# Belt Drive Conversion for Grizzly G0704



## SEK_22Hornet

I've seen a couple different sets of plans that could be bought to build a belt drive conversion.  I decided to try my hand and designing and building my own.  I purchased some XL series timing pulleys and a belt from Econobelt to work with.  The driven pulley for the spindle is a 36 tooth metric bore (8mm) with a 45 mm hub.  That works out to be the same diameter as the G0704 spindle, which simplifies mounting the tach wheel. The driven pulley is machined to fit over the end of the spindle in place of the tach wheel and is mounted by the same holes that held the tach wheel in place.  I'll either draw this up or post more detailed dimensions once I get a little farther. Here is what i have so far.



	

		
			
		

		
	
Here are the parts that I started with.  The largest one is the 36 tooth pulley.  The other three are pulleys that I intend to select a drive pulley for the motor from.  The black ones are 25 and 27 tooth nylon with aluminum hubs and 10mm bore, which is very close to the motor shaft size.  The flanged aluminum is a 25 tooth with an 8mm bore that i would need to bore out.




	

		
			
		

		
	
 These three views just show the un-machined pulley with the tach wheel sitting on the hub - since it is the same diameter as the top of the spindle, it will need no further machining.  






	

		
			
		

		
	
These views show the enlarged bore of the pulley (to clear the drawbar), the recess to center the pulley on the spindle (bored into the flat side of the pulley), the shortened hub, and the mounting holes drilled to match the holes in the spindle and the tach wheel.  They also show how the tach wheel and pickup will sit on the new pulley.


	

		
			
		

		
	
Here are the pulley and tach wheel mounted in place on the spindle.  I bored the recess that sits over the spindle to a nice snug fit so that it transfers any side force tot eh spindle directly instead of to the two 3mm socket head cap screws. Out of time right now, so I'll post more later.


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## Rbeckett

Is that a pneumatic drawbar on top?  If so could you explain how it works withoit having a swivel fitting to turn at the top.  I am pretty uninformed about power drawbars and would like a bit more info to help decide if one is for me or not.

Bob


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## SEK_22Hornet

Nope - not a power drawbar - that's just the way it is  on these mills.  The drawbar is captive - the top little square is the part you have to turn to tighten or loosen the drawbar.  The part that looks like a cylinder is just the cap that holds it down.  It does eliminate the need to tap the drawbar to release the collet. The cap screws off if you need to pull the drawbar out for some reason.


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## kizmit99

Definitely interested is seeing how this comes together!
Thanks for sharing.


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## SEK_22Hornet

Haven't had much time to work on my project but do have a couple updates.  I pulled the gear off of the motor. There is a snap ring that hold the gear on, but it is a very tight fit. I had to use a gear puller to remove the gear. The key was staked into the motor shaft.

- - - Updated - - -

The pulley has a 10mm bore, but it is too tight to fit the shaft. It would probably press on, but I don't want to take the motor apart or take the chance of damaging anything, so I opened it up to a slip fit and drilled and tapped the pulley for a 6-32 x 3/8" set screw. I clamped the pulley in the vise on my mill, chucked up a small end mill and lowered the cutter until it made a small flat on the highest point on the hub. This marked the center for me.  I used center drill to spot the hole location then drilled the hole and tapped it. (If this sounds familiar to some of you, I am pretty sure i read about doing it that way here on this forum  ) I positioned the set screw in the keyway to prevent the end from marking the shaft. Next step is making a motor mount, which I hope I will get to work on this weekend.

Dan


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## fretsman

> I'll either draw this up or post more detailed dimensions once I get a little farther. Here is what i have so far.



Wow, that would be fantastic as I would like to do this as well. 

