marker pen driven over an 8x4 sheet help.

[Danny]

Hi there can you tell me if there is any issues with using fixed rack of teeth rather than belts , can you drive the stepper motors along a rack of fixed teeth ? just wondering if its cheaper im looking a allot of belt for an 8 x 4 could i half the amount needed by switching to a fixed rack set-up?

[JAZZCNC]

Hi there can you tell me if there is any issues with using fixed rack of teeth rather than belts , can you drive the stepper motors along a rack of fixed teeth ? just wondering if its cheaper im looking a allot of belt for an 8 x 4 could i half the amount needed by switching to a fixed rack set-up?

Hi Danny,

What I think your referring to is (R&P)Rack & pinion.!
There are no issues as such and it's often the prefered setup for longer length machines due to technical issues like whip etc with using screws, also it's slightly cheaper.

If by halfing the amount you mean only using R&P on one side then NO Bad idea.!! . . With a machine of this width, even thou the load will be light, you will potentially suffer from racking which could cause sticking and inaccurecys. Driving from one side is bad and not recommended even for machine of this light duty. . . . Drive it from the centre and it will be ok.

That said R&P does come with it's own set of requirements.!!. . .It still needs gearing for resolution thou not quite so larger 2:1 - 3:1 max, larger motors are needed because it's quite inaffecient this also means larger more expensive drives which in turn require higher power supplies.
On a techinical side it's far less efficient than timing belts with much more backlash (Timing belts are very low to zero backlash) and it's noisy as hell.

IMO for your light weight machine needs you won't get better or cheaper than using timing belts. R&P will certainly be far more expensive and perform far worse on a techinical basis.

Don't know what machine design you have in mind regards belts but let me just point out you don't need looped belts.? . . . Just a single length fixed at each end and looped around 2 rollers and the drive pulley is all thats required up each side.

If you look around you tube you'll see what I mean something like this http://www.youtube.com/watch?v=VPlyTTFo6w0