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squeezing the last bit of accuracy on a BP V2XT cast Iron

johansen

Stainless
Joined
Aug 16, 2014
Location
bainbridge island
rotary encoders are produced in a variety of ways but many are an etching process using a master. the substrate can be plastic or glass.
a company i work for buys a custom reticle and its chrome plate on glass about 1/16" thick. about $60 each, about 1"diameter. a new master is like 2000$. can get anything you want, complexity is of not much additional cost because the cost of making the master is just the human labor of verifying what is produced is what the drawing shows. we send the reticles back that actually have defects and they give us new ones in exchange, and i personally inspect the every single one. they are almost always perfect, with the occasional pinhole. less than 5% of the time the chrome is not removed where it should be removed, and a rotary encoder this wouldn't matter if its not in the path of a detector.

there is no such thing as being off by a few counts without also a complete loss of tracking. (because two light sources and two receivers are used in quadrature and a missing line, or an extra one in the wrong place would totally screw up your system.)
 

madmachinst

Stainless
Joined
Jan 15, 2007
Location
Central FL
since you've got what looks like a 3:1 ratio, it should be very easy for you to hold a ruler against the servo pulley and scribe a line on it, anywhere. then move the machine one turn of the servo repeatedly (whatever that turns out to be)

and you should easily be able to witness the error, if it is from the servo.

ok sharpie then scribe a line on both pulleys and see if they continue to line up when one rotation of servo shaft is made. Or are you talking about something else, cause it just hit me, I can't scribe a line on both pulleys in one shot. These are 2:1 ratio not 3:1, that is from Bridgeport manual.

You don't think the misalignment would have anything to do with this error?
 

madmachinst

Stainless
Joined
Jan 15, 2007
Location
Central FL
I would have to be big big no on this with my limited experience.
This is insane, Never have seen 100 to 288,000 be off by one count unless mounted badly. This sort of goes with how these things are made.
No...... they are not engraved in stone they are engraved in glass. If this count off other problems.
Now rotary to actual linear inches moved. Many things become involved here.

BTW, 5 years ago when I had this running, I was using the old servo motors with crappy capacitive encoders. CUI I believe was the name. Their problem was they were very susceptible to EMF RFI and all kinds of other junk. I believe if my memory serves me right adhesive was part of the installation process after using their dingy plastic collets. After a rapid I didn't know where I landed. Parts always came out good though, but always had to rezero cutter when reloading a new part. That means touching off X and Y on the semi finished stock. I got sick of that so invested in new electronics Now got it moving but it isn't there yet. Thanks for all the help folks.
 
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madmachinst

Stainless
Joined
Jan 15, 2007
Location
Central FL
Here is an observation about the Y axis. Pulleys are also out of align, I'd have to say between 3/16" to 1/4". I basically laid the straight edge on the machined surface ( fly cut marks evident) of the case and say that much of a difference between screw and servo pulley. On servo pulley the straight edge is interfered by the rim of the pulley. Again servo shaft seems too short but not as bad as X axis. Maybe no need to make extension for this one. At this point I suspect Z will have the same situation or maybe not since I made a thinner adapter plate out of steel instead of 6061.

IMG_20210730_131450411_HDR.jpgIMG_20210730_131435621_HDR.jpgIMG_20210730_131446655_HDR.jpg
 








 
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