Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

I have a coal stove that works great for melting a lot of aluminum, but it takes a good 45 minutes to start the wood fire and then get enough coal burning for a good melt and is a pain to just do a small pour. Small electric furnaces start at around $250, but i'm a tight-ass so i figured i'd make one.

My $15 walmart space heater bit the dust so i opened it up. The heating coils were still intact, so i connected the coils directly to power, eliminating everything but the tip-over switch so i could turn it on and off. Without having a fan to blow air across them, the coils glowed red.

I have several fire bricks from an old wood stove that i use to braze stuff on and such. I laid two of them flat on a steel table and sat the coils in the middle and then placed 4 bricks on their edge to form a box and put 2 bricks on the top as a lid. Done, almost.

I cut the bottom off of an aerosol can to use as a crucible and put some aluminum scrap in it and plugged it in. After 15 minutes my temp gun was reading about 850 degees on the aluminum. After 25 minutes it still said 850 degrees. Shit. Need more power. v R = ^ I = ^ P = :)

The way the coils were constucted, it made it easy to bypass a few wraps of the coil with a female spade connector. First i tried bypassing about 1/4 of the windings. It lit up a bright red. Then i tried bypassing 1/2 the coil. It lit up quick and bright yellow, headed towards white and the wraps started to sag just as i cut the power. Two more seconds and i'm sure it would have burnt open. So then i tried powering 2/3rd's of the coil. Perfect. A nice bright orange and no sagging wraps.

After counting the wraps i cut off exactly 1/3rd of each coil and put my box back together. About 20-25 minutes later the aluminum was ready to pour. Success.

In it's original configuration, the heater used one coil for the low setting at 750 watts, and both on high at 1500watts. There's no amperage data on the heater but basing things off of 110v, Mr. Watt says this thing should pull about 13.6A on high. With my alterations, i should be around 18A-2000w. Pushing the limit of a 110v circuit on a 20A breaker.

Then i start thinking, if i splice together the two pieces of coil that i cut off and added them to the furnace, i could increase my power by 50%. 3000 watts of kick ass. Oh wait, that would be 27amps. Ehh... What's the worst that could happen? Trip a breaker? That's what they're for, right? So i added the 3rd coil and turned it on.

I was amazed the breaker didn't instantly trip, so then i had a brief moment of concern. I felt the cord and was surprized that it wasn't even warm. I used the cord that came with the heater. Since it wasn't even warm, i wasn't concerned about the 20ft of 12-2 between the outlet and my breaker panel in my garage. Ready to pour in about 15 minutes. Hell yeah.

I wanted to bring my good meter home and actually measure how much it is pulling but i forgot it. At this point i'm guessing that the manufacures claim of 1500 watts may have been over-rated. However tonight on the first cold start it did trip the breaker. Worked fine after resetting it. The resistance of the coils goes up as they heat up, so current draw drops back as they get hotter. Self-regulating to a certain extent.

Now that i've seen how stupid simple it is, i want to build a larger more permanent 220v version. Hoping to get into the 1800 degree range to do silver and brass. I may go with refractory cement in a bucket and suspend the coils from screws that would be screwed into the cement. Or lining a bucket with fire brick and backfill it with sand/paster of paris. You can easily cut fire brick with a wood saw and drill holes in it with a regular drill bit.

Disclaimer: Hot stuff is hot. Electricity can be dangerous. Blah blah blah....

Here you can see the glow of the lower coil that is wired as original and the coil on top is much hotter with about a quarter of the coil being bypassed.

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The layout.

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These are the thinner fire bricks. 1.25"? I'm sure thicker bricks and sealing the gaps would make it heat up even faster.

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Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

Here's with the 3rd coil added. My "crucible" was too big to sit inside the coil so it's sitting up on a 1" socket.

3000(?)Watts of blast.

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Coffee can, moistened play sand, and some lost foam for a test casting.

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Re: Casting Aluminum: Making an electric furnace dirt cheap.

Mike Scouty McScoutington /

That's super rad. I was having trouble at work not too long ago and couldn't figure out why my kiln was

a) blower fuses and

b) not getting to temp

I got to doing some digging and came across this

And then when I pulled that coil out found why I couldn't reach temps

As for blowing fuses, I got a new set of custom silicon-carbide elements that had a resistance that was WAY too low. Felt like a fool until I decided to tap the meter to each of the 8 elements in series and remember what my good old friend Ohm taught me.

