02-furniture project by lutz strassburger

Project: router template

(by Lutz Strassburger, April/May 2014)

The purpose of this project was to use the laser cutter to make router
templates to be used for milling wooden shapes needed for making a
wooden piece of funiture. As template I used MDF boards (because MDF
is cheap). The DIY store (Leroy Merlin, Massy) had 3mm and 6mm
available. Depening on the router and the bit, for some templates 6mm
are needed, and sometimes 3mm are sufficient. I used both.

This documentation contains three parts:

1) InkScape vs. CorelDraw issues

2) A general aspect of drawing router templates

3) Laser cutter settings

The actual woodwork is not part of this documentation because (a) it
is not related to the FabLab, (b) it is not yet done, and (c) there
are many youtube-videos explaining it much better than I am able to do

Pictures will be included later.

1) InkScape vs. CorelDraw issues

For drawing the templates, I used InkScape under Linux. The software
for cutting is CorelDraw under Windows. Porting caused weird
surprises: sometimes parts of the image disappeared, sometimes the
printer did not cut edges although they where visible in the CorelDraw
file, etc.

What worked in the end:

 *** always export as pdf (300 dpi) *** 

If CorelDraw sees an edge in the pdf, the printer will cut
it. Exporting as plain svg caused surprises: change in the size of the
image, edges seen in CorelDraw but not cut by the printer, etc.

Sometimes edges where not seen in the pdf by CorelDraw. Possible
causes (Mainly conjectured by me, I did not try to repeat the error to
verify my conjectures):

- clipping was used in InkScape (in the pdf everything was clipped
 and not only parts)

 Solution: don't use clipping. Work around: before exporting, use
 "path - break apart" to get pieces, which can be deleted
 individually after porting.

 Also: ungroup everything before exporting

- some paths had opacity less than 100% (and thus became invisible in
 the pdf)

 Solution: before exporting, set opaque=100% for everything

- circles where duplicated in InkScape and then different parts of
 the circle were used as arcs (and only one of them was visible in
 the pdf) 

 Solution: mark everything and use "combine path" (ctrl+K)

- pdf can't handle layers properly. 

 Solution: before exporting, move everything to one layer and delete
 all others.

- the pdf is deleting everything that is outside the page borders
 (paper size: 610mm x 305mm). 

 Solution: make only templates that are smaller than that, and
 before exporting move them inside the page; use paper size 610mm x
 305mm also in the InkScape "document properties".

- Another thing: When a shape is composed of several paths (e.g,
 several circle arcs and lines), use the "node tool" to join the
 edges. This will make a smother cutting and create a closed path
 that is needed to produce a proper "outset" (see part 2 below).

Once the file is opened in CorelDraw, and everything looks as it
should be, make sure, everything is "black" (000000) and in
"hairline". Otherwise it won't be cut.

2) A general aspect of drawing router templates

When using a router with a template guide, the shape that is cut by
the milling machine is not identical to the shape of the
template. There is an offset determined by the difference of the
radius of the template guide and the radius of the bit. For example,
if you have a template guide with diameter 17mm and a bit with
diameter 8mm, you have an offset of 4.5mm. To get that you use the
"outset", ctrl+), of InkScape. The value is set under "inkscape
preferences - steps - inset/outset by". I found 1mm = 3.543px, and I
used 15px (15.9px would be more precise, however the cut of the laser
also has a certain width). Furthermore, use "object - fill and stroke"
to make round corners before taking the outset.

3) Laser cutter settings (for Epilog Mini 24)

For cutting, I experimented with the following settings

 1/8" (=3mm) official settings: 35/100/500 (did not completely cut)
 new try: 35/100/1500 (still a bit tight) 
 new try: 35/100/2500 (flames came up, still sitting tight)
 new try: 28/80/500 (more smoke, a bit tight) 
 numbers from webpage: 30/60/500 (less smoke, not well cut) 
 new try: 25/60/500 (less smoke, not well cut) 
 new try: 25/80/500 (some flames, but good cut) 
 new try: 25/75/520 (less flames, fine cut, but bad in corner)
 new try: 24/80/530 (some flames, good cut, tight in corner)

 1/4" (=6mm) settings from Romain: 7/60/500 (works just fine, but slow)