belt reduction, parts suggestions needed!

[tmbg]

Hi folks!

I'm designing a super simple 5:1 belt reduction for NEMA 23 steppers to drive pinion gears for rack&pinion setup.

The problem I'm running into is that all the pinions that suit my application have 1/2" bores, and all the MXL or XL timing pulleys have 1/4" or 3/8" bores!

Does anyone have any suggestions on what to use as a countershaft? Otherwise it looks like I'm stuck machining one, which I was hoping to avoid

[tmbg]

Ok, so I had some time to draw tonight, and here's what I came up with.

I'll have to machine the countershaft down to 1/4" for about an inch, but other than that it's pretty simple. The bearings are preloaded by a couple of belleville springs, and the countershaft can't pull out the pinion side because of the setscrews in the timing pulley and the fact that the pulley and both bearings are in compression between the plates due to the belleville springs.

Also noteworthy is that it's designed at 3:1 now. My original ratio was 12:60, but the smallest timing pulley with a 1/4" bore (steppers have 1/4" output shaft) were 20 tooth, so 20:60 it is!

[tmbg]

Here's the finished product. I added an idler for tensioning the belt.

[nomedia="http://www.youtube.com/watch?v=KP-gzXDXcaI"]YouTube- 3:1 belt reduction[/nomedia]

[harryn]

Hi, that is pretty neat.

I have been looking at belt reduction and drives for a while, but don't have the machining capability. Instead, I have been just planning around using either 1/2 in or 12mm shafting, as that seems to be sort of a standard for NEMA 23 and 34 sort of power levels.

I think the more common approach is to bore out the pulleys than to cut down the shaft, but either way works.

Similar to you, I could not find an easy way to do more than about 3:1 reduction in each stage, although I am not quite sure why it is this way. In order to go for a greater reduction per stage, it required changing shaft sizes.

The xl belt is pretty common, although I am still debating on using AT belt.

Thanks for posting that video. Is this just for your own use or are you planning to sell that setup?

Thanks

Harry

[tmbg]

I thought about boring out the pulley, and since the countershaft has the bigger pulley, I totally could, however I tend to always want to cut the cheaper part. A foot of thompson shaft was only a couple bucks and was enough material to make several shafts. The pulleys, on the other hand, are like $20 each.

My original thought was 5:1, because I could get 12t and 60t MXL pulleys. However, after I ordered and received them, I realized the 12T had a 1/8" bore, and my steppers of course are 1/4". The 3:1 however is better suited to my machine.

I built them for my own use, but I'm certainly willing to make some for others if there's interest! I make them by hand, so I won't have a tremendous amount of production volume. Also, I don't consider my tensioner setup to be exactly production quality.

Here's another video which was posted elsewhere, but it shows the drives in use:

http://www.youtube.com/user/imcmahon.../0/Js6UrSQZ2bc