Solution - throw an old worn out element in the middle of the series that had a resistance that was much higher...because resisters in series you know, equal the sum of the resistance. Higher resistance with the same current equals no more $40 fuses going bye bye

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Ѭ ɞŦЯʚOluv Ѫѫ /

I clicked thinking it was a furnace for your house.

I don't know what I expected.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

@ Blaine ~ You using hard coal ? why not coke it and get temps up 2 2800 f or better .. a old black smith friend showed me how 2 do it thus puddle steel or what ever .. just a idea ...

Re: Casting Aluminum: Making an electric furnace dirt cheap.

I haven't really messed around much with sand casting but I saw that you said you used used moistened play sand. Do you have to worry about the moisture coming out of your mold and causing porosity? It looks like it worked well and the part came out pretty nice for being cast in play sand.

I would love to get into casting at some point now that I have machining capabilities at my shop. I may give this a shot. Those broken space heaters are pretty easy to come by.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

Hey Eric. I'm new to the sand thing myself. When i did that casting the sand seemed a bit dry around the sprue so i actually poured some water around it to prevent sand from falling in with the pour and it seemed to work fine with no issue. I think the moisture just vents out thru the sand.

In that casting i tried to see if i could do a simple "core type" of mold to produce an internal void without actually using a core. I ran a hole saw thru my styrofoam mold and i just packed the holes with wet sand before i sat it in the can and packed the sand in. I was a bit surprised that it worked without any of the sand dropping out of suspension.

I bought some cheap cat litter that said- ingredients: natural clay, so hopefully it will work well to make some green sand for a smoother finish. Just need to crush it up in to dust and mix it with the sand.

Since my "kiln" is just sitting there with nothing holding it together, i always unplug it before opening the lid to add aluminum or to remove it for pouring. I'm really looking forward to playing with this stuff. I figured it's costing me around 40¢/hr when it's turned on in it's 3000(?)W configuration, so it's relatively cheap fun.

A light pass on the belt grinder after cutting the sprue off.

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Re: Casting Aluminum: Making an electric furnace dirt cheap.

Russell Greene /

Unless you use a mold formed foam pattern you will always get a rough, as cut, texture. Dipping it in a fire clay slurry won't help either.

Look up induction furnaces. I've never used one. They seem to be fairly easy to build. All of my furnaces have been gas fired, so I'm talking out my ass, but give it a look. Charcoal/coal/coke work well, but are dirty. Not that foundry work is clean. Propane is clean and easy to operate, but flipping a switch always looked good to me.

Are pulling a vacuum (shop vac) on the flask? It will pack the sand nicely and help with venting.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Aluminum fills in scratches in itself.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

Success. 240v at 24A= 5760 watts last night. :)

Failure. Fried it after about 30 minutes but i think i know why. I'll explain later when i've got some time.

Robbed the coil from a Patton electric heater that i picked up at Ollie's for $15. Nice 16 gauge(.050" wire) element. They're like $20 on ebay. Cost was about the same as just buying a roll of NiCr, but being already couled is a bonus.

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Re: Casting Aluminum: Making an electric furnace dirt cheap.

There's this place near me in Cleveland called HGR that sells surplus industrial shit and I been wanting to get maybe a lil furnace. mostly interested in a cheap SCR and TC for programmable temps and ramps. I'm on the ceramic end of things rather than metals so heatup & cooldown control makes life smooth

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

This PDF is a great resource for playing with this stuff. By checking the current draw you can get a good idea of the temperature range that it's operating in, so i picked up an amp clamp meter at Harbor Freight today. Wish i would have had it yesterday. I wish i would have taken a picture of it when it was running full tilt before the meltdown. The firebrick was glowing orange over an inch away from the coils all the way around the inside of the thing. I'm pretty sure i was probably more towards the 7000w range and over 2000 degrees.

With this larger coil i was able to lay things out much better inside with more room for the crucible so i wasn't too afraid to add aluminum and skim off the slag with the power on. I was skimming off the slag and just as i tapped my spoon on the table aside of the kiln is when the coil blew. 220v arcing sounds like a stick welder, only about 600 times louder. A first for me. Almost pissed myself then... Oh, better unplug it.

About 3 wraps of coil had vaporized. After removing the coil to inspect the carnage i could tell that it had burned through right where one of the bends were from when it was installed in the heater. I used 2 pair of needle nose pliers to "straighten" the coils back in to shape. It probably had a nick or crack from straightening it, and the fact that i was running it near it's limit.

