My "Learning to use a Lathe" Journal

[Brendon M]

Thank's Dave, I will give your suggestion another go.

This post was supposed to detail my victory and how I completed this part, alas I did not. By the time I had some food, and ground a new round nose cutter, and trialed the new cutter on a piece of scrap, it was almost time to go home.

And also, the latest and last video in the Clickspring series had came out, so we all gathered around at CCHS and watched it

In which case I decided to work on something completely different, and much easier: a sleeve bearing for my hand powered coffee grinder. Silly designers did not support the grinder shaft at the bottom, so on courser grind settings, the whole grinder was able to wobble about, producing a very inconsistent grind. Luckily, I had a lathe I could use to fix that 

[Jo]

And also, the latest and last video in the Clickspring series had came out, so we all gathered around at CCHS and watched it

I nearly missed that. Thanks for reminding me. 

Jo

[Chipswitheverything]

Hi Brendon, that doesn't sound like a bad afternoon to me!  Especially as I've just now got a workshop with the machines all covered up in blankets against the chilly and damp December air, not very useable in there...
  Just to pick up on a point that you mentioned earlier, it's IMHO a much better practice to jot down your workshop calculations as they arise, as you are doing. In fact, I don't personally know any model engineers who don't do just that, whether their mental arithmetic is good or bad. It's so easy to make a slip up, or plain forget,  - phone call, interruption -   and if something doesn't seem quite right, how are you going to look back for a check on what you did?  Just strike a line through the calculation as it's done with, so you know that's the old one...!     Dave

[Brendon M]

Thank you for the reassurance, Dave


OK, this will likely be another long post. This long post does have a happy ending, however!

In an attempt to get this part finished, I went to CCHS on Monday, Tuesday and Wednesday.

On Monday, I decided to tackle the step of slotting the part, mostly to see how I can do it, but also to get some practice on a scrap "practice piece" and address anything that might go wrong. So sometimes there is a benefit to mucking up parts.

The chosen approach was to mount a rotary tool onto the cross-slide. This actually worked pretty well, although on the next attempt, I will mount it 180 degrees so that the wheel is spinning anti-clockwise and thus the grit sprays downwards instead of upwards.



The part was held in the chuck using the only piece that has trascended the scrap pile: the threaded mandrel I created earlier.



This procedure went a lot easier than I was expecting. Here is the part now slotted.



The grinding disc cut a slot just wide enough to fit this pin perfectly.



Now why am I slotting it? The next part to produce is a 5mm rod that is threaded on the end, and has a pin. This pin sits in the slot and prevents the pin from rotating. Thus, when a nut is turned on the threaded rod, it will move the threaded rod back and forth.

Here is an image of that part that I will be constructing next.



So, with that out of the way, it was time to re-attempt "Trial Part IV: A New Hope". I decided to retry Dave's suggestion of performing all possible turning operations before parting off, so that I would spend less time re-centering in the 4-jaw chuck.

All the main dimensions that could be done with the RH tool were turned down. I then checked with the Test Dial Indicator to see if the very end had any runout. It was less than 0.01mm so I considered that good enough.



I proceeded to cut the thread with a M7x1 die (not shown). After cutting the thread, I checked with the Test Dial Indicator to see if I had somehow caused the part to bend. All was good, so I moved onto the next step.

For the non-threaded side, this meant that I would need a round nose cutter. After viewing this image of a round nose cutter, I realised the radius that I had previously ground was too big. I took this time to review all the tool bits I had ground, and found all the rake and relief angles far too aggressive, so they were all reground.

You can actually see the difference in surface finish on the non-threaded side and the outer-most diameter:



The LH cutter was reground back to sensible angles, and the cutting was so much better. Once again, I got out the Test Dial Indicator and checked to see if I had bent the part during the LH cuts. All was good! I should mention that I decided to make the non-threaded side 7mm instead of 6mm, in order to ensure good rigidity for the final drilling operation.

I took this time to regrind my RH cutter too, and turned the outer-most dimension to 9mm.



Once again, the difference in surface finish was much improved. I can't believe I didn't pick up on this problem earlier I once again checked with the Test Dial Indicator, and once again all was good!

I also discovered another reason for performing the turning operations this way. You may recall that I created a threaded mandrel to hold the part for finishing the outer-most diameter. The RH cutter tends to produce a lip of metal in the direction of cut, which then requires an application of the LH cutter to remove. So in the end, I would have still required some way to hold the part on the non-threaded side to remove that lip.

Now that I think about it, I should have turned the whole lot down to 9mm and then done the cutting of the 7mm non-threaded side.

Anyway, I got on the with drilling operation, also the most nerve wracking operation to perform.



