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Evan
10-10-2003, 02:45 AM
I really need a power crossfeed drive for my SB9 Model C. So, I have a perfect motor, all the needed gears and belts, will use a DC chopper with pulse width modulation to control speed. The end of the crossfeed lead screw is left hand acme and I intend to make a blind fitting to screw on the end of the lead screw with acme thread. No problem although a bit of a challenge. The direction of rotation will tend to tighten the fitting so no problem.

I want to make it so I can disconnect/engage the drive just as easily as disengaging the half-nuts on the carriage lead screw. I plan to make a lever that will back off a pulley (to disengage) a bushing to the rear that is driven by a gilmer belt that engages the fitting on the end of the crossfeed screw.

I need to make some sort of matching pair of parts that engage each other to couple the motor drive to the lead screw. A roll pin that drops into a slot in the matching part would work but would require up to half a turn to engage. This would take a while if I was using a very fine feed rate. I thought of using something like a pair of crown bevel gears with no angle but don't have any and don't have the equipment to make same. They also would tend to disengage under load.

I don't have a mill. Any Ideas?

Forrest Addy
10-10-2003, 05:28 AM
Hex nut and a socket?

You can mill on a lathe to the limits of your enginuity by grabbing an andmill in a collet.

G.A. Ewen
10-10-2003, 08:37 AM
Evan,
On my old Standard-Modern there was a friction drive for the crossfeed. One taper that fit into another. Having something that will slip instead of break may be a good idea. That being said if you think that you can use this old piece of bench clutter you are welcome to it.

http://www.photobucket.com/albums/0603/GAEWEN/5a7f5459.jpg

http://www.photobucket.com/albums/0603/GAEWEN/5bb0197b.jpg

JCHannum
10-10-2003, 08:56 AM
Get, or build, a proper milling machine. You are going to need it anyway and this is the perfect excuse to do it.

nheng
10-10-2003, 09:27 AM
A Colchester I just passed up had a castellated drive coupler on the leadscrew to engage it only for threadcutting. Mill one face of each of two shaft collars to create a castle-like fingers ... as many as you want but 2 are probably adequate. Make the fingers a lot smaller than the mating slots for easy engagement.

Missed the milling issue ... you could mill these on the lathe and if you include a slight negative engagement angle, they will stay together under torque without extra hardware.

Den

[This message has been edited by nheng (edited 10-10-2003).]

Evan
10-10-2003, 11:42 AM
JC,

I know, I know...

Nheng,

I do have a keyway mill and full set of collets. Hmmm.. I need to rummage through my junk. I might already have a castellated coupler.

Forest,

I thought of hex, might just work well with a 12 point socket.


As far as clutching goes, I'll use a gilmer belt with spring loaded tensioner to drive it. If the load is too high the gilmer belt will jump.

gamachinist
10-10-2003, 12:41 PM
Hi G A,
If Evan doesn't want that useless piece of clutter I'd like to have it for a spare!
That's the directional gearbox for my old Atlas lathe.
Thanks,Robert.

Evan
10-10-2003, 12:54 PM
George,

I don't think I can use that item, thanks for offering.

Weston Bye
10-10-2003, 01:16 PM
Could adapt an automotive air conditioner compressor clutch to fit on your gear reducer, when engaged turns the pulley, driving the belt.
Instant on, instant off, any position. Could even vary the DC to the clutch to limit torque.

Wes

Evan
10-10-2003, 01:22 PM
Wes,

That sounds perfect except too large for the space. BUT, thanks for the idea! I do have some smaller electromagnetic 24V clutches.

Just doing inventory in my head. I have the perfect electromagnetic clutch for the job, a brand new developer housing clutch from a copier. About 1.5" diameter and strong enough to twist off a 1/4 bolt if need be. Adjusting the volts should work nice for torque limiting. Oughtta work. I think that solves the problem. Thanks again.

[This message has been edited by Evan (edited 10-10-2003).]

Sprocket
10-10-2003, 11:27 PM
How about a Lovejoy coupling without the spider? http://www.use-enco.com/CGI/INLMK3?PMK0NO=93045

darryl
10-11-2003, 01:35 AM
Evan, it might be a good idea to power that clutch for a while to see if it gets too hot. I'm sure that has occured to you, though.

Thrud
10-11-2003, 01:40 AM
Evan

If you use a stepper and remove the power you should be able to turn it with little effort provided the motor leads are not shorted.

If you can't find a elctromagnetic clutch I also have some small ones out of laser printers - I still have not found a good use for them yet....

Evan
10-11-2003, 01:56 AM
Sprocket,

That coupling would work, but I don't need it. Thanks anyway, that is sort of what I originally had in mind.

Darryl,

The clutch is designed for continous duty.

Thrud,

I dug out the clutch after only about 15 minutes of looking. I found appropriate gears to drive it with the motor. I found my specially ground tiny acme boring bar for making the adapter to the lead screw. I had a visit with one of my customers today who is heavy into live steam. He suggested using a barbeque rotisserie motor. That sounds like it might work although I already have a suitable motor. I'll have to see if it will speed control with a dimmer.

The bastich offered me full plans for a 7.5" gauge shay locomotive. Nnooooo....

Thrud
10-13-2003, 04:24 AM
Evan:
Princess auto has power window motors for under $20 - they have tonnes of Jam - worm wheel type, subcompact - spiffy!

If you want that GPIB card (I think I called it an HPIB) let me know - its yours if you want it.

Evan
10-13-2003, 06:40 AM
Thanks David,

Perhaps we can swap. I have two HP pen plotters, eight color with lots of spare pens. The electrostatic hold down is dead on both but otherwise they work fine. I made an IEEE488 adapter to run them from the parallel port and modified the machine language code to accomodate these super high speed CPUs but have some glitches. Some timing problems. Anyway, If you have an IEEE488 HPIB card I am interested. E-mail me.

Bruce Griffing
10-13-2003, 03:29 PM
Another thought on the crossfeed drive. I have a homemade x axis feed on my minimill that uses a small gear head motor connected via a toothed belt. Without power feed, it is a little hard to crank the x-axis as you are moving the table and the motor through the gear head, but it is not bad. This turns out not to be a problem since the feed is so convenient to use I use it all the time. The interesting thing I discovered about this arrangment is that I can set the speed control for the motor so it doesn't move on its own, but provides a power assist for hand cranking (in one direction). Sorta like power steering. I actually use that mode. Between full power mode and power assist, I don't use the unpowered hand crank for anything but fine adjustments. A similar setup might be nice on your lathe.

[This message has been edited by Bruce Griffing (edited 10-13-2003).]

Oso
10-13-2003, 05:15 PM
How about this:
A slot in the end of the screw (I know, no mill, but there are other ways...)with a drilled out center area. For the hole, extend the existing center hole, which you probably will never need again, as the screw won't need to be re-cut.

Then the drive for crossfeed is a shaft to fit the hole, with a pin through it to fit the slot.

Retract the shaft to disengage the feed.

The pin could be made of brass or copper etc so it will release (break) on an over-torque situation.

Depending on relative fits, it could act as a U-joint to allow some misalignment. A ball-shaped end to the shaft would help that.

nheng
10-13-2003, 05:21 PM
Oso: I kinda like that idea and may try it on my smaller machine. I've got a tiny Swiss minimotor with gearhead (485:1) waiting to go !
Den