How not to Do Backyard Metal Casting

[GreenTwin]

Metal shrinks as it cools from a molten state, and so your patterns have to be made slightly larger than the finished part size.

There are all sorts of shrink-rulers out there, but in the modern world, people use 2D CAD and 3D modeling programs, not shrink rulers.

I draw my parts using the dimensions for a finished machined part, and then if I want to manually make a pattern, I print the drawing by scaling it up by a factor of approximately 1.02, or perhaps 1.015.
I always prominently mark in red on this drawing (Scaled up by 1.02), so that I don't start taking measurements off of the drawing during machining.

If you are making 3D printed patterns, create your 3D model 1:1, and then use your slicer program to scale the print up by 1.02 (or whatever factory you choose).

Any surface that is to be machined needs a little extra material added to that surface (called machining allowance).

Patterns generally need some draft angle on the surfaces that are perpendicular to the direction in which the pattern is pulled from the sand, to prevent damaging the sand when the pattern is pulled from the sand.
Draft angle is generally in the 3-5% range.

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[Lloyd-ss]

I can't find my comments, but I recall in general what they were.
I will skim it again and post comments.

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Skim and post comments? Those posts are more like an authoritative white paper on the topic. Your depth of knowledge on the subject is astounding. It sounds like you could write a book on casting iron, with the perpetual myths and misinformation properly corrected, with back-up information provided.
What became obvious to me is that the hobby of iron casing is something I will watch from the sidelines, at a safe distance.

 

[GreenTwin]

I was on two backyard casting forums over a period of about 9 years, and I read everything that was posted (tons of stuff).

We debated every casting topic imaginable, from refractory, burners, casting methods, materials, you name it.

One backyard casting forum vanished, and another was started.
I joined the new forum, and all went well for years.

One day I posted something that rubbed the forum owner the wrong way, and he permabanned me for a rather minor disagreement between me an another member. The loss is his, not mine.
I have one furnace building thread on that forum with 70,000 views.

Now I post here about backyard casting, which really works out better, because my goal was/is to cast parts for engines, and the backyard casting forums are basically art folks.

On this forum I can discuss engine castings, not artwork.
It all worked out in the end and everyone is happy with where they are (at least I am).
This is a much better place for me to discuss casting work for engines.

I have been reading everything I can about foundry work over the years, including reading several industrial casting trade publications.
One trend in the foundry world is to reshore casting work to the USA, and this became necessary after the COVID supply chain issues developed.

I have paid very close attention over the years to the methods and materials that others used that worked well.

We have a member here "ArtB", who makes and sells aluminum 356 ingots, and he is an absolute genius on all things concerning combustion technology.

I have learned a huge amount just from ArtB, and I have a large ArtB folder of information.

Backyard metal casting is one of the most enjoyable things I have ever done.
Not easy, but definitely fun when you are able to make some quality engine castings from scratch.

With so many casting kit companies falling by the wayside, I feel like keeping the knowledge and ability to design engines from scratch and cast them is really critical to the hobby.
This is one very important way to keep the casting side of the hobby going, in my opinion, regardless of what happens to the kit companies.
(I wish the kit companies the best of luck, and I am rooting for those that remain).

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[GreenTwin]

I watched the art-iron cupola folks pour iron for several years, and finally the lure was too great, and I said "I have got to do that".

Pouring iron is just really cool, and at demonstration pours I have done, folks young and old really like to see it done.
There is nothing quite like watching a river of molten iron being poured.
Its mesmerizing really.

That is me in the last photo doing a demonstration pour at a local art-iron event.
That was really a blast, with some very fun folks in attendance from all over the country.

Building model engines is fun.
Making metal castings is fun.
Making your own engines from your own castings is fun on steroids.

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[ddmckee54]

GreenTwin:

Don't know if you've seen it or not but somebody has done a frame-by-frame of the video you first posted, starting right before the explosion. I kind of wish they would have started a few frames earlier.


Don

 

[ajoeiam]

GreenTwin:

Don't know if you've seen it or not but somebody has done a frame-by-frame of the video you first posted, starting right before the explosion. I kind of wish they would have started a few frames earlier.


