er collet holder for pultra

[mark smith 20Participant @marksmith20]

Im wanting to make an er collet holder chuck for my pultra .  I have two lathes the pultra and a south bend 9A . My question is what is the best way to accurately make this. Should i cut the pultra blank end arbor to size and cut the taper for the collets on the pultra and then thread the chuck on the southbend or do all the work on the south bend ?

I have a 10mm 3c collet for the south bend but because of the shape of the pultra collets there is not much to grip onto. Also have a er32 mt3 chuck that will fit the southbend  or use afour jaw.

[JasonBModerator @jasonb]

I’d go with something that fits a backplate mount or direct to spindle thread rather then using a blank arbour as that will stop you being able to pass longer items through the spindle. Unless it can only take something in the taper.

 

If that is the case then cut the ER taper with it mounted in the Pultra and mark what poistion you have it in so it always goes back in the same place. Thread can be done on the bigger lathe, probably before doing the bore so you can us etailstock support.

[mark smith 20Participant @marksmith20]

Jason thanks , i dont need the through bore as im only holding small 1″ maximum length stuff . Im using the pultra fit blank arbor and  only goes in one  way as there is a sort of key way  down the side of pultra collets . So its more important to cut the 8 degree taper for the collets on the pultra that its to be used on?

[JasonBModerator @jasonb]

Yes that way the freshly cut taper will run nice and true.

Just be aware that ER collets are not good for short lengths, you really need to fill them to the full length of the gripping area. On the otherhand, your Pultra and 5C can holed very short lengths down to 1mm or even less.

 

[mark smith 20Participant @marksmith20]

Thanks.

Its not for heavy or particularly accurate  work ,its just  to replacement the cheap 3 jaw chuck which has too much run out .

[JasonB]

On JasonB Said:

Just be aware that ER collets are not good for short lengths, you really need to fill them to the full length of the gripping area.

 

I’ve never been able to see why this should be true.  While 5C collets only grip at the end, ER collets close parallel and grip all the way along.  I can’t see where a force would come from to make the rear end collapse. The closing force at the rear will be determined by the spring force from the collet rather than being equal from front to rear.  The torque specified for tightening the chuck will be for a collet filled all along so, for a short length should be reduced to avoid damaging the small piece being held.  I have often used an ER 32 collet on very short or thin pieces.

…or am I missing something?

Russell

[Russell Eberhardt]

On Russell Eberhardt Said:

On JasonB Said:

Just be aware that ER collets are not good for short lengths, you really need to fill them to the full length of the gripping area.

 

I’ve never been able to see why this should be true.  While 5C collets only grip at the end, ER collets close parallel and grip all the way along.

…or am I missing something?

Russell

Not in my experience.

A quick video to show the grip is anything but parallel. 1/2″ ER 32 collet with a 1/2″ cutter inserted 3mm into the hole and the nut only tightend by gripping it in my hand- no spanner. It is easy to feel that the nut is going on far more than it would normally. To show how much the other end has closed down I can’t even poke a 12mm dia cutter into the collet so would say the back end is 11.7mm or less. So if the front end is 12.7 then the gripping surface is not parallel so you only get line contact and the part is likely to wobble or at the minimum deflect under cutting loads.

This is why many members say that you need a butt plug in the other end when holding short work in an ER collet to stop the back end collapsing.

 

[Andrew TinsleyParticipant @andrewtinsley63637]

Jason, I would suggest that anyone trying to hold a 3mm length in any collet or chuck would be asking for trouble. The OP says that he wants lengths up to 1″ to be held. I don’t see and problem with this in an ER collet, unless you go to ridiculous short lengths, like your chosen 3mm. Or am I missing something? Andrew.

[mark smith 20Participant @marksmith20]

Andrew , I mostly i want to hold stuff around 14/20mm long so shouldn’t  be a problem ,also with minimal clamping force .Usually with  around at least 10mm inside the jaws /collet.

[bernard towersParticipant @bernardtowers37738]

to be fair there are other tried and tested ways of holding sub 3mm lengths of material. A wax chuck or s/glue chuck or if you have a mag chuck. As Andrew says if 1” long I cant see a problem.

[JasonBModerator @jasonb]

We have different ideas of Short.

But I did the same test again. This time a 10mm dia cutter inserted 10mm into an ER32 Collet. Hand tight I could just get a 9.5mm drill shank in the back end. Nipped up with a spanner it went down to 9.3mm so hardly parallel!

I’m not sure what the rest of you make or not but I often hold items by less than 3mm quite often 1mm is all I have to hold. Provided you don’t go silly with stickout or greedy cuts there is little problem with a 5C collet but I would not do it with my various size ER collets without plugging the other end. After all 5C are meant for holding WORK.

Here is an example, Cylinder cover for a 12mm bore engine. 1mm long spigot on the inside and a curved shape spigot on the other.

Hold by the stock dia, turn, face, drill, ream and turn the inner spigot so all concentric.

