Wood Lathe Conversion


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6 Nov 2021
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Hi all and thanks in advance for any information given. I have a Denford Viceroy lathe with single phase motor and 2 x 4 step pulleys for speed control.
I have been given a VFD and a 1.5kw 3 phase motor that runs at 2880 RPM.
The max speed the single phase motor and pulleys run at at the moment is 1440 RPM. My question is will the pulleys, v belt etc be ok to run at 2880 RPM.
I know torque will be less, but should still be fine because bigger motor, also know I can reduce RPM to 1440 by reducing frequency on VFD. However if I did want to speed up lathe above the 1440 value I just wanted to know if pulleys etc would take the extra speed. Many Thanks
Most lathes run somewhere in the 300 - 3000 rpm range which roughly covers diameters of 2" - 20". If the Viceroy lathe is already geared to cover the bulk of that range, you will probably not want to run it faster because it wouldn't be the optimum speed to turn wood - unless of course you turn a lot of small diameter things like pens, lace bobbins etc.
I don't think the belt or pulleys would have much of a problem if run faster but you might find the bearings got hotter Whether that was too hot would depend on the bearing type/spec.

Also worth noting is that chucks also usually have a maximum rpm. Probably worth checking that too.
Worst case scenario. You do the upgrade and the machine doesn't like the extra speed. Bearings may get hot but more likely it simply isn't balanced well enough and it vibrates as you push the speed up.
In that case, you could be limited to running your new 2800 rpm motor at half speed to match the present 1400 rpm motor, delivering only half of the 1.5kW power. Unless your lathe is only 750 Watts now, this would be a drop in performance.
A 2800 rpm motor isn't ideal. It has speed but lacks torque. Slow a motor down using electronics and the power output drops too. It's not as good as changing speed with a belt.
With your new combo, you may gain useful power in the mid range by running a low belt and fast motor, and little or no benefit at slow speed when you have to dial the motor a long way down and waste most of its power. At the top end, you will gain a lot of extra rpm if the lathe doesn't vibrate too much, but that's only useful for slim spindle work.
Try it. Tell us whether it was worth it :)
Thanks for the information. My single phase motor at the moment runs slow with no load connected, but if I spin it by hand it takes off and runs at full speed. It’s got a single start capacitor, I’ve tested it ( also tried a different one) and that is fine so I’m wondering if it’s the centrifugal switch. The single phase motor on it at the moment is 370 Watts. Thank you
These are the plates off lathe. Could I not run the lathe with new motor at full speed , but on the 3rd pulley 1330 on existing motor so when motor is running at full speed it will be at the equivalent to existing motor on 4th pulley near enough.
Thank you


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Your new motor is so much more powerful than the old one, I'd say you will be able to run it at half speed on the lowest range and still be better off than now. Your high range on the pulleys will be redundant.
One point to watch. The more powerful motor may have a larger diameter shaft than the old one. You're down to mechanics now of fitting the pulley, mounting the new motor so ebmverything lines up and working out the size of belt to tie it all together.
Thanks. I think the only difference is the bore on the pulley is 16mm and the shaft on new motor is 24mm. Does anybody know where I could get a pulley made to match my existing one? That way I could always put old motor back on if things don’t work out. Thanks again
Matching a new pulley to the old one can be tricky. That's why often motor replacement is limited to motors with the same shaft dia so that the pulley doesn't need to be changed. If you have access to someone competent with a lathe, you could bore out the existing pulley just a little to 19mm then spend under £100 and buy an 80 frame size metric motor, 4 pole 1400 odd rpm, power somewhere between 750 and 1100 Watts.
It will be much easier to mount than the big one. By keeping the pulleys all your belt ratios will be right. Power will still be double what you have now and if you buy 3 phase 240V , you can still power it from the VFD for variable speed.
You'll need to get a file out and make the "key" on the shaft fit the keyway in your pulley. The mounting holes for the feet of the motor will be in the wrong place and new ones need to be drilled.

If you don't want to go that way, you can look at chinese alloy pulleys but I can't advise further except that it is likely to be difficult to find a match to all of ratios, 4 belt grooves, 24mm bore, and belt profile.
Whatever you do, you will need to teach yourself about old imperial V belt profiles and modern metric ones like A and Z.
Also read up about IEC motor frame sizes. Your 24mm shaft motor is probably a 90 frame. An 80 frame is smaller. Your old motor is an imperial B56 frame. The 16mm shaft will actually be 5/8" which is 15.8mm. The easiest answer if you lack tools to modify the bore of the pulley is to look for a B56 frame replacement motor so the mechanicals will line up.

Nothing's ever easy is it !
👍👍 I know someone with metal lathe who said they could bore out existing pulley to fit. I just want to make sure of everything before I commit!! Thanks again
If you decide to change to motor, be aware that it is not an easy job. I did it on mine so not impossible, but not easy. I had to winch up the lathe to drop the motor mounting plate from below but the bolts were still tricky to get at. Luckily everything lined up when I put the replacement motor in. I replaced a 3 phase 415V with a 3 phase dual voltage motor so I could use my existing VFD.
Nice lathe though, almost as nice as my graduate, They seem to have risen in price recently, perhaps people are beginning to realie what solid machines they are?

I was given it about 6 months ago by an old boy I do some electrics for. I’ve actually got the single phase one working now, it was the contacts on the centrifugal switch. I would however still like to have that speed control from the VFD. Out of interest what motor did you fit? I was thinking 4 pole 1.5Kw1440 RPM? Don’t think I’m going to fit the motor I was given.. Thanks
and for anyone else,
Taper Lock pullies are the way to go without any machining.....
u buy the center to fit the motor shaft then the pulley to fit the taper lock.....
easy as pie....but remeber large centers wont take v/small pullies...
A bearing stockist will advise...

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