Introduction: Versatile Crucible Tongs From Old Bed Frame
I made a crucible furnace based on The King of Random's Mini Metal Foundry, but I needed vertical tongs for the crucible I bought, so I decided to make them, to both save money, and to have some versatility--all the ones I could find were either not exactly what I needed or were only available online, such that I couldn't get a sense of scale. After a moment of pondering, I figured an old bed frame I had already used for parts would probably be the easiest to work, and would make about the most compact tongs you could make, which would allow me to maneuver larger crucibles within my small furnace. Turns out I was right. There's probably a thousand ways to do this, but I don't have a functioning welder yet, so here's how I put it together.
An old, basic, adjustable steel bed frame (the kind that slide-locks together with a keyhole system)
Steel Masonry Stake or #6 rebar (3/4" diameter) - around 24" long
Leather gloves or welding gloves
Angle grinder with grinding and cutting wheels
Anvil (or something heavy, stationary, shaped appropriately, and made of thick steel)
Some sort of opposable tongs (preferably blacksmith tongs)
Hammer (preferably a blacksmith hammer)
Adjustable wrenches or whatever size wrenches you need for your nuts and bolts below
3 X 1/4-20X3/8 Hex Head Cap Screws (Preferably zinc plated for longevity)
1/4-20 Square Nut (preferably zinc plated)
1/4-20 Hex Nut (preferably zinc plated)
1/4-20 tap & handle
#7 Drill bit (or 13/64, if you can't find a #7)
Step 1: Dismantle the Bedframe
Note: be sure to make the effort to find your safety glasses for when you use
the grinder--it's easier to just go ahead and get them, than to realize you need them during your work, like I did.
Do this however you want, but this is how I did it. Anyway, for my purposes, I wanted as much of the frame to be intact as possible, because to be honest, I hadn't completely planned it out. However, I figured I could use those pre-drilled holes, keyholes, and cams/keys or whatever to my advantage, so I didn't want to lose any of them. I used one half of the bed frame. I drilled out the middle of the rivets holding the cross-members to the rail, thinking I was going to easily pry the pieces apart. It was harder than I expected, and I didn't want to bend the frame; so since I needed the angle grinder anyway, I ended up using it to grind/cut the rivets off. So, drilling was basically a waste of time, although it probably would have helped if I had drilled all the way through. Why did I show & tell that then? I don't know--I guess misery loves company. Once the rivet end was cut off, I then pulled the material apart easily, and used a hammer and punch to knock the rivet out of the rail. Just cut off all of the rivet ends that you find and punch them out, including those holding in the wheeled legs. You should have two cross-members, and one rail. You don't need the rail for this project, but I bet it will come in handy for making a cart to pull a small propane furnace.
Step 2: Cut Out the Tong "Fingers"
First, we are going to use the cross-member with the cam or key on it (not the keyholes). We're going to use the cam end of this cross-member for the tongs' fingers. For about a size B3 crucible, what I have, cut the frame 9-1/2" long with the cam in the middle (mark at 4-3/4" away from the cam, in either direction to make your cuts) to form the tong "fingers". You can use a hacksaw, but I used my angle grinder with a cutoff wheel. Make sure to use safety glasses. Safety squints wear out during this arduous cutting process. A mask helps here too--you'll be better off without all the steel dust in your lungs, and a day or two of black snot.
Note: If you're using a different size crucible, you will need to figure out the length of tong "fingers" you need. I figured out the length with a little trial and error, but I knew two basic things: that the tongs needed a gap through which the bottom of the crucible would fit, but not the top; and that they needed to wrap around the crucible past the diameter. I judged about where the tongs should engage the sides of the crucible as they would be pulled up the sides, measured the circumference there, drew that circle on paper, worked out the diameter of the crucible at the height of the tongs from the floor, measured the circumference about 1/4" above there (to provide clearance for the tongs to be slipped around the crucible without binding between the crucible and the furnace floor), worked out the diameter at that height of the crucible, and then intersected that line segment measurement with the diameter I first drew, to get the gap width. From there, I measured the leftover circumference to get the length of bed frame I needed to cut out. Here, I'll draw a diagram to show what I'm trying to say--check out the PDF here. Hopefully it helps more than it confuses.
Once you have the cross-member cut to length,cut the side of the angle-iron without the cam off, so that you have a flat piece with the cam sticking out of it's center. Grind off any burrs.
