experiment4.com

After building the Gingery Furnace, it was finally time to start making stuff out of metal!

11/20/2000 – An 8×10 flask

I made a flask out of scrap wood. A big problem is to get both halfes to match well at the parting. My scrap wood was a bit warped, and there was about 1/8″ of play between the halfes. I sanded that down by taping some 100 grit sandpaper gritty side up on my workbench, and sanding the parting for both halves on that.Even though Dave mentions it’s not really necessary, I made a groove in both halfes about 1/2″ back from the parting to hold the sand in.Of course I remembered about the locating pins only after I had varnished the thing, and so they are “natural” These days it seems that nobody varnishes their flasks, is it not necessary? I would think they would warp from being in contact with wet sand, so at least varnishing the interior would be a good idea.

11/21/2000 – Preparing green sand

I made green sand with play sand and fire clay. Play sand is
too coarse a mesh for molding, I’ll have to look for a finer mesh sand. But it works well enough to start with, and that’s all I have been able to find so far, at the local Home Base.

The important thing about green sand seems to be to not add too
much water. Just enough to give the mix some cohesion, and no more. It’s very easy to overwater it, and it will ruin the castings.

11/24/2000 – First Melt

For my first melt, I didn’t try anything fancy. Just melting some
aluminium and pouring it in an open mold.

I started the charcoal with the air on fairly low, and that went much better than during the curing.

Then put in some aluminium scrap in my “crucible” (a coffee can), put the lid on, and started the blast.

The furnace heats up very fast. The can almost immediately started glowing red, and I had to reduce the air to keep it from burning a hole through the bottom.

The furnace melts aluminium very easily. I used some window frames picked up at the scrap yard. You get some amount of slag, but not excessive.

Inspection of my first blob of aluminium revealed plenty of steam bubbles. My sand was far too wet, and I obviously packed way too hard, almost as hard as the lining. I’ll have to try again.

11/26/2000 – First Part

For my next project, I decided to try and make a very simple casting from the Gingery lathe project, and (since there was plenty of room in the flask) a small replacement part for my drill press.

	The original has been broken for ages, and this actually resulted in damage to the splines, which had to be repaired.
	As it turns out, the drill part, even though it was the more complicated of the two, came out quite useable. The other one was worthless, because I poured it as the aluminium was a little colder, and… I ran out of melt.The part is fairly small, there is far more metal in the sprue and the vent holes! It’s also a bit messy – my first attempt at making a mold after all – but that shouldn’t really affect its functionality.
	After about 30 minutes of cutting, filing and drilling, I had a perfectly working part.This is the part, after I cleaned it up. Compare to the original plastic part (super glued together for the last time, so I could make the mold).
	And here it is in place!Now my drill press is complete, for the first time in a long, long time.

11/26/2000 – Casting is HARD

After that, I tried pouring the lathe part again – which is very simple, it’s just a plain rectangular slab. And once again it came out quite horribly. It looks like the sand I’m using is quite a bit too coarse. It’s play sand, since I’ve had a bit of trouble finding fine mesh foundry sand.

Also, further reading of the book showed that I made no fewer than 4 mistakes: I left the pattern with sharp edges, when they should have been sanded smoother; I also left the pattern in unfinished wood, which heightened its adherence to the sand and made the pattern removal difficult; I did not vent the mold enough; And finally I put the sprue smack in the center of the pattern, instead of to the side with a cutout to the pattern, which caused a lot of shrinkage.
The book also mentions tapping the pattern from below with the venting wire, which is a nice way to both vent the mold and help extract the pattern.