Warped molds?

[44man]

I was just sent a mold by a friend because it was bad. One block was warped and the halves would rock. I have never warped a mold and have been wondering why I read so much about it here. I was able to fix the mold and get it flat again. The important thing is that I have determined how it got warped in the first place.
Most molds have screws going in from the bottom to hold the handles on. If you crank these in tight, the blocks will bend toward the handle slots. This tension from the screws gets worse when the blocks get hot. If you tighten these screws on a hot mold it will do more damage. Now how many of you are guilty of this?
The Rapine molds are made right with a pin held in with a setscrew. I make my molds like this too. There is no way to bend the blocks. Cast iron blocks will not bend very easy either but it can happen if you get too strong on the screwdriver. I know some of you get tired of the screws coming loose and really crank them down---WRONG!
Best thing is to drill and tap some holes for setscrews to contact the handle screws so they can be left loose, yet not unscrew. Better yet, drill the bottom of the holes a little larger, tap for setscrews and replace the handle screws with pins.
The blocks are thin at the handle slots, now subtract the hole for the cavity and you can see they are easy to bend in this spot.
How about some feedback on this guys!

[buck1]

Goog info!!! Thanks for the tip!!

[carpetman]

44Man--I have handles for most of my molds,so don't have to interchange them too often,but best I can remember some of the RCBS do have pins and the screw just holds them in place. Tightness of the screw would not be a clamping effect. But,if designed wrong and they should warp,I'll send them back to RCBS for correction before I start making alterations to correct their mistake.

[MGySgt]

But,if designed wrong and they should warp,I'll send them back to RCBS for correction before I start making alterations to correct their mistake.

Don't know when RCBS found out about their design flaw, but I have an old set of RCBS that has the screw and a new set that has a set screw and pin.

So - I guess RCBS fixed their problem!

Drew

[44man]

Carpetman, you will never have a problem with the RCBS mold. You can tighten the setscrews because there is play above the pins. The worst offenders are the molds with the threads in the top of the blocks. When you tighten them it draws the top of the mold toward the bottom. If you just snug them they will never give you a problem either, just don't over tighten them. Like I said, I never bent a mold so didn't know what was going on. RCBS and Rapine are way ahead of me because they must have had a lot of molds sent back and were able to figure it out. What surprises me is that the companies never sent a warning with their molds about over tightening these screws. Even Lee uses a pin that is free in the hole and just staked at the bottom to hold it in.
Takes some of us a long time to figure things out I guess.

[floodgate]

[QUOTE=44man]I was just sent a mold by a friend because it was bad. One block was warped and the halves would rock. I have never warped a mold and have been wondering why I read so much about it here. I was able to fix the mold and get it flat again. The important thing is that I have determined how it got warped in the first place.
Most molds have screws going in from the bottom to hold the handles on. If you crank these in tight, the blocks will bend toward the handle slots. This tension from the screws gets worse when the blocks get hot. If you tighten these screws on a hot mold it will do more damage. Now how many of you are guilty of this?
The Rapine molds are made right with a pin held in with a setscrew. I make my molds like this too. There is no way to bend the blocks. Cast iron blocks will not bend very easy either but it can happen if you get too strong on the screwdriver. I know some of you get tired of the screws coming loose and really crank them down---WRONG!
Best thing is to drill and tap some holes for setscrews to contact the handle screws so they can be left loose, yet not unscrew. Better yet, drill the bottom of the holesThe blocks are thin at the handle slots, now subtract the hole for the cavity and you can see they are easy to bend in this spot.
How about some feedback on this guys! a little larger, tap for setscrews and replace the handle screws with pins. [QUOTE]

44MAN:

Thanks for the "heads-up! I've got several dozen Ideal / Lyman moulds; I usually crank the screws up solid, and don't recall ever seeing any warpage (and I always check for any "line of light" through the sprue-hole before casting) but it certainly COULD happen. I collect some of the odder old moulds: Belding & Mull used staked pins like the Lees; Modern-Bond used screws threaded under the heads, held in place by set-screws from the ends of the blocks, and my two Hensley & Gibbs are made almost identically to the M-B's (with the sprue-plate locking into a slot in the stop screw), so these are - in principle at least - better designs from the warpage standpoint. Seems like I learn something new here every day or two.

[Buckshot]

...........44man, good thinking. All my mould miss-alignment issues have been with the alignment pins. No experience with warped blocks. I can see how handle screws threading into the upper portion of the block could very well bend the blocks toward the handle slot.

Without scientific testing I'd also think that mould blocks made of steel might be a bit more suceptable to this. My thinking (guessing) so is due to the grain structure of steel, and it's flexability vs cast iron. Speaking broadly, cast iron is a bit more thermally stable then steel. While it doesn't share steel's ultimate stength, good cast iron is a rigid and stable material. One reason it's so common in internal combustion and steam engines blocks and cylinders.

An interesting idea and certainly a plausible concern. You can exert quite a bit of torque via threads.

..............Buckshot

[StarMetal]

I thought warped moulds were only on Star Trek.

Joe

[felix]

Might be alignment pins, might be actually warped. My molds, that is. Close the mold, and you can rock it back and forth top to bottom, and across a top to bottom diagonal, but not directly sideways across in parallel with the handles. Lymans are the worst. Saecos the best along with LBT. So you all are saying I have the screws too tight from handle to mold halves, right? ... felix

[Greg5278]

I guess I might have made a mistake when I designed my moldblocks then. I drilled and tapped the handle holes in both the top and bottom of the blocks. I didn't think the pin and screw was a good idea, but I can always go back to it. The molds are bigger than normal, and the handle flages are bigger. It is unlikely that you could pull warp the blocks on my molds, but I will let you know. I am using 1.250" long 8-32 cap screws to retain the handles. The Aluminum could do this, but I think you would have to be a Gorilla with a screwdriver to pull it in. Greg

[44man]

Felix, yup! Just snug them a little. I got a heads up from someone on BPCR that leaves the screws loose and pours a drop of lead over the screw heads to keep them from backing out.
I am thinking of a tool to insert in the handle slot to spread the block back to straight. Of course I don't have any of mine that are bent so have to wonder if it is worth the trouble. Then again, if I figure something out, it will help those that do have a bad mold. If the block was spread a thousandths too much, it could be fixed by tightening the handle screws again so no harm would be done. Might be a good way to "Beagle" a mold too by spreading the block.
I have been surprised at how many companies recognized this problem and made their molds the right way. Yet I have a bunch that can be bent if the screws were cranked down. One is a very expensive custom mold with allen head screws. Can you imagine the force that could be applied?
Like I said, I wondered how a mold could be warped and then I actually had one in my hand to see it for myself. It is an NEI aluminum mold. I got it straight with blocks of hardwood and clamps but it was a lot of work. I can't see any light between the blocks now and it makes a perfect boolit.
I never tightened the screws much but now I am sure to be more careful.

[BOOM BOOM]

HI,
I've never had a warped mould, and w/ your heads up I hope I never will.
THANKS !