Jointery – 2nd Try

While thinking about what I want to ultimately do for my midterm, I realized that it would be a good idea to try and perfect the joint I’ll be using in order to save time. A double rabbet joint should suffice for the credenza I’ll be adapting from this work plan.

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I ran into a few problems when attempting this type of joint. First, I created two identically measured pieces in Vectorworks and brought it into Mastercam and then to the CNC machine. I laid down the wood only to realize once I had everything set and I was about to press “start” that I had aligned the wood improperly on the bed.

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I needed to set it up so that the blank area of the wood was along the X axis not the Y. So I re-positioned it and then I was all set to go.
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After about 12 minutes here’s what I ended up with:

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Not a great fit, I know, but it allowed me to see where I needed to subtract from each piece.
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I went back to Vectorworks and Mastercam and made my adjustments.
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By the end of that run cycle I ended up with two pieces that fit together almost perfectly!

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When I looked at the two pieces fitting together very closely I realized that in Vectorworks I didn’t round the corners on the inside of the pockets which could be why they weren’t sitting entirely flush.

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Nevertheless, I was very satisfied with the progress I had made and what I learned from taking the time to really get this joint down. I’d like to know how I can figure out the math behind this without having to make two identical parts first.

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Jointery

This weeks assignment to make a joint with the big CNC proved to be a very challenging task. Getting the tolerances right mathematically stumped me a bit and it was hard to conceptualize what was going to happen in a 2D model in Vectorworks. You’d think a simple looking joint like a half lap would be easy to figure out — it wasn’t! I decided upon a half lap joint in order to make a short corner bookshelf. Once I got home though, I realized that the 90 degree angle I had planned to put the furniture was anything but 90 degrees. Now I think I’ll make a short TV stand instead for the midterm.

In Vectorworks I ran into a lot of problems figuring out where I needed to add tolerance and how to go about adding it without ending up with a solid filled shape.

Unfortunately the first attempt to mill didn’t work out because of a common problem placing the X axis all the way forward on the Y axis when zeroing out. The next day the I was able to start milling!

Mastercam was a bit of a nightmare this time around. It wouldn’t let me mill completely around the left square so I had to invididually set each side of the square which is why I think I ended up with a nasty looking edge on one of them. Also the mill didn’t cut all the way through my material even though I set the breakthrough to 0.05 and I rounded up my material thickness. I may chalk that up to the spoil board being pretty wobbly and the position of the wood on the machine was further back to avoid any X axis problems again.
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After having completed my weird looking probably not a real sturdy joint skill exercise I’m a little freaked out about using joints for the midterm. I’ll definitely need some help figuring out how to do the math associated with tolerances and jointery in general.