posted this on October 31, 2011, 02:17
Ponoko's recent prototyping party reminded me how important effective nesting of parts in laser cut files is. This tutorial is about optimising line work to achieve faster cuts and thereby saving money. Cutting time is generally the most expensive component when ordering from Ponoko. In the forums recently, people shared their methods of saving money, but I think nesting line work requires greater exploration...
This is my design - a bin. It is designed to take standard supermarket shopping bags. It was cut from 6mm thick double sided P3 corrogated carboard. My first prototype came out to be about $40, I thought that was a little steep for cardboard. However, after a few design changes I was able to reduce the cutting time by nearly half.
First, consider good design as being the minimum necessary. The phrase “more is less” is a good mantra to abide by. Clever designers will figure out the best way to maximise the use of materials and processes they undergo.
Look carefully at your design, is there anything that could be considered superfluous? Is there anything that if you took it away, nobody would miss it terribly?
Curved lines vs. Straight lines
In my experience lasers slow down dramatically on curves, ask yourself, are there any parts that you can take away curved sections without compromising the overall design? Several vector drawing programs allow you to either simplify linework down to straight lines. If not try to reduce the size of radiuses as shown in the image below.
Also if you have lots of long straight lines try to align them parallel with either the x or y axis - this means the laser's lens is only traveling in one direction at a time, it is slightly more efficient for the laser cutting.
Check the laser won't see double
There can be an issue with overlapping linework, the laser doesn't know this - it just thinks you want to cut the same line twice. It may sound obvious, but some vector drawing apps are more prone to this than others, it is often very easy to duplicate or copy and paste linework on top of each other.
You usually can't see this, but the laser definitely can. In extreme cases this will double your cutting time (and cost) and increases the chances of burning the material. Do weed though your line work.
The Fix: ungroup lines and drag the vertex points around to check you have no double ups.
Are there any parallel lines, or semi parallel lines you can join to one another to make one section? This will give you greater control over the order of laser cutting parts. Remember to delete any shared lines that may double up.
You can see this below I had 12 individual strips, I changed the design to make them parallel on both sides and placed them together. The laser splits them after it has cut around the outside with individual parallel lines.
Laser cutters don't necessarily cut sequentially where you logically think they should. Sometimes they will travel to the other side of the material for the next line despite other linework in closer proximity.
Also due to the slight unpredictablility of the cutting order I'd encourage you to upload several slightly differently nested files. Sometimes the placement of parts next to one another might help you save a few precious dollars or cents.
These are some general guidelines I've found useful in the past, however your millimeterage may vary. Different materials have different cutting speeds and characteristics. Feel free to post any tips you find on reducing cutting time on these support forums. I'm interested to hear other's experiences.
Remember it is unlikely your first design is going to be the best, prototyping is always an iterative process. Plan to make several variations of your design and do small tests so you don't waste time, money and materials. As my results show a little tweaking of the design can save you a lot.
David is an industrial designer from New Zealand. He contributes a weekly article on personal fabrication for Ponoko. You can follow him on Twitter @dizymac