Erbschaft/Nahrung is a project I’ve been contemplating for some time.
For a history of the Danube-Swabian community (in German) please see this.
When my grandparents (mother’s side) sold their farm near Delhi Ontario, I rescued two wagon shafts that no-one else wanted. I’ve been moving them ever since. It’s been several decades. They represent the agricultural side of my heritage.
My father was a talented musician, maker of fine stringed instruments, and a Tool & Die maker. I worked with him for five years, most Wednesday mornings, learning the basics of making violins.
This sculpture brings those two quite different concepts together. The base is made from 5 45 mm thick Maple slabs, laminated from 2 or 3 boards each. It is in the general form of a fiddle. The shafts appear to have never been used. They are probably Oak. The right shaft is fixed, the left one is hinged at the bolt. The Acrylic rod is fixed at the right and mounted on the left shaft as a short Class III lever. The incised crest in the middle is that of the Danube-Swabian cultural community.
Acrylic has in the range of 9 times the thermal expansion co-efficient of wood. As temperatures change, the Acrylic rod will expand and contract more than the wood base. This causes the left shaft to shift left and right. Since the length change is very small, the lever ratio is as high as practical. The end result is that the top of the left shaft shifts about 1 mm per degree Celsius temperature change. It’s a small change, but visible even from a distance.
All parts are coated with two coats of brushed on epoxy. This should provide environmental protection.
The weight is a 50 mm Acrylic cylinder filled with epoxy. It masses about 1 kg. The base is made from off-cuts of two of the slabs. From the ends it looks slightly like horse collars.
The sculpture is 2.65 m from ground to top, about 900 mm in width, and 600 mm in depth. I don’t know the mass, but it takes two people to move.
The name “Erbschaft/Nahrung” means “Heritage/Sustenance”.
Now that I know the principle of what I’m calling a “Thermo-Kinetic” sculpture works, I may do another based on the same concept.
Erbschaft/Nahrung is done. Well, perhaps done.
I used the off-cuts from 2 of the slabs to make a base. From the ends it looks kind of like a horse collar, not an inappropriate image. I’m tracking the shaft spacing against ambient temperature. So far it looks to be in the close order of 1 mm per degree Celsius. I may eventually add some sort of scale near the shaft tops.
My neighbour Grant helped me move the assembly into position. The epoxy was still slightly soft, but close enough. I won’t have help available for a week, so best to get it done today. Once Erbschaft/Nahrung was in position, it was immediately obvious what my next project would have to be. Tomorrow I’ll work on a base to raise everything up 500 mm. I’ll use off-cuts and leftover pieces from the slab cuts.
I started a record of shaft spacing against temperature. Today it’s 14 out, and the spacing from the right upper eye bolt to the left shaft is 192 mm.
Erbschaft/Nahrung is almost done. I made the weight yesterday by mixing about 300 ml of ChemTech epoxy, dividing it into 5 small cups, and adding EcoPoxy metallic colours. Then I poured the coloured epoxy into the Acrylic cylinder, hoping it would mostly layer. It didn’t. The red and yellow vanished almost entirely, leaving only the blue/black and some greenish parts. It also shrunk down a bit, leaving a visible gap at the top.
I had made steel cables long enough to double as carrying straps. I decided this morning that they were too long when used to suspend the fiddle form and weight, so I made a shorter set. I’ll leave the carrying straps attached to the hold-down eye bolts.
Very little is left to do. I should protect the fitted shaft ends with epoxy, which I will do today. I’ll probably relieve the left shaft base a bit more as well. And I may make an indicator arm, but I think I might wait with that to see how much motion I get once the temperature drops.
The actuator arm is an Acrylic rod. It turns out that Acrylic has three times the thermal expansion coefficient of aluminum. And it looks better in this application. I thought about how to make the parts while falling asleep last night, so everything pretty much came together today. I also applied some additional epoxy to the base of the fixed shaft so it is now truly fixed.
The epoxy top coat was firm enough this afternoon, dry to the touch. It took a couple of hours to fit the ends of the shafts into their respective recesses. The one on the right is meant to be solidly mounted, but has a bit of lateral flex. I may seat it in epoxy putty, making sure to wrap it in Tuck Tape first so it doesn’t adhere. The left shaft has a small amount of flex that should suffice for the small change in the lever length with temperature changes. Both shafts are held in place by through-bolts so that the sculpture can be disassembled for transport.
I’m reconsidering using an aluminum bar for the actuator. The U-channel I have would block the crest. If an Acrylic rod has an appropriate expansion coefficient, I’ll make adapter saddles and use that.
