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Waves after rolling

I generally have a wavy piece of metal after significant rolling out a long and thin piece of metal, say a bangle sized strip of silver from an ingot. Its a lot of filing and sanding to flatten both sides. Normally this would be banged out as I form the bangle, but my current piece is going to require a second strip soldered on to the first. Any suggestions of how to remove waves without taking off a lot of metal?

Try running it at a diagonal through the rollers at the last setting. If that doesn’t work, anneal and try again. Unless you have really wide rollers you won’t be able to get much of a diagonal, but it is worth a try. When I am rolling an ingot I am usually rolling from about 4mm to a little bit less than 1 mm. The piece wanders all over until, all of a sudden it flattens out after an annealing and rolling at the last setting. My guess is that this is the point where every area of the piece is at the same level of stress. That question is for the metallurgists among us to answer. I just look for it to happen. I also do a lot of forging to the ingot before I start to roll. Again, I don’t know why, but it seems to make a difference in the quality of the piece when it is rolled, especially along the edges. Good luck…Rob

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Thanks Rob-- This particular piece started off as a 4mm ingot and its final destination was supposed to be 2mm but is now at 1.8 due to having to squeeze a little more length to make up for a defect that showed up at one end. I’ll try annealing and one slight diagonal pass. I also was thinking of annealing and squeezing it between two bench plates in a vice for a while, but I have no idea if that will help.

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Go ahead and try, but I have done the same between plates on my 20 ton hydraulic press and it doesn’t do much. Remember that a roller is concentrating its compressive forced into a very small area as you roll, the compressive force of the press is spread fairly evenly over the entire piece. There are ways to use pieces of urethane in a press to work on one place on your piece, but I have never tried it. Good luck…Rob

I am rolling some sheet right this minute. And I also have not worried too much about wavy metal as my sheet is usually domed after punching out disks or cutting squares and stamping for earrings. If I can pull back on the piece I am rolling this helps some too. I have noticed that it is less wavy if it goes into the mill as close to level as possible. And how it reacts depends on if I have annealed it. I have never really experimented with the process before but I will.

Don

Thanks Rob and Don. As Rob suggested, the pressing did not help much, some hammering of the plate sandwich helped a little. In the end I was able to solder the second piece on and that piece was supple enough that I could press on it to close any gaps that resulted from the wave. I’m really going to pay more attention to rolling out ingots the next time and use your suggestions.

When I am trying to sweat solder two long pieces together to form a bracelet, I will often just solder the ends first and then make a partial cuff shaped bend to pull everything together. Then I go back and solder the areas between the already soldered ends. This won’t work on all designs. Good luck…Rob

I melted a mass of sterling scrap and new metal (48 grams) with a Paige Rosebud on my Smith little torch and cast an ingot/slab of sterling in my adjustable Durston Ingot Mold. The flat slab is about 1/8" (.128) thick. I rolled it to .20 gauge in a Durston C-130 mill. And metal got pretty wavy early on in the process. I started by first annealing and then forging the slab on both sides with a cross peen and scrubbed it with a brass brush. I ran the slab through the mill for four passes and it seemed to remain relatively flat. I annealed once more and then the wavy silver started to arrive. Four more passes and I had the sheet down to approximately 12 gauge (.081) and then the metal began to flatten as I rolled it. I rolled it down to about 14 gauge (.064) and it stayed flat. One last anneal and as I rolled to 20 gauge (.032). And it rippled all over the thinner it got.

I repeated the process with copper and got nearly identical results.

There are variables involved that I can’t or perhaps more accurately didn’t try to control.

How big a bite I tool with the mill each time I dialed it down. Approximately an 1/8 of a turn is close but it was more and then less. Not a real method.

How fast or slow I turned it through the mill.

The big thing I believe is this. How steadily I was able to turn the mill. Turning it in pulses I believe to be the big contributor to waves. I don’t know for certain but I would bet a powered mill sees fewer problems with waves in the sheet.

What I think helps to reduce waving in hand powered mills is smaller bites with a steadier turn of the crank. Making sure the sheet goes through the mill level to the bench. And occasionally rolling the sheet a few degrees off 90 to the rollers to iron out or at least reduce the ripples.

Don Meixner

I realize this isn’t actually responding to the question, but I would like to share this little tip anyway. Think of the mill handle as a clock face. Then you can quite accurately turn the same amount for each pass. For example, rotate from 12:00 to 1:00 for a small increment.

Thanks Don and Vera-Don, I also suspected that the cause of the ripples was related to non uniform turning. The down swing is so much easier than the upswing and I have started to use two arms during the upswing to help with that. I also take pretty small bites when rolling out ingots on my Durston C150, because anything more than a 5-10 minute turn (clock face minutes) is just too much effort for pieces wider than 10mm. Honestly if I had to do it over, I would have purchased a motorized mill.

This may be difficult for you to arrange, but I used to use a method which gave excellent results for silver and for copper alloys (eg bronzes). The method is well known to silversmiths (well, was, now that there are very few silversmiths left).
Basically you trap the metal to be flattened between two flat plates of iron, held tight by clamps or cramps. The whole is placed in a kiln and kept at a suitable temperature (well below the melting point!) for an hour or two, then allow it to cool. Very rarely, the clamps need re-tightening and the process repeated.
I frequently used this method for flattening bronze sheet to make perfect mirrors, and occasionally for flattening silver if I had rolled it myself rather than buying sheet.
I’ve been retired (involuntarily) for a couple of years now so I can’t remember the most useful temperatures to aim for. I had the luxury of a large ceramic kiln for the process. It really hammers the iron sheets and the clamps, which can end up significantly corroded and rusty.

My reflection in bronze mirror

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Thanks for sharing that suggestion. I like your mirror…Rob

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I have had the same problem occasionally but it got better when I started taking much smaller bites and putting tension on the piece going through to keep it straight. That means you can’t use two hands to turn the crank. If it takes two hands, I think you are closing the rolls too much. Reducing the force also allows you to do a smoother roll without stopping. I don’t do alot of reductions, but reduce Mokume billets occasionally. The above seems to work.

Flipping and turning the piece between rollings also helps. The object being to not constantly apply force in the same direction. Having an output table can help if the piece is trying to curve downward. Other than that, slow and steady wins the race. Also anneal frequently.

Large motorized rolling mills have infeed and outfeed tables level with the lower roll to control bending, it may be possible to make similar tables for a small mill with hardwood and pieces of steel. Just for reference the stamping press industry have sheet straighteners based on multiple rolls bending the metal in some sort of crinkle progressively smaller until the sheet is perfectly straight.

What I do if I want to flatten a wavy piece of metal, I just anneal it hammer it down with a rawhide mallet (it doesn’t leave marks) on top of my polished anvil.
When I want a very straight strip of metal, I anneal it and stretch it a bit on a drawbench. I hope it helps

One factor that produces waves after rolling is not using a constant speed. If you speed up or slow down during the turns you will get waves. You should have a constant rhythm.

Problem for me is…a constant speed it quite literally impossible. The Durston’s handle is so long I whack myself each revolution. Can afford the new fancy 50:1 ratio so I guess I’ll never get flat sheets.

It might work if you take smaller bites each time. Close the rollers just enough so that the sheet is smaller each time but not so much you can’t turn the handle at a constant speed. You can do it little by little, it will take perhaps a longer time but it won’t require as much power.

Thank you Andrew. I am doing that now - but I’ll try smaller changes each time.

-sent via the interwebs🖖🏼