Hello All,
  I know some of you are running belt systems and I have a few questions first what are the formulas for figuring out speed and distance also I know in rack and pinion that you use pie on the gear etc but when I am looking at belt pullys they are giving me number of teeth so how do I fugure this stuff out such as there is a XL belt that has 120 teeth how do I figure out how long this belt is so I know what to order and what not this must seem dumb but just havent found any info as to where you learn this stuff? Also what kind of limitation is there with belts noise is not an issue for me so I have considered racks as I am building a new machine cut area 4'X4' and will build a second in near future that is 4'x8' and I wonder if this is to much for a belt drive thanks for all of your help.

Bearwen

Not sure exactly what you are looking for, are you meaning you have a pulley attached to a motor and the other one attached to a ballscrew/leadscrew?
 What speed and distance are you meaning?
If you have a motor with max speed of 1000rpm and it has a pulley with 10 teeth. This is connected by belt to a pulley with 40 teeth on the ballscrew then the ballscrews max speed will be 250RPM as the reduction is 4:1.
 If the ballscrew has a pitch of 5mm then your max axis travel will be 250 x 5 =1250mm/min.

If this is not what you are wanting please explain again and it might sink in

Hood

I got that no I want to go to a system of belts only no ball screws as whip seems to be a limiting factor on a machine of this size I want to build a machine like Arts if you look at the pics of his old machine in the forum there are no screws it is all belt drive. The question I have is how big of a machine can you use belts on I am looking at 4' x 4' and also a second machine of 4' x 8' and when I am looking at belts ( Irecentlly found a site that has the ibfo I needed) but I still have one question when looking at belts they say that for example the belt is 48 inches  pitch length with 240 grooves so is this the total length of the belt as a loop or is this the size of the belt if it was cut and layed out flat?

Can you give me a link to both Arts machine and also the info on the belt. Just dont really understand when they say "belt is 48 inches  pitch length with 240 grooves"
What that might mean is the belt is 40inch length with 240 teeth which would make a pitch of 0.166"

Hood

Ok well here is the link to sdp-si website where I saw the pitch lengthhttp://www.sdp-si.com/D790/HTML1/D790C02051_4.html and here is a link to Arts machinehttp://www.machsupport.com/forum/index.php/topic,1590.0.html I got everything figured out except what size belt to run such as .25" or 3/8 or 1/2" etc and what the pitch length means I am sure if I call them they will explain it but I am just curiouse right now and not in a big hurry. I am the most concerned with what size belt such as 1/4" wide 3/8 wide etc or does it matter ( I am looking at kevlar reinforced belts so they are really strong the above link will tell you the strength that is the belt I am looking at) for a wood machine running in the 300 ipm range with a total gantry weight router and all of roughlly 80lbs and I will cut woods all different types and foam maybe some thin light gauge metals with a 2 and 1/4 hp router the 300 is rapid of course except when cutting foam I cut at rapid speeds

48 inch pitch length should be if it were laid out flat measuring from tooth to tooth. Any belt is driven by something round, the inside diameter and out side diameter are different. Pitch is the inside circumference I think. The width will matter, depends on acceleration and velocity rates as well as mechanical friction, tool load, weight of parts to be moved, etc. I think the link you posted was for Stock Drive. They have a ton of info. and you could learn a lot in a phone call. Also, if Art's machine is using belts as racks, and this is what you want, ask them or look for continuous belts. Different belts have different accuracies as well. Some systems are by design better than others. The pulleys and belts have tighter tolerances.

Brett

Ok I still have no clue this is what I am looking at I have a motor with a pulley on it the belt is connected to the gantry then raps around the gear on the motor then goes and raps around an idler pulley of the same size as the pulley on the motor then the belt goes back to the gantry. I found out about the belt they sell just straight lengths but the problem I have now is how do I determin what size pulleys I need as the discription above I have no gear ratio it is direct drive I am not concerned withgear ratio I know how to figure that I need to know how to figure out what amount of torque I can get with a set size pulley directlly connected to the motor I can get figure the circumference based on the pitch diamter but I dont know how to figure what kind of driving torque or how much motor torque I need to move X amount of weight with X size pulley directlly connected to the motor once I can figure that out I can set pulley to given size and then figure out what drive ratio I need to get X amount of torque at X speed of motor and feed rate etc... so does anyone know how to figure what size pulley to get X amount of torque with a given size motor when pulley is connected directlly to the motor shaft?

I can't remember the formula for figuring torque required to move x mass at x speed.  I think the machinest hand book has those, can't remember. Once you know that, and have a torque curve on your motors, you can figure the pulley size. 

Brett

Pitch is the distance between the teeth. XL is 1/5 pitch. Thats 5 teeth per inch. 120 teeth is 24 inches. That would allow for around 12 inches of travel. Belt drive units are not cheap. In order for your 4X4 travel, you would need at least 8 foot of belt....per side. This is assuming that you are using a 'loop' method, and not a single strip of belting thru a tension system.  A 4 foot long gantry will have way to much whip without driving both sides. It may not seem like it does on dry runs, but wait until those cutting forces come into play. So thats 16 feet of belting, not counting the wrap around for the pulleys. With an 80LB gantry, your not going to want anything less than .75 wide belt. That gives you 1.5 inches of belting taking up forces. Forget about driving it at 300IPM. The belts would not hold up to the abuse of 80 pounds starting and stopping at such speeds. I'm not sure a direct driven motor could even stop it within a reasonable distance. A 2.25 HP router would CERTAINLY limit you from achieving anything close to that speed anyhow, at least in wood.

16' of "L" pitch .75 belt        $80.00
4 flanged pulleys                  $88.00  There are recommended minimum pulley diameters for belt sizes.

These figures are conservative at best. You would also need some way of driving both sides of the gantry at the same time. I achieved this using two 3/4" rod through 4 bearing blocks. Other methods are out there, I'm certain.

4 mounted bearings              $30
.75 rod                               $20

Don't forget about having a way to tie in the belts. Clamps are around $50 a piece. I would advise making your own.
I don't mean to sound harsh in this reply. I'm just stating some opinions that I have formed by similarly doing what you are trying to do now.
I have no idea about your torque requirements. Driving this gantry directly at 300 ipm would take one massive motor, for sure. Best of luck with your project!

I agree I do not intend to drive it directly I was using that as an example so everyone would know the setup I will have a reduction drive for sure I don't know about the prices you stated Sam I have looked at doing rack and pinion or belt the belt system seems to be cheaper and Art seems to love his I am not concerned with the noise of racks as I am using a router so I wont hear it anyways. I have seen where 3 1/4 hp routers were cutting 3/4 in deep at over 300 ipm I will most likely up grade to 3 1/4 in the future that is why I want high speeds also I can make shallower cuts faster and the project is done sooner and I cut foam so high speed is possible as for wood cutting the speed was mainly for rapids. I still have the problem of how to figure out the belt size that can handle the torque and how to figure the pulley sizes for the torque and speed. Sam you said that the XL belts were 1/5 which is 5 teeth per inch I am assuming that a 24 pitch GEAR has 24 teeth per inch correct if so then I should be able to use the rack and pinion calculator that I have as I input the pitch of the system and then the number of teeth on the actual gear and motor size etc.. and it gives me the speed available the theoretical cutting torque as well as resolution etc.. if anyone is interested I will post the calc for everyone to download it is a Excel spreadsheet I also have one for screw drives I did not write them so if there are errors don't blame me.

Bearwen