Author Topic: Elmer's #33 - a novice makes chips  (Read 39100 times)

Offline Thayer

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Re: Elmer's #33 - a novice makes chips
« Reply #15 on: December 27, 2012, 01:15:57 AM »
Moving to the other head, the process is much the same.



The obvious difference this time around is that you are also creating the home for the connecting rod seal and packing nut. Concentricity is key here and I was careful to ensure minimum TIR whenever I remounted the head. I know it is hard to tell, but in the image above I am recentering the 4-jaw/RT combo under the spindle before drilling and tapping the mounting holes.



Here I am obviously back on the lathe and getting ready to part it off. Leave it a bit long here for cleanup.



And again using the parting tool followed by the hacksaw.





I do not run the lathe while sawing though as I don't want to pinch the blade.

Before mounting the head I measured the step in the split bushing and determined it was 0.021 shallower than the desired 3/32 final thickness of the inner head. After cleaning up the parted/sawn face of the head I set the pointer to 0.079 (-0.021) when on the bushing face.



Below I faced the head until the indicator said it was 0.032 over. This gave the desired height of the registration spigot and I then turned the rest of the head down to the final thickness, determined with the indicator reading 0.079 on the bushing and zero on the head.



Note that the split bushing provides a nice way to hold the heads without worrying about having a spigot to turn off later.
« Last Edit: June 18, 2014, 01:04:44 AM by Thayer »

Offline Thayer

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Re: Elmer's #33 - a novice makes chips
« Reply #16 on: December 27, 2012, 01:20:46 AM »
That's it for detailing the cylinder block (except for the mounting holes, oops!), so next I reduced the two sides that are not mounting surfaces, leaving a few thou inside each end to clean up later. This was a roughing operation before I radius the corner between them. My plan is to tip up the RT 90 degrees and then clock it a little bit at a time while I mill away the excess to create the radius.



This image shows a small chip shield I made up from a piece of bent acrylic and chunk of aluminum slotted to accept it as a press fit. This does a reasonable job of containing the mess, or at least keeping off the left side of the bench, and still allows me to reach around and apply cutting fluid if I desire. I have since drilled a hole in the base with counterbore for a 10-32 SHCS so I can hold it in place with a t-nut in the slot instead of clamping as shown.

Here is the first side with the block held in the vise, about to go.


And the second milled down.


Offline Thayer

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Re: Elmer's #33 - a novice makes chips
« Reply #17 on: December 27, 2012, 01:23:43 AM »
A little more progress.

So, I went to a local machinists group meeting recently and took along a few of my bits and pieces. They were all very polite and seemed to be interested in what I was doing, without even scorning my table top machines. Anyway, at that meeting I realized that despite the near perfect fit between the cylinder heads and my bore, I would have to set them aside and make new ones. Why?, well I made them to fit a cylinder that was a few thou under target and wasn't finished. Yes, I know I could have used them and just let the engine settle in on its own, but the bore was tapered very slightly and I wanted a better finish before I ran it. Not enough spring cuts, I guess.

Cover your eyes now if you are squeemish. Not having any laps available, I decided a reamed bore would have to do. I loaded up the cylinder and .500 reamer with cutting oil and ran it through. That all worked out well, though I now had two heads that no longer fit like I wanted. The outer end was no issue, but the inner end with the packing for the piston rod could be tough to locate accurately. Besides, I plan on painting this engine, and thought brass heads might look nice against the paint. The aluminum heads will get saved for something else I can finish out nicely slightly undersize. And so it was back to the lathe.

I didn't have any 1-inch brass stock so had to throw away a lot of some 1-1/4 that I have. It pained the cheap Scot in me - I was throwing away 58% of the material before I even got started after all. Working through my steps before cutting the blank I realized that the split bush meant I no longer needed a spigot for holding and I could use less than 3/4 of an inch of stock if I was careful, including the initial saw kerf.



I didn't really take any photos since the process was essentially the same as before. First here is the outer blank turned to size with the small spigot to reference the bore. This fit is actually better than the original.  From here I parted it off and mounted it up in the 4-jaw/split bushing combo, indicated it true and cleaned the outer face with a light skim cut. Notice in the second photo that I also created a slight recess. Why? I simply thought it looked better.

