Making a Durable Aluminum Pattern For Casting Plaques

Making a Durable Aluminum Pattern For Casting Plaques

The idea is to make a durable pattern that can survive having text glued to it then pried off many times. If I get another casting session in before Christmas, this foresight will have paid off. If I don't, I guess it'll be to blame for the fact my sister won't be getting her house numbers for Christmas after all, and I'll have a little extra shopping to do...

first I had to make the wooden pattern to cast the aluminum pattern...

I used my edge sander to apply draft to the wooden pattern's flat edges, then switched it to spindle sander mode to put draft on the curved corner sections. The edge sander was also used to put (a little steeper) draft on the sprue well and runner pattern. The spindle sander, with the table kept at the same angle, was really useful fitting the tapered sprue well to the end of the runner, where I glued it. I gave the sprue a 1/2" diameter at its base (new sprue pattern: part of a dollar store turkey baster), just a little wider than the one I've been using for the past while, because this casting is a little bigger than what I'm used to. I did notice I had to pour a little harder to keep the sprue choked.

I made a paper template using MS paint to print out and glue to the baltic birch plywood I used for the wooden pattern. I printed it a little bigger than I wanted because I was going to glue it to the back of the pattern to use the lines of the borders as a guide to sand the draft onto the pattern, which would make the underside a little smaller to balance out the oversized printout. That part might make more sense in the video...

To put in the fillets, I used some stuff called Squadron Green Putty. Not necessarily recommending it over bondo or real wax fillets or whatever everyone else is using, it's just something I've had in my miniatures hobby (collecting, modifying and painting them, sometimes for use in tabletop games, think dungeons & dragons) toolkit for several years but never got much use out of before. After some experimenting, I found my fingertip to work better than any other tool I tried for getting a smooth radius with this stuff. I bet a real fillet iron with a smooth ball bearing tip would work great...

I shamelessly scammed major elements of Fishbonzwva's (over on AA) knife gate and trash gate plaque pattern design since his plaques seem to come out really nice.

I used a tip I got from Clarke E (AKA Porositymster on AA) via one of my youtube videos (the skull ashtray), which was to rap the pattern and blow off lose sand before making up the drag, which is supposed to reduce or eliminate flashing. I had only been rapping the pattern after both halves were already made before, in preparation to draw the pattern out of the sand. I did get a little bit of flash using that tip, but nothing that was a chore to sand off the casting or anything. I blame the temperature of my sand more than anything else for the flashing, the cold made the sand seem less sticky, so it was a little bit fragile around the edges.

I also had to build a new bigger flask for it - it's 12X16 (interior). Drag is only 2-1/2" high, but I made the cope a full 4" tall since I wanted to tilt the mold during pouring to make the metal flow uphill slightly, but I still wanted it to have plenty of head pressure at the far (high) end. Alingment pins in the drag, window sash locks keep the cope and drag locked tight to help prevent cope float. When closed and locked, there is no play between the two flask halves. Only thing I might be able to do better that I've thought of so far: replace the 1/4" bolts I used for alignment pins with something a little thicker.

The wooden plaque pattern is 3/8" thick. I was going to make it 1/4 but decided to glue on another 1/8" piece of ply for my own peace of mind when pouring it. The raised border is also 1/8" thick.

Here's the cast pattern, front and back. Note the ring-shaped oddity on the back (cope) side. I assume something was happening to the metal as it flowed out from the knife gate past the area where the ring shows up, like maybe it wanted to start to freeze, or maybe it slowed down due to less than ideal venting (I vented the mold but forgot to poke some extra vents in the trash gate) but I'm not at all sure what it actually indicates, would appreciate any insight there. It's not shrink or anything, and the front side looks great IMO, so I'm not overly concerned, just curious in case it comes up again some day. I was not careful about the ratios of sprue base area to runner cross section to gate area; I've read 1:4:4 is proper per the US Navy Foundry Manual and maybe I came close, but I'm not really sure. Maybe the metal front slowed down to give trapped air time to vent out of the mold, I did forget to put extra vents on the trash gate... Maybe one of those things explains why I am seeing that ugly ring on the back.

One other detail: My greensand was nearly frozen when I made this mold, so it was a little tricky getting the sand to stick. I probably ended up ramming it harder than usual to get it to hold together, hence heavy use of the venting wire. I might have hit the pattern once or twice, the casting has a couple of dots on the front (easily sanded them off) which I can not explain any other way. but I do not remember feeling myself hit the wood with the wire, a sharpened piece of 1/8" stainless welding wire left over from being used as rebar in my furnace lid...

Anyhow, here are the pictures and a video. No still pix of the new flask but I did go over it in the video. Happy to shoot a couple flask pictures and add them later if people are interested, but IMO that's not terribly exciting to see, so I did not bother.







Sprue has been cut off, the rest is the new pattern. Just needs a little more sanding and maybe some paint...

