of the waste and then tell F360 it is working with a rough cut L shape and it does not cut any more material than needed. Not much in the way of adaptive tool paths either

It was quite easy to use but there is nowhere near as many features to learn how to use.

[Jo]

CNC embroidery machine  I don't think I could justify one of those (yet).

Strange Jo only a couple of days ago you seemed interested in CNC embroidery yet now you don't seen to want to let a machine do some of the work

I am waiting to inherit one  but I would prefer it is a long way in my future 

Jo

[springcrocus]

Jo,

Just to whet your appetite...



Regards, Steve

[Alex]

3D and 4th axis.

MikeR - CamBam can do 3D profiles. I have played around with it, but currently, no need for it in what I'm doing, but it is there if required. Have Meshcam with the Alibre Atom3D bundle, but other than starting it up, I thought that CamBam was better. Not much to go on, I know. Alibre Atom3D - there was (and still is) no room for a windows box in the office as work/play is macOS and Linux, and one day I tried to run Atom3D in a virtual machine on Linux, and it locked the license. I installed FreeCAD and have not looked at Atom3D since. (yes, a good soul got the license unlocked, but by that time the Windows box was in storage and desk re-arranged) I'm sure Alibre Atom3D is great, but change the hardware, and watch out...

For 4th axis machining, I used CamBam with added GCODE files, simply to flip the rotary around. These little links on a Shay locomotive go from the reversing lever to the reversing arm on the engine, and are pretty well hidden when complete. Here are some photos of how I did it. It was really nice to see the parts drop off, with minimal finishing.

The biggest issue I had was taking the time to zero everything, I wanted to see how things went! I ended up shining the parts shown up, and they look great.

[steamer]

Actually I think having a CNC mill is very beneficial, if, you can afford one that will do what you need, if, you are familiar with a solid modeling program to make parts, if, you are somewhat tech literate to understand the functionality of the machine itself and it's connection with the computer, if, you can afford all the tooling (end mill holders, collets, cutters etc.) You think making fixtures to hold parts for manual machining is a pain well a CNC mill will only cut a part in the Z direction (I know it moves in X and Y also) just like manual machining so if the part has details on the sides or bottom then you have to use a fixture or tooling setup to do those sides. It's not just pop the part into the machine and wait for the finished product to come out. Some CNC mills don't have automatic tool changers so at the end of a cutting cycle the operator has to manually change the tools.

 Now don't take the preceding paragraph as me being against having or using a CNC mill. On the contrary! I would love to have one but do I really need one? No. To make one of two engines or models per year certainly doesn't justify having a CNC mill. Lord knows I spend enough time on the computer making 3d models for my 3d printer and 2d drawings for everything I make.

 Most of the long time members on the forum know me and my work. The one model I made (T-5 transmission) took hours and hours of manual machining and hand work to complete the housings alone. I would have relished having a CNC mill to do the work but after the parts were made how long would it have been before it was put to use again. I do a lot more machining on my manual lathe and mill in the course of day than I would on a CNC machine.

George Im one of your biggest fans!   I am always in awe of your work, since long before this forum started....

I've enjoyed my fairly new foree into CNC.    I've designed many CNC machines and parts of machines for Moore and Milacron, but I've always run manuals in my home shop....but I got the opportunity to get a small CNC at auction...and knowing the only person who ever ran it.......ME......ME advised ME to put in a nice juicy low ball bid and maybe I'd win.....and I did!    Otherwise I wouldnt have sprung for the cash it would have taken to get it....no way..

That said..  There are some economies of CNC.     While a dividing head is still a good thing to have   or a 4th axis..... I have not needed a rotary table...and I sold mine when I sold my last mill.....and I don't miss it ....I can engrave neatly, instead of using punches...which I never seem to get aligned no matter what I do.   Fixturing although necessary, I find to be very easy and intuitive with little more than a plate stuffed in a vise, fly cut it flat and machine what I need to hold the part, and with it anything is possible....as such ....compared to a manual mill, which I've run for near 30 years or so...I find processing parts to be easier,  especially in any quantity over say 2....With model engine work,  I'm always making some sort of fixture to hold something, and in general that doesn't change with CNC...other than avoiding rotary table work.     monotonies jobs....Like a index plate ...are easy on CNC...and while it's running, I'm over running my lathe...
I don't think it will make a better engine, but I do enjoy programming it, I find that a rewarding challenge.   It also allows me the opportunity to do something really complex in the 3D space....that I know I couldn't pull off with step off tables,   My bench vise is an example of that.    Hewn from billet....   I know I don't have the time to do that manually...my shop time is pretty limited, and time pressures are a plenty.   It's let me expand my project list to what I would never think of doing before ....and honestly, I think I spend less on tooling with CNC now than I did on tooling with a manual    there was always a need for some other piece of tooling, special cutters.........and they always seems to be expensive in time or money....

