Novaturn first test today, speed not constant, help please

[audio.fi]

Hi,

I have had great help from the forum members (thank you all), and today, had the confidence to test my novaturn.
It is running flstep in dos using a tutor keyboard.

When testing it, it homed properly and I tried the jog continuous function and this also worked but they seem to move very slowly compared to the mill; Is this correct?

Anyway more importantly, I tried out the spindle and put in 200 rpm and started it. The machine made a creaking sound, for want of a better word, and the speed varies up and down by about 30 rpm, I think in time with the creaking.

Anyway, I decided to investigate the source of the sound and took the headstock cover off. Please understand before I go any further, that I know the names of some of the components, but only have a small amount of knowledge of speed control.
Once the cover was off, I started it up again, and straight away, I could hear where the sound was from, and it was the toothed belt from the headstock spindle to the encoder.
I observed the action as it revolved and as the speed varied, the speed fluctuations seem to be in time with the creaking sound but I was still not sure.
Also, looking at the outer sruface of the belt with my eyes horizontal to the pulley, it seems to move up and down along one edge of the belt (as if there was debris on the pulley). Also, the belt is not as wide as the pulley and moves from side to side on it.
I took the belt off to have a look at it and the pulleys; The pulleys had small amounts of debris but not enough to cause the belt to lift up, however, there was black debris stuck to the inner rim (on one rim only) of the encoder pulley, as if the belt was rubbing on it but only for about half a turn.
I then had a look at the belt; Along part of one edge, it looked sort of melted, and certainly wasn't smooth as the rest of it. I also noticed the if laid on a table so you are looking at it's edge, then the continuous part of the belt (i.e. not the teeth but the part above it), it is not the same thickness all the way around.
I cut off the melted part in case this was the problem and fitted it back on the pulleys, then turned it by hand. It still made the creaking sound so knew it wasn't the main spindle drive making the sound. I also looked at the surface of the belt again as I turned it by hand and it still rode up part way round the pulley.
I also measured the belt and pulley width (i.e. the teeth width); The pulley teeth width is 11mm but the belt (at it's widest is only 10mm (thinnest is only 9.8mm where the damage seems to be)).
Could the belt be the problem ?
As far as I know, it was only used 2 or 3 times and probably has been left standing since then which was around1998 / 2000
the belt says on it "optibelt" and "180xl" then "8a868"
Can anyone help with this one, as I didn't expect it to have a problem like this and have no idea what to do to fix it.
Thanks.

[Martin]

The spindle speed will fluctuate at low rpm. Try running it above 500 rmp and see what happens. The belt is allways narrower than the pulleys on the encoder for some reason. It may be worth spraying it with a belt lubericant. Or you should be able to take it to a bearing suppliers & pick up a replacement for not much.

[audio.fi]

The spindle speed will fluctuate at low rpm. Try running it above 500 rmp and see what happens. The belt is allways narrower than the pulleys on the encoder for some reason. It may be worth spraying it with a belt lubericant. Or you should be able to take it to a bearing suppliers & pick up a replacement for not much.

Thanks Martin.

Should it vary by that much i.e around 30 r.p.m. , and if so, is this not mch of an issue because most items being made would require a higher speed ?

I have found the maker / distributer of the belt i.e. optibelt, which is not far from where I live, and since it comes off a roll i.e. it is a tube and they just cut off whatever width you require, I am going to get a 10mm and 11mm. You are correct, they are only about £4 each.

Their web site is :-

http://www.optibelt.com/index.php?id=1&L=9

P.S. Is there any such thing as a parts list for the novaturn or the novamill ?

[audio.fi]

The spindle speed will fluctuate at low rpm. Try running it above 500 rmp and see what happens. The belt is allways narrower than the pulleys on the encoder for some reason. It may be worth spraying it with a belt lubericant. Or you should be able to take it to a bearing suppliers & pick up a replacement for not much.

I got the replacement belts today. I bought three of different widths just in case it wasn't the original that was fitted, but it turns out it was, as only the 10mm that I bought fit which is the same as the one I took off.

I powered it back up, and the creaking sound was almost absent, but the speed fluctuations wasn't. It varies by up to about 30rpm (from the readout on the computer monitor), but looking at the new belt, it is doing exactly the same as the old one, i.e. when the speed fluctuates, the tacho belt (the one just re-newed), goes slack then tight as the speed changes, and the belt rides from side to side. I ran it up to 600 rpm and this was still happening. Surely this is not correct, as I am scared of running it up any higher.
Please can someone advise on this as I am convinced it isn't working as it should.

Thanks very much for any help.

[Steve]

I would run it faster.

At slow speeds the motor speed control will not be great anyway.

The Encoder is for monitoring the speed and for thread cutting. It does not feed back to the spindle drive.

The speed of the motor is set by the spindle analog out of the control card and the spindle drive. As its a DC motor the torque is low at low speeds and can cause speed fluctuation. As you get faster the speed will become smoother.

