Lathe conversion

[Garamanda]

Hi.
I've just bought a union graduate lathe (3 phase). It's in my workshop at the minute and working great. I want to take it home to my garage but it would require an inverter. Anybody out there got any experience with inverters? ie:- what type is best,cost,varying speed and fitting?

 

[graduate_owner]

Here we go again - there have been loads of discussions on this subject on the forum, so if you do a search you will find just about all you need to know.
Summary of points - but just my opinion

Avoid far east imported inverters
Avoid damp and dust getting into the inverter - buy IP enclosed or make your own enclosure
Run the motor connections directly to the inverter output - no intermediate switching allowed
Don't be tempted to run the motor at very low speeds as the motor's cooling fan will also be running slowly and your motor could burn out (or add supplementary fan cooling if there is space - not likely in the graduate casting).

This information applies to INVerters, which will give yoj the advantage of variable speed.
An alternative is a CONverter which generates an approximation to a 3 phase output and can be usec with existing switchgear, but no variable speed - basically like you have now but with a slight power reduction because it is not true 3 phase.

The inverter is likely to be the most convenient option and, unusually considering the increased convenience, also the cheapest option. It will probably come with a manual giving details of dozens of parameters which can be set to alter things like maximum speed, time to reach maximum speed etc etc, most of which will be irelevant. Usually the default settings are good enough.

Do a search, read up on it, then go ahead and ask anything that baffles you, that will be the easiest option.

K

 

[Garamanda]

Hi K.
Thanks for your post. It was helpful. Not sure the existing motor is all that good. It's an old machine and done a bit of work. I didn't pay much for it. If I'm going to do this I might as well do it right. There are kits on eBay for £400 preprogrammed and ready to go. It's expensive but electronics is not my bag. I don't know if there's a better/cheaper way to do it? Cheers. Gary.

 

[graduate_owner]

Hi again,
I bought an invertek model from willpowerelectrical on ebay, and have not changed parameters. I have several 3 phase machines so the inverter has a 5 pin socket, and I just plug in the required machine and they work fine.
Basically you connect a 3 core cable to the inverter mains input, and connect the motor (3 wires plus earth) to the inverter output. You can also connect an on/off switch to the inverter's control connections to give remote switching ( plus a potentiometer if you want remote variable speed). This last wiring is low voltage. It is a question of following the wiring diagram in the instructions, but if you feel unsure then get assistance from a competent helper.

A 1HP invertek inverter, IP 66 rated (i.e. dust and moisture proof) can be bought from ebay now for £266, so not cheap but if you are willing to make an enclosure then you can get one for £125. I made mine out of an old desktop computer case, and used some filter material to cover the ventilation slots while allowing some ventilation. The inverter instructions specify a maximum temperature of 50 degrees so I wired a temperature cut out switch into the mains input. That was a lot cheaper than buying an IP66 enclosed unit.

I didn't need to change the motor so didn't need to spend more than about £190 for a 3 HP inverter which is much higher power than I ended up needing (I was going to buy a 3HP machine, but didn't in the end).

If you decide to change the motor then make sure it is dual voltage (220/415 volt). It will need to be connected in delta mode, which again is trivial and well described on the web. If your existing motor is dual voltage then I would be inclined to use it and see how things go, rather than buy another - but if it is not dual voltage the you will have to replace it, or take it to a motor repairers and get them to pick the appropriate connections from the motor windings. I paid £35 to have one of mine done.

So overall, if your motor is suitable, you could get it up and running for probably less that £150, (including cable, remote switch and potentiometer), plus any payment for assistance in wiring.

If you decide to go down this route, then feel free to ask for any other advice. There are several other 3 phase users on the forum so I expect there will be more comments soon.

K

 

[Garamanda]

Thanks. Very helpful

 

[TFrench]

I've just ordered a bosch rexroth inverter for my lathe - if you don't mind waiting a week or so I'll be able to see how good it actually is. Not that expensive either, from inverterdrive.com. I went for it because the control panel is mountable outside the mahine so no messing about fitting an extra potentiometer or anything.

 

[monkeybiter]

When I bought my Harrison L5 20 odd years ago it had a three phase motor on it. I just bought a single phase motor to replace it. No variable motor speed but with a gearbox that didn't matter. Would that be an option?

 

[Garamanda]

Thanks T.
I'm in no hurry to do this( over the winter sometime) please keep me posted.

Thanks Mike.
It is an option. Quite like the idea of changing speed whithout the hassle.
Lazy I guess. And comes at a cost. I'll need to weigh it up. Cheers guys.

 

[Normancb]

The inverter route is a good way to go and variable speed is nice to have. I'd just add a couple of points if you go that route:

1) Get some screened 3-core cable for the connection between inverter and motor and make sure the screen is well earthed. Inverters work by rapid switching and produce a lot of RF. The motor doesn't notice but the workshop radio will! I have a home made setup on my wood lathe using a commercial inverter and screened cable and it all works fine. The commercial inverter-motor combination on my metal lathe wipes out the radio when it's running. You can get screened cable cut to length from people like TLC.

2) I found it worth investing in a 10-turn potentiometer for speed control - gives a much finer control, though most people manage with the usual 270 degree ones.

 

[Garamanda]

Thanks Norman. Will keep that in mind.