(Another) Mini Lathe Speed Controller Problem

Thanks Les.

Yes, the resistor is identical to the one that was blown.

I was surprised too that everything seemed fine until I put load on the motor.

The bearings aren’t tight in the headstock - they turn easily but I found that when released the locknut in the spindle the speed certainly increased although still not within the normal range.

If you are prepared to take the risk to do following test: how easy or difficult it is to stop the motor by hand (wearing appropriate leather gaunlets) at slow to medium speed.?

If difficult to stop, then issue may be mechanical.

Have you checked connecting pulleys to see if any have worm by the keyway?

Ketan at ARC

Ketan beat me to it!

Debugging a system is a matter of making measurements, thinking logically and not jumping to unjustified assumptions. We could assume that the resistor is the correct value, although to be sure we could measure it. The next stage is to do as Ketan suggests and load the motor when it is running on it's own. Can be done by hand, or hold a couple of pieces of wood either side of the spindle. If the motor slows more than it should then either the motor and/or the board is faulty. If the motor doesn't slow then the problem is the lathe spindle.

If the motor/board has a problem I'd start by making measurements. However I assume the OP doesn't have appropriate test gear? i agree with Les, don't fiddle with settings on the board. That is simply attempting to paper over cracks, rather than addressing the root cause of the cracks.

Andrew

Hi There is a correct way to tune the circuit to match the motor but not for the faint hearted or inexperienced.

It involves locking the motor rotor and setting the Amperage output to be LESS than the maximum of the motor rating by adjusting the correct Potentiometer.

I have the manual for adjusting a KB circuit on file. PM me for a copy if you want use it. I Strongly suggest the you have the setup performed by a qualified Electrician with the proper equipment to do the job safely.

One modification to a DC motor drive I keep on banging on about is to fit an Amp Meter to the motor leads to measure the motor amps under load.

Use this to set the power feed speed to be able to read that the power used is less than the motor output to prevent overloading.

A photo in my album will explain it better. The motor leads also have fuses on both motor leads

Edited By oldvelo on 17/02/2022 06:27:57

Edited By oldvelo on 17/02/2022 06:28:21

Thank you again OldVelo.

I think the manual you mention is one that I've found on the manufacturers site (https://acim.nidec.com/drives/kbelectronics/-/media/kbelectronics/documents/dc-drives/manuals/kbic_manual.ashx?la=en). I expect that I'll have a go, after I've marked the starting positions on the 'trimpots'.

My comment about my electronics education having stalled at the batteries and bulbs stage is the literal truth - I remember struggling and failing to understand the working of resistors in the Ladybird Book of the Radio. However, despite not having a brain that likes maths, I can follow a recipe (although perhaps not if translated from Chinese).

I'll have a look at your photos. I have already fitted one fuse to the + power lead to the motor.

Motor controllers don't necessarily react happily to the circuit to the motor being interrupted whilst running, your fuse could be a bad move...

Hello John and thank you for your comment.

The manufacturers of the board say that: 'It is recommended that both AC line and armature fuses be installed'. I interpreted the latter as meaning a fuse in-line with the positive power wire to the motor - is that incorrect?

KB electronics, the designer and manufacturer of these boards, recommend the fitting of fuses, line side and armature side, obviously of the correct rating for the motor being served by the controller.

Good point, and I should have remembered that I did manage to blow the motor side fuse on mine!

An epilogue…

It turned out that the motor was damaged too, so I decided to adopt a suggestion made on the forum to fit a sewing machine servo type motor instead. This was cheap and not hard to do and has permitted me to upgrade from the feeble 400W motor to a 750W unit. The speed controller supplied for the sewing machine works well too.

I haven’t finished the installation yet, there being some bodywork and other things to do but testing it today I found it worked very well. In fact, together with the new roller bearings for the headstock spindle the lathe is transformed. For example, parting off, which was usually a horrible experience, was done very nicely.

Wow, I didn't think sewing machine motors were that big. I have a typical sewing machine and the motor is quite small.

These are made for industrial sewing machines used in vast numbers to make clothes, quite different power demands from your domestic Singer...

With regard to keeping swarf out of the control board, there should be a "rubber" grommet to fit in the slot around the Leadscrew.

Arc Euro list it as C3-256 priced at £3 (plus postage )

If you have not got one, it would be worth fitting one to reduce the risk of expensive failures.

Howard

Posted by Howard Lewis on 04/03/2022 15:12:00:

With regard to keeping swarf out of the control board, there should be a "rubber" grommet to fit in the slot around the Leadscrew.

Arc Euro list it as C3-256 priced at £3 (plus postage )

If you have not got one, it would be worth fitting one to reduce the risk of expensive failures.

Howard

Hi Howard, I’ve no longer got the control board installed. Although I intend to do a little more work to protect the workings from swarf, the Jack sewing machine motor and ancillaries are all well sealed, much better than the original lathe set up.

Edited By Philip Coupland 3 on 04/03/2022 19:36:47

Philip, I'm thinking that one of the industrial sewing machine motors would be ideal to put on my X1 mill. Please could you say which actual model you bought as there seem to be two or three different versions.?

I wonder if any have adjustable accel/decel times like a VFD.....

Ian P

It’s a Jack 563A - available in the UK for around £150.

I don’t know the answer to the question about the adjustability but there are a few videos on YouTube.

Good evening,

I fitted a Husuper 550w sewing machine servo motor to my Unimat Sl lathe many months ago and have nothing but praise for it. The same company also does a 750w version. I bought it from Amazon for less than £100 with free 3 day delivery.

The controller has approximately 30 user defined settings like maximum speed, acceleration time, motor braking and motor power.

There is also a section for a PID regulator section.

I can photocopy and post a full list if you require, just not tonight.

regards,

David

New (roller) bearings will take some time to run smooth. You should run them (no load) at a low speed and increase the speed by small steps until you reach the max speed. This process should take at least an hour and it will improve the life time of the bearings. The bearing will get warm (not hot) and this heat will let the grease go to all corners. After this initial run, it will take hours before the new bearing will run very smooth.

You should check how much force it takes to turn the spindle by hand. It should be a bit higher then before swapping the bearing and changing the gear, but no more than that.

I also suspect that the motor doesn't get enough power and that there was more damage than just a power resistor.

Can I see it?

If it is not to many pages Your album here will do

Regards

Niels

Good evening,

I have uploaded the four page manual for the motor to my album.

regards,

David