collets on a lathe

F. George McDuffee wrote:
Thanks.
Peter

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    The original installation -- yes. However once that is done, simply removing a stripper bolt allows me to pull out the lever-style mechanism and replacing the bolt with it upside down allows it to rest against the back of the headstock. The stripper bolt *should* have a nut, but it is held in place nicely by gravity. I do this fairly often for putting larger diameter chuck-held stock through the spindle. (In particularly -- the largest hex size which will fit through the spindle without the collet drawtube in place.

    Yes -- that is one reason for the support/feed tube which I mentioned for long stock extending out of the back of the spindle. Anything which sticks out more than perhaps ten times its length is likely to turn into a dangerous flail if unsupported. But it does not take much to support it. I use white PVC plumbing for the purpose. As long as it prevents the free end (and the middle) from getting very far off center, it prevents the problem.

    That can work. Beware getting the faceplate very much off balance, as it will cause the lathe to walk around the shop.

    Agreed for all.

    You can also hold the six-sided one in a 3-jaw chuck, or the four-sided one in a 4-jaw chuck -- but this makes getting to the part which locks the collet in rather difficult. It can be useful for a one-shot job, but not for one where you are making a lot of parts. Especially considering that in a 4-jaw you will have to re-true it each time you change parts.

    Agreed. Let me mention here that you have mis-spelled the name of the taper -- it is "Morse", not "morris". This could result in problems when he is trying to find such things in a catalog. "Morris" is a UK car make -- part of the MG series from some time ago.
    The ER collets have the advantage that they cover a much wider range per collet, so it takes fewer to cover the entire range. A *full* set of 5C collets can be quite expensive, even at $5.00 per collet for the cheap ones. Usually, a set in steps of 1/16" is sufficient for holding stock of standard (inch) dimensions, and if you need to hold partially machined parts, you pick up a single collet to fit that size as you need it. 1/16" to 1-1/8" adds up to 18 collets, or $90.00 at $5.00/collet. Double that for 1/32" steps, and again for 1/64" steps. And when you get to the 1/64" steps, you are probably going to be limited to the vendors which charge on the order of $35.00 per collet, instead of $5.00/collet.
    The ER collets which I have for my Compact-5/CNC lathe each cover a 1mm range, so the total count is a lot lower.

    Agreed.
    Hmm ... that is a fairly reasonable price, and I can get the holder to fit my 40-NMTB Nichols milling machine.

    I believe that the 4-1/2 Morse Taper which my Clausing uses in its spindle is in reality a "stub", using the narrow end of the Morse taper #5. But ASA has declared it to be a "standard". :-)

    This will mar soft workpieces, just as a 3-maw would do.

    An interesting approach.
    Enjoy,         DoN.
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F. George McDuffee wrote:
Thanks George - good advise re the collet vise. Ufortunately, havent been able to locate one here in Australia (any suggestions from locals here in Melb. appreciated) - a conversation with my supplier (where I bought the lathe) tells me its a 3MT taper in the headstock, and they can supply 3MT collet holders in a range of sizes - I would need to make up a drawbar with 0.5inch Whitworth thread on one end to insert/remove Thats fine for the the job at hand, but would rather get a set NOW (Hey, their tools, what more excsue do I need?) rather than have to keep on buying individual sizes as the need arises....will keep looking, thanks to everyone for the tutorials - an absolute wealth of experience and information in this group, thank you all for responding - and tolerating the occassional recreational political rant..
Andrew VK3BFA.
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Hare & Forbes in Sydney carry a full range of collets. Purchase online ( www.hareandforbes.com.au ) or credit card phone order ( (02) 98909111) and in the post next day .... too easy

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Paul D wrote:

