turning a square part to small for the chuck

[kwoodhands]

I need to thread a 2/56 thread on a 1/8" square part. My chuck will not close tight enough. I do not have collets at this time.
I think I can accomplish this with a shop made fixture. Part is 1/8" square and 2-1/4" long. I will mill a slot 0.0620 deep and 0.125 wide in steel 1/4" x 1/2" and 5" long. Then cut this in half to about 2-1/2" long. The two halves close up tight on the part. If needed I can add a screw at each end to tighten the part. The jaws should tighten the part without any screws.
I would have tried this but just thought of it . The fixture will be 1/2" square and easily chucked in a 4 jaw.

 

[ChazzC]

I need to thread a 2/56 thread on a 1/8" square part. My chuck will not close tight enough. I do not have collets at this time.
I think I can accomplish this with a shop made fixture. Part is 1/8" square and 2-1/4" long. I will mill a slot 0.0620 deep and 0.125 wide in steel 1/4" x 1/2" and 5" long. Then cut this in half to about 2-1/2" long. The two halves close up tight on the part. If needed I can add a screw at each end to tighten the part. The jaws should tighten the part without any screws.
I would have tried this but just thought of it . The fixture will be 1/2" square and easily chucked in a 4 jaw.

Joe Pie made a small square “collet” for one of his miniature machine builds. IIRC, he milled a rod to half-round, milled a 90 degree groove in the flat face, parted off two lengths then sandwiched the square stock between them in a 5C collet. I’ll try to find the video in the morning.

 

[GailInNM]

Think about clamping on the corners of the part. If your 4 jaw chuck almost makes it on the flats it may be able to clamp on the corners.
You can also make a split sleeve that clamps on the corners by drilling a hhole is a short length,1/2-3/4 inch, of say 5/16 of3/8 diameter metal. The hole should just be large enough to insert your work into it, probably a #19 or #18 drill for 1/8 square work. Saw a slot length wise from the edge to the hole. When inserting the part make sure that no edge is over the slot and then when chucking make sure that no chuck jaw is over the slot.
Gail

 

[Jasonb]

Just drill a bit of scrap round bar the across corners distance of the square, saw a slot down the side and use that as a split chuck, did it myself recently though I usually prefer to start with larger round stock and mill a the squauare after turning unless it's very long. Use a larger dia bar than this if holding in the 3 jaw

 

[ChazzC]

Joe Pie made a small square “collet” for one of his miniature machine builds. IIRC, he milled a rod to half-round, milled a 90 degree groove in the flat face, parted off two lengths then sandwiched the square stock between them in a 5C collet. I’ll try to find the video in the morning.

@kwoodhands Found it: How to Machine a Square Hole in a Round Bushing

 

[kwoodhands]

Thanks for all the replies. I tried it my way and it worked out perfectly. I added a 3/48 screw to the two pieces to hold them together. Placed the jig in the 4 jaw and indicated each side. Threaded the part after turning.
thanks mike

 

[Bentwings]

Think about clamping on the corners of the part. If your 4 jaw chuck almost makes it on the flats it may be able to clamp on the corners.
You can also make a split sleeve that clamps on the corners by drilling a hhole is a short length,1/2-3/4 inch, of say 5/16 of3/8 diameter metal. The hole should just be large enough to insert your work into it, probably a #19 or #18 drill for 1/8 square work. Saw a slot length wise from the edge to the hole. When inserting the part make sure that no edge is over the slot and then when chucking make sure that no chuck jaw is over the slot.
Gail

Sometimes just clamping s copper tubing coupler in the three jaw with a small round piece in it then face off the excess coupling that might give you a bit more clamping size.

 

[Steamchick]

Corners on a square are 41% larger "diameter" than the flats... for the jaws to gain purchase. I like the idea of slipping the square into a tube for clamping the corners, as it will protect the corners and give more torque transmission. - Corners will transmit 41% more torque than the "diameter" of the flats...
K2

 

[TSutrina]

This may sound crazy! What came to mind is a friction planetary transmission. With this approach place round stock same size to touch the corners of two of the jaws but not touch each other. Then place the square stock so that each side touches the round stock. It should self center just like the sun in a friction planetary transmission. The lowest force position is when the contact of the round stock is in the middle of the square side.

 

[Steamchick]

TS. Not crazy, ingenious. But fiddly. Using the 4 jaws as 4 vee-blocks, each vee having 2 contact points on the round, the third contact point of the round being the flat of the square.
I wonder if clever, but not quite so practical or easy to set-up?
K2

 

[TSutrina]

I did think that this maybe hard to set up. So first one jaw of the four could be at the bottom. Then two cylinders can be placed against the two corners of this jaw and pushed against the jaws that are horizontal. Now the square is set to contact those two cylinders and the corners point to the jaws. Finally place the two final cylinders between the jaws and the square. Tighten the jaws and start the adjustment process to center the square.

 

[djc]

If you have some excess of the 1/8" stock, cut off four lengths and superglue them to the faces of the piece you want to use. It then becomes 3/8" square and grippable in the chuck.