toothed belt stretch

[erase42]

Hi, Im building a LARGE foam cutter for my business. Due to the lenght of the axis, 9 feet, I was considering going with some of the cogged timing belt and pulleys. With a foamcutter there really is no load other than the weight of the machine. But I also plan to build a device that will turn the whole thing into an 8 x 8 router table. I guess my question is what sort of stretch can i expect from a decent grade of that type belt. Im thinking .75 wide belt with the kevlar strands. Ill most likely fasten the belt at both ends and have the motor travel with the axis to shorten the length of the belt. Any input anyone ?

[millman52]

I am looking at this type of drive system also. I have had no dealings with it. Several other machines have been designed & built using timing belt most usually with both ends tied to the gantry & if driven from both sides a drive shaft is most usually used either at the gantry or at one end of the table.
Most seem to be using the steel cord belt as opposed to kevlar.
You can find several examples in the plasma & router tables Group(s)

[ger21]

If you read the info available at www.sdp-si.com, you'll find that supposedly you'll see a small amount of stretch at first, but next to none after the initial stretch.

[RCXPLANES]

I have been using an Emissions Technologies laser for over 3 years now. It is equiped with XL pitch 0.375" wide belts on the long "X" axis. I very slightly adjusted the tension once after 6 months and never since. The Laser focal head and "Y" axis gantry is the only weight or load on that machine and very high quality Igus Drylyn "W" series rails and bearings were used.
The "Y" axis gantry uses an even smaller 0.25" width belt and a NEMA 17 frame motor. This has never been adjusted and the laser will repeat within 0,001" after traversing the entire 24"x48" table.
I am designing a large foam wire cutter using the same components because of the reliability and durability that I have experienced with the laser design and components.

Bud

[chineguy]

Just make sure you don't get any oil on your belts. The belts hold up pretty well if kept clean and dry. I had to maintain some machines with timing belt drives. They actually got pretty nasty with goo and kept working. We did have 2 spindle drives that got a lot of oil exposure and heat. They failed alot.

[RCXPLANES]

Good point. I didn't think about oil. My laser is very clean. I have seen automotive T-belts taken out in a very short time due to oil seal leaks. Those dont stretch but the contamination attacks the material and teeth strip off. I know there is no where the load as driving a camshaft but definitely a good point if you plan to use coolant on a mill.

A dirrect 1 revolution to 1 inch linear belt travel pully is harder to find than I thought so I will probably have to copy the motor to jack shaft reduction pully system to get the most acurate 1 revolution to 1" linear belt travel.

Bud

[erase42]

just wondering, but why is it important for you to have one to one ratio on your belt drive?

[RCXPLANES]

Originally Posted by erase42 just wondering, but why is it important for you to have one to one ratio on your belt drive?

Now that you have mentioned it, I think it is actually 10 motor revolutions to 1" linear travel. Like when using a 1/2" - 10 lead screw. I will have to check the software and count the grooves on the current system but I think I was mistaken now.

Bud