# Transmission gear upgrade - G0781 Mill



## Spajo (Jul 12, 2022)

Well I busted one of the PLASTIC gears in the transmission of my Grizzly G0781 mill. Yes, I was experimenting and pushing the mill cutting some steel -  apparently a bit too hard. Last night I disassembled the head and got the gears and spindle out. A big thanks goes out to all those YouTubers!  I just ordered a CJ0618 metal gear set. The G0781 has a 600W motor and I think the plastic gears are just a bit weak for that much torque and rotating mass. That gear set may not be an exact drop in and at least one YouTuber had to use his lathe to bore out the diameter of the large gear. I like the mill and I like the hi/low transmission with a 600W motor. If this doesn't work out, I'll likely go with some type of direct drive. I'll bet this is fairly common. I'll follow up with a post about what I find.

I'm sure this has happened to a good number of hobbyist. I would like to know how you dealt with this. Even if the repair goes well, I would like to know what the options are down the road. Let me know.

Spajo


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## markba633csi (Jul 13, 2022)

It looks similar to the 0704 model (which also has plastic gears I hear) except for the tilting column
 A belt drive conversion would be a permanent solution- at the expense of the hi/lo feature (you could replace the motor with a variable speed one)
-Mark


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## Spajo (Jul 13, 2022)

markba633csi said:


> It looks similar to the 0704 model (which also has plastic gears I hear) except for the tilting column
> A belt drive conversion would be a permanent solution- at the expense of the hi/lo feature (you could replace the motor with a variable speed one)
> -Mark


The 0781 has a 600W variable speed motor, but it needs the low range for torque because the motor is an old style motor with brushes.  And, there will still be one plastic gear between the motor and transmission. However, it is cheap and easy to change. This fix is going to set me back about $60 plus (at least) 10 hours of time. But, having torn the machine down, I will have no fear of converting to a belt drive. So this story may be just getting started.

I didn't find much about this when searching the forums, so I decided to document the experience.

Spajo


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## markba633csi (Jul 13, 2022)

The "old style" motor with brushes should have good low end torque- if the controller is adjusted properly and has feedback
It may be the controller that's the limiting factor.  The aftermarket KB controllers have good torque regulation with dc brush motors
-M
I've seen some 0704 conversions that got rid of the gears completely, but I don't know about the 0781


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## Spajo (Jul 29, 2022)

I have my G0781 back up a running. I wanted to summarize my experience for others.

The first question to address is whether it is worth it to fix the transmission or as suggested above, install a direct drive. I ordered my gears from Walmart before I really thought about that. I can see going either way. The mill is running and working well, but it is still noisy. I learned a lot about my equipment and I would not hesitate now to take on some serious modifications. Frankly, I'm to much of a newbie to give advice except to suggest that you think about a direct drive.

Now to the install. I went by the Youtube videos and that is really all you need. I want to emphasize a couple of things.
1. Photograph the everything before you take it apart. The Grizzly parts list is great, but the real part may not look exactly like the drawing.
2. Beware the potential to loose the detent spring and/or ball when removing the 'downfeed handle and hub' and the 'range shifter'.
3. Here is the most important advice that I could give. The four hex head bolts holding the headstock casting to the headstock mount were unbelievable tight. My recommendation is to use only a high quality Allen wrench and with a straight end (no ball end). I had to use a 12" cheater on all four bolts and I could hardly believe that I didn't snap the wrench or round hex bolt. I soaked the bolt heads in WD-40.
4. I didn't have much trouble getting the lower bearing to come out. Maybe I was lucky.
5. The gear set that I used was CJ0618 metal gear set which is commonly used in miniLathes and miniMills.
6. I had to de-burr the gears and clean out the keyways with a file. For sure, I had to use some emory cloth on the inside of the large gear. It was pretty rough and wouldn't go on the shaft without smoothing the bore. One YouTuber smoothed the large gear bore by taking a skim pass on a lathe. A minute of hand work with emory cloth is all that I needed.
7. The fine adjustment (Z axis) on my mill head has always been very tight. When reassembling the pinion shaft, which raises and lowers the head, I saw that the gear casing was binding on the worm gear when the bolts were snugged down. For the short term, I fixed this with shims. I'm thinking that this is a design flaw.
8. I left one plastic gear in the drive train - the 38 tooth transfer gear (part number P0781105). The shaft key had twisted about 10 degrees in the plastic. I cleaned that up but had to cut another keyway. I believe there is a metal gear available on AliExpress for about $20 plus shipping. It appears to be a Module 1.25, 38 tooth gear with a 12mm diameter shaft hole. That is the only metal gear that I can find that looks close to the original.









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Best to all,

Spajo


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