Here's the heating coil in it's original layout. Notice the coil that's not glowing. It is added in series to give a low setting.

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This is the $15 heater i used. It uses a different configuration for it's high and low settings. The walmart unit used two identical heating coils. One on for 750w low setting and both on in parallel for 1500w high setting. This one has one long coil for high, and then when switched to the low setting at adds another much shorter coil in series, which adds resistance and lowers the current draw. I did a quick test with 110v, bypassing coils and i could power half of it without it looking too hot like the walmart heater, so i got real happy. If half the coil looked happy on 110v, i'd look happy with the whole coil on 220v.

So i went on a mission. I found about 20ft of 10-3 with ground in my basement, an extra 30A double pole in my electrical stash box, but i didn't have any 220 outlets or plugs, so a standard 110 outlet would have to do for now. This turned out to be a bonus because now i have a 30A source of 110v also, all in one outlet box. ;)

Most multimeters suck at trying to measure just a few ohms. More often than not, if you just short the leads together they read .2-.5 ohms. I used my brand new HF meter for the first time that i just got last week with the free coupon deal. I was rather impressed when i put the leads together and it read .2ohms. I measured this new coil and came up with 10.2 ohms. Subtracting the .2 for the leads left me with a 10 ohm coil. According to their claims of 1000 and 1500 watts and the way it was wired, it should have measured 14.4 ohms and would have pulled 16.6A using 220v. I was expecting to have to shorten it. 11.5 ohms would be ideal for where i wanna be. Like i said, most meters suck at very low ohms. I feel reading the current is where it's at when playing this game.

Later i decided to test my line voltage with it, so i look at the dial to find the ACV, knob looked to be pointing toward it so i stick my probes in the outlet and POP. Fuck. I look at the meter again and thought to myself, you dumb ass. I realized i never turned the knob from testing on the ohms scale, but to look at the knob, ohms and ACV are directly across from each other, you have to look closer at the knob to see the tiny arrow on it.

Yesterday i brought my good meter home and verified that i actually have over 240 on the line. However, i didn't test the coil to verify that it was in fact 10 ohms. After the meltdown i'm pretty sure it was less than 10 ohms. Since trying to accurately measure a few ohms sucks i decided to pick up an amp clamp and use the current draw to determine coil length instead of coil resistance.

Now that i have a 30A source for 110v, i decided to shorten my fried coil and just run it from 110v. According to the PDF i linked to, .050" wire pulling 25A will put it around 1600 degrees. I took my best guess and shortened it, with the thought of leaving it a bit long just in case.

I put it back together and fired it up. Cold start it pulled about 22A and once it warmed up it held a constant 18A. According to the PDF, 18A should put me around 1275F. Not much more than 1220F needed to melt aluminum. Sure enough, it took over 45 minutes for it to start melting and another 1/2hr to add and melt enough scraps to fill the crucible 3/4 full. Nothing even close to the 15-20 minutes like the night before with the mega-watter. I'll cut the coil by about 10% and hopefully that'll put me right where i wanna be.

The long amount of time that it took to get up to temp tells me that i'm probably right around 1300 degrees and all the data in that PDF directly applied. But there is one thing that doesn't quite jive. The amp/temp chart is said to apply to a straight wire. At the bottom of the chart is a note that says:

(Note: For *Coiled* elements divide *straight* wire amps by 2 for approximation purposes. Look for a separate table to be added in the near future.)

This just doesn't add up. I'm not even clear on what this even means. I can tell you that if i were to divide my amps by 2 ( i'd have to use a coil twice as long to drop my amperage in half), i'd be no where near temps for melting anything except maybe warm butter. This isn't the only instance i've seen this mentioned on the web either.

A few helpful tips. These are not the kind of bricks that can be cut with a hand saw or wood saw of any kind. Not even a circular saw with a carbide tipped blade. You might get thru one or two, but not three. Ask me how i know.

Once the wire has been heated it can become brittle. I had to heat the coils up with a torch to be able to uncoil a bit of it to extend out between the bricks.

The 1-1/4" thick bricks do work but thicker would be better. Once it's up to temp, the outside of the bricks were 350-400 degrees. I did put a single layer of 1"x 3"wide foil backed "pipe" insulation around the box and it did drop about another 100 degrees.