Don

Maybe this incident would scare the guy straight - - - I doubt it.
He's luck he's lucky he has feet left!

 

[GreenTwin]

Yes, he is extremely lucky.
If a piece of that metal had hit him in the neck, chances are it would be over for him.
He needs to stay far away from backyard casting, for his safety, and the safety of others.

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[100model]

You need to also preheat lifting tongs, charging tongs, stiring rods, skimmers, and anything else that will come in contact with molten metal, or come in contact with a red hot crucible.

I have never preheated my lifting tongs or my pouring shank and have never had a steam explosion, another myth busted. I also read about preheating lifting tongs because if you don't the crucible will crack because of the temperature difference between steel tongs and the crucible. What people forget is when a crucible is lifted out of a very hot furnace (1550C) and comes in contact with room temperature air it is a very great shock to the crucible and it should crack but never does. I have so many videos that show I never preheat my crucible tongs and never had a cracked crucible.

 

[GreenTwin]

To each their own, but sometimes I leave my lifting tongs out in the grass, and so they definitely have moisture on them.
No way I am going to put anything wet or damp into the furnace without drying it a bit.
Not really that big of a problem since you are not submerging the tongs into the molten metal.

I have various stiring and skimming rods that do go into the molten metal, and you can rest assured that I dry them in the exhaust stream every time.

Its not about air/crucible temperature differential, it is about high velocity expanding water/steam.

Err on the side of caution, as they say.
You should very definitely preheat every piece of scrap that you introduce into the molten metal in the crucible.

I don't hold my pouring shank in the exhaust stream, but typically the crucibile is set on a table after it is pulled from the furnace, and the shank hoop is very near the crucible, but not touching it. By the time you lift the pouring shank, I think it has had a bit of time to dry off any residual moisture on the hoop.

I do pour on concrete, and have spilled on concrete, with no problems, but I have seen what looks like someone spilling molten metal on wet concrete, with an explosion.

I guess someone will always come up with some sort of equipment/molten metal/water/water combination that will explode on them.
Makes for an exciting ytube video with lots of views and likes, if you don't take someone or yourself out in the process.
Darwin at work in many of these videos.

I was really surprised when I had an ingot of iron pop on me, and empty itself on me (see hand burn photos below).
I had heated the ingot molds beforehand with a propane torch, but did not get them very hot.
I welded a 24" handle on the ingot molds, and now I hold them in the exhaust stream to avoid the dreaded "ingot pop".
I never really believed that an ingot mold could eject all of the metal violently.
Having witnessed it, I am now a believer, and have scars to prove it.
I still don't understand exactly why they pop like that. Its like someone hits it on the bottom hard with a ball peen hammer.

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[timo_gross]

I have never preheated my lifting tongs or my pouring shank and have never had a steam explosion, another myth busted. I also read about preheating lifting tongs because if you don't the crucible will crack because of the temperature difference between steel tongs and the crucible. What people forget is when a crucible is lifted out of a very hot furnace (1550C) and comes in contact with room temperature air it is a very great shock to the crucible and it should crack but never does. I have so many videos that show I never preheat my crucible tongs and never had a cracked crucible.

Haha,

not that I totally disagree.
But.... absence of proof is not proof of absence.
Always keep in mind that absence of certain anecdotal evidence is not a proof of absence of the incident.



Guess what happened here? I do not know.

 

[awake]

CO can be a real problem, and is why I don't melt any metal indoors with a burner.

Another thing I run into in industry is low oxygen.
I sometimes have to enter large wet wells, pipe tunnels, etc., and in the old days, we just felt for some ventilation air flowing, and then went in.
These days I am much more wise about low oxygen and other stuff in the air, and they have some good inexpensive monitors you can wear on your lapel.

I go into these spaces with multiple people wearing multiple monitors.

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Send in the canaries first!

 

[awake]

Some don't believe I can do it.
Come over to my house, I can show how it is done and make you a believer.

Thanks for the invitation! How far are you from Raleigh, NC?

J/K - much as I would love to learn first-hand, there is this pesky thing called a full-time job getting in the way. "One of these days" I will retire and hopefully will begin to explore metal casting!