The inner head is the one that is critical. I did this by turning the spigot to receive the packnut, then drilled it for the piston rod, opened it up with the #21 tap drill and then tapped it 10-32 as indicated on the plans.

I then turned the rest of the OD before the chuck jaws down to match the cylinder head so I could reverse it and put it in the split bushing. After indicating it true I then milled the final thickness and bore spigot.



So now I have a little brass to polish on this and keep bright when I am done.

Offline Thayer

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Re: Elmer's #33 - a novice makes chips
« Reply #18 on: December 27, 2012, 01:24:21 AM »
Sharp eyes above will also notice that I rounded the cylinder.

The way to do this was with my rotary table, so I first indicated both Y & Z along the phantom lines with my Interapid. I had about a 2-inch run without hitting the outer chamfer or the centering ring so I was able to get it pretty close.



Next I gripped one end of the cylinder in my split bushing and used the lathe to get the 4-jaw close. I later fine tuned it on the RT because I know the threaded chuck mount misses center by a thou or two. Some beginners can be intimidated by a 4-jaw independent chuck but I find it is actually pretty easy to use. eyeballing the alignment within .010 with a bit of practice is quite doable and truing it up from there is pretty quick.

In the left image below I am zeroing the indicator with one pair of jaws horizontal. Once I do that I use the hex key to rotate it 180 and note the runout, shown on the right side at about .008. I now insert a ball driver into the far chuck and tweek the two jaws at the same time to split the difference. With that done I rotate the chuck 90 and repeat with the second jaw pair. A final check on the first pair will usually show it well within what I need before moving it to the rotary table for final truing. I've done it a few times now and can get to within .001 TIR within a minute or so. Not as fast as a centering 3-jaw, but a lot more accurate.



With the chuck moved I have to spin the RT to fine tune the centering and this is a great excuse for a CNC RT. I wouldn't want to hand crank it around too many times centering the chuck.

You can see below that I used one of the aluminum heads and Sherline's adjustable tail stock to support the outer end of the cylinder. I don't know if it was necessary with my light cuts, but it did make me feel better. No point risking that many hours to find out I should have...



I hand-wrote a little G-code file to clean off the corner of the cylinder first at 45 degrees to the original reductions and ultimately stepping around to 16 facets through the 90 degrees. From here a little quick file work got it ready for primer.

As always, let me know if you have any questions or if I am doing anything wrong.

Offline Thayer

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Re: Elmer's #33 - a novice makes chips
« Reply #19 on: December 27, 2012, 01:27:02 AM »
I'm not sure why, but for some reason I have been intimidated by the idea of making the valve. The only reason I can think of is because I don't have slitting saws. Well, I finally gathered up my courage and got into it, starting with a piece of .375 sq stock about .75 long that I milled down to .250 x .220 with a 3/8 end mill.



I left it a little tall just to give me more working room in the vise. Figured I could knock down the fingers once I was done.



That went well enough that I decided to push on. I used one of the wizards in D2nc (a fantastic addition to Mach3 by Graham Hollis) to generate the code for the pocketing, referenced off the near corner of the stock, jogged in 3/64 and pressed the go button. Sure enough, just like the scrap of wood I ran it on first to settle my nerves, the brass soon had a pretty little pocket in it that measured to the dims on the plans.



The bar coming in from the left gave me a position reference so I could end-for-end the block and cut a second one in case I needed it later.



30 seconds or so later, the second pocket was done and it was time to face the fingers.



Again I set up the stock using the stop so I could swap ends for the second. I had to hang it out the end of the vise so I could mill the slot for the rod. Since I do know enough to know that you don't want an asymmetric clamping load on your vise, I used a .25 sq. tool blank as packing for the other side of the jaws.



Did I mention yet that I can be a bit of a chicken some times? I was confident I had done all the math right, but given the hour, I decided the extra stock thickness could serve a purpose. I modified my g-code to take a .005 cut to show where the nut and rod slots would end up. With great relief I didn't see any gross errors and proceeded to cut the full depth.



Here is the first one all slotted to spec.



Cutting the second end, photographed in action through my acrylic chip guard. The transverse slot is for the valve rod which measures .086, hence the step you can see. For what it is worth, I stepped down .010 on each pass and the 1/16 carbide mill didn't seem to complain.



