Re: [CAD_CAM_EDM_DRO] Re: Timing Pulley Accruacy and Servo shaft runout

Polaraligned wrote:

>>When they call these parts "precision" they sure don't have machine
>>
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>tool
>
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>>axes
>>in mind.
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>>Jon
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>>
>
>Thanks Jon. I understand now.
>If the center bores can be so far off it makes you wonder
>about the outer diameter, the teeth cuts, etc. How far
>off can that be.
>
>

They use a precision machined mold to press the powder before
sintering the pulleys, in the ones made by powder metallurgy.
I guess they have to be careful lifting the pulley out of the mold
before sintering, but if they get rough with it, it will just crumble.

For the machined pulleys, they make a "log" with the grooves first,
and it is presumably quite accurate. Then, they slice them up and
machine the hub and bore. So, it is a machining process, and up
to whoever does the work as to how careful they are in mounting the
pulley slices in the lathe.

I've never seen a significant error in roundness on the OD all by itself.
As for exact diameter, well it has to be pretty DARN close or the belt
will not lay in the grooves. I found that out when I bought a belt for
a pulley I thought was MXL pitch. It turned out it was for the old
DP-40 pitch that matches gear teeth. MXL is .080, DP40 is .0816
I think. The belt would just slip because a couple teeth were always
out of their groove. So, a very small diameter error of a few per cent
will prevent the belt from working at all!

Jon