Peter Fearey

Computer-controlled cutting

Assignment

Design, make, and document a press-fit construction kit.

Ideas and Approach

For this assignment, I wanted to push myself to work on new kinds of joints and flexible wood. We have had our laser cutter for a few months and already we've done tons of projects with cardboard. For example, I had already created my Jeep iPhone holder with the following plans using press-fit construction. Another teacher at our school also made a press-fit kit for Pre-K and Kindergarten students to make sculptures.

So...because I've already built or seen these things built with press-fit construction, I wanted to try something that would be a bit harder with different kinds of joints used throughout...so I decided to try to build a charging station that will hide the wires using no glue and only press-fit joints. Here's my inspiration...

Inspiration

..too many cables always hanging around the kitchen counter.

Files

Steps Taken

Finding Inspiration (and Needs)

First, I decided to look for inspiration for different designs and ways I could put it all together. I found the following designs that helped me figure out what I was going to like/not like...

From these designs, I realized the following:

Must haves:

Needs to be able to see the screens (for when new messages come in)
Needs to hold iPad, iPhone and computer.
Needs to hide the cables

Should haves:

Should be able to hold extra items (pens, post-its, etc)
Should be made of wood (rather than acrylic or plastic)
Should show both the iPhone and computer screens so can see emails and text messages coming in. The iPad doesn't need to show.

Would be nice to have:

If could hold my wallet and keys in addition to other items.
A lock so children can't take cables
A drawer would be nice, but isn't that necessary

Second, I went to find some cool joints and designs for how to put it all together. That brought me to these two sites and example joints that impressed me. I want to find ways to use each of these in my design...

Kerf-Bending Joint

Cross-X Joint

Third, here are the measurements of each of the devices (with covers):

iPad	h: 9" 7/8 (875) w: 7" 3/4 (0.75) d: 3/4 (0.75)
iPhone:	w: 2" 5/8 (2.625) h: 5" 1/4 (5.125) d: 9/16 (0.5625)
MacBook	w: 14" 15/16 (14.937) h: 10" 1/8 (10.125) d: 15/16 (0.937)

Steps

Create (fun) Kerf Joings

I started experimenting with different kinds of kerf joints because I'd like to have the joints in the corners of the charging station. The first joint I made ended up breaking when I bent it more than 15 degrees. So I started changing the variables...the wood type (soft basswood and solid plywood), the width of the wood (1/8" and 1/4"), the pattern (different lengths of cuts) and the width / length of the pattern (1" or 2"). Each time I'd run the cut through the laser cutter and then would measure how far it would bend. Here's a picture of the different cuts when I tried three kinds of wood (solid alder, alder plywood and soft basswood), two depths (1/4" and 1/8") three patterns (wide gap and small cuts) and two widths/lengths (1" and 2").

At the end, what I came to learn/realize is that the thing that matters most is the width/length of the pattern on the wood. And then it dawned on me...depending on the wood width/type and the pattern, each instance of the pattern gives you some flexibility (e.g. 5 degrees of bend). Example: if you want 90 degree bend, you need the pattern (90/5 = 18) 18 times as each instance of the pattern adds a bit more bend. So, once you settle on the kind of wood and a pattern you want to use, you need to find a way to extend the pattern as far as you need to go to get the complete bend you need. While the physics of all this might not be perfect, it's a framework for thinking about it that I think might be right.

When all was said and done with this, I realized that I would need a REALLY long piece of wood that would be bigger than my laser cutter if I was going to do the Kerf joints. So I decided it wouldn't really work to use these in my design...doh! But, I did learn a ton from trying these and I expect I will use these in the future in other projects.

Joints

I spent a bunch of time trying to get the joints right. After three different tries, I ended up getting it right. Here is a picture of the different versions that I tried and the final plan with the different coordinates and measurements.

Joint tests Zoomed in joint

After going through this, I decided that these might not be the best joints to do for the main box as they didn't seem that strong. It seemed like it wouldn't be able to hold an iPhone for the side piece given the weight of the iphone. So for those joints I decided to go with something else. Here's the simple design...the 2.05" x .223" (the width of the wood) gaps will be for the "female" side of the joint. The "male" side of the joint will be shaped like a rotated L. It will be 2" long and the height will be .223" (again, the width of the wood). Here are the two sides of the joints as designed in Inkscape.
Second Joint

The male side of the joint will be inserted into the female side and then will be shifted down. While they won't look amazing (because there will be gaps), they should hold without glue- which I think is the definition of a press-fit joint.

