G0781 belt conversion

Austengeist

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Hi there!
I just wanted to post a few pictures and what I learned about converting my new Grizzly G0781 to belt drive.

I was excited and setup my new mini mill. Used it for about 3-4 hours and heard a grumbly noise. I was drilling 1/2” holes in aluminum. I switched to low gear and the grumbly noise went away. About 30 mins later.....snap! And the motor was free spinning...

I took off the cover and the plastic gear was okay. I called grizzly to see what they wanted to do. They suggested I tear into it more. This mean removing the head stock.

Every gear inside the headstock was shattered.

Grizzly had parts but were on back order. I started looking on google on every article I could find on mini mill belt conversion or metal gear upgrade.

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After tearing it all down and getting the spindle out, I was left with a bunch of plastic bits.

LMS sold different kits for belt conversion but after a call and email i was told it was not compatible.

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LMS did have other R8 spindles for conversion so I started measuring. My spindle necked down to 28mm from 30mm. And was shorter by 10mm.

I bought the spindle conversion kit and the belt conversion kit. This should get me pretty close.

Some differences I found.

My motor bolt pattern was 74mm. Instead of 72.

My motor had a 10mm shaft instead of 9mm.

And worst of all the CNC aluminum mounting plate pattern was wrong, again by a few MM.

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So I rotated and drilled a new pattern in the motor plate.

Next I had to cut a new mounting plate with the correct pattern.

Strange how I really needed a mill to fix my mill...

I drilled out the small pulley to 10mm and had to cut the small spacer off

The pulleys line up and the plate and motor fit!

I have to slightly relocate the electric panel on the side of the mill and need to mount the DRO for the spindle as the pulleys are in the way.

I also need a shield for the belt so if it breaks it doesn’t smack me in the face!

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I am thankful that you posted your experience with this mill. I have been on the fence about buying this very item from Grizzly but now that I read this I think I will be shopping for a different mill. What a shame... I thought these mills had metal gears combined with one plastic gear as a "fail safe" feature (to avoid damaging the metal gears that I see don't exist in this mill to begin with).
 
Littlemachineshop.com sells a nice mill that is close to this, but does not tilt. I like my mill now but would have started with the LMC had I known. I spent about $200 getting the parts to convert it.
 
Littlemachineshop.com sells a nice mill that is close to this, but does not tilt. I like my mill now but would have started with the LMC had I known. I spent about $200 getting the parts to convert it.

I think you must be referencing this LMC mill;

https://littlemachineshop.com/products/product_view.php?ProductID=4962&category=1387807683

If so, and had you bought that one you might NOT have been any better off since it too has plastic gears inside. Their newer ones like the 3990 have done away with the old gear drive and substituted a belt drive with a brushless motor which seems like a better system.

I wanted to ask you; did you have any problems with your mill column moving out of tram (due to the adjustable "feature") or did it stay solidly in tram for you? Also, before the gears broke were you milling anything other than aluminum? I ask because it just amazes me that the gears broke while you were milling or drilling aluminum. Seems like a cast iron machine that weighs 130+ pounds should be able to hold up better than that, but I am not a machinist. Thanks for putting up with my questions.
 
Thanks! I was referring to the 3990.

https://littlemachineshop.com/products/product_view.php?ProductID=3990

It’s close to the same price as the G0781 from Grizzly. You are right the Sieg based ones still have the plastic gears inside. I think that’s the same as the Harbor Frieght models too?

I was surprised as well. I was drilling 1/2” holes in aluminum. I was letting the bit do the work and was not pushing it. It is interesting that after the belt conversion, if it gets too much load the belt will slip. I suppose that would be the point it would strain the gears?

As a side note, I was not able to find replacement metal gears. Have you?
 
Sorry, I forgot to respond about the adjustment feature and getting out of tram. So far it has stayed where it is supposed to I have not had any issues with it. I have had to adjust the Gibbs several times just over the course of machining it doesn’t wanna stay. It seems to loosen up after use for a few hours.
 
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