Building a Mold Furnace

[don45]

I purchased a new brass mold from www.accuratemolds.com and have had some difficulty getting good boolits. Turns out it was mostly because I never cleaned the oil out first, go figure, but it also seems that brass molds need to be hotter than iron.
Thanks to a lot of folks here I got some great info and suggestion that the mold needs to be preheated. See this thread for details: "Trying New Accurate Mold" http://castboolits.gunloads.com/showthread.php?t=128393&referrerid=3645

Based on suggestions from Gear and others, I decided to build a preheat furnace.

I couldn't figure out all the details of the one shown and couldn't figure how to find more info with searches so off I went to Home Depot.

I bought this electrical box:
http://castboolits.gunloads.com/imagehosting/thum_36454e84958073c1a.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=2261)

Cut a hole for the mold:
http://castboolits.gunloads.com/imagehosting/thum_36454e8495a672ed9.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=2262)

For an extra 69 cents I added a shelf to keep the mold off of the hotplate surface:
http://castboolits.gunloads.com/imagehosting/thum_36454e8495f48fbe2.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=2263)
I drilled holes in the electrical box cover to match the holes in the bottom of the box.

Using #10 bolts and two extra nuts at the end of the bolts I attached the shelf plate so that it sits high to match the bottom of the hole cut which keeps the mold elevated and off the bottom surface.
http://castboolits.gunloads.com/imagehosting/thum_36454e8496333fe81.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=2264)

I added a Char-Broil Temperature Gauge part # 141199 in the back corner so that it's out of the way when the mold is inserted.
http://castboolits.gunloads.com/imagehosting/thum_36454e8496ffab549.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=2265)

I haven't found a suitable hotplate but had one to try and heated it up as high as it would go, about 300 degrees. It smoked a lot for awhile as it burned the paint off of the bottom plate. After it cooled I cleaned it with a wire brush and it now seems to heat cleanly with no smoking paint. I've yet to use it since I'm waiting for a hotplate from Amazon. Seems like nobody around here uses them anymore.

The cost of all this was Box 15.00, Box Cover (shelf) .69, Temp Gauge 6.95, Bolts and nuts 4.00. Total of about $27. Tools I used: drill, several drill bits, jig saw with metal cutting blade and a few hand tools. Not too hard.

Although I've yet to try this, I know the frustration of casting sometimes 50 or so boolits to get the mold up to speed, and also of loosing mold temp when you get interrupted. Too bad I didn't know about this years ago.

Don

[Roger Ronas]

Nice Job.

Rog

[Southern Son]

Don,
That's bloody fantastic, mate. I have been wondering how to make mine, but that is a great idea.

[geargnasher]

You'll like it. I used to worry a bit about the direct contact of the mould to the bottom, but I have yet to see a problem in practice. You will find you might want to weld up all the open corners, hot air leaks out quite rapidly and since you've removed most of the direct-contact heat transfer with your shelf, you're more dependent upon air temperature to heat the mould.

I use an 1100-watt hotplate and it gets the mould to 400+ in about 15 minutes on one tick below full-blast. It takes a while to get the mould hot through-and-through.

I used a galvanized steel electrical box, but it had no "knock outs" in it, it smoked and cooked-off too a bit on the bottom, the best thing would be to fab one out of plain steel, but braking (breaking)? sheet metal is beyond most of us. Sounds like the painted version should be fine.

Here's a pic of mine, and Montana Charlie might come along and post a pic of his if he sees this thread, he made a neat one with a hinged lid to minimize air leaks/openings.

http://castboolits.gunloads.com/imagehosting/thum_89094e5ad65ae2e31.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=1966)

Gear

[josper]

Thanks for this post,its better than a blueprint. I found a nice hotplate on amazon.com.A single burner that has a solid steel surface,the name is"Elite". I don't know what the wattage is but this I do know,if you turn it up on high the lead in your mold won't solidify for five minutes.Don't ask me how I know.

[plmitch]

Thats a nice little set up there. Thanks for posting this. I have most of that stuff around the warehouse and need to make myself one.

[Lizard333]

Just so you know, when you heat that galvanized box to the smoke point the fumes that are released are TOXIC! Defiantly use it in a well ventilated area the first few times you use it.

[geargnasher]

True Lizard333, thanks for bringing that up.

I've had a mild case of the "zinc fever" welding hot-dipped windmill struts before. You grind off what you can, but the edges of the zink still fume. I maintain a respirator with metal fume filters in it nowdays for such projects. I keep my mould oven next to the casting pot, so any fumes get sucked out with the fumes and smoke from the casting pot by the exhaust fan.

Gear

[josper]

The painted box,I think I would strip it an spray it with black hi temp stove or grill paint.Just an idea.

[don45]

I knew that the paint would burn and that it's not a good idea to breath this. I had it on the hotplate for a couple of hours outside. I heated it up to 400 a couple of times and no more smoke that I can see. It will be under an exhaust fan so I think it's ok.
I'm still considering stripping and repainting with high temp paint but not sure what would strip it. Any ideas of what to use as a stripper? I don't think it's necessary and will try it as is once I get the hotplate. What I've observed is that it only gets hot enough to burn the paint at the bottom where it is in direct contact with burner.

[MT Gianni]

A small camp fire should strip all paint or galvanizing off of it.

