Week 3 Computer Controlled Cutting
Summary
This week I printed out a simple design on the vinylcutter which was fairly easy to do although I did not pluck it perfectly I met the requirement. Learning to make a parametric design in Solidworks was more complex but I picked up a couple of the mechanics that I was struggling with before and with some help from my instructor was able to make a parametric model and working construction kit. It has no particular function other than the random combination of components for fun.
Assignments
1. Group assignment:
- Do your lab's safety training
- Characterize your lasercutter's I used the following student's page for reference Ahmed_Ibrahim
focus- The distance between the laser cutter and material to get the smallest focal point. Ahmed's lab has something called a focus coin which if we don't have it at our lab we should replicate.
power- The wattage of the laser needed to cut different materials Speed- The speed of the laser needed to cut different materials kerf- The width of the cut joint clearance- the tolerance of a joint needed for optimal fit. That is if I have a 5mm width "male" component should the "female" optimally be 4 4.5 4.6 etc for a good press-fit
For the power test we ran a power speed matrix to test how the laser would cut plexiglass. Johannes had set up a matrix with different colors and then created colormapping in the software so that each color represented a different combination of color and speed.
We have made some progress as a team, in particular [Olof] and [Johannes] have produced pdf files we can use to test the Epilog Mini 24x12 cutter. This is 61cmx 30.5cm in non confusing metric units.
Fab Lab Isafjordur has a Epilog Mini 24x12 cutter or 61x 30.5 cm. It is a class 2 laser product and there is fire risk involved in using it particularly if cutting acrylics.
It is important to always stay near the unit when cutting to be ready to turn it off if something is catching on fire. When operating it it is important to turn on the air assist units there are two of them in Fab Lab isafjordur.
The procedure to cut is as follows. Select the material and place it in the cutter. To adjust the focus we use a magnetic clip that we hang on to the laser and then gradually move the laser unit until the clip barely touches the surface. Typically it will overshoot a little and then we move it back with one push of the button. Next step is to select the starting point so we press x/y disabled and then go and then we can manually move it to our desired starting point. We need to make sure the pointer is turned on to see where the starting point is. Then we his set home and are ready to cut. We load a pdf in the printer software, hit print and then once the job appears in the cutter we hit go and it starts cutting.
The details of the group assigment can be found here.
2. Individual assignment
- Cut something on the vinylcutter
- Design, lasercut, and document a parametric construction kit, accounting for the lasercutter kerf, which can be assembled in multiple ways, and for extra credit include elements that aren't flat
Assessment Criteria for individual assignment
Design, lasercut, and document a parametric construction kit, accounting for the lasercutter kerf, which can be assembled in multiple ways. Cut something on the vinyl cutter.
Plan for the week 27 hours budgeted
This week I would like to try a little more rigid Fab Academy work-plan so that I can also get some scheduled downtime in particularly on the weekend when I am also recovering from my day job and have some time for exercise, social which I neglected the previous week.
Wed 19-20 Complete the plan for the week and start group assignment drawings. Read and watch videos about computer aided cutting
Thu 9-10 45 Complete drawings for group, start plan for parametric construction kit We have a team meeting from 9-10 which I forgot about, it kind of messes with the flow of the morning as I need to leave at 10 40 for work.
Thu 17-19 Group assignment in Fab Lab with Johannes and Svavar This turned out to be 17-20
Fri 16-19 30 Individual assignment time We finished the group assignment. I had a meeting with Svavar from 14-15 where we reviewed parametric design which was helpful.
Sat 11-13 Individual assignment time Sat 16-19 Individual assignment time
Sun 12-18 Individual assignment time
Mon 14-16 Recitation Mon 17-21 Individual assignment time
Tuesday 8-10 30 Individual assignment time
Tuesday 17-19 Fab Lab open house
As I am writing this it is 19 30 on Tuesday and I need to finish up my individual documentation still. In conclusion I still need to improve my time management a lot and get more things done earlier in the week and on the weekend as I am rushing to complete things on Mondays and Tuesdays.
2.1 Cut something on the vinylcutter
I am going to create a simple Robophysio logo using 2D Vector software like Inkscape or Sketchpad. I made the logo by importing the "Slaytanic" font from the logo of one of my favorite bands, Slayer, then I simply set the page to A4 and typed in Robophysio and then converted the object to a path. I then exported this to a pdf that I am going to use to make a vinyl sticker to put on my laptop. I meaasured the screen to 360x350mm and made the logo 80mm wide so it should fit nicely.
