Great job, Kelly. Thank you. I was polishing the rear bumper and before I put everything away, I polished one of the front parking lamp grilles to see how this alloy comes up.
That looks good Jack. It'll be neat to see the tail light buckets polished up on the rear along with that bumper. Best, Kelly
A '49 Caddy with 3 tail lights... I just realized that THIS is the Caddy that Johnny Cash built in "One Piece at a time!" Don
I did some fitting and polishing on the tail lights. They fit well and polished up pretty good but there's some porosity in the upper 1/3 of both castings. I'm going to keep them, I don't want to start the whole process over again. There's enough material to sand them a little more to eliminate the pits but I might just hit more pits below the surface.
That's the pits. Is there some kind of solder you would fill the holes with and then polish back out?
AHH.....that's a four letter word for sure! It would take eons to tig that, sand and polish. What happened to all that biofilm BS? I thought this problem was going to be a thing of the past? They still look sharp, It's not a riddler car right? Call it patina. No one will know but us and your secret is safe here. Or chrome them.
The tail lights were cast in essentially the position they are shown on the car and sprued at the very top. If there was going to be porosity, the upward facing surfaces near the sprue are the most likely locations. There weren't very many choices IMO as to how to orient and sprue them given the multiple deep undercut features and complex shape. Even so, I had to add a couple of feeder holes through the pattern to insure the mold would pack and remain stable. There was quite a bit of wood glue and some bee's wax on the patterns. I use lower melt point waxes and try to minimize anything present on the foam pattern other than foam itself. Those materials will produce more gas. I also poured these pretty hot because I only had one shot at it, all of which may have been a contributing factors. All the parts were poured from the same stock and same method. You polished the one grill. It looked pretty good in your picture. Have you polished a turn signal bucket? Whether they will polish out is hard to say but what do you have to lose? You might also polish a couple of small spots on the backside near the top to see what they look like. There are a couple the larger ones that I would TIG. The real fine stuff probably isn't worth it and you may be more likely to add porosity and defects with TIG because when it comes to aluminum, casting is not the only process susceptible to gas defects. Beyond that I'd say plating and polishing to fill the small defects is the best option. Best, Kelly
To be fair, I don't think anyone has suggested there are any bifilm control techniques which will eliminate porosity in lost foam casting.