VFD for old Myford ML8 wood lathe (0.5HP, single phase)

[happysteve]

Eh up

My dad (retired joiner) has been gifted an old ('40s or '50s) Myford ML8 wood lathe. (Made in the town where I now live).



It comes with what he thinks is (but may not be) the original motor; from the name plate (details read out to me over the phone, haven't seen it): English Electric, single phase a.c., 0.5HP, 1440 rpm, 3.7A full load, 230-250V, frame MS5126, continuous rating, SEE 5244/87.

The spindle speed is controlled between 700 and 2850rpm by stopping the motor, and moving a belt between two sets of 4 V-pulleys (much like a pillar drill). My dad would like to control the speed using a knob or some such.

I have seen this type of lathe fitted with a variable frequency drive (VFD), for example this one on ebay. It looks like the way this is usually done is to replace the single phase motor with a 3 phase equivalent, for which a single phase in/3 phase out VFD can be sourced relatively easily.

I'm aware of the Invertec Optidrive E2 single phase in/single phase out motor control (I'm sure other makes are available), this is only suitable for shaded pole and permanent split capacitor motors (no idea what sort my dad's motor is).

So what are the options? Should I just "get an electrician in," or is this something a trainee can safely do? I'm fine with terminations, and following schematics/instructions, but I've got no experience with motors or VFDs. I'd love to learn, though.

If the former, is there anyone in Norfolk (North Walsham's the nearest town) can help? I'll be going over there 20-30th this month.

Any advice appreciated, even if "leave it to the professionals, lad" (but hopefully not!). My dad's thrilled to be getting this old machine working again, I would dearly love to help him out.

Cheers all

 

[Darkwood]

The link on e-bay is somewhat illegal upgrade of an old non-compliant lathe, this is not a tea-time hobby to upgrade, a good knowledge of the machine code regulation, risk assessment procedures and knowledge of any special requirements for wood working machines is required.

This will include:-

Guard requirements
Safety critical circuits (E-stop)
Braking solutions

This is a job for an Electrical Engineer familiar with all the above not you average Electrician and when you weigh up the costing of bringing this up to standards you'll soon see why people see a bargain when they are on E-bay etc but are far from it unless safety isn't your criteria. .Lathes like this should be sold already upgraded or as a upgrade project but as far as I'm aware it is illegal to sell this as an operating functional lathe even as a gift it should remain as just a ornament unless you just ignore as most tend to do and use it anyway at least your aware of the risks now.

 

[happysteve]

Thank you, darkwood, for your very decent reply.

So it looks like variable speed control is the least of our worries.

Regarding the situation: as I said, my dad was gifted this by a neighbour who had lost her husband a couple of years ago, and was now clearing out his shed. My dad probably used one of these (or summat very similar) when he was an apprentice in the late '50s/early '60s. I will try to nudge him in the right direction with regards safety, but in practice, he's going to be using it (lack of guards and e-stops regardless). Put it this way... he used one of these for several years (only without the handy mechanism for pushing the logs onto the blade):

[video=youtube;8puKJ5dci4s]https://www.youtube.com/watch?v=8puKJ5dci4s[/video]

It had a lever to stop the engine in the event of an emergency. We tried it once. Took nearly a minute to wind down. Old men: they think they're indestructible.

I will have a look through BS EN 60204-1, and any thing else I can find that looks like it might be relevant (any pointers?) and see if there is anything I can do to improve things.

Any further advice gratefully received.

 

[telectrix]

your dad has probably enough common sense to use it safely, imbibed before all this h&s crap was even thought of.

 

[Darkwood]

You right tel' but as advice goes its always best to tell it as it is then his dad will tell him how it used to be and the middle ground is often reached.... my issue is I've seen the aftermath of too many accidents and most would never have happened had the machines complied to modern standards, most were not user negligence or complacency but worn parts on old machinery failing, last one was a bolt head on the tool stock flew off shattering the operators cheek bone, this guy knew this lathe back to front and used it 30yrs but you cannot predict these things but had the guarding been in place where it should have been he would have been protected. H&S is a pain sometimes and just pointless red tape jargon but others times I have to agree its essential... but very hard to convince these old boys on site as they know best.

