Spindle Thread

[antman]

Hi all,
I am having a few problems getting the correct insert for a VM100 chuck I have purchased for my Carba-tec MC900 lathe.

The lathe is supposed to have a M30 X 3.5 thread but the vicmarc M30 insert does not fit. It starts to thread on but it gets tight after approx 1.5 turns. It has a similar feeling to using an imperial bolt in a metric hole. The thread measures at 30mm dia and 3.5 mm between threads (pitch?) so the insert should be correct. As far as I can measure the thread is 3.5 wide in the insert but this is only an approximate measurement.

Carba-tec have been helpful by sending up another M30 insert and a 1 1/8 X 8 insert but none fit.

Has anybody else experienced this? Is there another thread that is an M30 X something? The face plate supplied with the lathe fits easily but it has no markings so it could have any thread.

Any suggestions?

Thanks in advance,
Anthony

[Zsteve]

Anthony,

You may need to make a few accurate measurements - like with a vernier for diameter etc. Could also use a thread pitch gauge which will also give you the thread angle as there is a difference, ( cannot remember of hand and do not have my trusty machinist handbook with me).

The Vicmarc web site also lists a M33x 3.5 thread and did not see a M30?.

The 1.250" by 8tpi ( =3.175 thread pitch) may be a close match although to make sense of what you actually have the threads need accurate measurement with a pitch gauge and diatmeter measured.

Usually when threads a mass produced they are given a fair amount of clearance to accomodate varying brands that could be used - so an M30 by one manufacturer will fit another, as overall thread pitch and major and minor diameters will all be roughly the same. based on that it is likely that one of the threads that you have is not what you have been told it is.

Make a few more measurements.

Regards
Stephen.

[gatiep]

I have a Carbatec MC 900 with the M30 x 3.5 thread. I bought a Bonham chuck with insert and it fitted like a glove. The other day I bought a Nova chuck with the M30 x 3.5 insert. Same problem as you are having. However if I unscrew the insert from the chuck, it fits OK on the spindle. Screw it back into the chuck, which is a tight fit and 'Bingo" no go. It seems to be a problem with the inserts, perhaps the outside is tapered. I applied some 'Coppa slip' to the threads and screwed it in as far as it would go, then unscrew, repeating numerous times. Mine now turns all the way in, fairly tight but nothing to complain about.
Well that is my experience for what it is worth