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

wthomas@... wrote:

>Hi Juan & all:
> I just spent an hour on sdp-si web site,and the phone with
>their help and engineering people. As an engineer I knew close to
>what you needed but I could not find it in their engineering section
>or the order page of their cat. After talking with their engineer he
>lead me to the pdf file of their paper cat. on belts which gives the
>breaking strength of the belt but, it then states that the breaking
>strength of the belt is not representive service.
> What I would recommend is to measure or estimate the amount of
>torque needed to drive the shaft. You can easily do this with a pair
>of locking pliers and a scale. If you are designing the unit and
>can't measure the force needed, a quick idea of what it will take is
>to go to a mill or similar sized machine and measure the torque it
>required to move its table. Then double the force amount and
>determine the width of the belt for the size you want to use.
>

This may not be good enough for a milling machine - don't know what he
is trying to CNC, though, he didn't say. But, the static + dynamic friction
on a mill may be MANY times less than the cutting load. A good Bridgeport
(not mine) has VERY little sliding friction, and the table can be easily
moved
with a few Oz. of force on the handle. During heavy cuts with large cutters
deeply engaged in the work, it can take 50 Lbs or so on the handle to
keep the
table advancing! So, that is a dynamic range of at least 500:1.

I did a very rough calc on the absolute worst case tangential force from
the spindle to the table with the motor at full load on the lowest speed.
I came up with something around 1000 Lbs force for a 1 Hp Bridgeport.
Here's how I did the next part, converting axis motor torque to linear
force through the leadscrew : http://www.timgoldstein.com/cad_cam/Servo.htm

Jon