Holding hex stock in ER32 collet?

[DICKEYBIRD]

Got a possible job coming up to do some work with my little CNC lathe that requires machining a feature on the end of 1/2" hex stainless stock. The lathe has an ER32 chuck only.

So far I've been unable to find ER32 hex collets so I guess it comes down to making a hex ID split bushing of some sort. I am broachless; anybody have a brilliantly simple solution or a source for ER hex collets?

Hmmm, just as I was going to press the submit button, the lightbulb flashed on and I thought about using a thinwall 1/2" deep socket with the square drive end cut off and slit horizontally. That ought'a work; should it be split at a point of the hex or the middle of a flat?

[Arbo]

No need for any special fixture as long as you can get the hex stock far enough into the collet. The collet will easily grip on the corners of the hex as long as you dont go crazy taking hogging cuts. I've done it numerous times with no adverse effects.

[DICKEYBIRD]

Thanks Arbo. I don't have a drawing yet to see how accurate this part has to be but usually they want it pretty close.

I drew a quick sketch in CAD and lining the 6 points up on the 8 "leaves" of a 15 mm ER collet looks a little iffy. If the hex is put into the best position so no point lines up on a collet slot, the points will hit at widely varying positions on the leaves (or fingers, whatever) and would tend to get distorted when tightened and may cause the work to run-out. Hard to say without clamping one up and checking runout. Sounds like it worked OK for you though; that's a good sign.

From the verbal description of the part, it sounds like I'll have to remove a relatively large amount of metal and will have quite a few of these to do. I'll need a solid, predictable mount to hold the stock.

[RussZHC]

dickeybird:

This topic, ER system not having those collets that 5C and other systems regularly use, has come up a few times within the last year IIRC and to my knowledge (trying to keep ahead of this topic) there are no hex or square ER system collets generally available (I say that since I assume someone, somewhere has made their own). Again, IIRC, a few way more knowledgeable than I made comment as to why this was the case...with no real answer.

The "solution" so far, from over on HMEM, seems to be packing around the shape of the material (square or hex) and then fitting the whole works into a collet...to me this means somehow fitting pieces around your hex, holding them in formation and turning the exterior down to fit into a round ER collet interior...the thing is, to me, they can not be fixed in formation or there will not be enough flexibility to actually grip the part...it will fit tightly but not really with grip, if that makes any sense...(or fixed, turned and then split apart?).
I explained that poorly and it is fussy but should work...I can see it just can't explain it well.


Edit: your splitting the socket, or any other sort of bushing for that matter, accomplishes the same thing from what I can see

Edit II: are there going to be issues, even if split, of there being enough flex of the socket so as to actually grip?

Edit III: good 5C hex collets appear to be split every other point (Royal as "good"); and I guess that answers my edit II question

[Toolguy]

Hex stock

A 3 jaw chuck works pretty good on hex stock. Is there any way to mount a 3 jaw to the spindle?

[DICKEYBIRD]

My current line of thought is to cut a groove in the socket OD for an O-ring, slit the socket into 2 pieces, use an o-ring to hold the pieces together and slide the whole mess into the collet for clamping. Now to decide whether to place the slits at a point or a flat.

[DICKEYBIRD]

A 3 jaw chuck works pretty good on hex stock. Is there any way to mount a 3 jaw to the spindle?

Unfortunately no, the CNC lathe is an add-on cobble-job spindle/motor mounted beside a tiny Sherline mill using the mill's X-Y movement for lathe ops. It has a TINY footprint and no room for even my teeny little 3" 3 jaw.

I threw the thing together to help with making prototype model airplane engine venturis for a buddy/customer but my other buddy/customer keeps coming up with jobs for it and keeps me too busy to build a more usefully sized CNC lathe. The money's great but it's frying my brain trying to come up with work-arounds to allow the little feller to get the job done.

Anybody know of a little CNC lathe fixer-upper for sale? Seems like all the work I get requests for is perfect for CNC lathe ops.

[Allan Waterfall]

Wrap some brass shim round the hex so the two ends meet over a flat part.

Allan

[John Stevenson]

Get a cheap thin walled 1/2" socket, grind the 3/8" drive end off and grind a split up it.
Simple hex bush.

If necessary grind the split, or saw it, cheap sockets aren't usually that hard then clamp it with a temporary clamp over the drive part and take a skin over the plain part to make sure it's running true.

[DICKEYBIRD]

Got a possible job coming up to do some work with my little CNC lathe that requires machining a feature on the end of 1/2" hex stainless stock. The lathe has an ER32 chuck only.

So far I've been unable to find ER32 hex collets so I guess it comes down to making a hex ID split bushing of some sort. I am broachless; anybody have a brilliantly simple solution or a source for ER hex collets?

Hmmm, just as I was going to press the submit button, the lightbulb flashed on and I thought about using a thinwall 1/2" deep socket with the square drive end cut off and slit horizontally. That ought'a work; should it be split at a point of the hex or the middle of a flat?

Dangit John, stealin' me idears again!

You reckon the slits ought'a go on the points or in the middle of the flats?

[Lew Hartswick]

Definitely on the "Points" so the /-\ will squeeze the part symmetrically. And take a good section out with the cut
...Lew...

[DICKEYBIRD]

Thanks Lew, that makes sense to me.

[pressurerelief]

My addition to the prevailing thought, take a bit off the OD where the socket is not split. This will allow the splits to collapse and grip better in the collet as opposed to the collet grabbing the full OD of the socket.

[DICKEYBIRD]

Actually I plan to split the socket into 2 halves. I haven't checked one yet but I'm hoping it'll be long enough to stick out the back of the collet and have room for an o-ring or rubber band to keep the halves together.

I'll make a threaded bushing to screw onto my collet stop that'll set the depth of the socket halves and the stop rod will set the work's depth in the collet.