Re: [CAD_CAM_EDM_DRO] Re: Newbie: Two halves not aligning properly : part 2...long again

kaptainkarst wrote:

>Thanks to all that have replied so far.
>I tried to keep the original posting as short as possible but still
>convey my delima.
>
>The material I am testing/learning with are blocks of wood that I have
>planed, squared and joined the edges of.
>Granted this is not the best case scenario, but it's cheap and I can
>burn the scrap this winter in the shop (I can hear the die hards now
>complaining about getting sawdust on the ways....so please don't go
>there in this thread ;-) )
>
>I am using a .375" drill bit in a collet (not a chuck) for the index
>holes.
>I am using a .25" router bit in a collect as well.
>I am feeding at 2 inches per second.
>
>

2 IPS? Well, there's your problem! Unless the spindle is spinning at
20,000 RPM, this is WAY too fast for metal. You want a feed per tooth of
about .010" * the end mill diameter for aluminum, and .005" for mild steel.
You probably still want the beed no more than .025" for very rough wood
cutting, and maybe stay in the .005 - .010" range for a decent finish and
accurate dimensions. Well, to get a feed per tooth of .010" on a 2-flute
cutter, you need a spindle speed of at least 6000 RPM.

Are you really feeding at 120 inches/minute (2 IPS)? Or, are you
meaning to say 2 IPM? (Although that would be on the slow side for wood,
it is not out of the question for metal cutting.)

>The depth of the drilled holes are .5"
>The depth of each of the slots are .125" and I do it in one pass at 2 IPS.
>
>The 3 randomly spaced index holes line up fine, so I don't think my
>drill routines are the issue.
>
>The milled slots are nothing special.
>The horizontal slot is 4" long on the X axis only (not at an angle).
>The Vertical Slot is 3.5" long on the Y axis only (again, no angles).
>
>When the two halves are joined, the end of the slots do not align with
>each other (I'll attempt illustrate this below).
>XXXXXX
>X X (half A)
>-------
> X X (half B)
> XXXXXX
>
>The above "skew" is present in both the X and Y slots.
>
>Now that I'm looking at it and thinking deeper... It is almost as if
>the table is traveling at a slight angle in BOTH directions. This
>angle is then multiplied X 2 when the mirrored half is milled and then
>joined with the first half.
>In other words, the slots are NOT parallel from end to end.
>If the first end looked like the above cude illustration, the the
>other end of the work piece would look like the below illustration.
>
> XXXXXX
> X X (half A)
>---------
>X X (half B)
>XXXXXX
>
>So even though I indicate the edge of the work, it appears that maybe
>the machine is indeed off and the X axis and Y axis are not traveling
>at perfect right angles to each other...
>
>

One thing that comes to mind is that the work may have been forced to shift
on the machine table. You might want to indicate the corner of the part
AFTER
the cut to see if it has moved any.

Otherwise, 3 holes with enough distance in both X and Y between them should
detect any orthogonality problems when you flip one part over, and you
say there's
no misalignment then. So, that seems to indicate the misalignment only
happens
on the linear cuts.

Jon