mini lathe circuit board

Sounds like the original controller was triac or scr based, with little or no velocity feedback, hence the speed variation. If the motor is a

90 volt item, that system was probably designed for a US 115 volt line and they just backed off the phase control limit to prevent motor burnout on 240 volts. Problem with that is high peak currents in the motor and controller, which may account for the reliability problems.

Now, sounds like you have a pwm mosfet based controller, but in that case, you are chopping rectified 240v volts AC to the motor, which may cause overheating, or armature breakdown. Have bought several of those cheap pwm controllers and they work pretty well, but you need to match the pwm voltage to the motor. In this case, could be 300 volts + peak to peak across the motor. Suggest you try running that controller from a 110 volt tool transformer to see if it works, then use that instead of 240 volt mains...

Regards,

Chris

Scr. Does have some velocity feedback, but .. The boards do come in

115v and 240v versions, but afaik the differences are minor, eg the pcb itself is the same, with just a few components switched.

Indeed.

Time was they advertised Chinese mini lathes and small mills as having "American" circuit boards, because the Chinese boards were supposedly bad.

Nowadays ...

It seems to be working fine as-is, despite any high peak currents. Next time I take it apart I'll put a 'scope on it and see.

But if it ain't broke ..

I just turned down a hardened ballscrew end. Gave it a good workout, there was an overheating smell which had me concerned for a moment, but the motor was cool, the smell was blue/black chips!

isn't overheating at all (and the controller doesn't even get warm!!!), so I don't think the motor is in mortal danger (and I'm just looking for an excuse to fit a 3-phase motor and inverter I happen to have picked up to the lathe anyway).

Or to _a_ lathe, I may change my small lathe from a mini lathe to a Myford ML4 or Something7 or ML10 .. is there anything better?

Or - has anyone got a small machine tool with a brushless motor, like the AET Seigs? Opinions? Useable, brilliant, still wanting backgear?

-- Peter Fairbrother

Hardinge HLV or HLV-H are much nicer, even my 1952 HLV after 4 years of rebuilding work... Of course, they're half a tonne with the cabinet and the rebuilding is a big investment in time.

Look at Boxford AUDs, they're not quite as versatile as the Something7s, but better lathes for turning with. Prices don't have the Myford premium either.

Regards Mark Rand

awhile back, needed some TLC but .. but ... but .... but I don't have room :( [1]

And they do a proper metric version too :)

I don't really consider them small lathes though, more small-to-medium size. The 7x1x size of the minilathe is enough for almost everything I want to do - just the lathes themselves are too light and flimsy to work hard and accurately.

So yes, I've been looking for a (metric) AUD - don't suppose anyone knows of of one for sale? Got a bit of spare cash at the moment. They seem hard to find right now, there were lots (fsvo lots) a while ago when I was broke, but not now.

Hmmm, I'd have to chuck out the sofa to fit it in. Ah well, all in a good cause ..

Regards Peter Fairbrother

[1] even if I chuck out the sofa. And the only bookcase with books.

ps just bought another BCA

Just recently finished an old mid 50's Boxford A bought many years ago. Originally planned to ditch the countershaft and use a direct drive belt from motor to headstock, but the layout makes that difficult.

Eventually settled on a 1 hp 3 phase motor, with different motor pulley to give a slightly higher speed range of, backgear included,

60-2475 rpm at the headstock. I wanted a higher speed for collet work, but have no plans to run chucks at that speed. The inverter is an old Altivar 16, with 3 phase input, driven from a 500volt dc power supply. Programmed for a frequency range of 25-75Hz and the 1 hp motor to take account of the reduced power at low speeds. A bit unconventional, but already use the same technique to drive other 3 phase kit in the workshop. 3 phase 440v input inverters are much cheaper s/h and can even be found in scrapyards from time to time.

The only problem with the Boxford is the small spindle capacity, but other than that, a strong and robust little machine ideal for the sort of work done here. Did consider Myford, but overpriced and not as rigid as a Boxford...

Regards,

Chris

Whatever works, but long term, I would replace the motor. I bought a

220v 3hp treadmill motor this year on the usual site. Quite inexpensive and a commutator with no wear at all. It was a possible for the Boxford, but would have had to design and build a controller for it and actually prefer 3 phase motors. Often find complete treadmills in local press, car boots or gumtree etc and that would include the motor, pulleys, belts and a controller. A useful resource...

Regards,

Chris