I'm following your thread with very much anticipation to see your results,

Thanks for sharing-
Dave


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## SEK_22Hornet

I did manage to get a motor mount made this weekend but still need to take some photos of it.  I need some different hardware as well.   I was able to run it with the belt drive and actually made a couple small cuts, just trimming off a couple brass spacers to mount the tach pickup.  Then the set screw in the motor pulley let loose, so I know I need to rethink the motor pulley mounting. I was using the nylon pulley with the aluminum hub, but I will probably end up using an aluminum pulley so that I have enough metal to cut a keyway. That presents a problem for me, since I don't have a broach.  I'm thinking of using an end mill to make a cut then square it up with a file. I'll probably wait to post the pics until I have the right hardware.


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## SEK_22Hornet

I have some work to do on the motor pulley to get it to hold on the shaft. I'm trying to figure out the easiest way for me to cut a keyway in the bore, so I'll have to think on that for a bit.  Here is the motor mount that i came up with - very basic - just 4 round spacers made from 3/4" 6061 bar stock.  The motor mount plate is a simple piece of 1/4" thick 6061 plate.  I'm still very much a newbie, so the not so round cut-out for the motor shaft and pulley shows my lack of experience - I need to get a flycutter.


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## SEK_22Hornet

I have all the hardware I need, except one set screw that should be here this week.  I still need to machine a couple spacers to set the tach pickup at the right height, which won't take long.  I think it is going to work out pretty nice.  I'll take some final photos as soon as I get the last couple things done and put a parts list together. All of the work can be done on a mini lathe and the mill itself, unless your mill is down.  Cost wasn't bad at all - probably under $100.  Nothing hard to find - everything I used came form either Fastenal or Econobelt, except the materials for the new motor mount, which I got off ebay from exact_metals.

More later - Dan


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## fretsman

Thanks so much for the update, Dan, looking forward to it- )

Dave


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## pestilence

This mod precludes the use of the quill, correct?  I actually prefer using the quill rather than the Z axis when I can.  It's frustrating to me how non-knee mills want to dive downward and I pretty much have to run with the Z axis locked.  I'd really like to get the extra RPMs out of a belt drive conversion, though.


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## SEK_22Hornet

pestilence said:


> This mod precludes the use of the quill, correct?  I actually prefer using the quill rather than the Z axis when I can.  It's frustrating to me how non-knee mills want to dive downward and I pretty much have to run with the Z axis locked.  I'd really like to get the extra RPMs out of a belt drive conversion, though.



This mod allows full travel and use of the quill. As soon as I get the tach pickup mounted, I'll let you know what the RPM is. My shop isn't heated and it just started getting cold here, so my shop time will a little more limited. I suppose an industrious person could calculate the rpm based on the original gear train ratio compared to the new belt ratio - I used a 25 tooth motor pulley with a 36 tooth spindle pulley.  I had seen one on the net done with two 32 tooth pulleys but that one indicated that the bearings would not take the extra RPM, so I opted to gear it down a little.

Dan


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## pestilence

Oh AWESOME!  Time to start planning


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## mrich0908

Ive tore mine apart . 
Took my spindle out stared at it scratch my head put it all back together... I have a very pretty Nordictrak 3.5hp/Kbmm 125 board & motor here waiting to go on it but just cant figure out how to mount the pulley and keep my quill. 
I like using it for setting my Z height and power tapping. 
If you would be so great to me and explain how to add a pulley to the set up and keep you quill I would be grateful. 
Thanks
Mark


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## SEK_22Hornet

First of all, have you looked at the photos? Look them over and read this a couple times and maybe it will be a little more clear.  If you look at the spindle while it is installed, you will note that there is a small amount above the snap ring at the top of the bearing.  The tach pickup ring is mounted to this with two small screws. Take the tach ring off.  What I have done is turn a recess in the flat side of the aluminum pulley just large enough to fit snuggly over the small amount of spindle sticking up past the snap ring. It should bottom out on the spindle and not against the snap ring.  I then drilled two holes to line up with the holes that originally mounted the tach pickup, and bored the rest of the pulley to the same diameter as the inside diameter of the spindle, to allow the drawbar and everything to pass through it.  I then bought screws long enough to go through the pulley and the pickup ring and thread into the two holes in the spindle that originally held the pickup ring in place. Now in my ideal world, I would like to drill two or 4 more holes int the spindle to make a total of 4 or 6 screws holding the pulley on, but I don't feel confident doing that just yet, so I'm leaving it at 2 screws for now. I used socket head cap screws - make sure you use good ones.  I'm hoping that the recess will help support the side stress of the belt and leave the screws to hold the pulley in place with more of a clamping action with less shear force on them. I used a couple spacers to move the pickup ring u in line with the new location (just finished that today!). Here are a few more photos.  With a 25 tooth motor pulley and a 36 tooth spindle pulley, I'm getting about 2600 RP forward speed.


