Paging Tony Jeffree (or anyone with an opinion!)

I've been using my CNC Taig mill for a while now and I'm generally a happy camper. There is one thing I'd like to improve though. Occasionally I manage to stall the cutter (I really need to uprate the motor, and will go with Tony's suggestion of the Sherline motor).

What I'd *really* like though is a way to kill the power to the mill if the cutter stalls (i.e. the motor stops turning). I'd like to turn off the motor and the steppers. That way I could leave it chewing at a lump of stock and wander off with a slightly clearer mind to do other stuff.

I've got zero ability with circuit design (or, come to that, building). How feasible would it be to do something along these lines?

Reply to
Nigel Eaton
Loading thread data ...

That's a must as far as I am concerned. A good alternative might be to source a 1/8th horse 3-phase motor and a VFD - probably comparable in price to the Sherline motor option by the time you've had one shipped in from across the pond.

It is certainly feasible, but would obviously depend on some means of detecting spindle stall. Starting point for that could be pretty simple - for example, you could use a simple detector attached to the spindle (magnet on the pulley, reed switch held near to its path) to generate a "keep alive" signal that would hold a relay in the energised state while the switch keeps getting regularly "pulsed"; when the relay drops out, it kills the power to the stepper drive and spindle. Of course you would have to override the relay if you wanted to run the steppers without the spindle, and when you wanted to start the spindle. Could be pretty simple stuff though - a few switches, a relay, a small magnet & reed switch, a 555 timer & a couple of discretes & you're done! All you need now is a circuit design... ;-)

Regards, Tony

Reply to
Tony Jeffree

I'd go for the 3-phase motor & VFD if you could. I have burnt out several Sherline motors on CNC machines. They don't seem to like running for extended periods of time, and if placed under heavy load will thermal out easily (giving you similar problems to your current stalling motor). But perhaps I was trying to push them too hard, this may not be an issue on a smaller mill like the Taig (depends what you cut though ). Millhill supplies are the UK distributor for Sherline, and usually have motors in stock -as well as a good range of spares -collets, fly cutters, etc. I think Tony is the chap there, very helpful. I used to get them to "fine tune" the electronics for 240v use and found that this improved things a bit, despite the fact that they are supposed to run on 240v as standard. Keeping down from full speed also has a big effect on temperature -but as you usually have small cutters in them you want max speed all the time.

Regards

Kevin

PS drop me an e-mail if your interested in a s/hand sherline motor (it needs new brushes -they are a service item, their web site tells you how to fit them)

Reply to
Kevin Steele

Hi Nigel,

You could perhaps use a centrifugal switch, as used to switch out the start cap on a capacitor start motor, using it in the opposite direction and weakening spring tension to suit your speed, or a device that I think is used in some motor car window winder, that detects the high current from a stall situation and switches the motor off. Best regards

Tom.

Nunce excretia in exractum est.

Reply to
Tom Jacobs

In article , Tony Jeffree writes

It's definitely on the list.

(Snip 'how-to' kill power if the cutter motor stalls)

One tiny flaw in the whole plan, and you have to go and find it. Make it for me, market it as "StallMaster". I hereby waive my patent... :^)

Reply to
Nigel Eaton

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.