Collet Question

Have the remains of an old benchtop milling machine / jig borer. Looks quite a bit like a BCA / Excel, but xy slide / rotary table assembly
missing and no makers name anywhere on the frame. Have an xy table to adapt and am planning to use a lightweight aircraft 400Hz motor, around 1/2 hp, to drive the spindle. Question is re the collets, which are much longer than the usual watchmaking type and wonder if anyone can identify, or suggest a source. Have one 1/4" collet with the machine, whose dimensions are:
Length, tip to tip 2.875" Nose dia 0.625" Shank dia: 0.432" Thread dia: 0.346", external Thread tpi: ~25 (metric ?) Thread length: 0.6"
Any ideas ?...
Chris
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Any use?
http://shopswarf.orcon.net.nz/collet.html
Steve Sheffield
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Steve wrote:

Steve,
A usefull reference in any case, thanks, but doesn't have a collet of the above dimensions. Suspect something metric, since a thread gauge at 24 and 26 tpi doesn't fit. but a 25 is just about right, though the thread is stretched a bit from over tightening.
The bca page on lathes.co.uk says something about "Lorch long series", but can't find any reference to these on the web and have also tried a few watchmaking sites. A mystery - may end up adapting something smaller, or make up some of my own, once I have a functioning lathe again...
Chris
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My understanding was that Lorch long series are the 12.5mm shank dia collets used by some Lorch Schmidt lathes (including mine!). Thread is 1mm pitch in some really silly size (11.5mm OD I think). The CC code is 1580.
I've never found any source of these other than the ones which came with the lathe, which form more or less a complete series with some annoying gaps like 10mm.
If you have to make them, the secret seems to be to leave a piece of metal holding the jaws together on the collet nose, and grind this off after hardening to avoid distortion problems.
Alan
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Alan Bain wrote:

Alan,
Thanks - still not quite the same dimensions, though the example I have is quite worn, so is probably correct. Lorch Schmidt becomes an Ebay search term :-).
Failing that, the easiest way to get round the problem is to find something more standard that's close, then make an adapter. Only a single item to make, rather than many...
Chris
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The nearest Lorch collet dimensions I can find are
length 73mm Nose dia 14mm Shank dia 10mm Thread .362" dia x 1mm pitch. Cone angle 38.5 degrees.
May be of some help
Chris.
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rack2000 wrote:

That sounds pretty close and thankyou. I don't suppose you have a general reference to continental, rather than us size collets ?.
Mark has a similar machine and the collets do appear from time to time on Ebay, so will have to keep eyes open. The new price for a single collet would probably be more than I paid for the machine :-(...
Chris
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ChrisQuayle wrote:

That's the "Lorch long" collet, as used in the BCA/Excel jig borer, and they are about as rare as hen's teeth. :(
The Lorch collets you sometimes see on eBay are 10 mm body diameter - these are different, being 7/16 inch body, with a 9mm x 1mm thread (go figure).
JS pointed me to the below, which might be of interest - please let me know if you decide to follow it up, as I'd like some too.
BTW, what would be a good material to make collets from?
Peter Fairbrother
************
Posted on 2nd January
For Sale Tools Best Wishes for the new year to all. I am thinking of having another small batch of BCA blank collets made. If you are interested please contact me. It is possible that a batch of BCA collets may be made with a boring attachment fitted. Just a thought, and to be pedantic (pedantry in its right place is very important) I am a trader in the BCA sense of having some collets made and selling the surplus to other like minded and consenting adults to be used in the privacy of their own workshops in a non judgmental and all encompassing way, not of course forgetting all those who do not share knowledge and pleasure of the Craft. Best Wishes Mike
Mike Flannery mjpflannery [at] hotmail.com 01903 883974 Sussex GB
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pete wrote:

