MT3 imperial 7/8" collet ... can it be bought singly ?

I have a need for a MT3 7/8" collet to machine multiple components out of 7/8" aluminium tube .

The only source I can find for such a collet is on Australian sites, and they only sell the item as part of a set ...and the set is like $250 +

RGD tools ( who are excellent and from whom I have bought a lot of stuff) only offer MT3 collets up to 3/4".

is it possible to buy a single MT3 7/8" collet ?

TIA ...

I would be surprised if there is, the small end of an MT3 is .7780 and 7/8" is .875.

Isn't the small end of an MT3 taper less than 7/8" ?

By my reckoning the small end should be about 19.8mm (depends on the length) which is cutting it fine for 3/4" at 19.05mm.

Andy

Surely it's the big end that's important. I don't suppose that this is going to be a through collet, it will be secured by a drawbar. How about making one from a 3MT soft centre?

Rod

Yes, the 3/4" and 5/8" MT3 collets which i am about to buy from RGD tools have a M10 drawbar , and will also (leastways I hope so) have a shoulder up to which I can register the turned end of the workpiece for accurate cutting to length.

Rod, your suggestion makes sense, How would you cut the slots in the end of the collet ?

Just to clarify, these are very short components which I will be machining , (maximum length 40mm ) and they will be initially sawn off, with one end accurately faced prior to machining to length.

The components will made from aluminium tube with 1/8" wall, 7/8" OD, 3/4" OD and 5/8" OD,

Thanks Chris ... I had never even heard of a Keats plate until reading your post. yes, that would work, but a collet will be cheaper ... the 3/4" and the 5/8" collets from RGD are like £8.25 each ... a Keats plate is something like 3 times that.

Further investigation leads me to believe that a Keats plate would work fine for facing off the workpiece to length, but I also need to be able to centre it accurately for subsequent boring... so it has to be a collet ...

Does anyone sell an "emergency" MT3 collet i.e. one that you bore out yourself? I know they are available in 5C but not sure about MT3.

Come to that, is it possible to bore out a 3/4" collet with a carbide tool?

Could always use a MT3 ER40 collet chuck as they go up to 30mm diameter

Bob

Murmac, one point on facing to length, it depends how accurate you want to be or what tolerance you have because with this type of collet it will "stop"at a different point each time you close it thus the end stop will be in a different position.

If you want a more consistent length I would use a collet and suitable bar as a back stop in the headstock and grip the work in a chuck then you will have a "dead stop" to locate the length and all components will be the same. Even if the work runs out a little for the facing to length this will not matter then revert to the collet for subsequent operations where concentricity is required.

Regards John

Bob, I may well one day rise to purchasing a MT3 ER40 chuck and collet set, but ... just a little out of my reach at the moment.

John, I had assumed that these MT3 collets would have a shoulder internally against which I could insert a short "dead stop" which would be slightly less than the collet diameter. Is this not feasible ? I am ordering the 3/4" and 5/8" collets today so I will soon find out !

Your suggestion of facing off to length in the chuck and reverting to the collet for concentricity makes perfect sense, and is indeed what I shall do if my "collet dead stop" idea is a non starter.

I would use soft jaws in a 3 jaw chuck and machine the jaws to the correct diameter, you should be able to retain a stop in the jaws very easily. If you secure the jaws on a piece of material at the back of the jaws then machine to size they should prove quite accurate. Then just use a mandrel to machine the od

One thing you could try is to make your own collet to fit in the 3 jaw chuck. Something like this:

Ignore the dividing plate. The collet has a peg that snugs up against one of the jaws (always use the same one) and I always tightened the 3 jaw up with the same pinion hole. You can bore the collet to suit, incorporating your depth stop then remove from the chuck to saw the slits ( there is one you can't see from the picture that goes across the diameter flush with the flange. I made both of these with a junior hacksaw, there is room to remove the blade and pass it through the hole before re-attaching to the saw frame). I guess it depends on your 3 jaw chuck but the errors are usually reproducible at the same place on the scroll. It worked for me when doing some helical gear cutting.

HTH

Rod

Bore a hole in a bit of metal (steel, aluminium), a couple of inches long, cut a slot down one side, put it with the bit of aluminium tube in it in the 4 jaw chuck and centre it. Drill the hole under size, and bore it with a boring bar, it will then be straight (drills wander). Ian S C

Thanks again to everybody for their advice ... very much appreciated.

btw, Ian, forgive my temerity in venturing to question the advice of somebody much more experienced than I, but wouldn't a 3 jaw self centering chuck be better for this operation than a 4 jaw? I am thinking along the lines of Rod's post above ...I will be repeating this same operation from time to time, so as long as the homemade collet is aligned the same way every time it is inserted, it should be perfectly concentric every time . Or a meringue? (Scottish joke ...)

FWIW I ended up today buying a 3MT - ER32 COLLET CHUCK AND FULL 18PC COLLET SET from RDG ... the price of £114 inc vat and carriage seemed very reasonable compared to buying MT3 tapered collets individually. Also, this set will handle every size between 2mm and 20 mm, including imperial sizes, so I am well chuffed.

For the 7/8" tube, I will make a shop-made collet as suggested above by Ian and Rod and others ... once again many thanks, and apologies for the weird change in font ... no idea how that happened.

Edited By murrmac on 01/08/2014 18:10:41

A bit late to ask now, but if you are only facing to length, is there any requirement for a high level of concentricity?

Neil

Well, yes Neil, when it comes to boring the tubes out, then there is a requirement for concentricity.,

These tubes are going to become bearing housings ... (for miniature bearings obviously) ... if the bored recesses ( is that the right word ?) are not concentric, then the shaft/axle won't run to maximum efficiency.