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How to hold a small part. 3/4 sq x 1.38 long


Hot Rolled
Oct 20, 2015
I have a small part that could be made from 3/4 square bar or from 1-1/16" dia .

I want to hold the bar in the 4th axis and hang the part out about 1-3/4" in order to machine 5 of the six sides.

So how to hold it?
Round collet with stop? Might be less secure.
Round soft collet with blind bottom. Perhaps less likely to move sideways.
Dovetail? Is there a dovetail that will hold a 3/4" square?
Grip jaws in Orange vise? Will that be secure? Mill dovetail grooves first?
I'd be okay holding 1-1-16" in my 5c collet closer I have for my 4th axis; not sure what you've got to work with.

If you go the square bar route I'd mill a 0.06" 45 deg dovetail on the end then hold it with the orange vise. Though it'll be kinda bulky.
Square collet an option? Probably not ... generic square bar what it is ... 'trapezoidal'. There's got to be a collet profile that would work... maybe a flat at 1/2 bar size, and the other 3 a convex radius tangent?

Yeah, I'm optimistic the 'flats' measure somewhere close to the same.

... Upon further review...

I'm thinking *rd bar* ??? ... duh, 'out of rd' ... 'something' somewhere back in time... nasty chatter or a turned diameter that wasn't round because of the scale gripped in the chuck jaws ... I think maybe I now understand why the shops running 'screw machines' had a 'centerless grinder' in house.

Cutoff in the 4th? Right angle head and saw... or plow it off with an endmill ... BTDT ... FML ... LOL!!! ...

So possibly 'bar fed' with a stop pin in the spindle. Hmmm, requires an operator ...
The part is small, but has some very thin parts. It currently seems to be machined out of tool steel and measures up about 60 HRc but the customer says that is too brittle.
So I'm opting for 4140 and have it heat treated to 40-45 RHc and machine it after HT.
I was thinking if I could saw bar chunks to 12-18", whatever doesn't flop around on a speedio, and then plow off with an endmill.

It is the first time to make these, and all I get are sample parts, no drawings because that is cheating.
Hi Houdogforever:
Have you considered 17-4 PH in condition H900.
Close to 45 RC and machines like a dream.
McMaster has it in stock but you can't get 3/4" square bar, so you'd have to mill down 3/4 x 1 bar.

I'd just stick it in a 3/4" square 5C collet.
Mcmaster has them too but they're made in India and are not very accurate.
Fifty odd bucks will get you one.


Round soft collet with blind bottom. Perhaps less likely to move sideways.

I don't think this will help much. I'd rather put it all the way through a collet.

Do you have a through hole on the 4th? Put a bushing on the back side, even with setscrews. Solid as hell. Of course you'll have a long remnant.
Can you hold it in a 2" wide production vise and machine all 6 sides in two ops? I can't tell for sure if this would work from your photo. This is how I would try to do it, but I already have the vises.

Here is a part I made this way from 3/4"sq x 2" long 416SS bar, with a video of my Brother making them in a 2 station vise. Please excuse how slow it is, I will speed it up considerably the next time I run them and they will go faster when I am doing them on 4 sided 8 station versions. With a single table mill I swap the vises with 15-20 seconds of spindle down time with a pneumatic tailstock. If you don't want to deal with a tailstock you can bolt them to the face of your rotary, but then you can't load parts while the machine is running :ack2:(n).

One hole is counterbored from other side for a bolt. The smaller hole must be a locating pin. it only goes about half way thru
Can you machine up the one side with the holes and used it to hold the parts? I have had success using expanding dowels to hold parts down especially if you are taking light cuts.
What kind of quantity are you looking at? If a low volume, I would agree doing it in your 4th would be great, but if a higher volume, I think I would be looking at a pallet of sorts to run multiples.
It is a wear part and they said they would order in quantities of 20 of each hand.
There are other plants so there is an upside too.
I'd want to know more about the application before I jumped from ~60Rc mystery steel to 40-45Rc 4140. You might know that information. Based on what you've said, and what I can see, I'd consider A2 at 50-54 Rc. Very stable, shouldn't have any movement with a decent heat treater, double draw.

Depending on what features we might not be able to see, it looks like you might be able to drop essentially complete (tab on back) from 3 sides?