That's more or less what i'm finding, no examples on Ebay and none found anywhere else thus far. There are two solutions: 1) Make an adapter and new drawbar so that more common (watchmaking ?) collets can be used, or 2) Have a go at making some. As for material, it's 35 years since I was anywhere near a toolroom, but we used tool steel and silver steel rod, hardened/tempered, for small items like press punches and would probably get the job done. I'm sure there would be better materials and local steel stockist should be able to advise. Talking of which and for those in the Oxford area, a very helpfull specialist steel stockist is Kingston Steels. Rang up the other day fo a piece of 1/2" gauge plate, ready in a couple of hours accurately cut to size and not overpriced. 01865 820 629. No connection, but they were very helpful.
The problems arise if you want to heat treat, as I would think some distortion is inevitable and you may need to finish grind all the mating surfaces afterwards.
In short, not any easy task to get right with limited resources, especially if you want serious accuracy...
Chris
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Chris,
I just spent some time machining parts from EN24T - never used it before, but it machined surprisingly (to me) well with TC tools, though perhaps harder to get a really high finish. From specs it is a lot tougher than EN1A. Just a possibility, it might be good enough for collets which will not be getting serious production usage. AIUI, the T variety has already been hardened and tempered, so there is no risk of distortion on heat treatment. Drilled quite happily with ordinary HS drills as well.
Anybody used it for such purposes?
EN19T might be another possibility, though with a slightly lower UTS.
BTW, the modern ref nos are 817M40T and 709M40T respectively.
(My thanks to AWEM for the gift of the bar end of EN24T. Saved my bacon as I forgot to order up some 3" EN1A required for my project, and I could have lost days waiting for it.)
David
--
David Littlewood

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On Thu, 28 Jun 2007 02:33:49 +0100, David Littlewood

I've been using EN24 and EN24T for the gears and pinions that I'm (still) making for the Hardinge apron gearbox. It was a very hard call between that and EN19. If I had access to induction hardening equipment or was confident about flame hardening, I would have gone for EN19. As it was, I have done a trial run with salt bath heating and oil quenching of the EN24T and could not measure the resulting distortion. That's good enough for me. I'll be finish grinding the needle roller journals with the toolpost grinder and letting the gear teeth take their chances.
It is possible to get a mirror finish, straight off, with heavy cuts and high speed, but is very hard to do this consistently with the little lathes that we tend to use. Built up edge seems to be a real problem with this steel. I have found that, for small diameters that won't be hardened and ground, that the best results can be had by creeping up on the last thou of diameter with wet and dry paper or an oilstone in the toolpost (Yeah, I know it's really grinding, but it's different...).
For long holes, I've been starting with a gun drill that I got off fleabay. This gives me a guaranteed straight hole with a good finish. After that the holes can be bored to size and/or reamed for finish. Collets could be done with drill and reamer with careful setup. I would probably still gun drill the back, clearance, hole to size in one step.
BCA collet manufacture is probably in my future, but it's going to be at least a couple of years before it gets near the top of the to-do list.
Mark Rand RTFM
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Mark, thanks for that, most interesting - as I said, I am very much a novice with this material, but I will certainly be considering it again. Could you please say more on the hardening and tempering, I thought it was already hardened and tempered but detailed information was sparse.
BTW, I agree with you about build-up - I had experienced this, and it was probably the cause of my finish problems. The finish I got was OK, just not brilliant. Will try your idea next time.
What make is the gun drill? - I assume it is one of those with a coolant hole down the middle.
David
--
David Littlewood

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writes

Slightly off this topic, but intended as encouragement for the would be hardener.
I have just made some through hardened and ground crankpins for my loco. They are EN9 and were cooked in molten table salt at 840'C for 50 minutes before water quenching. They were tempered at 250'C in the domestic oven. I had left them about 20 thou big for a ground finish because I didn't know how much scaling I might get. As it turn out, they were barely discoloured by the hardening, whereas the tempering caused blueing afterwards, but no scale. I could have finish ground them before hardening and polished them up afterwards.
I used a graphite /clay crucible which suffered no ill effects from the salt - be very careful if you use it, the hot salt is as mobile as water, but about as deadly as molten brass!
Steve (Sheffield)
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On Thu, 28 Jun 2007 10:09:02 +0100, David Littlewood

