Introduction: Slipstream Table (Experiments in Aluminum and Plywood Lamination)

Picture of Slipstream Table (Experiments in Aluminum and Plywood Lamination)

The Slipstream Table is the culmination of a number of side projects and experiments in CNC profile cutting, lamination, sheet good manipulation and traditional woodworking. The project is the result of the economy and efficiency of cnc fabrication, as well as the realities of the hand finishing required after these products are processed by these high-tech robots.

Inspired by the aesthetics of mid century modernism, the name 'Slipstream' is inspired by the tapered aluminum points at the ends of the top and legs of the table. For me these features evoke the imagery of Airstream trailers, early fighter planes and motorcycle fairings all crafted out of aluminum in a fight against the forces of air resistance in the endless pursuit of aerodynamics.

The table is a finished product that took numerous ad hoc twists and turns throughout its conception and creation. It is a result of the process of serial profiles of birch plywood being cut and being laminated together to create a objects that is unexpected and visually dense. This Instructable outlines the process by which this table was created, as well as failures and triumphs that were discovered throughout the nearly three week build time.

Step 1: Smaller Study Project Precedent

Picture of Smaller Study Project Precedent

Before embarking on the full scale table fabrication, I wanted to test the fabrication and design qualities of this process through a smaller project. In this case this project was a small end table that was built using the same construction processes. I will not go into any detail in this step, other than to say, when beginning a large project that will require large amounts of time and materials, tests are always worth their time and effort in allowing you to feel confident and comfortable moving onto the primary project.

Step 2: Design Goals and Process

Picture of Design Goals and Process

The design of this table was governed by a number of factors, chief among them: aesthetics, machine processes, minimal waste strategies, precision, and structural stability. In the context of aesthetics, I looked towards precedents from the modern movement. These pieces of furniture with tapering features and subtle angularity were crafted with hardwoods and traditional joinery, but the lines and figure of the pieces could be distilled, reproduced and carried over into the world of digital fabrication.

The physical elements of this project were fundamentally simple, there were no complex shapes or cuts, and so it was important for me to make sure that the lines and design of the object were specific and satisfying. The stacking language of the extruded construction method allows for a pure object, and with this clarity, the quality of the lines is easily transmitted.

I toyed around designing the project in both 2d and 3d. Between sketching, drafting and modeling, the language of the smaller table was carried through to the larger full-scale project. These details included tapering edges, angled and tapered legs and the ridge between legs. These details allowed me to create a table with subtle features, that could be immediately understood. But also an object that had more depth upon further investigation.

Step 3: Layout

Picture of Layout

As mentioned earlier, material efficiency quickly became a focus of the project. Upon looking online, I found a great number of inspirational and intriguing examples of laminated plywood furniture and sculpture. Something that continued to nag me when looking at these projects was how their laminations came at the price of efficiency. Creating swooping forms that occupied countless sheets of ply was indeed romantic as a product - but the lack of nest-ability and the implicit material waste associate with these forms made me shy away from any form that could not be built efficiently.

The concept behind the nesting and material use of this table was as follows: the tables large and cumbersome end pieces used the majority of a sheet of plywood, and did not allow the left over material to fit other pieces of the table. However, in this leftover space, there was room to fit pieces of a smaller piece of furniture. In this context the idea became to nest a bench in the off-cuts of the cumbersome end pieces.

This model did end up working on the first sheet, though eventually I realized I could break the leg pieces into segments and re-attach them with glue and clamps after they were out of the cutter. This separation and re-attachment model lead to even more efficient nesting of cuts.

Step 4: Wood Cutting Setup

Picture of Wood Cutting Setup

Here at Pier 9, we have the luxury of having access to a number of large format profile cutting tools, including an Omax Water Jet, Coherent MetaBeam Laser and Shopbot CNC Router. For the purposes of the wood portion of this project, I opted to use the Shopbot for the following reasons:

Firstly, the shopbot uses a router bit that allowed me to specify a specific and accurate hole size that I drilled into my layers of material. This specific bit size and corresponding hole size (in this case 3/8") allowed me to effectively thread the layers of material along a finish dowel, making precise indexing much simpler in the assembly stage of fabrication.

