Collet chuck

[Allen Smithee]

One of the things I have yet to get for my Myford is an ER32 collet chuck so that I can use the same collets as I use in my mill. I don't want a shank-mounted one because that has limitted depth and blocks the spindle bore. Looking around I could find backplate-mounted ones, but that strikes me as a bulky solution to the problem. What I really wanted was a spindle-mounted one, but the only one I could find was only available with a set of collets (that I already have) for £150 (which is far more than I want to pay). So I've decided that as it's essentially just a piece of turning, albeit one with a high-precision requirement for the collet-holding taper, I'm going to make one (although I'll buy the collet nut) - it can be a useful part of my "getting back into machining after a 20 year layoff" programme. Looking through my stock of scrap I find that I have a suitable* chunk of 50mm mild steel bar, so it look's like Robert has just married my mother's sister.

For once I've decided that this job should be planned rather than making it up as I go along, so I've broken the habit of a lifetime and actually done a drawing of the essential features - aside from a few chamfers I think I have it right, but I'd welcome any comments before I commit to swarf production:



Before anyone explodes - my justification for the mixed units is that the Myford spindle is defined in inferial units while the collet chuck is defined in proper metric ones, so it's probably clearer if the drawing uses the appropriate units for each end.

AS

*Actually it's VERY suitable, for reasons that will become clearer later!

[Mosey]

Allen,
I think those units are properly called "Colonial", hehe.
Nice project, and I contemplate a similar one...ER-32 to W-20, so I am watching your work carefully.
Mosey

[pgp001]

Allen

I hope you don't mind me making an observation on your design.
If I was doing this I would think twice about the 1/4" dia holes for the tommy bar to lock it to your lathe spindle, a 1/4" bar will probably bend too easily.

Maybe you could put some flats on the body then you could use a decent sized spanner on it. Or maybe some slots for a "C" spanner.

Phil

[Dan Rowe]

I agree with Phil about the tommy bar, but another option for holes is a pin spanner. I have pin spanners for my Cowells and my South Bend heavy 10.

Dan

[smfr]

Hmm, Chronos stock an item like this (currently made by Soba):

http://chronos.ltd.uk/acatalog/Lathe_Type_Collet_Holders_for_ER_Collets.html

I have an earlier (non-Soba) one from them, and, after skimming the bore once mounted to my machine, it's pretty accurate. But making your own sounds fun too!

Simon

[Allen Smithee]

Allen,
I think those units are properly called "Colonial", hehe.
Nice project, and I contemplate a similar one...ER-32 to W-20, so I am watching your work carefully.
Mosey

Oh dear - my work rarely stand up to close scrutiny!

I really need to make a saddle stop before I start in ernest (because it's the only way I know how to do some things) and for that I need about 100mm of something like 35x16 mild steel flat. (or 4" of 1-3/8" by 5/8" mild steel flat in colonial-speak). Have to see what scrap I can source locally.

AS

[Allen Smithee]

I hope you don't mind me making an observation on your design.

I absolutely do want comments - that's why I posted it.

If I was doing this I would think twice about the 1/4" dia holes for the tommy bar to lock it to your lathe spindle, a 1/4" bar will probably bend too easily.

Maybe you could put some flats on the body then you could use a decent sized spanner on it. Or maybe some slots for a "C" spanner

My reason for choosing 1/4" for the tommy bar holes was simply that I have several suitable lengths of 1/4" silver steel (and some 1/4" stainless, but that may be too soft) in my scrap box, but your comment makes me wonder if I'd be better off leaving the overall diameter at 50mm(ish) and putting slots in it to take the C-spanners that go with the collet nut (I have a pair of these that came with the ER-32 chuck I got for my mill). That would add some rotary table and/or dividing head use to the training programme (although my dividing head is one that hasn't been used for decades, and it needs stripping and servicing before I can use it).

The tommy bar was intended for use when tightening/loosening the collet nut rather than for snugging the chuck to the spindle - I was always told that chucks should only ever be had-tightened onto the spindle [is this true or an old wives' wind-up?] so I was thinking of knrling a portion of the spindle-end of the chuck.

Thanks for the comments - I'll need to think about it. I may cross-drill a piece of bar and see how easy it is to bend a 1/4" silver steel tommy bar. No substitute for physical trials IMHO!

