Re: [CAD_CAM_EDM_DRO] Re: Pulse Gen

In partial response to your post I would like to mention that I just
found a great motor to run the Sherlines. As you know the Sherlines use a 20
TPI leadscrew. I mounted a 200 count encoder on one end or the motor using
an adapter plate and directly drove the sherline leadscrew with a solid
coupling. Thus it has 16000 counts to the inch or .0000625 resolution.
I have some nice extruded motor mounts to adapt my model 5400 mill to take
stepper motors. I had to make an adapter plate to have the PMDC motor line
up with the leadscrew and my adapter plate. I test ran the sherline and have
it running at 72 IPM
on a 486-66 using Maxnc deluxe. So doing the math it looks like the
leadscrew is turning at 1440 RPM.
I would not add any side load to the Sherlines leadscrews unless I
modified the end plate for radial ball bearings. I don't think the end plate
bores would last very long before wearing out. The direct drive seems to be
a better way. The only problem is that I loose the handwheels because of
the encoders. I have more tests to run but hope to have a batch of motors
available for sherline servo retrofits.
BTW I measured the side force at 20lbs plus at 72 IPM !!!!
Dan
-----Original Message-----

>
>The 5tpi is something to think about. I have 20 tpi on the little
>Sherline, and a few pairs of what I think are 8tpi. x 3/8". I think
>they may possibly be metric, as the shaft end was not a simple English
>dimension, and some of the 3/16" (?!) hardware associated with them
>turned out to be metric! Anyway, I am just realizing that the belt
>reduction used with ball screws must also be to get more steps/inch, not
>just for power as I originally surmised. Would have been nice to drive
>them direct with a flex coupler. What steps/in should I be shooting
>for? And what's realistic?
>
>I'd appreciate your input.
>
>Alan KM6VV
>
>
>Wally K wrote:
>>
>> Alan, are you talking about writing a driver for EMC.
>>
>> As for pulsegen circuit. It seems overly complex for the performance
>> and cost. If i remember right it takes 14 IC's per axis and has a
>> max freq of 8khz.
>>
>> If my calcs are correct a 5tpi screw with a 2-1 belt reduction and
>> 1/2 step mode will require 13.3Khz for 200IPM rapid.
>>
>> I do not think you should settle for less than this performance with
>> the complexity and cost of the pulsegen circuit. (but this is a dam
>> cleaver circuit).
>>
>> Let me know what your thoughts are.
>>
>> Wally K.
>
>> <SNIP>
>
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