Making a 5C Collet Chuck

[Robert Turner 1Participant @robertturner1]

[Robert Turner 1Participant @robertturner1]

Hello all – I have been 'lurking' on these forums for a while, and I have a question about making a Collet Chuck for my Boxford AUD.

First a quick introduction: I'm not trained as an Engineer, but I have built lots of full-size hobby projects, such as Wind Turbines, Furniture, a car, a motorbike etc etc. I have had my lathe for about 10 years now and I am working on my accuracy (and patience!) with a view to making a model beam engine.

I don't have much budget, so I have been making various tools for the Boxford out of bar stock, like a cross-drilling jig and a Dividing head.

I realized that I will need more accurate workholding to be able to make a model, so I decided to make a 5C collet chuck, as it seems to have the biggest range of sizes and shapes (Hex and square are handy collets to have). My design for the chuck is pretty simple and it uses a captive 'nut' inside the body to thread onto the end of the collet, tightened up with a tommy bar through a slot. My question is this: will I wear out or damage the threads on the collets by using them for the full force of the collet closing 'pull' while tightening? It struck me that when you have a drawbar you thread it into the collet first, then use the thread on the drawbar to do the heavy pulling. I don't want to use a drawbar, as the whole point of the 5C collet is to hold long bar through the spindle bore – my 3MT collets only allow me to hold a workpiece about 3" long.

Maybe I am worrying too much – It's not going to get heavy industrial use. I would appreciate it if someone with 'real' industry experience could assist……

Sorry for the long rambling post

[jason udallParticipant @jasonudall57142]

As you have identified this use would not be best practice.

The external threads on the 5C are fine..ie shallow.
( so are the internal)..
So not a good idea to end up with say only 4 threads engaged..if you were working with most and say the last one or two leads for adjustment then for light work maybe..the torque is via keyway and friction on the hardened cone of the chuck….

ER collets chucks are easier to make

Edited By jason udall on 11/06/2014 14:50:52

[Gray62Participant @gray62]

If you have access to the archives or back issues, there was an article describing the build of a 5C collet chuck in issue 131 of MEW.

The commercially built 5C chucks work in a similar way to what you have described. If I get time tonight, I'll pull my spare one apart and upload some photos of the internals which may help you.

regards

Graemei

[Robert Turner 1Participant @robertturner1]

Thanks for the replies – I think I will have about 12 turns of the thread engaged when the 'pulling' part of the action starts. If it looks like this will strain the threads too much, I might add an external locking ring with a coarser thread that pushes a set of pins onto the face of the internal nut.

The other reason for considering 5C collets is that there is more likely to be second-hand ones available.

By the way, does anyone make ER collets for hex or square bar? That would be one of my main reasons for wanting to use collets – I will be making a lot of nuts and bolts for the beam engine and my three-jaw chuck has had 45 years of abuse in a training college….

[Clive FosterParticipant @clivefoster55965]

Conventional screw drawbar 5C systems on industrial size lathes use the collet threads to apply full closing force so things work just fine given sufficient thread engagement. 5C has around 1/2" of thread. I figure the drawbar on my Smart & Brown 1024 VSL screws on approaching 3/8" before the collet closes up. Collet block system nuts which also apply full closing force, are around 10 mm or 3/8" deep too so I guess thats as good a figure as any to aim for.

Although your proposed design is conceptually sound tightening the nut with a tommy bar through a slot is "somewhat frustrating" if you have any amount of components to make. Conventional practice is to have a cam operated sliding sleeve to tighten and release after the basic setting has been obtained by screwing the collet into a body or by doing up a round nut with a tommy bar through the slot in the manner you propose. I have one of this style **LINK** 5C horizontal / vertical carriers for use on the milling machine which uses the tommy bar and nut method. Bad enough to inspire creative commentary when used for initial set up. Prospect of using the tommy bar for every component is distinctly un-appealing. I also have a high quality 5C collet chuck, purchased for my Pratt & Whitney, on which the collets screw into the body via the slots using a three blades spider. A hex socket let into the body actuates the closing cam. Much nicer to use but probably beyond easy home shop replication.

The push from the front variety of screw closure, as used in the Chronos H/V fixture Ref: 2356085, looks easier all round but I've not seen or used them so they may have other disadvantages. From a cost / work / performance viewpoint it might be worth considering purchase of the Chronos, or similar device and turning down the body to an accurate cylinder which can be held in the four jaw chuck or a custom carrier screwed onto the spindle nose. Hafta get rid of the tightening lever but thats no great chore.

