Thread: Mars Lathe DC motor conversion.

Hi,

Could you pass on the details on the tacho. I'm interested. Would make a great addition to my lathe and drill press.

Thanks

Originally Posted by Com_VC

Hi,


Could you pass on the details on the tacho. I'm interested. Would make a great addition to my lathe and drill press.

Thanks

OK here they are.

Ebay Tacho

0.56" DIGITAL Red LED Frequency and Tachometer Rotate Speed Meter Two Function | eBay

Ebay Hall sensor

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



Wiring details

TACHOMETER =========== CONNECT TO


[5] VCC (RED) --------------------------> Sensor VCC, Power Supply [+]

[4] NEG (BLACK)------------------------> Power Supply [ - ]

[2] SIGNAL GND (BLUE) ---------------> Sensor GND

[1] SIGNAL IN (YELLOW)--------------> Sensor signal AO or DO


Notes

AO (real time direct signal) and DO (stabilized signal) can be interchanged.

DO will give a more stable reading at very low speed (lightly averaged).

The power supply can be a recycled generic 9 – 12 volt DC power pack that plugs into the mains.

Important: Check the voltage output to ensure it’s within range, as these types of cheap power packs often over voltage.

The Hall sensor is sensitive to magnet orientation and requires south pole to work. A small rare earth magnet works OK.

The sensor will read up to 10 mm from the tip, depending on magnet strength.

To set the tachometer multiplier you input a nominal starting figure and change it up or down until you reach the correct pulse rate and reading.

Start with 0.0167 (which is likely to be correct for 1:1 ratio)

You will need a comparison tachometer to verify the reading is correct.

Eg : I used one of these cheapies - work excellently

Digital Laser Photo Tachometer Non-Contact RPM Tach New | eBay



Cheers all

Rob

Hi,

Thanks for that, looks simple enough for me to do

So with the magnet, something like these should do? 10pcs Disc Rare Earth Neodymium Super Strong Magnets N35 10mm x 2mm 10x2mm | eBay

Is there any lag with the tacho readout or is it pretty much consistent?

Originally Posted by Com_VC

Hi,

Thanks for that, looks simple enough for me to do

So with the magnet, something like these should do? 10pcs Disc Rare Earth Neodymium Super Strong Magnets N35 10mm x 2mm 10x2mm | eBay

Is there any lag with the tacho readout or is it pretty much consistent?

They would be OK.

Smaller diameter would be better for small diameter shafts as they will sit "flatter" on the shaft circumference - if you get what I mean. So it depends where you are going to put it - on the flat side of a pulley would be no problem.

I'm using DO output and there may be a bit of lag, hard to tell as the controller and motor picking up may also be causing it.

I briefly tried AO and it is definitely more direct. It 's up to you how steady you like the reading to be.

I mounted the sensor on a non ferrous support (aluminium) to avoid any chance of magnetic interference - it's extremely unlikely.

I've attached a photo to show how I did it.

The magnet is on the spindle and glued on with a bit of clear silicon - that way if I have to remove the spindle bearings I can just scrape off the silicon and magnet easily.

You will need something to keep the magnet from flying off at high RPM.

The sensor has two LEDs (left is power) (right is switch mode - flashes on or off as it reads the magnet flux)

The bottom (underneath) side of the black sensor is the bit that has to pass near the magnet.

The connector is just something out of a junked PC power supply - you can use anything that fits.

Fit an insulator (fibre washer) between the back of the sensor circuit board and the metal mount to prevent short circuiting.

I hope that all helps

Cheers

Rob

Yeah thanks I understand exactly what I have to do now, your photo and explanation helped a lot.

I like the way it came out, looks very professional compared to the bike type setup.

I guess it is going to be a long wait till the parts arrive, argh 3-4weeks shouldn't be too bad.

Hi Rob "Start with 0.0167 (which is likely to be correct for 1:1 ratio)"
Mine was correct set to 1.....?
Com_VC, i reckon there is 2 seconds lag maybe?

