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G0781 belt conversion

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Austengeist

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#1
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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Austengeist

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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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Austengeist

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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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Woodsman 22

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#6
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).
 

Austengeist

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#7
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.
 

Woodsman 22

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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.
 

Austengeist

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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?
 

Austengeist

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#10
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.
 

Woodsman 22

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"Thanks! I was referring to the 3990"

- Ah yes, okay.

"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? "

- Yes, the HF model is just the same as the Grizzly G8689 and is, I think the oldest version of the mini mills around anywhere.

" 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? "

- Yes, that is the point exactly. LMS actually got the Sieg company to build their (LMS's) version of the mini mill to their own specification. A mill with the belt system will have the belt slip if it can't take the load of a hard cut as opposed to breaking plastic gears. My Taig mill works this way but I am trying to decide on a larger more powerful mill to replace it. But I do not want to have to replace broken plastic gears! To answer your question, no I am not aware of replacement metal gears for the mini mills but oddly, LMS DOES sell metal replacement gears for the mini lathes. But, those metal gears are a different design and cannot be used in the mills.

"....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."

- Okay, thanks that is what I was wondering about when I was considering this Grizzly mill as a future buy (but the plastic gears are a turn-off for me now that I know about them- thank you:)). I guess that locating pin in the back of the column above the big washer is helping to keep the column in place and that is a good addition to the design. The other tilt-column mills don't have it.

You shouldn't be having that problem with the gibs loosening up all the time. Are those gibs maybe too thin to fill the gap between the sliding dovetail members? I ask this because that was the case with my 9X20 Chinese lathe that I have. I had to mill new gibs to fit and I milled the new ones to fit that space as tight as I could make them while still having free movement. The original gib strips were way too narrow for a decent fit. It is great that you managed to refit your mill with a drive belt system. Good job!
 

Austengeist

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#12
Thanks! I am considering milling a tight fitting gib to remove any of the movement. The Z axis is by far the worst on mine.

Glad to hear you were able to make yours with success.

I was also looking at the air spring upgrade but this mill is capped off at the top and I would have to make a hole for the shock to go thru. Other than that, it would be a welcome upgrade!

Thoughts on upgrading my motor to a brushless one? Currently there is only 3 wires connecting the motor. I will have to look into this process of what all is needed.
 

Woodsman 22

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#13
Austengeist,

Earlier in this conversation you asked if metal gears were available for the X2 type mills and I said no. I was wrong about that. LMS does sell metal replacement gears for Seig type X2 mills. As a matter of fact they have different sets for both the R8 spindle type mills and another for the MT3 type spindles, but these are for the Seig X2 mills and might not fit your Grizzly. Here is the link for the R8 spindle metal replacement gear set:

https://littlemachineshop.com/products/product_view.php?ProductID=3449&category=879658189

As far as a brushless motor for your mill goes, the only company selling that type of motor/mill combination that I know of, is LMS. But that requires (again, as far as I know) a entirely different power supply/ speed control box which LMS does not appear to offer as an add-on kit for your mill. Still, you could phone them and ask them if adding a brushless motor to your Grizzly mill is a possibility.
 

Austengeist

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#14
Thanks for the link! I will have to send LMS an email asking the shaft sizes of those gears. I think I’ll use the motor I have until (IF) it gives out. Although some better low be torque would be nice. I’ll have to do some digging. Thanks for the help!
 
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