 

[GreenTwin]

11 hr drive on a good day without too much road construction.

I am still a working stiff too; I envy the retired folks.
I should be retired, but need the money at the moment.

The joke I tell my wife and family is "I hope to semi-retire one day and drop back to working part time, like only working 80 hours a week".

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[awake]

11 hr drive on a good day without too much road construction.

I am still a working stiff too; I envy the retired folks.
I should be retired, but need the money at the moment.

The joke I tell my wife and family is "I hope to semi-retire one day and drop back to working part time, like only working 80 hours a week".

.

I hear that! I keep discovering that there really is a limit on how much one person can do ...

 

[GreenTwin]

Here is a backyard caster.

I have not watched the entire video yet, but I did see him drop a big block of aluminum scrap into the molten aluminum pool, but it does look like he had that scrap on top of the furnace lid, in the exhaust stream, to get it completely dry.

I will watch the entire video and then comment more.

Edit:
1. I would never use a propane tank right next to my furnace, much less a 100 lb propane tank.
That is not a good idea in my opinion to store your fuel right next to the furnace.

2. His castings look pretty decent, and with petrobond (tm) and the right pour temperature, he gets a very respectable surface finish.
I am not sure why he has excess runout round the plaque, but overall it looks quite good, and the flash can be trimmed off.

3. He also mentions that he does iron melts, so I will look for videos for that.

4. He uses a liftoff furnace, which is somewhat rare, and totally unnecessary, but it works well for him.
He does not have enough clearance to get his lifting tongs into the furnace, and so just lifts off the furnace, and gets away with using an oversized crucible in that size furnace.
Not a bad setup for aluminum.
I would not use a lift-off furnace for iron, since you get a lot of intense heat out of any joint.

Aluminum pours are pretty tame, with the low pour temperature (about 1,350 F), and so you can get away with short sleeve shirts like you seen in the video.
Iron pour temperature is in the 2,400-2,500 F range, and wearing a short sleeve shirt would be rough, given the amount of radiant heat.

 

[GreenTwin]

3D printed piston, for a casting pattern.

 

[vederstein]

Ok,

Let's go the other way. Below is a short video of one of my casting pours.

I'm not trying to be stupid here.

Review and let me know what, if anything, I'm doing wrong. (I already noticed my arms were bare and I wasn't wearing a jacket. So you can skip that critique.)

...Ved.

 

[minh-thanh]

Ok,

Let's go the other way. Below is a short video of one of my casting pours.

I'm not trying to be stupid here.

Review and let me know what, if anything, I'm doing wrong. (I already noticed my arms were bare and I wasn't wearing a jacket. So you can skip that critique.)

...Ved.

What really matters : experience !!!!
You know what you should, must and need to do...or at least you know what is okay and safe...when casting...
That's a huge difference between you and a newbie like me
I have a little time doing work related to heat, I know about drying, ...I know about thermal shock, ..I .know a little about casting But I have never cast so experience = 0
I can do the same as you but at least I must have the same experience as you

 

[GreenTwin]

Ok,

Let's go the other way. Below is a short video of one of my casting pours.

I'm not trying to be stupid here.

Review and let me know what, if anything, I'm doing wrong. (I already noticed my arms were bare and I wasn't wearing a jacket. So you can skip that critique.)

...Ved.

Your setup looks pretty good.
My recommendations would be:

1. If that is uncoated ceramic blanket, you should spray on Satanite so that you don't get fibers in the air.
General note to all: Once you inhale ceramic blanket fibers over some period of time, your lungs are ruined forever.

2. I like to use a crucible retainer, since I had a #10 crucible full of iron slip out of my pouring shank in mid-pour.
I had an initial crucible holder design, but that design failed even though I thought it was a good design.
I redesigned the holder so that it would adjust down on the top of the crucible, no matter where the crucible sat in the loop, and that works well.
Some folks use a crucible retainer, and some say you don't need one, but I did have a crucible flip out that was full of iron, so I know it happens.
People will tell you sometimes that you don't need stuff, and you can find out in a very rude way that yes indeed, you do need it.

