Which belt material?

[Fiero Addiction]

I've read as much info on timing belts as I can find, including the pages at SDP-SI. I'm still uncertain which belt material and cord material is best to use for transmitting linear motion on a CNC machine (in place of ballscrews or gear racks). I'd like to hear the opinions of some experienced users.

What is the preferred belt material:
Natural rubber
Neoprene
Urethane

What is the preferred reinforcing fiber:
Polyester
Kevlar
Fiberglass
Steel

I understand there may not be a simple answer and not every machine has the same requirements, but I'm just trying to get an idea of what works for others. I'm designing a 4' x 4' plasma cutting table, steel frame and gantry, I want to drive both X and Y axis with long belts.

Thanks,
Jon

[harryn]

I learned a great deal from reading information on the brecoflex web site, which thankfully is also consistent with my engineering training. I have also read a great number of the forums on build logs on cnczone.

www.brecoflex.com

I cannot say that I have personal experience to back up my reading in this area, but so take my comments with that in mind.

Properly done, ball screws will of course provide the best motion control, but are probably not a good choice for a dirty environment like plasma cutting.

Your question was specifically about belts, which I studied a great deal for planning my DIY router (still in progress). The best belt is one that the main part of the belt will hold its dimensions during back and forth forces, but also the teeth will not deflect (much). This should be combined with a pulley set which has low backlash as well, which means that the teeth should have very little clearance. Standard timing pulleys have a lot of clearance, so I was planning to use zero clearance pulleys (2 x as expensive)

The most durable all purpose belt material is urethane, and there are variations of this as well, but the belt mfgs have this down pretty well. There are plys of other materials added to obtain specific properties, usually quieter operation or lower sticking action.

Steel reinforced belts will stretch less than other materials, usually including kevlar. Kevlar is a great material for tires because of its great flex and high strength, and ability to stay in the tire under high heat conditions, but these are not typical belt operating conditions.

There is a dramatic loss of tooth strength going below a tooth pitch of 10mm, which is unfortunate as the 5mm would probably be better for precision movements, and common steel racks have a tooth pitch closer to 1.5mm (20 per inch). For a 5 x 10 machine with strong motors, I had estimated / rough calculated) happiness if I had 2 belts on each axis 50mm (2 in) wide for 10mm pitch belt. This wide of belt can be a pain. Long belts need to be in some kind of guide way or tray to keep from slapping around.

My current thinking is that for systems with approximately this level of precision (wood routers / plasma) that a steel rack and pinion setup are going to be just as precise, easier to build, and prossibly cheaper.

Of course, if I had no budget constraints, I would probably use a ball screw setup on my router, but that is not the case.

[nwrepair1]

Again. I do not get this negative belt postings from people who have not built a belt drive router. I state again that I have a 4x8 Precix commercial router that runs on belts since 2003. The belt size is AT5 and 25mm (1 inch) wide. Two belts move the gantry along the long x axis and one belt moves the y axis. The z axis is a ballscrew. the z has a 36 lb. 8hp Femic spindle on it. I use this machine to cut and route solid phenolic. That is more than most hobby people will do. Never broke a belt but I have a ballscrew router next to it that needs all the screws replaced because of the gritty phenolic dust.

[harryn]

Originally Posted by nwrepair1 Again. I do not get this negative belt postings from people who have not built a belt drive router. I state again that I have a 4x8 Precix commercial router that runs on belts since 2003. The belt size is AT5 and 25mm (1 inch) wide. Two belts move the gantry along the long x axis and one belt moves the y axis. The z axis is a ballscrew. the z has a 36 lb. 8hp Femic spindle on it. I use this machine to cut and route solid phenolic. That is more than most hobby people will do. Never broke a belt but I have a ballscrew router next to it that needs all the screws replaced because of the gritty phenolic dust.

Hi - sorry, I should have more correctly pointed out that I was looking at a way to use a belt as a pseudo rack and pinion concept, not the way they are designed to be used. That made the tooth strength challenge much larger.

nwrepair - just curious - are your motors located on the trolley with fixed belt end points, or are the belts in a continuous loop ?

Thanks

[nwrepair1]

The x axis is two 136 inch belts with fixed ends in a trolley configuration, but only one motor with a shaft going across the back of the gantry. Belts and pulleys are connected to the trolley system (like a rack and pinion reduction system). Y axis moves the Z axis across the gantry with one motor and one belt.

[mnwolgamott]

I have recently powered up my machine. plain old poly belts .200 pitch 375 wide. two on X axis one on y axis. machine 39" x 96" gantry style.100 inches minute. I do see some stretching in the X axis should hve gone for the wire reinforced belts, When you do this you must be careful of the overhung load put on motor shafts as you can quickly exceed rating.

My belts are fixed at each end the belt is wrapped around the motor puley 70% which helps eliminate the slop in teeth mentioned in another post. Motors mounted to the gantry with an idler puley arrangement to configure the 70% wrap. I have Z and A axix slaved from Hobby CNC pro board, a belt on each side one on each motor.

The stretch I see or it could be slop in teeth on X is very minimal, I tend to say it is stretch as the y axis is right on, (checked with dial indicator) however it is a lot lighter. I have enough power to quickly out run my router (due to be changed soon). I think the wire reinforced belts would have been better, But I'm not building space shuttle parts either wheen checcked on a wooden part my x was off approximatly 010" in 6 inches.

by the way software is Mach3.

fwit
Mac

[SNERLAND]

I have had a notion to use one inch belts on a plasma table. I thought to use linear encoders running on the frame rather than rotary, then belt stretch wouldn't matter..
I am wondering what diameter pulley and idlers should be used.