Bronze mold half must be warped

[duhbob]

I have made 10,000 9mm (135gr R.N.)castings without problems. My 6 cavity Policlips MX93 recently began leaving fins at the ogive end of almost every drop. I can slip a .008 shim between the mold halves. And there is a mild arc (Daylight) when held to a straight-edge. Parts are rare I think. So I'm seeking help from the FORUM. Anybody who has ever bent bronze molds , please tell me how. Or is that unwise?
Thanks.281284

[Dusty Bannister]

Have the alignment pins moved or is there a burr or debris at one of the holes? Check mounting screws as they might be binding and preventing the blocks from coming together correctly.

[MarkW]

Paint one side with lipstick then squeeze them together, then look at the pattern made to see where the high spots and the binding spots are then make a plan.

[John Boy]

Mark, never heard of doing the lip stick trick... a neat idea

[duhbob]

Thanks DB. I spoke to a "die guy" who said its almost impossible to warp/un-warp bronze. He asked about other factors like changes in alloy and casting temperature. MAYBE since I did add significant TIN to the mix it created a more fluid alloy. My next step will be reverting to an earlier mix of range lead and co ww(without additional linotype tin)

[duhbob]

I will use a yellow china marker. Don't want to borrow her Revlon...too many questions:neutral:

[gwpercle]

I will use a yellow china marker. Don't want to borrow her Revlon...too many questions:neutral:

Just get her to go to the store and help you buy "your own" lipstick , "Honey ...does this shade go with my eyes ? "...Now you hear some Questions !
You can have a field day with it ...I use fingernail polish for front sight highlighting , needed a day-glo shade and got my daughter to take me shopping .... my Daughter wont go to the Mall with me any more ... I had some fun with her that day !
Gary

[Cap'n Morgan]

There's only two explanations: Either the mold halves are warped or they cant close completely because of "something".

I watched a youtube video of the machine in operation. The mold halves seems quite long compared to their width. If made from casted bronze stock they should be stable enough, but I suspect they are made from rolled brass? If that's the case, lengthwise warping can easily occur. I would dismantle the mold and lap the faces lightly with fine emery cloth on a flat surface to remove any dings and check for warping.

Judging from the video, the mold halves are thin enough to be straightened in a heavy vise or hydraulic press. Bronze will be more "springy" than brass, but it will still take a bend without breaking.

[duhbob]

Thank you Cap'n
I guess my "fear" was one of breaking the mold in my vise. I think the warp (.008)is beyond lapping but I will start there. Then the vise, if necessary.

[oley55]

after 10k and suddenly warped, what do you think caused it?

[Mal Paso]

There is more flashing on the left. If the alignment pins (not pictured) are on the bottom of the mold face, I think the pins have moved. The CLEAN mold can be heated to 400F, put in a vise and squeeze the 2 halves together reseating the pins.

If there is really a bow in the mold face, find someone with a hydraulic press, who knows how to use it and try +.002" at each end on a flat plate at a time.

[rboeser]

There is more flashing on the left. If the alignment pins (not pictured) are on the bottom of the mold face, I think the pins have moved. The CLEAN mold can be heated to 400F, put in a vise and squeeze the 2 halves together reseating the pins.

If there is really a bow in the mold face, find someone with a hydraulic press, who knows how to use it and try +.002" at each end on a flat plate at a time.

The key words here are "someone who knows how to use it". Be careful pushing bronze or brass around. If nothing else can be found to cause this issue, then try the hydraulic press as a last resort. When trying to "straighten" something, you my have to place a thin shim at the high spots and overbend it a few thousandths based on the spring back your bronze has.

[45DUDE]

What about using several C clamps and let sit on a hot plate or another heat source for a while and let cool and check the results. I don't see it could hurt anything. You should be able to hold to the light and see the gaps before you tighten.

[oley55]

If it is warped I fear our amateur mature efforts/recommendations (me included) will probably make it worse. That said...

The warping after so many uses would seem to eliminate the likelihood of residual stresses from manufacture. So that would seem to leave uneven heat either rapid heating or cooling to one half.

