"Dumb" question about machining thin parts

Me, I grind 'em on my surface grinder. If I had to do it on a mill, I'd use 3M brand double-sided tape and go slowly with a dead sharp HSS milling cutter.

GWE

There are a couple ways to attack this. One is to make the stock the correct thickness first, then drill a hole in it. Now, grip a bolt in the lathe chuck with the threads sticking out. Run a nut on the bolt, the stock with hole, and finish with another nut. Tighten the nuts together with 2 wrenches. Now, you can turn the OD as desired. I make a number of odd spacers, etc. like this.

If the entire part needs to be concentric and the faces parallel, make an arbor from random stock, by chucking in the lathe and facing true. Superglue the stock to the arbor. Perform all operations, facing, ID and OD turning, etc. Both faces will be parallel to the extent the superglue formed a uniform thickness film. When done, pry thicker parts off the superglue, or use Acetone to dissolve the superglue and release thin parts.

Jon

Things like these I make often that way:

Have some stock, bore & turn to desired ID/OD but do not part off. Clamp it in the vice on a mill and cut off with a circular saw*) (a thin one; 1mm thick; diameter about 50mm). You can get the thickness to within 1/100mm. If you want, 0.1mm thick. Astonishing what _sharp_ and good circular saws can do! I use the "REBO" brand.

Might help to know exactly what you want to make. It often helps to have quite some stock left for holding/gripping/clamping and parting that off in the very last step.

Nick

Start with a washer, then do what you need to it. You might need a custom-made mandrel or a faceplate with a bolt to hold it rather than an edge-clamping chuck. You might even use a magnetic lathe chuck and a custom-made recessed faceplate ($$$).

Very thin parts are just a damn nuisance. As "parting them off" is indeed nigh-impossible, you'll probably start with something that's already thin, then make it circular. Other good techniques are punch tooling instead of a lathe, or changing the design so that the thin part is indeed a plain washer, maybe with a small turned boss added to it.

How do you do this if the hole size doesn't match up with an existing bolt, though? Assuming you want your hole to be centered in the piece, anyway.

--Donnie

On 1 Dec 2005 13:32:59 -0800, "ducque" wrote:

In The Home Shop Machinist, Projects Two, Page 22, (Available from Village Press), D. E. Johnson wrote a piece on "Machining Thin Disks and Rings. His is a three step process that results in a part of proper diameter and thickness, but does require a hole in the part. At the risk of getting flamed for "disseminating copyrighted material", a paraphrase of the steps follows. Step 1: Chuck a piece of stock and turn a stub end, OD to the diameter of the hole in the finished part and length to allow re-chucking after step two. Face the shoulder as it will be one of the finished faces. Drill a hole, centered in the part and as deep as the stub length + the finished parts thickness + say 1/8". (This hole diameter should be large enough to allow a boring tool to enter) Step 2: Part of the piece allowing for enough material to finish the thickness. The drilled hole should be deep enough to meet the parting tool. The result, in cross section, is a 'T' shaped piece with a hole through it. Step 3: Reverse the part in the chuck, chucking now on the stub, finish the parts OD. Face off to the parts thickness and clean up the edges. With a boring tool, enlarge the hole to meet the OD of the stub. Quoting Mr. Johnson here, "... the finished part will fall off leaving only a slight burr for cleanup. Feeding the boring tool in at an angle using the compound will produce a countersunk hole" I've used this process a number of times with good success. It takes a little longer but the results are worth the time. YMMV :)

Regards Bob rgentry_at_oz_dot_net _AT_ = @, _dot_ = . to eMail

Soft jaws. Soft jaws. Soft jaws.

There's not better tool in your arsenal-------

Harold

That, of course, should read "there's no better tool in your arsenal". Sorry, my fingers got away from me.

You can hold thin sections and face them dead parallel with no effort, and do it time and again. You can also hold complex configurations the same way, with the added benefit of the jaws acting as a perfect linear stop. Great for multiple pieces that must be concentric, perpendicular and the same length.

