Newbie Question: Machining Disks on a lathe

HMF

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If you needed to make disks with an OD of roughly 3" with a hole in the center the is 1", how would you do it? In other words, how would you hold the workpiece centered so you could do the facing and cut off accurately?

Thanks,

Nelson
 
Need more info like the thickness, but I use a couple different techniques. Very often for thin disks I make a flat faced arbor, maybe with a small step if the disk has a hole, then I put a live center in the tailstock and use round cylinder having a center drilled spot, to apply pressure to the disk. I.e., I clamp the disk between the arbor and the tailstock so I can turn the OD.

I also make up rings for my chuck so I can clamp the disks near the end of the jaws for facing and boring. Think of the rings as round parallels that are slightly smaller than the disks to be machined.

Lots of people use pot chucks, but I ain't got any.

Conrad
 
As Conrad said, thickness has a bearing on the method. If there is chucking thickness, this is a good place to use soft jaws bored a few thousandths less deep than the disk thickness. Turn finished OD, rough drill hole, part off, flip into soft jaws and finish machine.
 
I have 3 ways that I use to cut disks and a washer would not be a huge jump to do with any of these ways. Just depends on the thickness of the part.

I have used hot glue on a sacraficial plate and bolted it to the face plate. This can work if you are careful to the cutting forces and temperature. At times I have had to use a air cooler gun (Vortec) to keep the metal cold. Removal is easy and so is the clean up.

I also have a plastic insert faced in cork, that fits in the center hole of a chuck mounting plate with a smaller also cork covered piece that fits on the live center for the tail stock. I put the piece between the two and apply pressure via the tail stock. I center the part up and apply MORE pressure. I have used this method down to about .050" with soft metals. On really soft metals you have to freeze it and work faster or refreeze again. Cutting the center hole is another operation either the next one below if possible.

Word of warning. Do not take a heavy cut as it will either just spin the disk or spit it out. I use a guard for these jobs and it has caught a couple of disks over the years.

I have replaced the jaws on a 3 jaw self centering chuck with soft jaws that are cut for the 3 different sizes that I have to usually make. 2, 3 and 4" recesses that are about .080" deep. I then can face both sides of a disk in the chuck.

All 3 will work within their limits.
 
As has already ben stated, depends on type of material and thickness.

Flame cutting discs leaves a really hard slag edge and is murder on cutters, so I will usually go the holesaw route and cut out a disk slightly larger than my finished size. So for 3" diameter, that means using a 3-1/4" Holesaw. Remeber holesaws are sized for the hole, not the disc that is left over and often considered as discard scrap so you have to account for the saw kerf.

This will leave you with a rough washer that is just over 3" dia with 1/4" hole if you used the pilot drill, no hole if you left out the pilot. Chuck up by OD and drill, bore and finish the ID.

Mount on a suitable mandrel and turn the outside to dimension. Now you did not say if you needed to face the disks as well. If that is the case, you may want to look at using an internal expanding collet.

Walter
 
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