 

[Marvo]

Using VFD's on old single phase motors is likely to end in tears for several reasons. If I was doing this as a project I'd look at replacing the single phase motor with a 3-phase one then I'd use a VFD that had a single phase 230v input and a 400v 3-phase output, it would be a much better end result. There's several drives available like this, I've personally used the Mitsubishi drives on a couple of occasions for fractional HP motors without problems.

 

[ElectroChem]

...I'd use a VFD that had a single phase 230v input and a 400v 3-phase output

Are you sure about that Marvo? I only ask as my master has told me that single-three phase VFDs can only output up to the voltage they are supplied. What we tend to do with them is wire the motor delta but treat it like star, the voltages balance out that way.

 

[Darkwood]

Are you sure about that Marvo? I only ask as my master has told me that single-three phase VFDs can only output up to the voltage they are supplied. What we tend to do with them is wire the motor delta but treat it like star, the voltages balance out that way.

Not true, I have twice built panels with 110v 1ph in and 3ph 220v out and is a common drive for small motors up to 1.5KW

PS ...Get a new master, yours is out of touch :biggrin5:... check the input and output voltages of this VFD

http://www.vfds.com/variable-frequency-drives/hitachi-l100-vfd/0.75hp-115V-hitachi-vfd-L100004MFU2

 

[telectrix]

here new master is:

 

[ElectroChem]

Well, how about that. I'll have to do some more research before I start designing systems myself.

 

[Marvo]

Yep, they're not very common and usually only available for small fractional HP motors up to maybe 1HP but you do get drives that accept a single phase supply and have a higher voltage 3-phase output. I'd assume they just have a step-up transformer stage added on the AC input.

 

[happysteve]

Eh up

Thought I'd follow this up with an update...

So we arrived in Norfolk end of last week, and I had a look at this lathe. It's a thing of beauty.



The motor is mounted underneath in the (mild steel) cabinet, with the pulleys on top transferring the power from the motor to the main spindle. (Dad's already bought a new chuck for it.)



To change the speed, you release a bolt on the motor foot mount, hinge it up, tighten the bolt, and hope it doesn't slip as you move the belt over.

The motor just had a plug top on it, and was started and stopped by (I kid you not) turning the 13A socket-outlet switch on and off. So far, so scary.

I've learnt an awful lot these past few days, mostly about motor frame sizes. It seems there are essentially two standards - imperial (NEMA) and metric (European, IEC). (Forgive me if I've not quite got the terms right). Needless to say, this old thing is pre-metric, and most UK motor suppliers seem to sell metric. New holes in the mounting plate wouldn't be too much problem, but the 19mm shaft diameter (rather than 5/8") would require a bit of engineering and/or new pulleys and belt. This was starting to look like a bit more work than I had hoped, but not exactly wanting to leave this in the state it's in, my dad and I came to an agreement that he would buy a third party conversion kit, so at the very least it will have an e-stop, DOL starter and no need to risk trapping your fingers as you move the belt over the pulleys.

So we've ordered one from these guys: http://www.haydockconverters.co.uk/lathe_conversion_kits.htm

We've taken off the old single phase motor in preparation, which I get to keep and poke about with by way of thanks:



If it arrives this week I will help him fit it.

So that's that. Hope it was worth posting this. I'm pleased I looked into this, I think I've learnt a fair bit about an area of the electrical art I've not had much experience in.

I'll post more pictures when the kit arrives.

 

[Darkwood]

Thanks for the update.. and you just had a little taste of my world

PS - I'll be interested to know if that wire feeding the motor from their site pics is screened?.... if not it won't meet EU directives.

 

[Marvo]

Just out of interest, if the lathe is for owner use only and it's kept in a secure location do all the machine regs still apply? I know where I am the electrical installation regs would apply but not the machine regs.

The speed changing system you describe Steve was very common on basic machinery that didn't need frequent speed adjustment. The more upmarket machines came with semi-automated pulley called a slip pulley as described here that changed it's diameter as its width was changed and it gave a wide range of speeds.

Also don't be worried about getting replacement pulley wheels, taperlock pulley wheels are really cheap and they're available in most sizes including imperial. A quick google threw up these guys but I'm sure there's many others.

 

[davesparks]

In the link in post 12 the second picture down appears to have a neutrik speakon connector used for the output to the motor.