X-axis power drive

Hi all. I first became a "Beginner" in late 2018 with the arrival of my Warco WM290V lathe. On Saturday I became a beginner again when My WM18B mill arrived, (thank you Egyptian river pilot) and my hand-picked volunteers managed to carry it into my workshop.

I've seen several mentions on here of the capacity of a cast iron lathe bed to bend and/or twist. With that in mind I wonder if someone could tell me what is the risk of my much less substantial mill table doing the same with a dirty great lump of motor and gears hanging off one unsupported end?

Or do I worry too much?

I looked at your mill specs and as long as there is clearance for the drive hanging below the bed at the right hand side the weight is not going to be a problem. Move the bed to its extreme left end and look before committing yourself. The weight of the common type on ebay is 6Kg.

Edited By old mart on 24/05/2021 14:28:25

Old Mart, thank you Sir. I had a feeling they'd be quite a bit heavier than that. As the table is only about 40-odd mm deep it looked a wee bit susceptible to me, at least at reasonable extension.

Terry

According to legend the big three phase motor and gearbox power feeds used on older Bridgeports, up to early / mid 60s, were sufficiently heavy to bend the table over many years. Was told that it was not good practice to leave the feed end hanging way out to one side. Ive seen no evidence for this but that motor and feed box unit is very, very heavy. Two man lift off the floor heavy!

No issues with the little one on your mill.

That said its still good practice to park things pretty central when finishing work for the night. Its not a bad idea to regularly give the slideways and screws a decent oiling then wind the table from one end to the other a time or four on a fairly regular basis. Keeps adequately fresh oil on things so they move smoothly, helping to protect them and scrapes off all the dust and stuff. Over many years old, exposed oil starts turning into a varnish like substance on the little travelled parts which doesn't help free movement. Once a month, every other month or thereabouts should do.

Nail the regular "deeper clean and lube" habit early like wot I didn't!

Clive

Haha, thank you Clive! I'm pretty much "into" the regular oil wiping now after finding one day that the chuck on the lathe had started lightly rusting overnight. Fettled when I realised I needed to keep my workshop conversion warm. My Arc type 2 vise arrives today and I'll mount that centrally. When the time comes to add the power feed I'll leave the table centred between the two while idle. Thanks again

You can make a very adequate power feed using a stepper motor that will work out cheaper and considerably lighter than one of those commercial ones.

Or a 24vdc wiper type motor unit that I'm building one from.

Martin P

I’ve just made a 12V version loosely based on THIS video.

I intend over-driving it for a faster return ‘cos I’ve used a 19V power supply to the speed controller. Fiddly to line up but works fine. All items on stock/to hand except £13 for the generously rated speed controller.

I watched the very same video and thats why I decided on the 24vdc unit that he had used.

Martin P

+1 for stepper motor, you don't need to declutch it for hand winding, so all it needs is a tooth belt pulley instead of one of the handwheels and a bracket to mount it on

Not sure you won't need to declutch for hand winding. If the stepper circuit is powered, the holding torque of the stepper will block any input from the handwheel. You can turn off the circuit, and then it will be easy to turn the handwheel, but as the stepper is still connected you will generate back voltage into the stepper circuitry.

I don't know if the stepper controller can handle this, so with my powerfeed I added a clutch. This is how I went about it. **LINK**

The advantage of the wiper motor is definitely cost. I was wondering if a window winder motor would work for a small mill.

My alternative plan was to coerce into use an old 7.2 volt ‘Skil’ screwdriver motor with an already fitted variable speed. It weighs less than half a kilogram but needed considerable speed reduction - so a couple of pulleys with a toothed belt drive. With aluminium bracketry it would likely weigh in at much less than 3kg.

The motor on my Centec 2B is only 1/8th HP, so not that much power should be needed for a mini mill?

I have seen the LEDs on the controller light up with the generated emf when driving a stepper, so I prefer to declutch for hand feeding just to be on the safe side. Plus, there is a reduction drive between stepper and screw so you are back-driving against the cogging torque of the motor. I just have a removable drive pin between the bored-out timing pulley and a hub that's keyed to the leadscrew.

Could you not put a simple switch into the stepper wiring so there is no circuit for the generated EMF to flow through? That way you can just flick the switch when you want to use the handwheel rather than having a mechanical clutch

I guess you could, and would be much simpler solution than a clutch.

NDIY, steppers are cheap, easy to install and control no gearboxes required, infact I mounted mine directly to the handwheel shaft.

Picking the wiper style motor for me is not because of cost, I wanted a simple system that if it goes wrong I can easily check and repair it, You are all discussing EMF and ways around it, I dont want that hassle.

Martin P

Through? If you short the stepper the cogging torque increases. If you open the circuit to the driver when it's energised you will probably blow it up.

John I was assuming if you want to go manual you switch the drive off therefore not energised and then flick a switch to stop EMF rather than a clutch. So as the switch "disconnects" the stepper you won't be shorting anything and as controller is off you won't be energising it.

The Sherline CNC machines suggest unplugging the steppers when using the retained handwheels, would my suggested switch not do the same thing but much quicker?

I'm sure someone with more knowledge than me could do it all with only one multipole switch to do both at the same time.

Edited By JasonB on 26/05/2021 08:46:28

Some stepper drivers don't like being energised and not connected, though others are perfectly happy. Most suppliers specifically warn against connecting/disconnecting the motors when energised, especially disconnecting because of the inductive voltage spike. Sooner or later one will leave the drive circuit energised and throw the switch by mistake. But I really don't see the issue here - why make turning the handwheel harder by turning the stepper as well, especially through gearing? It's no great feat of engineering to add a removable drive pin. If you use a DC motor there will probably have to be gearing anyway, and a clutch of some sort needed.

John, a disconnected direct driven stepper motor will offer next to no resistance and will be unnoticable when turning the handwheel. If geared then as you say it will be harder.

Mine is clutched, but if there was a way of disconnecting electrically I think it would be much easier and makes for a smaller, lighter installation...I think that's what Jason was trying to point out.