I found a 9" square baking pan that has a taper to the sides. Two fire bricks side by side fit nice and tight about half way down in the pan. I had to round 4 corners of the brick a little to fit the corners of the pan. So i filled the pan half way with sand and tapped the bricks down in. I cut 1-1/4" off of 4 bricks so i could place them on their side and overlap the corners to form a 9" square box. Then i wrapped around all 4 sides with some foil duct tape to hold things securely.

Then i placed the 4 pieces that i cut off on the inside of the box to use as a shelf to lay the coil on. When i had the full 220V coil in, i placed the coil on the floor of the box first, then sat the cut-off brick on top of the coil and then ran the rest of the coil around the box on top of the cut-off bricks to give me two rows of coil. It really was the shit. I miss it already.

I'm gonna see how it does once i shorten the coil a little more. If i'm not happy with i'm just going to order some wire and roll my own, without nicks and cracks.

If i decide to get stupid with this and do the math, i might order some wire to put together a 10,000 watt monster.

I've got several 9x6-1/2 curved fire brick that have grooves in them. I can tuck the coils in the grooves to make way for a large crucible. A 20Lb propane bottle will make a good nest for the fire bricks. Gonna need a 50A double pole breaker for that one. :)

TL/DR: i fried a bunch of stuff in my quest for adventure.

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(edited)

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Mike Scouty McScoutington /

We use these guys at work to verify temp. They are similar to pyrometric cones, but as I have lab scale roller kilns I can't get a regular cone to pass through. They are stupid cheap as well, I think about $20 for the box. All you do is measure you change in diameter after firing for a set time and read the temp range off of the included chart. They work great for a verification but not much else.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Rollo Tomassi /

When I build a casting furnace I just would filled the bottom of it with charcoal briquettes and used a squirrel cage fan to blow in lots of air to the fire. It was simple and cheap.

The furnace was a built out an old turkey fryer lined with fire bricks on the inside.

I used a muffin pan to make aluminum hockey puck shapes like someone in one of the posts above. They were a handy starting point for lathe projects.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

no one of covfefe /

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

Thanks Mike. That's one i haven't heard of. I've been looking into these PID controllers. A rather large investment considering one of the main goals here was to keep it cheap, but in the long run it would probably save on blown coils all the time.

What really got me started on this is that a friend was looking at buying a small one for melting silver inside his small shed where he tinkers with shit which only has 120v. He said the ones he was looking at were like $500.

He won't be spending anywhere near that now.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Andrew Squiggman /

That heater, no one of consequence, is a gas heater.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

grim ripper /

chk ths out

gouging electrode. you could hook it up to any old welder and pull it off.

somebody make me some daelim intakes!

Re: Casting Aluminum: Making an electric furnace dirt cheap.

grim ripper /

he tries to do titanium too. in a bucket full of argon, and fails, but still posts the vid.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

Ordered some PID controllers, 40A SSR's with heat sinks, and some "K" thermocouples to put together two of them. U.S. seller less than $40 shipped. If they work more than once i'll be impressed. Hopefully this will cure any meltdown failures. It says Feb 7th for delivery. :(

I spent 96¢ total on 6 ceramic bathroom tiles to try a little experimenting. I used the foil duct tape to hold them together and used the .025" coil in it(actually two coils in parallel running 120v). Within 2 minutes i heard a crack. Then about 3 minutes in i think it was the adhesive on the tape that burst into flames. After about 5 minutes the flames burned out and some of the foil flaked off and you could see the tiles glowing orange in the area near the coils. After about 10 minutes and no new activity, i shut it down. Somewhere after the 7-8 minutes the one coil took a shit.

After it cooled, i checked out the carnage. Amazingly, only the bottom tile shattered and the top tile had a hair line crack in it. The coils melted into the glazing on the surface of the tile everywhere that it was touching the tile, but it was lightly adhered to it. These tiles may have some merit. I think they suck for insulating like fire brick, but all in all, i think they'd handle the heat if they'd be in contact with refractory type cement. If anything other than being cheap as hell, they'd the inside of the kiln all pretty and clean like a McDonald's restroom.

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Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /
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Re: Casting Aluminum: Making an electric furnace dirt cheap.

Mike Scouty McScoutington /

Don't get glazed tiles if you are going to go that route, try to find bisque wear. We get our tiles for testing from Dal Tile and they are stupid cheap. I have had a few tiles take a trip down my roller kiln and really cause and decide to fuse to some elements. It was a huge pain in the ass to fix.

