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How make a disk?

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Bill Kahn

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#1
This is a total beginner question. I need to make a 2” diameter aluminum disk 1/4” thick. Nicely machined on both sides and the perimeter. This must be a routine operation. I guess I grab 3/16” of the perimeter with the three jaw and do one side. Maybe with some sort of standoff’s I repeat for the other and get the second face parallel to the first.

Now how do I machine the edge to finished diameter and nice finish? How do you “grab” it?

Thanks.

-Bill (PM1030V)
 

benmychree

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#2
You can put a center hole in it and push the blank against the chuck jaws, set to a diameter a little less than the finished diameter of the disc. If you use enough pressure against the disc and take light cuts, it should work well. If you can't tolerate the center drill, make another (smaller) disc to apply the pressure, and add some double sticky tape in between, or just a piece of paper.
To do the sides, put a spacer behind the blank to space it out enough beyond the face of the chuck jaws to allow for cleanup on the second side.
 

mcostello

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#3
What is the size of the stock You are starting with? A 1 1/2" piece of stock faced off would hold a small disc with pressure sensitive tape to finish one side and the edge. Use small careful cuts then flip the part and finish.
 

DHarris

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#4
How nice is "nicely machined"? Couldn't you just chuck a 2"+ diameter bar in the lathe, turn to desired diameter, face the end and then use a nicely sharpened cut-off tool to remove a 1/4" piece? then step out the blank and repeat. If it needs a mirror finish you could then replace it in the lathe and polish all sides? Dunno, just a newbe suggestion.
 

rgray

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#5
I'd probably do it somewhat like Dave (above) I'd cut it long and do the second side in the mill. (not sure if you have a mill)
 

petertha

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#6
I've made parts like this. Assuming you are seeking bit more dimensional control than a shiny puck, I would:
- chuck the rough stock (here again, if you want 2.00" then are you starting with 2.25" or starting with 2" and 1.98" is fine?)
- turn the OD & turn the face. Machine any corner chamfer. Now you have 2 good surfaces established
- a) part the segment say .025" oversize if you have appropriate parting tooling but that's getting to be a reach for most hobby equipment, b) just hacksaw it off
- holding the piece rigidly & accurately to machine the back face looks simple enough but you need to be aware of not a lot of grip area between chuck jaws. I would use spacers between the machined face & chuck body. I've used MDF for this which is surprisingly accurate. Take light cuts until you achieve your 0.25" finished width & ,matching chamfer as necessary.

Another option is to glue the disk to a sacrificial blank which has been machined true in-situ. Use CA glue, allow to fully cure, then again just light cuts (like 0.010" per pass). When done, remove the assembly & release the glue just apply gentle heat with a torch. Check out Clickspring YouTube videos, he does a lot of this. I had several washer like parts to make & this technique came in handy.
 

GoceKU

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#7
About half an hour ago i just made two small (38mm) stainless discs, i started with 40mm solid piece, drill the center hole, face it, machined it down to 38 mm chamfered all the edges i could then parted it off with carbide parting tool, i speed up my lathe to 1200 rpm to get that smooth finish.
DSC_0260JPG.jpg
 

kvt

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#9
how many or how often will you need to do this procedure? Like several have said Finish the diam to size, Then face, and cut off with a little extra thinckness. If you are doing a bunch, you could make a block set up to go behind it and soft jaw to hold it, Then re chuck it up and finish the other side. I have done that on several things, Make a piece I could put behind It and that way when I put the piece back in properly I had room to face off the second side, to the proper thickness. Tried the tape etc, but if doing several does not seem to work that great for me.
 

cg285

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#10
it's only 1/4 thick and he says routinely. i would do like others have said and part or saw off - then using the fixture you made (that is indexed to the chuck) face/chamfer the other side. i would visualize the fixture as round bar, bored to size and the bore shallower than the part thickness with the edges split and clamped to the part
 

P. Waller

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#11
Place bar in lathe, face, turn and chamfer the end.
Either part or saw to near length.
Pocket soft jaws and face and chamfer the back side, you may make hundreds of parts per day this way in aluminum depending on the alloy of course. I personally find it difficult to part such a piece to 0 and achieve a good finish, when the part comes off it will always leave a center nub which will require back work anyway.

316 SS discs, pre-sawed, 3"+ OD that finished at .375 +.000 -.005 thick, 50 parts ordered so I made 55 just in case, the remainder of the work was milling pockets and holes in each part (-:
It took about 6 hours for the lathe work.
 

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petertha

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#12
Here are some pics of my 0.138" thick drive washer using the CA glue mandrel technique. Another pic showing the cheapo MDF spacer disc method, happens to be backing for RT drilling operation but same technique for lathe turning.

I've just got to make me some of those soft jaws!
 

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Crank

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#13
never mind, I didn't read the answers posted and I was repeating an idea.
 

P. Waller

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#14
Here are some pics of my 0.138" thick drive washer using the CA glue mandrel technique. Another pic showing the cheapo MDF spacer disc method, happens to be backing for RT drilling operation but same technique for lathe turning.

I've just got to make me some of those soft jaws!
Buy them, far less expensive then making them yourself, we sometimes run several dozen at a time when one of the mills is busy doing nothing for a few days. As with most other simple products you can not make them nearly as economically as a shop that does nothing else, we use H&R, Dillion and Monster Jaws mostly. Monster makes some very inexpensive pie jaws in aluminum that are excellent for thin parts of largish diameters, aluminum jaws do a bang up job of not marking finished surfaces as well.

http://monsterjaws.com/
 
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