Thread: Mars Lathe DC motor conversion.

Hi Techo,

Have you tried moving the decimal point in the multiplier?

Cheers

Rob

Rob, I read the instructions again but can't find any reference to changing decimal point location or multiplier, am I missing something?



Lex.

Hi Lex,

Yes, it's all a bit vague.

To move the decimal point I think I used the tab function to move the starting point of the multiplier across.

What multiplier did you use?

Put an extra "0" at the end of it if less than a full number.

Try that

It's a bit hit and miss.

My tacho doesn't flash at all - rock steady display. What is flashing ? - just the decimal point ?

Cheers

Rob

Hi Rob,

If you are referring to what they call the Divider Value I have that set to 8 because the sensor picks up 8 pulses per revolution from the slots in the spindle bearing locknut so I don't think I can change it.

The flashing that I mentioned is the last digit scrolling up and down annoyingly and I don't need tenths of RPM's anyway so I would like to remove the decimal point.

Hi Lex,

Yes I was referring to the divider value - didn't use the correct terminology

It may be that the sensor you are using is the problem - or the multiple reference points on the nut are not uniform.

I used one of these:

Hall Sensor Module M44 Switch for Magnetic Field Detecting 16mA DC 0-15V | eBay

This has a real time signal, and a stabilised signal (lightly averaged), which I use - this is excellent - you can see from my videos. I use a single reference point.

I don't think you can avoid having a decimal point reading. I played around with the divider quite a bit until I got the RPM reading correct.

At no stage did the decimal point go AWOL.

The nut may be the problem given you are using a real time signal. Can you reference onto something else with just a single pulse per revolution?

Cheers

Rob

Mine has the 1/10th too, no getting away from it.....With a single magnet it will pick up my 2nd lowest backgear speed, 7.9 rpm.....at 4ish rpm (lowest gear, thats about 90-1 reduction) it doesn't register anything....not that i'll be needing such a low speed for anything in the foreseeable future.
I got my nichrome wire earlier in the week, but have been working nights doing a shop "de fit" so i've not been able to wind a resister yet.

Originally Posted by Techo1

Hi Rob,

If you are referring to what they call the Divider Value I have that set to 8 because the sensor picks up 8 pulses per revolution from the slots in the spindle bearing locknut so I don't think I can change it.

The flashing that I mentioned is the last digit scrolling up and down annoyingly and I don't need tenths of RPM's anyway so I would like to remove the decimal point.

What happens if you set the divider value to 80?

Bryan, setting the divider to 80 reducing the reading by a factor of 10 but the decimal point remains.

Ewan, my lowest speed is 7.9 rpm also with the VFD and gearbox set to the lowest speed, the reading is 100% solid at that speed.

Rob, the slots in the locknut and the inductive sensor are producing very accurate pulses throughout the speed range, 7.9 to 1350 rpm as checked with a non contact tacho.


Lex.

Originally Posted by Ueee

Mine has the 1/10th too, no getting away from it.....With a single magnet it will pick up my 2nd lowest backgear speed, 7.9 rpm.....at 4ish rpm (lowest gear, thats about 90-1 reduction) it doesn't register anything....not that i'll be needing such a low speed for anything in the foreseeable future.
I got my nichrome wire earlier in the week, but have been working nights doing a shop "de fit" so i've not been able to wind a resister yet.

Hi Ueee,

So, you get a sufficient reading with just one magnet? I was thinking I would need at least two for stable low RPM readings but you rekon 1 is fine? I'm still working on the tacho sensor for my mill. There is not a lot of room around the gears and it's gunna be immersed in oil most of the time so I have opted for one of these:
5-8mm Hall Effect Proximity Sensor Magnetic Switch DC 6-36V NPN NO 300mA | eBay and
eBay Australia: Buy new & used fashion, electronics & home d

I hope the magnet is strong enough....
Let you know how it goes once it arrives.

Cheers
Simon

Originally Posted by simonl

Hi Ueee,

So, you get a sufficient reading with just one magnet? I was thinking I would need at least two for stable low RPM readings but you rekon 1 is fine?
Simon

I have one magnet and it works fine. Rock steady. My lowest reading is 2.7 RPM - which is pretty academic as you wont be turning at such a slow speed.

If you go multi magnet then the spacing will have to be spot on or I recon the display will be rolling up and down a lot.

I considered the sensor you are getting. It looks a lot like a m/cycle gear selector sensor

Incidentaly using the lathe in the 0 - 800 RPM range is awesome. This is where most of my turning is done.

The conversions we have done actually produce a better result than the factory variable speed lathes such as the Titan TLV250V which only has two speed ranges (0 - 2500 and 0 - 1250) and a smaller motor.

Others don't even have a second range.

Having a much lower range such as 0 - 250 is a huge plus in comparison.

Cheers

Rob

Hi Rob, I had thought that if the magnet spacing is not exactly (or very close to) then it would produce two differently spaced pulses but I figure that the tacho would just even the pulses out if it only updates the reading once per 1/2 second or so. If one magnet works down to 2.7RPM then that's good enough for me!

I'll have a play when I get the magnets and sensor. I hope it works for my particular application, I was thinking that if I can't fit the magnet/sensor on the final gear which is on the spindle drive, then I would put it on the next gear. If I did this then I would have to fiddle with the ratios so that it reads the spindle RPM and not off the gear it's on but from what you guys have been saying it seems there is plenty of ratio adjustment to take care of this?

Simon

Originally Posted by simonl

I was thinking that if I can't fit the magnet/sensor on the final gear which is on the spindle drive, then I would put it on the next gear. If I did this then I would have to fiddle with the ratios so that it reads the spindle RPM and not off the gear it's on but from what you guys have been saying it seems there is plenty of ratio adjustment to take care of this?

Simon

Yes, that's the idea of the divider. Should be no worries.

Cheers

Rob

Bad news from DC land....

I started on an arbor for my gear cutters today. I had a piece of old axle that i figured would be more than just mild, i know they are case hardened at least. I was cutting through the hardening, 600rpm, 5-1 ratio, carbide....the lathe was doing splendidly until i pushed her a bit hard....phffffffffut! No blue smoke but a large flash from the commutator and the circuit breaker went...... I took the belts off, reset the breaker but as soon as i turned the lathe back on more arcing and the breaker went again.......I will have to do the risking thing and pull the motor apart tomorrow and see what has gone wrong.

Originally Posted by Ueee

Bad news from DC land....

I started on an arbor for my gear cutters today. I had a piece of old axle that i figured would be more than just mild, i know they are case hardened at least. I was cutting through the hardening, 600rpm, 5-1 ratio, carbide....the lathe was doing splendidly until i pushed her a bit hard....phffffffffut! No blue smoke but a large flash from the commutator and the circuit breaker went...... I took the belts off, reset the breaker but as soon as i turned the lathe back on more arcing and the breaker went again.......I will have to do the risking thing and pull the motor apart tomorrow and see what has gone wrong.

Bad luck Ewan


Maybe if you used a slower speed , the back gear maybe , and a HSS tool - that may have been less of a strain on the old girl

Mike

Hi Ewan,

Hmmm, sounds bad.

Coincidentally I was looking at your video tonight to see how your tacho responded compared to mine, and they look much the same.

In the video you say that you are running the motor up to over 3 K RPM. I don't think that is such a good idea.

I've stuck with the 60 % of maximum RPM maximum as recommended and everything stays quite cool even over extended periods.

It sounds a bit terminal.

In this situation even checking the armature with a multi M is not very reliable as you can have internal shorting and still show low resistance. The 2 HP motor I have is like that - a junker.

Cheers

Rob