Secondly, the shopbot cuts with a blade and not a laser or water beam, this means that the cut you get off of the shopbot is clean, unmarred and uniform in color. This is particularly important in the context of this project, where the cut quality defines the quality of the surface, so it was vital that the tool with the highest quality of cut was selected to ensure the most uniform surface quality.

Step 5: Shopbot

Picture of Shopbot

The wooden core of the table is constructed from 42 individual laminations of 3/4" inch thick void-less birch plywood. Each of these laminations are cut out on the Shopbot 3 axis CNC router. Starting with 4'x8' sheets of plywood, the components were cut out with the aforementioned nesting strategy. This cutting process was both interesting and frustrating for a number of specific reasons.

The largest hurdle was a function of the nesting strategy itself. Because the cuts were so densely arranged, the typical 'tabbing' strategy of securing the cut pieces to the existing material was not possible. The cuts could not be secured to the wood itself because there simply was not enough left over material. In order to secure the wood then, a vacuum table would have been ideal. Unfortunately this was not a feature we had on our Shopbot. Instead a system of work-holding was devised that involved the use of a brass screw and plastic washer holding the pieces to the table, all inserted into the existing holes drilled for the indexing. The holes were drilled first, then the screws and washers were fixed, then the ultimate profile cutting happened around the screws.

This fixturing and cutting process was time consuming, and there was some trial and error involved. The main issue was that I originally bought 1-1/2" screws for the job, these ultimately proved to be too short, as they only grabbed into the mdf base 1/2". On multiple occasions these screws were ripped out of the mdf and sent unsecured pieces flying into the router bit, cutting into the pieces and destroying them. After the first sheet the screws were exchanged for 2" screws and this issue was resolved. One issue with the 2" screws was that they were driven into the plywood backing sheet, with an impact driver these screws tended to shear off leaving a useless nub of brass that had to be removed with pliers. Not as elegant solution in practice as it was in theory.

Step 6: Shopbot Post-Process

Picture of Shopbot Post-Process

After the shopbot cutting was complete all of the pieces needed to be cleaned up before they were laid-up in order to ensure that there would not be abnormality in the profiles. Uniformity would lead to void-less surfaces without high-spots.

The pieces were first taken to the router table and cleaned up with a flush-trim router bit, then any other high spots were hit with 120 grit sand paper.

Step 7: Dry Fit Layup

Picture of Dry Fit Layup

Before heading in with wood glue and clamps the first step in construction was trying the dowel and hole method dry. I got about 1/3 through the table before I realized there was a problem. Between the imperfect straightness of the finish dowel and the unfortunate reality of the inaccuracy of the shopbot, the stack was not lining up in the perfectly robotic error-free, so this is the time when I must admit an unfortunate truth about the project.

Step 8: Just One Thing...

Picture of Just One Thing...

So I have to admit something here: my master plan of drilling, screwing, doweling... was a flop.

In order to ensure the most precise layup, the pieces were referenced against the face of my work table and ultimately glued, brad nailed and clamped. The nails were almost surely overkill, but in order to register each piece to the next without clamping and laying up in sections, it fastened the pieces together during glue up.

The body of the table was completed and glued up. While it dried, the leg assemblies were also glued together. Each leg assembly is comprised of three layers of wood. These three layer assemblies were then attached to the table using compressed dowels, glue and a whole bunch of clamps.

Step 9: Wooden Core Complete

Picture of Wooden Core Complete

Once the core was fully assembled it was a misaligned stack of plywood. I was pleased with the structural stability of the table, but the finish was really quite terrible. I had to come to terms with the fact that the robot had failed me yet again. With this realization, I armed myself with an arsenal of belt, orbit and Fein sanders and got to work.