For testing purposes I'd try applying a good amount of propane torch heat to the inside of the warped half just to see if the expansion on the heated side temporarily lessens or eliminates the light gap. You could clamp them together at that point, but I highly suspect it will spring back to it's warped shape after cooling and clamp removal.

If all of that goes as suggested, try it all again, but this time with your shims. If it works, I still fear we have only managed to straighten it by introducing our own opposite stresses and the warping will eventually return during the normal heating and cooling processes, and probably be worse.

All of that is pure conjecture from someone who has no practical experience. Hopefully, someone with a smidgen of metal working expertise will jump in here and politely suggest I must have lost my mind suggesting something so stupid.

[Mal Paso]

I still think the alignment pins moved. I've had pins "walk" out on a couple molds. Tapping on the hinge pin is enough to do it on a hot mold. I drilled and cross pinned the alignment pins one to put an end to it.

[Cap'n Morgan]

One way to straighten the mold would be mounting another bar on the back with a set screw in each end - as far towards the ends as possible. Placing a shim in the middle and tightening the two screws will easily pull the mold halve back in shape - so to speak.

[Conditor22]

I'd scrub the mold faces clean with dish soap and a stiff-bristled nylon brush.
Check around the alignment pins for any residual lead.

dry -- put the halves together and hold up to a light to see where the light comes through the most
(pay close attention to the area around the alignment pins).

IF it looks like the alignment pins have moved I would put the mold halves together in a vise with blocks of hardwood at least the width and length of the mold centered in the vise jaws.

IF the pins still don't move you can tap them in with a punch and see if that helps, then you would need to clamp the mold halves together and tap the pins back to where they touch/align the mold halves but don't hold the mold open.

hold a straight edge to the faces of the mold and determine IF you can safely sand the end and get a flat mold or if you need to try "bending the mold back in a heavy vise with shims.

Worst-case scenario I have put 600 grit wet/dry sandpaper on a heavy piece of glass then holding the cavity half without the alignment pins as flat as possible sand lightly until the sanding marks cover the whole face (I dealt with some molds in really bad shape) [you don't want to sand into the cavity areas.]
you may have to drive the pins in to do that half IF the one half doesn't do it.


IF your sanding starts getting into the cavities you may have to try "bending the mold in a big vice with some thin shims something like this
{One way to straighten the mold would be mounting another bar on the back with a set screw in each end - as far towards the ends as possible. Placing a shim in the middle and tightening the two screws will easily pull the mold halve back in shape - so to speak.}


My 2¢, use my suggestions at your discretion, it's worked for me/my applications, not seeing your mold in hand makes it hard to diagnose.

[john.k]

A lot of bronzes and brasses become quite soft around 400C,I learnt this trying to bend some customer supplied bronze bars......i thought I knew better and ignored his advice to heat,and bang,one snapped in a sort of diagonal fracture......Unfortunately he was standing there as it went bang......anyhoo ,I heated the bar,and it was soft as butter,could have bent it by hand.......But unlike steel ,it suddenly melts if you apply too much heat,and you have a very expensive lump of slush.

[john.k]

If you lap out 008 warp ,you will have undersize bullets by near 008 at either end.

[barrabruce]

I have one mold that you can easily see daylight through.
It casts good round bullets.
Only if I positively pour with the ladle with a quick fill and not dwell.
Otherwise I get fins that look like the coral reef.
Too much Lino and it will pour like water if it’s way hot.

I’d try your other mix and check all the pins etc before I thought about removing any metal.
Was it warped before?
Did they get a water quench on a bench when hot or something.

I’ve always found half the battle is finding out what caused the fault in the first place so I can fix that to stop it happening again.

Good luck.

[oley55]

duhbob,

wondering how you are doing with that mold??

[Mossy88]

if the mold is warped...wouldnt bullets cast on the end with the gap cast oversized bullets? Dangerous?

[Walter Laich]

if the mold is warped...wouldnt bullets cast on the end with the gap cast oversized bullets? Dangerous?

If/when he sizes the bullets after casting them they will be brought back into specs. Depending on how much they are out of round it may not be able to do this without possibly damaging the press/sizer