Clive

[JasonBModerator @jasonb]

As Clive says you will soon get fed up using a tommy bar when changing collet sizes, takes long enough with a proper scroll type 5C chuck. I'd be looking at another way to insert and then close them or go to ER collets with a nut.

J

[Clive FosterParticipant @clivefoster55965]

Arceurotrade also do a front screwed ring closing 5C collet fixture designated type B in their catalogue. Bigger and better picture than Chronos.

Looks as if construction would be no more difficult than the usual ER collet chuck design. A cylindrical body made to screw on the spindle nose with the requisite collet cavity inside and a ring nut to close with either tommy bar holes or (more professional looking) slots for a special spanner. I guess the closing rim bore and lip needs to be similar depth to that used with an ER 32 collet, around 1 1/8" bore by 1/8" thick.

Imagine that the only disadvantage relative to a normal pull from the back or cam operated tightening sleeve design would be an inability to work really close to the collet nose due to the nut getting in the way.

Clive

[Nigel McBurney 1Participant @nigelmcburney1]

Assuming your Boxford is the usual 4.5 centre height with a spindle bore of just over 3/4 inch , I would say that a fixture holding a 5c collet would protrude a bit too far out from the front of the lathe spindle for my liking ,work will tend too chatter . The Boxford where I worked had a set of Boxford collets ,there was a nose piece which fitted in the spindle taper, collets up to about 1/2 inch capacity,and a collet draw tube which slid into the spindle bore,one end screwed onto the collet the other end had an aluminium handwheel for tightening the collets by hand , The advantage of this system is the work is much closer to the spindle nose, and long lengths of rod would go the length of the spindle. I expect Boxford collets could be found it was 50 years ago that I last used that Boxford.

Some time ago I bought a Marlco indexing fixture at auction,it was fitted with a 5c geared scroll collet chuck and had one collet , I took it off and replaced it with a 3 jaw chuck much more useful , On removing the collet from the chuck I found it was left hand threaded, as I wanted to use my stock of 5c s from my Browne and Sharpe lathe I made a new r/hand nut for the chuck and then fitted the chuck onto a colchester back plate ,only snag to tighten the chuck the key goes anti clock ,so watch out when buying used collets some may be l/hand.

[BazyleParticipant @bazyle]

The standard collets for the Boxford are 3C with caspacity up to half inch. Above that you would be better off getting a 'new' 3 jaw chuck anyway if your original is worn. As mentioned above the overhang seems undesirable.

[Robert Turner 1Participant @robertturner1]

Thank you everyone for all your help. I did consider the Boxford collets, but the 1/2" limit is too restrictive, plus getting a set out here to Halifax, Nova Scotia would cost $$$$. I found some section drawings of the 'Bison' Collet chuck and the collet threads are indeed used to both pull and screw at the same time, so I'm not worrying about wrecking the collets each time I use them. I also notice that the Bison chuck has an oiling point next to the thread, so I will be including one of these.

I realized a long time ago that my engineering hobby would be characterized by plenty of time, but no money, so I think I will have to live with the compromises inherent in my 'Tommy Bar' design. The overhang of the front of the collet from the spindle nose will be 85mm and as the 90mm dia chuck body will be screwed directly onto the spindle, I don't expect too much chatter.

[SteveIParticipant @stevei]

Hi,

You might consider a hybrid approach. use spindle mounted collets upto 1/2". You'll get the best run out and rigidity. Then for large items you'll need one of the other solutions proposed.

I thought that the old style boxford lathes "327" collets are as per the Hardinge 3C specification. I would expect that 3C collets would be readily available new and second hand in North America. You'd only need to decide to either make or buy the closer and drawbar. One of the advertisers to the right on the web site have 2 listed with some collets, although genuine Boxford accessories are never cheap. (I know since I also have a boxford lathe but the more modern design for which the accessories are even rarer and more eye watering.)

Good luck

Steve

[thaiguzziParticipant @thaiguzzi]

$6.95 in the States. Crawford 327 / Boxford / Harding 3C are all the same dimensions and readily available in round and hex. Sq can be difficult to obtain, especially in imp. Don't ask me how i know.

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