Since I had enough stock between the two parts and don't have a slitting saw, I used the 1/16 end mill to cut off the valve to length. Again, photographed through my chip guard.  I don't have a photo of the last step, trimming the fingers to length. I just put them side by side in the middle of the vise and passed back and forth with a 3/8 end mill until they were the right height.



And the fruits of my labor, ready for some final cleanup and smoothing of the face. I love how the light plays between the fingers. Almost makes the one look precious. As I always knew, they weren't hard to make at all and I now have g-code that will let me knock them out pretty quickly next time I need a few.
« Last Edit: April 19, 2013, 03:12:23 AM by Thayer »

Offline Thayer

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Re: Elmer's #33 - a novice makes chips
« Reply #20 on: December 27, 2012, 01:34:08 AM »
So that has us all caught up so far, at least in terms of what I have posted elsewhere. I've got a few more photos and will be following up with them shortly.

One thing I know about myself is that if my main goal is the completed project it better be simple enough for me to sprint through it pretty quickly. On the other hand, if I get to the workshop only planning to make one thing, like say some nice slide valves, and do that reasonably often, it won't too long before it is time to assemble my new engine kit.

Thayer

Offline smfr

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Re: Elmer's #33 - a novice makes chips
« Reply #21 on: December 27, 2012, 02:53:38 AM »
Following with interest! It's neat to see what you can do with a bit of CNC, and comparing it to how you'd do things manually. I also like how you think ahead (the end-stops, and making a valve on each end of the bar).

Simon

Offline zeeprogrammer

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Re: Elmer's #33 - a novice makes chips
« Reply #22 on: December 27, 2012, 03:59:58 AM »
Interesting thread and nicely made parts.
When I started this hobby (3 years ago?) I thought about Sherline and CNC.
You've reopened that question.
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Offline Jo

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Re: Elmer's #33 - a novice makes chips
« Reply #23 on: December 27, 2012, 08:10:19 AM »
Thayer,

Thanks for taking the time to bringing this thread on to MEM :ThumbsUp:. It is most impressive what you are doing with these small machines and I watch with interest to learn more on the CNC.

Jo
Enjoyment is more important than achievement.

Offline Thayer

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Re: Elmer's #33 - a novice makes chips
« Reply #24 on: December 27, 2012, 09:06:36 AM »
Thanks for the support guys. I have been having a great time working on this engine.

One of the fun things about using tools like the Sherline, A2Z and Taig is the reactions from people who are used to working on much larger machines.  For instance, I made some vintage style spoked wheels for an RC airplane a while back and because I didn't completely think things through, I ended up having to retain the wheel on a 1/16 music wire axle with a hub sized for the axle and no room to ream it out for a bushing. I ended up cross drilling the axle and using a washer and wire pin.  It wasn't that tough, but as I was telling this story at the local machinists meeting I came to realize that dropping a #75 hole through 1/16 music wire isn't something you normally do on a Bridgeport.

Here is the thread for the model and its wheels on an RC forum. It has a fun story that goes along with it and the thread only runs 62 posts if you are at all interested in model airplanes. There is also a video showing how the wheels are made.

Anyway, lets move along with ol' #33, shall we?

Offline Thayer

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Re: Elmer's #33 - a novice makes chips
« Reply #25 on: December 27, 2012, 09:45:45 AM »
Next up is the packing nuts for the steam chest and cylinder. I figured it only made sense to make them both at the same time since they are identical, save the bore size. The final size is 1/4 inch across the flats, so I started with some 3/8 brass and threw it in the 3-jaw chuck since I had plenty of room to true it up. As much as I enjoy the challenge of dialing in the 4-jaw, there really is no good reason to do so when the 3-jaw is up to the task.





Here I have cleaned the OD, turned down the spigot to 0.188, drilled the center hole and milled the relief in anticipation of threading. Yes, I have the stock in the 4-jaw now and for a good reason you will see shortly.

I learned a lot about the lowly thread gauge from Ted Stoutenberg at the afore-mentioned meeting and thought I would pass some of it along for those who aren't that familiar with this seemingly simple tool.

As you can see the gauge has one outside and three inside angles that measure exactly 60 degrees. These are used to guide you while grinding threading tools, as well as while aligning the tool to your part. I've only got one of these, so used a little Photoshop trickery to show both sides at the same time.



