Timing Belt Style (Gear) Reducers Experience

Is there any interest in a discussion about using timing belt reducers on earlier generation 'bots with 1:1 (non-geared) steppers for the purpose of improving resolution/smoothness?

I recently acquired a 2005 Alpha that is turning out to be in better shape than I thought and am wondering about investing in belt drives as a cost-effective way to upgrade. I know that it's a very popular approach for metal working mills and lathes because of cost as well as elimination of the backlash issue. It seems likely I could have a set of four of these using quality bearings, belts, gears and housing materials and made to tight tolerances for under $1000 perhaps a little more if the Z axis proves more complicated.

I've found a couple of discussions in the archives but have not come across much from anyone currently using these. The only issues that came to light seemed to be tied to too-loose tolerances when, at the prototype stage, precision machine tools were not used or available to build them.

Gerry,
I would be interested in knowing what develops from this topic. I do not know allot about the different ratios that are available, but do understand it. I have a prs alpha with an indexer. The one from S.B.. I want to do something other than the gear box that is on there now. There is to much back lash for me.

You have broached this subject a little early than I was going to. It will be a few months before I get around to messing with this.

We have two other routers (big iron ones) with servos and they have a timing type belt for all movements.

Sorry I can't be of much help on this one, haven't gone there yet myself.

Gentlemen...
Here is a link to a thread, even tho it wanders some, was authored by Mike Richards, who does a great job of explaining the mechanical and technical aspects of putting beltboxes on a PRT.

http://www.mechmate.com/forums/showthread.php?t=366

BTW, I just may know someone that has a 9-1 double belt redution box that will be a bolt on replacement for the PRS. Higher resolution, more power are the good news. Bad news is that cut speed will max out between 6 and 7 ips due to comm rate. Other ratios available.

Gary,

Thanks for posting the information. I would have gladly given up speed for quality when I owned a PRT. My next door neighbor has an old 6'X12' Gerber with steppers and an old Porter Cable router. The quality of the cuts are so far beyond any other CNC I've seen. However, their cutting speed is a little slow. Gerber has focused on High Resolution and the results are stunning. I wondered for years how they were able to get such good cut. Now I know. They also have a aging high dollar Thermwood which takes a back seat in quality to the Gerber.

J.

Good idea. Maybe some plans and specs to build them for the PRT alpha. Even a place to shop for plans or purchase them already engineered for that model.....;)
Shari

http://motadistribution.com/ac-motor...gearheads.html

found this site, not sure if these could help

good luck
mark

Building a belt-drive transmission is not difficult. I've built several different models out of Polycarbonate, aluminum and Delrin. All worked equally well.

I'm attaching a simple drawing that shows the three main pieces:

- Motor mounting plate

- Base plate

- Spacer

In the jpg file, the Blue parts are 3/4" round spacers, the Red parts are the timing pulleys (20 tooth and 60 tooth), the Green parts are the shaft collars.

You could make the motor mounting plate and the base plate out of 1/4" plywood or 1/2" MDF to test the design and then make the final parts out of Delrin or aluminum. The large holes near the center/bottom are for bearings. I used 1.25" outside diameter bearings that fit a 1/2" shaft. Both the flanged bearings and non-flanged bearings work. I used the flanged bearings when I made the plates out of 1/4" material.

The spacer plate was cut from 0.08" thick aluminum. The hole in the middle is sized to fit the protruding 'ring' on the motor. It is simply a 'filler' plate so that the front of the motor sits fully against the motor plate.

The distance between the motor's shaft and the axle is 3.25", which allows the use of a 150 tooth XL belt (assuming that you use a 20-tooth pulley on the motor and a 60-tooth pulley on the axle.

I used some rubber O-rings between the shaft collars and the bearings to allow the bearings to turn freely.

Be sure to have a machine shop bore the pulleys for you. Trying to drill the holes with a drill press will probably leave you with parts that are off-center. A machinist can use his lathe to accurately and quickly bore the holes.

With the standard Alpha motors, a 3:1 belt drive driven through a 25-tooth spur gear (1.25" pitch diameter), will give you 0.001309" per step (assuming that you use the standard 1,000 steps per revolution on your Alpha stepper drivers).

With Oriental Motor PK299-F4.5 or PK296-F4.5 motors and Geckodrive G203v or G201x stepper drivers, you will have 2X better resolution because the Geckodrives use 2,000 steps per revolution.

With a 3:1 reduction, torque will multiply by 3X.

Mike....
When you say "standard alpha motors" can I assume that you are NOT referring to the 7.2 TH motors that are standard on the current PRSalpha? Note: this is clarification for users of PRS machines, as the current alpha does not suffer from a lack of resolution with the 7.2 motors. Backlash, IMHO, and holding power may be another story for those that use them hard.

My prototype solution above requires replacement of the existing 7.2 motors and integral gearbox with different model Oriental motor and belt reduction box. Also requires reprogramming of the driver along with another set of unit values.

http://www.mechmate.com/forums/showthread.php?t=3138

There are also several other threads about this on this site.