Making a Flask
What is a flask? A flask is just a box type shape that is used to hold a sand mold when casting aluminum. It comes apart in two pieces. The top piece is called the cope, and the bottom piece is the drag. This post shows how I made one of these so called flasks out of some wood I found lying around. It really is quite simple to make, and could easily be done with far fewer tools than I had at my disposal.
There were a couple of things that I wanted for this flask that I didn't have on my previous one. The first thing I wanted was for it to be adjustable. I wanted the mold area to get larger or smaller depending on the size of the pattern. I also desired for the cope and drag to fit together better, and to fit together the same way each time.
The first thing I had to do was make the 4 sides of the cope. I wanted the short side pieces to be 7 inches long, and the long sides to be 20 inches long. I decided to use a boards that were 4 inches wide. I cut out two long pieces, and three short pieces. The third short piece will be the adjustable part of the assembly.
The next step was to make the notches that would allow the adjustable board to slide back and forth. I just cut two notches on each of the long boards. Each notch was 1/2 inch wide, and located 1/2 inch from the edge of the board. I marked the locations of the notches on both ends of the boards, and set the table saw blade to be 3/8 inch above the table. I then ran the board through multiple times for each notch.
I broke away all the slivers of wood that were left. Then I cleaned up the notch with a 1/2 inch chisel. I made sure to get all the pieces of wood out so the board would slide smoothly.
The next thing I did was mark my cuts on the short adjustable board. I then cut it out. Actually I cut two of them out. One for the cope, and one for the drag.
I checked to see if it fit nicely, and rasped away the parts that were rubbing.
The next step was to connect the 4 sides. I didn't want to go and connect them all at once, as there might be warping from boards not being flush with each other. Therefore, the first thing I did was connect each long side to a short side. For each set, I drilled two holes, and put two screws in.
I then tested the frame by clamping the two halves together. If it sat flat on the table, I was good to go. If there was a part of the frame that wasn't touching the table, I needed to rasp away the ends of the short boards until it was all flush. After I was satisfied, I connected the two halves together. I then made an identical frame for the other half of the flask. I also labeled them so I always know which one is which.
The guides were next. I needed to make a set of connections that would allow the cope and drag to go together the same way every time. My plan was to make dowel rods slide into holes on either side of the flask. First I took a 2 x 4 and cut out a pair of identical blocks. They measured 6 in x 1.75 in x 1.5 in. I actually made 4 blocks, two for each side of the flask.
The dowel rods were cut to lengths of 3.5 inches. I cut four of those out. I used 1/2 inch diameter dowel rods.
The holes were next. I drilled two holes in each block. I clamped them together as I drilled them so that the holes would be nice and lined up. The holes needed to be a little bigger than 1/2 inch diameter in order for the dowel rods to fit well. Unfortunately I didn't have any sharp drill bit that was big enough to do the job. Instead, I drilled a hole with a 1/2 inch drill bit, and then widened it with a drill rasp. It worked beautifully.
Now I needed to connect the guides to the cope and drag. First, I drew a line down the center of each pair of guides so that I could line them up well. Then I clamped the top of the first pair of guides to the correct placement on the cope. The bottom of the cope is flush with the bottom of the guide.
I then drilled pilot holes and screwed it in place. One important thing to remember is to not put the screws through the holes that are drilled in the blocks. I repeated this for the drag side, and then I attached the second pair of guides on the opposite side of the flask. When you screw the blocks in, make sure the dowel rods go through them smoothly.
The next step was to put screws in the dowel rods to keep them attached to the cope. All I did was drill a pilot hole that went into the block, through the dowel rod, and into the block again. Then I put a screw in. I did this for the two dowel rods on each side.
The last thing I did was make the holes that would allow the adjustable boards to stay in place. I created a grid with 1 inch spacing between the holes, with the holes centered on the two notches. I also drilled holes into the tabs on the adjustable pieces.
And that's it! Here are some photos of the finished product in action.