A Better Hinge

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This is a pretty typical lead casting (sinkers, jigs, spinnerbaits, etc) mold. The hinge shown works pretty darn well. It moves easily, and does a good job of helping to hold the mold halves in alignment at the hinge end. The opening (handle side) end has two alignment pins with radius ends that mate the plates at that end. Over all my customers are atleast acceptably happy with it. However to make a mold like this that finishes as to 1/2 inch (apx) plates with a hinge I start out by throwing away a third of the raw material. Basically I start with 3/4 inch flat bar and remove 1/4 inch to leave the 1/4" hinge bosses. It just irks me to throw away 33% of the raw material on every one of these molds.

No. Bolting a flat metal hinge to the ends is NOT a better way. It simply will not hold up over time, and even if its handled with kid gloves the heat cycling will cause it to work loose. I've seen molds made by other mold makers with tacked on hinges, and they get pretty beat up and very sloppy over time. It often results in damage to the mold itself. Especially if cores, pins, and other inserts or materials need to be placed in the mold before casting. These one piece boss pinned hinges last through thousands of heat cycles. I've done larger molds this same way that customers have told me they have literally run tons of lead through. It would also require another setup to drill and tap to tack on a sheet metal hinge.

Casting a billet with preformed mold bosses is not a great answer either. The aluminum that results is more porous with the type of foundry I could setup, and my quantity is to small to have them forged cost efficiently. I think it might also drive up the per unit cost too much unless I could cast or forge them in great quantities. On top of that castings or forgings then have other machining that needs to be done to make them useable. One mold company sells cast "blanks, but I absolutely hate to work with them because the metal doesn't machine as nicely and the surfaces are more of a pain to square up and also keep the hinges squared up with both haves coming out aligned.

I did think of maybe using a third piece between the two plates with 4 pins instead of the two I use now, but then it would not help as much with mold alignment. It would also be slower and more cludgy for the customer to use the mold. Every idea I come up with is also more manual work, or more secondary setup work.

Maybe they way I am doing it is the best way to get a decent result within my work constraints, but I can't help but wonder if there isn't a better way.

Tangent: If anybody is curious. No I do not use a round over mill to get the hinge bosses. I tried that in the past and I was not happy with it at all. I cnc mill a radius on the boss with a .001 depth of cut and then sand smooth when it comes off the mold. It would be faster to use a round over mill, but because of the lead on the cutting flutes and lack of consistency from one to the next it would waste part of the useable surface of the mold plates. Make larger mold blanks to make up for it then means slightly higher (few cents per unit atleast) material cost and higher machine time clearing the face of the blank. It works out to be a wash on that for cost and produces a CNC cutting the radius gives better result in my opinion.

*************** I sure need to remember to proof read before I hit send.

Why not make the mold bosses separately, and have them drop into pockets in the mold, then get pinned or bolted in place? You could make them rectangular to keep them in alignment. Much like a mortise & tenon.

Unequal leg angle or a custom extrusion are the two thoughts that come to mind.

How about machining the ends to use something like size 50 motorcycle chain. Basically a pivot on each half. Then machine in 2 more alignment pins to ensure proper closure. That would allow you to start with 1/2". Sort of how hinged hand cuffs work.

How does MIG welding a thicker bar on the end compare in cost and effort?

You could mill steps for the beads in the end to retain strength and minimize cleanup.

Unequal leg angle or a custom extrusion are the two thoughts that come to mind.

How about machining the ends to use something like size 50 motorcycle chain. Basically a pivot on each half. Then machine in 2 more alignment pins to ensure proper closure. That would allow you to start with 1/2". Sort of how hinged hand cuffs work.

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Yeah Steve I have considered a connecting link type design. I'm not convinced its equal or better, but it would definitely reduce wasted raw stock. It?s a good idea.

How does MIG welding a thicker bar on the end compare in cost and effort?

You could mill steps for the beads in the end to retain strength and minimize cleanup.

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I hadn't thought of that. I do have a MIG with a spool gun for welding aluminum. I'm not very good, but I expect for a repetitive weld I could setup, make a couple practice passes, and then do several at a time. I'm not sure that overall it?s the best solution for me, but it is a good idea.

P.S. When I was learning to make molds, I had my first ultralight CNC mill, and stock was more precious to me since I wasn't making any money with it I often welded up mistakes in a plate and remachined it.

Machine one up and beat it to death in testing.

