How tight is tight enough?

[doubletop]

I've just bought myself a Super X3 with it an MT3/ER32 collet set. Seig supply a nice hefty Allen key, with handle, but how tight do I need to tighten the drawbar? To release the chuck I needed the quill lock full on to stop it moving and whacking the cr8p out of the top of drawbar wasn't a good feeling after only 3 days. I dreaded to think where the load of the blows were going and flashbangs link on new spindle bearings crossed my mind with each hit.

Pete

 

[Lew_Merrick_PE]

I've just bought myself a Super X3 with it an MT3/ER32 collet set. Seig supply a nice hefty Allen key, with handle, but how tight do I need to tighten the drawbar? To release the chuck I needed the quill lock full on to stop it moving and whacking the cr8p out of the top of drawbar wasn't a good feeling after only 3 days. I dreaded to think where the load of the blows were going and flashbangs link on new spindle bearings crossed my mind with each hit.

Pete,

The ER32 collet needs only collapse in to firmly grip the tool. That's usually a fairly light torque (30-40 lb-in = (about) 30-40 kgf-cm) to lock everything up. Similarly, the MT3 is a self-holding taper and only needs moderate retention. Unless you are making violent chattery cuts (which tells you there is another problem), you should be able to hold the pulley on the end of the spindle shaft with your hand while tightening the drawbar. It is much more important that your spindle recess and toolholder taper be clean and free of chips or oil than that you "whack the crap out of it" in tightening it.

The danger to your spindle bearings from overtightening has more to do with the impulse load from "whacking the crap out of it" than it does the overtightening itself. The tightening force lies entirely within the spindle steel. Unless you have a really wimpy spindle, the wedge force from the overtight drawbar should not expand the spindle in the area where your bearings lay.

Sorry about the "kgf-cm" notation, but I have been working with Chinese vendors enough that I have not made a conversion from lb-in of torque to N-m in a long time. The entire point to using metric measures is to differentiate mass from force, but the unit "mesh" of the Newton is so "fine" that it is almost worthless in real world applications. I had always assumed that it was just my own inexperience with Newtons and Pascals that was the problem until I headed up development of automotive airbag restraint systems. It was kind of amazing to watch French, German, and Japanese engineers who had never used anything but Newtons and Pascals screw up their calculations by orders of magnitude and blow up inflator gas generator bodies.

 

[bearcar1]

" It is much more important that your spindle recess and toolholder taper be clean and free of chips or oil than that you "whack the crap out of it" in tightening it."


THAT is an understatement at best. There should be no immediate need to resort to such abusive tactics as that in order to get any taper to release from its intended receiver. After loosening the drawbar a few turns, all that should be required is a few sharp, firm whacks with a dead blow hammer using a block of wood or other similarly soft material as a cushion, to release the grip of the taper. Anything more than that and their is either foreign material inside the spindle, (ALWAYS double check that the surfaces of the tool holder taper and the socket in the spindle are free of dirt and debris before seating) or the seating surfaces are not true to one another. When tightening the drawbar up, use only enough torque so that the bolt feels firm and snug and do not get ham-fisted and give it an extra 1/2 turn, it is not required unless the above mentioned defects are present.


BC1
Jim

 

[kvom]

Assuming an R8 spindle, about 17 ft-lbs seems to be about right. On the mills I've used this gives about 1/4 turn beyond finger tight.

 

[don-tucker]

I agree with Bearcar1.undue force is just not needed,after all it's not as though you are going to use a 6" dia inserted tooth face mill,I find a sharp tap with a toffee hammer is enough to release the taper.A bit of grease on the thread and under the drawbar seating also helps.
Don

 

[Cedge]

Here's a possibly ignorant question. You mention the 3MT/ ER 32 collet set with a Sieg SX3 mill, which normally has an R8 spindle. Are you trying to use the 3MT in an R8 spindle?

On my SX3 even with a full armed Paul Brooks torquing, the R8 tooling requires only a mild tap to loosen from the spindle.

Steve

 

[doubletop]

Thanks for the feedback guys; The answer for me comes ftom kvom "a 1/4 turn from finger tight." I think I was trying to avoid the chuck slipping under load. I should know that MT3 is up to this, they've been around long enough, and as Don says its not like I'm trying to use a 6" inserted tooth face mill

To clarify I wasn't whacking the crap out of it tightening but in tapping the end of the drawbar in trying to release the MT3 taper. I was using a Thor hammer with leather head. Everything was spotless, not a chip in sight and the MT3/ER32 chuck was straight out of the box.

Cedge: Seig do their kit in MT3 or R8 and with imperial or metric scales. As a matter of interest the drawbar thread turns out to be 1/2" whitworth, I had to trim off 5mm as it was too long for the ER32 chuck and to clean the threads tried one of those old dies in the bottom draw that never normally see the light of day.

Thanks again for the feedback everybody

Pete

 

[Cedge]

MT3 is notorious for having to beat the crap out of them.....LOL. My X2 had MT3 tapers and you'd have to beat me with barbed wire to make me go back. After one evening of using R8, I was sold completely.

Steve

 

[doubletop]

After thoughts going through my head of a strip down and having to get the torch to it after three days I wasn't too enamored by MT3 myself.

Finger tight and "nip it up" it is.

Pete

 

[Noitoen]

I used to have difficulty to remove my MT3 taper from my mill with a soft nylon hammer. Had to knock the "hell" out of it, hurting me more than the machine :'(. Once, not having the "soft hammer" around me, I gave it a little smack with a regular hammer and it came off with ease . I guess the nylon was absorbing all the energy.

 

[Hobgobbln]

I am having the same problem with my X2. For some reason though it is only with the drill chuck. Collets just about fall out from the wind of the deadblow coming at it, but the drill chuck won't budge until I threaten it with acetylene ;D

Unfortunately, I destroyed the bearings. Pulled them yesterday, which was no fun what-so-ever.

I'm debating on whether to replace the spindle with an R8 since I have it torn apart or just order the new bearings and try a new drill chuck since the M3 and R8 have 1 different bearing. Any thoughts?

Griz

 

[Cedge]

With the machine already torn down, I'd be terribly tempted to go the R8 route. the transition only required me to replace the boring bar arbor and add a set of R8/ ER 40 collets from 800watt on Ebay.

Steve

 

[tel]

I have no trouble with the MT2 & MT3 collets on my machines- run the drawbar down by hand, then about 1/4 turn with the spanner locks 'em up just fine, to release, undo the drawbar about 3 turns and give the end a moderate slap with copper or steel hammer - they pop free every time.

 

[bentprop]

I have to say my mt3 collet chuck lives permanently in the spindle of my zay45.
But the very odd time I have removed it,i undid the bolt a few turns,then just a couple of taps with a hammer freed it.I should add that the taper in the mill is actually 4,so the chuck sits in a 4-3 mt sleeve.
Wouldn't a leather hammer just bounce?Like tel said,copper or lead hammer would be my choice.

 

[tel]

I love my copper 'ammer - the 'bacon rind' on t'other end wore out and disappeared years ago, but .....

 

[lordedmond]

I use MT3 as well another vote for a copper hammer I use the thor (the smallest one )one two copper heads the weight of the hammer helps just let if fall no problems