Holding short lengths

That's what I pointed out. You don't want to read who knows how many pages there are on the ER collet thread - so just believe me.

John

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The hardened steel doesn't need to compress noticeably ... The ER collet is split at both ends; it's the shape that can 'compress noticeably', not the material.

MichaelG.

JS, John, there is no need for sarcasm. I appreciate you're efforts in this as I do Jason's, Nick's, and the others.

I stated that I wanted collets only question was what system. I have cut soft jaws before and yes they are extremely accurate and very versatile. But in this case I want collets. Had I known that you were very helpfully going to take pics of the soft jaws, I would have told you not to bother.

So I repeat, Thanks to you and all others who posted on this. Its going to be Collets of some type, nothing else.

cheers.

Raymond,

I note you mention a possible solution based on 16C collets. Is this solution for your DSG 17T, and does the 17T not have a bigger spindle bore (D1-8) than the range for 16c? Would you not be better off with 20C or 25C? Perhaps i have missed something and it is for another lathe.... It would also be interesting to learn what chuck or closer solution you plan to use with the chosen collets.

5C collets have a very limited working range. In my (limited) experience I think some of the responses are misleading and that the actual range is much more limited. Outside of this you risk poor runout and damaging the collet. Normal range is just a thou or so oversize and approx 4-6 thou undersize before they are being used outside specification. So a 64ths set (which is a lot of money for the hobbyist) does not provide a continuous clamping range solution, nor would a 128ths set but only just. Hardinge make them in 1 thou increments in imperial and 0.1mm for metric for a reason. In my (limited) experience the top brand collets have a slightly larger undersize range than the no name. Even so that is just a few thou and for such an expensive item why risk damaging it?

I've tried a google but I have not yet found the working range of 16C. I expect it is a little more generous but it would be educational to learn if it was more than 0.016" under size.

Steve

it seems "riten" offer a undersize range of 0.010". So perhaps my info above is a little conservative.

http://www.riten.com/wp-content/uploads/2014/12/collet-chuck-catalog-2007.pdf

I haven't spotted the Schaublin spec yet.

Having said that for the hobbyist if you are looking at name brand, new collets, then perhaps the funds for a large set is achievable.

Hello SteveI thanks for you're post.. yes, I am going to use them on the DSG. As these are only for my hobby uses I only want ones up to around 40/45 mm The B60's go quite a bit above that and the 16 C's stop at around 42.50 [I think ].

I understand exactly where you are coming from as regards "damaging " them, got some prices in today and even though I get a very good discount they are still extremely spendy But if they do what I want then fine.

I did look at the Riten ones and very nice gear. The ones I got prices for are by Crawford. I am still at the checking stage just now, and you will appreciate that I have to get this "right " first time or sell a kidney to go along with me remaining arm and leg.

Would you have any views on another option ie, Me making bigger ones than my test ones that I posted pics of .

They work very well, and are repeatable to within the 0.01mm which is good enough for my uses. Only be a case of keeping the same angle of taper and just beefing up the body size and upping the drawbar thread from M8 to M12. 

cheers.

Ps, They are only for holding short length parts.

Edited By Raymond Anderson on 26/09/2016 14:59:46

Raymond,

How short is short?

For a D1-8 spindle out of the C collets you would be wanting 25C to maximise future flexibility, but you'll not have the very small sizes available and you'll need a chuck. However if you only need short parts and 40 something mm bore then the 5C system will do the job. The Number "5" spindles that were native for a 5C collet also have a fixing arrangement for step collet closers, chucks etc with either a spindle screw thread or 4 deg taper and bayonet mount system.

With a step collet (a collet that does not have the rated size right through the whole collet) will do all you need. You'll need the step collet and the correct closer which mounts on the outside of the spindle. Then with 2",3" and emergency step collets your all set. Either regular or extra depth depending on how short, short is and make each you can't buy manually. With this system I get less than 0.01mm repeatability so no problem on 2nd operations.

Hardinge used to make a speed chuck "sjogren" for 5C collets with either plain (not step collet support), 5C-X (4 deg taper nose) or 5C-T (threaded nose). I have a 5C-X with a D1-6 back plate. "ATS work holding" make them these days and they also do a D1-8 sized version. (I am not sure if Hardinge ever made a D1-8.) They won't be cheap though but Hardinge have more than a reasonable reputation regarding work holding.

Having said that, to my mind this is a variation of the soft jaw solution you have already rejected. However in case it was something you were not familiar with I thought it might be of interest. Plus it will be cheaper than a larger collet based system and more flexible.

Steve

Just had a quick reckon up and my soft jaw setup which only uses one set of chuck jaws and for an outlay of £20 ? for the rest can hold 324 different sizes. If I open or close the jaws by 2mm either way then it's up to 1,000's of sizes.

Nothing new, because industry has been holding short lengths of bar for nearly 300 years so why do we have to reinvent the wheel unless you have shares in the OCD Collet Co, Ltd.

Ref soft jaws, point taken they are much more economical. Yet many model engineers buy collets and don't buy soft jaws. The OP wants a collet solution so I suggested one that was cheaper than the other options discussed. When it came to the large sizes an emergency collet or emergency step chuck is simply a variation of soft jaws.

Raymond, Hardinge make it. Hence it is expensive. You can see the whole solution on shophardinge.com. 

