FDM: Model Position = Futile Effort?

From: Dustin_Neifer@amway.com
Date: Tue Mar 03 1998 - 22:52:55 EET


 We have a little problem with our Stratasys FDM-2000 when running multiple
files at the same time. The problem is that the model tip seems to lay down
material which is off in X by -1.250" (in respect to the support material -
i.e. bases). This is ONLY in cases when we're running a batch job of
several .stl files AND relocate the origin to be as close as possible to
the ABS wipe brushes. We don't see this problem when running a batch of
parts and locate the origin (during the hardware initialization cycle -
right after the .sml file is sent and the machine goes on pause) close to
the front/left corner of the foam base. Nor do we see this problem when we
run single parts in any origin location on the foam. And yes, the machine
was calibrated w./ sscal prior to running the batch job.

 I thought it'd be a good practice to set the origin for any job to be as
close to the wipe brushes as possible. I hoped that moving the footprint of
the job being run to being as close as possible to the rear/right corner
(for ABS, rear/left for elastomer) would minimize head travel (rapid moves)
when the tips go to and return from brush wipes (I usually set to wipe on
every level). I theorized that this would minimize overall machine run
time. I have yet to determine whether or not this practice is worthwhile.
Does anyone else do this? When I explained this to Stratasys' customer
support they said it was an unusual practice.

 Another thing that Stratasys customer support said is that they heard of
this problem before and that it was usually encountered in cases where the
origin was relocated past either -.100" in X and -.100" in Y or past either
4.000 in X and 4.000 in Y. They didn't comment on whether or not this had
anything to do with batch jobs. This doesn't jive with me because I've run
single model jobs where I set the origin at @ 8.500" in X and 8.500" in Y.
Stratasys attributed this as a bug which was hard coded in the machines
controller. Is there a fix or should I just conform and set my origins to
the front/left?

 The net effect of this problem is that the model material drapes over the
bases to the left (by 1.250) and we get some nice spaghetti in the areas
where there's nothing for the model material to lay on. The tips are also
confused by this increment and their roads have "crosslinked" overlap. This
makes it impossible to remove the supports from the model because they're
so embedded.

 Does anyone else have this problem? What about other machines (1650, 8000,
etc.), do they do the same thing?

Dustin Neifer
Amway Corp.
Water Treatment R&D
Ada, MI, USA

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