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Treadmill motor conversion for a Grizzly 6x26 knee mill

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mattthemuppet2

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#1
I bought this second hand last year and it's awesome (1st proper mill!), but I've been spoilt by the variable speed treadmill motors on my lathe and drill press, so I've been waiting awhile for the opportunity to add a treadmill motor to my mill.

The 3 usual challenges are 1. how do I stop the flywheel (LH threaded usually) from spinning off in reverse, 2. how do I go from the poly-v pulley on the treadmill motor to the 1/2" V section belt on the mill (or whatever tool it's going on) and 3. how do I gear down the treadmill motor (4700rpm) so that spindle speeds don't go through the roof?

1. is easy with this motor as it is rare in having a keyed and pressed on flywheel

2. and 3. are somewhat related and involve either adapting the intermediate shaft/ countershaft of the tool to poly-v or putting the smallest possible V pulley on the treadmill motor, somehow. I couldn't adapt the intermediate pulley to poly-v as there wasn't the space and the rework would have been rather tricky (though it was easy to take this approach on the lathe). I could have turned down the flywheel poly-V pulley and press on a 2" diameter V pulley, which is what I did on the drill press, but that would have precluded the full range of motor>intermediate pulley ratios and I wanted to try something different this time. Thus began a time consuming, convoluted and thankfully successful project to make an arbor adapter that would also take the original motor pulley if I wanted to use it. I was also an interesting experience turning the mystery stainless that I used for the flange. Beautiful finish but OMG what a squealing racket.



pulley was pulled from my "this might be useful oneday" pile of pulleys. Crazy amount of porosity in the casting. Detroit original


mounted to the motor, a "2.25hp" motor, that works out to ~1 1/2 real world hp.


on firmer ground now as I've done a couple of these already and they're pretty straightforward.

The guts are an MC-60 treadmill controller, courtesy of a user from another site called Maxheadroom - thanks! Power cable, main switch and fuse holder from some treadmill I salvaged. Cheapo 4 digit ebay tach and 9V wall wart guts. DPST lighted switch for controlling power to the controller. DPDT with center off switch for FWD/REV. Choke for the DC power line to the motor. 5k pot (also thanks to Maxheadroom) for speed control, with a large dial off some random salvaged peice of equipment. Oh, and a 2 port wall plug at the bottom for ancillaries.


looks complicated but it's pretty straightforward - board is already bolted in with heatsinks on the back, main switch, cord and fuse are installed on the left. Controller switch (top left), wall plug and wall wart for tach (bottom right) are connected to the main switch, controller switch then connects to the controller board AC power plugs. Trim pot is plugged in to the left of the board. FWD/REV switch is plugged into the DC output plugs - one line connects to the choke and the other goes straight to the motor.

FWD/REV is easy - inputs come in at the center, outputs come off one side with that side connected to the other in an X. Super simple, but I ALWAYS wire it the wrong way round, every time. Thankfully that's as simple as swapping the plugs on the board or the wires on the motor.


Back of the front panel showing the controller switch, FWD/REV switch, tach and wall wart (hotglued to the panel, it works!)


Another perspective


motor mount, from ultimate scrapbinium - I dug the large piece out of the ground at the scrap yard, which is why it looks so tatty. nice to have a 2 x 1 1/2ft piece of 1/2" alu plate lying around though.


mounted up


installed (you can even see the lathe controller box in the background!)


other side


I since found a shorter belt in my box of random belts. The original was an A32 which did fine for the low speeds, the AX28 I found fits perfectly for higher speeds like the one shown. Before the magnets I casually placed on the spindle pulley were flung off and attached themselves to some part of the mill, the best ranges I found were 0-250, 50-500 and 150-1200rpm with one more higher ratio to be tested above that (I'm guessing 300-2000 or so). I wasn't able to run the motor flat out in the higher ranges as the intermediate pulley sounded like it was going to fall to pieces, so that may be a future project, but that would probably net me another 200rpm or so.

Haven't used it in anger yet as I was tired of being in a 100F garage and I had some data analysis to do, but a face mill arbor is next on the list so I'll have a play with it on that. Pleased as punch with it though, this'll make life alot easier.
 

mattthemuppet2

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#2
just realised that I might have enough link belt to try out the old motor pulley and drop the intermediate shaft (it's several degrees off vertical which doesn't help). Once I can some up some energy to go out to the garage I'll give it a shot and report back.
 

Z2V

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#3
Looks good Matt, I have the same mill that I did a 2hp VFD back in the spring. You must have had a cold front come thru S.A. if your garage temps are 100*:eagerness:
Stay cool my friend
 

mattthemuppet2

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#4
thanks! If I had the cash, I would have gone with a 3ph motor and vfd, but it's hard to argue with mostly free :)

ha, yes it's been pretty cold here - under 100F for more than 3 days in a row! I insulated the double door with R13 and R15 batts when we first got here and that makes a huge difference. Also keeps the heat of the car in, which is bad in summer but great in "winter". One day I'll save up for a minisplit AC system..
 

Dave Paine

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#5
Very nice job on the conversion. I have a Grizzly 8x30 knee mill of similar design. One day I may get to upgrade to 3ph motor and VFD or DC motor and controller.
 

