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Hold square bar in a 3 jaw chuck

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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:

--- Quote from: Andrew_D on January 08, 2012, 10:33:07 PM ---........

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

--- End quote ---

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 :Doh: 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 :beer:

daz

DaveH:
Daz,

You will get plenty of use out of your new 4 jaw chuck. :clap:  It's a very useful piece of kit to have :thumbup:
 :beer:
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  :palm:

BR

/Peter

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