4 jaw chuck - max rpm too slow?

[pmurdock]

I've been in the market for a 4 jaw independent chuck for my CNC lathe (haas sl-30).

However I have searched for Kitagawa, Rohm, Bison and they all seem to be extremely slow on the max rpm. Is this just the nature of a 4 jaw chuck that I simply cannot spin it as fast as the machine can go (3400 rpm)?


It would appear that if I mounted this on the machine the drawtube of the CNC would be in the way as well. Does anyone know if the drawtube can be unscrewed so I can use the manual chuck?


cheers,
Paul

[Billiam]

The imbalance at 3400 rpm could destroy your spindle bearings.

What's the application?

[HuFlungDung]

I've always thought it had something to do with the casting quality of the four jaw chuck body. Some of them are pretty rough. To a certain extent, the manufacturer may limit the top rpm because they cannot be bothered balancing them, but that you could do yourself. Nonetheless, I would be concerned about the chuck bursting if taken too far over the recommended limit.

The chuck diameter is also a factor in the top rpm, due to the increase in centrifugal forces acting on the chuck rim, which is where there is a large bulk of the material in most 4 jaws.

It goes without saying that you would need to be chucking symmetric workpieces if attempting to run fast.

Do you have to run it at 3400rpm for a good reason?

[pmurdock]

thanks for the input guys - as always!

application is to be able to chuck up cylindrical (symmetric) parts without going to a 5C collet system (where I need emergency collets for every job), or a soft jaws 3 jaw chuck (where I need a soft jaw for every job). Can we see where this is going? <grin>

In my reading it appears that a 4 jaw is very good for precision work and I don't have to have a new collet or soft jaw for every piece.

There no real reason to run at 3400 rpm - I was just wondering why they don't rate them. I suppose if I'm doing 1 off jobs and taking the time to chuck it up on the 4 jaw then I can make pretty much any cut I need at 1500 rpm or less since time is not of the essence.

Is that the consensus with 4 jaw chucks?

cheers!
Paul

[Geof]

If you are chucking cylindrical parts that are small enough to go in a 5C collet why don't you use a three jaw chuck.

Come to think of it you could get a 6" three jaw and hold it in the standard chuck on that machine which is a 10" Kitagawa isn't it?

Even better get a 6" six jaw.

[pmurdock]

I would just go with the 3 jaw chuck but for the precision of 2nd operations wouldn't you lose the ability to dial the parts in (that the 4 jaw offers) by going with the 3 jaw.

cheers!
Paul

[Geof]

You can indeed dial the parts in with a four jaw independent if you want to take the time.

Why not rig up a system where you dial in a three jaw or six jaw chuck held in the machine's chuck.

Get a Set-Tru and machine a backing plate that is held in the main chuck then you only need to dial in once on a part held in the three jaw. Everything else the same diameter will grip true.

[pmurdock]

Interesting... I had never thought about stacking up chucks like that..

so the 2nd 3 jaw mounted (or 6 jaw) would be a smaller one. What would be the best way to create the mounting plate to mount on the large 10" kitagawa - grip it on the OD or ID. Should I just be buying a blank cast iron mounting plate that is normally used and make it work. interesting! thanks for the great ideas!

cheers,
Paul

[DareBee]

precision of 2nd operations

I suggest a 6-jaw "set true" chuck is ideal for this.

Chuck stacking works OK but it can also be more difficult to get the axis of the part running true, as well as some loss of rigidity.

[Geof]

Originally Posted by pmurdock ... What would be the best way to create the mounting plate to mount on the large 10" kitagawa - grip it on the OD or ID. Should I just be buying a blank cast iron mounting plate that is normally used and make it work.... cheers, Paul

Actually you want to run the machine at its maximum speed so you want the second chuck held firmly and if you grip on the OD the Kitagawa jaws are going to be spinning a big circle with high centrifugal forces opening them up.

If this setup will be frequently used do it correctly by bolting a mounting plate to specially modified soft jaws. Machine these jaws as low as possible even as far as to fully expose the bolts which can fit in holes in the mounting plate. Clamp this jaws on a short stub of bar and machine a step on the OD. Face the back of your mounting plate and machine a recess to engae the step on the jaws; now you have the ability for precise replacement. Machine the mounting face for the chuck in position and just remember to mark all the parts for re-assembly. There is no reason it will not go back together as precisely as a chuck can be replaced on a regular spindle nose. And you could even drive this assembly faster than the top speed for the Kitagawa chuck because there is no way the jaws can lift, this I do not suggest.

This approach is intensive but it should address Darebee's comments and axial trueness and rigidity.

[Geof]

I just re-read your first post. You were considering taking off the Kitagawa and then mounting a four jaw. Compared to that my approach is not intensive at all, it is probably the same amount of time for the first setup and then much quicker ever after because you do not need to remove the big chuck.

Incidentally to answer your question about the drawtube it cannot be unscrewed until the hydraulic assembly is removed.

[DareBee]

This approach is intensive but it should address Darebee's comments and axial trueness and rigidity

Most definitely