Cut it off the bar, hold by the 12mm dia x 1mm long spigot to turn the other side

Something a bit longer for the current Clarkson build. 1.6mm dia, 2mm of M1.6 thread, dome the end. Easy enough holding the stock to do that. Now cut off and face the other end back to 4.5mm overall length and dome the end. Move from 5C lathe chuck to 5C collet block to cut the slot 0.5 x 0.5.

Or want to hold a larger cylinder cover for drilling stud PCD. Hold by 0.75mm long spigot and drill. Take care on breakthrough as there is not much room to spare, and don’t lean on the drill too hard. Turning was done with soft jaws

 

[DellParticipant @dell]

I made my own ER11 to Pultra 10mm arbor by starting with a blank https://www.chronos.ltd.uk/product/soft-blank-end-arbor-to-suit-10-mm-pultra-watchmakers-lathe/

i have through drilled it and it’s very handy for holding odd sizes because even though I have a fairly comprehensive selection of metric & imperial collets there is the odd time I need it.

[JasonB]

On JasonB Said:

We have different ideas of Short.

But I did the same test again. This time a 10mm dia cutter inserted 10mm into an ER32 Collet. Hand tight I could just get a 9.5mm drill shank in the back end. Nipped up with a spanner it went down to 9.3mm so hardly parallel!

I’m not sure what the rest of you make or not but I often hold items by less than 3mm quite often 1mm is all I have to hold. Provided you don’t go silly with stickout or greedy cuts there is little problem with a 5C collet but I would not do it with my various size ER collets without plugging the other end. After all 5C are meant for holding WORK.

Here is an example, Cylinder cover for a 12mm bore engine. 1mm long spigot on the inside and a curved shape spigot on the other.

Hold by the stock dia, turn, face, drill, ream and turn the inner spigot so all concentric.

Cut it off the bar, hold by the 12mm dia x 1mm long spigot to turn the other side

Something a bit longer for the current Clarkson build. 1.6mm dia, 2mm of M1.6 thread, dome the end. Easy enough holding the stock to do that. Now cut off and face the other end back to 4.5mm overall length and dome the end. Move from 5C lathe chuck to 5C collet block to cut the slot 0.5 x 0.5.

Or want to hold a larger cylinder cover for drilling stud PCD. Hold by 0.75mm long spigot and drill. Take care on breakthrough as there is not much room to spare, and don’t lean on the drill too hard. Turning was done with soft jaws

 

On JasonB Said:

We have different ideas of Short.

But I did the same test again. This time a 10mm dia cutter inserted 10mm into an ER32 Collet. Hand tight I could just get a 9.5mm drill shank in the back end. Nipped up with a spanner it went down to 9.3mm so hardly parallel!

I’m not sure what the rest of you make or not but I often hold items by less than 3mm quite often 1mm is all I have to hold. Provided you don’t go silly with stickout or greedy cuts there is little problem with a 5C collet but I would not do it with my various size ER collets without plugging the other end. After all 5C are meant for holding WORK.

Here is an example, Cylinder cover for a 12mm bore engine. 1mm long spigot on the inside and a curved shape spigot on the other.

Hold by the stock dia, turn, face, drill, ream and turn the inner spigot so all concentric.

Cut it off the bar, hold by the 12mm dia x 1mm long spigot to turn the other side

Something a bit longer for the current Clarkson build. 1.6mm dia, 2mm of M1.6 thread, dome the end. Easy enough holding the stock to do that. Now cut off and face the other end back to 4.5mm overall length and dome the end. Move from 5C lathe chuck to 5C collet block to cut the slot 0.5 x 0.5.

Or want to hold a larger cylinder cover for drilling stud PCD. Hold by 0.75mm long spigot and drill. Take care on breakthrough as there is not much room to spare, and don’t lean on the drill too hard. Turning was done with soft jaws

 

Yes, that cover is the sort of part I often hold in my ER chuck without plugging the other end and never had a problem.  I have repeated your test with a 12 mm cutter inserted in a 12 – 11 mm collet and yes, the back end closes down, but I only measured about 0.2 mm of closure (perhaps my arthritic hands are getting weak).

My question remains, what is causing the back end to close up? There is no contact at the back between the collet and the socket so the force must come from elswhere.

HYPOTHESIS: Perhaps the problem is caused by the short front taper of the collet not matching that of the nut.  If the initial contact between the collet front taper and the nut taper occurs at the back end of that short taper, then as the chuck is tightened the front of the collet will be pushed out creating a levering effect.

Any other suggestions?

Russell

[mark smith 20Participant @marksmith20]

From what ive been read ,its simply because of the way the collets work/ designed,mostly with short engagement of the toolbit/workpiece.

It seems i’ll be ok for holding light stuff (mainly made of exotic wood and soft silver)  with minimal clamping force. For toolbits regofix recommend a minimum of 2/3 engagement inside the collet.