2. Design, lasercut, and document a parametric construction kit, accounting for the lasercutter kerf, which can be assembled in multiple ways, and for extra credit include elements that aren't flat
My idea is to create a gameboard that can be put together in different ways to get a different "World" anytime you play it. For example for games similar to risk where you always have the same playing field this could be random each time. To make this work I need to cut earth pieces out of MDF, ocean pieces out of blue plastic.
I had been working in Solidworks and was infinitely confused about why I could not find parameters and constraints anywhere. Discussing this with Svavar I discovered that they use different terminology for this, parameters are global variables and contraints are relations. As if CAD wasn't confusing enough without having two names for exactly the same thing. Thanks software engineers. After walking through this with Svavar it seemed doable and I think it looks like it will be easier to create designs by using variables rather than drawing everything with the mouse.
Next up is to watch a creating finger joints in Solidworks tutorial that Svavar sent me and see if I can figure out how to make the construction kit.
It requires the use of a sheet metal tab that is not in my software so I go looking for a tutorial on how to add this Tutorial
I click MBD dimensions and add the sheet metal tab. I know have access to the tab and slot feature that I need to add to my design. I am confused though if I need to add another drawing of the part to create it or not. The tutorial shows a complete box and I essentially have a 4mm thickness, where thickness is defined as Global variable (T) and I then need to add the tab and slots. Where the width of a tab will be defined as 3.85 mm plus a variable "K" for kerf which is the width of the laser beam. In the group assignment we calculated kerf as 0.205 mm for mdf and x for plexiglass.
I have created an assembly with the two identical parts and mated them but I cannot figure out how to then get to the sheet metal tab that is shown in the tutorial to create the joints. Maybe I just need to make them by hand with extruded cuts.
I decide to abandon the more complex design and go for something simple that meets the assessment criteria.
I found an instructable which I think could help me. These types of joints might work for what I want to design here
I had to go through several iterations of this and had a bit of trouble getting the printer settings right. I made 60x60mm squares and then made 4mm x 4.055mm cutouts on each side. I wanted to cut and paste this but couldn't figure out how so I ended up drawing each one individually.
When I first attempted to print it out I had the settings wrong and had color mapping checked which meant that the printer rastered the shape rather than cutting it. I also didn't check actual size in the beginning so it was also to small. Second attempt it rastered it in the correct size and then I figured out if I turn off color mapping then it cut the shape. I tried putting the shapes together and they fit ok but are a little wobbly when they are picked up.
I then created rectangle shapes that are 120mmx60mm with the same 4x4.055 cutout and tried putting them together and it works Ok but it is wobbly. I wanted to try a deeper cut to see if I can get a better press fit so I changed the depth of the slot to 8mms on the rectangles and ran the cutter again. The 8mms fit better so I am going back to Solidworks to change everything to 8mm depths on both the rectangles and the squares to see how that comes out.
On to the next iteration. Still struggling with Solidworks, it is so hard to select and change the depth dimension that I want. Something is off in how I am doing it. I am going to ask Svavar about this in the morning.
Discussing with Svavar I discovered I had several things wrong. My model wasn't completely parametric, I had some global variables but there were others that were just dimensions. One thing I hadn't noticed is that in order to change something you must go to the extrusion you want to change, double click the sketch and then select the smart dimension. When you input a global variable then you must click a green check mark twice in the little popup and and then click another blue icon to properly save the model with all the changes saved. You can then notice that the model is ready if the lines turn black as they are now defined and can't be moved. Another thing I learned was how to use a line that connects the midpoint of the side of the rectangle to the midpoint of the slot and then add a constraint to make this either horizontal or vertical, that way they line up correctly one either side of the square or rectangle shape.
Another thing I got wrong was the kerf/joint clearance. I was under the impression that I needed to add the kerf to the dimension of the cutout but in fact since kerf has already impacted the 3.85mm joint when it was printed the correct dimension to use is 3.85mm. So in the final iteration of the parametric model this is what I did both slots that fit together are 3.85mm. I also changed the "cut" parametric or depth of the the slots to 12mm.
Once it was completely parametric it was easy to change the model from square to rectangle and make the print file in Inkscape using the written instructions in the lab.
You export the drawings as .dxf files and then you edit them in Inkscape. The cut lines must be set to 0.02mm and the color to RGB 255 using the fill and stroke function in Inkscape. Then you can cut and paste as many shapes as you want.
I made four printouts of each shape and then put it together in two different ways and made sure I could pick them up without them falling apart. The pictures are at the top of this page.
Here are the design files for the week.