Step 10: Sanding...

Picture of Sanding...

Sanding... It's not a quick process. Using 80 grit paper on a belt sander I must admit I spent over a dozen hours getting the surface uniform and all brought down to the lowest point. This end-grain surface is full of glue, and requires a ton of work to sand down.

The finishing was done with 320 grit paper on a random orbit sander.

Step 11: Aluminum Cap Cutting

Picture of Aluminum Cap Cutting

The aluminum caps were incorporated for a number of reasons. Firstly, the use of the bright metal helped to break the monotony of the plywood-on-plywood aesthetic of the table. Secondly, the face of birch-ply is soft wood and would not hold up well against years of use, so the aluminum serves as an advantage in terms of durability. Thirdly, this project was undertaken in the context of the pier, and so it was interested in taking as much advantage of the tools available to me as possible. In this light it made good sense to add a waterjet-cut metal component for the 'because we can' element.

Using the Omax waterjet cutter and 1/8" aluminum, the exterior profiles of the table, as well as the interior leg profiles were cut.

Step 12: Aluminum to Wood Attachment

Picture of Aluminum to Wood Attachment

There were a few potential ideas for fixing the aluminum to the wood. Fixturing with screws or bolts was an original idea, but the interruption of the surface felt like a misstep. Ultimately gluing became the answer. It was decided that contact cement would be the most viable adhesive for the metal-wood connection.

The metal was roughed up with a pneumatic sander and cement was painted on both sides of the connection. You only get one shot with the contact cement, it has to be laid down perfectly in place, then fixed in place with pressure, in this case a rubber hammer. After 30 minutes of curing, the layup was preformed and luckily went off without a hitch.

Step 13: Aluminum Trimming

Picture of Aluminum Trimming

The reality of all the sanding of the wood was that the entire profile of the table lost about 1/16" on all sides, since the aluminum cutting was based on the original dimension the aluminum needed to be routed to fit the final profile exactly.

Using a trim router and a flush trim bit the work was fairly simple. The only part of the process that was precarious was routing the ends of the table and legs where the router did not have a sold base to reference off of, and so there was the danger of digging into the material and a more than 90 degree angle. In taking my time I avoided these gouges.

Step 14: Finishing

Picture of Finishing

I decided to hold off on finishing the wood until after the aluminum was applied in order to not mar the finish while routing and applying the aluminum.

Once all the pieces were attached and trimmed flush, I applied five coats of polyurethane semi-gloss and finished by wet sanding by hand with 600 grit paper.

Thanks for taking a look!

Comments

clazman (author)2015-05-29

Many
problems

1: Baltic birch plywood can be had that is 100% birch.

2: I cannot understand the use of brass screws to secure the work to the
platen.

3: I cannot understand why you did not pilot drill for the brass screws and
drilling these holes with the precision of CNC.

4: The variation from piece to piece could very likely be due to the cutter
forces moving the work piece because of clearances between the brass screws and
the tooling holes and the low strength of the brass screws and the inadequate
penetration of the brass screw into the platen. I would have used 1/4 inch
machine screws with a light press fit. I would have utilized the full platen
thickness (3/4 inch good, but a 1-1/2 inch platen would better) to engage these
screws. This would greatly reduce the chance of the screw being
"pulled" out of perpendicular by the cutter forces. Wood screws, by
design, do not provide this precise registration capability. For example, in
the tooling arena there are shoulder bolts and dowel pins for precise
registration. With the use of machine screws comes the need to utilize another
platen material than the lousy MDF (just calling MDF an "engineered"
product doesn't make it so). I cannot understand the popularity of such a
poorly engineered product. I accidently dropped a piece of MDF landing on the
corner. I was disgusted with the breakage that occurred. MDF may be even more
stable than plywood, but that is it’s only attribute.