3. I have not seen anyone pour from that direction, so I assume you are left handed?
Your pour technique is not bad.
You have the crucible down very low, which is good in keeping the metal velocity low, and avoiding the waterfall effect which entrains a lot of air into the pour.
In some pours, you are a little slow on getting the spure filled, and so you can sometimes aspirate air if you fill with a partially filled spure.

4. Rough surface finish is most often caused by pouring too hot.
Aluminum is generally poured in the 1,350 F range.
If you don't have a pyrometer, watch the miniscus at the wall of the crucible.
When the metal miniscus goes flat, pour immediately.

5. I like a handle on one end or the other of my pouring shank, and I have the handle pointing straight down when the crucible is upright and level.
The handle gives the leverage for fine pour control, and the vertical handle puts the wrist in a natural position to apply force, as opposed to a sideways handle that puts the wrist in a very awkward position as you pour.

6. I had a furnace with a hand-removed lid (before I got my lid lifter completed), and I got ridiculed for not having a lid lifter.
For aluminum pours, you don't need a lid lifter, and the manual lift works fine, and keeps the furnace simple.
I bought a round metal bbq grille at the hardware store, and I set the lid on that, which was elevated off the ground a bit, and that worked well.

7. I have not tried a lost PLA casting yet, but your investment castings look very good.
Not sure what happened with the metal.
I use aluminum 356 ingots, which is the aluminum alloy used for casting.
Some of the other aluminum alloys don't seem to work as well for casting, but I can't tell you exactly which do and don't work.

Everybody has to learn as they go with casting work.
I knew absolutely nothing about foundry work just a few years ago.

I made mistakes, and learned as I went.
I also asked a lot of questions from those who were making successful castings.

My approach was to solve one problem at a time, such as learning to tune the burner correctly for an iron melt, learning what sand to use and how to mold it, learning how to get a good surface finish, how to avoid inclusions and air aspiration, etc.
It is a multi-step learning process.

You are well on your way, and making some impressive pieces.
I really enjoy watching other's casting videos.
I watched all of your foundry videos.
Its is a fantastic hobby in my opinion, and so very handy when you need an engine part.

Good luck.

Pat J
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Edit:
I use to post my videos on ytube, but moved them to Vimeo, and I don't think anyone sees them there.
But some of the experienced folks use to watch my videos, and the comments were often harsh.
I look at all criticism (good and bad) as helpful, as long as the criticism can be used to improve the casting process.
Some folks are crazy and just enjoy launching personal attacks in the comments.
I ask the crazy folks "Show me the castings you have made, and lets comment on your setup, your castings, and the progress you have made in the last year". Sometimes the armchair guys who say the most are the ones who have done little or no foundry work at all. That is life I guess.

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[GreenTwin]

Here are my videos on Vimeo.
There are a number of steam engine videos stacked on top of my foundry videos, and so you have to scroll down to get to my foundry videos.
The steam engine machining videos are by Randall Marquis, showing his compound marine steam engine being built.

Green Twin Oscillator

I have folks watch my videos, and say "You are an absolute moron, your setup is terrible, you are doing dangerous stuff, and your castings are terrible".

All these statements were true when I started learning backyard casting.

One guy said "All I see you doing is pouring metal on the ground". (that was a demonstration of the furnace/burner operation, not intending to make a casting). Some folks just won't cut you any slack.

I could make a full length movie of all my casting mistakes and blunders.
Its all there in my videos; the good, the bad, and the ugly.
I don't hide my blunders, but rather post them for others to learn from.

It is hard to learn foundry work without jumping in there and actually doing it.
You have to get in there, try some things, make mistakes, learn, and get better as you go; just like learning how to machine metal.
I have tried a large number of of burner types, and various lid lifters, tongs, shanks, etc., and have finally found the equipment and burner style that works well for me, and more importantly works consistently and safely every time.

I would say that there are many things in my videos that you should not do.
LOL, my videos fit in very well with the topic of this thread.
I do have some very respectable pour videos that were made after a lot of practice over the years, such as the Bearing Cap, or the Phoenix iron pour.

I was in the learning phase, and really was clueless about backyard casting at the time these videos were made.
I was basically the blind squirrel in the forest, who stumbled along, and occasionally found a nut or two just by chance.

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