WEEK 4
COMPUTER CONTROLLED CUTTING

ASSIGNMENT DETAILS
Cut something on the vinylcutter. Design, make, and document a parametric press-fit construction kit, accounting for the lasercutter kerf, which can be assembled in multiple ways.


LASER CUTTING


TESTING PARAMETERS

For this assignment, I was unable to work with the group at echoFab so my tests were conducted at the LCC Fab Lab. I used the same test pattern on the same machine as at echoFab which is a Trotec Speedy 300 60w. While both labs have the same model of laser engraver, it is possible to require different settings as nuances like the age of the laser tube might make it so that our findings are different. The same plywood on LCC's machine might require slightly different settings on the machine at echoFab which is a bit older and sees more traffic. We decided to try different materials so that we can compare more general aspects of the material settings. To see Marc's results, click HERE. To see George's results click HERE.

I decided to do some tests with natural canvas and Trotec Plywood which are two materials that I had on hand that differ from the materials being tested by others in my group. An interesting future test would be to determine the difference in settings between machines of different age. Different labs will have different results with the same parameters.

JOB CONTROL

Trotec uses a software called Job Control. You can assign different functions to different colors. A drawing with multiple colors can be processed in multiple ways. For example, cutting different depths within the same job or prioritizing zones. If you are manufacturing parts or multiples, job control can be sequenced to help speed your jobs. Any fills or strokes that are bigger than 1pt (Adobe Illustrator) will be seen as engravings while hairlines and strokes less than .1pt (Adobe Illustrator) will be seen as cut lines.

Most mistakes occur when color or stroke widths are not set right. What is good about Job Control is that it makes it easy to catch mistakes in your drawing before you cut. The worst case would be to cut an intricate pattern that is meant for paper or wood on a more flamable material like cardboard. The default setting should be weak on purpose in case a user forgets to check property settings. However, it is important to get into the habbit of double checking your material settings before running the machine to avoid surprises and wasting material.



USEFUL LINKS
Trotec has a good set of tutorials and useful information to start from.
Laser Parameter Basic Settings
Laser Parameters for Trotec Materials


CANVAS

I started with testing the cutting of canvas. I lowered the power and the PPI significantly and used the initial settings for paper which were included in the Job Control software. Even though you can get good cuts at higher power settings I prefer to find the lowest power settings needed. As the Co2 laser ages, you can make small adjustments to compensate. If you are not careful, novice users of the machine, like many k-12 students, will be putting a lot more power into jobs than necessary.



For the cut test I settled on 50% power and I adjusted the speed for 8 different cuts. The sweetspot was at 50% power with a speed of 4. The material cuts through but maintains just enough tension to keep the material attached. This means the edges of the fabric are less charred.


Once my initial tests were done I had a good idea for the minimal power settings needed to cut the canvas and a threshold for the engraving.


The ideal settings for Canvas on a relatively new Trotec Speedy 300 60W machine are the following:
---> Engraving: power 60, speed 50, PP1 500,
---> Cutting: power 50, speed 4, PP1 500,


TROTEC PlYWOOD - 3mm

Trotec sells an engineered plywood that is ideal for laser engraving. It is more expenive but is very flat and apparently contains less of the nasty stuff you might find in generic plywood. The wood is much lighter than generic plywood and does not require the same settings. One of the things I dislike is seeing laser cut plywood with lots of burn marks. This is hard to control sometimes when you jump into a cue on an unfamiliar machine in a lab and I won't toss a good cut just for the look of it unless it is specifically necessary. The goal in this test is to find the minimum cut settings required to cut Trotec plywood with no burn marks.



To start I put transfer tape on the plywood. This helps keep the surface clean from the smoke that can stain the surface when cutting.

I started by testing the cut settings using close to the ideal parameters I received from my group members for generic plywood and worked backwards from there. Which were:
---> Power 100
---> hz 1000
---> speed .8 - .5

On the surface, they all cut nicely and the transfer tape did the job. So using these settings, .8 speed is ok.

When I flipped the piece over, I could see all kinds of burn marks. This is a result of the laser pushing through the material and having enough force to refract and split off the noneycomb plate burning the underside of the wood. While I could cover the underside with more transfer tape, this is still a sign that the power is too high or the speed is too slow for this material.

The next test I did was trying different speed settings to find the minimum power/speed required for a clean cut. You can see from my markings, the parts even cut through at a speed setting of 2. This is 1.05 faster than the generic plywood setting from another lab however it rquired a slight push. at 1.8 the material cuts completely through with no push required.

At this setting, I can get a very clean cut. You will notice that the sides of the plywood are not a dark/burnt brown. This particular piece was cut without transfer tape.

I learned from this test that the difference in settings can be quite large between seemingly similar material. These tests will have to become regular practice in my design process.

