A Day of Small CNCs Busy in a Furniture Design Lab...
Some of you know already that I teach furniture design to college design students. I don't post photos of student work as their projects are their intellectual property. Yesterday was a day that didn't start out with any expectation of being in the lab. I'm off for summer break. It ended with me helping 4 students taking a summer session from another professor solve last minutes challenges using one or more CNCs to complete their projects.
Emme and Jasmine and Jaquelynn and Lucy are the students in this story. Steve is their professor, and is a friend of mine who doesn't know how to use the CNCs.
It started with an email from Emme that promised a drawing but didn't include one. "I'm trying to figure out how to make a joint for a table leg. The idea is that four identical legs will each have a section of quarter round that will come together, form a full round, and then penetrate at the center of the table surface. How do I connect a piece of quarter round with a 1-1/8” dowel rod at a 20(160) degree angle? "
I thought I knew what she needed to figure out so I opened Aspire and started "sketching" a few ways it might be accomplished.
Then she emailed the image. It was a snapshot of a poorly drawn sketch that didn't look at all like what she had described. I concluded I'd need to see her project parts in person to better understand what she need to do with them. Up to the fabrication lab I went.
Emme needed to connect a 1.25" diameter oak dowel (leg) to a 3/4" radius oak quarter-round section. The angle between them would be 20 degrees, and four of these assemblies would join to become legs and center post of a small cafe table. We ended up cutting an elliptical tenon on the bottom of the quarter-rounds using one of the 4 small CNCs we have. The tenon was elliptical to force perfect rotational alignment when the parts were assembled. Another CNC was jigged up to hold her leg posts at 20 degrees from vertical. The legs needs three toolpaths including a pocket to level off the top, a profile cut to cut two faces 90 degrees to each other, and another pocket to cut the elliptical mortise for the elliptical tenon. A third CNC was used to for her table top where I cut a small cross pocket into it's center to receive the top end of the 4 quarter rounds. The detail on each quarter round was 1/4 of that cross, and also cut in a jig clamping them vertically in a CNC.
We were both delighted to see all the parts come together perfectly. Fit was snug despite small allowances I'd programmed in. A little sanding helped.
Jasmine was watching me help Emme, and caught my attention to see if I could help her. She needed the center cut out of a 2.25" thick wood circle to leave a ring. Our old CNC Shark is the only small CNC we have with enough Z-axis travel to cut into such thick parts. I can't cut much deeper than 1.25" deep with a 1/4" end mill, so I set up a 2-sided job to profile cut the center out of her thick circle. We used a center hole we drilled through the board to center both side cuts. If you are keeping track I now have 4 CNCs in use. The Shark did the job, but does vibrate a bit when cutting deep profile passes in hardwoods. I steadied it with my hand on the router bracket as it worked its way through the slab. I truly hate the Shark, but it can do some things I can't do on the 3 Probotix CNCs we also have. Jasmine used the drum sander to smooth out the inside face of her ring after the CNC was done with it.
Lucy then approached me with a simpler request. She needed a slot cut. 1/4" deep and 1/4" wide around the perimeter of her coffee table top underside. The slot would receive a rounded apron made from 3 layers of bending plywood glued together. The only challenge here was making sure her 44" x 20" top was clamped down truly flat to the CNC for the cut. The MDF tops of the Probotix CNCs can sag in the middle over time, so I check the bit distance above the panel all along its length and width, and shim until flat to the CNC plane. The cut took about 3 minutes. It took Lucy about 10 minutes to clean up the area after.
Jaquelynn didn't know she needed a CNC solution. Her project was searching for a nice detail to hold up the outboard end. Her table's top was hickory with a 3/4" wide strip of walnut down the long center. Steve and I suggested several solutions. They evolved down to using a piece a 3/4" square steel pipe as a vertical support, aligned under the walnut stripe. It would screw into the end of her lower shelf, pass through her middle shelf, and die into the bottom of her top. The steel pipe had rounded corners so I suggested the CNC could cut square pockets for the pipe with matching rounded corners through the middle shelf and into the bottom of the top. We cut a quick test pocket using a 3/16" endmill in a scrap to verify a good fit for the square pipe. The challenge then was careful layout to verify all the pockets would line up vertically when her table was assembled. I zeroed from different edges depending on whether the cut was in the top or bottom of a shelf.
Jasmine came back with two more requests. She had fabricated a ring of 1/4" x 1/2" steel that needed to be embedded into a 12" wood circle. The ring wasn't perfect though, varying 1/8" from between length and width. It also twisted a bit as it went around. The challenge here was to draw up a pocket this ring would drop cleanly into. Given the twist, I knew I couldn't use a simple 1/4" wide pocket. We started with 5/16" wide. Resized the circles to be 1/8" wider then they were tall. I added a bulge area where the weld was, and joined all the vectors to set up the pocket toolpath. I cut the pocket with a 3/16" downcut endmill to leave a clean top edge. The ring dropped in easily. Her last request was for a cross pocket for 3/4" x 1/4" steel bar in the bottom of another 12" wood circle. This was simple drafting. The cross wasn't yet made so would be made to drop into the pocket we would cut. I added a small allowance overcut so the 3/4" wide steel wouldn't be tight in the slot. Fillets in the corners for expected welds.
Such is the nature of CNC requests I get from students in the last week of summer school classes. The open frame design of the Probotix CNCs let me make complex cuts I can't do on the Shark. The fab lab also has a large Multicam. Productivity for furniture projects though comes from having 4 little CNC with varying capability I can spread jobs across. The large CNC generally does large panel work that will hold down on its vacuum table.