Re: What pulleys and timing belts do I buy from sdp-si???

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "apples0_17" <apalais@s...> wrote:

>
> Hi all, I need to knock up a timing belt reduction. I was thinking of
> around a 6:1 ratio. ie 10 tooth and 60 tooth pulley. I would like to
> use a 3/4" belt.

E-mail SDI back and tell him the motor hp, and the expected load
weight, like a 1/2 hp motor on a 250 pound wood router gantry. dual
purpose machine with a plasma cutter as the other use.

Ask them to first recommend the belt type and ask why. I did this on
the phone some time ago, and foolishly didn't write it down. I seem
to vaguely recall it was that a belt has a strength of roughly 125
pounds per 1/8 inch. this was regardless of belt, MXL, XL, GT2 and L.

I found that they recommended a better belt. the GT2 it is a Gates
belt and what I was told was that the XL was an original design and
original spec, but that Gates did a little more research over the
years to find a better shape that lasted longer and transferred more
power.

I had talked to a Gates engineer and gave him numbers and he did some
calculations for me as to belt and pulleys.

Not sure if it is sales hype or real. The prices were not more than
about 15% for the sizes I checked, as compared to XL belts and pulleys.


As for calculations , you must start with the physical and the physics.

how much force do you need ?

once you have a belt style, (the XL and GT2 are both really close to
the same pitch) then look over the listed pulley sizes. There is a
range available.

an XL belt is 0.2" pitch so a 10 tooth would have at maximum 5 teeth
engaged, but with a ratio (and no guide rollers) it will have less.

5 teeth, 0.2" = 1 inch total of belt in contact.

second, look at the pulleys, what is the motor shaft size and what is
the smallest pulley to fit ?

I think 28 teeth on the XL is the smallest with a 1/2" bore. you might
be able to open them up though.

As for the largest, the largest I am aware of from SDI is 72 teeth for
the XL series. People have been known to make their own.

As for the material, The nylon pulley with aluminum hub will not have
much strength to it. the aluminum is only pressed into the plastic.
there is no interlocking frame to speak of.

I prefer to use a metal as the drive pulley as it is smaller.

then I make the larger driven pulley with my own hub, if the price of
the pulleys are much different. A couple years ago, McMaster had
total nylon pulleys and a 60 tooth all nylon was like $3.00 the
aluminum hub was around $11 and the all aluminum was like $18. They
no longer list the all nylon.

As for the final calculation to determine the belt ratio, consider the
motor type. you mention steppers. a NEMA34 stepper has a 1,200 RPM
top speed ? (do you have a data sheet ?)

assuming a spur gear of 1.5", that would be pi times 1.5 or 4.7" per
spur gear revolution.

1,200 times 4.7 = 5,654 so your 10:1 would offer a top end of about
560 IPM. very legitimate.

Hope this is of any help.

Dave