I hooked up a simple momentary push button switch today and had a play with threading. I must have known in the back of my mind that i was going to do this as the way i wired the forward/reverse made it so easy to add the switch to the forwards wiring only. I am very very impressed with how easy it makes high speed threading.

Originally Posted by Ueee

Hi Rob "Start with 0.0167 (which is likely to be correct for 1:1 ratio)"
Mine was correct set to 1.....?
Com_VC, i reckon there is 2 seconds lag maybe?

Gday Ewan,

He, He, well that worked for me on that sensor. I can't really comment on the lag. AO would be OK if you want a direct readout, but DO is OK by me. Nice and steady.

I played around briefly with some large diameter stainless today and I think I will put the original motor pulley on to slow things down a bit.

Played with my $8 oil can as well today.

Ain't life grand ?

Very impressive video Ewan. Looks like you've got it nailed.

Cheers

Rob

Great work Ewan. That kind of work fascinates me but I do feel an explosion coming on. Well done. It will make work in' in the shed even more funner.

Phil

Ewan
Very impressed with the cam operated compound slide.
Was that one of your own developments?
Or was it on the original Lathe?
Very nice, & very practical.
regards
Bruce

Originally Posted by Ueee

I hooked up a simple momentary push button switch today and had a play with threading. I must have known in the back of my mind that i was going to do this as the way i wired the forward/reverse made it so easy to add the switch to the forwards wiring only. I am very very impressed with how easy it makes high speed threading.

Very slick, the stopping looks pretty consistent as well.. I imagine it was a bit nerve wracking when doing the first tests..

Regards
Ray

Originally Posted by Abratool

Ewan
Very impressed with the cam operated compound slide.
Was that one of your own developments?
Or was it on the original Lathe?
Very nice, & very practical.
regards
Bruce

Hi Bruce,
It was on the lathe when i got it, and it looks original. Unfortunately my lathe seems to be one of a kind, it is an ex ministry of munitions machine. I cannot imagine such a small machine used for production, so i don't know what its use would have been. The cam itself is beautifully made, using 2 needle roller bearings and a large sliding bronze block. It moves a 1 1/2" dia x 2" long (or thereabouts) block that 2 deep groove bearings for the screw run in. The only problem with it is that it locks over center, and for the threading with no run out groove once the cut got deeper i couldn't back the tool out due to it having to push forwards slightly first.

Originally Posted by RayG

Very slick, the stopping looks pretty consistent as well.. I imagine it was a bit nerve wracking when doing the first tests..

Regards
Ray

Hi Ray,
It sure was nerve wracking to start. I did half a dozen "dry" runs first just to make sure, and even then my hand was on the switch for the first few runs. I also started much slower and build the speed up. I tried it at the next belt ratio up at about 400rpm but the lathe doesn't stop quickly enough, the extra gearing coupled with lower motor speed means slower breaking. Its really counter intuitive to think the faster the motor is spinning the faster it stops due to the higher voltages and current produced.

Overall i am absolutely wrapped with the results, i just need to get a decent sealed switch and mount it on a spring much like the HM50 powerfeed stops.

I'm still getting bad cogging when the motor is cold, it only takes 10sec to go away, but it can't be good for the motor coughing and spluttering like that.

Hi Ewan,

Your IR may be just a tad high.

According to the manual that causes the cogging.

When I played around with the 2 HP motor IR changes did make it cog as I increased it.

I haven't got any cogging issues , just a tiny bit at very very low (unusable) speed.

I'm going to sleeve and fit the original motor pulley today if time permits.

Cheers

Rob

Originally Posted by Ueee

i just need to get a decent sealed switch

I used a proximity switch for the stop, and that works pretty well, if you use a prox, then be carefull to mount it so that swarf doesn't trigger it.

Regards
Ray

Hi Ewan,

I like your setup. What a success! I would be wrapped with it too if it was my project. I particularly like the electric stop switch it seems to stop very consistently and makes threading so much easier and no need to dis-engage the half nuts. To me, that's just cream on the cake.

I can see myself doing a similar thing once I sort out my mill.

Simon