Best gearbox style for torque?

[Davek0974]

Looking for ideas for a power drawbar project for my Bridgeport conversion - i use BT30 tooling with a threaded drawbar so need a motorised option.

Really dislike the pneumatic wheel-nut wrenches, looking for a more civilised option

Options....(so far)

AC motor with VFD & worm reduction box.

Stepper motor with worm reduction

Stepper motor with planetary gearbox

AS far as i can tell, i need a tightening torque of around 30ft/lb or 40Nm? Likely more to loosen it.

The VFD idea could use current limiting to limit final torque maybe, as can the stepper i think.

Any other /better ideas?
Thanks

[MattiJ]

DC motor with current limiting power supply and planetary gearbox.

[J Tiers]

Torque is just directly related to gear reduction ratio, less losses.

So if you want 40Nm, you can do it with a 1 Nm motor (any sort) and 40:1 reduction gearbox, if you get a usable speed with that reduction.

So, what RPM do you need on the output?

Can you get a motor of a speed and torque (power) that works with the reduction ratio you can get, to provide that torque?

The motor type is almost irrelevant, unless you need a feature that one type provides.

[Davek0974]

Yes, i guess speed matters, should have explained more.

The drawbar uses maybe 10 threads to lock/release so we need to turn at least 10 revs in a sensible time period - no use at all going 1rpm.

Say we want to lock or release in maybe 2s so i need a 300rpm motor/gearhead combo capable of 40Nm? I think i worked that out right

Is that possible without blowing a mortgage on the unit

[old mart]

What about an adjustable slipping clutch in the tightening direction and no clutch slip in the undoing direction. Then a higher powered motor could be used.

[ikdor]

Get an electric wheel nut wrench. It's going to be hard to beat on size and price.

[Davek0974]

Get an electric wheel nut wrench. It's going to be hard to beat on size and price.

Still impact drive though - if going that way an air drive would be cheaper as no PSU to make.

[Davek0974]

What about an adjustable slipping clutch in the tightening direction and no clutch slip in the undoing direction. Then a higher powered motor could be used.

Interesting.

Still need to sort out a motor though

[ikdor]

There are mechanisms that automatically switch gearing when the torque climbs above a certain level but I'm not sure if they're bidirectional.

[Cuttings]

I have been using a manual drawbar in an R8 spindle machine. Most of the time after releasing the torque on the drawbar I need to give it a tap on the top to release the holder I have in the machine.
How is this accomplished with a power drawbar?

[ikdor]

I don't think iso30 sticks as bad as r8

[Toolguy]

I have been using a manual drawbar in an R8 spindle machine. Most of the time after releasing the torque on the drawbar I need to give it a tap on the top to release the holder I have in the machine.
How is this accomplished with a power drawbar?

On my mills, the drawbar is made captive by going up against the bottom of the drive unit. If you take the air impact part off, the drawbar is free to pull out. There is a steel washer just below the driving splines on the drawbar to keep it from going up.

[Baz]

By the way you only want 4Nm not 40.

[Davek0974]

I don't think iso30 sticks as bad as r8

Yep, usually as soon as the drawbar is loosened, the tool holder pops out.

[Davek0974]

By the way you only want 4Nm not 40.

For 30+ft/lb of torque?