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## mrich0908

Thanks for the explanation. 
It really helped me . I going to give mounting mine a try 
~Mark


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## SEK_22Hornet

mrich0908 said:


> Thanks for the explanation.
> It really helped me . I going to give mounting mine a try
> ~Mark


You do realize that photos of the work are expected )


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## mrich0908

SEK_22Hornet said:


> You do realize that photos of the work are expected )


Will do , 
I hope to get around to it soon me or the machine is making parts usually .  The stock motor is a real dog when your use to using bigger.


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## ozzie46

I'm thinking of doing this to my g0704. My plastic gear just bit the dust. 

 How do you figure which belt you need? And how long it needs to be.

 I see you used the 25 and 36 tooth pulleys so I will go with them. 

 Ron


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## Madmiller

HA- 
 My nylon gear just stripped as well! Im taking this on along with ac bearing switch out. 
Thanks for the info this is a great jumping off point! 

:thumbsup::thumbsup:


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## zaaephod

I'm curious how this worked out. Are you cutting steel with it using the factory motor? I'm planning to do this conversion as well, but I was worried that at low rpms, the motor may not have enough torque, even considering the vfd.

Thanks!


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## zaaephod

I went ahead and did this mod yesterday, I'd post pictures, but it's pretty much identical to what the OP did. To answer my question, the machine has no problem cutting mild steel down to 600 rpm, the VFD does a great job of maintaining the rpm. As an added bonus, my cuts are looking much cleaner than when it was gear driven. I'd imagine that's because there's no backlash now between the motor and the spindle, where the gears would obviously have a bit of play.

I'd recommend this project!

Thanks for taking the time to post your work, you've saved me a bunch of time.


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## fretsman

C'mon zaaephod, please post pics, there always something new to see )

Thanks-


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## zaaephod

Tell ya what, I'll post pics when I'm done with my pneumatic draw bar project, hopefully this weekend.


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## fretsman

That would be awesome thank you, might as well start your own thread then, but looking forward to both projects!

Thanks again-
Dave


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## zaaephod

I did end up posting a new thread for the pneumatic draw bar, here's the link .. http://www.hobby-machinist.com/show...Pneumatic-draw-bar-and-belt-mod-with-pictures


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## mrich0908

As I promised I would post a pic when I did the new motor. I still have allot to do .Sorry for the crappy pic I will try to post a better one if any one wants to see it.


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## SEK_22Hornet

ozzie46 said:


> I'm thinking of doing this to my g0704. My plastic gear just bit the dust.
> 
> How do you figure which belt you need? And how long it needs to be.
> 
> I see you used the 25 and 36 tooth pulleys so I will go with them.
> 
> Ron



With the extreme cold weather, i have not had a chance to use the machine much since the conversion - as for how to figure the belt, I took center to center distance between the pulleys and added half the circumference of each pulley to come up with the belt length.  Or, since you can see the part number on the belt I used in one of the photos, if you use the same pulleys, you should be able to use the same belt. I chose the 36 and 25 tooth pulleys to get a slight speed increase without going too far - one article I read about the conversion used two 36 tooth pulleys, I believe, and the author warned that the result was faster than the stock bearings were rated for, so I deliberately kept it on the low side. I'm hoping to spend more time in the shop now that the weather is starting to warm up a little. Glad my tinkering helped some of you out with your machines! Nice to hear positive reports from those of you that had good luck with this method. Interesting to hear the comment about smoother cuts, too.


