InTheBay's Open Source G0704 Belt Drive Conversion

Disclaimer! Currently, the design is in revision DRAFT. As such, it is not complete and will be updated as I complete the build myself

Hey Folks!

I'm a big supporter of the Open Source movement. So, I'd like to share for you all a simple G0704 Belt Drive Conversion. The plans are free to use and share, but not for commercial purposes, meaning they fall under Attribution-NonCommercial 4.0 International of the Creative Commons Standard.

This design is made to be elegant but simple. I could have gone with a two bolt pivoting method for tensioning of the belt, but that would require shoulder bolts and other more difficult to find fasteners. The key plan here is to make everything reasonably easy to do, with easy to find hardware. The gearing chosen is a slight bump in speed, but not enough to exceed the stock spindle bearings. For me, this is mostly a jumping-off point for me to play with gearing and motor sizing until I'm happy. And, of course, to quiet down that damn gear drive! I will update the hardware list once I have the full build speced out, but for anyone trying this early you can figure out which bolts need to be longer I'm sure. To reduce complexity its entirely possible to leave some of the more decorative features out (counterbores) to make this easier to manufacture.

Stock Required

Steel or Aluminum
2x 1.25 x (0.5 or 0.625) x 7.85
1x 4.375 x 3.75" x .5

Models and Drawings for Standoff and Motor Mount Plate

Link to Google Drive

Belt Drive Components
42 tooth "L" Series Belt, 1/2" Wide - PN# A 6R 4-042050
.375" (L) Pitch,21 Teeth, 0.625" Bore, 2 Flanges / With Hub, Aluminum Alloy Timing Pulley for 0.5" Wide Belt - PN# A 6A 4-21DF05020
.375" (L) Pitch,14 Teeth, 0.375" Bore, 2 Flanges / With Hub, Aluminum Alloy Timing Pulley for 0.5" Wide Belt - PN# A 6A 4-14DF05012

Quick Math
The max motor RPM I can see on my Spindle motor is around 4000. The above gearing choice gives a stepdown of 0.6667, equating to a max RPM of 2666. This is just slightly higher over stock, but take care if you wanted to gear your spindle up, you will have to select different pulleys. This system was designed with a 4.574" center to center distance. SDP/SI's center distance calculator should be able to provide you with some options. I chose to not bump my spindle speed up much as I plan to install a larger motor and bearings that can handle a higher speed soon.

Pulley Prep
Finish ream small pulley to 10mm shaft diameter (or 14mm, depending on your motor). This part is now done

Attachment 312542

Bore large pulley to 0.8515". Measure your quill shaft diameter to find your actual measurement, the preceding one is what worked for me.
Bore a step down 0.15" and to an ID of 1.000". This step will be where the threaded cap that retains your drawbar will sit.
Part protruding hub of large pulley. (Note: I knocked off one of the retaining side plates in order to get a good clamping location for my lathe, then pressed it back on with an arbor press after turning)
Drill and tap 4x 6-32 screws through the root of 4 equally spaced grooves in the center of your pulley. These are used to hold set screws to secure the pulley to your quill shaft

Attachment 312544
Attachment 312546
Attachment 312548

Installation: Will flesh this out with photos when I have completed my work.

Additional Hardware: Will flesh this out with photos when I have completed my work.

Sample G Code: Will flesh this out with photos when I have completed my work. <--- Would anyone actually want this? Conservative toolpaths with standard tooling, or is everyone like me and wouldn't trust a random .nc from the internet?

Reserved.

This is awesome. 3D models would be more useful than Gcode, but those drawings are all I need.

I didn't quite follow what you said about the gearing/RPM's. If I use the stock motor I should choose the pulleys to keep a max RPM of ~2600? But since this doesn't have a low gear option so we lose quite a bit of torque right?


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Quote:

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Originally Posted by Hypnotoad

This is awesome. 3D models would be more useful than Gcode, but those drawings are all I need.

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I found high gear with the stock motor and drivetrain to give me around 2200 RPM, so really, you're not losing much at the top end with a bump up to 2700. Even in steel it's possible to run a small endmill at the correct surface speed at 2700rpm and not worry about torque, in my experience with test cuts so far.

In the google drive folder there are parasolid files (.x_t files), can you not see them?

Note to all building at this moment, I have to make some slight changes to the Motor mount, as the width of the bolt holes is off a few MM, and I've had to use washers to stand off the motor in order to get clearance for a 5mm allen key to hit the mount bolts. Also, the counterbores should be a bit larger. Again, that's why there's a disclaimer. EDIT: Modifications complete, will be making changes and testing on my end shortly.

