1" Bore Timing Pulleys

[AdamHeard]

Originally Posted by Gdeaver

Our choice of the 32t HTD5 pulley is part historical and torque requirements. Do not under estimate the abuse the steering components take. The 15 mm belts do stretch over the life of the robot and our key ways do loosen up. That's after a whole season with over a hundred hours of drive time. It sucks up enough of the build season with just boring the pulleys. I don't want to add the time to make them. If we could find a cots pulley I would buy it to save time. Custom pulleys add cost and lead time.

This certainly depends on the team and their specific resources.

We now have the resources in house, and at sponsors, to make a pulley with all the pocketing and mounting holes (for a bolt circle) we might desire out of solid stock in about 10 minutes of machine time (this includes a 2nd op on a manual lathe to face to thickness) per pulley, and at a lower material cost than purchasing pulleys. This reduces both cost and lead time (for us).

There are certainly many cases where COTS is the better option.

What's really key is constantly re-evaluating your own resources and best designing to match what you have (and also pushing to add resources to fill the holes you have).

[Jared]

Originally Posted by AdamHeard

This certainly depends on the team and their specific resources.

We now have the resources in house, and at sponsors, to make a pulley with all the pocketing and mounting holes (for a bolt circle) we might desire out of solid stock in about 10 minutes of machine time (this includes a 2nd op on a manual lathe to face to thickness) per pulley, and at a lower material cost than purchasing pulleys. This reduces both cost and lead time (for us).

There are certainly many cases where COTS is the better option.

What's really key is constantly re-evaluating your own resources and best designing to match what you have (and also pushing to add resources to fill the holes you have).

Do you mind sharing your process? I've played around with toolpaths for pulleys in MasterCAM, but we need a smaller than .125" endmill for the 5mm HTD profile. Do you put a circular feature in the center and broach a hex, or do you try to make the hex on the CNC (if you even use a hex at all)?

[AdamHeard]

Originally Posted by Jared

Do you mind sharing your process? I've played around with toolpaths for pulleys in MasterCAM, but we need a smaller than .125" endmill for the 5mm HTD profile. Do you put a circular feature in the center and broach a hex, or do you try to make the hex on the CNC (if you even use a hex at all)?

We use a 2.5mm end mill for the teeth. (after roughing with larger end mills as described above).

We've run the hex both ways. Round then broach, or milled on the machine with the corners drilled out.

Let me know if you need more information.

[sanddrag]

For those of you making your own pulleys, what CAD files are you using?

[Aren_Hill]

Originally Posted by sanddrag

For those of you making your own pulleys, what CAD files are you using?

I've had decent luck cutting from SDP-SI's Cad files before.

All of the VEXpro pulley CAD models are True HTD profile.

-Aren

[Jared]

Originally Posted by AdamHeard

We use a 2.5mm end mill for the teeth. (after roughing with larger end mills as described above).

We've run the hex both ways. Round then broach, or milled on the machine with the corners drilled out.

Let me know if you need more information.

Do you have any techniques for doing this well? We had a bad experience with really small tools (1/8" end mill for hex, 1/16" drill for corner point holes) in steel. We were feeding at under 1 IPM for most of it yet we managed to still break bits. I'm guessing it's quite a bit easier to do this in aluminum.

Also, would you recommend purchasing a hex broach? We don't have one, and we've recently ended up buying a bunch of gears/pulleys/sprockets that we could likely broach ourselves.

Originally Posted by sanddrag

For those of you making your own pulleys, what CAD files are you using?

We've 3D printed with vex pro, B&B manufacturing for gates profiles (http://www.bbman.com/catalog/category/timing_pulley) and SDP-SI.

[AdamHeard]

Originally Posted by Jared

Do you have any techniques for doing this well? We had a bad experience with really small tools (1/8" end mill for hex, 1/16" drill for corner point holes) in steel. We were feeding at under 1 IPM for most of it yet we managed to still break bits. I'm guessing it's quite a bit easier to do this in aluminum.

Also, would you recommend purchasing a hex broach? We don't have one, and we've recently ended up buying a bunch of gears/pulleys/sprockets that we could likely broach ourselves.



We've 3D printed with vex pro, B&B manufacturing for gates profiles (http://www.bbman.com/catalog/category/timing_pulley) and SDP-SI.

We don't do it in steel, there is no reason for the pulleys to be steel imo. I do know feeding too slow can be a problem, there are formulas out there for all this that others can cover.

We rough cut the OD of the pulley with a larger cutter (1/4" and above) to .020" or so larger than the actual OD. Then we rough the teeth partially with a 3/16" or 1/8" cutter (I forget), and then finish with a light pass with the 2.5mm cutter. I don't know exact feeds, speeds, depths, etc... but on our router (which is not a very fast accelerating machine currently due to steppers) it was ~ 6 minutes for the entire pulley (including pocketing) for a 24T 5mm pitch.

I would heavily recommend broaches, at least a 1/2" one at this point. Followed by 3/8". It really opens up your COTS options as quickly adding hex bores becomes easy. I'd recommend getting the matching size reamers to make machining that much faster.

[asid61]

Originally Posted by AdamHeard

We don't do it in steel, there is no reason for the pulleys to be steel imo. I do know feeding too slow can be a problem, there are formulas out there for all this that others can cover.

We rough cut the OD of the pulley with a larger cutter (1/4" and above) to .020" or so larger than the actual OD. Then we rough the teeth partially with a 3/16" or 1/8" cutter (I forget), and then finish with a light pass with the 2.5mm cutter. I don't know exact feeds, speeds, depths, etc... but on our router (which is not a very fast accelerating machine currently due to steppers) it was ~ 6 minutes for the entire pulley (including pocketing) for a 24T 5mm pitch.

I would heavily recommend broaches, at least a 1/2" one at this point. Followed by 3/8". It really opens up your COTS options as quickly adding hex bores becomes easy. I'd recommend getting the matching size reamers to make machining that much faster.

A side note on hex broaches: if you do buy one, make sure you have a press big enough to fit the broach. My team bought a $200 1/2" hex broach, only to discover we would need to go to Lynbrook to use their hydraulic press to broach anything.