A problem with eccuracy
|John Wood1||05/11/2009 16:13:38|
116 forum posts
I have an elderly ML7 lathe which, although well used and a bit worn in places, is otherwise in fairly good order. I recently purchased an ER25 collet chuck from Warco which screws directly onto the lathe's spindle. Upon trying this out (having very carefully cleaned the threads first) I find that the collet runs about 5 thou out of true - not what we want from a collet.
I have clocked the spindle itself - no problem. The collet butts nicely onto the flange. I have clocked the main chuck body - OK but the tapered seating for the collet itself shows an error. Now I know that in the lathe's history it had sustained a small amount of damage to the mandrels thread caused by screwing on a 4-jaw chuck with a bit of swarf found hidden in its thred. A suitable die was used to clean up the thread and the other chucks re-aligned for truth. Could it be that this old damage is still causing a problem? maybe I should consider a flanged collet chuck fitted to a backplate, or perhaps give it up and provide a suitable chuck for the Warco WMT300 lathe instead and use the new collet set on that.
Any ideas please?
Is this thread in the right section or should it be in Workshop tools and tooling? - sorry
Edited By John Wood1 on 05/11/2009 16:21:21
Edited By John Wood1 on 05/11/2009 16:23:50
|David Clark 1||05/11/2009 16:42:46|
3357 forum posts
I doubt the thread is the problem.
The thread is to hold the adaptor on but the register is what aligns the chuck.
I suggest you compare the register bore of the holder with the register on the lathe.
It needs to be a very good fit.
Within a thou I would expect.
|chris stephens||05/11/2009 17:14:26|
|1049 forum posts|
Welcome to the wonderful world of disappointment.
David is of course correct it is, or should be, only the register which aligns the chuck or collet holder not he thread. A thought occurs, are you sure the collet was properly placed in the nut before you put the nut on the chuck. You must do it that way round or things will be cocked and the self extract will not work. If you are unused to ER collets you might not be aware of the offset ridge in the nut.
If the above is not the case, you are left with 2 alternatives one, send it back it is clearly not of merchantable quality. The replacement might be right or equally wrong. Two, the engineers way (?) screw it on and "refine" the taper, by cutting the 8 degree true to the lathe. This will only work for small errors because like it or not the thread where the nut screws has some bearing on alignment.
I hope to post a successful report on my remedial work to a collet chuck, have been slowed down by the fact that I found some hard metal in the chuck, which surprised me. I always thought " hardened and tempered" were two workers in the Chinese factory, not a description.
|1017 forum posts|
Hang about gents. I had EXACTLY the issue that John mentioned on my Myford spindle. A very small burr was raised and I couldn't find the error but faceplates etc all showed a definite but small wobble.
Sent hte spindle back to Myfords and the estimable Mr Parker, now I believe retired, diagnosed and fixed. Cost nothing but the postage. (typical Myford IMO)
So I would check the thread given the history. Get a facepalte or something relatively unworn and run it under a DTI. I would then face something, clock with a DTI, turn trhough 90 deg and reclock.
Then I'd look at the chuck, as described above.
A purpely personal opinion - I have on the Chinaman an ER32 collet chuck. Had to be backplate mounted. That is spot on. For the Myford I have an ER25 screw on collet chuck and that does show a tiny bit of run out. However, I have a Grip tru so for absolutely critical work, I use that. I should fix it, I know.
If I were doing it again, I'd do a proper backplate mount, and I'd bore and thread the backplate myself.
|John Wood1||06/11/2009 13:46:30|
116 forum posts
Thanks guys, lots of useful information so I will go away now and look further into it, it's all part of the learning curve.
All the best
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