Re: [CAD_CAM_EDM_DRO] Building A Cheap DRO

Answers interspersed below (Bold)
At 03:33 PM 3/18/02 +0000, you wrote:

>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.

Yes, this is very workable. I used 1000 line encoders with a mechanical
doubling circuit to achieve close to this resolution.

>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).

This is a double edged sword as the smaller the diameter, the greater
likely hood of slippage. Therefore, the larger the resolution of the
encoder (eg. the larger the diameter of the axle), the better off you are.
Of course if you are adventuresome, go for the smaller diameter and the
larger resolution 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.

Based on the original calcs that I did, you are close enough for all
practical purposes. In the software that I used, you tweek it with a final
calibration routine anyhow so the calcs are strictly theoretical anyhow.
You can see how I did it on my website as noted in the tag line. Of course
YMMV.

>Addresses:
>FAQ: http://www.ktmarketing.com/faq.html
>FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>
>OFF Topic POSTS: General Machining
>If you wish to post on unlimited OT subjects
>goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to
>reach it if you have trouble.
>http://www.metalworking.com/news_servers.html
>
>http://www.jobshophomeshop@yahoogroups.com I consider this as a sister
>site to the CCED group, as many of the same memembers are there, for OT
>subjects, that are not allowed on the CCED list.
>
>
>
>Post messages: CAD_CAM_EDM_DRO@yahoogroups.com
>Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
>Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
>List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@...
>Moderator: jmelson@... timg@... [Moderator]
>URL to this page: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>bill,
>List Mom
>List Owner
>
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

Bubba

OLDER THAN DIRT
Country Bubba
(Actually the inventor of Country and Bubba)

axtein@...
LaGrange, GA

http://members.dicomm.net/~axtein


[Non-text portions of this message have been removed]