Sunday, July 12, 2009

Using a Cricut cutter for Model Railroading

[Hint: I got better results after this post. Check later blog entries for my experiences with the Cricut.]

Ok, here's my full first-day impressions of using the Cricut. I posted this to the ModelersCad mailing list at Yahoo as well.

I'd seen some questions on this mailing list about using one of the scrapbooking / vinyl cutting die cutter machines for model building. Here's my experiences after one day of experimentation. (See the previous post for pictures of sample cuts.)

Short answer: the machines are interesting, but they're not a substitute for a laser cutter. My cutter (like, I suspect, other die cutters) works best when cutting curved, closed shapes, and tends to put 0.050 radius curves on right angle intersections. Using non-meeting line segments didn't really help; the software with my machine sometimes ignored unconnected lines (that were probably below some size threshold).

If you're doing mostly curved shapes (such as cutting pieces for a model airplane's wing cross members) you could probably do some interesting work in thin wood. If you want to cut lots of right angles, you'll be less happy.

My cheap machine did really well with my modeling materials. 140 pound Bristol board (0.020 inches thick) cut cleanly. It could cut into, but not through heavy (0.050 inch) matboard. Cuts in paper were usually clean, though I did see minor tearing when cut lines intersected. The machine only scribed 0.010 and 0.020 inch styrene, but it was really easy to snap on the scribe lines to get a clean result. I suspect it would work really well scribing 1/16" styrene sheet.

I also tried it on 1/16" basswood with the "thick material" blade. The Cricut didn't cut completely through with a single cut, but it did score the wood pretty deeply so that cutting the pieces fully out would have been easy. The basswood moved around a lot even though it was taped down, so accuracy was a problem.

The other big problem is that while cutting curved letters by hand might be tedious, my models with lots of straight lines are much less work to do by hand. The die cutter helps if I'm doing multiple duplicate pieces, but tweaking cut lines and artwork when doing mock-ups is almost as much work as cutting a new model out of paper by hand.

Long answer:

I'm a model railroader, and I've been interested in doing my own laser-cut buildings in HO (1/87 scale). Unfortunately, I'm too cheap to buy my own, and too lazy to drive 20 miles to TechShop in Menlo Park to use theirs. I was curious if a vinyl cutter like the Klic-n-Kut would give me usable results.

I found a cheap way to start; the craft stores (Michael's, Joann's) often have the Cricut die cutters on sale. I got a 6" x 12" die cutter for $99 on sale yesterday. To use the machine, you place or tape your paper or cardstock on a sticky plastic cutting mat, feed it into the printer, then tell the machine the letters or shapes you want it to cut. The cutting blade is a tiny pointed blade on the end of a 2mm rod; a larger blade holder sets the blade to an appropriate depth that will cut the media but not the cutting pad. The holder stays stationary, but the blade can turn in the holder to handle changes of cutting direction. This turning (and a slight amount of play in the blade holder) means that cutting continuous shapes always results in curves at corners. This is great for lettering (which the machines are intended for), but less good for miniatures having lots of right angles. By contrast, laser cutters are great at square corners.

Cricut cutters only do fixed fonts and shapes, and require you to buy their cartridges ($45) to get new fonts. To use the machines, you type in the letters you want into an attached keypad, and the machine does the cutting.

The Cricuts do have a USB port, but their software won't let you cut arbitrary shapes. Luckily, a third party ( sells a program called "Sure Cuts a Lot" (SCAL) that lets you import SVG vector art from a drawing program and cut it on the machine. I had some problems with the SCAL software; it wouldn't connect to the Cricut when I used it with a computer running Mac OS X 10.5, but ran decently on Mac OS X 10.4.(Bzzt. I'd already installed a USB->Serial driver in the past, and it would grab the Crikut device when the OS booted. Deleting /System/Library/Extensions/FTDIUSBSerialDriver.kext got rid of the problem, though now I have to worry why the other driver was installed.) It also imports the art at a different size than my original drawing; I added a 1x1 inch square on my art so I could scale the drawing representing the cuts to the rough size I wanted.

My first project (after a few test letters with the stock Cricut) was a smaller building model. I'm trying to mock up a potential design, so I've been cutting cardboard models out of Bristol board, assembling them, and putting the models on the layout to check size and composition of the scene. Recently, I've tried to make the buildings more real, so I've been drawing the wall shapes and details in a vector drawing program, then printing out these drawings and cutting the pieces free.

Making this model requires some larger cuts for the walls and window openings, and finer cuts for pieces of the windows.

The walls come out ok. Sometimes, the rounded corners are pretty short; on other cases, the blade seems to have trouble finishing the curve and ends up with a spline-like curve that only ends up going straight after a tenth of an inch or so. Interior rounded corners are a little annoying, but can be cleaned up by hand (especially in styrene). Rounded corners on the outside edges are more troublesome; for model buildings, I might be able to cover these with trim.

To really challenge the cutter, I tried cutting the individual window panes out as a laser-cutter would, even though I've not been cutting these by hand. I really hoped the machine could do all the tedious cuts to do individual window frames and panes in a piece whose total size is an inch by 1/2 inch. The laser cutters do beautiful jobs with these sorts of pieces, and it's possible to build up some beautiful windows by layering together multiple pieces. Unfortunately, the rounded edges are a problem.

I also tried cutting the geared calling card available at Thingiverse. (I converted the PDF version of the drawings to line art in the Mac drawing program Intaglio, then exported the line art as an SVG file that could be read in by SCAL. Note all the curved surfaces are set up as line segments, so replacing them with arcs makes the cutting go much faster.) SCAL managed to cut the gears with a lot of up-and-down cutting action, but didn't actually cut through the cardboard fully. It made quick work of the non-gear parts, though. I'll need to try again another time.

So far, I'm not convinced that I can let the computer do all the cutting for my models; the die cutters (at least from what I've seen with the Cricut) just aren't intended for the right angle cuts that all my structure models require. Some of this might be the machine, but I could imagine that some of the problems are with the software that assumes you're cutting out rounded, connected letters. I could imagine tricks the software could do to do better on work like this. It could always do right angles as separate cuts, and do all cuts in the same direction at the same time to keep the blade pointed in the same way. The software could get the blade pointing in the correct direction by starting on a bit of waste material. Nearby cuts could be done at the same time to avoid losing accuracy over several cuts. It's too bad there's no open-source drivers for the Cricut available, or I'd be playing with driving the cutter in different ways to try to get better right angles. Other makers (such as Klic-n-Kut) might do a better job with different kinds of cutting jobs, for all I know.

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