Re: Which to trust, home-built DROs or hash marks?

Did you measure the end mill? I have a boatload of 1/2" EMs
that measure 0.450 - 0.480.

Also when you manually manipulated the knobs, did you account
for backlash ? like approaching both locations from the same side?,
and clamp the gib of the non-used axis?

Just trying to rule out the easy stuff.
-Damon

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "John A. McFadden"
<mcfadden@c...> wrote:

> I recently completed fabricating and installing the Y axis of my

home-built

> DRO (using a 25 cycle per mm linear strip from Encodertech.com,

which gives

> a DRO resolution of 0.00039xxxxxx inches per jump of the encoder

after

> quadrature) using Art Eckstein's DRO program and interface plans (I

used

> linear strips instead of rotary disks because I dont have a lathe to

turn

> the bushings).
> Now that I have the Y axis complete, there comes the question of
> calibration. My mill is an Enco 16 3/8" Mill/Drill, and I found

that when I

> milled two flats onto a billet of aluminum such that the flats would

be

> 1.500" apart (using the hash marks on the mill's Y handle to

determine size)

> using a 1/2" endmill that the following measurements resulted:
> The Mill/Drill's hash marks read out 2.000" between centers (so the

flats

> should have been 1.500" apart)
> My digital calipers (cheap chinese) said its 1.514" between the

flats

> My standard calipers (not dial) said its 1.515" between the flats
> and my digital readouts (I calculated the incremental value using

the 25

> cycles per millimeter and calculated it out to be the 0.00039xxxxxx

number

> which I then plugged directly into the program, rather than using a

scale

> and needle for the calibration because I just ordered the scale on

Thursday

> and it hasnt shown up yet) said that the endmill moved 2.0164"

(saying that

> flats were 1.5164" apart).
>
> Now the question comes up, what to trust? Should I just accept the

1% error

> in the hashmarks on the mill and only use the DROs (the X and Z axis

parts

> should be arriving on Thursday)? Or should I investigate further to

find out

> if there's any other error in the system?
>
> Thanks,
> John McFadden