5: I do not agree with you that the dowel system was at fault. I would still
suggest that a flat work surface be utilized to aid in "creep"
reduction. Yes dowels are not perfectly straight, but if you did not provide
for a light press fit of the dowel in the holes you will be allowing an ever so
slight offset from one layer to the next. A miss location of only 0.01 inch per
layer will amount to one tenth of an inch every 10 layers. I doubt that the
dowel was being miss located in the hole due to asymmetrical stresses. By
design, the plywood veneers should result in a symmetrical loading on the dowel
keeping it centered on the machined hole. Your use of a flat work surface to
aid in the assembly can be applauded. Yes, even with the dowels.

In summation, the precision of the product can only be less than the tooling
used in its manufacture. I am saddened by the fact that so few realize this
axiom.

I do commend your attempt to understand tooling/fixture concepts and your
attempt to analyze problems. You only need to improve your thoroughness.

I am planning on constructing a work bench from plywood lamination's Yes; I
will utilize the precision and stability of plywood. Also, the strips will be
cut without changing the rip fence location thus ensuring that the strips of
any given width, will have a smaller variation, thus improving quality of the
product.

DavidC333 (author)clazman2015-12-03

Clazman is spot on. Your miss alignment is more than likely do to the space between your brass screws and the sidewalls of the clearance holes. I have a lot of CNC experience as I currently work directly for CNC Software Inc, we produce the Mastercam CAD/CAM system. I have visited countless machine shops over 15 years including many wood router shops and have seen a lot. Couple things:

First - The forces from the router more than likely shifted the pieces. To correct this you should not be putting a screw in every hole. You should insert dowel pins in some holes to keep the pieces from moving. I'm not talking about wooden dowel pins but proper steel dowel pins available at any machine tool supply company by the box. they are precision ground to what ever you need, in this case 3/8. The dowel pins will locate the part, place in at least 2 hole per piece, then use the remainder of the holes on each piece to screw to the sub-table. The dowel pins are reusable forever. You can reduce forces by taking multiple step downs instead of cutting straight away to final depth. Your feed rate and RPM are very important to control forces, take a more scientific approach using chip size and standard feeds and speeds formulas to calculate feed rate and RPM so you are pushing material, you want to cut material.

Second - Most people using a router cut their parts out straightaway to size, then manually finish them on a router as you did. Well you just took something precision machined (assuming the use of dowel pins) and jacked it up with manual methods which is fine if you are making a one off. The machining process needs to be more refined than just cutting shapes out to mass produce or to make a one off with less work. Use multiple depth cuts to rough out material while still leaving some material on the wall of your parts. This is called stock to leave in your CAM system, maybe leave .05in on the outer walls during stepdown roughing then create a new toolpath to final size leaving 0.0in stock to leave cutting one depth cut at final depth. This final pass can be dialed in to leave a much nicer finish on the wall as the cutting forces are drastically reduced since the tool is only encountering .05in of material.

Third - Did you know there are special compression bits for CNC routers? Bits that apply down force while cutting. The top edge is often rough from tear out as you mill with a traditional endmill, the flutes are pulling material up and away. The bottom edge usually looks good. You can purchase a down cut spiral carbide endmill made for CNC routing wood and laminated materials. Not cheap but they will change your life. These bits put down force as the cut leaving a very clean top edge. The bottom will not tear out since it is firmly pressed against the table. If you are milling the edge of material with no table underneath (over hang edge) you can even purchase an up/down compression bit that can actually put both up and downward force in essence squeezing the material to prevent tear out on the upper and lower edge of laminated material. Check out Onsrud tooling, there's videos explaining the tech.

abertoni (author)clazman2015-05-29

Hi, sorry your response has a ton of information in it so my answer may be incomplete.

