So you want to get a plastic or ply part cut on a laser machine? I get asked all the time to
make some small part for a model aeroplane in balsa or a pinball machine part from plastic
as I have a mid sized laser machine with a cutting bed size of 500 x 900mm. The biggest part
of the job is usually preparing artwork that the machine can use.
The following applies to the preparation of artwork for ALL laser machines and probably all
CNC machines in general (but check with the person who will make your part to confirm BEFORE
going to the trouble of making artwork this way).
First it must be understood that the laser cutter is simply a dumb printer and all it wants
to "see" is an outline of where it has to cut. Anything else in the file will confuse it and
it will probably just hang and ignore the start command.
So lets start by looking at a part to be made from 2mm clear plastic. We can scan this in
the usual way and then import the scan (in any file format) into a drawing program. I use
Corel Draw but most drawing programs are OK. Here is the original (broken) part as scanned.
We now need to trace the outline of the part and also create any holes that are in it. I do
this manually by creating an outline and curving it as required. You can see in the
following screenshots that a bit of artistic licence is required if the scan you have is low
resolution (this is an actual scan that was provided to me to make a part).
Here is the result when I tried to get Corel to automatically create an outline - you can
see it is not successful using a low res picture as the program follows every slight change
in the outline shape - this is why it is a lot faster and cleaner to draw the outline
manually.
The good thing about using a program like Corel Draw is that you can create the part 'actual
size' so when finished the exported file is ready for the laser machine.
OK, so we have traced the outline and made any holes we need and placed them in exactly the
right positions. Here is the finished part, created the correct size using the scales in
Corel.
Now we need to export this in a format that will retain the size information and allow the
laser machine to use it. I use a format called .plt for a few reasons. Corel can export from
the screen directly to .plt so that solves my problem easily. Alternatively you can export
as .pdf as that will retain the correct dimensions and the person cutting the part can
convert the .pdf to a file of their choice. In my case, if supplied with a .pdf, I import
that to Corel Draw then export it as a .plt - again, problem solved and all size information
is retained.
Here is the .plt file imported into the laser cutting software.
I then select the outline and change its colour. This then gives me two separate things that
I can specify to the software. You can see the arrow on the red outline, this tells me which way the part will be cut,
not important for this piece but sometimes it can be. There are other markers tha show where the cut will start and end.
Now I tell the software what order to cut my red and black items in. Naturally I want all of
the holes cut first and then the outline. If I did it the other way the part would be cut
free from the sheet of plastic and then the holes would not be cut in an accurate position.
I set the machine to make two lighter cuts rather than one single cut. This results in a
smoother finished edge. The video shows the machine doing the second pass.
You can see the holes are already cut free.
Here the part has been cut and is ready to send to the pinball owner.
The owner has fitted the metal mounting spacers.
and finally - the finished part installed in the machine, ready for another 20 years of
play.
As it happened, the front left door of my ute was causing the interior light to flick and
flash when travelling over bumpy roads - I tracked down the problem by banging the bottom of
each door near the switch - I used one of the circles cut from this part and a dob of
contact cement to force the door switch in a further 2mm. Problem solved!
I hope the info above will help people prepare artwork ready for laser cutting. Most of the
time the cost is in preparing for the job not actually doing it. Once I had the artwork (and
it took an hour to make) the actual cutting only took a few minutes.
