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A Day of Small CNCs Busy in a Furniture Design Lab...

11K views 49 replies 17 participants last post by  4DThinker 
#1 ·
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.

4D
 
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#2 ·
Interesting read. But still don't want a CNC - other than Coffee 'N Cookies. :grin:
 
#4 ·
Couch 'N Coffee is better.
 
#6 ·
@4DThinker...
did you just describe a variation(s) of a jack miter???\

KUDOS to you for what you are doing...
 
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#7 ·
@4DThinker...
Did you just describe a variation(s) of a jack miter???\
Nope. Not a single miter of any variation among the jobs I did. One elliptical mortise/tenon to join two parts 160 degrees to each other, a simple profile facing off, and a slew of pocket cuts. All started with just an idea or description from the student of what they needed. No useful drawings were provided to import. I drew up every required vector, created toolpath from them, and cut those toolpaths into their parts.

4D
 
#10 ·
just trying to wrap my brain around this..
 
#11 ·
That may not be possible, Stick. The student and her professor watched me figure out and draw up what needed to be done, and both confessed they couldn't have done what I just did. 10+ years of playing with CNCs and 35ish years of teaching furniture design preceded by 3 years of drafting courses have pushed me into an inventive state where drafting and woodworking experience exposes solutions that no one comes up with any other way. Emme's table leg parts join together with a wholly original cnc-cut joint that likely exists nowhere else. I've documented many CNC-cut joinery examples and none are in any way similar to her joint.

4D
 
#15 ·
You are a patient and involved teacher. The best kind. My brother worked for a prototype shop in Southern California. He often complained about designers who produced unbuildable projects. He was often tasked with finding solutions so the design could be manufactured. Glad you're on faculty! Your post was also very readable and I suspect a number of members also learned something from the post.
 
#16 ·
Your post was also very readable and I suspect a number of members also learned something from the post.
I dunno. A snapshot of something not resembling whatever? Suspiciously like not doing their homework and getting the teacher to do it for them. I've run into that a lot in the pat. "Oh, I just don't know how to do this". Then finding out they didn't even try. So I didn't even try either, just told them how to do whatever, and turned them loose, to sink or swim. A few learned to swim quickly.
 
#20 ·
Taster in a brewery.
 
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#24 ·
I could likely scrape up enough to get one, including a rather large loan, and I do enjoy some posts on them. But unlike you I have no desire for one. I think partly because I would rather someone else have all the problems, instead of me.
 
#32 · (Edited)
Besides the cool ones 4d has invented, many others possible with CNC.

These require working on ends of boards


These are mostly or all cut flat:
50 Digital Wood Joints by Jochen Gros ? WINTERDIENST

Add a lot of flexibility to have a machine that allows working on ends of boards, even more so one that allows angles as 4d has demonstrated.

I have a few I am working on for a special project. Hope to show soon.

And of course ger21 has software to cut some traditional joints
http://www.g-forcecnc.com/jointcam.html
 
#33 ·
There is a difference in aesthetic joints vs practical, and it takes some learned woodworking sense to know what will have the strength needed for an application. Samples I make are fine no matter how they look as they aren't tested/expected to meet any performance standard. When I'm designing a solution for an actual product, resisting loads that the joint will suffer is my main consideration. A 4 or 6 tenon array will have greater glue/friction surface area that a single large tenon within same area. The single tenon will resist greater shear and bending loads though, and would be more appropriate in cases where shear and/or bending forces will be present.

My point? Using a CNC you can cut joint details that no sane woodworker would try and cut using other methods. More important though is the application and strength needed from the joint.

4D
 
#34 ·
Interesting joints. A few I could duplicate, the ones I like, and may do so (saved them) if I ever get back into making furniture. All interesting tho, always ready to learn. For you other guys, no I ain't gonna get a machine - but I did buy a new calculator recently, and six new pocketknives.
 
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#36 ·
Calculator is very nice, think I paid about $3 for it. Smart Phone? Got a flip phone, does just what I got it for, and more. Got the time, call people, receive calls, text, alarm clock, camera, video camera, keeps track of the TV shows I watch and sounds an alarm when they are due to come on. Cost me around $6 new, and a great deal it was too, if it dies, I'll get another.

