RE: [CAD_CAM_EDM_DRO] Building A Cheap DRO

Take a look at the usdigital's linear encoders. They are 360 CPI and in
quadrature that is 1440. 1/1440 .0006944" Then if you use the Tom
Kulada's dro+ software that I can email you and my pcb that connects
between the pc and the encoders you will have a nice dro (see
www.seanet.com/~dmauch). If you try using wire or machining pulleys to a
certain diameter to make it come out right, then you could run into
problems if the wire isn't perfectly smooth to a few .0001 of and inch.
Also look at the pulley diameters. If you are off tenth of an inch in
diameter that you will be off quite a bit over several revolutions. I
did the math a long time ago and was surprised at how precision the
pulleys would have to be.
Dan

-----Original Message-----
From: cutsgems [mailto:chuknospam@...]
Sent: Monday, March 18, 2002 7:34 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Building A Cheap DRO

I'd like to add a 3 axis DRO to my mini-mill. I've investigated the
Calareo/Wholesale tool import digital machine scales & readout box,
nearly $500 to cover all three axis. So what I had in mind was some
encoders from US Digital, something like 2000 PPR?? to get 0.0005"
resolution, use a simple wire under tension wrapped around the axle of
the encoder to convert the linear motion to rotary. Use an old laptop
& printer port & available software for the readout.

My questions are the mechanics for the encoder.
Would a 1000 PPR encoder give me the resolution required if I used
0.6369" diameter hub on the encoder as opposed to a .3183 diameter hub
which would only yeild a .001" resolution. Or am I better off using a
2000 PPR encoder with the .3183 hub? (The .3183 is a rough calculation
required to convert 1" of travel into 1 rev on the encoder).

Secondly, when calculating the hub diameter, how do I account for the
wire diameter in the calculation? Is it 1/2 the wire diameter +/- the
hub diameter???? Thanks.


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