Encoders

[justCNCit]

Haven't been able to find any linear encoders. They are on all the mills at school, although I'm not sure they are the kind best fitted to CNC applications.

I'm building a router using a stepper drive and it's about 6' long and 3.5' wide.

I'm trying to plan ahead, counting on the fact that some work may end up being scrapped because of missing steps & resonant frequency issues.

Also, I wanted to go with linear encoders rather than rotary, because rotary does not account for ACME screw backlash. However I imagine a 6' long linear encoder won't be cheap.

What are your guys thoughts on this?

[Al_The_Man]

With a 6ft long router, what resolution are you seeking to justify a 6ft long scale?
Believe me you don't want to know the price, even if you can get one.
I know of no commercial plasma or router table that uses or needs scales that large.
Also I personally would forget the acme screw method.
There are some very acurate tables out there using rack and pinion.
Al.

[justCNCit]

I spent about the last year researching ACME screws, don't know a thing about rack & pinion, save that it looks pretty sloppy & not to mention probably pretty expensive.

This is one of those cheap setups, I'll be giving dumpsterCNC some business. So I'll be sticking with ACME for this M/C.

Even so, encoders would still be needed. I figure maybe a rotary encoder on the gantry that tracks on the frame somehow might be an idea to develop on.

[Al_The_Man]

I spent about the last year researching ACME screws, don't know a thing about rack & pinion, save that it looks pretty sloppy & not to mention probably pretty expensive.
This is one of those cheap setups,

Rack & pinion is the method of choice of most manufacturers, not sloppy if done correctly, it is also fairly economical.
A rotary encoder that tracks the Gantry will probabally entail a rack of some sort, anyway.
Try to get a look at some commercial gantry's to compare methods also.
Al.

[Fifty_ohm]

Check out this site for a solution to your actual table movement with rotary encoder. http://bellsouthpwp.net/A/r/Arts_home_page/DRO1/

I've seen this type of setup used before and it can be highly accurate depending on the effective gear ratio of the pulleys.