Don't need web based drawing sites, free hand all of my designs. Make a rough sketch first, then lay it out on graph paper, full size. I'm not sure I even know what an app does, and not really curious. Too close for comfort, thinking I need a few more hand tools, and to start watching Roy Underhill more often. CNC in my world is, Coffee N Cookies, Coffee N Chat, Cognac N Coffee, and so on. Which reminds me, I did get a new power tool not long ago, a nice coffee maker. I think I need to pick up some cookies. Besides, I hear those CNC machines have cooties.
:grin:
 
#42 ·
I was up at the university today for a meeting, and a few of the summer projects were on display in our small office gallery. This is the table with the most challenging CNC cut joint. You can't really tell from a glance, but the center post is actually 4 oak 1/4-rounds clustered together. Each joins a solid dowel on the bottom that is 20 degrees tilted out to make the legs. The joint between the 1/4-round and leg dowel is what I cut using the CNC. The legs were held in a v-block, on my jig clamped at 20 degrees from vertical. They are held together in the middle by that metal strap clamp. The X-knob on the clamp is the shape of the through joint on the table's top that result when all four 1/4-rounds slip through. That joint was also cut on the CNC. Enjoy.

4D
 

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#45 · (Edited by Moderator)
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.

4D
[duplicate quote removed by moderator]

You did a great job teaching furniture design to college students. If a student wants to open their own office or business in the future, they will be already aware of office furniture design. Well, if you want to show some examples of new furniture designs then you can show your students these pictures that I have shared.
Furniture Table Chair Product Computer desk
 
#46 ·
Welcome to the forum, Sofiawood,
 
#48 ·
Old thread I know. But I'm now retired from teaching. I've been looking through some old student project photos and came across this one you might enjoy.
Chair Wood Tool Pet supply Basketball hoop

This was another summer workshop class that I visited mainly to collect something I'd left in the shop. The student was debating with her professor how to make a form for S shaped laminations, each slightly different to make something that looked like the table above but out of 3 stacked S shapes rather than intersecting simple curves.

I had a small sample of the 3-way intersection joint that I showed the student. Using that joint would greatly simplify the formwork needed as now all curved sections could use the same form. I added a 120 degree section of a 1/4" hole perimeter to each end cut so when put together there would be a 1/4" hole for the furniture connector bolt that holds all the parts together. I had to clamp her curved parts over an inner edge on the CNC bed to position the ends for the interlock cut.

The 3 top parts interlock. The 3 bottom parts also interlock with the same joint. A single center bolt holds all 6 parts together. The tension cables and glass top lock the geometry.

This was a project for a Workshop 2 class. The project description requires the design to break down for packing. All six leg parts nest together when taken apart. This student then took her 5th year furniture class from me. Her chair design has a unique feature that my CNC software "solved". That's another story though. ;)

4D
 
#50 ·
very clever design, great aesthetics and execution!

will you still have access to the cnc's?
I have my own (actually 2) CNCs along with a shop full of all the other common woodworking tools. I predicted out loud to a student the last time I had a class that the small room of 3 CNCs I oversaw would go the way of the dodo bird once I retired. No other shop professor ever made use of them and they were all there based on my recommendations. As our new fab lab has "security" cameras all about I know I was overheard by the Dean and Department Head. When I announced my retirement they gave me a semester off (with pay) in exchange for documenting the "process" I used to come up with CNC joinery so a students helper could duplicate what I'd been doing for the students. Both idiotic and rude at the same time, implying any random student with no CNC experience or even a design degree could replace me. When time to turn in my "Process" I informed them that as neither of the new instructors ever used the small CNCs for fancy joinery, and I was retiring that their would be no upcoming demand for fancy CNC joinery that a student would need to cut. I had no specific process. I had experience, an engineering and architecture aptitude, 4 decades of teaching furniture design and making my own, and a creative talent for finding solutions to impossible furniture fabrication challenges. They couldn't and didn't argue with that.
4D
 
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