In answering your concern around brass screws -- at the workshop that I work at they will not let us fix things down with anything other than plastic (polymer brads) or soft metal (brass screws) for fear of shrapnel,

Also, I did drill all the pilot holes on the cnc Shopbot. The brass screws actually do not hold the work as it is being cut, they only hold the pieces as the cutter completes its cut so that the torque does not shoot the loose piece into the blade, so in theory the work holding should have nothing to do with the precision of the cutting. The lack of precision comes from a 12" Z axis range that is maxed out at the bed depth and has deflection. Ultimately issues of precision will be solved with a tortion box.

dhengen (author)2015-08-03

Hey - Really great project here. Hats off for doing something different. Looking to do something similar myself and I have a few questions:

1. Was there a reason for the baltic birch? since you ended up covering up the exposed wood on the sides with aluminum (which looks really nice, btw), could you have gone with a cheaper plywood and acheived the same look? Is baltic ply stronger or something?

2. What is the thickness of your table in the centre? I'm looking to do a 8 ft long table, with approximately 6ft span between the legs. Is 2" thick going to be strong enough to not sag?

Thanks - Dave

BartholomewH (author)2015-06-17

As a flat pack professional I can only admire your work!
Great furniture assembly project!

BartholomewH (author)2015-06-14

I love how precise and detailed your flat pack assembly and manufacturing guides are! I think that if I had a local furniture manufacturer like you, I would totally back down on IKEA! Great project, totally fav-ing it

mmarolda (author)2015-06-02

Apart from the great job in documenting the build, when designing something, please do a little bit of research first :). "Life is too short, and you don't want to repeat".

http://www.untothislast.co.uk/?/categories/TABLES/ply-table-tapered/

rybitski (author)2015-05-28

Have you done any weight testing? I'm just curious how strong the plywood is parallel to all the seams. looks like a ton of work, but a beautiful project.

abertoni (author)rybitski2015-05-28

Good question, all I can tell you is I have stood in the middle of the table, so its got that going for it. I debated using some aluminum dowels in the center for rigidity, but a woodworker friend of mine told me that would be totally moot, so it was skipped.

rybitski (author)abertoni2015-05-29

Standing in the center seems like a pretty good test. Sounds like it is plenty strong.

bongodrummer (author)2015-05-29

Nice concept, and a really interesting looking table. The chair in the first photos looks awesome too.

Curious, why did you choose contact cement over epoxy (wouldn't that be the obvious choice?). Which make did you use?

Love the project, and thanks for the well written share - always cool to get some design stage insights.

dbowe (author)2015-05-29

I'm going to admit that my favorite part is seeing the original plan, the problem, and the work around to get it done. If anybody doesn't have those problems in their projects, more power to 'em...but I always have them. Congrats on a really awesome build!

cammers (author)2015-05-28

Very nice Instructable. Great result.
I think you missed the first step though... Become Artist in Residence for an organization with incredible tools and resources.

abertoni (author)cammers2015-05-28

Valid... Hard to argue with that.

Jake Maverick (author)2015-05-28

wow, beautiful table- but that sure was helluva lot of work.

Sure you must be very happy with it.

rolandcontreras (author)2015-05-28

Very wWell done but a lot of work

MekinizemX (author)2015-05-28

Are you on the navy pier?

abertoni (author)MekinizemX2015-05-28

I am an artist in residence at Autodesk and Instructable's Pier 9 Workshop in San Francisco - thus the great tools and killer view.

MekinizemX (author)abertoni2015-05-28

You have no idea how jealous I am :). My highschool has a pretty overfunded Fab Lab, (Our FRC team makes it to worlds almost anualy( but it's nothing in compaison to that facility.

lifeinbeats (author)2015-05-28

This is absolutely beautiful. And I love that you included the explanation of your missteps. Very thoughtful design and process. I had a few minor suggestions (mostly just as a discussion piece): I wonder if there is a way that you could have "scanned" the end profile of the plywood before cutting out the aluminum so that you could avoid routing. Perhaps if you took a photo of the side of the table from a distance straight on? You could then use a scale reference in cad. Or maybe even measuring the wood profile again would have worked since it's so uniform.

