Making a non standard collet

[frank brownParticipant @frankbrown22225]

I need to make some collets for an obsolete machine. For my sins I have decided on EA24T – any comments?

I intend to use scrap to tryout my thread turning and try the scrap in the collet holder for thread fit, then the do the actual thread, centre drill end first hold the other end in chuck. The actual thread is a 1.2mm, I shall use 21 TPI, its pretty close (21.16 tpi or error of .2mm/1" = .008&quot ) – any comments?

Hold the blank between centres, reduce the shank to size.

The bit that really worries me is the set over to get the include angle of the taper of the collet, its a nats under 20 degrees (19 deg 50&#39. I have a sine bar but never set it up in the "wrong" axis. Can anyone suggest how to set the compound angle correctly?.

Put scrap in chuck and turn taper. "blue" it up and try out in holder. if its not correct, I guess I'll have alter the compound, but how do you rotate the compound, so the area of contact is increased/decreased by .001"?

Put shank in chuck and turn taper. Drill for the bore undersize (.01&quot and ream out to +-0 on size?, face off collet nicely.

Put in rotary head, mill .02" slits and holding keyway.

Put in collet holder and have a beer Phil if you are lurking, you can have a chuckle.

Frank

[frank brownParticipant @frankbrown22225]

[Sub MandrelParticipant @submandrel]

I've made a few ER25 collets from EN24T. They work OK and open back up when released. They don't have as much range (fewer slots), but I made them dead to some sizes I needed anyway.

I used 0.063"/1/16" slots as that's about the size in my commercially made collets.

Neil

[AndyfParticipant @andyf]

If you can accurately measure the distance your lathe carriage travels, and are confident that your top slde dovetail is parallel to the slide's rear edge, maybe you could try this,:

Set up the topslide at roughly the right angle, and bring the plunger of an indicator which is fixed to the lathe bed to bear on the far side of the top slide. The indicator must be both at right angles to the lathe bed and parallel to the bed in the horizontal (i.e. flat). Trim the top slide angle until the indicator shows a deflection of 36.07 units when the carriage is moved 100 units. The units might be millimetres. If you work in inches, try something in proportion like 1.443" over 4".The greater the distance over which you measure, the more accurate the result.

Note: this assumes that the included angle of your taper is 2 x 19° 50' = 39° 40', which sounds a bit steep. If the included angle is 19° 50', you will want to set your topslide to half that which is 9° 55", and the figures then become 17.48mms over 100mms, or 0.699" over 4", or any other pro rta figures.

Do check my maths carefully; I was always a bit of a duffer at trig, and find aids like this calculator useful, though it needs decimal parts of a degree rather than minutes, and setting to more than the default 3 significant figures.

Andy

[BazyleParticipant @bazyle]

Don't forget the collet initially has a slighlty different taper from the holder to allow for a compression and it must end up with contact at tthe outer most edge not the inner most.
To make a small adjust ment or at least to see what your gentle tapping has moved it by clamp a laser pointer to the toplside to work as a 6 ft pointer.

Interesting you should raise this as I have been wondering what to make a collet holder out of .

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Frank ,

Make a master setting gauge for the taper .

Gauge consists of a long parallel section and the actual taper . This is all turned true between centres .

The parallel section is for you to reset it true between centres each time of use .

Make the taper section best guess to the taper needed and then by any means true it to a dead fit in the spindle nose . Getting as near as possible by turning and then hand lapping with slipstone and testing with blue will do it but there are other ways .

To use to make actual collets just reset gauge true between centres and clock topslide to it .

Regards ,

Michael Williams .

[Gordon WParticipant @gordonw]

Set a collet on a bar in the chuck, so that the taper you need is sticking out. Put a dial gauge in the toolholder and set topslide to the taper. To make small adjustments I put a length of square bar in toolholder and move that, gives a good lever ratio, for very fine adjustment put the bar against ,say, the tailstock and move the cross slide.

[frank brownParticipant @frankbrown22225]

I think Gordon W gets the cigar , I think I'll try that out. I'll use a 4 jaw to try and get the "master" collet to rotate squarely first, by indicating of its shank. then using a clock in the cross slide get the angle correct. looks a bit tight at the moment. Many thank one and all. sorry about all those funny faces don't know where they came from.

Frank.

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