Box Construction

Once I decided what joints I wanted to use, I spent a bunch of time in Inkscape trying to design everything at once (this was also partially because I was on two 9 hour bus rides). Using the measurements of the iPhone and the MacBook, I started with the top and then worked my way around each of the sides. Once I had one side, the front and the top, I printed them on cardboard. Here were the results of "rev 1" with the different issues I learned I needed to fix...

Issue #1: When shift siding with joints, the front gets shifted way off to one side. So need to lengthen on right side and shorten the left side.

Fix #1: Make siding 0.713 in long on right side and 1.25" shorter on the left side.

Issue #2: The holes for the joints were EXACTLY the same size as the parts that were going to have to fit through. I realized given my Jeep iPhone holder that the wood needed some extra space.

Fix #2: Make the holes 2.05" rather than 2.0". THANK GOODNESS I CLONED THEM...IT MADE FIXING THIS MUCH EASIER :->

Issue #3: Angle is all wrong where siding meets the front.

Issue #4: Front is too long so need to shorten.

Issue #5: On the high side of the siding (not pictured here), the bottom needs to be lengthened and the top needs to be shorted

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Fix #3: Make it 0.281" longer where siding meets top and 0.117" longer where rounded corner meets bottom

Fix #4: Make the front 0.268" shorter.

Fix #5: Make the top 0.134" shorterand the bottom 0.336 longer

Once I made the above fixes, I did a second version. Unfortunately, on the second revision I still had a problems with the angles...and...it made me realize I had other problems. Here's a picture of the second version.

Issue #1: The angles still weren't right. I wanted the siding to be flush against the front (the right side of the picure) and the back (the left side of the picture). I thought I had fixed this, but apparently not.

Issue #2: It didn't occur to me till I saw the sides, front and back attached to the top, but because of the angle of the side, I realized that the joints I created would work. The joints I made are so precise that the wood needs to be attached by sliding the wood in at a 90 degree angle, which isn't possible for the front and back if the sides are at an angle.

Fix #1: I measured the gaps between the sides and the front/back and then extended them.

Fix #2: I got front and back off so that the bottom won't attach to them. They will only be attached to the sides.

After making those changes, I finally had all the parts that fit together. I ended up with final project that had cutouts for the cables and a place for both the MacBook 15" and the iPhone (on the right). The final project is pictured below. Now I just need to get my wife to agree to keep in on our kitchen counter.

Plans for the top and bottom (with gratuitous carving of lacrosse sticks)

Plans for back, front, iphone holder and sides. NOTE: the top and the sides don't include the shaving of the bottom joints. This is because I ended up marking and laser cutting them off.

Below is the final project with the wires organized under the charging station.

Learnings

I learned a great deal doing both my Jeep iPhone holder and the FabLab charging station- two press-fit construction projects. Here are some examples of key learnings:

Angles suck! By introducing an angle to the siding, it make the project much more complicated because the joints no longer worked.
Cloning is great, but it has issues: I tried to use the cloning as much as possible. I figured that, once I got the size of the joints I would be able to easily edit them if I needed to (as Neil has been saying). Unfortunately, this came at a price. Here were two big learnings about cloning in Inkscape:

I like to name to objects in Inkscape for easy identification when looking at the XML list. Unfortunately, I decided to rename the parent (cloned) object. When I did this, it broke all the links to the clones. I figured out why this occurred. It was because each cloned object has an "xlink:href" property that contains the name of the parent object. Unfortunately, this doesn't update when you change the name of the parent. I tried editing that attribute to the new name, but it didn't really work (the object got moved and there were other side issues).
Cloing doesn't work when the cloned part is going to be a part of another joint. I figured out that in some cases I can ju

Material Matters: My Jeep iPhone case took many iterations to get right. Perhaps the most interesting learning was that the material I used really mattered. At first I used Basswood. This wood turns out to be a soft wood that breaks easily. Once I switched to plywood, the iPhone holder was rock solid. As it turns out, plywood intentionally has the layers put down with grain going in different directions so it is stronger.
Wood Grain Matters. In addition to the type of wood, the direction of the grain matters. After my Jeep iPhone holder broke twice, I showed it to someone who used to be a contractor. He laughed and immediately pointed out that the grain was cutting across the weakest point in the iPhone holder. This is what was causing it to break so many times.