There are times when I am amazed at what does people find in internet. Like all tubular ovens out there. Well, I was not able to find anything that suited my needs, so had to proceed along the hard route, build it myself.
Kilns are not difficult to build, just watch some tutorials on youtube and you are pretty much set, however, a tubular oven has slightly different demands:
- The glass tube must be Quartz to withstand the working environment, borosilicate won’t cut it.
- The filament is not NiCrom! wich is good for 900ºC max. You have to buy Kanthal, good for 1200ºC and not much more expensive.
- You want the heat as even as possible, hence the tubular shape of the filament guides/kiln shape.
- Also, since we’re at it, dual temp controllers will ensure that heat rise doesn’t generate hot/cold spots.
Skecth in Fusion 360.
Alumina bricks are easy to saw, but once you want precison shapes, hand carving is not going to be enough. So, what do you do?
I had lying around a 14mm sliding bar from an old scanner, so I bought some linear bearings (14x21x30mm) for it, and encaging those in 20x27x4 radial bearings (via some sleeves), I designed a support for all that (2x) to be anchored into 20mm normalized aluminium extrusions.
Since this is a low load, more or less single use tool, I decided to 3D print it instead of make it from a durable material like aluminium. 7h later, I had this:
After a few more hours of printing and designing a motor mount and such, this is what I got:
I had to add an axial bearing to this assembly, it’s shown in the videos below.
So what does this do?
The effector (rod) will have attached some apropriately sized diamond circular saws on it’s end. Once the tool and the brick are aligned, you can handfeel the pressure and go as slow as you want on the drilling (because the material is so soft).
I know, I know, I could have used one of the guides as driver with a gear attached to the bearing, however, the motor was an afterthought. I had planned to drill it by hand, but I’m a lazy bastard I guess.
Under power (the video is in slow motion) looks like this:
This only drills the central section and front/back coil recesses but the oven has this shape:
For the coil guides themselves, another machine has to be made, using 6mm drill guide, 6*10mm linear bearings (LM5LUU) and 15*21 ball bearings.
Failed print due to nozzle clog. (dammit, 10h lost)
But each half has six coil guides! how does this work? Magic? xD
No, not really, this adaptor works exploiting the axial simmetry. Once you have drilled three holes, turn it 180º and it will align to drill the other 3.
Since the print failed, I redesigned to be less volumetric and put the printer into another 15h shift (2x):
That’s it while I’m waiting for the rest of the pieces to arrive!