[leftiye]

A 1/2 gallon can (just like a gallon can that's cut in two, which you could also use - if you can find one) turned upside down on an aluminum plate which in turn sits on a hot plate works muy fine too. Oh, cut a door in one side to put the mold into the heater. Tip, the aluminum plate (coud use steel too, I guess) collects heat and dumps it into the mold when the mold is replaced while casting - yes I use the heater while casting, not just to heat up molds - this flattens out the effect of the hotplate cycling. No more (ever) problems getting 37 grain aluminum molds on aluminum handles hot enough! And keeping them thataway whilst casting.

[geargnasher]

Tom's two-pound brass moulds soak up a lot of heat also. A heat-sink plate of some variety would probably be a very good idea.

Gear

[fishnbob]

I made one the other day out of an electrical junction box and tried it out. It took a lot longer to heat the alum. mould than when I just sat it on the burner. Also I had to cut the heat up a lot more. I used a laser thermometer on the burner and got over 600* on the burner and the mould inside the box was only 180*. The top of the box was only 99* but when you wet your finger and touched the top, it sizzled! It makes a lot of difference when you add another variable to any procedure. And like you Josper, I have had the melt to boil in my mould and I thought it would never set up. I didn't have the laser therm. then to check it but boy was it hot! I thought I was the only one to do this.

[uscra112]

Best material for a heat sink in this case is cast iron. Aluminum disperses heat fast, but it doesn't hold a lot of it.

[josper]

I read some where that if you heated an alum. mold past 600deg you might ruin it. I kind of held my breath until it cooled back down and was relieved when I checked my boolits.won't do that again.

[don45]

That's why I included the shelf and thermometer. Keeping the mold off the hotplate surface makes the thermometer reading more representative of the mold temp. It it sits on the hotplate you would have no idea but the mold would be much hotter than the thermo indicates.
I have molded many tens of thousands of bullets, all by heating the mold by just casting. As noted in my first post, some molds, including the 4 cavity shown, throw perfect bullets with the first pour. Others may require 50+ bullets before they fill properly. My 4 cavity 311467 is one, probably because of the relative small bullet size, thus not much lead to heat.
With this setup I can bring the mold temp up to 400 before I start, and keep it from cooling completely if I pause. I still believe the mold must maintain proper casting temp by just molding at a proper pace. Every mold I've ever used will eventually start to frost bullets at a normal-quick pace which indicates the mold is too hot and perhaps the alloy is too hot. It remains to be seen how the brass Accurate works but I do not intend to use the oven other than for preheat and during a pause. One of these days very soon I'm going to cast some...

[geargnasher]

That's why I included the shelf and thermometer. Keeping the mold off the hotplate surface makes the thermometer reading more representative of the mold temp. It it sits on the hotplate you would have no idea but the mold would be much hotter than the thermo indicates.
I have molded many tens of thousands of bullets, all by heating the mold by just casting. As noted in my first post, some molds, including the 4 cavity shown, throw perfect bullets with the first pour. Others may require 50+ bullets before they fill properly. My 4 cavity 311467 is one, probably because of the relative small bullet size, thus not much lead to heat.
With this setup I can bring the mold temp up to 400 before I start, and keep it from cooling completely if I pause. I still believe the mold must maintain proper casting temp by just molding at a proper pace. Every mold I've ever used will eventually start to frost bullets at a normal-quick pace which indicates the mold is too hot and perhaps the alloy is too hot. It remains to be seen how the brass Accurate works but I do not intend to use the oven other than for preheat and during a pause. One of these days very soon I'm going to cast some...

Exactly the way I use mine: Preheat and maintain heat during breaks, even very short breaks of 15-30 seconds. The mould oven gives me a convenient place to "park" my mould, also, so I did away with the ceramic tile I used to use to set my moulds on when I needed both hands to do something. Once the session is going and boolits are dropping like I like them to, I adjust pace to keep the mould temperature right where I want it, and adjust sprue puddle size to keep the sprue plate at the temperature I want it. It's just like driving a car in hilly country and keeping the speed consistent with proper and smooth corrections to throttle position, you get a "feel" for it after a while.

BTW, I like to run my heavy brass Accurate moulds quite hot with as cool an alloy as I can, so that means a brisk pace, cutting sprues by hand while still slightly soft, and getting a light, even, satin frost on the boolits that shows up after they cool for a few minutes. I get the best fillout that way, your milage may vary.

Gear

[josper]

A small camp fire should strip all paint or galvanizing off of it.

I tried this today and it worked good.I loaded up the chiminia [sp?] with some pine scraps ,touched it off and came back 3/4 of an hour later.The paint was just white ash.when it cooled I took a wire brush to it,perfect.

[11B-101ABN]

Where can a person purchase a 4 cavity 311467?

[Sonnypie]

Being that electrical boxes are of mild steel, they will rust when the paint is burnt off.
Not a big deal. But don't be disappointed.
VHT paint, or stove black, can be used to tidy it up once "seasoned."

[josper]

Being that electrical boxes are of mild steel, they will rust when the paint is burnt off.
Not a big deal. But don't be disappointed.
VHT paint, or stove black, can be used to tidy it up once "seasoned."

Stripping the paint was only the first step ,next weld the open edges ,then paint with hi temp grill paint.

[G__Fred]

I went to Good Will (my FAVORITE parts store), and picked up a waffle iron for $5.00. WORKS WELL!