Re: [CAD_CAM_EDM_DRO] Re: what gear ratio ??? - more

Doug Fortune wrote:

>cnchomeman wrote:
>
>
>>Doug wrote:
>>
>>
>>>Let me further say, a 10:1 ratio might be best with those smallish
>>>motors, to get decent machining power at typical machining speeds....
>>>however the rapids might suffer. Also, to get more than 2.5:1 or 3:1
>>>you'll need more than 1 stage of belt drives, which complicates things.
>>>
>>>So all in all, try the 2.5 to 3:1 first and see if that works for
>>>you. Put the encoder on the motor, not the leadscrew.
>>>
>>>
>>>
>>Why does the encoder need to be on the motor? For resolution?
>>
>>
>
>Because (if there is any gearing) there will be a discrepancy
>between the position of the leadscrew and the position of the
>motor, thus probably leading to nasty oscillations.
>
>True, mounting the encoder on the (geared down) motor shaft, will
>increase resolution - this is good (generally).
>
>

But, using toothed belts, there is no problem. When properly tightened,
there is no backlash. I have the encoders directly driven by the leadscrews
(using helical-slit couplers) and a 2.5:1 belt ratio. This is on my
Bridgeport. it works extremely well, and I have high-precision ground
screws, and get an overall accuracy of about .0003", disregarding some
backlash.

Jon