Week 4: Computer Controlled Cutting

group assignment: • do your lab’s safety training — characterize it in a few points • characterize your lasercutter’s focus, power, speed, frequency rate, kerf, joint clearance and types

Getting to Know Our Lasercutter

Fab Lab NODA has a 30 watt C02 Laser (EPILOG Helix) that is 24’’ x 18.’’ It is a co2 laser.

For this week’s assignment, we would use 1/8’’ acryllic, cardboard, and plywood.

Laser Settings

Material	Speed	Power	Freq
1/8” Cardbord	25%	60-100	500
1/4” Cardbord	15%	65%	1000
1/8” Plywood	15%	100%	500-2500
1/8” Clear Acrylic	10-40%	100%	5000

Characterizing Focus, Power, Speed, and Frequency Rate

Some notes on workflow: To do characterizations for varying power, speed, and frequency settings, we used color mapping to run different settings for one cut. Doing this we can layout the cut setting based on the color. Once we’re done with inputting color and/or settings, we have to make sure to push a specific button to apply. The order of the list is the order in which things will be cut. Checkbox for color mapping also needs to be checked for any changes to be applied. There are also check boxes for whether you want the laser cutter to cut raster or vector. 99% of the time we will check air assist to make sure there is needed airflow during the cut.

Here’s how we color mapped our test cuts to help us characterize settings on our laser

Focus Our laser’s focal length is 2in. That means the distance from the laser to the center of the “x” where all the laser beams converge is 2 in.

Power Our laser is just a 30 watt laser so it doesn’t have much power. For materials like acryllic and plywood we max out power. For cardboard we wanted to test how change in power effects the material since we have to be extra cautious with the flammable material.

With our 1/4’’ cardboard we kept frequency and speed constant (500 and 25) and we varied the speed 0-100. We did the same with 1/8’’ cardboard.

For the 1/4’’ cardboard, it never cut through. We could have cut it twice or bump up the frequency (we tried this out a lot as we experimented with our own prototypes).

For the 1/8th’’ cardboard, the cut started to go through at speeds of 60 and above.

Frequency

Frequency is the pulses per inch in our Epilog machine.

With our 1/8’’ plywood and while keeping power and speed constant (at 100 and 15 respectively), we varied the frequency in the cut from 500-2500

Since we were bumping up the frequency, we watched extra carefully. All lines cut through and visually the charring didn’t change much.

Speed We ran some tests with 1/8’’ acryllic first. Keeping power and frequency constant, we varied the speed from 10 to 25.

Something we observed: the suggested cut was very off for the acryllic – the laser didn’t cut all the way through until we brought the speed down to at least 13.

Next we ran test with 1/8’’ plywood varying from 10 to 20. The laser cut reliably up to 15 speed.

Characterizing Kerf, Joint Clearance and Types

Kerf The kerf refers to the small amount of extra material removed by the laser. To measure the kerf for our laser, we cut out a 1’’ x 1’’ square, and used the caliper to measure the difference between measurement we gave the machine nd the actual measurement of the resulting cut. We intended to cut a square with sides at 1 inch. When we measured with the caliper it showed the actual cut was 0.9930 inch, so the difference between that dived by two gave us the kerf: (1-0.993)/2 = 0.0035 inch. Thats 0.0889 millimeters.

kerf = 0.0035 inch = 0.0889mm

To test joint clearance, we made a test kit and designed it parametrically in fusion. The joint width we varied by several degrees of kerf. We assumed material thickness of 3mm.

The best press-fit was the joint width that subtracted 2 times the kerf from the thickness. The next biggest joint width subtracted 1 times the kerf and was slightly on the loose side. At 3 mmm and more was too loose for press-fit.