Hold square bar in a 3 jaw chuck

[DaveH]

I’m sure this may have been shown before, I did look and search.
So apologies for repeating it.

If you are new to machining you may not have seen it.

I’m basically lazy, - sort of goes with my good looks,  so sometimes rather than changing to the 4 jaw chuck I just use the 3 jaw chuck.
The square bar is just held using a split tube.

This one is for holding 25mm square bar to bore a 20mm dia. hole.




Just to give an idea of the tube size (“collet”) the I/D is 33.5mm dia. the wall thickness is .100” (2.6mm) which gives an O/D of 38.7mm dia.

The way I make them is I first do the I/D first so the square bar just goes in (with a push), then cut the outside to give a wall thickness between 2.3 to 2.8 mm  (.090” - .110”) The wall thickness is important from the fact that if it is too thin it will crush under the force of the jaws. If it is too thick then too much force is required to hold the square bar securely – risk of straining the chuck.
I just cut the slot with a hacksaw.

This one was for holding 10mm square bar to cut a 9mm dia. boss. The wall thickness of the “collet” is .100”




Now obviously it is not as accurate as using a four jaw chuck. But sometimes it doesn’t have to be.

Just remember you are using edges (never the best way) so just check for burrs and such.

A few more – from left to right to hold sq. bar 25mm,      10mm,      20mm




Can be useful for the quick hole or boss.
 

DaveH

[sparky961]

Very useful indeed.  I've seen this method before, but with all of the information constantly bombarding my brain it's always good to bring the most useful things to the surface again.

Thanks for posting it.

-Sparky

[Stilldrillin]

Thanks for the explanation and pics, Dave. 

Two nights ago, I was on the phone, trying to explain the technique to Ross....... 

I'll make sure he reads this!

David D

[saw]

Yes, why not, sometimes the simples way is the best 

[Ross]

Thanks for the explanation and pics, Dave. 

Two nights ago, I was on the phone, trying to explain the technique to Ross....... 

I'll make sure he reads this!

David D

Don't worry David, just read it!

Very good explanation, now I'll go look for some suitable pipe.

[Rob.Wilson]

Handy Tip Dave 


Rob

[Anzaniste]

Is it possible to hold square bar in an ER32 collet?

[AdeV]

Is it possible to hold square bar in an ER32 collet?

ER collets appear to only be available in round form. Whilst you probably can hold square stock in a regular collet, I wouldn't because I suspect it would damage the collet.

5C collets can be had with round, square or hexagonal grips, but I guess that's no good if you've already got ER32 stuff....

[Anzaniste]

That was my point really. Isn't a round collet essentially the same as the split collet that started this thread. I was just wondering if anybody had tried it. Idle curiosity really.

[andyf]

Is it possible to hold square bar in an ER32 collet?

As a last resort, it is possible with care, if the collet has 4 or 8 slits as you look at either end . You have to be careful that the corners of your square bar are gripped by the lobes, and aren't trapped in the slits, so don't put the corners in the middle of the lobes you can see at the front, because that will place them in the slits which run from the back. If the bar shifts, a corner is bound to catch up in a slit and try to twist the collet out of shape. So, light cuts only, which isn't easy because of the interrupted cut which you will get on square bar.

On reading this before I post it, I wonder if having the corners caught up in the back slits could be  be an advantage, if the diagonal of the bar is not much less than the uncompressed ID of the collet.

I've only ever done it once, because it was proving difficult to get a smallish square bar well centred in a 4-jaw chuck.
 
Andy

[Andrew_D]

Regarding the ER32 idea....

Let's say you put a 3/4" ER32 collet in the chuck and some 3/4" stock. Drill out the center and bore to the appropriate size. Remove the bushing you just made and slit one side. Re-install the bushing and your square stock. Tighten down.

In order to keep that 0.100" side-wall, you need to do some quick checking before you start to see what size of stock/collet you need to start with! Alternatively, use that 3/4" collet, leave enough sticking out so that you can do the internal bore and then turn down the outside to get your 0.100" wall. Now use the appropriate collet depending on your OD.

As mentioned above, trying to use the ER collets without the bushing could be a problem since the ER's are split from both ends - it will be hard not to hit those slits front and back!

As a side note, does anyone know why there isn't square/hex/??? collets in the ER styles? It should be relatively easy to do at the factory level on the big CNC machines isn't it?

Andrew

[DMIOM]

........

As mentioned above, trying to use the ER collets without the bushing could be a problem since the ER's are split from both ends - it will be hard not to hit those slits front and back!

As a side note, does anyone know why there isn't square/hex/??? collets in the ER styles? It should be relatively easy to do at the factory level on the big CNC machines isn't it?

Andrew

Andrew,

Yes, maybe easy to do at the original design stage but not always so easy to modify afterwards.

ER collets have slits around the circumference (and as you say offset front & rear) and all segments move in near-identically along radial lines when the outer surface is driven into the receiving tapered bore - this is what helps with reduced run-out.

I belive any non-circular collets would need to have an appropriate number of slits so that the compression was identical on each face (e.g. one per face at the front and one per corner at the back) - giving collets that were extremely size/shape specific.

Dave

[daz]

No appologies Dave, well apart from not showing it earlier that is! I just bought a 4 jaw chuck to do one job Never mind, the work picked up the tab so I shouldn't moan, neat idea though and will have to bear it in mind for the future. Simple and clever ideas are always the best, thanks for showing

daz

[DaveH]

Daz,

You will get plenty of use out of your new 4 jaw chuck.   It's a very useful piece of kit to have
 
DaveH

[PeterE]

Coming a bit late into this thread about holding square parts in a 3-jaw or collet chuck.

I remember something about Harlod Hall describing how to make inserts for an ER-collet to handle square stock. I think they were made using four smaller square pieces of bar held together and nipped in a 4-jaw to be turned round. Eacjh of the four parts were then placed in a milling vise and the remaining square inside corner being milled off flat in parallell with the rounded outside. That willproduce four inserts that when placed around a square bar turns it into a round bar.

I hope you could make sense out of this 

BR

/Peter

[welafong1]

nice idea
thank you
Richard Westerfield

[ddoyle]

Old thread I know, but I think this is my solution for drilling my pen blanks, since I don't have a drill press, and only have a 3 jaw chuck on my mini lathe .  Thanks !!