Work Holding

[kingmt01]

Let me get your thoughts on this. I have a 1/2 plate 5" squareish that I'm turning to a 4" circle. The only crucial dimensions at this point: I've already bored the center to .830" finish size & squared one side with that hole. I need to keep the outside concentric to the center hole. I'd normally chuck a piece of round stock up & turn a stepped shaft that I could press the part on them turn it to size but this is a interrupted cut. It is a unknown metal but seems to cut exactly as a medium carbon steel in the annealed stage. What I'm calling medium carbon is about like 1040 steel.

Hind sight I shouldn't have cut the center to size yet. If I'd cut it small it wouldn't have hurt it to slip & I could have finished it in the mill when I done all the other finish operations. It would have been easier staying on center too.

 

[T Bredehoft]

We need to know more of your machining capabilities, Mill? Rotary Table? its a breeze,

Only a lathe? Mount it on an expandable arbor on a face plate, put a screw through one of the to-be-cut-off corners, on a 1/8 sacrificial aluminum base. Trepan it. Like a curved (to fit in the kerf) cut off tool. Slow, steady, and well lubricated.

 

[kingmt01]

I do have a rotary table but I've never never used it. I was planning on making a center to align it but haven't gotten that far.

Equipment is a G0709 lathe, HF knee mill, 6" rotary table, HF portable band saw, piece of Steal rod to make a custom shaft.

 

[RJSakowski]

Your idea for a stepped shaft should work if you thread the end for a 3/4" nut. You shouldn't need a press fit. A slip, tight slip or light press, depending on your concentricity requirements should work fine. Use as large a shoulder as practical to maintain your perpendicularity. The torque from cutting will keep the nut tight. As Tom says, slow, steady, and lube.

 

[aeroHAWK]

If you have a scrap piece of 2" (or so) diameter stock, chuck it up and face it off leaving a short spud that is .001" smaller than the hole in your part. Drill and tap the center of the spud for... say, 1/2 - 13. Bolt your part to the face, using the spud to center it.

Turn O.D. - Voila!

 

[kingmt01]

If you have a scrap piece of 2" (or so) diameter stock, chuck it up and face it off leaving a short spud that is .001" smaller than the hole on your part. Drill and tap the center of the spud for... say, 1/2 - 13. Bolt your part to the face, using the spud to center it.

Turn O.D. - Voila!

This is actually one of the ideas I had with one more step of drilling the head of the bolt to run my center in. Actually it wouldn't have had to be concentric if I wouldn't have already bored the center to size but I need it now so I can find center again in the mill. Whenever I try to center of the inside of a hole with my center finder it is hard to get dead on. Outside world well with it. Maybe I'm using the wrong kind of tool for inside diameters.

I need to run a hole pattern concentric with the inside bore the outside doesn't really matter after that.

 

[aeroHAWK]

You shouldn't need a center if the 2" piece of stock is short.

Also, throw away that center finder and use a dial indicator. In all my 35 years running these machines, I have never found a center finder useful.

If you need to run a hole pattern, bolt your part to the mill (with spacers so you don't drill the table). Pick up the center hole with a dial indicator, using that as your zero, proceed to locate and drill your holes.

You will then be able to use those holes to hold the part while you cut the O.D. on the lathe or rotary table.

 

[pineyfolks]

Use your bandsaw to cut as much of the corners off as you can. It'll save a lot of time turning.

 

[RJSakowski]

This is actually one of the ideas I had with one more step of drilling the head of the bolt to run my center in. Actually it wouldn't have had to be concentric if I wouldn't have already bored the center to size but I need it now so I can find center again in the mill. Whenever I try to center of the inside of a hole with my center finder it is hard to get dead on. Outside world well with it. Maybe I'm using the wrong kind of tool for inside diameters.

I need to run a hole pattern concentric with the inside bore the outside doesn't really matter after that.

If you turn and tap your spud on the lathe and leave it in place, it will be concentric to your spindle and you won't have to find the center.

 

[kingmt01]

RJSakowski I only need to find center to drill my hole pattern so I was talking about in the mill.

pineyfolks I'd thought about profiling it worth a band saw but really wasn't looking forward to that task. Just cutting the end off however might not be as bad. I think roughing the conners off in the mill would be easier.

aeroHAWK I don't have a indicator that could sweep that tight of a inside radius. At least I can't figure out a way to mount it so it would.

The tool I use zero my machine is probably actually called a edge finder. It works well on the outside edge but can't move as much running on the inside. It looks like this.