Tentacle Sculpture

I've been developing the technique of taking a 3D model, unfolding it into connected pieces, getting those waterjet cut out of steel, and then bending and welding it into shape. This has been detailed in severalpreviousInstructables. (Please view those for technical details.) I recently finished taking it to an entirely new level, however, making a 6' high permanent public art installation.

The piece is called "The Visitor", a rusty steel tentacle pushing its way out of a manhole. It can be found at 23rd and Main in Vancouver, WA.

Step 1: Applying for Commissions

I started applying to public art calls last spring. This is all rather new and different for me, given my academic computer science background. I have experience in big kinetic installations, but it's all weird flaming death sculptures at Burning Man. Not exactly your standard artist background!

I've only had two successes so far out of about 15 submissions, so obviously I'm not the greatest expert on the process. I can only share what I've learned so far.

Types of calls

You'll see two basic types of calls: Request for Proposals (RFP) and Request for Qualifications (RFQ).

RFQ: You submit your resume and your portfolio. The committee will then choose 3-5 artists and pay them a nominal amount to come up with a design. One of those is then picked for the actual contract. This is how all the big, serious commissions are done. (And, yes, there are some *very* big commissions out there.) So far I've had no luck at all with these, probably because my portfolio and experience aren't solid enough yet.

RFP: This is when they're asking artists to submit more-or-less complete designs, from which they will choose a winner. These tend to be smaller (under ~$40K), since artists with an established reputation probably won't bother. You are providing free design work, after all! But they've proved to the best place to get started, at least for me. By providing an actual design, you have a chance to wow the committee a bit despite an unusual resume.

At the moment, I don't bother applying to anything above about $75K, as I just don't have the portfolio and experience that they seem to be willing to look at. Hopefully that will change after I compete a couple more permanent, mainstream installations.

Finding calls

There are several places you can go to find calls for artists. The callforentry.org system is pretty widely used, though that means anything listed on there will get a LOT of entries. Your local city probably has an artist opportunities page. For instance, I check the Seattle listing every week, as well as several others from across the country. Local artists mailing lists/Facebook groups are also a good source, as people will often pass along calls that they find. If I'm really bored, I'll sometimes try open-ended web searches.

Applying to calls

Once you've found a call that looks promising (and I find 5-6 a month at this point), what do you do? I think it pays to be organized. I keep a calendar with the deadlines listed, so I can keep track of what I need to be thinking about. RFQs rarely take much prep, but RFPs will need a nice rendering or sketch. I download all the supplementary materials into a cloud drive, so I can pull up the PDFs whenever I have some downtime, to brainstorm ideas.

Calls all want the same basic things, so you'll develop a standard framework after a couple of submissions. They'll want a resume, portfolio images, descriptions of the portfolio images, a letter of interest, and references. If it's an RFP, then design renderings and description as well, of course. I have no idea if my resume is a good one or not, as I've never found an example to compare it against.

Most submissions are electronic these days, thankfully, but some still require them to be physically mailed. I bought a bunch of cheap thumb drives off Amazon, so I always have some on hand as needed. Remember that usually the rule is that submissions must be received by the given deadline, so they'll need to be mailed considerably earlier!

Step 2: Meeting With the City

Once a commissioning agency is interested, they'll call you and let you know. Usually they'll have questions at this point, or will want to talk about potential design changes. For the tentacle project, I provided them with a list of some different surface finishing options, making a strong argument about why my original choice was still the best, and talked to them about vandalism concerns.

After they were happy I knew what I was doing, I was officially offered the commission and invited down for a meeting. (Vancouver is about 3 hours south of Seattle.) There I met the person at the city I'd be working with, the neighborhood art representative, and a city engineer. We worked out a timeline, payment details, the rough plan for how to install it, and what the city would need to do to prepare the site. I was also able to pick up a manhole cover from a city depot while I was there.

After the meeting I finalized the design. This covered purely aesthetic issues, like endlessly tweaking the curve of the tentacle to my final satisfaction. It also included practical concerns raised at the meeting -- like making sure the manhole cover would be too steeply inclined to make it a tempting resting place for trash. I then drew up precise plans for the mounting frame, and provided the city engineers with more details such as dimensions and centers of gravity for different parts of the structure.