Thanks Paul - Hare and Forbes here in Melbourne have been helpful - I bought my HAFCO lathe from them. George D gave me a clue to terminology, so I did a search on "Collet chucks/holders" and got some local results. H&F also have some sets with MT3 arbors, (as well as the individual holders I mentioned in an earlier post) so will check them out as well as some on EBAY - the EBAY ones do not mention what type of collet they are, so upgrading and getting different sizes might be a problem The H&F sets say they are upgradeable. and I have had good service from them in the past. I just sold some semi-derelict test gear, so the workshop kitty has a few dollars in it at the moment - buy these before the next gas/electricity bill comes in and SWMBO spends in on fripperies like food and clothing...
Andrew VK3BFA.
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    Hmm ... it sounds as though you are talking about 3MT *collets*, especially with that 0.5" Whitworth thread on the drawbar. One thing to be aware of with these is that they do not have the ability to pass long workpieces through the spindle.
    3MT collets tend to come in fewer sizes -- simply because they are normally sold to hold the shanks of endmills when milling in a lathe (or in inexpensive vertical mills), not for holding workpieces, so it does not *need* as many sizes.
    However, with a 3MT spindle taper, there is no way that you can use the 5C collets, except in a "collet chuck" such as is offered by Bison, with the tradeoffs which I mentioned before.
    If you want to see what they look like, visit:
        <http://www.brassandtool.com/Chucks-Collet.html
probably too far away for you to purchase from, but you may be able to find a Bison dealer in your country. Note if you scroll down, you will find various mounting systems, including 1-1/2x8 spindle nose, which *may* be the spindle nose thread for your 3MT internal spindle. You have not yet mentioned who made the lathe, so this is only a guess.
    If it is an Aisan manufacture with imperial instead of metric leadscrews, it may not even be able to cut its own spindle nose thread. I do know that one importer to the USA, JET, turns off the existing spindle thread, heat-shrink sleeves it, and turns an imperial thread in the sleeve, so it *can* cut its own spindle nose thread. But this is an exception to the import lines.
    You *could* use 3C collets, with an appropriate closer nosepiece, but that is a significantly smaller collet, and typically more expensive per collet.
    A 5C collet can handle up to 1" diameter through the spindle and the drawtube, and for short workpieces, up to 1-1/8".
    A 3C collet limits you to 0.500" through the spindle and the hollow drawtube. The thread on the ID of the drawtube is a 0.640x26 right hand thread.
    The hole in the closer should be 0.650" ID. The overall length is 2.688".
    I don't have the proper angle inside the nose of the closer. You'll have to get a 3C collet and measure that with a bevel protractor to machine your own nosepiece. Once you have it machined, install a pin to engage the key in the collet's shank to prevent the collet from rotating in the nosepiece while you're screwing the drawtube onto it.
    You'll need a hollow tube to reach through the spindle with a bore of at least 0.500", and need to enlarge it a bit at the end to accept the thread. It looks as though a bore of 0.5984" (I would actually start with 0.600" as the bore before making the internal thread.
    Note that some collets (e.g. the "WW" and "D" sized collets) require a buttress thread. You would have to examine the 3C collet threads to make sure that you did not need to grind a special shaped internal threading tool.
    Once you have the thread made, slide the tube into place, and screw in the collet until it bottoms -- then push the collet into the closer as hard as possible. Mark the point on the tube which lines up with the end of the spindle tube.
    Then, make a handwheel, with a bearing which pushes against the end of the spindle tube. Install it on the tube so the bearing surface is perhaps 1/8" closer to the collet than the line which you marked from the end of the spindle.
    It is nice to have a thrust bearing between the handwheel and the spindle end, so you don't have to fight the friction of the handwheel on the end of the spindle.
    Nicer would be a lever-style mechanism -- but that can wait, and you can get use out of the collets and drawtube while working up the lever mechanism.

    Good Luck,         DoN.         
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DoN. Nichols wrote:

Thanks Don - how come you always set homework for me < G > - keep on needing to get out the textbooks to look up what you are saying! - but appreciated, thank you.
The bore of the spindle is approx 17mm - so, for the moment, and the job at hand, the collet arbor chuck will have to do - its my first lathe, and as I gain more skill will probably have to upgrade - been using a Colchester at trade school, and its lovely, so smoooth to use. Doing simple machining exercises to learn how to work to 0.05mm tolerances - not easy! (only crashed it a few times, getting better...)
What I need to do at the moment is make up extension shafts for microswitches - the originals are NLA, so using ones I could get, and make up new pushrods from brass round bar to fit the housing they are in. Overall length is approx 20mm, so not being able to run long lengths throught he bore is not a problem (but I can see what your talking about)
Again, thanks for the tutorials - such an enormous field, so much to learn - and loving it !!
Andrew VK3BFA.
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    The idea is that some of these days *you* will be the one answering the questions -- after you learn enough. :-)

