Is this scrap?

[RussellT]

I've been attempting to make an ER32 collet chuck to screw on the spindle of my lathe and all was going well until I took if off the lathe and had a closer look.



I have an MT mounted chuck and I was planning to use the nut from that.  Here it is.



The problem can't really be seen in a photo so here's a sketch.



The problem is the thin portion in the middle.  Effectively there are two cylinders that overlap by about 0.5mm (0.020").  The two cylinders are quite thick walled (about 5mm) so should be quite rigid but I have no idea whether this will be strong enough in practice.  My current feeling is that I throw it in the bin marked "Experience" and start again.

Any other suggestions?

Russell

[John Rudd]

It can be quite dis-heartening when embarking on a small project to get through to almost finishing and then having a doubt about the finished job........
Been there all too often myself....

I think you have already answered your own question....the seed has been sown so to speak.

If you think the part is scrap and can learn from it then nothing is lost....

( I think I might yet make it as a philosopher )

Apart from that 20 thou isnt a lot...Imagine taking a heavy cut on a job only to find the collet holder gives up? What could go wrong probably will..
I'd start again

[philf]

 My current feeling is that I throw it in the bin marked "Experience" and start again.

Hi Russell,

 

I agree - bin it and make another 5mm longer.

It's always worth doing a to-scale drawing before cutting metal - it's quicker and cheaper in the end.

 

Phil.

[andyf]

I suppose the overlap might be stronger than 0.5mm suggests - in surface area terms, it's probably something like 50 sq mm.

So it will probably be fine until the moment you are putting the finishing touches to some item in which you have invested hours of work. 

Andy

[Rob.Wilson]

Hi Russell     , I would say it was scrap ,chalk it up to experience and make another , I have done similar in the past 

Just a thought how are you testing the collet taper for fit ?  its just I have seen lads just adding a bit blue to the taper of the collet and trying it in the socket , pressing it in ,bit twist and bobs ya uncle a good contact patch , Doing it WITHOUT something in the collet bore . If there is nothing in the collet to stop it closing up it will take the shape of a taper near enough a deg out.

So take say a 12mm end mill as there shanks are generally ground cock on (check) fit to collet , blue and test socket taper .

You probably no this ,but thought I may as well post so others dont fall into the trap of ill fitting collets .


Rob

PS , your threading looks nice and crisp 

[doubleboost]

I am one of the lads who fell in to the empty collet trap 
John

[Brass_Machine]

Learn from it and scrap it.

Great advice Rob!

Eric

[RussellT]

Well that's unanimous.  It's scrap.  Thanks for all the comments.

However there was lots of useful practice in thread cutting etc.  In fact I was really pleased how the threads came out. (Thank you Rob for noticing).

As far as the taper goes I was relying on the computer to get the angle right for me.  I did test it with an empty collet held lightly but next time I will use one with something in it.

I'll do it again.  Looking on the bright side - with all that practice and the tools already ground it should be much quicker.

First though I need to fix the lathe switch. 

Russell

[AussieJimG]

Thanks for the tips on testing. I am about to embark on making some of these and the tips have come just in time.

Jim