I am probably starting to sound like a broken record, but I rechecked for wobble with the Test Dial Indicator, which showed that all was good. If I was going to mess up the part again, I wanted to know which step was causing it. This is my machining equivilent of "step-debugging" programming code

Here is a picture of the parting off:




At this point, I was almost shouting "Woohoo!", until I remembered that this has taken me four attempts. (D'oh!).



I've said it before and I should take my own advice: no cutting with blunt or badly ground tool bits!

After a bit of deburring, which I learned I can use a tap instead of a large drill bit for a better finish, the exit and entry holes appears to be concentric with the outside diameters. I am also able to pass the 5mm ink cartridge through the part without binding.



So in conclusion, in producing this part I have learned the following:

• Incorrectly ground tool bits - in all cases, wobble (due to chatter) and poor surface finish was due to this
• 3-jaw chucks are not repeatable - not a problem if you can avoid parting off until late, but otherwise use a 4-jaw
• Try to delay parting off for as long as possible - but don't try to machine too far out or you could bend the part
• Maybe don't try and produce 0.5mm walled parts, unless there's a good reason
• Using a chuck for turning between centers is OK, as long as the part as running as true as possible, and the tailstock ways are not considerably worn

I still have to slot this part, but usually I have stuffed up before I get to this point, so I have made progress!

Thanks for reading

[Chipswitheverything]

Hi Brendon, great stuff!, and I admire your persistence in giving the awkward little component another go.
 Very pleased that you found the suggestions about making the component in one continuous process, remaining in the chuck throughout, to be a help.   It does often solve a few problems if you can scheme out a way of not having to remove or re-chuck an item.

Cheers, Dave

[MJM460]

Well done Brendon.  It might seem to have taken a few false starts, but when you consider how much of the work on a lathe consists purely of the operations you have completed so far, centring the stock, turning to diameter with left or right shoulders, drilling, threading, parting off and you have included machining a slot as a bonus.  Now to try boring, then practice, which of course never ceases.  It is a lifelong pursuit.  You will learn to improve accuracy, and surface finish, and you will gain experience with different materials.  And as the need arises in your future projects you will continue to learn many other techniques which further increase the versatility of the lathe.  The many interesting posts and fabulous build logs by the experts on this site will keep inspiring you as to what is possible.   But you are now up and running.

MJM

[Mosey]

A good book of fundamental machining I have found helpful is "

Machining Fundamentals: From Basic to Advanced Techniques"
by John R. Walker
Amazon has it used for $2.00 + shipping.
It covers most of the techniques you would want for some time, and is clearly illustrated.
Mosey

[Brendon M]

Thank you Dave and MJM for your words of encouragement

Also thank you Mosey, I shall check that book out.

I am going to finish the part tonight by cutting the slot, after that it's time to do the pin.

*edit: hundredth post!

[Brendon M]

Wow, 3 months since the last post.

On my pen project I got stuck on - of all things - cutting an M5 thread. I think the die might be blunt, but then again I could just be incompetent. I am going to purchase my own tap and die set, but of course a good set is over a hundred dollars and right now I need to be spending my money on other things. Blasphemy, I know!

So I decided to have a go at Clickspring's Benchtop Gyroscope, for something different. At the very least I'd practice on a bit of aluminium bar that was laying around the hackerspace.

Now the plan calls for 3 inch brass rod stock but I only could find 2.5 inch brass rod. And in this "prototyping" session, I also only have 2.5 inch aluminium bar, so that will have to do.

First up was cutting off a roughly 1 inch chunk... with a hacksaw. Because I thought, how hard could it be?


An hour later, I swore to myself (lots of swearing actually) that I'd much rather a mechanised cutting process! It wasn't just that it took me about an hour to get through the 2.5 inch alum bar, but I also cut on a angle


The angle of cut translated to quite a bit of time and wasted stock facing on the lathe


Now I also don't have layout blue, but I found that using a cutter to scribe lines into the part worked well enough. I picked my target inner and outer radii, and computed the necessary movements of the cross-slide in thou.


I'm only loosely following the plans in terms of looks rather than dimensions. The video talks of scaling up or down but in this case I'm just copying the look of Clickspring's design.


I made a few mistakes during this session which luckily could be corrected

• While removing the bulk of the metal in the recess I nearly cut too close to the target lines. I would not have been able to form the tapers if I'd cut any closer
• While cutting the tapers, I forgot to rotate the toolpost back into position so that the toolbit was perpendicular to the flywheel again. This meant that I was effectively plunging the tool into the stock (at an angle), producing a bad finish. Thankfully I figured out my idiot mistake that there was enough material to correct.

And just one last thing to mention, this was my first time cutting aluminium, and it just flies off the tool in long streams! Compared to brass and steel, this was making a giant mess.


Next week, I will cut the other side, and outside using a so called "superglue arbor". Thanks for reading!

