Green Sand Cores

[bmac2]

I know I haven’t finished the Whippet castings but some things have to happen when my wife is out. For the past couple of years she’d been putting out water for the birds all summer in basically a dog dish so I thought I’d try casting a birdbath for her for Christmas. I wanted the pedestal around 2 feet long but the crucible for the Troll can only melt around 4 pounds of aluminum. With that it had to be done in 3 sections and be hollow. I made up the split pattern for the pedestal out of some scrap pine. I don’t think I’ll be using this again and I was in a hurry so no paint just a quick coat of wax.

 

[bmac2]

I didn’t want to have to make up three 2x9” sodium silicate cores and I remembered nudge over on alloy ave talking about using green sand cores with metal rods and thought I’d give it a try. The pattern for the core is just a 9” length of leftover 2” PVC split in half. The ID is 1 13/16 not 2” but this is a birdbath so who cares ;D. Held the two halves tougher with masking tape and rammed the sand in hard before sliding in a couple of pieces of brazing rod (it was close at hand) to support it. The cores came out great and though very fragile and heavy they pulled from the mold easily by just cutting the tape along one side.

 

[bmac2]

I got a small crack in one when I placed it in the mold but it still sat straight in the prints with no discernable sag. Closed it up, added a couple of risers and it was ready to pour.

 

[bmac2]

The cores held up great and it has to be the easiest cleanout I’ve ever done, just poke it with a screwdriver and pour it out.

 

[bmac2]

Now the reason I had to wait for my wife to be away to do this was the pattern I want to use for the top. I’m not sure how she feels about the salad bowl I’d been eyeing but it doesn’t match anything and it was way in the back of a top cupboard . As long as I don’t break it it’s only sand and the clay is the same as they use in a lot of cosmetics. My biggest flask was 10x12 so I had to make up a new one 14x18”. My crucible won’t hold enough aluminum to fill it but I have a couple of empty MAP bottles I’ve been saving for just such an emergency Thm:.

 

[bmac2]

This beast is going to take just over 50lbs of sand and the cope (top of the pattern) has to hang down 2 ½” to form the inside of the bowl. To help support the weight of the sand I put in 4 of the rods I used with the cores about half way through filling (think rebar). At the same time I put four 2” course thread drywall screws down into the sand to support it vertically. I’ve seen this done before but it was the first time I’d tried it myself and I was surprised to find that I had to use a screwdriver to get them all the way down.

 

[bmac2]

The casting came out way better than I had hoped being as thin as it is. Now I just have to do a quick clean up and wash some dishes before my wife comes home :.

 

[MRA]

Hey, that's lovely!

How thin is it the bowl? I've had trouble with Ali (and even worse with my only attempt so far at bronze) freezing due to heat lost to sand with a thin pattern - leaving a hole in a thin plaque I was trying to cast.

You have me wondering what romantic item I could cast for my missus for Christmas. So far all that springs to mind is the physical manifestation of the ball-and-chain with which she seems to have shackled herself to her career.

Or as my mate says when I complain - 'you have it hard, you do, your wife won't stop going out earning money'

 

[mcostello]

Does Your wife realize the treasure that You are? Better remind Her when needed!

 

[bmac2]

Thanks Mark.
How about a ball-and-chain paper weight with a hart?

The bowl is about 1/4” at curve along the bottom, only 3/16” (ish) along the top curve and rim. I hot glued a disk of Masonite/hardboard onto the bottom to bring it up to ½” so yep it’s pretty thin in my book.

From what I’ve heard from guys with actual foundry experience what happens with thin castings is when you pour you get a thin layer of metal flowing flat over relatively cool damp sand. This cools very quickly and blocks the passage.

 

[bmac2]

What helps is to place a small block under one end of the flask to tilt it 4 of 5 degrees. This way the metal can fill the cavity as it flows across the pattern. I also like to extend the sprue and riser to increase the head pressure. These are just rammed up soup cans with a hole to match the sprue and riser. Oh and vent the cr*p out of it.

 

[bmac2]

The beauty of the postings is it only shows the Second casting. The first one was a truly epic failure. I hadn’t put any clamps on the flask and had a blowout:wall:. Then just to put the cherry on top the cope collapse. I’d only put 2 rods in for support the first time so live and learn. I got a nice impression of the screw heads though.;D

 

[bmac2]

Mcostello no need. I’m probably one of the most spoiled people I know. There have been lots of times when I’m supposed to be doing something but instead I’m entertaining myself with some uselessly fascinating thing in the shop and she’ll just show up with a grilled cheese sandwich with a pickle, shake her head, laugh and leave me too it.
Not bad . . . even get a pickle. Thm:

 

[MRA]

Bob - that's a really useful tip (and oddly encouraging to see other people's scrap - in the right gallery with a pretentious title, that thing could be Art ). 1/2" seems pretty substantial to me - my plaque drops to only 3/16" or so where there is no lettering. Before I thicken up the back of the pattern, I'll try your tip of pouring it on the squint.

I think the 'domestic treasure' comment might have been aimed at me, with my career-driven wife. Well, were roles reversed, I'm sure I'd be keeping things sweet with that kind of comment all the time. But she suspects me of having too much fun in the shed...I need to work on my doleful countenance...