Einhell MTB3000 minilathe potentiometer

[cre8tor]

Hi!

First, thank you for letting me join in MadModders forum!

I bought 10 years old fairly used Einhell mini lathe. For first start nothing happens, I rotated motor by hand and it scratches.
I took off it and cleaned, now it works fine. Next problem is (maybe only pot) on control panel. Potentiometer says B4.7K, so
I think its linear 4.7KOhm pot with on/off switch.

When I turn little bit clockwise potentiometer, it cliks and lathe turns on (when all other switches has turned on), but I can't
adjust lathe motor speed on potentiometer. Is this potentiometer problem or something else in circuit board?

I find it to be hard to find exactly same pot on internet, but one I ordered from ebay, I don't know if it fits?
http://www.ebay.com/itm/161675373526?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Please give me any help with this lathe electronics, thank you!

[John Rudd]

Hi and welcome to the forum......

If the speed pot has no effect on the motor then in all likelihood the problem is the control board.....

If you disconnect the motor from the wiring, connect a 100 watt lamp bulb in its place, does the speed pot vary the brightness of the bulb?( make sure the bulb voltage is the same as your line voltage....)

Can you post up,some photos? Control board?....pot? Lathe?

Where about in the world are you?

[cre8tor]

I ordered potentiometer today and haven't got it yet for testing.

I am from Finland. So do I try 100W 230v AC light bulb on motor wires? I really don't know if there is rectifier and motor
works DC supplied voltage? Or is these all voltages AC?

I took some pictures of lathe, pot and circuit board:

[John Rudd]

Ok,
The board is made by KB electronics in the USA, generally reliable but they do blow thyristors...(scr)....Do you have a multimeter?

The motor is a dc motor, so do not connect it to an AC supply...!! 

The dc for the motor comes from the pcb, there is a Full Wave bridge rectifier made up from 2 thyristors and 2 diodes, mounted on the heat sink....Don't work on the board Live.....!! risk of electric shock..

The potentiometer may be a 'special'.....but for now concentrate on getting the motor controlled by the controller.....
Disconnect the motor wires, make a note of where they go! Then connect a 100w bulb in its place.....does the brightness vary as you adjust the speed pot? If not then you need a multimeter to diagnose further.....

[cre8tor]

Ok. My thought of that motor is DC were right

I have Fluke multimeter ofcourse, why I have to use light bulb to check voltage? I can measure voltage with multimeter.

Have to try that. If SCRs are bad, are those hard to get? I give that circuit board and motor to my friend, who are guru of
electronics. He can find the problem

[John Rudd]

It's not a case of measuring the voltage at the motor connections.....you need to see the effect....hence the variation in brightness of the bulb...
The out
It from the control board to the motor is not pwm signal more like 'burst fire control'.....the thyristors are switched on at various angles of their conduction from a zero crossing point detector....without getting too technical.....

The spare thyristors are or can be expensive to source....Are any if the fuses blown? If not then they may be ok....check with diode test function on you Fluke between Anode/Cathode and Gate....

[cre8tor]

Ok, I got it. No fuses blown and motor runs but on very low speed and potentiometer won't speed it up.

I found those SCRs from aliexpress, price was 15€/pcs, not too much, but if they are ok, I don't even need
those.

I hope that pot is the problem.

[John Rudd]

Ok,
A few things to check.....
Check for 12v between I2 and the outer legs of R1 (max speed pot....one end goes to the 12v rail, the other goes to P3.
If that checks out, check the voltage varies, connect Fluke to I2 and P2..... Does this voltage vary when the speed pot is varied?

Don't forget mains is present, keep your hands clear when measuring(use croc clips....)

[cre8tor]

I have measured points you said, between I2 and 12V Rail were 12V. And between I2 and P2 voltage varies between zero
to 7V.

[John Rudd]

Hmmm...to go much further needs more test equipment......

Oscilloscope, low voltage transformer (around 40v ac).......to start....

You need the transformer to operate the board at a lower voltage that is isolated from the mains, the scope to check the waveforms.....

[cre8tor]

I took motor and circuit board(s) to my friend, he have oscilloscope and other electrical stuff needed and skills to check
out, what is the problem with lathe's electricals.

[John Rudd]

If you any further help let me know....I also have the schematic if needed....

Good luck with the repair...

[cre8tor]

I tested motor before I took motor to my friend and run it (slow) about one minute and after running motor it was very hot.

So my friend opened motor and noticed something like this, maybe this is the real problem  :
I have to take dremel to my hands and try to get motor work.

[bertie_bassett]

What do the brushes look like?

Looks like your armature segments are touchi g each other, useba small hacksaw blade to scrape between the segments and make sure they are not shorting to each other

[cre8tor]

What do the brushes look like?

Looks like your armature segments are touchi g each other, useba small hacksaw blade to scrape between the segments and make sure they are not shorting to each other

That's what I think I should do on next week, hope to get it work. Brushes were in good shape. But First time when I get this lathe, lathe wouldn't start at all and
when I rotated motor from spindle, it like scratches very badly. But when I opened motor, I couldn't see anything what could have damaged commutator.

[lordedmond]

From your pic Bertie is correct

It looks to me as if someone in the past as skimmed the com and rolled over the Segs

Do not use a dermal as the ginding dust will embed in the copper as wear out the brushes, a well used  hacksaw blade with the side kerf ground off to the grove width is the accepted tool

As a ex armature/stater winder during my time that's what we used even on the big stuff we did try a air powered slitting saw and guide but the old way was better.