Jeff

 

1&2: Hack of a woodworker that I am, at some point I realized I had made the runner go deeper into the well than I had intended, so instead of scrapping it I decided to sand the choke into the runner to make it shallower there, so that the well would have to fill more before the runner began to fill, if that makes any sense. That was what was going through my head at the time anyhow, right or wrong. Short answer: the choke is there to try and make up for my own poor planning!

Do you think it will cause me trouble having it that way, or that it might have had anything to do with the weird arc that appeared on the back of the casting?

3: That is great info, thanks! I always get some of that from your posts, but as you see I sometimes don't remember all the details when it counts - when I find emough time to get out and try making stuff, I sometimes get ahead of myself I guess. I certainly took that approach this time, I didn't measure the area of the runner and gates or anything like that either.

I appreciate the feedback and the examples, if I have any trouble using the new casting as a pattern, I'll try to incorporate your suggestions in fixing it, maybe by digging the choke out of the runner and making the well a little deeper after ramming it up or something.

The aluminum was all 'wheelium' that was previously broken down into small pellets in my wood fired water bath stack melter. Mostly still in pellet form, plus a sprue or two from previous pours of same. There's a thread about my wheel melter in the furnace section: http://forums.thehomefoundry.org/index.php?threads/tobhos-water-bath-bulk-scrapper-for-aluminum.20/

I've always believed that method of turning wheels into crucible friendly nuggets yields really clean metal for casting, because I get hardly any dross in the bucket in the end.

Thanks again,

Jeff

 

Thanks again HT1.

Here are a couple pictures showing how I usually set up the sprue/splash well/runner connections, which I believe to be closer to what HT1 recommends. Best pix I could find without going into the videos looking for a perfect screenshot. Note the different shape of the runners casting aluminum bronze vs. alumimum:



So that is how I normally do it. As always, constructive suggestions for improvement are more than welcome!

Jeff

Edit - adding a pic of the new cast pattern painted, with the unfinished numbers.



I painted it so the sandable primer and gloss enamel would fill in the porosity I found on some parts of the raised border, which seems to have worked really well. Not sure what caused that, too wet sand, missed blowing out some parting, or what, I'm open to theories and suggestions... I expect the paint on the main section of the front will get ruined by prying off numbers, but I can sand it back to bare metal there if needed; I just wanted the border to get smoothed out, and it has...

 

Thanks Joe, that sounds really interesting. Worthy of its own thread, so that people can find it easily when they're looking for gating advice. I suspect a lot of us here and on the other forum are working from old books and the examples other hobbyists have provided, and, like me, have not heard of any of that before.

Good tips from you also, Pete, thanks!

Jeff

 

Lol, yeah, the light switch cover business didn't work out like I hoped, lol...

Seriously though, I would be happy to sell a few if people are interested, and I have some ideas for plaques to cast other than just house numbers too... but the day job keeps me busy and fed too well to give it up for full time metal casting, so I'm still just a hobbyist. If I can pull off 13 more years of writing COBOL code on the mainframe, my pension will actually be worth something. If I haven't been sent to the loony bin from sheer boredom yet, maybe then I'll try seeing if I can make a few actual bucks from casting since I'll have time to really get a lot of work done. For now I'm happy just recovering some of my expenses on rare occasions, so I can afford to build new foundry gear, buy more sand, and all that good stuff.

I cast this one as a blank pattern mostly because I do want to pour more than one plaque, but I don't enjoy wood working as much as I do ramming up molds and pouring metal.

Jeff

 

People look at me like I'm a caveman when I tell them I'm a COBOL programmer who works on an old-timey mainframe conputer, but in fact there's a lot of accounting type stuff running on COBOL that people never think about or realize, like banks, insurance companies, etc. I heard once that many traffic light control systems also run on it. I can believe it, COBOL running on a mainframe is great for processing huge amounts of data very quickly. Without getting into great detail, the stuff I do controls online forms (some in Windows, others on the mainframe blue screen of doom) used to enter and process/validate insurance claims.

That's what the drama/fun out of my pouring, since I spend ~37.5 hours a week trapped in the office.

Looking forward to that new thread...

PS. I use at least 4 fingers to type, most of the time. Sometimes as many as 7!

Jeff

 

I'd be interested Joe. Maybe start a different thread on the subject?

Best,
Kelly

 

Hope you're all enjoying the holidays and staying safe...

Got the numbers all ready to glue on the aluminum pattern.

Still haven't worked up the nerve to spend enough time out in the freezing cold to try thawing my sand out enough to use, but that's probably good or I would have wound up casting a 659 plaque for my sister... who lives at #695...



HT1, I made sure to pass on your notes about the Ill-advised choke I put in the runner pattern to the handful of people who may watch the video, in case a handful of them attempt to imitate any of this. Thanks again!

Jeff