Need Help!- Timing pulley to stepper adapter.

[croosh]

Hello everybody,
I am building my first serious CNC router table (36" x48"). I decided to give timing belt a try, since ball screws are prohibitively expensive.
The problem I have is that the stepper has 1/4" shaft, and the pulleys I have have 5/8 taper bore.
Is there a commercially available adapter or a bushing? I don't have the axes to a lathe, unfortunately.

Thank you
Yuriy

[ahren]

You could drill the taper out to a standard dowel pin size, and then get a rigid stepped coupler and a dowel pin to adapt from your dowel to the 1/4" shaft. If you're careful, even a hand drill should self-center as you drill the hole. But the cost of the coupling will likely be the same as a new pulley, so unless you're set on using this pulley for some reason, I don't know why you would. Shaft couplers (and dowel pins) here: www.mcmaster.com, www.mscdirect.com, www.use-enco.com. Pulleys here: https://sdp-si.com/eStore/. Good luck!

Ahren
www.cncrouterparts.com

[jeb]

Hi,
I too am working on a belt drive machine of about the same size. What kind of belting do you plan to use? (THK uses 25mm wide ~5mm pitch steel reinforced belt. This stuff is really expensive, but it works well.) What kind of drive ratio are you planning on? I am using THK linear actuators that have a ~35mm pulley. I ended up making a 20:1 worm drive gear reduction because otherwise 1 stepper revolution= 110mm travel!
Hope this helps,
Jacob

[croosh]

Hello,
I am using 25mm (1") wide "L" bet with 0.5" pitch (about 12mm) with kevlar reinfocement. I found it at $6/ foot (~330mm)
I will have two of those on the long axis. According to my calculations 1 will be mre than enough. I will probably use 5:1 reduction or so. My steppers can do 2 degree steps with 260 oz in holding torque, and the driver I have can do 1/8 step. 1 rev of the motor is about 8" or about 20cm. For what I will be doing 0.01" resolution is more than enough (since for all practical purposes DIY machine will not be more accurate than that anyway... I figured that 50lbs of force on the router spindle stops my router dead. Bearings have 0.01 coefficient of friction. The "gantry" will not be heavier than 30lb.
I'm not a mechanical engineer, so I'm pretty sure there is a huge potential for a mistake, but according to what the physics are this is a good start for me. I'm making the whole setup "modular", so if something doesn't end up working right i can redo that module.
I'll keep posting to this forum as the build progresses...

Thank you for the replies
Yuriy

P.S. i found a set of oldham coupling that will let me attach 1/4" to 5/8" shaft, so i'll see how that goes. They are rated at 30 lb in.

[jeb]

Hi Yuriy,
It sounds like you are off to a good start. I look forward to seeing some pictures. It might be tricky to get a 5:1 reduction in one stage, but it could be possible if you have enough space. There is a great resource for belt drive design here: http://www.sdp-si.com/Sdptech_lib.htm
Cheers,
Jacob