The colour looks ok it should be a chocolate brown , one last point well two really when you have cleaned out the slots take a craft knife and gently de burr the edges , and do not use any emery cloth on the copper if you feel the need to shine it us use the glass paper the wood butchers use its th yellow stuff else it will embed the grit and wear out the brushes PDQ

I hope you ran it on test on DC not AC if you did Use AC it would have got hot

Good luck John knows more about the actual board than I do but I have save a few for friends
Stuart

[John Rudd]

From your pic Bertie is correct

It looks to me as if someone in the past as skimmed the com and rolled over the Segs

Do not use a dermal as the ginding dust will embed in the copper as wear out the brushes, a well used  hacksaw blade with the side kerf ground off to the grove width is the accepted tool

As a ex armature/stater winder during my time that's what we used even on the big stuff we did try a air powered slitting saw and guide but the old way was better.

The colour looks ok it should be a chocolate brown , one last point well two really when you have cleaned out the slots take a craft knife and gently de burr the edges , and do not use any emery cloth on the copper if you feel the need to shine it us use the glass paper the wood butchers use its th yellow stuff else it will embed the grit and wear out the brushes PDQ

I hope you ran it on test on DC not AC if you did Use AC it would have got hot

Good luck John knows more about the actual board than I do but I have save a few for friends
Stuart

Good advice from Bertie and Stuart there.....
As Stuart says, a group up saw blade is best for cleaning.....

I also have a few spare boards of both Chinese and American flavour as a backup.....only trouble is they do need setting up to match the motor..... so although they are a drop in replacement, there are a few tweaks need to 'tune' them...and I have the setup procedure too....if needed..

[bertie_bassett]

just had a better look at the photo, and to me it looks like the damage is isolated to that groove near the windings. looks like something has dug in at that point. iv seen similar damage from brushes that were so worn that the internal cable was poking out, thus damaging the segments.
a small bit of debris could easily do the same.

[John Rudd]

The comm doesn't look too good.....

I had another look.....agreed there is a mark at the top right, but if you look further down towards the termination points, it looks like there are copper shorts between some of the segments.....
If these can be cleared, the motor might be in a better state....

[awemawson]

I reckon that some previous owner let the brushes wear down dangerously low, and as Bertie say got the com mangled by the wire holder. Then changed the brushes and it failed to fix the problem so got shot of it. Hence there being no apparent problem with the brushes.

[cre8tor]

I got motor working!

Small hacksaw blade used between comms and the I sanded comms, first 240 grit sandpaper and then 500grit paper. Then cleaned whole comm with
brake cleaner and blowed all **** away with compressor air.

I bought this lathe from my friend who has noticed it 500km away from my house on some of his friends grandfather estate (heirs collectively?). So anyone who's alive,
doesn't know, what's happened to lathe motor earlier. But who cares, now it works perfectly, and nothing wrong with electricity. I think there may have
been some debris between brushes and comm.

Today I got lathes ways and all stuff cleaned and tomorrow I will assemble all things together and start using lathe.

[lordedmond]

Well done
Stuart

[John Rudd]

Good result.... thanks for letting us know you fixed it.

I'm glad you have it sorted and without expense.....


So, when you have made something with your new machine, we need to see it 

[bertie_bassett]

glad it was a simple fix and is now working.

[Stilldrillin]

Great result! 

  

David D

[cre8tor]

I thought I can ask this question here now..

So I would like to buy indexable lathe tool set, but I really don't know if 10mm shank is suitable for my minilathe. Original tools
are with 8mm shank with fixed tips. Under these tools need to be approx. 1-1.5mm spacer if I want tip to be center of metal, which
is going to be turned or faced.

[John Rudd]

I use 10mm tooling on my mini lathe  but have a qctp to accomodate the centre height....

[cre8tor]

Ok!

I think I must buy too that QCTP. Is there any suggestions, what manufacturer and what model QCTP is suitable for my 300mm Einhell
mini lathe? On my lathe is fixed bolt where original tool post stands. Do I need make any modifications to fit QCTP for my lathe? Or is it
just straight fit to it?

[Kjelle]

Hi, have a later version of the same lathe, and I bought c2/c3 qctp from Arc... No fitting, no fuss, no muss. Not sure if your lathe is an earlier c2-300 in blue, but if it is, Seig stuff fits directly... And spares are easy to come by, mostly from the "normal" vendors in the UK (Arc, Warco etc.).

Kjelle

[cre8tor]

Ok, good to know. My lathe is Einhell MTB3000 and in this forum I found some picture of it: http://foro.metalaficion.com/index.php?topic=6474.0

400W motor, and colour of blue

edit. Looks like same as this Warco: http://www.warco.co.uk/metal-lathes-metalworking-lathe-machine/302983-mini-lathe-hobby-lathes.html

[Kjelle]

Sure looks like a Seig C2....

I have changed the gibs (for Arc's brass one's), made one h**l of a difference! Lots of info on these on the 'net.

Kjelle

[modeldozer]

Hi,

Have the same lathe (highly modified),  it is actualy the same as the Real bull ones as sold by Amadeal. 

Abraham

[cre8tor]

Sure looks like a Seig C2....

I have changed the gibs (for Arc's brass one's), made one h**l of a difference! Lots of info on these on the 'net.

Kjelle

http://www.arceurotrade.co.uk/Catalogue/Machines-Accessories/Lathes/Model-C3-Mini-Lathe/C3-Super-C3-Mini-Lathe-Upgrades#Mini-Lathe-Brass-Gibs-Set

Does these fit directly for my 300mm lathe ? Or do I need to made modifications for these?

edit. Answer to myself, yes it fits From LMS: "These gibs are items 94 and 107 on your parts diagram. Fits all 7x10, 7x12, 7x14, and 7x16 mini lathes."