Getting acquainted with the conversational aspect of programming is very helpful in saving time on 1 pieces runs......without getting into CAM.....which is how I program most jobs.   

I use Fusion 360....which I admit is limited on the CAD side, but pretty powerful on the CAM side.....this coming from a guy who started his Engineering career on the drafting boards almost 40 years ago.....

Dave

[FKreider]

I am blessed (and cursed) with adequate shop space to have "full size" machinery. In the region of the USA that I am located many commercial machine shops have gone out of business and as a result some older CNC machinery can be had at very reasonable prices.

I started out with a manual knee mill (without a DRO) and a manual 14" toolroom lathe. Just about two years ago I sold the fully-manual mill and upgraded to a 1994 Kent USA knee mill with a 2-axis Mitutoyo CNC control on it. I cant imagine going back to a full manual machine now. I feel that having the 2-axis CNC motion control combined with the traditional "analog" feel of using a manual knee mill makes for a fantastic blend of technology for a home shop machinist. You can easily throw a piece of stock in the vise and square it up using the crank handles and then a few minutes later be using the conversational programming to punch in a simple bolt hole pattern.

That said I also have a small benchtop CNC mill which has no quill or crank handles so its very similar to a modern CNC machining center - you have to jog the table around via the CNC control screen to set your zero point and touch off tools. I also cant imagine just having this machine as a hobbyist because there is no "feel" involved. 

I am also extremely interested in patternmaking and metal casting however I am not a skilled woodworker so I spend all my time in the CAD program designing parts and patterns in 3D and then mostly 3D print them although I also eventually plan to use a CNC router for larger wooden patterns and match plates.

For me its all about a mix of the old school analog technology blended with enough "new" school (even though all my CNC's are from the 90's) to get things done a bit faster.

[Pete49]

The closest I come to cnc machines is 3 3D printers and a small cnc router which I use to make wooden clock gears as using the scroll saw was a bit slow and needed truing. The mill and metal lathes are manual as are the wood lathes. CNC has its uses but as an older generation and self taught computer user some things are beyond my ken. 

[Jasonb]

For those not that familiar with CNC it might be worth explaining a couple of the terms being used such as "Conversational"

There are a number of ways in which the tool can be positioned on the CNC

1- Manually. Some hobby machines have a handle on the motor or still have handwheels, converted machines may also have their handwheels intact so they can be used to move the axis.

2- Jogging. This is probably best likened to using power feeds on the three axis, you just hold down a button or mouse to move the axis, this can be done at variable speeds or in increments the size of which can be altered. There is also the option to enter a "goto" position and twork will move under the spindle to that position. This is mostly used when setting up the work but can be used for simple machining where the constant jog is just like using a power feed.

3- Conversational - Most operating system will have this in some form or wizards that simplify basic tasks such as milling a circle, facing the top of  apart or drilling a hole PCD pattern. Taking the last of those this is virtually the same as entering the details on a DRO except when you press go the work will move rapidly from one position to the other no faffing about because you overshoot with the hand wheel or that last digit keeps changing and the ball screws and motors will hold position so no need for locking axis

4= G-code. This is the language that the CNC uses to tell it what to do, some enter a few lines manually others use a post processor combined with their CAM package to generate this code. Once the code is loaded into the CNC a suitable tool loaded and position (datum) of the work and tool set the program can be started and the tool will just work down the lines of G-code

I mostly tend to use number 4 with number 2 used for setups and the odd bit of fixture machining such as skimming the top flat and adding a couple of holes to fix the work to.

[Jasonb]

The point was mentioned about how much a CNC might stand idle once a "casting" had been created on it until the next part came along. I've just looked through the drawings and photos of teh James Coombes that I have just started to write up.

There are 52 different parts, that does not allow for multiples eg the columns are counted as one not four.

Out of those 10 had some machining done on the CNC, run times ranging from about 2hrs down to 2minutes.

Of those 10 parts only 3 would have been supplied as castings, other work as will be seen in the build used the CNC for shaping parts that would have been done on a rotary table which I seldom use now as the CNC is the best tool I have where one curve blends into another.

So with the first photos of progress being early November I've been working on that model for 3 months and it has just run, there was some other model work going on too so not my only project but a good indication. over that time the CNC got fired up 8 times as I did a couple of items at the same time, the last item shows it being machined on 1st January so idle for a month.

