Holding short lengths

This post is a spin off from the one posted by Raymond Anderson on ER collets.

In that post Raymond remarked about having to turn short tubs of material up to prevent the inner of the ER collet from collapsing when holding short pieces, which they do.
At the same time a reference was made to the Bernerd Grip True collets as not doing this . Now as the Grip true collets are made with loose tapered vanes I'm not sure how this cannot happen the same as the ER's but it's been many years since I have used this type of collet and possibly never held short lengths anyway ?

For reference this is what the Bernerd collets look like.

Another reference was made to 5C's which can hold short pieces as being spilt from the front only they close at the front first, one drawback with this tpe is they have a very limited closing range before they become bell mouthed and although they do make the imperial range in 1/64" steps this means a total of 72 odd for a whole set.
I frightening outlay for a home shop.

Another Collet system that seems to has lost flavour this side of the Atlantic, if it was ever in flavour to start with, is the Jacobs Rubber Flex system.
There are two systems of this type, small and large. Small is usually tool holding and used on tapping heads small collet chucks fitted to high speed spindles and the like. This system I will not discuss.
The larger system is work holding, I have never seen it used for tool holding but that doesn't mean to say it's never been used for this purpose.

Similar to the Bernerd in capacity but they have hardened vanes moulded into rubber as opposed to loose vanes in the Bernerd type held by spring clips

I have had to go looking for pictures of this system as I'm away from the workshop and it's hard to find some that show the full set. Most just show one of the two or three types of chuck and the collets but this is the best I can do.

Note the differences between the bigger sizes in the Jacobs having far more vanes than the Bernerd and so a greater gripping area. Downsize of these is the rarity and price.

However the point of interest is a full set has the rubber bushing in the set, one to each collet although only three are shown here but the double ended ones do two sizes.
You fit these in from the back of the collet before fitting and they hold the collet from going completely bell mouthed.
Now my inquiring mind would like to know whether one of these which is designed for a far clearer closing gap than the 1mm used by ER's could be used in an ER ?

I do have two full sets of these collets, bungs and chucks but as I'm away from my workshop next week I cannot get a chance to try these out for a week but they are nothing special, just a hard rubber bung.

I have another way to hold short items as I do loads of the same. Thing like Myford gears get made it batches approaching 500 at a time and they need facing to 3/8" and boring accurately before they get mounted on an arbor and skimmed up in batches of 10 before going on the gear hobber.

I'll address this in another post later after folk have had a chance to add their comments.

I find the bell mouthing of 5C collets less of an issue when holding short lengths of other than nominal size say 2mm long in the collet as the slight taper that results is so small over this short distance it is not really an issue, different if you are holding a long part in the 5C which will then only get gripped at one end.

It is also possible to bore out an emergency 5C or just use good old soft jaws if you need an odd size and both these methods have the advantage of giving you a positive edge to place the work against which stops it wobling.

I rarely use my ER32s for work holding, only when I don't have a suitable size 5C do they get put to use.

Thanks for starting this, John

So far as I recall, Burnerd did not condone gripping short lengths in the MultiSize.

MichaelG.

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P.S. please forgive the pedantry but, I think you meant MultiSize not 'Grip True'

Right John, First off, thanks for sticking up the pics and the info.  When I upgrade me workholding collets If I go with 16C, then I think I would need 84 for the metric, set up to 42.50 mm Ø more if I also included imperial. the 42.50 would be big enough for my needs. yes it is a big outlay, although I do get good discount   They also come in square and hex and of course blanks so I think I would find them equally as versatile as the er's,,, just need more of them !!.   Also thought about the B60'S because they to are only split at the front. and should hold short lengths They might be overkill for my needs.

It is maybe just me, but I just detest having to turn plugs. I want away from that. I really think it will be the c 16's for me.    That is  me only gripe with me er's.  . I use them a lot and they are fine as long as me part fills at least 60 % of the collet length,. the shorter parts just annoy the hell out of me.

cheers

Edited By Raymond Anderson on 24/09/2016 18:27:54

I haven't seen any of the Jacobs rubber collets for years so thanks for the pic John. We used to use these in the cutter grinding dept. on a pair of Pratt & Whitney cutter grinders and very good they were. From memory we could hold milling cutters up to about 1" diameter but sorry cannot comment on the bell mouthing business on short lengths - never used them for anything like that. They did have a good "squeeze down" factor so again from memory I think we only had eight collets to cover 1/4" up to 1".

By the way, thanks for pointing out the short comings of ER collets when holding short bits. I did not realise there was a problem. But then and all, I've never tried holding short bits in my ER25's so I would not have known had you not pointed it out.

Rik

Correct MIchael. They are more correctly known as bar chucks where I come from. They will grip bar to a pretty high degree of accuracy, a couple of thou but not as well as a normal spring collet. That's simply because they are made of lots of separately made different parts and tolerances stack up.

The rubber flex may be better. Say special purpose machine tooling was used so that the blades were ground after they were fixed in the rubber. Otherwise they may have the same problem to a greater or lesser extent.

Multiple contact points have there own problem which is why 3 jaw chucks have 3 jaws. Things are seldom truly round at some level of precision so not all jaws grip evenly. That's the reason spring collets have 3 as more is seen as not really offering any advantage. I've only clocked work on a DSG using this style of collet. Just out of curiosity. What run out would be the best way of putting it but they would have been extremely expensive collets. I've heard the same comments about sets provided by CVA.