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Why not grab some hard kiln bricks? You can even get them with channels for the elements. They are a little spendy if you buy them new but I have seen used bricks and older dead kilns come up on CL free a number of times.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

Lol.

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Re: Casting Aluminum: Making an electric furnace dirt cheap.

Russell Greene /

Like.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Mike Scouty McScoutington /

I can just about see the headlines now.

"Local PA man burn down garage. Fire investigators found 73 disassembled space heaters in a nearby dumpster"

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

^ lol. Come on now. It was only 2. Ok, i bought a third one, but i didn't take it apart yet. Besides, i'm not prejudice. I'll stuff 240V up a sandwich makers ass too. ;)

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My thought was that since this appliance was only rated at 800 watts, it would only pull 13.3A on 240V, which it did. And if it was a nichrome element, with the exposed element wire measuring .077", and according to that chart, this thing should have been in the 600F range. Apparently there is different math for this type of element. Obviously with it's short length and high resistance of 36 ohms per coil, there's something different going on inside this type of heating element.

Well, no more sandwich maker, but there's good and bad.

The good: i have cool little neon bulb that works on 120-240V.

The bad: my garage smells like fast food.

I may just plug a fan in to my "special outlet" next time just to see what happens. Fun with electrons. :)

Re: Casting Aluminum: Making an electric furnace dirt cheap.

grim ripper /

ha, cool.

Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

A little update for those following along here. If you recall, i fried the 16 gauge(.051") coil from the cheapy Patton utility heater. They're on sale for $12 right now. Since i fried it, i've been shortening the longer piece that was left of the coil little by little to get more heat out of it using only 120V. I've got it to where it's melting aluminum in about 20-25 minutes from a cold start, which is close to as quick as it was on 240V.

Once the coil is warm it's warm it's pulling 21.3A, over 2500 watts. If i let it soak for awhile to hit it's peak temp, according to the chart below, it's reaching 1600-1700F. I've got several hours running on it without issue so i may just build a frame to house the brick in and finally cement them together. Yes, it's still just taped together. ;) And i'll probably make a stand with wheels to sit it on because it's too heavy to be a portable benchtop unit and i'm too damn old to play foundry on the floor.

Once it's up to temp i can put more aluminum in and within 5 minutes it's melted, and i can add more. It may be even sooner. By the time i cut pieces small enough to fit in with the band saw, it's already melted. I'm using the bottom of a propane torch bottle as a crucible. Once it's full i can pour 3 full muffins, which total about 1.5 pounds of aluminum. There's enough room inside to use the fatter propane bottles which would put me at an easy 2 to 2-1/2 pounds of aluminum.

Once the PID controllers arrive i'm going to try trimming a few more wraps from the coil and try and get to copper melting temps. Still not finding kanthal wire info as far as amps vs temps goes. I may just have to take a good guess at which wire gauge, order some and experiment.

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Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

It's still working good at 2400W on 120V without an issue. I've found that Tractor Supply sells these hard fire brick for $2.99 each, in stock, so basically half of what lowe's wanted to order them in a pack of 6. But these are not "insulating" fire bricks. Even with two layers of these bricks(2-1/2" total thickness) the outside reaches temps over 400F, and it's only in the high 30's in the garage right now. Even with welding gloves, i need to be quick lifting the bricks aside to feed it. Not the most perfect choice for bricks, but they work, for aluminum anyways. I could probably get to copper melting temps without doing anything to the coil with better brick and sealing things a little tighter.

K23 insulating fire bricks are expensive so i'm looking at other ways to insulate this thing to keep it cheap, since that was the main goal. I've seen video of someone melting copper in a k23 insulated furnace and they placed their bare hand on the outside to demonstrate how cool it remained. Very impressive, but i'm not using this thing all day every day, so that kind of efficiently isn't very critical. Perlite and vermiculite seem like viable options. I'm still toying with the idea of ceramic tiles on the inside and out, with an insulating layer in between. I've picked up 6" and 12" square tiles all total less than $10.

For the price of the space heater and if i had to but the brick, this setup would have cost me about $65 total invested, but if this tile idea pans out i could figure about half that.

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Re: Casting Aluminum: Making an electric furnace dirt cheap.

Blaine- The artist formerly known as Plumber Crack "(OFMC)" /

When Lowes doesn't have just what you're looking for, cast it yourself.

Made these to hang a clothes hanger rod from under a wall shelf in the laundry room.

Green insulation board works way nicer than regular styrofoam.

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