1" Bore Timing Pulleys

Does anyone have a source for a 1" diameter timing pulley? I’m flexible on HTD, GT2, GT3, etc. I just checked the usual suspects and nobody seems to have one. We’re working on a swerve drive project and were hoping to use one to rotate the steering tube with.

SDP-SI - no
B&B - no
McMaster - no
Martin Sprocket - no aluminum bushings
Quality Transmission Components - out of business

Gates appear to be the only game in town. I’ve never purchased anything through them outside of their KOP vouchers. From what I gather, all their pulleys are machineable and you have to add the bore yourself, which is doable but less desirable.

Anybody have any insight on where to get these, preferrably as a COTS item ready to use out of the box? If via Gates, do they work directly with teams or do you go through a local distributor?

It’s not likely that you’ll find a 1" bore on a metric sized pulley. That being said, you may be able to find a 25mm bore pulley, which can be opened up (25.4 mm = 1") for your needs.

If you don’t have machining resources, you could likely sand down the steering tube by hand. It’s only .014" difference, assuming you can get the 25mm bore pulleys

There are plenty of inch bore options available for all the sources, but I can’t find anything above 0.75". 25mm would be fine, we could work with that, but I can’t find anything that large.

Using a lathe, you can just buy pulley stock and make your own 1in bore pulleys. For example #A 6A24M024TM20 from SDP-SI is 24t 5mm HTD aluminum pulley stock. From this you drill in the ID of your choice and then wafer off individual pulleys with a parting tool.

If you go this route, always try to design around sprockets with a multiple-of-three number of teeth; this way it’ll be much easier to clamp the pulley stock into a 3-jaw chuck since the soft jaws will all align to the same phase of the pulleyteeth.

You make this sound fairly easy. Working with pulley stock has always looked like a lot of hassle to me. We have a G0602 bench top lathe, so I think this would be tricky for us to handle in house. Are there any other tips to working with these? And what is the intention of the shank that comes as part of the pulley stock?

Its not very hard to open a pully up. Just something to make sure of though is that when you try to bore out a plastic pulley with a aluminum center it will generate a huge amount of heat if done wrong potently slipping the plastic around the metal. This could really hurt the operator. We ran in to some problems on our swerve; lost a boring head…

Also make sure the aluminum core has the room for a one inch bore.
In the end we went with a solid aluminum pulley for the steering.

The 1640 history with the development of there swerve is a great tool for this type of thing.

We could not find a cots pulley that was with in a reasonable price with the bore at 1"

We use HTD5 all AL pulleys and then bore them out on the lathe. Plastic pulleys we have found do not have the clearance to drill out with a key way. We found it better to drill in several steps from 1/2" to 1". Our HTD pulley supplier got out of the business and we are looking for a new supplier. Lead time can be a problem.

I’m making the assumption that because you are making a swerve, you have some sort of CNC milling ability. When we made ours, we bought pulley stock, cut it on the band saw, faced it, and drilled a small center whole in the lathe. Then we put it in the mill, and put the zero on the small whole with a center finder. We then ran a program that lightened the pulley and opened the 1" bore.

It’s a bit of a long process, but we only have a table top lathe as well.

For 5mm pitch and above pulleys it’s actually a big enough tooth to comfortably cut on a mill.

So for a pulley where you might be doing a lot of machining. Pocketing, mounting holes, custom bore, etc… it’s actually easier for a shop to make the entire pulley (versus precisely zeroing on existing geometry).

We found a 2.5mm cutter is about the biggest cutter you can fit in 5mm pitch teeth. The OD of the pulley was roughed with a fairly large cutter, the teeth were roughed with a 3/16 or 5/32 and then finished with the 2.5mm. It wasn’t crazy runtime, a few minutes per pulley iirc.

That’s a fair point, and if we trusted ourselves using a bit that small at the time we cut our pulleys, that’s probably what we would have done. Some What against our best judgment, the swerve that we built this year, was one of the first things we had done with a CNC mill. The smallest bit we consistently trusted ourselves with was 0.25". It would have been nice to cut it ourselves thought, would have saved money and possibly time.

That lathe should be able to handle that task with no problem. Is there anyone with lathe experience you can find? If not, PM me and we can go thru all the settings and tooling needed to slice off, face and bore your own pulleys from pulley stock, or to just bore out pre-made pulleys.

Cutting keyways, if needed, may be a little tricky but not awful. If broaches are not available you can use the lathe as a shaper.

Opening up the bore on a pre-made pulley can be done on a manual mill relatively easily with a boring head. Just indicate the pulley bore, put the boring head in and bore it out to 1".
On a lathe the operation would be pretty similar, I would think, except you would not need to indicate.

As a side note, swerve drives do not require CNC capabilities provided you are okay with a small amount of added weight (due to less pocketing).

Or people with a lot of free time and some decent skill.

Gdeaver - I noticed in the 1640 CAD models that you guys chose a 32T, 5mm HTD x 15mm wide setup. Are you able to offer any details about how you arrived at this selection? I’m curious if it was a function of product availability, or if it was more based on torque requirements?

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).

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.

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.