Harold

If the part is flat on one side, and you didn't say, part it off to thickness. Sharp and rigid parting tool, lots of cutting oil and a steady hand on the feed.

If neither side is flat and it's small, add soft collet to what Harold said.

Rich

Laser job shop.

This gets a bit more complicated, but you certainly can do it. One way is to build a shoulder into the arbor, to support one side of the work. You turn a smaller diameter out from the shoulder just slightly smaller than the ID hole in the part. Then you turn down and thread the rest of the arbor to a convenient thread size. So, one side of the part rests on the shoulder, the ID is centered by the rod next to the shoulder, and a nut can be run down to hold the other side of the part. You can also turn a disc that supports the part almost out to the OD, if it is very thin and flimsy.

Umm, did I describe this well enough to be understood? I hope so.

Jon

The old machining and watchmaking books suggest soldering thin parts to a custom fixture. If you tin the part, wipe off the solder and clamp it in place while heating it the error due to solder thickness should be small and repeatable.

I cut a shallow recess in a soft collet or the top jaws of a Microcentric chuck when I need to turn a thin washer that can't be surface-ground. Sometimes the part also needs clamping pressure from the tailstock

I've made an aluminum hydraulic pump rotor shim 0.008" thick by etching a thicker machined part with drain cleaner.

jw

Making jigs is a substantial part of learning machining methods. I'd probably make up a round block with two slits in it so that it will compress around the part and hold it. The hole in the front will be somewhat less than what the part finished surface needs to be so that you don't cut the jig to finish the part. I'd also recomment a 4 jaw chuck for this work and that you make sure that everything is clean before doing the final work.

-- Why do penguins walk so far to get to their nesting grounds?

I have a 45 year old Surface grinder - and noticed the spindle nut was turned nicely. What made it unique - remember it has to be flat and have the threads exactly done as they should - very high speed turning and pressure on a rock.

What they did was use an expanding dovetail chuck on the lathe. They likely did the front, and turned the dovetail - 2" in diameter or so and then bore the hole and turned the threads. Parted the nut - It is maybe 3/8" thick - held it with the dovetail in a special lathe or perhaps the same lathe. Once mounted, the back is faced - and maybe ground.

I suppose there are expanding dovetail chucks that are metal lathe rated - I have them on my wood lathe. I have never seen them.

But I think that was a neat way to do things.

The front of my new one has an internal dovetail (likely used in manufacture) but a reverse dovetail - so a small dovetailed chunk of metal can be moved and then locked with an Allen screw.

Neat way if you can live with a dovetail - or grind it off after screwing on the nut...

martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder

Harold and Susan Vordos wrote:

The old watchmaker book used the technique used in diamond/precious stone cutting - a 'stick' with hard wax - heat the wax and place object. Now an object with a handle. Tin is a harder 'wax' - good idea. Lead might - might be strong enough. Ca glue is used and might work. .... Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder

snipped-for-privacy@segway.com wrote:

try double sided carpet tape.

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

There are more options left. You can put the part between brass shims that you (partialy) mill away. I call this "lost vice". Also soft soldering and LockTite often helps. Sometimes, parts get frozen to a plate (didn't try this, you must be either fast or constantly cooling). An other option is casting (and thus clamping) the part in low melding (100°C) alloys like Wood's metal or some Cerobend alloys. They are very stiff, you won't have bending. This is often the only way to clamp irregular shapes. You can play tricks with it when milling very thin tubes if you fill the tube with the alloy, etc.

Nick

I guess basically you're saying to do the same thing (secure part between two nuts over a bolt), but turn down a shoulder in one nut that matches the ID of the part in question. Makes perfect sense. Some of this shit is so

--Donnie

I once had to make some thin parts for some medical device. These were printed using the Metalphoto process and needed to be accurate to about plus or minus 5 thou. They also had adhesive on the back with a paper liner. So what I did was.... punch a center hole in them with a Roper whitney hand operated punch press... then I stacked them all together on a mandrel, Very fresh HSS cutter chucked them up in my 6 inch Atlas lathe and turned them to final outside diameter. Everyone was happy what more can you ask for?