RE: [CAD_CAM_EDM_DRO] DRO Encoders

-----Original Message-----
From: Larry Edington [mailto:larrye@...]
Sent: Friday, April 07, 2000 2:09 PM
To: CAD_CAM_EDM_DRO@egroups.com
Subject: Re: [CAD_CAM_EDM_DRO] DRO Encoders

> It is not as easy as you think. If you add up all the time it takes
> research, manufacturer and install the brackets for the encoders it's
>about the same cost as linear scales.

>For a hobbiest, time isn't a factor. Cash usually is. I really doubt it'll
>take anyone that could use a mill and DRO very long to mount three encoders

to it. I mean

>gee, I designed, posted and CNC machined two mounting brackets for encoders

yesterday,

>mounted them on the machine ( and they fit first time ) in less than 1 hour

start to finish.

>It wasn't a mill or lathe though.

I guess if your hobby is to make custom brackets then you have all the time
in the world.
I don't know a lot of hobbyists with a cnc in their garage either.

> Then you have the issues of inaccuracy due to the measuring device being

so far away for the work area, repeatability

> due to backlash in the machine, the screws might be english pitch while

the

> encoders are metric so the count per revolution are not correct and other

matters.

>
>If you are measuring the actual movement of the slide, NOT the rotation of
>the lead screw, then you are measuring the actual movment of the work piece

as

>accurately as possible since the encoder wheel is rotating against the
>actual slide the workpiece is mounted on. I don't see how backlash is an

issue unless you are

>trying to measure the rotation of the screw. Backlash is the difference

between

>commanded movement of the screw versus actual movement of the slide isn't

it? It comes from

>slop in the lead screw / nut union or slop in the fit of the ways and gibs.

Maybe I am mistaken but I thought the discussion was referring to mounting a
dro on some sort of mill or lathe type machine.
Of course in general terms you always want to measure the actual movement
but on a mill or lathe it is not that easy and usually done on the screws of
the machine when using a rotary encoder. With this in mind them my previous
statements do apply.

>The issue of metric versus English doesn't matter as the movement of the
>slide is what is being measured, not the rotation of the screw.

As I stated above.

> A set of calipers that are 20" x 9" are still expensive and not a as
> accurate as a standard dro system
>
>True, if your machine is that big, calipers won't be practical.

>later,
>Larry E.

Best Regards,

Tim Barnard
Fagor Automation

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