    O.K. That would be 0.6693" -- just a bit over the "bearing diameter" of the collet -- 0.65". 0.0193" larger, or 0.49mm. That should be enough for the purpose. You might turn up a plug to 16.51mm and make sure that it will make it the whole way through the spindle bore. Some of them are full size only at the ends, and get a bit rough in the center, so they need cleaning up for a drawtube.

    There you go -- an excuse to turn something to 16.51mm, with a reason which you can give the instructor. Probably thread it internally, and screw in a much smaller bit of rod (say 6mm, perhaps?) long enough to use as a handle to push it through your spindle.
    Hmm ... does the Colchester have collets? If so, you might examine them, and the way they fit to the lathe, to make some of what I have described more clear.

    Good enough. This will serve as a start -- and later you can use them in a small milling machine which you will eventually get.

    It is fun to learn -- and fun to share what you have learned.
    Enjoy,         DoN.
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wrote:

===============Sounds like you may be in the market for Uncle George's "cheap screw" collet special.
Basically a faceplate add-on.
In imperial dimensions, get two pieces of reasonably flat steel or aluminium 1 inch by 1 inch by 4 to 6 inches. Drill and tap one block 3/8 UNC in from each end. Drill the other block with 3/8 holes on the same centers. Bolt the blocks together with 2 inch UNC cap screws with a 0.010 to 0.020 shim between them. Unwrinkled bear can works fine for this. The thickness of the shim determines how much "crush" you can get. You can get fancy and mill the sides of the blocks, but I find that for most home shop projects the normal cold rolled finish is adequate.
Approximently center the blocks on the face plate. Mark the faceplate slot locations on the block with the threads. Drill the block such that you can bolt it to the face plate, making sure you don't hit the clamp screws.
Bolt the block assembly to the face plate and center as desired. Tighten everything up and drill/bore a hole to fit your stock such that the C/L of the hole is on the shim.
leave the one block bolted to the face plate, unbolt the top block from the fixed block and remove the shim. Bolt everything back up. Insert your stock in the hole, through the spindle if you wish, and tighten the clamp screws, and machine away.
Suggestions:
(1) Put a dutchman [punchmark] on the blocks so they will go back together the same way, and the same side will be "out" every time.
(2) drill and ream the faceplate and fixed block for dowel pins so you can remove and replace.
(3) If hole/stock is larger than will fit in your tailstock drillchuck, turn a step that will fit the drill chuck. You can clamp this end in the drill chuck and the clamp the other end with the blocks. This will get you to within a few thou TIR.
(4) If the stock sticks out of the spindle it is a safety hazard. You will need to fabricate a stock tube. Steel pipe is noisy and you can insert rubber tubing to both muffle the noise and protect the stock.
(5) For accurate work you will want to support the stock in the spindle. Make up some bushings. These don't need to be a super close fit, but close enough that the stock won't whip/rattle in the spindle. Plastic works for me.
(6) You can turn tapers and thread the hole if you wish to hold tapered, threaded, or even taper threaded [gas pipe?] fittings for machining.
(7) You can make up "Weldon" [set screw / grubb-screw] style end mill holders from a single block of material and a set screw.
The only thing I like better than machining is cheap machining.
If you look at history you'll find that no state has been so plagued by its rulers as when power has fallen into the hands of some dabbler in philosophy or literary addict.
Desiderius Erasmus (c. 1466-1536), Dutch humanist. Praise of Folly, ch. 24 (1509).
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blocks. These are made in square and hex shapes, and take 5C collets. Simply chuck a square block with the appropriate collet in a 4 jaw chuck. This approach allows use of bar stock extending through the collet, as well as dialing in the required concentricity in the 4 jaw chuck.
John Normile
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