[steamer]

Great stuff Brandon!    There appears to be a burr on the face of your flywheel there.  Make sure you take that off before you try tp glue it to a glue chuck.

When the time comes....let us know, and we can talk you through the glue chuck....it's not hard....just need to pay attention to some points is all

 

Dave

[Brendon M]

Thanks Dave, it could be a burr, but it could also be my dodgey camera work the shot seemed to come out slightly blurry no matter what I did, but I'll double check that the surface is free of burrs.

[MJM460]

Hi Brendon,

Good to see more good progress.  Sharp tools are always the issue in community spaces, so the area in which you start to build your own collection.  They will come in handy when you eventually get your own machinery.

In my experience the time taken and angular cut indicate the the blade was blunt - you could have cut steel in that time.  I suggest the first addition to your private tool box be some good hacksaw blades.

I suggest you visit that well known green warehouse and buy yourself an assortment of good blades.  Get one each of 18, 24 and 32 tpi. And try them out, generally the coarse one for large soft stock like your aluminium, fine for thin rods and sheets.  Only buy the best quality on the shelf.  I like the white ones, and have now bought packets of 10.
Use a blue felt tip maker for layout until you get some proper blue, it is quite adequate for most purposes.  Then wrap a piece of paper around the bar, when the straight edge lenses up is is perfectly square and your felt tip, half on the paper will give you a good line to follow.  A wide blue line will also give your scribed lines good contrast.  Clamp a 3/4 square length of pine so the rubbing the saw on th timber keeps it on the line use a few drops of oil on the blade and you will get a much better cut.  The wood will guide many cuts before it it better to discard it and use a new one.  I usually have to waste only about 1 mm to face it up in the lathe or mill, and I do not have that much more experience than you.  I suspect the experts around here do much better.

And eventually, perhaps for Christmas get yourself a set of taps and dies for threading.  Only buy hss.  I have found the set a bit over $100 from the red and blue warehouse very satisfactory and has lasted for years (many threads in all metals, only just starting to replace the sizes I use most).  The cheaper alloy steel ones will soon be blunt, and are only good for the odd sizes they sometimes contain like your M7x1 which you might never use again as it is difficult to buy nuts in that size, but not included in the hss set.

MJM460

[Ian S C]

Brendon, as taps and dies go, it's best that you buy best quality HSS, but rather than buying a full set, get the ones you are using, maybe a taper tap and plug tap, you don't need all three.
Ian S C

[Chipswitheverything]

Hi Brendon, good to see that you are back in action on the lathe after the break.  As you have found, some aluminium swarf from turning can be difficult stuff, and it can be dangerous too, the long streamers of cuttings can bird-nest up around the tool and job:   and of course the stuff is like cheese wire as far as fingers are concerned. A tool with a chip breaker ground in, or a carbide insert that has one already formed, can be helpful.  But for safety, stop the lathe entirely when the swarf builds up, and clear it away from the work/tool bit  area using pliers or some metal implement to yank it away.     Dave

[Brendon M]

Thank you MJM460. The hackerspace has a cold cut off saw I can use, but I'll give the hacksaw a go again. The cut off saw went through the aluminium OK but I had to nurse it a fair bit, and I have doubts about going through 2.5 inch brass.

... I have found the set a bit over $100 from the red and blue warehouse very satisfactory and has lasted for years (many threads in all metals, only just starting to replace the sizes I use most).

and

Brendon, as taps and dies go, it's best that you buy best quality HSS, but rather than buying a full set, get the ones you are using, maybe a taper tap and plug tap, you don't need all three.
Ian S C

I think I understood MJM's "red and blue" warehouse reference. I saw that they had a HSS tap and die set but but they are not split. Are split dies better?

I was originally thinking of getting a set from Sutton tools, but now looking at those again, they don't seem to be HSS.

Hi Brendon, good to see that you are back in action on the lathe after the break.  As you have found, some aluminium swarf from turning can be difficult stuff, and it can be dangerous too, the long streamers of cuttings can bird-nest up around the tool and job:   and of course the stuff is like cheese wire as far as fingers are concerned. A tool with a chip breaker ground in, or a carbide insert that has one already formed, can be helpful.  But for safety, stop the lathe entirely when the swarf builds up, and clear it away from the work/tool bit  area using pliers or some metal implement to yank it away.     Dave

Thank you Dave. My first time cutting aluminium and I wasn't used to the swarf building up around the tool bit. Without thinking I used pliers to clear away the swarf without stopping the lathe, to which I was later informed is dangerous behaviour. Thank you also for pointing this out. 


On that note, I didn't get anything further done this week because the lathe gear head needs to be topped up with oil before I can start using it again. Hoping to have that sorted next week.