Ideal Settings:
---> Power 100
---> hz 1000
---> speed 1.8


VYNIL CUTTING

The Vynil cut ter I used for this assignment was from the LCC Fab Lab. It is the Maxx Air from a company called Kilc-N-Kut. I was not part of my group on this assigment. They were using a Roland GX-24 at echoFab. The KNK Max Air machine at LCC has a lot of features for a very reasonable price and it was the first purchase of the Fab Lab. I was looking for a versatile machine that had enough force to cut a variety of material. We have several kinds of knives you can put on it and It can be used to cut or emboss. The build quality is not as nice as the Roland GX 24 but otherwise is very easy to machine to operate.

It uses a software called Make the Cut. The KNK and Make the Cut (MTC) are more popular around scrapbooking communities than they are in Fab Labs. It is software developed for PC but there is a mac version which is an emulator. keystrokes remain PC formated. The machine can be used with a roll of vinyl or you can use cutting matts.


This is a design I wanted to cut. I am interested in using the vinyl cutter to make circuits. This isa 555 LED blink circuit.


When loading files, you have to select the file format. Make the cut has lots of editing features making it easy to fix mistakes.


Once I imported the .svg I had generated I notices a small line on one of the traces.


I could have fixed this issue in MTC directly but it is best practice to change the master file so I went back to Illustrator to find the mistake in the original drawing and proceeded to delete it.
Note: It is a good idea to select all with the "direct select" tool. This will show you all the lines or nodes. Some of whom may be hiding under a shape. In this case, I only noticed the unwanted line when I converted the shape into an outline.


Once cleaned, I re-imported the file into MTC.


Once ready to cut, you must verify your settings. Which are:

---> Machine = KNK Maxx Air
---> Baud Rate = 57,600
---> Serial Port
---> Blade Offset = *
---> Force
---> Speed
* The right blade offset is crucial to getting a good cut. The offset for the lighter blade designed for Vinyl should be @.25. However, after some lengthy research into wobbly shapes and having ruled out pressure or speed as the cause, I found a forum thread suggesting that it was potentially a mac issue. The way to fix it was to double the value. In this case, the manual says a blade offset of .25 but we put an offset of .50 and it works as it should.

The most important setting is speed and force.


My first cuts, the force was set to 50 which was a bu too high. The vinyl was popping out in the delicate areas a little too easily.


I made several tests and smakk adjustments finally settling on a speed of 195 and a force of 45



In the end it looked pretty good. Getting a clean cut of the "+" & "-" symbols.


Next, I covered the decal with transfer tape and stuck it to the back of my computer.


The "555" was cut off a bit from the curvature of the Apple logo so I made another version with the goal being that the entire graphic would be lit up.


Another thing I wasnted to try was to use this decal as screen for coductive ink.


It looked decent but the wood is too porous and the ink could not complete the circuit. I would normally do multiple passes but decided to leave this test and move to the next.


My final test was to cut some copper tape. The settings I chose were higher but I over did it. speed or velocity(v) was at 165 and heh force was at 100.



I took the copper tape off its backing and mounted it to another piece before sending it to be cut. This time I brought the force and velocity down so that speed was at 195 and teh force was at 52 and it cut nicely.




I added transfer tape and successfully planted it on a small piece of scrap wood. It was a bit tricky weeding teh material and it required a bit of manual manipulation to lay get it right. The end result si a bit crooked but I generally enjoyed the experience of my first copper cut.



PRESS FIT

Before cutting a press fit kit, I designed a parametric key to test tolerances of the press fit.

Each notch is based on an initial notch size minus .10 mm.


I made a unique parameter for each notch. It would have been more efficient to simply subtract within the dimension tool. I would then only need one Notch parameter and then individually identify how much to remove from each notch right in the sketch. For example: Notch-.10 / Notch-.20 / etc.


The final sketch looks like this. The overal size of the press fit key is also adjustable with a parameter.



Once the press fit has been evaluated I wanted to create one shape that could do a few things. This design is rather common but what is nice is that the trianglar portion is rather flexible making it possible to squeeze this shape in a few ways.




I will continue to explore this idea and perhaps make a more complex set of shapes for a more interesting press fit kit.


ASSIGNMENT FILES

---> Trotec Plywood Test Pattern:REF_Template_TrotecPLYWOOD.svg
---> Canvas Test Pattern:REF_Template_CANVAS.svg
---> 555 Graphic:amathewson_555_Circuit_vinyl_v2.svg
---> Press Fit SVG:amathewson_Press Fit Kit_v1
---> Press Fit Key Fusion 360:Files/AM_PressFit_Key.f3d
---> Press Fit Kit Fusion 360:Files/amathewson_PressFItKit.f3d