AS

[mklotz]

I think those units are properly called "Colonial"

No, Mosey, "inferial" is the perfect term.  It's a portmanteau of 'inferior' and 'imperial' and both words apply perfectly to the insane set of units currently used in the backward USA.

[Allen Smithee]

Hmm, Chronos stock an item like this (currently made by Soba):

Yes, but they don't offer a myford-sized one for ER32 - only for ER25 (and that's not currently in stock). ER25 is too small and limiting for the Myford, and the point of the exercise is to share a collet set that I already have for the mill!

I also feel that if I can make a decent job of cutting the spindle register on the back of the bar then everything else will be done with the material mounted directly on the spindle, so in terms of concentricity/axiality etc it *should* be as accurate as it is possible for the myford to make it, although it's still dependant on my ability to cut that 8 degree taper accurately and then put a decent finish on it - this is by no means a "given".

 

AS

[mklotz]

+1 on the larger diameter tommy bars.

I used 3/8" bars on the 5C collet chuck I made for my lathe and even those have been a bit marginal  in a few cases.  Interrupted cuts on a larger diameter workpiece can tighten the chuck up, even on well-oiled threads, to the point where a dead-blow hammer on the tommy bars is required.

I finally bought a pin spanner and never looked back.

[Allen Smithee]

I think those units are properly called "Colonial"

No, Mosey, "inferial" is the perfect term.  It's a portmanteau of 'inferior' and 'imperial' and both words apply perfectly to the insane set of units currently used in the backward USA.

If you prefer - the myford spindle thread could be labelled "142.045 micro-furlong diameter by 9,504 tpc (Threads per Chain)"...

AS

[Mosey]

Marv,
Of course you are perfectly correct about those units, as even our military uses the metric system.  I hear that as soon as we get a proper NFL team in LA, we are going to finalize the annexation and statehood for Californica.   
Mosey

[Allen Smithee]

I think what I'm calling a C-spanner is what you call a pin-spanner. I have a pair of these for the 50mm dia of the collet nut and my mill spindle, so I'm coming round to the idea of milling some slots instead of tommy-bar holes.

AS

[Allen Smithee]

Incidently - the ER collet nut thread is defined as 40mmx1.5tpi. The gearbox on my Myford can give me 0.058" pitch, which I'm hoping will be near enough (i can always cut the thread a bit on the "loose" side if I have to I suppose).

AS

[kev]

HBM have an ER32 that screws on to a myford (that's what I use) and it uses a "C" spanner to tighten and loosen it on the spindle, its handy to have two one for the "chuck" and one for the nut

[kev]

and here is another on ebay, but pricy compared to the HBM one

http://www.ebay.co.uk/itm/Spannzangenfutter-ER32-fur-Myford-/111358144396?pt=LH_DefaultDomain_77&hash=item19ed766f8c

[mklotz]

Marv,
Of course you are perfectly correct about those units, as even our military uses the metric system.  I hear that as soon as we get a proper NFL team in LA, we are going to finalize the annexation and statehood for Californica.

Yes, and to eliminate the necessity of changing the flag, when that happens we're going to sell Joisey to Russia so they have a place worse than Siberia to send their criminals.

[Stuart]

why not do as John Mills (doubleboost) and make the tommy bar holes the same size as your chuck key handles then you will have it to hand

Stuart

[Roger B]

This may be what you need,

http://www.rc-machines.com/en/accessories/acces.-turning/chucks/collet-chuck-er32-myford-thread-1-1-8-x-12tpi

If you decide to make your own I would suggest trying to borrow a Myford fitting one or one which will fit the Headstock taper so you can set the taper from this. I have an MT 2 - ER25 which has the same angle but it's a bit far away 

[Dan Rowe]

Here is a UK link to what I call a pin spanner. These are made to DIN 1810 standards. The text calls it a hook spanner with a pin.

http://gedoreuk.com/default/products-1/gedore-2012/spanners/hook-spanners/40-z-hook-wrench-with-pin

Dan

[mklotz]

Or you can get the adjustable type...

http://www.use-enco.com/CGI/INSRIT?PMAKA=307-3639

[Jim Nic]

Just to add confusion to a subject you thought had been sorted  , I have an ER 32 chuck on my Warco lathe of a similar size to your Myford and it uses an 8mm tommy bar to hold it while a "C" (or peg or pin) spanner is used on the nut.  I have never had a problem with undoing the nut and my experience of C spanners is that I would rather not use 2 of the things at once.
As to tommy bar material I would not advise silver steel; I have used silver steel, albeit thinner, in a similar way on my Unimat and it bends far too easily for my liking.  I have no idea what sort of steel my "real" tommy bar is made of as I found it amongst some old tools in my garage, it's probably good old 1960s English Unbendium.
Jim