You are not going to cut anything at slow speed other than threads and the encoder will keep the slide in sync with the fluctuations at this thime.

Most cutting will be done above 2500RPM where the drive and motor will have better performance.

You probably have a Sprint spindle drive and SEM motor. The motor has a tacho built into it and this will allow the drive to compensate for speed fluctuations.

Crank it up and see what happens

[Denford Admin]

This sounds more like the drive / motor which is speeding up/slowing down... this could be because:


a) the drive is not setup properly eg, the gain is too loose, or current settings too high/low
b) the DC spindle motor brushes or commutator could be worn out / dirty
c) the DC spindle motor TACHO brushes or commutator could be worn out / dirty
d) tacho wiring is not screened / connected properly

Note that the tacho for motor speed feedback is built into the back of the spindle motor itself - the encoder (the bit driven by the belt you are talking about) is seperate and only feeds back the roational speed of the spindle (ie chuck) to the control - it has no effect on controlling spindle speed

PS - I'm guessing here that your version of Novaturn has the black DC brushed SEM motor ?

[audio.fi]

This sounds more like the drive / motor which is speeding up/slowing down... this could be because:


a) the drive is not setup properly eg, the gain is too loose, or current settings too high/low
b) the DC spindle motor brushes or commutator could be worn out / dirty
c) the DC spindle motor TACHO brushes or commutator could be worn out / dirty
d) tacho wiring is not screened / connected properly

Note that the tacho for motor speed feedback is built into the back of the spindle motor itself - the encoder (the bit driven by the belt you are talking about) is seperate and only feeds back the roational speed of the spindle (ie chuck) to the control - it has no effect on controlling spindle speed

PS - I'm guessing here that your version of Novaturn has the black DC brushed SEM motor ?

Is there any help I can get on how to test the motor control, i.e. is there any procedure for setting it up, or could you perhaps advise me. I have the right equipment, i.e. a multimeter and a scope.

I just remembered that I have a leaflet that came with the unit entitled sprint electric 400,800,120 controller. I had already uploaded this to the downloads section of your site last week. if you could look at it, perhaps this could help you, help me. Thanks.

[Steve]

Have you tried running it faster?

There may be nothing wrong.

[audio.fi]

Have you tried running it faster?

There may be nothing wrong.

I have ran it up to 600 rpm and still have the problem. Even without looknig at the speed on the monitor, it is quite clear it is fluctuating, from the sound and looking at it.

If you think it is o.k. then at what speed would you think this fluctuation should stop at, as I will run it up by increments until I get to where you think it should be o.k.

Thanks.

Update:-

I think I have found the problem, so I thought I would let you know.
When I originally ran the lathe, the speed was fluctuating and there was a sound in time (it seemed) with the fluctuation. I also noticed that the toothed belt that runs the speed sensor would creak and also move up and down the pulley of the sensor only and not the one on the headstock spindle.
Anyway, I looked at the belt and noticed that the side of the belt was not a uniform width, varying from about 9.5mm to 10mm. Thinking that the diffrence was wear from rubbing on the pulley, I went to the stockist and bought a new 10mm belt.
Alfter fitting the new belt, the problem seemed to be more than it was before, not less with the belt riding even higher than before.
I then found out why. The new belt had the same width difference as the old belt, i.e. this one was between 10mm-10.5mm, so it must be the way the belt is cut, therefore, I believe the original belt had been on it since new, and was not rubbing as such, simply getting to the part that was too thick for the sensor pulley, and riding up it, giving rise to the sound I heard. I simply went round the original belt with scissors and made the belt smaller than the sensor pulley (in width), and the riding up and down problem went away, along with the sound.
I now had the confidence to run it up to a higher speed and went all the way up to 3400rpm (in increments) and in all cases the speed fluctuation was about the same, around 20 rpm, so I think this would indicate it is working properly, i.e. at 100 rpm the fluctuation is about 15rpm, and at 3400rpm it is about 20-30rpm

[Steve]

Does the speed variation create a big vibration?

If not just run it up and see what happens.

If the machine is vibrating badly there may be more of an issue.

We do not normally run the spindle slow other than for threading.

I would normally run the spindle at max rpm or close to it.

[audio.fi]

Does the speed variation create a big vibration?

If not just run it up and see what happens.

If the machine is vibrating badley there may be more of an issue.

We do not normally run the spindle slow other than for threading.

I would normally run the spindle at max rpm or close to it.

Hi Steve,

Thanks for the help, I have updated my post (didn't know you had replied at the time), Does it sound o.k. after reading it. Thanks.

[Steve]

OK

Glad its working.

The fluctuation you are getting seems OK. The speed displayed is an average of the pulse count in a very short time so variation in the readout is inevitable.

[audio.fi]

OK

Glad its working.

The fluctuation you are getting seems OK. The speed displayed is an average of the pulse count in a very short time so variation in the readout is inevitable.

Thanks very much for the help.