There are other sources showing less engagement of a bit or bar, and when fully tightened it causes a permanent deformed step inside the collet.

[mark smith 20Participant @marksmith20]

Well almost finished the collet chuck ,just need to mill two flats for a spanner . Very negligable run out and a massive improvement on the 3 jaw chuck i was using. Its an er 20 size.

Bought a nice selection of 24 er 20 collets off ebay for £35 , several unused and many are good quality regofix.Had a straight shank regofix er 20 holder but not really much use for me..though i’ll think of a use for it.

 

 

[Michael GilliganParticipant @michaelgilligan61133]

Make a split clamp for that plain shank … then you can hold it in the bench vice, to work on stuff.

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

Is using an ER collet to hold short work a bad idea or not.  Let’s try SODs patent Risk Analysis technique.

What could possibly go wrong?

On a round bar that’s gripped full length by the collet, nothing.   My memory of ‘full length’ is ‘at least 75%’, but I see Mark says: “For toolbits regofix recommend a minimum of 2/3 engagement inside the collet.”   The difference may be related to how well-made the collet is. A genuine Regoflex is more likely to resist abuse than an inexpensive alternative.

The big issue is gripping short lengths, where Jason showed a 3mm front engagement causes severe distortion at the rear.  The problem is that an ER collet is a concentric / coaxial spring, which adapts as pressure is applied to grip the full length of a tool shank.   If the shank is short, the rear will displace, risking two problems:

1. High run out because the rod is no longer parallel to the axis due to the spring deforming.  However, run-out, if present, can probably be corrected by tapping with a mallet.   I think this is low risk and low impact, provided the operator checks the run-out!  (Can’t be assumed because the collet is being used outside it’s normal design envelope.)
2. More dangerous, uneven tightening risks damaging the collet.  By crushing a step into the interior bore of the collet, AND/OR by destroying the set of the spring.  I think the risk of damaging the collet is HIGH, especially if a short item is tightened to specification (ER32 is calls for a lot or torque – 130Nm / 96ft lbs).   But the impact is low because damaged collets are easily replaced for under a tenner!

In other words, don’t fret!  The sky won’t fall in when a machinist wrecks a collet, and that only happens if he aggressively tightens one on a too short workpiece.  Might have to do it several times before the damage becomes apparent.

That said I take care of my ER collets.  It’s because I use the same collet-set to hold cutters in the mill as well as work-holding in the lathe.   I don’t want to find mid milling job that I’ve damaged a collet by careless work-holding.  The cost doesn’t worry me, it’s the stoppage and faff of ordering a replacement.

Dave

[Ian PParticipant @ianp]

I don’t want to muddy the waters, but…

I have several ER25 collets in which the bore is shorter than the collet. For example ER25’s are nominally 34mm OAL, my a 4mm collet back end is opened out to 10mm dia by 14mm deep. This same depth of relief is also on a couple of other collets, all purchased or obtained individually rather than being in a set.

An earlier reply explained how the collet bore became tapered when very a short part was gripped, OK 20mm out of 34mm is still a good proportion, but presumably bore parallelism must still suffer?

Ian P

 

 

 

[JasonBModerator @jasonb]

And why I said the bit in bold and not the collet length

“Just be aware that ER collets are not good for short lengths, you really need to fill them to the full length of the gripping area.”

Quite a few of my smaller dia collets are the same with a counterbore at the back but gripping area is around the 2/3 collet length mentioned elsewhere as the amount that should be gripped.

[Ian PParticipant @ianp]

I admit I missed that bit Jason.

I suppose that whether relieved or not, there must be a minimum length (of gripped part) where compliance with the DIN specification is not met. Two thirds is obviously OK and maybe 50% is usable in our workshops but I would not feel comfortable holding work shorter than the diameter other than in extreme situations.

Ian P

[derek hall 1Participant @derekhall1]

It does seem good engineering practice as well as common sense to make sure that the workpiece or cutter is inserted into the collet at least 2/3 of its length.

Anything less than half the depth or length of the collet appears to be asking for trouble, such damaging the collet or failure to hold the workpiece or cutter securely.

[mark smith 20Participant @marksmith20]

Well the stuff im making out of exotic wood and silver need only slight hand tight clamping so im ok,but iagree that if i were holding something else id want it going in the collet as far as sensible,just makes sense. Glad someone mentioned the collets bored at the rear ,as i have a 5 of er20 in the lot i bought . The collets are approx 31.5mm long ,the back bore is 13mm deep by 9.2mm wide. That equates to only 58.73 %.

[mark smith 20]

On mark smith 20 Said:

[…] Glad someone mentioned the collets bored at the rear ,as i have a 5 of er20 in the lot i bought . The collets are approx 31.5mm long ,the back bore is 13mm deep by 9.2mm wide. That equates to only 58.73 %.

I’m happy to be corrected, but I think the general idea is that it keeps the aspect-ratio of the clamped portion within reasonable limits.

MichaelG.

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