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Thread: Mars Lathe DC motor conversion.
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20th October 2012, 12:24 PM #106SENIOR MEMBER
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Thanks Ray.
I would have liked to mount the controller in the headstock cavity to reduce the exposed wiring, but there's just not enough room.
So I had to hang it off the back.
I had a chat with a guy in the UK recently, and he mounted his KBIC-240 controller and potentiometer in a largish alloy project box (for his mill) in a similar fashion to Ewan.
A good idea as you can bolt the controller against the alloy box with a bit of thermal paste and it will act as a giant heatsink for large HP applications.
I also gave him the links to the Ebay red tacho and Hall sensor I used, and my wiring diagram - to replace the bicycle computer he is currently using as a tacho.
So it looks like we have another convert on that
Cheers
Rob
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20th October 2012 12:24 PM # ADSGoogle Adsense Advertisement
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20th October 2012, 12:57 PM #107Senior Member
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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
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20th October 2012, 01:21 PM #108SENIOR MEMBER
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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
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20th October 2012, 02:43 PM #109Senior Member
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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?
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20th October 2012, 03:42 PM #110SENIOR MEMBER
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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
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20th October 2012, 04:48 PM #111Senior Member
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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.
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20th October 2012, 07:12 PM #112
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.
1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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20th October 2012, 08:14 PM #113SENIOR MEMBER
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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
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20th October 2012, 08:57 PM #114SENIOR MEMBER
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Mars Lathe DC motor conversion.
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
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20th October 2012, 10:48 PM #115GOLD MEMBER
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Cam Operated Compound Slide
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
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21st October 2012, 01:06 AM #116
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21st October 2012, 11:26 AM #117
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.
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.1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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21st October 2012, 12:46 PM #118SENIOR MEMBER
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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
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21st October 2012, 01:04 PM #119
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21st October 2012, 01:27 PM #120GOLD MEMBER
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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
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