Why not make the mold bosses separately, and have them drop into pockets in the mold, then get pinned or bolted in place? You could make them rectangular to keep them in alignment. Much like a mortise & tenon.

************ That is a possible consideration. It deserves atleast weighing the extra operation time vs the time saved roughing off stock and the better cost efficiency on material. A press fit dovetail with a locking screw might make for quick assembly. If I do a really good job it might even eliminate one of my other secondary operations. Another good idea to think about.

Personally I'd sub that job to a certified welder friend who is much better than I'll ever be, and ask him how he wanted the parts prepared so that the beads stay below the upper and lower surfaces.

I am better on steel and build up shapes like bending brake hinge forks that would require removing a lot of metal from a solid block.

-jsw

Personally I'd sub that job to a certified welder friend who is much better than I'll ever be, and ask him how he wanted the parts prepared so that the beads stay below the upper and lower surfaces.

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Now that's something I won't do. I used to just try to take certain types of welding jobs over to the professional shops and leave it. I'd ask how long, and that's when I'd come back to pick it up. I would never bother them in between. The job was never ever done when they said. Not one time. Usually I was told 2 more weeks several times (after an intitial 3-6 week time window) before they finally did the job The last two times it was done wrong. I just quit. Sure I get that Mr big farm owner or Mr government contractor is a more important customer. I knew that up front that's why I just asked how long and left. Its why I ultimately bought a decent dual gun MIG welder and learned to weld aluminum in the first place. No point in taking paying work to them if I can't get it done. I'm not good, but my welds don't break either and ultimately they get done when I want them done. Had nothing to do with money. I spent a lot on the welder. I took a lot of years to pay it off. I'd have rather just had somebody do it and not worry about it. Its why I work on a lot of my own stuff.

I don't know if it is worth the bother but you might want to look at Lyman bullet molds. The hinge is in the handles and the mold is simply two blocks aligned with pins. see

I don't know if it is worth the bother but you might want to look at Lyman bullet molds. The hinge is in the handles and the mold is simply two blocks aligned with pins. see

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That?s a decent idea John. I actually have some Lyman and Lee stuff, and atleast on paper I am a dealer for Lee Precision. Unfortunately those molds do not open far enough to load hooks, pins, screws locks, wire forms, etc, easily. Its definitely a good form for bullet molds and allows a home boo-lit caster to own several molds and only one set of handles. Thanks for the thought John.

There's some options with extra parts (mainly, though, I don't like loose parts...). In particular, your alignment pins could go through the mold and a wedge can snug the halves together. On a lathe, it's only gonna take a bit of a head on the protruding pin end, that engages an external wedge of the sloped-metal-with-keyhole type.

With a CNC setup, the wedge can be simpler, if you slot the pin, but that might eventually score the mold. Internal wedge (like for Morse taper release) also needs a radius'ed edge;

Just to go further outside the box, if you have a hydraulic press you could bend a short L on the end of your bar to give you the raised material for your hinge. You'll get some distortion between the edge of the die and the bend so you will have to make your mold maybe 1/2" or 3/4" longer than before. Either keep the radius large to prevent cracking or set up a torch (or crab pot propane burner) and firebrick oven with a slot just big enough to stick in the end you are about to bend and experiment with how hot you need. The $30 harborfreight IR thermometer (frequently on sale or coupon for $20) goes to 968F for easy measurement. Most cheap ones don't go nearly that high. Not sure what the emissivity of aluminum is up there so you need to calibrate if you want actual accuracy but reproducibility should be good and you will just keep trying an indicated 25F higher each time until you get a good bend so who cares :-). Definitely want a real press brake or air over hydraulic for speed, then quench in water immediately after bending. I've done the heat and bend but never bothered with this but if you want maximum strength you could age at 400F for an hour to get the region you heated somewhere near T5 while the rest should still be pretty much T6.

Just to go further outside the box, if you have a hydraulic press you could bend a short L on the end of your bar to give you the raised material for your hinge. You'll get some distortion between the edge of the die and the bend so you will have to make your mold maybe 1/2" or 3/4" longer than before. Either keep the radius large to prevent cracking or set up a torch (or crab pot propane burner) and firebrick oven with a slot just big enough to stick in the end you are about to bend and experiment with how hot you need. The $30 harborfreight IR thermometer (frequently on sale or coupon for $20) goes to 968F for easy measurement. Most cheap ones don't go nearly that high. Not sure what the emissivity of aluminum is up there so you need to calibrate if you want actual accuracy but reproducibility should be good and you will just keep trying an indicated 25F higher each time until you get a good bend so who cares :-). Definitely want a real press brake or air over hydraulic for speed, then quench in water immediately after bending. I've done the heat and bend but never bothered with this but if you want maximum strength you could age at 400F for an hour to get the region you heated somewhere near T5 while the rest should still be pretty much T6.

