Metric Sprockets?

[lukevanoort]

I've been looking for some small (tooth counts in the teens) 6.35mm pitch sprockets with an 8mm bore and a 2mm keyway, ideally hubless. I have looked at WM Berg, McMaster-Carr, SDP/SI, Misumi USA, the Robot Marketplace, Small Parts, Motion Industries, MSC, and Grainger; unfortunately, none of them have what I am after (even with hubs). The closest I have found to what I want are the hubless 6.35mm pitch 8mm plain bore sprockets at SDP.

So, anyway, I'm wondering if anyone knows of another place that I've overlooked that might have them, or, if there aren't any available, how realistic it is to file a keyway in one of SDP's sprockets (we lack an arbor press, but have a decent number of freshmen). If it matters, the sprockets would be driven at 0-5.5k rpms and at a maximum torque of ~1.5N-m (although they would usually be operating at much less).

[chris31]

Have you tried Boston Gear? I would check for you but I cant seem to find my catalog in my room. Even if you dont have an arbor press I would think someone locally would and could do it very cheap.

[Teched3]

If you are looking for metric sprockets because of the 2mm keyway, you would be better off using SAE chain and sprockets, and getting a 2mm broach and a bushing to match the bore in the SAE sprocket. You can buy an arbor press pretty inexpensively from Northern Tool Supply or Harbor Freight. You can also check a local machine shop on using their arbor press, or another school/team in the area to use theirs. There are limitations of the length of the keyway that is dependent on the length of the bushing. Check in MSC catlogue for these items.

[lukevanoort]

Originally Posted by chris31

Have you tried Boston Gear? I would check for you but I cant seem to find my catalog in my room. Even if you dont have an arbor press I would think someone locally would and could do it very cheap.

I just looked at Boston Gear (they seriously need to revise their website, I usually avoid them because of it... Martin sprocket is worse though) and they don't seem to have metric sprockets at all. However, #25 and 6.35mm pitch chain are pretty much the same, but the bores were too big anyway

As for the broaching, I agree, there probably is someplace local that could broach the sprocket, but I'd rather try to keep machining "in-house," if possible (or, at least, have it be possible to do with our current resources and have external machining just be a bonus)

EDIT:

Originally Posted by Teched3

If you are looking for metric sprockets because of the 2mm keyway, you would be better off using SAE chain and sprockets, and getting a 2mm broach and a bushing to match the bore in the SAE sprocket. You can buy an arbor press pretty inexpensively from Northern Tool Supply or Harbor Freight. You can also check a local machine shop on using their arbor press, or another school/team in the area to use theirs. There are limitations of the length of the keyway that is dependent on the length of the bushing. Check in MSC catlogue for these items.

I just looked at Harbor Freight, and it seems that they have a 1 ton arbor press for ~$30 and a 2mm broach with bushing is $53 from MSC. $83 without shipping isn't that bad I guess and the arbor press could come in handy in other ways.

[Tristan Lall]

I believe that ANSI B29.1M is equivalent to the ISO sprocket standard, meaning that the 6.35 mm sprockets are designed to be interoperable with 1/4 in (#25) sprockets. That means you can just search for ANSI sprockets, which are far more common.

Also, for the bore, if you can find something smaller than 8 mm, would you be able to enlarge the bore on your equipment? 5/16 in bore would be especially good, because 5/16 in = 0.3125 in, which is close to 8 mm = 0.3149 in, so you could ream it.

The keyway is a sticking point, though; without the right tools, it's not easy to make a good one. I've used an awesomely ugly setup involving an end mill ground into an approproiately wide chisel, and inserted into the quill of a milling machine (), which was then moved up and down (manually) as the bed was slowly indexed. It's ugly, but lacking an arbour press, the machinist who owned the mill suggested this.... More recently, I've used an ancient EDM machine for the task, with mixed results (it's slow, and the setup has to be very accurate); in any case, EDM work is probably not an in-house operation. If you're desperate, you can file it, but be very diligent with the setup process. It would be best to transfer the outline of the keyway to the sprocket on both sides, so that the ones doing the filing and cutting can make sure that the keyway is not skewed (which is just about inevitable, otherwise). This might possibly be done by printing out a scaled drawing of the part, and overlaying it to make scribe marks, or by aligning everything in a fixture in a mill, and using the readout to find and mark corners, then scribing lines.

In any event, what you've found is hardly ideal, but I don't think you're going to easily find anything better, at any price.

[sanddrag]

An arbor press is one of the most useful of the large tools to own for FIRST robot building. However, if you lack one, you can use a drill press (not recommended really. They aren't well built enough for the force required), milling machine, or lathe as a press, as long as you are careful, go slow, use lots of oil, and most importantly, the material isn't too hard.

[Fe_Will]

I'd look at Linn Gear if you are set on metric over ANSI sprockets. They can make any sprocket or gear you will ever want.

I can't see building a robot without a good set of broaches and an arbor press.

[Dick Linn]

Some people use a lathe to broach keyways, similar to the mill idea above.

[Greg Needel]

try this http://electricscooterparts.com/sprockets.html they sell parts for most of those cheap electric scooters you see at pep boys and since most are made in Asia they use metric sprockets.

There are also some really neat other things on the site, like large dc motors, one way drive clutches and a few other things I have used for projects in the past.