Step 3: Making the Mounting Frame

The first priority was making the mounting frame, as it had to be set into concrete at the site as soon as possible. I welded the first ring of the tentacle together, then bolted the internal frame verticals into place with 1/32" spacers before welding in the frame ring. This guaranteed a smooth fit, as I wouldn't have another chance to test it until installation day!

The mounting frame was driven down to Vancouver at the beginning of November, to give them plenty of time to get the groundwork done. I wrote up instructions for the team doing the concrete work, to make sure the frame was installed properly. I didn't have any direct contact with them, so I thought it was worthwhile to create diagrams for the really important parts. This included spacing and alignment issues, to make sure the tentacle would fit and would end up facing the way I wanted it to.

Step 4: Welding the Tentacle

The design for the tentacle followed the same workflow I've described here before. I designed it in Blender, used Pepakura to unfold the shapes, then got those waterjet cut out of steel. This time we were using 3/16" weathering (AKA corten) steel, which is an alloy which is made to rust a bit, and then stop rusting. It's commonly used for sculptures and architectural details.

Note: Weathering steel doesn't work if it is in standing water, or if there is a lot of salt in the environment. It can also bleed a lot of rust over the first few months, staining the sidewalk.

All the pieces together were about 300 pounds, which meant it was a lot cheaper for me to take the ferry to Vashon Island and pick them up than get them shipped. The thicker material also meant that my old welder wasn't going to cut it. Not only couldn't it handle 3/16" thick stock, but the MIG wire for weathering steel only comes in 0.045" on the giant 33 pound spools. So I took this opportunity to upgrade the 240 circuit in my shop to 30 amps, and to upgrade my welder to a Millermatic 212. Working on paid projects sure is convenient at times!

Because of the size and thickness, we didn't etch the bend lines in the steel, but cut them entirely through except for tabs at either end. This worked okay, but the steel was thick enough that the tabs often broke when I was bending them into shape. The weathering steel alloy might have made this worse, as it seemed a lot stiffer than normal mild steel. I often ended up breaking pieces apart entirely, then grinding down the tabs so I could weld the pieces together cleanly. I still would stick with the tab approach, though, as otherwise it would be a nightmare keeping track of which piece went where. As it was I had to etch a binary code into the smaller rings, as they looked too much alike to distinguish by shape.

For the lower part of the tentacle, things went pretty smoothly. Each ring is nonagonal (9 sided) in shape, which means 140 interior degrees between faces. As long as I used an angle gage to make sure each face was the correct angle relative to its neighbors, it went together just fine.

Step 5: Bending Pieces to Precise Angles

I started to have serious troubles farther up the tentacle. Here the geometry gets more complicated, because of the bending and twisting of the tentacle. Before, only 1 or 2 pieces in each ring would have a diagonal score in them, but now basically all of them did. This drastically complicated the geometry, and the techniques I had developed farther down stopped working. I started taking hours to complete a single ring, having to reweld it many times to fix the gaps. As there were still another 25 rings to fabricate, this was really bad.

I decided I needed to be more precise about the angle of the bend across the diagonal scores. I was able to pull out the exact angle each one was supposed to be from Blender, I just had to bend them properly. Once those were right, the old 140 degree jig should work great again! So I bought a digital angle gage to try it.

It worked! ...kind of. The angle gage was super crappy, tending to re-zero itself randomly, and holding it up to the tiny pieces I was bending was very awkward. I decided to talk to some people at work about it, to see if they had any better ideas. I happen to work at a dimensional metrology R&D lab, so I know some people who are very good at measuring things. One of them made a very simple observation: It's always better to measure distances than angles, if you can at all avoid it. Of course!

That night I used Blender to calculate the linear offset of the far corner of each piece from the opposite plane. I then used my height gage to measure each piece, tweaking it back and forth until it was as close as I could get it. (Usually within 0.05mm.) And this time it really did work! It was slower than I wanted, but it reliably got good results. Using this technique and a 140 degree jig I got the rest of the tentacle pieces welded together.

After that was just many, many, many hours of grinding to clean up all the welds.

Step 6: Manhole Cover

The design called for the tentacle to be holding a real manhole cover. The city of Vancouver was kind enough to give me one of theirs to work with. It then sat untouched in my garage for 2 months before I needed it, though I did bring it out for a Halloween party. What good is a chocolate-covered manhole cover? Well, it makes a decent party tray.

