View Full Version : timing belt and pulley

22-08-2015, 01:23 PM
been searching since yesturday to try and find an awnser for my question but cant seem to find one, im following a design ive seen regarding the z axis and i like how he has hidden his z axis motor rather then have it sticking up in the air but he uses pulleys with a 10mm pitch and im just trying to find out how to work out how wide you need the belt and pulleys, what ratio, how many teeth and the difference between 5mm pitch and 10mm pitch.

also how would i go about fitting a pulley onto this nema 34 motor?




Robin Hewitt
23-08-2015, 10:12 PM
Are you sure the pulleys are 10mm pitch, not the lead screws?
I usually use XL pulleys because I like a lot of teeth engaged and there is no slop like you get with a T5.
Spread the load, belts do not break they shed teeth, use big pulleys with lots of teeth.
Cutting a key slot without a broach is not hard if you have the right file and know how to use it.

24-08-2015, 08:04 AM
Just use a HTD-5M pulley that accepts a taper locking bush, then there is no need to bore it out or add a keyway. Robins advise about having enough teeth meshing is a must.

Boyan Silyavski
24-08-2015, 10:28 AM
HTD 5M 15mm wide is the standard belt size most people on this and other forums use for nema 23 and 34 motors and servo motors.

20t pulley is the perfect balance of size, teeth in mesh, torque, limiting space and speed, etc...

20t:20t for 1:1 is perfect. 20:30 for 1:1.5 is perfect, 18:36 for 1:2 is perfect

where according to me 36t is the limit for large pulley and the same time fast machine. for ratios 1:3 and bigger, additional considerations must be made, inertia, weight, motor type and speed, acceleration desired, teeth in mesh, etc...

The best and most correct belt calculator (http://www.bbman.com/catalog/belt-length-calculator.html). Where if say 100mm is calculated distance even a bare 102-103 mm will tighten the belt excellently, especially important where you have servomotors in play which have quite wide central part that limits the adjustment possibilities of mounting holes, though an additional plate for an additional adjustment can be fashioned

manufacturers recommend ~6t in mesh at least for that belt. where doubt arises due to weight or speed, more belt info should be read and check spec tables for the correct belt choice.

When i say "perfect" above, i mean long belt life, low inertia, not pushing the belt to its limits.

Hope that helps

Web Goblin
24-08-2015, 07:31 PM
I would bore out the pulley and broach it for a key. Also drill and tap above the keyway for a grub screw. I would because ive just done it for 4 pulleys for nema 34s.
The only problem I had was that I bought a spare nema 34 a while ago just in case I needed one. All bought from zap and all have the same part numbers. The only difference was that the new one has a smaller shaft diameter than the older ones. No prizes for guessing which shaft I measured before I made the broaching socket, drilled the pulleys and cut the keyways.
Ah well at least a smaller hole can be bored out.

Tom J
07-10-2015, 09:40 PM
Personally I use only HTD pulley - mostly 5M - 15mm wide. I used to try T5 and was not happy with backlash.
As Boyan explained number or teeth matters, so my smallest pulley has 15 teeth. Ratio:
I never use bigger pulley than 60t due to size.
for bore start from 10mm I use broaching tool with key way 2mm wide. Biger bore wider key way. For 1/4" =6.35mm I drill and tap grab screw - start from 3mm for 15t - see photos