Starting a new thread as not to sully this one: https://forums.thehomefoundry.org/index.php?threads/exp-styrofoam-followers.1254/ Did OK making a foam follower but ended up with some defects in the casting: -surface pits -sbrink Wondering if humidity and possibly damp calcium carbonate parting powder contributes to the pits and what to do differently for the shrink. Also wondering if filling screw holes and scratches is overkill when molding off a found object. No issues drawing pattern from sand either time. Still need to get my 'piddies' in there better to tuck sand around the pattern, the undersides of the horn going to the base were a little soft. Thanks as always for suggestions- Used scan data from the part to rough it up in Fusion360 to start routing the follower, would have finished faster doing it by hand (derp!). Used hand 'dremel' to make real part fit into foam. Filled in the cleat at screwholes and major scratches, sanded, waxed, graphited Pounded sand, follower worked without incident. Did not think hard about sprue and gate just did something that seemed right at the time. Poked a next to useless vent hole... Fired up the furnace. 80 somehthing percent RH and not getting better for over a day. Pour went fine, basin overflowing but vent not full. Part pulled. Vent seems to have obeyed basic flow concepts for being too small and choked by sand. There is also a substantial shrink near the vent. Part is about 5.5" (137mm) long and weights 4.33 oz (123 g) before sprue and basin.
Part as-is weights about 5% less than the source part. Bottom flange cope side also has shrink. Should I have gated lower in the drag or runner-ed to the tail of the base flange?
The shrink is from the bullet portion being the thickest part and solidifies after the throat. I built up the throat with bondo and also added draft to the bottom of the flange. I hate putting risers directly on a part so I used the sprue and gate as feeders by carving the gate in both the cope and drag. It's a small part so pour as cool as possible. I would kill the burner 30 seconds after the last ingot melts, skim and pour. Edit: The 30 seconds is for a full A6, if you're melting less then cut the time down to 20 seconds or so.
Thanks Fish! My smallest crucible (used yesterday) is between A2 and A3 and the largest between A4 and A5. It started raining during the melt and I used that and it being a small pour to justify not getting out the thermocouple and meter. I probably should have rammed up more than one and tried other gating systems too, slow learner. Your procedure for making the follower worked great.
That vent probably isn't helping the shrink either. It would have frozen fast and drawn a little bit of metal that could have been feeding the casting instead. Not much, it's not your real feeding issue, but in any case a vent that just comes close to but does not touch the mold cavity is more effective than one that fills with metal. If it's even needed. I don't use vents much, but when I do I use a sharpened vent wire so that if I do touch the pattern when I poke it through from the top of the cope, it doesn't make a mark on the casting or allow molten metal to enter the vent. Good luck! Jeff
Got 'a round tuit' again today ... I rammed and poured 2 more cleats and the tuit pattern. Changes were: -graphite instead of straight calcium carbonate parting powder --result: better surface finish, less clumps/pits --- does commercial parting powder clump too or is it treated (stearates?) not to do so? -no vents on cleats --result: unknown, but one less thing to sand -blind risers and bigger gates on cleats --results: less shrink, no wrinkles, but still not 100% solved for the throat ---I will still need some 'buildup' with Bondo on the cope side of throat like FishbonzWV mentioned -side gated the tuit instead of center feeding it --result: should be easier to remove sprue and gate this time The pour was a bit unorganized. I packed the tuit while the furnace was heating up and did not weigh or calculate alu needed. My workspace was overwhelmed by 3 flasks and I did not have a metal shield for each. I ended up doing a last minute add to make sure I got enough melted, the batch was mostly basins and sprues with about 20% new material. I was pouring from higher than I like due to my big SCUBA weights on the flasks, 'bomb dropping', and burned all three flasks with spillage. I did not get the larger (pencil sized) vent on the tuit to fill more than 1/2" (13mm) before I ran out of molten alu. Having extra shields and self-locking flasks would have helped as well as a longer bench (something is in the works, thanks Daryl!)
Make your pattern symmetrical, build up both sides. On mine, I used a 1/2" sprue and matched the gate to it to act as a riser/feeder. It was just one of those times to throw out the 'proper' way of feeding and get the job done.
10-4 on getting the job done. I think I am also going to draft the base too as you suggested before and maybe install a nub for a gate, had issues cutting then in without collapsing some of the adjacent sand. I need to treat the original more like a pattern and less like something 'precious', if that makes sense...
Yeah, they're out there by the thousands. Popular in the 50's - 60's. I made a pattern out of the one my buddy sent me, cast him 4. I've got a 2" set on one of my boats just for hanging fenders on. The little bastards will snag your bathing suit and leave you dangling upside down over the water.
Now there is a sight nobody wants to see, me dangling upside down off a cleat with my suit in some fashion of disarray.... These are bigger ones, 5.5" (137mm) at this point they might get used as nautical clothes hooks or towel racks.