I mentioned in the other thread that it would be pretty easy to reduce the grip length of ER type collets by relieving the bore from the back just as normal spring collets are.

Also the other type of collet that is typically like the Schaublin ones. Flat face for the nut to press on. It does have a slight advantage as there isn't a taper in the nut that may due to tollerances tend to screw the collet off centre a touch.

John

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They already are , for example a 2.0-1.5 ER 32 only has a gripping length of about 10mm.

Have been doing some more "brain picking " Asked the brother if he had heard of B60 collets and he has used them many moons ago on a Weiler lathe. He says they are no use to me as they are a "dead length " system which means they don't alter the part position in the Z axis unlike a pull /push back collet such as the C series and the ER series

The B60's are installed hard up against the rear of the front face of their chuck and it is a tapered sleeve that pushes forward and so closes the collet with no movement in the Z axis. Sounded just fine for what I want, but they are no use to me... Why me asks, because they need air or hydraulics to work them, arrrgggh. All the B system are the same whatever the size. I should have twigged when I saw the front of the collet had a step

John S, would that be the same B60's as you mentioned ? either way sounded great until I heard about the air / hydraulic bit.. He reckons I should stick with the ER'S, but that aint going to happen, no way, no how.

I had a piece of 7075 Alum and decided to try and make some collets they have a slow pull back taper and to my surprise wok fine. Can remove a collet and replace it and repeats to within 0.01 mm so that is good enough for me So folks on here can give me their thoughts. As 1 of me tests I bored 1 out to take a 1p coin to see how short I could grip and got the 1p down to 0.43mm might have been able to shave a bit more off but that test was far shorter than anything I would ever need to hold.

I am also pondering whether to make a load of them in a bigger size [ maybe to accept up to 40/45 Ø ] and forget about the C16's any thought on that aspect ? All criticism welcomed as long as it's constructive

Raymond would it be worth trying to make similar draw in collets that can be pulled into your existing ER chuck that way you would not have to change chucks, just remove the nut, insert home made collet and slip a draw bar up the end.

I'm assuming you are drawing them into the larger steel parts in your photo and then holding those in something.

I turned some small brass components from short bits of brass some years back. I used an ER32 collet and had no issues. Was I just lucky?

Good point Jason I never even thought of that. Although I would ideally like to go up to a capacity of around 40/45 Ø You are correct in thinking the collets are pulled into the matching taper holder, the one with the 4 cut outs also match the taper and are used for the slitting. The actual collet holder is held in me ER 40 lathe chuck. It would just be a case of upping the dims to get the 40/45 Ø. Which would mean starting with around about 50 Ø stock. I could either dial in the holder in the Bison 4 jaw ind, or even use the soft jaws for the Bison 3 jaw. I am not concerned about the fact that they have a blind bore because they will only be used for short parts. These were only a "test " to see if it was feasible. I think I made around about a dozen of these blanks [ just used up the 7075 ] I actually enjoyed making them and would have no qualms of making up a load of blanks. ready for me to use when needed. I would actually do this, rather than faff around with those ******* plugs .

cheers.

Hi Vic, No I don't think you were just "lucky " It all depends on how tight you grip your part. and that will all depend on what operation you are doing on the workpiece and also the workpiece material. The tighter you grip it the more the ER will collapse at the back unless you use the things I detest "plugs "

cheers.

I use ER32 in my mill and lathe and both chucks have an internal taper that fits precisely the external taper of the collet. I don't see how the "rear" of the collet can close more than the "front" to cause bell-mouthing. Can somebody explain please?

Thanks John. Rather than clutter up this thread with pics I have stuck a pic of a B60 collet and the Chuck in an album called B 60 collet system. When you get a chance have a shufty and see if that is the same as the type you remember. These are the ones that I was disappointed to discover they are either Pneumatic or Hydraulic operated. so thats a no go.

cheers.

B60 collets don't have to be air or hydraulic operated. My repetition lathe uses topologically similar dead length collets, nearer to B42 in size, and the operation is purely mechanical via a lever. Of course, in practice, with an auto or CNC lathe and bar feeder collet operation would also be automated.

Andrew

Hi Gary, Ideally the part should be inserted around about 60 % of the collet length then no probs It is when holding short parts where you maybe only have around 5 / 6 mm that the probs can start. [ not always ] The collet closes more at the rear the more you tighten it because the part is not the 60% or so into the collet. A lot of folks use plugs of scrap the same Ø as the part and insert it into the rear of the collet to prevent the rear collapsing more than the front. This is the only part I don't like. and why i'm looking to get away from that if possible. Most folks on here get on fine with them even with the "plugs" So it's probably just my awkward ways, but I don't like it [ the plugs ].

This only applies to workholding, not you're mill as the cutters will be long enough.

cheers.

A lathe drive centre can be handy, woodworkers use them a lot.

Thanks Andrew Just saw you;re post. So it might be possible to use them on a manual machine, lever operated.

That might put them back in the mix again. I said earlier I have to get this right first time, cos the numbers are "scary " there is no second chances with this, not without doing away with me remaining arm and leg

cheers

Hi Ady 1, I have 2 Rohm Face drivers they have a little dial on them for the pressure and yes, they can be very useful for turning a dead length part between centers. No need for excess material or lathe dogs. Don't use them much though.

cheers.