Re: [Emc-users] Stepper drivers

[Jon E. <el...@pi...>]

Gene Heskett wrote:
> On Saturday 27 September 2008, Jon Elson wrote:
>   
>> I have put a DPDT switch on
>> mine so I can run the motor off a servo amp.  I can't get full RPM, as
>> my servo box has a 50 V power supply, but the servo amp gets me
>> computer-controlled variable speed and reversing.
>>     
>
> I'm running mine with a PMDX-106 interface, which gives me full control from 
> its panel and from emc2.x
>
>   
But, no reversing, I assume.
>> I have an encoder 
>> patched on to the spindle, and can do rigid tapping, which is a hoot!
>> So, it can do something my Bridgeport can't do!
>>     
>
> If only that spindle had the power to do that, but sadly, its about tapped out 
> with a 1/4" 28 tpi tap in cold margarine.  Ditto for the spindle motor in my 
> 7x12.  I have cut threads with it using single tooth carbide bits, but they 
> are a bear to sharpen correctly.  That is how I cut the threads for the 1/2" 
> acme bronze nuts in the new z axis of that HF mill.
>
>   
I'm a lot more interested in 4-40 and 6-32 size threads than 1/4".
> How did you attach the encoder to the micromill spindle?  Patented? :)
>   
No patents for me!  Starve the lawyers!

See the last picture here http://pico-systems.com/minimill.html   for a 
good view of the encoder and mount/drive.  I found some nice plastic 
pulleys in my junk drawer, and an oddball encoder with index.
The pulleys turned out to be 2mm pitch instead of .080", that's what you 
get when you use scrapped parts, so I had to order different belts from 
a specialty belt dealer.  (You would almost think a 2 mm belt would work 
on a .080 pulley, but they would jump a tooth every full rev or so.)
Anyway, I just bored one of the pulleys to the same ID as the toothed 
nut that holds the bearing tension.  I superglued the pulley on, but 
that eventually worked loose.  So, I made a thin spacer disc of PC board 
material (so it wouldn't fatigue) and put it under the nut.  I then 
epoxied the face of the pulley to the disc.  This has held quite well.  
If it ever breaks down again, I'd be tempted to buy new aluminum pulleys 
and make a custom clamp nut/pulley hub unit, but this is working quite well.

I'm probably going to convert to all brushless motors at some time and 
make a new control box with a higher voltage for the servo spindle.

I also need to figure out how to get an on-screen RPM display.  I really 
wanted to work on that at the CNC Workshop, but got distracted.


Jon