I recently have been having trouble with the cope half of a split pattern falling out of the sand as I split the packed cope off the underlying packed drag. I guess that shows that I have good draft (1.5 deg), good fillets, no undercuts, and a slick surface on the pattern. So, ya, that's good. But having the pattern fall out tends to break sand edges as it does not release perfectly straight down or may only release partially. To counter this I installed two retractable short tapered 7/16" tapered pins one at each end of the 48" long pattern. When extended they protruded about 7/8" into the sand at each pattern end. The idea was to have them extended while packing the mold and then to split the mold and retract the pins prior to drawing the pattern from the sand. They helped some, but were unreliable at retaining the pattern and too often still allowed one end to fall with disastrous results. So, being pretty frustrated Wednesday morning, I decided to try using monofilament fishing line to suspend the pattern half in the cope. It worked. I simply drilled a small hole through the pattern a few inches from each end and then counterbored that hole from the split side. I tied a 1/2" length of coarse string on the end of the monofilament and snipped off a 1 foot length of it. I threaded the line from the cut side up through the hole and out the "good" surface of the pattern. The coarse string prevented the monofilament from pulling through the hole and was the most expedient of the various possible means of putting a stopper on the monofilament. While packing the cope I often pulled the strings straight up through the sand so that they laid in a straight line in the sand. When finished packing, I tied the loose ends of the mono to a couple of 1/4" diameter short pieces of stick that provided a stopper on the top of the cope and prevented the mono from pulling down through the sand as the mold was split. It worked well! I will probably continue to use this method for the short run of castings I am making---5 or 6---but I think I will convert the split mold to a match plate and that will improve productivity and eliminate this fallout foolishness. Just passing this along as I can't be the only person to have this problem. In fact, I have had it happen occasionally before on other patterns, But as I make slicker and smoother patterns, the frequency of the problem seems to increase. Sorry I have no pics. I'll be going out to the foundry today or tomorrow and will try to make a couple pics. Here is a pic of the casting, at least. It is the wider (heavier) half that is in the cope. Denis
I have seen wooden dowels stuck through snaps that are left in the mold. One side had hole in snap so you could slide it in and the opposite side just had a recess that accepted it. Make a mold and open the snap to release the dowels and leave them in place. Limited by location of the casting..cant be too close and sometimes can be a booger to stay in place while molding around it.
I like the dowel pins. They could be aluminum or steel tubes if not real close to cavity. Something to definitely consider in future. For this patter, converting to a split pattern will happen in the next two days. Starting on it I half an hour. Thanks, Billy. Denis