I also wonder if a drilling jig would have helped with the dowel process. I know that's what most woodworkers do, although I would imagine that precision really comes into play when you have to go through 50 (or however many) layers with a single dowel.

Like jpeck6 mentioned, it could be neat on your next project to use more aluminum (perhaps scattered throughout the plys) to be more efficient with your metal sheet. It could be an interesting effect too. You could play with their position and even stack several in one area creating some serious banding.

abertoni (author)lifeinbeats2015-05-28

Thanks for the feedback. The scanning process totally crossed my mind, Autodesk has a program called 123d catch that likely could have 3d captured this. The issue was that I was willing for the cut to be too large since the routing is a fairly foolproof process, conversely I would be concerned that if the 3d scan shrank some areas I would have issues having to then sand the wood down to match the smaller piece of alu.

lifeinbeats (author)abertoni2015-05-28

You have a good point! Removing the aluminum was certainly easier than taking another 1/16 of an inch off of the entire plywood tabletop. Looking at my comment just now, I'm a little taken aback by the disproportionate amount of "suggestions" to praise. I really do think this is absolutely wonderful.

jpeck6 (author)2015-05-28

Great project and design. I like the addition of the aluminum. How would it look if you added more of the aluminum throughout the whole stack or even made a whole table out of aluminum. great project. I wonder if there are shops that would cut that out for me locally and I can assemble it myself.

abertoni (author)jpeck62015-05-28

Thanks! That actually was the original design intention, I was going to add bands of alu in the middle and countersink screws to both sides to attach it all. Ultimately I didn't do this for two reasons - one was structural continuity, and the second was finishing and ensuring a cleanable, functional table. So it totally could be done, and that would be a good push, I just wasn't ambitious enough to figure all of that out.

vegatek (author)2015-05-26

Table looks excellent, and I am sure that it is structurally sound.

Thank you very much for your honest and in-depth description of the whole process. Your approach was to create the end product with the minimum amount of waste, but the problem is that securing the plywood sheet is difficult because each additional cut makes it weaker and less stable.

I was in charge of machining 4x8 sheets of 1/4 Lexan in a similar manner (low waste, numerous identical pieces). Our first test run on a CNC router was not good because Lexan was shifting too much while being machined. That convinced me that we will have to first cut the sheets using the CNC table saw and then trim each smaller piece on a CNC router.

While being machined on the CNC router each piece was held by vacuum on a piece of 1" MDF that had the seal (foam rubber) along the edge. MDF piece was slightly smaller then the finished product, and connected to vacuum system on the CNC router.

We had good results with this setup and made thousands of pieces with identical dimensions.

You might have more luck with this approach with the pieces you were making. Holes and shapes will align with great precision. You will also be able to use a bit with bigger diameter that will last longer too

abertoni (author)vegatek2015-05-27

Thanks for the thoughtful comment! I think you are right in that there are processes that might yield more uniform / precise results. I was stubborn and wanted to work with the shopbot in the context of future projects I hope to undertake, but I think that a vacuum table could have made all the difference - alas we don't have one!

BrianJewett (author)abertoni2015-05-28

I can't see how you're holding your sheets but if you have a base piece you can cut into, you could do your locating holes first and run them deeper into your base. Then you can then slip pins or dowels in before cutting the profiles.

anjoze (author)2015-05-28

Beautiful...

ringai (author)2015-05-27

Maybe woodturning is a handy new skill you. You could turn your own dowels to size and know that it's straight.

I love the look of the table set. It is very sweet.

Łukasz (author)2015-05-27

Wow your workshop has a great view

BrettHacks (author)2015-05-26

Spectacular table. Very interesting to see the build process so well explained.

sypage (author)2015-05-26

The end result is absolutely stunning. I would expect to see this in a high-end showroom.

repeels (author)2015-05-26

Beautiful table! I so need a water jet or a laser cutter!

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