[Xldevil]

Hello.
Maybe this is of interest ,drawings included.
http://homews.co.uk/page130.html
Cheers,Ralph

[ths]

Arnold's build of his ER chuck for his ML7 is here

http://www.homemodelenginemachinist.com/showthread.php?t=5179

I did what he did when making mine. I bought two ER closing nut pin spanners from CTC Tools, one is used in the body of the chuck, the other (naturally), on the nut. Hugh.

[Allen Smithee]

This may be what you need,

http://www.rc-machines.com/en/accessories/acces.-turning/chucks/collet-chuck-er32-myford-thread-1-1-8-x-12tpi

Yes, I saw that. But with postage it gets rather expensive (100 euros!).

If you decide to make your own I would suggest trying to borrow a Myford fitting one or one which will fit the Headstock taper so you can set the taper from this. I have an MT 2 - ER25 which has the same angle but it's a bit far away 

I'm reasonably confident I can get the collet seat taper right - I set the compound to a marked 8 degrees, check & tune it by clocking the cross movement over a measured advance of the compound and that should get it within a few tenths of a degree at least. I then bore the seat for part of the distance, blue it up and lightly rotate a collet in there to confirm that it's touching over the whole length (or not - adjusting as necessary). The bit I'm less confident about is achieving a decent surface finish in the taper. My cunning plan is to make the whole thing about 5mm longer than the drawing so that if I need to I can have several goes at boring that seat!

AS

[Allen Smithee]

Here is a UK link to what I call a pin spanner. These are made to DIN 1810 standards. The text calls it a hook spanner with a pin.

http://gedoreuk.com/default/products-1/gedore-2012/spanners/hook-spanners/40-z-hook-wrench-with-pin

Yes, that's what I was calling (wrongly, probably) a "C-spanner". Actually it's not *quite* the same because that one seems to have a round pin to engage in a round hole, whereas mine have "square" pins to engage in a slot. I have two of them in the required size already - one came with my mill and the other came with my MT3 ER32 chuck (that I got for the mill). They suit a 50mm dia, so I guess there's no reason why I shouldn't use the same tools on both mill and lathe (as well as the same collets!) and they just need me to mill slots in the chuck body after the rest is done. I think I'm leaning more and more towards this in preference to the tommy bar.

AS

[ths]

Allen, this is how I use mine. I'm not sure if this is the information you're after.



The two spanners work well, I think that a 6.5mm drill provided the holes in the chuck body.

Cheers, Hugh.

[Andy]

I made one from Harold Halls site. 
I did make a copy of my register and spindle thread first though to enable easy testing of the part.
The metric thread was easy as well (Myford S7 with gearbox using another gear)
The only thing I did wrong was not to make the holes, to tighten it up, the same size as my chuck key.
Probably the hardest part, for me, was cutting the internal thread for the spindle.
In the end I have a very accurate way of holding material   
Good luck
 

[Stuart]

Allen

when you test fit the collet make sure you remember to fill the round hole in the collet with a sutable nominal size bar else you will get a bad test because they spring without the hole filled


Stuart

Don't ask how I know 

[Allen Smithee]

At the start I said there was a reason why my piece of 50mm bar was *particularly* suitable. The reason is that when I looked it it I found that the previous owner had tried to use it to make something that fitted a Myford, so it already has the internal thread at one end. The bad news isthat whoever it was made a hash of cutting the register diameter, and has bored it oversize. I tried using a boring bar with the lathe running backwards, but it refused to bore the hole back down to the right size (must be that cheap boring bar insert), so my plan is to bore it out another 3-4mm and press in a collar of new metal so I can bore the register to the right size. I was thinking a 1-2thou interference fit should be enough - any thoughts?

AS

[Allen Smithee]

So taking on board some of the comments my design now looks like this:



The bit of material, and my planned use of it, looks like this:



I was thinking that I'd initially cut the ring aboy 1-1.5mm over-length and bore it to have a "wall" thickness of something like 5mm (so it doesn't collapse when pressed into the bore) with a short 2 degree (or so) chamfer at one end. I was thinking of machining the bore in the material a further 3mm in diameter and sizing the ring such that it was a 1-2 thou interference fit (sorry, but for fits I still speak inferial!). After pressing in I would then be boring a smidge under 2mm off the insert to get to the register diameter.

