Re: Open ended belt drive for cnc router?

Mike,

As Dean already mentioned, the precix routers use this system. So do
others. SMS, in the UK, used this system in their woodworking routers.

This design is also seen often in fast moving, relatively low
precision pick and place (warehouse automation systems). In these
types, the belt is used as a cover for the linear bearing, which is
usually a plane bearing type enclosed in a use-specific aluminum
extrusion (I believe this is what the other respondant to this
message has). Dean mentions 9:1 on the precix; I thought it was 4:1,
which is what I used. I conducted industrial espionage<G> at a trade
show where the precix people were showing...

I have built two machines using these belts; one of which used them
in this fashion. First, my usual preference for the HTD style over
the xl type must be mentioned. Better power handling, more tension
capability. Next, consider that there are several different tension
member materials used in belts of this type. Steel used to be the top
of the line. Now kevlar has largely replaced it. Polyester is used in
lower cost belts. You want to use kevlar if possible, or you will
need to re-calibrate your machine quite often at first, and fairly
often over its lifetime; as the belt(s) stretch. My first machine
used 5mm x 25. If I were to do it again today, I'd use 5mm x 15. Be
sure to have a good means of tensioning the belt, and solid mounts
for the idler roller(s) Yes, you can get by with one, if you don't
need the belt to lie flat.

FWIW, a company called Brecoflex sells both belt and end fittings for
this type of arrangemnt. I didn't go with them due to cost, and the
xl trapezoid tooth form.

One slight downside to this technique (compared to a single closed
belt of the same type) is that the motor moves, which can lead to
increased motor supply cable wear. In a gantry style router, the x
will need a cable carrier, and the y will go through TWO cable
carriers. With closed belt and stationary motors, the x will have no
flexing, and the y will have only one cable carrier span. This of
course means that the z cable will have either 1, or 2, or
3 "flexing" areas, depending on how you stack these choices up...

So in conclusion, it is a proven and acceptable means to achieve your
stated goals, with only a few gotchas to consider...

Hope this helps,

Ballendo


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "aerowright <mnemesh@m...>"
<mnemesh@m...> wrote:

> I'm gathering parts to build a CNC router (say 5'x3') and was

looking

> at McMaster-Carr for rack and pinion info and happened across this
> image (uploaded image to the files folder beltdrive.gif) and was
> wondering if anyone had ever used (seen/worked with/your favorite

verb

> here) this type of system. I'm looking for possible alternatives to
> ballscrews since I'll be cutting mostly wood and keeping the screws
> clean can be a problem. I'm thinking of using two belts on the on

the

> x, one on the y, and a screw on the z axis. Any info would be

greatly

> appreciated.
>
> Regards,
> Mike