Now lets take as an example someone with a high quality lathe that they do most of their work on and a larger capacity ex industrial machine that sits unused for  a lot of the time but when a large part needs machining it is used as it is the best tool for the job. Same if you have a small lathe for delicate work. I see this as being the same as having a CNC you may not use it all the time but when a particular job comes along it is the tool of choice.

[vtsteam]

Just to illustrate how on the fence I am:

Since I don't particularly enjoy manual milling, I'd probably convert my round column mill to CNC, but that seems like a long project, (even though I have the controllers and steppers to do it already) if ball screw conversions etc are needed. Also I wonder how good this mill would really be as a base for that. I did add a DRO last year (built the control -- it's a bluetooth to phone DRO) and that was a huge step forward in usability.

My present lathe is my second homemade lathe, after the Gingery, and was designed to be massive for a small footprint. It is a 9" swing by 15", but not much bigger than a 7x12  Mini lathe on the bench. MUCH heavier, and stiffer with a good sized boring table.

For that, I've 95% finished my own-design electronic lead screw using a stepper, a 600 line rotary encoder and a FORTH programed Arduino. Yet I have not electrically connected it, even though the stepper is already mechanically installed, and the electronics and programming have all tested out. No idea why I've procrastinated on that. I guess it was just a flagging of interest toward the end. Maybe I'll get inspired to finish by talking about it with you all here. I've been doing without power feeds or the ability to  single point thread for 5 years, now, for pretty much no reason. 

[Mike R]

I forgot to add another reason I got into CNC machines - at the time I was travelling ALOT for work (200+days a year) and I had more PC time than shop time so I figured a way to leverage my PC time into something beneficial to my hobby endeavors was to play with CNC - CAD and CAM so I could "in theory" pop into the shop and run a program when I was home.  It didn't quite work out that way, but I still enjoy the path CNC has taken me on.

[Jasonb]

Agree that the CAD CAM part of it can be done at any time you have spare such as that odd half hour when you don't fancy going out to a cold workshop, while half watching something on TV, etc.

The job can also be left "set up" on the computer so you can come back and do a bit at any time then once the code has been spat out by the post processor it's just a case of mounting the work and pressing Go. You can always break the paths into shorted run times if you don't want to leave the CNC running for a long time and then just come back to that and run the next bit(s)

[Hugh Currin]

Here are a few random thoughts:

I find a CNC mill far more useful than a CNC lathe. If it was one of the other I'd take the mill hands down. I mainly got into a lathe conversion for the ability to cut inch and metric threads easily without change gears.

The cost of CNC is less if you convert a manual machine to CNC.  One advantage of doing this is you know that machine inside out. This, however, quickly leads into another hobby/rabbit hole. It is a lot of work to figure out the details and make the parts for a conversion. But it's much easier to track down problems and fix them if you have intimate knowledge of the machine. Alternately, purchasing a CNC machine costs considerably more but is obtainable now. Since they are purpose built they will likely be more accurate and better optimized. There are two in-between paths. There are now conversion kits for some popular mills, such as my PM728. This leaves you responsible for the electronics and controller. Putting that together is a bit of work but a lot quicker than starting a design from scratch. The resulting machine is on par with a economical ground up conversion (i.e. inexpensive rolled Chinese ballscrews etc). The second is to buy a used CNC machine with an outdated or dead controller. Then replace the controller with a new PC based one. This isn't done commercially because of the time involved, so outdated/dead CNC machine is quite reasonably priced. But it requires your time to do the conversion. Easier to do if the axis drive motors are usable, even better if the motors and drivers are both usable. (How good are you at digging though electronic diagrams?) This will result in a, better than hobby, commercial quality CNC. One problem here is they'll be large and likely require 3 phase power.

I'm sold on CNC machine in my shop. I likely use then more in "manual" mode that running programs. Using the jog option you can move any axis under control at a specified speed. Push the button it moves, release the button it stops. And in MDI mode which accepts single line G-code commands. For example move to X=3.250 at 4 in/min feed. Likewise gives digital readout on each axis. I have not gotten used to using "conversational" mode with has built in routines for common tasks, like a bolt circle. My controllers, LinuxCNC, doesn't have such built in. For these I use a CAM package. I use CamBam and Fusion 360. Tilting more towards Fusion but each has its place.

Most model plans are designed to not use CNC. Most parts are simple and tend towards rectangular or round. The complex 3D shapes where CNC shines are avoided because they're very difficult to make on a manual machine. Model designs, and their plans, are made for home shops which, by a large margin, don't have CNC.

You may not need CNC to do fantastically complex parts. George Brittnel and Ramon, plus others, carve marvelous complex engines from solid on manual machines. I can't do this but can get, for me, complex parts using CNC. I like doing this.