I'd appreciate any thoughts anyone has on this plan before I go ahead!

In the mean time I screwed the piece of material onto the myford's nose, just relying on the face land of the spindle to square it up, and was surprised to see well under half a thou of runout ("well under half a thou" meaning "when I clocked it there was a very slight shiver on the needle, but it was less than half of the division, so as far as I can see it's pretty damned concentric!"). This was true down the length of the bar, surprisingly. So I thought I'd clean off some of the rust and dirt to give the chuck a nice surface to work with by taking a skim cut. Having just touched the workpiece with the tool (one of my cheap Warco insert tools with the original chinese insert) I advanced the (metric) cross-slide by 0.05(dia), so about a 1 thou cut and let it go in fine-feed (at 2 thou per rev). The result was OK, but not brilliant. So on a whim I thought I'd wind the speed right up and see how the tool took it for another 0.05 cut.

According to my calcs turning a 50mm mild steel bar with an HSS tool should be at about ~500rpm, and I was now running at 2140rpm with this cheapo insert tip. I was surprised to find that the tool just loved it. The chip came away in strings (nicely blued!), but the surface finish was beautiful - had there been a smidge more radius on the tool I'd have been happy with this as a finish turn on a piston. SO maybe those cheap inserts aren't quite as bad as I'd thought.

I then took it off the spindle, refitted my 5" 3-jaw and mounted the bar, intending to part-off the end (as above). But it didn't look to be running that true so I clocked it and found that it was running out by nearly seven thou (inferial clock). Damn. I checked it all the way down the bar and found the run-out was essentially constant, so I clocked the chuck's OD but found that to be OK. Then I remobed the bar and clocked half a dozen pieces of assorted sizes of silver steel, PGMS and larger peices with a turned OD. The result was the same - a fairly constant run-out of nearly 7 thou across the whole range of the chuck scroll (always with the high spot when the "0" key hole is at about 11 o'clock).

I stopped there last night - this evening I'll see if I can null it out with paper/shim under one or two jaws, but it looks like I should consider either a new chuck (yeah, right!) or mounting the dremel on the toolpost and grinding the jaws a smidge. I know a 3-jaw can't really be expected to be much better than 0.0025ish, but I think 0.007 is excessive.

AS

[Jasonb]

Alan, I thought that the wide end of the taper socket should be 32mm for an ER32 collet and the same for all others that teh widest part of the opening is the collet ref eg 25, 16, 11, etc. At 31mm you may not get as many turns of the nut thread engaged.

Not quite sure why you are adding a bit of metal. I would just hold in the 4-jaw to machine the spindle thread and register, then screw it onto the spindle to do the rest.

EDIT. Just read the last post on teh previous page about the register.

J

[Stuart]

Allen

Is this a screwed back chuck or a chuck on a backplate.
You have realy carefully cleaned the chuck theads a small spek of WHY will cause mischief

 if it's the latter the pop the chuck off the backplate true up the face and turn a wee bit off the register , remount the chuck , chuck up a good round bar of the size you normaly turn and with a lead tup bring the chuck into truth , cheap griptru mod

If your chuck is screwed back and it's theads are clean ,as is the scroll then you have what you have , but good chucks a spendy , Pratt chucks are not what they used to be , far eastern ones a lucky dip Indian one are not bad .
I have have similar problems in the past with a Hebdon bridge back plate and a Bison 160mm three jaw, I would turn up the back plate face mount the chuck bring it to truth , six months on it as bad  so go though it again year later you guessed it it's off again , so the cycle repeats for three years and now it's ok
I have put it down to the back plate having stresses in it because it was not aged .
Before you ask this could not be corrected by moving the chuck axis because it was a wobble true at the chuck excentric at the end of the test bar.
My Myford has a the 42 mm thread with a 25 mm pass though

Your new design look ok from here in the cold North
Have fun and be safe I am sure you will sort it but the run out will not matter if you mount the new chuck blank to the spindle nose and finish turning it then external work and taper in one sitting then it will be true to your spindle nose

Stuart

[Roger B]

This was my attempt at a flange mounted ER chuck, with plenty of blue chips 

http://www.modelenginemaker.com/index.php?topic=3925.0