Metal Casting Zone

After reading several books on how it used to be done, and pondering patternmaking on a few difficult-to-cast items, I decided to experiment with an old technique this past weekend, and I am fairly impressed with the results so far.
The old technique is using what are known as "sweeps" to form parts or the whole of a pattern for a sand mold(amongst other things). It was considered a quick and cheap method of patternmaking for certain items. I have been working on a traditional pattern for a blower case and was (still am, I WILL finish the damn thing) not too impressed with both the pace of completion and the quality of the pattern. A light dawned that this may be a good application for sweeps. So a little mental organization and brain sweat later this is what I came up with.

That's the pattern set for a 10" blower housing. Both halves. Took me all of an hour and a half to lay it out and cut it. And no, it doesn't look like much, but it works suprizingly well. Here's how it works. The first thing I did was to fill both the cope and drag like I was making a normal mold, just leaving out the pattern. This establishes the parting plane and makes sure there won't be runout between the halves. I separated them and set the cope aside for the moment. I then swept up the core on the drag half. I set the outline in place and clamped it so it woudn't move. I had to add sand to make the raised core so I riddled a pile on and packed it by hand. I then went around and around with the first core sweep, carving out the shape of the core:


After cleaning this up, I set the drag aside and started on the cope half.I set the outline on and dug out the majority of the excess sand with a spoon. I then set to work with the outer sweep and not too much later this is what I arrived at:



In the bottom pick you can see that I cut the ingate and sprue, had to do it rather directly, I didn't have much room left in the flask. After removing the outline, I cleaned up the cope a bit, and set it on the drag, melted some aluminum, and poured.

And wouldn't ya friggin know it, I didn't melt enough. Short pour. Took a lot more than I thought it would. DOH!!! However, it definately proved it was a viable technique. What did come out of the sand was 80% of what I had hoped for, the wall thickness was very even, and no warping, the surface finish was rough but I was expecting that. I don't have any more pics of the failed casting, my poor old foundry camera died about then. Time for a replacement. I'm going to try again in the next few days, I already have the other side molded up, just have to have a bit of time to do it. I'll try to post pics if the camera cooperates.

That looks really good OddDuck, I need a big blower like that. Can you use the same sweeps for the other half, I'm guessing you just turn it over and do it backwards?
Time for a bigger crucible!!!

That is a really neat technique!

Thanks for sharing

definetly a cool technique!! I see alot of possibilities, thanks for the eye opener

Thanks guys. I see a lot of possibilities as well, A1. And yes, Jammer, it can be used for both sides, all you have to do is flip the outline over on the second mold. I labeled both sides A and B, and I start out doing the core on both, so on the first I did side a, then flipped to side B for the cope, and on the second mold I started with B and flipped it to A. It is a bit tricky to remember, but heck, if you are making patterns you probably have a pretty good head for this kind of stuff anyways.
I got the first half re-molded today, and noticed a flaw in my outline, and was able to correct it without changing the patterns. Then I re-opened the second mold and corrected that one as well. Gotta make myself a full set of slicks and spoons, now, this is kind of fun. I'm going to pour them tomorrow, ran out of time today.

excellent odduck! ive been doing that sort of thing for a while now. i didnt know it actually was a oldtime foundry methods.mostly i use it to get a rough item and clean it up as a pattern.

Thanks XL. The nice thing about this method is that it is repeatable. And it works! I poured today and darned me if it does work a ot better when you use enough metal.



The surface texture is a little rough, but the one that I had previously cast and remolded is the smoother of the two, so it may be technique sensitive. I spent a little more time smoothing that one up, and it did turn out better. The thing in the center is the impeller, I am going to make sheet metal paddles instead of trying to cast them. That way i can use the same impeller for different sized blowers. Now just a little cleanup work and they will be just fine.

Looks good!
How much does each half weigh?

Thanks, Jammer. They weigh more than they should, I think I have to make a few tweaks to the outer sweep, I may have layed it out a bit wrong, the curved portion and the flange is about 1/4", but the face is about 1/2" thick. I found this out when I broke up the failed one for re-melting. This one will work fine, and it's all to the good because I am going to be mounting a motor to one side, a little extra thickness won't hurt. The one with the lettering should have the opening for the air inlet on it, you can see the depression I made for it, but the core didn't reach all the way through.

Update, I finished the blower (and forgot to take pics of the process, sorry...) and installed it in the new forge. I am now Odd Duck & Son Foundry and Forge. My son is happy, he can now whack on red hot metal, and I have one more thing to hold over his head if his grades drop... Pics:

The blower installed in the forge, I also lost foam cast the flange for the air pipe and the mounting bracket.
And proof that it does blow air:

Got the steel to sparking hot in no time.
I am going to draw up plans sometime soon and post them here for anyone who wants to try this, works pretty slick. Just to tease, I also figured out how to use this method to build the shell and impeller for a roots blower. I hope to have something cast by the end of the week. I'll post progress as I go!