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Wednesday, February 5, 2014

Venturi Forge Build Part III - Housing

Continued from Part I here
         and from Part II here

The housing of the forge, while extremely simple in principle compared to the burners and lining, was where I encountered most of the problems. Allow me to preface this by saying it is MUCH easier to find a prefabricated shell to use (old gas cylinder [CAREFULLY EMPTIED OF ALL GAS BEFORE CUTTING OPEN] or a metal barrel or bucket or anything cylindrical really) rather than build your own. My intent with building the shell was to be able to emboss a design into it similar to this armguard-

but quickly found that .06" is far thicker than I thought and less forgiving than the malleability brass. So, after a very quick and decisive attempt at starting the knotwork dragon I designed in part I, I abandoned that for the possible future engraved design with better results.

Another point of contention I would like to mention is that, through this entire process, I have learned that it is painfully clear how true it is to say that having one forge that is good at doing everything I set out for it to do is all but impossible. Unless you have a very specific and unavoidable need for a door on the side, I urge you do NOT do this. Barring some creative problem solving, it was nearly catastrophic, and even now I am working to make the forge run efficiently at welding temps.

As a final point, it is recommended, at least if you pursue a similar construction of a forge, that you have access to power tools. Throughout the remainder of the build, all I had to work with was a drill and about two minutes with an angle grinder to cut down the sheet for the body of the housing. The rest was done with tin snips, hack saws, punches, wrenches, and files. As a result, this took far longer to complete and a considerable amount of headache trying to get it all fitted together.

First things first, the housing. My intent when I ordered the sheet was to use the entire thing, sized as it was, but after physically looking at it the on-paper dimensions did not feel right. So I cut an arbitrary amount off one end with an angle grinder (much easier with a bandsaw or even scroll saw, or anything really). The end was jagged and unruly, so I had to file it into submission. With the flat sheet, I had to bend it into a can. This was harder than it sounds, especially when a kink begins to form. I tried bending it around a log, but that did not work at all. In the end, I clamped it to the bench and pulled one end up, shifting it so I never put a corner in one place. Obviously, the easiest thing to do would be to start with something round.

Sometime later, I had the ends overlapping. Now I marked where to rivet it together, spacing eight or ten rivets along the entire length and marking the places to drill.

For the rivets, I cut 1cm or so from the end of the 1/4" steel bar. as a general rule, rivets should not extend out of the thing being riveted by more than half the thickness of the rivet shank. Here, I grossly over estimated that in order to set the first one (the two ends of the housing were not perfectly flush until later).

This is the progression of the rivets. Keeping an equal amount of the rivet on either side is critical to this working correctly. If not, there will be little to nothing holding the rivet in place other than the natural expansion as it shrinks from being stricken into submission. Another challenge here is keeping the two halves aligned properly. A clamp only goes so far, and when drilling the holes the two sides were not perfectly against one another, meaning there is a bit of an angle when they come together. I had to ream a few of the holes to get the rivet through.

Here is the body all riveted together. I did have to touch up the cut side so the corners met. Otherwise, one overhung too much, but the tin snips took care of that with only minor bruising.

And now for the fatal error. The side door. While I am glad I will have the capability to forge sheet (armouring), insert crucibles (which I will eventually build a vertical melting furnace for), and forge axes/hammers/other things too large to fit in the front, this was the worst decision I have made in the project. Here is why. By having a door, there are now four more places for the flames to escape, along each edge. Insulating only goes so far, especially when getting a tight seal means having the edges of the door meet the edges of the forge lining. That works only when the two are soft, pliable materials, and when coated with satanite, IR coating, and bubble alumina, this becomes impossible. As I would later learn, the holes cannot be completely sealed the way I did this. More on that later.

Next comes the feet. There are a thousand ways to do this, and here is the one I went with. I used the 1/8"x1/2"x6' bar, cut in half, for the lower supports. Again, this was mostly arbitrary. It is difficult to see in the photo, but I sketched the pattern on the bench and used a piece of string to measure how long a piece of steel it would need to make. Conveniently, it was exactly 3'.

The curved surface of the forge will sit in the top side of the bracket, and the two outer points will be the feet of the legs.

I drilled three holes into the housing to affix it, the two that are obviously visible and a third between them. They are offset a little to mitigate stress fractures in the same axis of the steel (that isn't a thing but I invented it to account for my poor drilling job). If I had planned better, I would have drilled a hole in the outside two corners before riveting it on to the housing so there could be support farther away from the centre, but with it in place I could not position the drill through the bottom half of the leg. Live and learn.

In accordance with the standard procedure here, I eyeballed where to place the burners, traced it with a marker, and winged it from there. The two are about centred on the long axis, and down about 20 degrees from vertical so there will be swirling action from the flame. The two smaller holes for each 3/4" flange that will hold the burners to the forge. The larger hole is hammered out so to accept the end of the burner, reducing the turbulence of the flame's cone.

Burners temporarily held to the forge for a better idea what it looks like.

Cutting out the door was difficult to say the least. And with all things, it is impossible to remove a piece from a whole without some waste. To cover the gap left behind, I cut pieces of the 3/32"x1" bar to act as a seal. Riveted on in the same way as the legs to the forge, the only thing that needed precision here was marking the 45 degree corners that would join the sides with the bottom. I left the top long just in case, which was cut off later.

Originally, I intended to make my own hinges from a piece that would support the burners, but the housing was more than strong enough already, and I didn't want to file out that hole in the 1/8" thick bar. So I used some generic hardware store hinges. They had to be formed a little to accept the curved surface (which I did after this picture) of the door and housing.

Before starting the lining, I stood the forge on end and traced the two end shapes on the two 1'x'1x.06" sheets that will close off the ends after the lining is finished. I did not do much with these, as I knew it would change a little in size and design after the lining was in place.

Finally, here is the door attached (without burners). It seems to close nicely and seal entirely. And now for the lining to change everything.

Continued in Part IV Here

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