The Shop > Metal Stuff
Simple steel flasks
vtsteam:
Thanks Andrew. :beer:
re. angle inserts -- I didn't want to add inserts unless absolutely necessary because they reduce the capacity of the box. A 1" wide insert on each side would convert a 10" wide box to an 8" box. But an 8" box generally does not require inserts at all, so one might as well just make an 8" wide box with no inserts.
The limit seems to me somewhere around 8-10 inches depending on the sand and the roughness or shape of a box, and its depth. Length also affects it. My wooden 10" x 10" x 3.5" flasks never slipped -- they were roughened up on the inside with a handsaw before varnishing. These were deep, and relatively small.
Now I've gone to 12" x 10"x 2" and smooth metal -- and to me, with my sand, I'm pushing the limits. That's why I roughened up the inside with rough welds.
Ironman's boxes have draft -- and are 12" x 9" x 2". The draft helps as long as it is oriented the right way, though the drag is usually turned over, so at least one point the draft doesn't help.
Commercial boxes like yours and Rob's have a pressed in bulge -- but that goes outward so it doesn't cut down on the inner dimension of the flask relative to the flask size and quantity of material used.
If I do have to add something more than the welds, I will try to minimize the width reduction. I could spot weld 1/8" steel wire along the sides for instance. But I think I'm okay -- I did a test ram-up today and had to abuse it fairly hard to get the sand to shift, although I was able to shift it.
There are two things at work in slippage, as I see it -- one is true slip along the edges, the other is deformation -- sag -- in the middle. Inserts can't control the latter it's mainly a function of width, depth and green strength. Wider shallower flasks will tend to foster that kind of collapse. Mine mainly seemed to true slip when pushed to it, so if needed, inserts would counteract that.
Sorry to talk about these small details so much -- just stuff I was thinking about while building and trying these.
DMIOM:
--- Quote from: vtsteam on August 11, 2013, 10:38:27 PM --- ....... Commercial boxes like yours and Rob's have a pressed in bulge -- but that goes outward so it doesn't cut down on the inner dimension of the flask relative to the flask size and quantity of material used........
--- End quote ---
If you haven't finished welding them, how about flipping the channel on the long sides through 180 degrees so that the C faces inward ?
Dave
awemawson:
Some large commercial copes and drags have a grid cast into them to resist sag. I have some 'railing flasks' designed for casting iron fencing that have braces across the width for this reason. Mind you when on those rare occasions that I've used them for long thin items I've had to use a block and tackle to both invert while ramming and place for pouring.
vtsteam:
--- Quote from: DMIOM on August 12, 2013, 03:23:28 AM ---If you haven't finished welding them, how about flipping the channel on the long sides through 180 degrees so that the C faces inward ?
--- End quote ---
You could. This kind of thing really just boils down to personal preference. When I thought about it before making them, 1" seemed a lot more than needed, you'd need to make 48 miters or 24 cutouts at the ends of the pieces, make and attach handles, add long pins, and wouldn't be able to bolt them together as simply, so for personal preference I chose this way. It's extremely simple to build -- all pieces are 12", and cut square. I like things simple.
They are really great to work with, I have to say -- it's wonderful having a handle that extends all the way around the flask, very short pins that slip right into place. They just really pull and go together nicely. Hard to describe. Size and balance feel right. The cope also stands up on edge very positively even with sand on the table. Just a bunch of small things i noticed, compared to my wooden flasks. They feel good to work with.
EDIT: Just noticed you said flip only the long sides -- so no cutouts or miters -- that would work. Personal preference again.
vtsteam:
--- Quote from: awemawson on August 12, 2013, 03:40:35 AM ---Some large commercial copes and drags have a grid cast into them to resist sag. I have some 'railing flasks' designed for casting iron fencing that have braces across the width for this reason. Mind you when on those rare occasions that I've used them for long thin items I've had to use a block and tackle to both invert while ramming and place for pouring.
--- End quote ---
Andrew, I was thinking a heavy wire grid would work similarly on a fabricated flask if needed. I think I'm okay as-is with reasonable care in molding, but will alter if needed. I know what you mean about the cross pieces on larger flasks -- I have a flask with cross braces -- a custom wooden one required to cast the bed for the Gingery lathe.
Sometimes commercial flasks have bolt in cross bracing which can be shaped to fit the pattern without interfering.
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