How do you Accurate Mill a Full Circle?

[T Bredehoft]

Bullard VTL's. The shop I worked in had a number of them, the largest had a 6 foot table, buried so the table was flush with the floor. They were installing a new CNC model when I retired. I ran a couple of them on occasion, not production, though.

 

[jdedmon91]

A rotary table (or a lathe compound, or other machine slides) feed can be operated quite smoothly and predictably using this relatively simple technique:

Starts at 6:15, money shot starts at 18:00
A drill with variable speed and an adjustable stop for the trigger is needed, along with a fabricated adapter to fit the handle. The end mill can be ramped down into the work as the rotary table rotates, and also ramped out at the end, leaving a nice smooth cut. This technique can be used with many machine tools to make an axis feed smoothly, a poor man's power feed and stepper motor.

I made on similar for my Grizzly. Thought I had a picture or video of it but can not locate it.


Sent from my iPad using Tapatalk

 

[pineyfolks]

For an interesting trepanning tool forward to 15 minutes into the video.

 

[MrWhoopee]

One thing to consider is size. I sometimes feel cramped on my 9" Troyke rotary table. Clamping stuff to the table takes room! I'd be hard pressed to clamp much onto a 4" rotary. But, if the stuff you're working on is small (yeah, I know, a relative term) then it might do the job..
MetaKey

+1
For just milling the OD, you might get away with a threaded center stud as a clamp. In most situations, you need to put clamps around the OD of the part and, for that, the table must be significantly larger than the part. To clamp a 10 in. diameter securely, you would need a 14 in. RT. Don't buy one of those baby RTs, it will only serve to frustrate you.

 

[BaronJ]

Hi Guys,

Depending upon size and sometimes material I just use an adhesive between the work and faceplate.

This is a piece of 3 mm thick brass plate that is about to be made into a 65 mm round disc.

Almost completed ! Just needs facing off to remove the slight bow in the plate. As it happens the chuck is also 65 mm diameter. But since the chuck is sacrificial it doesn't matter if it gets damaged.

 

[oskar]

+1
For just milling the OD, you might get away with a threaded center stud as a clamp. In most situations, you need to put clamps around the OD of the part and, for that, the table must be significantly larger than the part. To clamp a 10 in. diameter securely, you would need a 14 in. RT. Don't buy one of those baby RTs, it will only serve to frustrate you.

Very good point which I never thought about it. Thanks

Nicolas

 

[BaronJ]

Hi Guys,

But why ? You would probably need a hoist of some description to lift a 14" RT up on to your mill, assuming that your mill would even be big enough to support it.

If you wanted to cut a disc, and your mill could swing a 7 inch radius, a six inch rotary table with a flat plate mounted on it, that you could glue your work to, as illustrated above could easily machine a 14" diameter disc in almost any material you wanted to use.

The method of workholding that I've shown, called a "Wax Chuck" has been in use for well over a couple of centuries. It is still in use today.

 

[oskar]

That's another option to think, I was thinking to go with a 4" RT but I'm sure it is kind too small so perhaps a 6" RT might be the best. Anything over that for my hobby use will be an overkill. In any case have lots of time before I buy one, will happen around X-Mas hoping it will come as a "gift"

 

[Bob Korves]

+1
For just milling the OD, you might get away with a threaded center stud as a clamp. In most situations, you need to put clamps around the OD of the part and, for that, the table must be significantly larger than the part. To clamp a 10 in. diameter securely, you would need a 14 in. RT. Don't buy one of those baby RTs, it will only serve to frustrate you.

A smaller rotary table can be made to act larger by putting an oversize tooling plate on it. That makes mounting parts a lot easier, just drill holes in it where they are needed. Rigidity will not be improved, however, bigger rotary tables help that. On my Millrite mill with 8x32" table, I find an 8" rotary table the Goldilocks solution.

 

[BaronJ]

Hi Bob,

Yes I agree. It bothers me when chaps who should know better drop hundredweights of tool holding on to a machine that obviously isn't designed to support it. A 6" RT is right size for my Optimum BF20LB. And as you say, a tooling plate solves a lot of issues. Lack of rigidity was the reason I said that Oskar should avoid a tiltable RT.