Christopher Purcell wrote:
> I would like to improve my home-made 3D wood carving router. It has  
> stepper-driven 1m long THK ball screws (bless you Ebay) which seem to  
> be moving exactly as EMC2 commands, now that I have Helical couplers  
> fixing the backlash.  The next thing I want to check and maybe tweak  
> is the perpendicularity of the 3 axes, which I bolted down using only  
> a carpenters square and level as guidance. This is in a home wood  
> working shop so the only instrumentation available is a dial  
> indicator. If I can measure the axes, then corrections can be included  
> in EMC, presumably as hinted at in the kinematics chapter of the  
> Integrators handbook.
> 
> How do you measure the perpendicularity of 3 axes of a mill?
> 
> [EMAIL PROTECTED]

How fancy do you want to get?

If you trust your square, loosely fasten it down to the table, on
spacers that are high enough so that you can set the plunger of the
indicator horizontal and run it along the edge of the square.

Mount the indicator to the head of the machine, and aim the plunger at
the edge of the square that is roughly parallel to X.  Run X back and
forth, carefully adjusting the square till the indicator reading remains
constant over the whole length.  Then tighten down the fasteners holding
the square and check that nothing moved.

Now rearrange the indicator so the plunger runs along the other leg of
the square.  Run Y back and forth, and write down the indicator readings
at each end.

If you don't absolutely trust the square, you can double check it.  Flip
the square over around the Y axis, and repeat the X alignment and
clamping steps.  Then run the indicator along the Y edge again.
Comparing the two sets of readings will tell you whether the error is in
the square or the machine.

Drawing pictures with grossly exaggerated errors will help you figure
out the geometry and how to tell where the errors are - I'm not going to
try to put it into words.

Regards,

John Kasunich

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