Step 3: Forge the Tong "Fingers"
Once your length of frame with the cam is cut out for forming the fingers, you can then forge
them. I used a homemade (by my uncle) forced-air coal forge to heat the frame section up, one end at a time, and struck them with a hammer over the edge of an anvil to form the curve. I didn't have any professional blacksmithing tools at the time except a broken antique anvil and a (too) heavy pair of tongs, so I used channel locks to hold the steel, and a household hammer. I would suggest getting a blacksmith hammer if you're going to be doing this sort of thing often--I ended up getting one after this. I suggest heating it one end at a time to avoid damaging or loosening the cam pin or whatever they call it, in the middle. At this point, as MJ would say, "just beat it". Heat, beat, and repeat. For the second half of the circle-segment finger you are creating, you will need to forge it over the horn of the anvil (my horn was broken off and missing, so I ground a pyramid into the end of a masonry stake, and drove it into the square hole of my anvil to use as a makeshift horn). Once you start getting the curve close, start testing for fit on your crucible, and fine tune it, so that the fingers just barely slide around it when held close to the bottom, but hold on tight once the tongs are pulled upward. Use the cam in the middle by which to hold it when testing.
Step 4: Cut Out Handle Riser Sections
For this part, we use the other cross-member, the one with the keyholes in it. Hopefully your bed frame looks like the one I have, as the holes they have pre-punched lend themselves well to the design I came up with. If not, you'll figure out something--if you have a drill, a forge, a punch, and a grinder, you can do a lot, if you have more time than money. Check out the notes on the pictures. You will be cutting along the lines, to end up with two specially-shaped sections that will be joined back together a different way. As always, grind off the burrs, so that everything is perfectly flat and snag-free.
Step 5: Attach Tong Fingers to Lower Riser Section
Slide the tong fingers' cam into the keyhole at the bottom of the flat riser section. Hold steady and mark the tong fingers through the riser, at the center of the big circular part of the keyhole, and take the tong fingers back off. Drill a hole at that mark in the tong fingers with the #7 drill bit and tap the hole with a 1/4-20 thread tap. With the fingers slid back into the keyhole, put the square nut into the large part of the keyhole and thread one of the bolts through the nut and into the tapped hole in the riser. Tighten it down to lock the fingers into place.
Note: the benefit of this design is that you can make multiple sizes of tong fingers for different crucibles and quickly change them out on the riser as necessary. Also, the small amount of play between the fingers and the riser allows wiggle room for getting the tongs around crucibles.
Step 6: Connect Upper and Lower Riser Sections
The section of the keyhole cross-member where the wheeled leg used to be attached, now has some convenient holes for connecting it to the other part of it. That other section with the slotted L-bracket at the top, already has one hole in it, but you will need to drill and tap a second to secure the two sections together. Join the first set of holes with a 1/4-20 bolt and hex nut, align the sections, and make a mark through the center of the remaining hole. Then take them back apart, drill through the mark with the #7 bit, and tap this hole also. Now assemble the two sections with the bolt and nut, and the remaining bolt.
Step 7: Make Keyed Handle
Take your piece of rebar, or you masonry stake (what I used), mark the center, and use the angle grinder with the cut-off wheel to remove a 1/8" thick slot around a 3/8" square adjacent to the edge of the bar. See the diagram. This will fit into the slot remaining at the top of the handle riser. You want the slot to be deep enough to provide a positive lock with the riser, and plenty of leverage when lifting a heavy crucible. As Stephen Denette would say, "you want to sneak up on" the final thickness of both the slot width, and the key width, so you don't over-shoot the optimal dimension. 1/8" & 3/8" is the reference measurements, but you want to make sure you get the handle to nest into the riser slot as snugly as possible, while still allowing easy disconnection.
Step 8: Test Final Product
The final product should stand up on its own if you do nothing else with it, but if it doesn't, no big deal. The handle is relatively floppy, as tongs go, but as it leans over slightly, it puts the center of gravity more centered over the tong fingers, so it stands up. If this matters to you and you have trouble getting it to do this, just bend the handle riser slightly to adjust the center of gravity. If you've cut the key slot in the handle correctly, when you engage the riser with the handle, you will be able to turn the crucible around two different axes without the riser falling out of the handle slot, as you can see from the photos. I have tested this with multiple metal pours and it works great. For safety, I suggest testing with a crucible full of water, sand, or scrap before trying with molten metal. If I wasn't lazy, I might would tweak the tong fingers a little for better performance. They don't go quite as high up the crucible as I would like, such that it currently becomes a little precarious to try to get the last "drop" of metal out. When tipped past horizontal, the crucible starts to tip out of the tongs slightly. But if you're just making ingots all day long, you don't really need to tip it all the way over anyway.
Important note: optimally, you would want a more rigid set of tongs, for the safest, most responsive and accurate pours, but as one always needs to be careful with molten metal anyway, these will get the job done. Never be careless with molten metal--be aware of your surroundings, others present, and where you put your feet. These tongs can be modified to make them more rigid. Heat treating them might do the trick without having to add more material. I like the lightness and compact fit of these as is.
I hope this helps or inspires someone.