Soft jaws

[Mr Ron]

I finally figured out how to set up and use soft jaws, but there is only one other thing I can't figure out. When boring the jaws, how do I measure the diameter needed to hold the work pieces without one of those 3 point inside micrometers?

[SteveM]

If your jaws are wide enough, you can probably get two points 180 degrees apart.

Short of that, you can bore until the part just slips in.

If you turn something just shy of the target diameter, you can use that as a p,lug gauge to let you know when you are close.

Steve

[John Hasler]

Measure between the centers (or any two corresponding points) of two jaws and do the trig.

[tetramachine]

Take a piece of stock, and bore a hole to some size you can measure. Make a note of size, now bore the jaws to whatever size you need.

[Mr Ron]

Short of that, you can bore until the part just slips in.

If you turn something just shy of the target diameter, you can use that as a p,lug gauge to let you know when you are close.

Steve

I think this will work for me. Thank you all.

I am making train wheels that are 2.625 diameter. I will be cutting blanks with a hole saw. Maybe the blank diameters will not be perfectly 2.625, but off a few thous. Will I be able to still use soft jaws if the diameters are off a few thous? I will need to set up twice; to cut the tread and to cut the flange. Am I thinking this correctly?

[John Hasler]

I would bore the center hole first while holding the (oversize) rough cut blanks in a three-jaw. Then I would mount the part on a mandrel to finish the OD. This should let you finish the tread and flange in a single setup. That's what I do when I make pulleys.

If you don't have a mandrel that fits the final center hole size bore to a smaller size you do have a mandrel for and then bore the center out to full size later using your soft jaws (or a four-jaw).

[SteveM]

What John said.

Using a mandrel turned on the lathe will ensure that the tread is concentric with the bore.

DO NOT remove the mandrel until you are done with ALL of the wheels.

If you are doing the holes on the lathe, bore your center holes, do not ream. Any misalignment in the tailstock will give you a tapered bore.

Don't ask how I know.

I ended up making the attached shoes to go on my existing 3-jaw chuck and used this to re-bore the wheels.


if you are drilling oversize blanks on a drill press, you can use a reamer because a reamer will follow the drilled hole.

Steve