The EN24T is supplied tempered to 248-302HB or 24-32HRC. Quenched from 850C in oil and tempered at 200C can get 520HB or 54HRC (that's what I got on my test piece). in comparison, EN1A is about 103HB or off the bottom of the Rockwell C scale. So it's significantly harder than EN1A (so's cold butter :-), but can be made much harder if needed.
My plan on the gears I'm making was to leave the large gears as they are and harden the pinions and any needle roller races.
I've got three or four gun drills from fleabay. varying from 8.1mm to 11.15mm diameter. I think they are all made by Sterling. I've got one of them Loctited into a hole bored in a 2MT blank arbour with a spigot sticking out of the side of the arbour for coolant. Whilst they are normally used with high pressure coolant, I've got good results with a normal coolant pump and cutting oil. On the round-tuit list is the job to cut a couple of gears and some plate to make into a gear pump to mount on the lathe change wheel banjo.
Here are some pictures that I prepared earlier:-
http://www.test-net.com/hardening-test /
Steve's comments fit with my one-off experience.
I _know_ that I took some pictures of the gun drill in use, but I must have forgotten to save them before her indoors stole the camera for more bloody pet photos. I'll take some more one day.
Mark Rand RTFM
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Mark Rand wrote:

Fire and brimstone indeed and wonder if this is what hell would be all about :-). Anyway, got the brain going and wonder how easy it would be to build a small induction heated crucible,. Perhaps some parts from a domestic induction hob might do, but the electronics shouldn't be too difficult to design. For a small crucible, you would probably need no more than a kw or 2. A thermocouple and omron controller completes the job in terms of dial in temperature.
The tricky bit might be how to keep the coil cool, but I guess if you used thin copper tube, you could circulate water through it. No idea of required frequency, but will do a bit of digging.
Great pics of the workshop build, btw...
Chris .
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Talk to Andrew, I think he melts down unwanted HGVs in his.
David
--
David Littlewood

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David Littlewood wrote:

Found a couple of references to home brew induction furnace stuff:
http://www.hvguy.4hv.org/ih/indheat.htm
http://www.richieburnett.co.uk/indheat.html
Looks pretty straightforward as a home build project (Mark ?). Would think that it would scale up fairly readily using higher line voltage and / or more devices in parallel + water cooling the coil...
Chris
---------------------- Greenfield Designs Ltd Electronic and Embedded System Design Oxford, England (44) 1865 750 681
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writes

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Many people have struggled to get small scale induction furnaces going - if you look on the CNC zone site:
http://www.cnczone.com/forums/showthread.php?t 545
There is an on going discussion with one or two people having some sucess.
AWEM
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Andrew Mawson wrote:

The power supply shouldn't be a problem, nor the coil. I think the main points are to choose the right frquency for the desired depth of heating (skin effect) and also the matching of the power supply to load. If you only want harden / temper temperatures, you shouldn't need really exotic materials for workpiece support
Not really enough time to build at the mo, but do have some old 5 volt 200 amp computer supplies which might be a good starting point for a psu, though the typical switcher 20 or 30Khz frequency might be a bit low. Definately on the to do list, even if I don't have the time at present. Would be a usefull addition to the workshop, even if only good for small items...
Chris
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You might be surprised how low the frequency needs to be for melting even relatively small crucible loads. My 100kW furnace runs at frequencies ranging from 2.2 kHz to 3.25 kHz for crucibles of about 3 - 12 kgs load in iron. My low power experimental unit that I made last year ran at 20kHz for a 500 gram load. The resonant frequency is of course very dependant on the charge in the crucible. Remember that standard graphite crucibles conduct electricity so will heat up when empty and waste energy. You should use an alumina one.
AWEM
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