Thread: Fat MT3

Originally Posted by ftkalcevic

I just got a new boring head with an MT3 arbor and I was excited about giving it a go today.

I slipped it into the spindle of my milldrill and noticed the drawbar didn't reach the threaded part of the arbor.

I measured it, wide end 24.6 mm, narrow end 20.9, and 73mm between measurements - this approximately gives the correct taper of 2.9 degrees.

Because of the extra thickness, my draw bar is at least 10mm short, and boring head seems to stick out an extra 20-30mm or so.

Is this ok, to just make a longer drawbar or will the extra overhand cause problems?

Thanks,
Frank

Hi Frank,
I would just make a longer drawbar. Or if the threads are different a short adaptor to screw into the boring head and locktite it in.

A longer draw bar will get you by of course but the extra stick out will reduce the rigidity of your set up. From what you say, the fat end is about .8mm fatter than it should be, which is well out of spec. http://en.wikipedia.org/wiki/Machine_taper

If you can I would take it back. Having things hang out more than required only works against you. Rigidity, reduced headroom, possibly greater runout and now extra work to make a non standard MT fit. etc.

If its a PITA to take back then live with it and make a new drawbar or mods to work around it.

Simon

If you can't take it back, ask if one of the members on here, could mount it on a grinder and take off the required amount to bring it down to suit. I am sure that there are members here that are more than capable of doing it.
Kryn

Thanks for the replies. I'll contact the seller on Monday and see what they say.

Apart from the overhang and more flex, I was also concerned about less taper surface area contact that could cause boring head to slip - is that an issue?

Depends on the size of your mill and what its capable of. My 45 size mill would not be capable of creating enough cutting forces to make a MT slip even with reduced surfacd area. If you had a monster mill and performing big stock removal then maybe. Probably not with a boring head though.

Simon

Originally Posted by ftkalcevic

Thanks for the replies. I'll contact the seller on Monday and see what they say.

..................

I take it from this that you are dealing with an Australian supplier, if so they don't have a leg to stand on, don't let them snow you. Its entirely your decision whether you go for a refund or an arbor that is within spec.

Originally Posted by bob ward

I take it from this that you are dealing with an Australian supplier, if so they don't have a leg to stand on, don't let them snow you. Its entirely your decision whether you go for a refund or an arbor that is within spec.

It was from a UK supplier. They checked their remaining stock and they were all the same. I'll try it with a longer drawbar and see how it goes.

For the record, it is a Vertex Boring and Facing head with MT3 arbour. (VBHU202). It looks identical to the one at machinery house, (http://www.machineryhouse.com.au/M185#)