As usual, the first complete epoxy coat soaked in. I had gone over it with a heat gun to even out the thickness and reduce dribbles. That appears to have worked. I only waited a day before applying the second coat. There was no need to sand and the first coat was only slightly tacky. For the second coat I blended some of the remaining “Caviar” black EcoPoxy pigment. It gave a mild darkening effect, pretty much what I had hoped for. I again applied a heat gun to even out the finish. I’ll leave this for a couple days for a full cure. I doubt a third coat will be necessary.
The third epoxy coat is now on the base underside, and a complete second coat on both shafts and the fiddle form. In order to reduce drip marks I suspended the shafts and form. Even so, I was brushing away drips all afternoon until the slow-cure ChemTech epoxy started to set up.
It’s a good think I bought a 13 l epoxy kit! The underside of the base is double-coated, and each interface has epoxy applied to both surfaces. The shafts have a single coat on all sides, as does the fiddle form. Once this layer is cured I’ll sand everything smooth and apply overall coats to all components. The shafts and fiddle form will need to be suspended so I can access all sides in one pass.
I decided to do Slab 5 even though it would mean using expensive power. As it turned out, the finishing pass ended at 11:10, only 10 minutes into peak rate time. I used a tooth brush to apply black Grumbacher artist’s oil paint to the crest. Once it’s quite dry I’ll sand it down so only the incised lines are black.
The next step is to epoxy the underside, followed by laminating the slabs together with epoxy. Given the cure time of the ChemTech epoxy, all that will take at least a week.
Now that almost all the parts are in the same photo, I can explain the plan better. The dowel is for aligning the 5 sections. One of the shafts gets fixed into the closer square recess. It will be bolted into place with a tight fit, so it can be disassembled for transport if necessary. The other shaft will be mounted in the far square recess, bolted in place with some relief so it can swing a bit on the lengthwise dimension. A short section of the aluminum channel gets bolted into the longer rectangular recess, allowing some vertical motion at the far end. That end gets attached to the far shaft, as close to the mounting as possible. As temperatures change, this should force the far shaft to move slightly in the lengthwise dimension. The violin form will be suspended between the shafts near the top. The slight motion of the shaft will be magnified into vertical motion of the violin form, thus indicating changes in temperature. Hence the generic title of this piece as a “thermo-kinetic sculpture”.
Slab 4 took the longest on the CNC – almost 6 hours. There were no problems. I was concerned about the crest. I had never done a mapping onto a 3D surface. Aspire took care of it all. I just had to tick a single checkbox and the programming wizards at Vectric did the rest. I did reduce the size of the crest though, so that it all fit onto Slab 4. The fits of the parts in the recesses are tight and will require a bit of manual adjusting, but that’s better than having them too loose.
The first three slab slices are done. Each took about 4 machine hours. Slab 4 will take about 6 hours, and slab 5 about 4. Once they are all done I will assemble slabs 3 and 4 and machine in a crest, which will straddle the narrow centre area. The fiddle outline is the central suspended feature. I also sanded down the wagon shafts and purchased most of the necessary hardware.
The other necessary purchase was of the full version of Aspire. That cleaned out the accumulated holiday fund for this year.
I’m back to work on Erbschaft/Nahrung. Last week I started getting serious with Vectric Aspire (Trial Edition). I now have the 3D file sliced and the design laid out in what I think is a good configuration. Over the long weekend I laid out the 7 8/4 planks for the 5 slices.
Yesterday I spent half the day re-aligning the tables on the Hammer Jointer/Planer. I’ve always found it hard work to use it as a Jointer. It turned out that the outfeed table was high by almost 2 mm, and the infeed table wasn’t parallel to the outfeed. The outfeed wasn’t hard to set up, even though the owner’s manual dedicates only a short paragraph and a poor picture to the process. The infeed table had no instructions at all, so it took a couple of hours of trial and error to get it close to acceptable. Jointing is now much less physical work, and the results are excellent. The moral of this story is: don’t assume that an expensive Austrian-made product is set up properly.
In any case, yesterday I flattened all the 12 slabs. Today I dimensioned them to 46.5 mm. The final thickness will be 45 mm. I glued up the first, base panel. Once all 5 are glued up I will flatten them again on the CNC (if necessary) then thickness them to 45 mm. I would prefer to thickness them on the Hammer, but the maximum capacity is 410 mm. These panels will mostly be about 600 mm in width, just within the capabilities of the CNC. I designed this whole project around the dimensions I can machine on the CNC.
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