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Myford vfd

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Manofkent23/09/2019 08:27:08
142 forum posts
29 photos

Hello.

I have a Myford lathe with a single phase motor.

I want to put a vfd speed control on it, but have struggled to find one that is just single phase. All I can find are 3 phase output ones.

Can anyone help me either to suggest what to look for, or what you are using and how successful it is?

Many thanks

John

John Haine23/09/2019 08:33:38
4714 forum posts
273 photos

I'm afraid you won't find one. Single phase induction motors inherently have only a narrow speed range as they use a capacitor to get the needed phase shift at least for starting and sometimes running too. I believe there are vfds for low power single phase fans but they wouldn't have the grunt needed. You'll need to change the motor to a 3phase one.

Andrew Johnston23/09/2019 08:36:26
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6668 forum posts
701 photos

That's because speed control on a single phase motor doesn't work well. You need to change the single phase motor to a 3-phase motor and then fit one of the many single phase to 3-phase VFDs.

Andrew

Mike Poole23/09/2019 08:45:57
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Moderator
3376 forum posts
77 photos

As John says you will need to change the motor but it will be well worth it, the machine will be smoother and can be programmed to slow quickly though if you have a clutch then that it not such an advantage. Being able to make slight adjustments to the speed can often improve the finish. Easy reverse is another advantage but be wary of unscrewing the chuck. Complete ready to go packages are available which save some work and provide a well engineered solution, probably not expensive if you build your own to an equivalent standard.

Mike

Baz23/09/2019 09:18:29
756 forum posts
2 photos

I can thoroughly recommend Newton Tesla’s package, can be easily fitted in under an hour and is a joy to use. Usual disclaimer applies.

Harry Wilkes23/09/2019 10:39:30
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1369 forum posts
66 photos

Cant add to anything already said upgraded my S7 to 3phase motor and VFD suppied by Transwave smiley

H

not done it yet23/09/2019 12:40:48
6887 forum posts
20 photos

Just don’t use the VFD as a brake with a screwed chuck. Heavy braking can unscrew the chuck with possible painful consequences.

I have VFDs on my already mechanically-operated variable speed lathe and mill and also on the spindle and table power-feed on my other mill. I wouldn’t want to be without them. Definitely a luxury I can live with!!smiley

Manofkent23/09/2019 13:59:21
142 forum posts
29 photos

Thanks all for your good advice. Now I understand.

Interestingly two if my machines are already 3 phase, which I run from a rotary converter.

Looks like I shall be adding the Myford to the 3 phase list!

John

not done it yet23/09/2019 22:40:00
6887 forum posts
20 photos

VFDs are so much more useful in that they can be programmed to follow all sorts of programable instructions - soft start, variable speed settings, brakes, etc. Also, they don’t use much power when idle and are relatively quiet in operation.

But when dead, they are expensive to get repaired (often cheaper to buy another!). The instruction manuals are often designed for computerised sparkies, not hobbyists, and it’s easy to get it set wrong. I have two which look very similar but each requires the appropriate manual, to avoid programming hiccups. They are not all equal, of course - the more expensive ones having better motor protection, for instance.

Neil Lickfold24/09/2019 06:19:38
890 forum posts
195 photos

What I like best about the VFD and 3 phase motor on my myford is the use of a microswitch for the stop of the lathe when thread cutting. Especially when cutting internal stuff. I know some run it backwards and then feed out, but feeding in knowing that is is going to stop within 0.1mm every time is just great . I have breaking and soft start settings. I put a 3/4 kw motor on my myford about 1hp approx. I just wish I had done it many years earlier. It is smoother running and quieter over all. The smother running shows up in the improved surface finish of parts.

Not cheap , that is true, but well worth it in my view.

Neil

Neil Lickfold24/12/2021 09:34:35
890 forum posts
195 photos

Here is my micro switch in action, cutting an M14X1.5P thread. The microswitch just stops the forward direction of the motor. It is running about 420 rpm or so and stops within +- 0.1mm each time, depending on the depth of cut or total load it is experiencing. I have been meaning to upload a video here but don't know how to. So it is on my youtube channel and the picture is from my album VFD-For-S7. If screw cutting at a slower speed , like 200 rpm, then the end stop position is alot more consistent. I had plenty of room for the runout so did not run it slower. The micro switch is screwed to a piece of delrin that has an 8mm stem that is help by the Noga stand. I can fine adjust the end point position if need be, ( like if I had the compound set at 60 deg and was feeding on the compound,) by using the fine adjustment knob on the Noga head.