Silverbullet

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#6
I may try this for my enco like your grizzly. My biggest problems still my back . The pain is at least livable now just can't sit up and lie back . I'm hopping for more relief.
 

mattthemuppet2

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#7
thanks all, looking forward to using it in anger!

I discovered that I had a whole load of link belt left over from a previous project, so tried a 2 pulley set up with the original motor pulley. Had to remove the belt cover safety switch (or make an idler pulley, switch removal was easier) for the belt to clear. Works alot better and much quieter. No need to swap between different length belts either, which is a plus. Predicted speed range is 0-1200, ?-2000 and ?-3000rpm. Higher would be possible by moving the motor pulley higher up, but I doubt that I'd either need it or that the spindle bearings would like it.



worked out the best belt length and ordered a Gates AX belt to fit. Link belts are a PITA in my experience.
 

Dave Paine

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#8
Interesting. I also removed my auxiliary pulley. I do not have variable speed, so I flipped the motor pulley upside down. I now have three speeds which are useful for my needs.

I am not finding the link belt to be a problem. This runs quiet and smooth on my mill.

Mill_link_belt_no_auxiliary_pulley_7944.jpg
 

mattthemuppet2

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#9
neat, thanks for the pic. Lots of people like link belts, but in my experience they don't sit fully in the pulleys and will slip easily eg. if drilling a large hole at low speed. Useful in a pinch, but I've had alot more luck with AX or poly-v belts thank with link belts (1/2 and 3/8).
 

middle.road

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neat, thanks for the pic. Lots of people like link belts, but in my experience they don't sit fully in the pulleys and will slip easily eg. if drilling a large hole at low speed. Useful in a pinch, but I've had alot more luck with AX or poly-v belts thank with link belts (1/2 and 3/8).
Have you got any more picts of the control housing? I don't see any straight on. and some more details on how the RPM/Tach setup was done?
 

mattthemuppet2

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#11
here you go


not quite straight on as the car is in the way :) but hopefully close enough. It's a BUD box with the MC60 heatsink bolted to the box with some extra heatsinking on the outside. Hasn't gotten beyond hand warm yet.

The tach is a $10 ebay cheapy. It's dead simple - power it with a 9-12V wall wart (hotglued to the BUD box faceplate) and make a small angle to attach it to the mill head underneath the spindle pulley. Buy a strong neodium magnet and epoxy it to the bottom of the spindle pulley, then adjust reader height until it picks up the magnet passing above it.
 

middle.road

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#12
here you go
not quite straight on as the car is in the way :) but hopefully close enough. It's a BUD box with the MC60 heatsink bolted to the box with some extra heatsinking on the outside. Hasn't gotten beyond hand warm yet.

The tach is a $10 ebay cheapy. It's dead simple - power it with a 9-12V wall wart (hotglued to the BUD box faceplate) and make a small angle to attach it to the mill head underneath the spindle pulley. Buy a strong neodium magnet and epoxy it to the bottom of the spindle pulley, then adjust reader height until it picks up the magnet passing above it.
Oh, so the tach is separate from the MC-60?
I was thinking that you used the 'whatever that lead is' off of the treadmill.
Might I ask if you could post a link? I searched on "electronic tachometer" & "machine tachometer" and the results were not steller.
Found one @ $49.00. I believe that my ability to search properly this evening is lackluster.
 

middle.road

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Z2V

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#15
I’m using two of these eBay tachs in my garage, they work fine for what I’m using them for. One is on the belt grinder and the other is on a buffing stand. They are stable enough for these applications. On the mill I’m using the MachTach http://www.machtach.com/, while it’s way more involved, it works well also.
 

mattthemuppet2

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#16

markba633csi

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#17
Nice conversion, nothing better than practically free!
Some like the link belts, but they aren't a perfect solution, as you discovered
mark
 

middle.road

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#18
here's another
https://www.ebay.com/itm/4-Digital-...Hall-Proximity-Switch-Sensor-NPN/232462662722

I've used both the ones like this, with the threaded pickup, and the type with the orange cube pickup. Either will do the trick.

I looked into a MachTach - very appealing but I could stump up the funds at the time.
So the Orange Cube pickup works... cool. I wasn't sure about those when they showed up in the search results.
I like the 'Blue' readout.

..."Stump up the funds" I like that phrase.
 

mattthemuppet2

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#19
Nice conversion, nothing better than practically free!
Some like the link belts, but they aren't a perfect solution, as you discovered
mark
thanks, it's really made a world of difference. The other day I was milling a 1/16 slot, running the mill at ~2500rpm, then did some work with a 3/16 end mill at 1400rpm, then a 90 countersink at 700rpm or so, all without changing a belt.

As for the link belts, they're handy in a pinch, but I would always prefer to use poly-v belts first, then AX belts second. If I could have figured out a way to use a poly-v belt on the mill I would have.

So the Orange Cube pickup works... cool. I wasn't sure about those when they showed up in the search results.
I like the 'Blue' readout.

..."Stump up the funds" I like that phrase.
yeah, I was a little worried about the cube pick up, but so far it's working fine. I have 2 of the other style - one on my DP and one on my lathe. the on on the DP has gone a little flaky (reading jumps between real rpm and double), but it's much less critical than the others so I'll just leave it as it is.
 
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