When I had the upper sections of the tentacle tacked together, it was time to work out the exact mounting details. I had had some hatch covers waterjet cut, and now that I could see how exactly the manhole cover would lie on the tentacle, I could fit them into place. These gave access to the interior of the tentacle, so bolts could be screwed into threaded holes on the manhole. Except... the manhole didn't have threaded holes. It was only 7/8" thick, so drilling and tapping a blind hole of the size needed would be tricky. And you can't just weld to cast iron, of course, as it will crack.

I decided to get mounting blocks TIG brazed into place. This was done by someone I know through a local metalworkers mailing list, who has far more experience with such things than I do. We used the actual section of the tentacle to hold the blocks in place as they were brazed, so everything was guaranteed to fit later.

After all that, I decided to get the manhole cover powder coated. This results in a flatter, more artificial look than I normally like, but it felt important to me to provide a strong visual contrast between the manhole cover and the rusty steel tentacle.

Step 7: The Suckers

The final step was making the 84 suckers that would be welded along the tentacle. (These are practical as well as decorative, as they also serve as anti-skateboard deterrents.) I had rings of 1/8" weathering steel waterjet cut along with everything else, but forging them to shape was slow going. I was happy to put in the effort for the larger ones, as it resulted in lovely, organic, wibbly-wobbly edges, but on the little ones it was just a big pain.

I decided to make a cone mandrel to simplify the process. This meant cutting 2 cones (one positive, one negative) on my lathe. This ended up taking several days of effort, and generated about 3 grocery bags worth of chips in the process. It was worth it, though, as it let me form about 60 suckers in a single day, and didn't even trash my elbow too much in the process. I'd pull a ring out of the forge, place it on the cone, and then hammer the negative cone down on top of it. Very easy going once I'd established a good rhythm.

The suckers were then all welded into place, mostly just going by eye to see what looked good. (This is art, after all.) The last 10 were too small to be done with rings, so I drilled a hole through some 1/4" copper plate, clamped that where I wanted the tiny suckers and welded into the hole. Molten steel won't stick to copper, so you can use it as a template to get crisp edges when welding.

Finally I spent about 8 hours cleaning up the weld beads in the suckers using a pneumatic die grinder. I was picking metal slivers out of my hands for days after, but it worked.

Step 8: Installation

I drafted some friends, loaded everything into a van and drove down. This was particularly stressful as I hadn't had an opportunity to see the installation site after the city had done the concrete work.

It's quite a feeling to see that the power of your art has convinced a city to tear up their sidewalk and install a weird stainless steel frame in a hole in the ground, let me tell you! Unfortunately, it wasn't quite the manhole ring that I expected. This mean it was shallower than I had planned, and it had 3 flange tabs sticking out from the ring, preventing the tentacle from slipping into place. And the cordless angle grinder I had brought for these kinds of emergencies couldn't reach.

Luckily I have some very resourceful friends, who quickly went to rent a 7" angle grinder and a generator. (Note to self, always arrange for power at future installation sites!) We cut 3" off the bottom of the tentacle, so it wasn't too long. We couldn't quite cut all the way through the flange tabs, but far enough that a cold chisel and hammer handily took care of the rest. And after some other last minute grinding to get it to fit on the frame properly, it was in place! We retired to a nearby pub for beer and Thai food, victorious.

Step 9: Results

So far, the response has been overwhelmingly positive. I was able to attend the dedication ceremony, which drew what I thought was a surprising number of people. The local newspaper wrote a very nice article about it. And I keep running into new places where it has been reshared online, which is very flattering. (There have been a few "what a waste of money!" comments, of course. I suspect I'll just need to get used to that if I'm to continue making public art.)

I'll only know in a year or two if I designed it strong enough. Public art takes a LOT of abuse, and while it felt rock solid, it's hard not to worry. This was my first time working with weathering steel, so I'm eager to see how the rusty patina forms on it. We'll also have to see how well the drainage inside the sidewalk mounting works, which is needed to keep the bottom from being submerged in standing water. I'll post an update if anything goes terribly wrong, I promise.

As for public art... yeah, I think I like it. This wasn't a particularly large contract (<$10K), but it's a good start. I have another contract already lined up for a much larger piece due in May. I'm hoping that with those two under my belt, I can start successfully applying to larger and larger things. I'm not quitting the day job yet, but every project is moving me closer now. I hope!