Week #6 Group Project: ShopBot Testing

Alexia, Treyden, Noy and Claire tackled this week's group project together.

First, Alexia set up a Fusion 360 file with some shapes to test cut. This would show us how the ShopBot handled various sizes of squares and circles and allow us to measure the kerf (width of the sawblade).

Then, Noy, Treyden and Claire formatted the design file for the ShopBot using Aspire and ran the job. Finally, Claie put together the writeup (this one!).

We quickly noticed a few things:

SPEEDS: Curved lines = cut more slowly than straight ones.
MATERIALS: OSB produces way more wood chips compared to plywood, and a rougher finish.
TOOLPATH: It's vital to cut holes first, before outlines, in order to make sure your material doesn't shift enough to misalign your holes.

KERF
Unlike the laser cutter, which cuts on the center of a line, (meaning you have to calculate and allow for kerf, the material removed by the blade/laser), the ShopBot offsets its cuts based on a user's programming selections to account for kerf. That means you need to tell it whether you're making an "inside cut" or an "outside cut, so that it offsets to the appropriate side.

The end effect is that you get a clean cut directly along the desired line, meaning your final result ends up being exactly the size you wanted it to be, with nothing lost to kerf. (The kerf comes entirely from the outside perimeter for an ouside cut, or from the inside scrap for an inside cut like a hole.)

Still, it's interesting to see the kerf width! We determined it to be 3mm.

FRICTION-FIT TESTING
The test we must needed to run for the purposes of this week's design challege was for press-fit joints. Most of us were planning to use a slot-and-tab assembly strategy, where some elements would slide together like two interlocking combs (hint, hint).

To determine the optimal slot width for this approach, we designed a few test pieces. These included a series of slots of varying widths (only increasing by 0.1mm at a time) along with a T-shaped plug to insert into them, and two interlocking combs, (go figure!) with the same series of gradually increasing widths between their "teeth."
Once these were cut, we tested them out and determined that an 11.5mm slot offered the best friction fit and did have to be tapped into place with some force. However, a 11.6mm slot actually offered the best comb-fit. (For reference, our piece of OSB measured an average of 11.6mm thick, with some spots closer to 11.4 and some up to 11.7.)

We determined that it would be best to err a bit smaller than average if we didn't want to use glue, knowing that we could always file things down later.

All this being siad, because OSB--the material we're working with this week--is made of compressed wood chips, it's thickness varies (sometimes significantly!) from piece to piece. Therefore, we'll still need to measure our own boards before designing/milling so that we can account for any differences.