For me the only option has been the 2nd hand market. The closers are made from cast iron and could very well be home made most easily for the threaded nose variant. I estimate I've paid about 10% on average of new price for crawford or hardinge brand and then I have a few Chinese new items. It still adds up  and much much higher than soft jaws. 

Post edited due to being out of sync with prior responses.

Edited By SteveI on 26/09/2016 19:56:50

Raymond, about page 8 & 9 in the hardinge catalogue, you need the ring to apply the pressure to teh outside of the large dia collets. The cheaper multi stepped collets you can buy don't close down so well using the standard 5Cs taper

But 5C won't hold long lengths above 1 1/8" ( or pass through above 7/8" or so) so you will still have to have a bigger collet system to cover you between 28 and 45mm which would up the costs and mean more chuck changing

Edited By JasonB on 26/09/2016 19:51:28

Not relevant Michael. The compression under discussion in this area is the actual compression of the metal that makes up the collet not the fact that it can collapse to accept different sizes.

It's not a hard point to grasp. Put something in one and clamp it in the chuck. The tapers match and the collet collapses until it grips what ever is in it. It will only go so far before the part needs to compress for the collet to close up more. The tapers still match so there is no reason why they should go bell mouthed or anything else. The only way they could do that is if the material that makes up the collet actually compresses significantly.

That just leaves alignment issues that I mentioned. So on that basis if 2 x dia is always griped everything will be ok. However 2 tapers being exactly the same is unlikely. That may be why some one came up with he idea that 2/3 of the length of the collet is fine. The difference in the tapers will translate into a taper in the bore so in real terms grip length apart from alignment doesn't matter.

My conclusion is that they need a longer grip length than typical spring collets because at some limit they will have a number of problems. This also holds with the general view of them. What finally put me off was using ER40 to grip small things. If I had ER on a lathe I would try using any size gripping a length of at least twice the diameter of the work and expect it to be ok. Certain factors such as lack of true roundness, number of parts in the collet that should be in contact with the work but wont be make me wonder so it wouldn't surprise me if the 2/3 collet length rule was about ok.

But as I mentioned no way would I just stick to one size of ER collet even on a miller. It just doesn't make any sense - to me.

I can't see that making slugs to put at the back will help really - will they be exactly the same size. In terms of people who buy the very accurate types unlikely really so no help or make things worse. It would make more sense to try 2 diameters and see what happens.

John

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Edited By Ajohnw on 26/09/2016 20:33:53

Jason,

The round go up to 1 1/16" max size for pass through admittedly without the internal threads. With internal threads they max out at 63/64". For none pass through a little bit more, and then with the 2" step chucks up to 2" for short lengths. The regular depth 2" step collets are deep enough for the OP's specs. If I've read it correctly I don't think Raymond would need to change main chucks (but would need to change collets and collet closers) for his stated entire short part working range. As you correctly point out if he wants to pass through bar or longer parts in the diameters above approximately 1" then it is not the right choice for Raymond but if I understand his posts correctly he is clear he doesn't need to do that. So why pay more for a larger collet solution that meets the specification of the OP?

Thanks Steve, could not remember the exact sizes off hand but know a few of my larger size ones won't pass stock through them though they are all internally threaded.

I thought Raymond was looking for a complete new system upto 40-45 and with the ability to take short lengths not just a system for short lengths only, Raymond can you con firm which you are after.

AJohnW,

As was pointed out before in this or the other Er thread, you really should read the post in order to comment constructively. When you state;

"It's not a hard point to grasp. Put something in one and clamp it in the chuck. The tapers match and the collet collapses until it grips what ever is in it. It will only go so far before the part needs to compress for the collet to close up more. The tapers still match so there is no reason why they should go bell mouthed or anything else. The only way they could do that is if the material that makes up the collet actually compresses significantly."

it is obvious that you have no grasp of the geometry involved. The conical form only mates in a coincident manner when the two cones are co-radial at a particular diameter. Think about a cork being forced into a bottle, the cork must compress as it is forced down the taper - this is much harder with metals (requires several tens of Kbar if I am not mistaken) which is why the collets are always split to allow them some space to deform due to elastic/spring behaviour of the collet design.

If you take a close look at Crawford multisize collets (there are lots of pictures on the web) you will see there is a tapered relief on the segments to allow the collet to transit from the open position = broad line contact in central section to the closed position = broad line contact at the edges of the collet external tapered flanks.

Mark

Edited By Mark C on 26/09/2016 21:00:48

John,

It's good to see you contributing again, instead of sitting smugly in your corner humming "up yours".

Frankly, however, I don't understand your post ... I thought we were trying to clarify something for Gary.

MichaelG.

Jason, Just had a chance to look at the Hardinge Catalogue you linked to Page 8 / 9 The 5 C step chuck and closers appear to suit me needs although I cant see any mention of manual lathe spindle nose fittings. All appear to be the A series which I think is a CNC nose [although not fully sure on that ] I would require a D 1-8.

Looks promising if I can resolve the Spindle nose fitting. Will e-mail Hardinge and get their answer as regards the spindle nose.

cheers.

I know they fit a Hardinge HLV nose which is 5C internal and tapered externally. You hould not have too much of a problem replicating this nose type with a D1-8 mounting if nothing is available off the shelf

Thanks Jason. I have e-mailed Hardinge and await their reply.re the nose fitting.

cheers