This is a link to the video I have uploaded.

https://www.youtube.com/watch?v=LW1-UfYKGCE

carriage-stop-microswitch.jpg

Ady124/12/2021 10:28:25
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5169 forum posts
738 photos

There is cheapo stuff out there already but it's a relatively unresearched subject in here

I have a 240v drill which compensates for lower torque work (got 2 actually because they're so cheap)

Had one in bits for lubing up and there isn't much in there, just a small PCB, but you can hear it cranking up the power level if it gets forced to do harder work

EDIT I actually have it in the back of my mind to use one as a VFD for a small high speed lathe but the duty cycle is quite weedy

Edited By Ady1 on 24/12/2021 10:31:38

Tony Pratt 124/12/2021 10:34:02
2023 forum posts
12 photos

So Neil L, where does the micro switch go in the electrical circuit? I might have a go at fitting one on my Warco

Tony

Robert Atkinson 224/12/2021 10:41:46
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1240 forum posts
20 photos
Posted by Ady1 on 24/12/2021 10:28:25:

There is cheapo stuff out there already but it's a relatively unresearched subject in here

I have a 240v drill which compensates for lower torque work (got 2 actually because they're so cheap)

Had one in bits for lubing up and there isn't much in there, just a small PCB, but you can hear it cranking up the power level if it gets forced to do harder work

EDIT I actually have it in the back of my mind to use one as a VFD for a small high speed lathe but the duty cycle is quite weedy

Edited By Ady1 on 24/12/2021 10:31:38

Those almost certainly use a "universal" burushed motor. much simpler to control. Not as smooth torque as a 3 phase. Brushed motors are sometimes used on small lathes but a 3ph and VFD is much better.

Robert G8RPI.

Zan24/12/2021 12:47:50
313 forum posts
20 photos

I converted mine in 1990 and have never looked back, except I used a 3/4 horse, to match the original but and at times it lacks grunt so 1x1.25 hp would be better. I increased the motor pulley size in order to increase motor speed and cooling at low speed. I still use the headstock belt change from max to min when big stuff or ci is being turned . If you can try to get a resilient 3 phase motor, they run a lot quieter.

 

i like the look of the micro switch limit. I’ll have to investigate that, but it will need very disciplined use as the motor will start again as soon as the saddle is moved it probably needs some form of electronic latch building in so a reset button has to be pressed before a restart is possible .  Not difficult!

Edited By Zan on 24/12/2021 12:54:15

Martin Connelly24/12/2021 16:36:32
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2179 forum posts
227 photos
In YouTube select share then embed then copy. In the forum when posting select the YouTube Icon and paste into the box, edit the pasted data to width 450 (I also set height to 253)
Martin C
Neil Lickfold24/12/2021 20:45:16
890 forum posts
195 photos
Posted by Tony Pratt 1 on 24/12/2021 10:34:02:

So Neil L, where does the micro switch go in the electrical circuit? I might have a go at fitting one on my Warco

Tony

So on my VFD, the S1 out, is where the microswitch breaks the circuit. The micro switch is set to normal closed. When it opens, breaks the S1 and then only the S2 reverse direction can be used until the microswitch is closed again. For me, where this comes into its own, is for internal threading with a run out groove for the end of the thread.

The noise in the video is all from the gear train and the gear box. The motor itself , is very quiet and smooth running. It is smooth enough that the motor can be left running when indicating a work piece.

The VFD I am using has a lot more torque in the lower rpm ranges compared to the other VFD I was going to buy. I purchased the motor and the VFD from a company that used to match motors and VFD's for customers. But sadly they don't do that anymore. They still sell the equipment but are no longer doing the programming and matching of units. The motor does have a thermal over heating cutout. It has never activated yet from running for too long at low rpm and under too much load. So I guess I don't work it very hard at all.

Thanks Martin for the example of how to get a video link. Very much appreciated. By the way, Merry Christmas to all.

Edited By Neil Lickfold on 24/12/2021 20:46:24

Peter Baverstock24/12/2021 20:54:17
7 forum posts

Neil

Please check your P.M,s

 

Edited By Peter Baverstock on 24/12/2021 20:54:40

Neil Lickfold25/12/2021 20:31:08
890 forum posts
195 photos
Posted by Tony Pratt 1 on 24/12/2021 10:34:02:

So Neil L, where does the micro switch go in the electrical circuit? I might have a go at fitting one on my Warco

Tony

It was too late to edit, but here is the pictures of my VFD and the wires.

Close up of the S1 connection.

s1-through-microswitch.jpg

VFD Drive and wires. Red/black is wired to the microswitch and microswitch is normal closed.

vfd-with-si-microswitch.jpg

3 way switch. Forward, stop, reverse.

3-way-switch.jpg

John Haine25/12/2021 22:01:31
4714 forum posts
273 photos

How do you stop the chuck unscrewing when it's stopped that quickly, Neil?

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