You shouldn't need to be logged on to see the image.

This is a pretty typical lead casting (sinkers, jigs, spinnerbaits, etc) mold. The hinge shown works pretty darn well. It moves easily, and does a good job of helping to hold the mold halves in alignment at the hinge end. The opening (handle side) end has two alignment pins with radius ends that mate the plates at that end. Over all my customers are atleast acceptably happy with it. However to make a mold like this that finishes as to 1/2 inch (apx) plates with a hinge I start out by throwing away a third of the raw material. Basically I start with 3/4 inch flat bar and remove 1/4 inch to leave the 1/4" hinge bosses. It just irks me to throw away 33% of the raw material on every one of these molds.

No. Bolting a flat metal hinge to the ends is NOT a better way. It simply will not hold up over time, and even if its handled with kid gloves the heat cycling will cause it to work loose. I've seen molds made by other mold makers with tacked on hinges, and they get pretty beat up and very sloppy over time. It often results in damage to the mold itself. Especially if cores, pins, and other inserts or materials need to be placed in the mold before casting. These one piece boss pinned hinges last through thousands of heat cycles. I've done larger molds this same way that customers have told me they have literally run tons of lead through. It would also require another setup to drill and tap to tack on a sheet metal hinge.

Casting a billet with preformed mold bosses is not a great answer either. The aluminum that results is more porous with the type of foundry I could setup, and my quantity is to small to have them forged cost efficiently. I think it might also drive up the per unit cost too much unless I could cast or forge them in great quantities. On top of that castings or forgings then have other machining that needs to be done to make them useable. One mold company sells cast "blanks, but I absolutely hate to work with them because the metal doesn't machine as nicely and the surfaces are more of a pain to square up and also keep the hinges squared up with both haves coming out aligned.

I did think of maybe using a third piece between the two plates with 4 pins instead of the two I use now, but then it would not help as much with mold alignment. It would also be slower and more cludgy for the customer to use the mold. Every idea I come up with is also more manual work, or more secondary setup work.

Maybe they way I am doing it is the best way to get a decent result within my work constraints, but I can't help but wonder if there isn't a better way.

Tangent: If anybody is curious. No I do not use a round over mill to get the hinge bosses. I tried that in the past and I was not happy with it at all. I cnc mill a radius on the boss with a .001 depth of cut and then sand smooth when it comes off the mold. It would be faster to use a round over mill, but because of the lead on the cutting flutes and lack of consistency from one to the next it would waste part of the useable surface of the mold plates. Make larger mold blanks to make up for it then means slightly higher (few cents per unit atleast) material cost and higher machine time clearing the face of the blank. It works out to be a wash on that for cost and produces a CNC cutting the radius gives better result in my opinion.

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First off I want to thank everybody who made suggestions. Just about everybody put some real thought into options. Thank you. I'm going to keep mulling it over, but for now the way I am doing it is the simplest easiest method. Yeah it wastes 33% of the raw stock, but then I have seen other machined parts result in much greater waste than that. For now the material waste will continue. Down the road if my volume increases some of the other options will certainly be considered again.

Greetings Bob, I'm curious about your description of the faults of round over cutters. I use some HSS ones but for steel I use mostly carbide cutters. In fact, I use carbide cutters almost exclusively now. I have old HSS ones in many sizes and only use them when I don't have a carbide one. If I have to do a lot of milling I buy another carbide one if all I have is the HSS version. But even the HSS ones cut accurate radii. As far as neding extra mayerial all the cutters I use would be able to mill the bosses as shown. I also have and use cutters that can mill the bosses in one pass but you would need to stand the molds up which would require another setup. One of the reasons I like the carbide cutters is that they are ground with a finer finish so the parts look better. I also sometimes use carbide router bits meant for wood to machine metal, even stainless steels. They typically have a pretty rough grind on them which leaves a poor finish on the parts. To correct this I make a brass lap, charge it with diamond paste, and lap the router bit cutting edges to a much finer finish. This process doesn't take long. Carbide router bits have saved my butt a few times when I have forgotten to order a cutter or when a cutter fails for some reason. Living on an island makes getting cutters in a hurry tough. Eric