Currently I've designed the small pulley offset to be 0.125" from the motor, the width of a standard parallel. This should place your pulleys in line.

Quote:

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Originally Posted by inthebay

I found high gear with the stock motor and drivetrain to give me around 2200 RPM, so really, you're not losing much at the top end with a bump up to 2700. Even in steel it's possible to run a small endmill at the correct surface speed at 2700rpm and not worry about torque, in my experience with test cuts so far.

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Yeah, but if I want to run something big like a flycutter at low RPM you're giving up a lot of torque vs the stock low gear. Is there enough room to stack another set of pulleys like the Hoss belt drive design? I really like that this uses off the shelf parts instead of custom turned pieces.

Quote:

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Originally Posted by inthebay

In the google drive folder there are parasolid files (.x_t files), can you not see them?

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There's a lot of files in there and I didn't know what a .x_t file was. My CAD program can open those, so that should be helpful, thanks.

Quote:

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Originally Posted by Hypnotoad

Yeah, but if I want to run something big like a flycutter at low RPM you're giving up a lot of torque vs the stock low gear. Is there enough room to stack another set of pulleys like the Hoss belt drive design? I really like that this uses off the shelf parts instead of custom turned pieces.

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There should be room to stack pullies, but that's ultimately up to you to design. You would likely need to go to a smaller belt width in order to achieve this. I'll be refining this design over the weekend, and I'll be able to provide you with some numbers for max pulley clearances.

Yep, stock parts was the whole idea! And easy to find material as well. I'm running into some issues with clearance for the mounting bolts for the back side of the standoffs at the moment, I'm trying to alleviate that with some clearance slotting and offsetting the motor with plastic washers for isolation and clearance to boot.

Quote:

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Originally Posted by Hypnotoad

Yeah, but if I want to run something big like a flycutter at low RPM you're giving up a lot of torque vs the stock low gear. Is there enough room to stack another set of pulleys like the Hoss belt drive design? I really like that this uses off the shelf parts instead of custom turned pieces.
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I made Hossmans simple L belt version that just bores out a stock L timing pulley to fit the spindle like here but went with a 1:1 ratio to get about 5000 rpm. I did the bearing upgrade too.
am

Any updates?

I was wondering... If there isn't room to stack pulleys to get two sets of gearing, is it possible to just swap the spindle pulley when you want to use a lower gearing? That just involves loosening the belt and undoing some set screws right?


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Yes, you're correct there, you can always swap pullies. In my main post I list the designed center to center distance, so if you use SDP-SI's belt drive calculator (on their website) you can design a system with whatever gear ratio you want and that center distance, then bore the pullies to fit my listed dimensions and it will work. Everything on my end is on hold due to my machine being down from a bent X axis ballscrew. Awaiting Chai's replacement double-nut screw to arrive from China.

Would be nice to only swap the spindle pulley and not both pulleys + belt. Looking at a belt drive calculator I guess a ~5" pulley would work fine. But it will need a different length belt, obviously. Maybe I can just have two belts with one resting out of the way while the other is in use? I'm trying to avoid having to swap both pulleys and a belt to make the "low gear" thing happen.

I wonder if it might be better to just switch to bigger DC motor with way more torque and live with a single torque range.

How accurate does the boring out of the pulleys need to be? I have a boring bar and I think that will work fine, but I'm concerned about finding the center of that hole in a super accurate fashion. I don't have a lathe... yet... yet...

Bummer about your X screw. It always sucks to go into the shop thinking "I'm going to get this done" and walk out thinking "I guess I have to order some parts for the mill".

Quote:

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Originally Posted by Hypnotoad

It always sucks to go into the shop thinking "I'm going to get this done" and walk out thinking "I guess I have to order some parts for the mill".

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Story of my life....

I would want the hole to be within a thou, you can fudge it around some with the setscrews but ultimately any runout you get will create harmonics that could show in your surface finish. Stick a dial indicator in your spindle and zero her out then run your boring head through and scootch it out half a thou at a time.

Any Updates?

Just replaced my X axis ballscrew with a double nut unit due to a bent screw. Will have more on this in the next week or so. My slightly hacked up version is working quite well, and the only intended changes I have for it right now are moving the motor plate mounting holes outwards to give clearance for the allen key/boltheads holding that to the standoffs.