Re: Rotary table DRO

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "babinda01" <a_k@a...> wrote:

>
> Hello,
>
> I was wondering if someone may be able to help me with a problem

I

> have at the moment.
> I am trying to add a DRO to my 'little' rotary table. It is 6

meter

> diameter. I am looking to get .05mm accuracy if at all possible.

I

> was thinking of puting a rotary encoder onto the main spindle which
> is coupled directly to the table, but to get the resolution I am
> looking for I need approx 400 000 pulses per rev (0.00095 deg).

All

Sir:
I have two possibilities to consider. Both require that the outside
of your little table be smooth and concentric to the axis of rotation.

1) Purchase some gear rack and attach it to the outside of your
table. You would need about (11) 6 foot lengths and at each joint you
would have the opportunity to "adjust" the spacing to maintain the
accuracy. Drive a spring loaded rotary encoder off the rack for your
data out.

2) There is thin stainless steel reflective scale available with the
associated read head; it would need to be bonded to the SMOOTH OD of
your table. This option would be much less tolerant of a hostile
environment than option (1)

I like option (1) better. I'm using some 1/10 inch circular pitch
rack which is .31w by .38high (inches) and this would curve nicely
around your almost 10 foot radius. The increased tooth spacing error
from the curvature radius would be approximately 1.0016066 times!
That means that 1 meter of circumference would read 1/1.0016011
or .998396 meters. Decent quality rack is not too expensive, can be
adjusted at each joint, and is quite dirt tolerant.

Regards,
Jack C.