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