So today I did my first melt, following the advice given previously from this site I ditched the drinks cans and once I started looking around my workshops / garage I found plenty of cast aluminium (I am a hoarder) . Rather than just melting it and making muffin ingots I thought I would try a bit of lost foam casting. I am wanting to put a DRO on my lathes tail stock so I made up a couple of different thicknesses of the clamp needed and also did a couple of 20mm blocks of polystyrene I didn't think I had enough metal melted as it didn't fill the feeder or riser but it must have just been enough It wasn't to bad to machine there was a bit more dusty swarf but it turned out ok I could have machined it a lot quicker but that wasn't the point of the exercise and it was very satisfying taking some scrap to a finished product. I need to try some denser foam next time as I needed to take about 3mm of every face to get rid of the holes, but an enjoyable afternoon I think Im hooked. Dirk
That's a great first go Dirk. I just made a tail stock and compound DRO not long ago myself....no castings on those though. A couple lost foam tips: For foam patterns, if you use the extruded PolyStyrene (XPS) foam insulating board like the pink stuff in the big box stores, instead of the white Expanded PolyStyrene (EPS) beaded foam you will find the XPS machines and sands/finishes much better. The pink board is Owens Corning product under the trade name "Foamular". Grade 150 and 250 is what is typical in the big box stores. 150 is slightly lower density than 250 but both work fine. Dow has similar product and their product is blue. The finish on XPS will improve with sanding all the way to 320 grit, but I usually stop at 220. I still use EPS for sprues. If you coat the foam pattern with a thin layer of plaster or drywall joint compound and let it air dry overnight, it will reproduce the surface finish of your pattern down to the last detail and eliminate sand adhesion to the casting. Non-setting drywall wall joint compound works best. Thin it with water to the point it will just begin to run off brush and then just brush it on. I've done a lot of lost foam casting and if you look at some of my posts in the lost foam subforum you might be surprised at the quality of castings possible with the lost foam method.......and it's fast and simple. Also, looks like you used bound sand to pack the molds. For lost foam you can use dry unbound sand. Helps to vibrate it a little bit for packing. Best, Kelly
Hey Dirk, great looking first attempt. If you haven't already done so, take Kelly's advice and look at his lost foam posts. He is, without question, our forum's lost foam guru, the results he's gotten are way beyond what I would have thought possible for someone working at a hobbyist's level.
Looks like we've snared another one fellas! Nice going Dirk. As Kelly mentioned I'd get yourself some dry sand for future lost foam projects. It's probably not good for your petrobond plus it makes it stink way worse than it already does. I know it will make some others here cringe but I sometimes use XPS as actual patterns that I ram and pull from petrobond to make cylindrical and rectangular machining blanks. The blanks are often not pretty, but it works. Pete
I just finally got around to machining one of the castings I made for the FIRST robotics team CNC Router. Doesn't machine as nice as wrought aluminum but I was pleasantly surprised that I didn't see any voids in the casting so far. One screw up on my part, the parts shrunk much more than I anticipated and I really should have applied shrinkage factors to the parts. It appears they will all work by adjusting hole locations on mating parts, but it is a lot of extra work.
Yeah, really didn't consider shrinkage. However the dimensions were not at all critical as long as I accurately machine the bearing mounting holes relative to one another. Next project I will know how much to add from this experience. Not a failure, just learned more than I expected.
