The idler pulleys push them together on either side of the pinion, which is where the force is transferred from the upper belt to the lower one. The lower one is glued to the machine frame along its entire length, so the force is then transferred to the frame. Neither belt has any significant tension outside the area of the idlers, so there isn't much needed to keep them together - gravity does it.
I don't think it would work with regular trapezoidal timing belts (like the MXK, XL, L, etc series), because the teeth are smaller than the spaces between the teeth. So they belts wouldn't mesh tightly. A GT or HTD belt might do better, I haven't looked up those belt profiles to see if they would provide a positive mesh. Thinking about it a bit, maybe even trapezoid belts would work. The teeth on the upper belt don't need to be centered in the spaces on the lower belt. On the left side of the drive unit, the right flank of the upper belt tooth could be in contact with the left flank of the lower belt tooth, so it could transfer tension to the lower belt. On the right side of the drive unit things are reversed, with the left flank of the upper tooth in contact with the right flank of the lower tooth. Again, it can transfer tension to the lower belt. The main problem is that force is transferred between belts by only one or two teeth - the ones directly under the idler pulleys. Making the idler pulleys as large as possible would improve that a bit. It all comes down to how much force is needed, and how expensive is strong, wide belting compared to alternative ways of doing the same thing (like rack and pinion). By comparison, if you used only the upper belt, and stretched it tight enough that both sides were under tension loading even with maximum force on the carriage, it would be stronger (load limited by the teeth in mesh over 180 degrees of pinion) but springier (tension members of the belt are long and thin, and even if steel they are elastic). But you have to buy half as much belting, so the belting could be bigger. It would be an interesting design exercise. Econobelt and SDP-SI are both belt suppliers with a good bit of technical info on their sites. The ultimate choice depends on your requirements. If you have lots of cutting force, rack and pinion would probably be better. If you need speed and low noise and not so much stiffness, a single timing belt with two idlers and a pinion would be better. The interlocking belt thing is weaker than both, I think, but much stiffer than the single belt. On Sat, Jul 21, 2012, at 07:38 PM, Jeshua Lacock wrote: > > On Jul 21, 2012, at 6:47 PM, Peter C. Wallace wrote: > > > Ahh here it is: > > > > http://bell-everman.com/products/linear-positioning/servobelt-linear-sbl > > Thats pretty cool. > > I wonder what keeps the belts together? Gravity? > > > Cheers, > > Jeshua Lacock > Founder/Engineer > 3DTOPO Incorporated > <http://3DTOPO.com> > Phone: 208.462.4171 > > > ------------------------------------------------------------------------------ > Live Security Virtual Conference > Exclusive live event will cover all the ways today's security and > threat landscape has changed and how IT managers can respond. Discussions > will include endpoint security, mobile security and the latest in malware > threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users -- John Kasunich jmkasun...@fastmail.fm ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
