Monday, December 31, 2012

Diacro Heavy Ring Forming

Over the holidays I needed to form several rings from fairly large diameter steel rod. When I say large its kind of related to the forming method. For these they will be formed by hand cold. So 5/8 diameter is pretty close to my limit. The project is several spoked handwheels for a custom door installation in the art studio. There are several rod benders in the shop tool crib but for this job I pulled out the big  #2 Diacro bender. Its big and heavy and runs on roller bearings making it smooth and accurate for heavy duty bending. When I got this bender it didn't really have many of the factory accessories. Over the years I have cobbled together enough stuff to do most of the things I need but not in this case. For these handwheels a large center die was required to size the handwheels. Scrounging around the shop I came up with an old steel wheel that I made for testing on the English wheel. It was more than obsolete so it became the inner forming die for the handwheel rings. Guessing at the amount of springback it seemed close to what I was shooting for on the finished rings.
This is one of the proof rings. Its a little over six inches in diameter. The rod is 5/8 diameter copper plated steel. I wanted plain old cold rolled but all the steel suppliers I use in the Bay area for quick stuff were closed for New Years eve. I tried Lowes but almost died from sticker shock at the hobby metal rack. Lurking around the store I found this copper plated ground rod from the electrical department. The price was right and If I need to remove the copper plating it shouldn't be too hard.
Here is the re-purposed English wheel and a ring rod blank. The diameter of the die is large enough so that I can't use the standard eccentric pin to lock the blank in. I just tack welded it to the steel die to keep it from slipping. The first couple of tries the weld broke much easier than I thought it should. Upon further inspection it appears the copper plating is much thicker than I anticipated. This will most likely make these unsatisfactory for the handwheels but its still a fun forming project. The slope that's ground in the end of the rod is there for a purpose.
This is one of those jobs where using stainless filler to join two steel parts is beneficial. The standard steel rod E70S is less ductile than the stainless steel even though it has a higher tensile strength. The rod is actually bending right next to the weld so maximum ductility is more important than raw tensile strength. The copper needed to be fully removed to produce a weld strong enough to resist the forming forces.This is when I discovered just how thick the copper plating is on a ground rod.
Here is the ring blank ready to form. You need room all the way around the bender to form a full circle. Clear the area before you start bending because you don't want to release tension on the bender handle halfway through the bend. If you release tension you will be rewarded with inconsistent results and out of round rings.

Many years ago I wound a several long lengths of stainless tubing for a heat exchanger I was building. Think hillbilly type moonshine stills and you will be close. The tubes were so long I had to move one of the heavy welding tables out into the shop parking lot so I could get a full sweep with the long tube. I wish I had some pictures of that one. The tubing was 5/8 or 3/4 diameter and the coil was roughly twenty or twenty four inches in diameter. Several of the wound "springs" were connected to make the necessary length for the heat exchanger. The forming die was built up out of regular plywood and bolted to the welding table.
Some initial pre-bending on the start end. I'm putting almost yield pressure on the left hand holding the rod blank and then using minimal pressure on the bender handle to get the first part of the bend to lay up against the die better. This stresses the hold back device less which in this case is a weld.
Here we go. Make sure you have everything you need within arms reach when you start. Cheater is two inch pipe which was the only thing I had around that would fit around the Diacro handle.
Coming around nicely. You cant see it in this picture but I had to hop the cheater over the bench vise as I swept around. Once you get ninety degrees wrap on the pressure on the hold back weld is minimal.
Now you can see what the little ramp is for. To make rings you need to wind more than a full circle if you want the best looking and roundest rings. The ramp allows me to go up a turn on the die and continue around. I need to form well past the starting point still.
This 5/8 rod is stiff enough that I had to use a cheater to get the rod up to the next level. It was lifted up the ramp as It was being formed around the die.
Another shot of the same part of the process. All this time its important to keep pressure on the main handle so you don't lose any of the winding tension you have formed in.
I could probably stop here but its way better to have more overlap than you need than to come up any short of a full circle plus fudge factor.
Here is a shot after releasing the winding tension. The amount of spring back varies for a couple of reasons. The main reason is material condition. Harder materials spring more than soft ones. The second is the severity of the forming. This would qualify as semi severe. If this same rod was wound around a fifty five gallon drum the spring back as a percentage of the diameter would be much less. Material springback unfortunately is not a linear curve. It is the art part of bending. You get pretty good at predicting how much a particular setup will spring but for accurate results test bends are required. Start slightly large as its easier to make the die smaller that make it over larger. In sheet metal we call this springback material condition effect the K factor. It applies here with rod bending as well. Here is a link to a nice document on the Art of Bending. This was put out by the Diacro bender company about a thousand years ago. In the old days you got one with your bender and thats it. Now you can get it and download it online. Print it and put it in your shop book of knowledge.
The last step is to mark the rings and cut them. Pick a spot that has the correct radius in both ends of the ring. I like to cut them apart with a thin blade hacksaw or bandsaw.
Don't go too far and cut your die!
Viola! Two more to go. Shifting the rings sideways to mate them up is pretty easy compared to the main forming. They don't need much weld prep. I like to leave them slightly open, like the band saw kerf and just fill the gap as the weld prep. Be sure to build up the weld higher than the OD of the rod. It looks bad when somebody digs down below the natural surface of the rod to get the weld to clean up. Properly finished the weld will be almost invisible. I won't be welding these up because of the copper plating. I'll wait until I get some proper cold rolled steel for the job.

5 comments:

  1. Interesting post, Tom. I had a feeling you made a run to the home improvement store when I saw the photos before reading.

    My question is why you don't salvage these rings and use chemistry to remove the plating instead of abrasives. I've successfully removed stuff electrolytically, but I think this may even be easier than that.

    I found this thread
    http://www.practicalmachinist.com/vb/gunsmithing/removing-copper-plating-161632/
    where strong ammonia was used. I know this plating is pretty thick, but a few baths might do it, and all you have to do is set some buckets aside and do some scrubbing when they are done - That is, unless you despise anything resembling washing dishes. haha

    Just a thought.

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  2. Hi J,

    This copper plating is pretty thick. I think it would take a pretty aggressive chemical attack to do anything. The residue from the chem warfare approach is not something I relish the thought of dealing with. Its all academic anyway. We found a better solution to the custom handle problem. Stay tuned more to follow. I will have to measure the plating thickness on those rods. I was quite surprised at how thick it is. Thanks for the suggestion. Want a couple of copper plated steel rings to experiment with?

    Regards,

    Tom

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  3. One of my former workplaces made a lot of steel rings on an old lathe. They had a mandrel with a hole in it, stuck the end of a 20-foot stick of 3/8 round in the hole, and turned on the lathe. In a very low gear. It just wound the round bar up around the mandrel like a big spring. When they were done, they cut the coil into rings with a torch, right there on the lathe.

    This was done on a very old and worn-out lathe that was reserved for just such barbaric uses.

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  4. Hi Propelled,

    Many years ago some friends and me made chain mail armor from steel wire. I had an old decrepit Prentiss lathe from 1915 that we used to wind the rings from welding rod just the way you described. We held the end of the rod with vise grips and when we came up against the winding mandrel the lathe would pull the wire out of the jaws. Not for the faint of heart. The wire would then sproing open suddenly. We used the same portable bandsaw in the article above to cut the coils into individual rings. One shirt of mail could have 10,000 rings in it. It was a lot of fun putting those all together into a shirt.

    Thanks for the comment.

    Tom Lipton

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  5. Wait! What?! You Blanchard ground your welding table?
    I can't take my eyes off it. It's downright pornographic!

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