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## ReP_AL

Hello,
New to the site and just in the middle of my own belt drive conversion albeit on an Optimum BF20.  

I had been wondering how to fix the Drive pulley onto the spindle carrier and see now how its done on the G0704.  The 5mm flange that sticks up has no screw holes in it on the Optimum as the RPM's are measured with a sensor and magnets.  

Can I ask you the diameter of the screw you used and the thickness of the 5mm flange?  In other words how much meat was left on the flange around the threaded holes.  I am a little worried about making the hole too large and the walls too thin, but at the same time want enough thread bite to hold the pulley.

Thanks!
Phil.


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## compsurge

If I examined your previous photos and description correctly, you opted to not reinstall a key on the motor shaft and instead just used a set screw? Please correct me if I am mistaken on my observation, but this will only serve to destroy your keyway as the screw digs into the sidewall due to the cutting forces on the spindle. It didn't look like Grizzly gave you a very pretty motor shaft keyway from the start either, so it may not be any worse with your method.

Do you have plans to build a better stand? I find the sheet metal stands are too flimsy for the feed rate possible with higher spindle speeds on these machines and only serve to add vibration.

Others may want pics... I expect YouTube video of high speed material removal!


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## SEK_22Hornet

Rep_AL - The screws are 3mm. I have been using my mill recently for work on brass, so I have not been too worried about the pulley mounting and have not had any problems with it yet. I did not measure the thickness of the wall, but it is pretty thin - from memory only - I would say between 5 and 6 mm. I would still like to pull the spindle out of mine and add a couple more screws sometime.

compsurge - yes, you are correct - I did just use a set screw in the keyway. The 6-32 did not work out, so I ended up going with a 10-32. It holds now. I'd love to cut a proper keyway in the pulley and do it right but I'm just not there yet. Oh - and yes, the shaft of the motor (including the keyway) wasn't very pretty! The stand is working OK for me right now - I actually  need to work on the shop floor so that I can get it sitting a lot more solid! 

I have a round column mill/drill that I use for heavier projects, so I keep the work on the 704 on the lighter side. the heaviest thing I have been doing lately is cutting a radius on .75 x 1.25 blocks of brass using a small rotary table and a .5 end mill.


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## Inskeep

I know this is old thread.
Where did you get that 36t pulley with that large hub.
I cant find any that look like yours
Thanks


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## zaaephod

Inskeep said:


> I know this is old thread.
> Where did you get that 36t pulley with that large hub.
> I cant find any that look like yours
> Thanks



I tried to find where I ordered my pulleys, but can't seem to come up with it. It has been a few years since I did this modification. I can tell you though, the pulley I ordered had a much smaller bore, I had to turn it on the lathe to get the bore size needed, as well as drilling the mounting holes.


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## Inskeep

Thanks for reply
So how is it holding up? Did you add more screws?
Again Thanks
Ken


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## zaaephod

I did not add any screws more screws, they held up just fine, however I have made some other changes. 

A bit of back story is needed, I think. Shortly after I got my mill, I managed to break one of the plastic gears inside the mill head (my own fault), which led me to doing the belt drive upgrade. The problem was, the rather weak stock motor sometimes wasn't up to the task at hand, there just wasn't enough torque at low rpms being run direct. I have since converted the machine to CNC with ball screws. (I used the Hoss Machine Phase 3 plans) Currently, I'm running the belt drive to the gearbox so I can use the high / low selector knob. My hope here is that while I am still using the plastic gears, with any luck the belt would give instead of breaking another gear. That's also the reason for the narrow little belt. I've been running it like this for the last two years with no issues, but to be fair, it doesn't get run all day every day. 

If I ever find a worthwhile and affordable VFD motor and drive, I might either make my own metal replacement gears, or consider building some sort of pulley system. I'm always interested to see any modifications other people have made to their G0704 machines.


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