Thread: Mars Lathe DC motor conversion.

If you want particular speeds are you better off having a bypass switch on the panel (connected to a trimpot)? Trying to accurately mark positions so that you can print a label could be tricky.
Another option is that you have some preselection switches but rather than having a pot for absolute speed control you have it as a modifier - that is, you preselect a speed and the main pot will allow you to adjust that to say 50% to 150% of the base speed.

Michael
(You can tell I don't do electronics as I'm merrily making these sorts of suggestions)

Hi Ueee,

FA, FB & FC? I'll have to look at that! WRT specific speed settings with the POT. The only thing I can suggest is to use one of these type of switches, a 12 position rotary switch: 1 Pole Sealed PCB Rotary - Jaycar Electronics

And then, each of the 12 positions is connected to an individual 10K trimpot. These trim pots could be neatly soldered on a board and then individually adjusted to the required speed setting. If you did them in order, each turn of the rotary switch would increment your speed up to the next selected trimpot speed.

Hope I explained it properly. It looks a little fiddly but if you made up a dedicated board, it would work out quite good and very useable. I had thought about doing the same thing at one stage.

Glad I'm not the only one with a birds nest in the control box! I'm going to try neaten it up a bit with some cable ties!

Cheers,

Simon

Hi Ewan,
I'm confused, you say it struggles at 10hz and yet its way to fast to be useful? If I've guessed correctly at what you are getting at. I think you'll want a different jog speed for each gear. Why not use the speed pot to set the speed you want then move the jog switches from jog fwd, jog rev to run fwd, run rev? If moving the pot is an issue you should be able to use a 4 pole*** switch allowing you to have a run pot and a jog pot.

Strange you cant "turn the brake down". Just remember if you crash you will be waiting 2 seconds before the VSD turns off*.

As far as setting the speed goes, I have a 10 turn pot that has a clock in the front. Though not as pretty as you're thinking, with one of those you could have a table of what clock number equals what rpm in what gear. You can** use settings on the VSD so you use less than the full 10 turns. In fact you can even set it up to let you use the speed pot to go from fwd to rev, 5 turns each way(though I can't think of a good reason for this on a lathe)


Hi Simon,
I think you'd need to use a double pole switch at least.


Oh the up side I now have extended my network with a wireless router in the shed, even if I do hate typing on my tablet.

Stuart

*yes I know I've said it before

**I'm pretty sure

***You may even need a 5 pole depending on how you switch the VSD. Turns out I use a way the isn't in the manual lol. Seems to work...........

I've played with that for/rev bias setting. Its pretty freqy! Not much use to us i don't think. 2.2Kw motors have torque and power to burn at any setting. Simon

Originally Posted by Stustoys

Hi Ewan,
I'm confused, you say it struggles at 10hz and yet its way to fast to be useful? If I've guessed correctly at what you are getting at. I think you'll want a different jog speed for each gear. Why not use the speed pot to set the speed you want then move the jog switches from jog fwd, jog rev to run fwd, run rev? If moving the pot is an issue you should be able to use a 4 pole*** switch allowing you to have a run pot and a jog pot.

Now it is i that is confused, not ever having a machine with jog buttons, i thought that jog was supposed to be slow?
I have played a bit more and did some "real" machining making the thumb screw for my cross slide stop today. Oh variable speed, how i missed you ......
I did use the jog (at 10hz) to thread the screw with an M5 die, worked a treat at the 5-1 ratio, i'm happier than i was before with it.

As for marking the speeds on the pot, it just so i can go, hey i need 650rpm, thats about there, and then tweak the speed if needs be.

Originally Posted by Ueee

Now it is i that is confused, not ever having a machine with jog buttons, i thought that jog was supposed to be slow?

Hi Ewan,
Rereading it this morning I see what you mean now.

Still the "jog" on my lathe is just a non latching fwd button, so yours has to be better than that surely!

Stuart

Hi Stuart & Ueee,

Yes, the jog button on my lathe is what I call a non committal forward (momentary) switch! I use it to check for clearances after setting up. It helps me prevent a crash when turning large or odd shaped pieces. I'm not sure if that's what it's meant for. Its the same speed as the selected gear speed.

When it came to setting up a jog button on the mill I thought it would be advantageous to have a very slow jog, to suite my use.

Cheers,

Simon

The only time I use the jog button is to bump the motor when the gears don't line up in the gearbox or feed/thread selections.
Functions just the same as manually turning the chuck when trying to change gears.
Andy

Got another free treadmill lined up

So hope it's DC, and see how version two with better cooling goes this time.

Going to use a 12 volt boat bilge blower on it to keep temperatures in check this time.

So many ideas and so little time

Rob

Got the freebie treadmill motor this morning and it looks really good. 1.5 HP 180 volt, but a really big unit for the HP.

It's on a commercial grade treadmill, and the motor has those magic words "continuous duty" on it. You little ripper

So things are really moving down my way, but this will have to wait till later.

GumTree came good again - magic site.

And I've been assured it goes.

The peg wasn't free, only there for scale cause I couldn't find a box of matches.

This is the second one I've got where people have unloaded them because the things suddenly speed up to a near death situation and they're afraid to use them. Seems to be a common problem.

Hey honey, look at this, whoooosh - I'm flying - er can you call an ambulance please.

Rob

Nice one Rob

When i think of treadmill mishaps i always think of this one

MythBusters- Adam Savage Drunk On A Treadmill - YouTube

I haven't checked out the fan on the motor yet, but I intend to get a centrifugal bilge blower to put on it this time - $30 (see catalogue below).

https://www.whitworths.com.au/pdf/ca...2012Summer.pdf

Apparently these are much quieter than the in line type. 90 CFM should be adequate.

Will run it off of a converted PC power supply 12 v rail (these could also be used as a free power supply for the washing soda de-rusting thread).

Good article on it here:

Convert an ATX Power Supply Into a Regular DC Power Supply!

Really easy and I've got about 4 or 5 old 300 W ones in the shed - I just knew would come in handy for something one day .

Cheers

Rob

I have been keeping my eye on baldors etc on ebay, most of them seem to be TEFC, unlike the ones we have both used. I wonder how the commutator is kept cool enough with the TEFC design? I still think the air flow restriction of the motor internals is still the biggest problem.
Do you run an air compressor full time? Another thought i had was blowing a low pressure (say 10-20psi) stream of air through the motor, that should solve the restriction problems.

I think the difference is that a TEFC motor is designed to cope with the heat generated (especially if rated for continuous use) - but the thing here is that the fan must be spinning at the design speed. The average home treadmill motor is only envisaged for say 10 to 20 minutes use per day for a month or so before the owner gives up because it is boring/ too much work/ not losing the weight they thought they would etc.
If I had to use a treadmill motor I think I'd probably make up a large bolt on heatsink that would be in very good contact (thermal paste and so on) with the stator and then use a fan to blow as much air as I could across it. A finned Al flywheel on the rotor would probably not hurt either.

Michael