Making One Washer

I was going to post a question about making a large washer -- 2.625 OD, 1.06 ID, about .375 thick -- until I realized I could buy almost exactly what I needed from Fastenal .. problem solved. The tolerances are pretty loose in this whole problem -- 2.5" or 2.75" OD would be OK, as would a 1.125" ID, or .400 thickness, etc.

But since I was going to ask about this sort of thing anyhow, I might as well proceed.

My plan was to make this from some flat stock: Mark a center and a 2.625" circle, drill a 1" hole using the milling machine, cut that out roughly with the bandsaw, put the piece on a mandrel and chuck it in the lathe, and then make it a bit more properly round (which probably means doing an interrupted cut, since my bandsaw work will probably end up making something like a 16-sided polygon rather than a circle), press out the mandrel, re-chuck the piece in the 3-jaw chuck, and bore it out a tiny bit larger (or use a 1 1/16" drill, which is close enough).

Alternatively, I could have gone back to the milling machine to drill that last hole, and that's where my question arises:

When you've got a relatively small, relatively thin, piece of material that you want to work on using the milling machine (imaging that I want to make the center circle into an oval, say), how do you hold onto it? Or is this just a bad idea, and I'm supposed to do something entirely different? This problem, in various forms -- small pieces that I can't seem to hold well -- keeps arising, and I figure someone must have solved it. My only thought so far was to make a "sandwich" with my piece between two slabs of aluminum, with through-bolts to clamp the aluminum pieces together. Of course, that means I can't see the workpiece any more...but at least it'd be held fairly securely.

Any suggestions for an amateur like me? (My general approach is to give up, because I'm really scared by what can happen to pieces that get loose...)

Lots of unknowns here but ....drill an undersize hole in that plate , mark your OD , cut it on the saw , either use 2 sided tape on your jaws or take light cuts with your live center acting as a pressure pad . It may spin but it won't fly out . Then you could finish your ID hole to size in your 3 jaw . As far as milling . Get yourself a piece of aluminum suitable for your millvise . Put some tapped holes in it thus you have a mini sub plate and can clamp your workpiece down . You can re-skim the plate as necessary if you need .

mmcmdl said:

Lots of unknowns here but ....drill an undersize hole in that plate , mark your OD , cut it on the saw , either use 2 sided tape on your jaws or take light cuts with your live center acting as a pressure pad . It may spin but it won't fly out . Then you could finish your ID hole to size in your 3 jaw . As far as milling . Get yourself a piece of aluminum suitable for your millvise . Put some tapped holes in it thus you have a mini sub plate and can clamp your workpiece down . You can re-skim the plate as necessary if you need .

Click to expand...

Thanks very much for the quick answer.

I'm not sure I entirely understand (in fact, I'm sure I don't). The hole in the middle is for the live-center to hold the rough-cut piece against the faces of the chuck jaws, with the two-sided tape providing spin-resistance. That much makes sense. Presumably I cut the thing to something like 3" or 3 1/2".

Now to get it to 2.625, I come in with the tool by moving the saddle towards the chuck, cutting deeper and deeper into my material. At some point, I've gone all the way through, and the disk falls into the space between the jaws, while the remaining "ring" at the outside, no longer held by the live center, is free to move (although held in place by the two-sided tape, we hope). And we hope that the tape is thick enough that my tool, making the last bit of the cut, didn't actually try to start cutting the chuck-jaws.

I must be misunderstanding, because this sounds like a recipe for disaster...that loose piece could get wedged between the tool and the jaws (which are separated by only a small distance, or the tool, which is now cutting only the outer ring, could apply enough force to overcome the strength of the tape, making that ring get loose, and then get wedged, and ...

As I said, I must be misunderstanding.

For the mill: I get the idea here, I think. But when you say "clamp my piece down", do you mean "catch an edge of the piece under the lip of the screwhead", or "hold it down with a strip of aluminum or steel that's held down by some screws in those threaded holes" or something else?

Your finished part must be on the tape , on the jaws . You will be turning the OD , not trepanning it to size as I believe you mean . Use a backer to avoid cutting into your jaws . Clamping on your subplate can be up to you . Step blocks can be cheaply purchased or made .

Edit . I guarantee you won't overcome the tapes strength if done correctly !! It's an mfer to get your part back sometimes ! LMAO .

Thanks. That makes total sense now that you say "turning the OD rather than trepanning" (a term I've only heard used in the context of 19th century medicine, for removing a piece of skull!). And now that I see that the piece is held throughout the process, it seems totally reasonable. (And you can surely see my concern with what I *thought* you were suggesting!)

Ahhaaa . Sure do . I've turned many a parts into " spaceflight material " thruout my years !

I have made many washers from flat stock or plate. I drill a suitable hole in the center and rough out the O.D. with a band saw. I then take a suitable bolt and cut the head off. Next, I thread a nut on, place the blank on the bolt, followed by a second nut. The assembled mandrel is chucked in the lathe and the O.D. turned to size. The mandrel is removed and the disk chucked in the lathe and the I.D. finished to size with a drill or boring tool.

Hole saws are quite handy for roughing out a circle with a hole in the middle, very easy to over heat them on steel though so lots of coolant.

Stuart

Here's the problem when using mandrels in a lathe or grinding situation . The L over D ratio ( length over diameter ) tends to throw your faces out of perpendicularity . You may have ..500 bore by 1/4" length and an OD of 3" just to say . It would wobble . Mandrels are better suited for longer length parts . Any mandrels I've used or made are .0005 per inch taper on the diameter .

Better option and possibly cheaper ..........turn your ID on an aluminum bar with a tapped hole . This is called a " spud " . All planes run true in this set-up . Don't ask me why it's called a spud , but it sounds good enough to eat !