Additionally, there are four pitch scales and a chart that tells you how deep to cut the threads, times two, or the overall diameter reduction to plan on while threading. While not every thread pitch is covered directly, simple math lets you sort out the ones that aren't. For instance, I will be cutting a 10-32 thread on these parts and while there is a scale for 32 tpi, there isn't a listing on the chart. No worries, as it does show 16 tpi as being 0.081. I just divided that by 2 to get a combined thread depth of 0.0405, so 0.0203 on the dial.

This is a pretty small part so getting the thread gauge in place to check its alignment against the stock wasn't going to happen. Instead I got all clever and aligned the back of the tool with the turned stock. Unfortunately, when I went to check it with the gauge it was clearly out more than I wanted.


 
I then realized that I don't need to align it to the part. The lathe bed is also parallel to the spindle and could stand in. I used a soldering clip to hold the tool parallel to the bed while I adjusted the tool post.  A2Z CNC Quick Change Tool Post, in case you were wondering.



Finally, here is the cross-slide dial set to 0.020 before the zero to give me an obvious stopping point.  The adjustable handwheels on the Sherline equipment are a great feature that in this case saves having to end a thread at 0.027, or some other nonsensical number.



I am not going to cover the Sherline threading attachment here since you can read the manual online if you really want to know how it works. Basically what you do is remove the motor and put a hand crank on the main spindle. A variable set of gears ties the Z-axis leadscrew to the spindle and lets you cut consistent threads, given a little patience.
« Last Edit: December 27, 2012, 04:14:43 PM by Thayer »

Offline Thayer

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Re: Elmer's #33 - a novice makes chips
« Reply #26 on: December 27, 2012, 09:57:50 AM »
First off I made a light skim cut and confirmed I had chosen all the right gears and set them up properly.



Comparing to the 32 pitch gauge shows one thread for every mark. If I were cutting a 16 tpi thread I would look for them to align with every other tick on this scale.



Here I am part way through the cutting operation and have just gotten to the relief. Basically you set a cut depth of a few thou, crank the spindle until the tool gets to the relief then back out the tool, rewind, reset the depth and do it again.



This shot shows why it is so important to back the tool out of the thread while back-winding between passes. There is enough backlash in the system that the tool tip gets kicked out of alignment while you back-wind. You can see here that the backlash amounts to about half the thread pitch as I reset the tool to the start. You don't want the tool binding in the groove. Besides, since you are turning the spindle backwards at this point the part would be rubbing against the back of the cutting edge. Not good.



This is why I switched to the 4-jaw. Threading the chuck onto the rotary table doesn't center it perfectly, missing by a couple thousands or so. Holding the stock in the 4-jaw lets me bring it into near perfect alignment before cutting the 6 flats. CNC makes quick work of this, with multiple light cuts and auto indexing on the angles. Or at least auto indexing if I program it right.



Here is the nearly finished part, ready to part off from the parent stock.
« Last Edit: December 27, 2012, 04:20:35 PM by Thayer »

Offline Thayer

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Re: Elmer's #33 - a novice makes chips
« Reply #27 on: December 27, 2012, 10:08:20 AM »
Getting set to part off.



Not so fast, Champ! Milling that part to length and getting a nice chamfer on the threads would be pretty tough with my fingers and a file. Let's make it pretty before cutting it off.



That looks much better! Now where's my parting tool?



Once the part is nearly free, take a small piece of wire or a drill bit and thread it through the center bore to catch it as it separates. The troll under your workbench will make a quick snack of your efforts if you don't.



And here are the two finished packing nuts. I haven't made the steam chest yet, so I'll leave one in the original aluminum cylinder head for now.

Incidentally, I know some of the above photos seem out of order but they aren't all of the same part.

Offline steamer

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Re: Elmer's #33 - a novice makes chips
« Reply #28 on: December 27, 2012, 01:10:58 PM »
And a fine job your doing Thayer...I .....and my 10 year old daughter ....are very impressed and watching with interest!

Dave
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Offline Bearcar1

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Re: Elmer's #33 - a novice makes chips
« Reply #29 on: December 27, 2012, 01:46:40 PM »
Thayer, this has been a relaxing and interesting thread so far. Great job, please continue.


BC1
Jim