Machine Digital Read Out

[JeffKiper]

Does anybody have a low cost source for incremental rotary encoders? I don't need the top of the line stuff this is for one of my home macines.

OK I am a little to tight with my money. I bought a used mill to add to the shop. This is a older mill so it doesn't have DRO. I have ran machines for years without readouts with no problems. So this is more of a I want this. I have leftover and taken out of service HMIs, PLC, panels, and all the other stuff except the encoders.

 

[HJTRBO]

Maybe head off to the autowreckers and grab a Cam Angle Sensor. 360ppr on 1 channel and a Z reference on another. Grab one off a VTEC Honda engine and that should be good for 9,000rpm

 

[OkiePC]

http://cgi.ebay.com/ALLEN-BRADLEY-8...temQQimsxZ20100120?IMSfp=TL100120235009r14157

 

[PLCRookie]

As long as it linear

Jeff,

Are you talking about a rotary encoder(attached to the lead screws for positioning of the axis)? If so, you will not get great accuracy with that. yuo really need to have a linear scale to make ti work. I think I would try to find a used DRO instead. There is so much surplus machinery out there now, you should be able to get something fairly cheap. Also, don't forget you time to get it working. Don't re-invent the wheel. There is more to a good DRo than meets the eye.

$.02

 

[HJTRBO]

I forgot that a camshaft rotates twice for every crankshaft revoloution. 360 x 18,000 ~ 6.5mHz. Chur

 

[JeffKiper]

Guys thanks for the replies. It was a MONDAY today. You all know how those days are.

Jeff,

Are you talking about a rotary encoder(attached to the lead screws for positioning of the axis)? If so, you will not get great accuracy with that. yuo really need to have a linear scale to make ti work. I think I would try to find a used DRO instead. There is so much surplus machinery out there now, you should be able to get something fairly cheap. Also, don't forget you time to get it working. Don't re-invent the wheel. There is more to a good DRo than meets the eye.

$.02

Why don't you think I can get the accuracy out of a rotary? 1 turn of the screw is 0.100". A 1000 ppr would give me 0.001" resolution wouldn't it? It is a garage mill. I will have to play with it a little to see what happens.

 

[kamenges]

I think Rookie is referring to things like backlash, screw thermal expansion and screw pitch variation. For example, some motion controllers have lead screw compensation tables that allow the user to map the actual position of an axis versus the reported position and compensate for errors. This doesn't help for all error sources, however.

BTW, 0.1 / 1000 is 0.0001. So you have more resolution than you think. If you count in quadrature, the resolution increases to 0.000025"/count. Assuming you can trust the reported position, that is.

Keith

 

[PLCRookie]

I think Rookie is referring to things like backlash, screw thermal expansion and screw pitch variation. For example, some motion controllers have lead screw compensation tables that allow the user to map the actual position of an axis versus the reported position and compensate for errors. This doesn't help for all error sources, however.

You are right on Keith. Depending on how much accuracy you want, you really should get the real thing. Many of these mills also suffer from lots of wear in the "center position" of the X and Y axis, as most people mount their vises in the center of the table, and usually only run it in that area. You get lots of wear in only one spot,(I have seen the lead screws "peaked" on some). Trying to tighten the gib or nut backlash will not help, as it will then be "tight" everywhere else. Also consider the effects of roll, pitch and yaw, and you can really get some problems. The actual DRO's also can give you multiple reference points, inch/metric conversions, automatic bolt circle features. Not that all of this could not be done in a plc, why re-invent the wheel? Your time is worth something..........

Yeah, it would be a cool project though.........

 

[PLCRookie]

Browsing on e-bay.... it looks like you could get a decent system(new)for $700-$1000...........They do take some skill to get mounted properly, but it is not difficult.....