On castings. I believe castings came about for large parts. At scale the waste in material and time/effort to cut from a large chunk is excessive. For models this isn't the case. The reason to start with castings is the look of a casting in the resulting part and the exercise of finishing cast parts. Cast parts start as a mold plug which is "easy" to make with curved edges. Thus castings tend to have a more flowing shape than manually cut parts. Gives a nice look to a model engine. To get this when cutting from solid requires a lot of work and/or CNC. Castings for models are, to me, very expensive. A lot of work to get a small casting compared to a chuck of stock.

CNC is a different mind set than manual machining. For most of us it required a CAM package to interface between the electronic model of a part and the G-code program the CNC needs. You lose some feel for the machine using CNC, but there is still feedback in sight and sound. But for me, the "manual" modes a CNC offers is a good alternate to a manual machine. A professor where I used to work was happy to teach CNC classes without machines, just a CAM package. All the rest of us thought this was foolish. So many things can go wrong between the CAM and a finished part that you must teach the whole process. A CAM model is the start not the final product. To have success with CNC almost requires some manual machining background, and certainly machining time on a CNC. There is a great deal of skills transfer between manual machining and CNC, and vise versa.

I'm happy with my CNCed shop and just wish I had more time/energy to use it.

You all have a great day. It looks like a great day here. Thanks.

[FKreider]

The cost of CNC is less if you convert a manual machine to CNC. 

I think this can be very dependent on where you are located in the world geographically.

Where I live in the U.S. there used to be a very large amount of manufacturing/industry, a lot of this industry has since moved to other parts of the country and more commonly outsourced to the far east. As a result of this you can go on Facebook marketplace any day of the week and find an old Bridgeport mill for $800.

The same can be true for older CNC model machines, you can find very good deals if you are patient and jump on them when they come up. I couldn't buy the controller and servo or stepper motors for the amount that I paid for my milling machine with working and installed 2-axis CNC capabilities. I also have a Hardinge chucker lathe with Omniturn CNC controls that I purchased at an auction for less than you can buy a typical used manual lathe for.

That said I know in other parts of the world like Canada or Australia that same old worn-out Bridgeport that is only worth $800 in my area would easily get $3000 or more.

Based on this I would suggest that the cost of CNC machines MIGHT BE less if you convert a manual machine to CNC. As you suggested conversions/retrofits can be a bit of a rabbit hole.

[Djangodog]

I learned to program an NC lathe many years ago, (paper tapes, no internal memory or crt screen).  I moved on to cnc turning and machining centers and manually programmed four axis simultaneous machines.  I was a journeyman tool and die maker at the time, but I didn’t want to get left behind as the industry evolved. 

As capable as these machines were, they could never compete with a good jig bore.  Circular interpolation is not accurate enough for a bearing pocket or anything that needs to be perfectly round.  Angles and tapers are more perfect when done manually as well. 

A cnc has good value, but if the programmer does not understand how to properly cut the part, then there is little chance that it will turn out well.  Surface speed, chip load, chip evacuation, rigidity of setup and an order of operations to insure accuracy are still necessary.

My only cnc equipment is a 2 axis Proto Trak on my Bridgeport and a cnc servo feed threading unit on my Hardinge HLV.  There are times when circular interpolation would be helpful on the lathe, but not necessary, (I have a ball turning attachment that does a nice job). 

If I was in a great hurry or needed to make money on production parts, then I would take the cnc.  For the pleasure and satisfaction of making something, I prefer my manual machines.

[Jasonb]

I see most of the tooling manufacturers do "Finish boring heads" that are set to a specific size and after using interpolation or insert drill to remove most of the waste the finish head is loaded from the tool changer and used to do a final sizing pass. Not really any different to reaming a hole after drilling or boring and always possible to do some test cuts first to set the head to the exact size you need for the job.

typical heads

One in action about 3.30 into this video. I like the parting off at the end too

<a href="https://www.youtube.com/watch?v=I--_63_wysk" target="_blank">http://www.youtube.com/watch?v=I--_63_wysk</a>

Not really practical to have a range of these in the home CNC shop but nothing to stop you using a boring head for holes that matter just adjusting like you would on a manual machine and the CNC provides a nice power vertical feed be it for a one off hole or the same hole in a small batch of parts that you may find in a multi cylinder model engine.

5th axis would also make the angles and tapers as good as setting the work at an angle on a jig borer as the work can then move in a straight line rather than a series of minute steps. I know not many have 5 axis in their home shop but many have a 4th axis capability which would do on most occasions if the setup was right.