Michael Cochran

In search of consistent circles

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I have a couple projects in mind that require a few hoops and I cannot figure out how to get them truly round. I've tried differing sizes of steel bar and still cannot get it right. I got it close a couple times and welded the ends together thinking I could finish trying up the circular shape afterwards. I was wrong. I don't want to keep wasting time on failures so I thought I'd ask my favorite brain trust for suggestions. I'm considering getting or building a small ring roller but was hoping I could keep from doing that. Before anyone suggests using a mandrel, I don't have anything the sizes I need. Any and all other suggestions are welcome.

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How many rings, what size, and from what stock? How are the ends of the ring connected to each other?

Your a blacksmith, BUILD a mandrel. If the ring is large enough build a half or even quarter mandrel and bend in sections. Calculate and factor in spring back for cold bending.

Fire up the ole CNC machine and cut the rings. Or if using plasma. build a jig and after a couple of rings, tweek it to fit what you need.

Lots of ways to skin a cat, but we need to know what kind of cat and how big it is.

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What sizes do you need? Can't make good suggestions not knowing if you need 6" or 6' diameter rings.

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I'm sorry, I neglected to mention the sizes. Right now I'm looking at some around 6.5" OD and some around 4" OD. I'm planning 1X1/4" and the 6.5" ones and probably 3/4x3/16" on the 4". Both will be mild steel. As to a quantity, not many right now. If all goes well I'll need more later but for now less than 10 each. At work we have some 6 3/8" schedule 40 pipe I thought about using until I asked about the price, I might get some at a later date making it easier on me but only if I develop the need for it. If I can figure out a good method to make them, I could use rings for a few other projects.

These ring will be used as decorative elements on light fixtures and will be riveted to flat bar in a different plane. 

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You bending this 1 x 1/4 inch flat bar to a 6.5 inch circle the easy way or the hard way?  You bending the 3/4 x 3/16 inch flat bar to a 4 inch circle the easy way or the hard way? Still wondering how you are going to connect the two ends to tack other.

As you say around and probably, may I suggest that you get close with a bending mandrel and then adjust the design to fit the ring the mandrel actually makes. (grin) Work is not the only source for round things. Pipe comes in all sorts of sizes, but you may find an old fire extinguisher about the size you need. What about a brake drum or rotor, or the drive shaft from a truck? 

Why not just make the first ring a little small (allowing for spring back of cold metal) and them use it as a jig for the rest that you need?

Do not build a box, that way anything available is an option. 

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The mandrel can be wooden, such as a 2 x 6 or 2 x 8 cut into a circle. If you bend cold, no problem.

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After a good wake up call last night (thanks Glenn) I have some mental gears turning on how to solve this. The flat bars will be bent easy way forming hoops almost like the ones on old wooden barrels but my goal is for them to be straight sided.

During our chat some ideas were presented to me that I overlooked when I started this project and I just wanted to share pictures of the mandrels I have.  I didn't even think of them until my gears got unstuck. I'll post pictures of some of the resulting hoops when I have time. 

Some mandrels might work for this project, others will not.  In a brief 10 minute look around I found the following items. If anyone has any doubt as to what one of them is I'll gladly tell. I know I have more lying around but didn't have the time to dig them out this morning.

 

IMG_1241.JPG

IMG_1242.JPG

IMG_1243.JPG

IMG_1244.JPG

IMG_1245.JPG

IMG_1246.JPG

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The mental gears were not stuck, you just had yourself in a box so tight you could not think (grin)

Cut off a section from the dead tree and use the diameter. What about the oxygen tank, the wife's pots and pans (be careful with that one). Use the 20 or 55 gallon drum, paint cans, 2-1/2 or 5 gallon metal or plastic buckets, and plastic pipe in all sorts of sizes.

Because you are now OUTSIDE the box seeing possibilities, the list goes on and on.

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Please remove the wife's pots and pans as a suggestion.

Raiding HER kitchen for YOUR project is not worth the resulting conversation that could last several years. (grin) Source the pots and pans at the flea market instead.

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That's why I didn't make a suggestion about some of the rounds I have in my shop. I have an old sauce pan that's about 8" across and a large stock pot that's at least 12" across as well as a couple other kitchen cast offs I use occasionally. 

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Is the size of the rings flexible or is it a set spec? If you can be flexible with the size find pipe that works and cut rings in the cut off saw. I have a 7" x 13" HV,Jet band saw that makes this kind of job an EASY routine I can set up and do other stuff while the saw works. It's the ONLY power tool I'll put to work and walk away from, even if something goes catastrophically wrong the worst that can happen is breaking a $13.00 blade which goes in the broken band saw blade pile just in case I want to do some pattern welding. 

A ring bender would take a LITTLE while to make but not a big thing. Scarfing the lap would take longer than turning the ring. (Angle the vise in the cut off saw and the scarf is a done deal) Once turned a little time heating to welding temp with a torch ON the bender's die and a tap with a hammer and you have a hammer welded ring. Squirt some water on the hot metal, remove the ring and do it again. Keep the die reasonably cool, if you have a bucket of water under the bender it won't make much of a mess on the floor and if you mix in a little vinegar it will descale the rings and die as it cools them.

You're talking production, think about the flow from raw stock to packaging and set up your work space to make it all flow smoothly. 

Open a different box it's FULL of techniques and methods. There's no sin in using good production methods, done competently there IS better access to the black ink zone. :o

Frosty The Lucky.

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Disks of heavier stock are the sort of things I like to pick up on spec at the scrapyard.  I have shelves in my shop piled high with "stuff" to be used with forming hot steel! 

I like my bending forms to be stout enough to hammer on.  (Got a place that does hydrotesting on gas cylinders?  Make a friend there and see about some heavy walled sections.)

Now will these hoops be hammer textured or smooth?

 

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1 hour ago, Frosty said:

Is the size of the rings flexible or is it a set spec? If you can be flexible with the size find pipe that works and cut rings in the cut off saw.

As of right now the sizes are not set in stone and are just approximate measurements. I have considered the pipe approach but will have to find a way to get a more even cut if I go that way. My cutoff saw cuts at an angle coming down and I haven't figured out how to fix that as yet. 

 

1 hour ago, ThomasPowers said:

I like my bending forms to be stout enough to hammer on.  (Got a place that does hydrotesting on gas cylinders?  Make a friend there and see about some heavy walled sections.)

Now will these hoops be hammer textured or smooth?

I will have to do some looking but I'd imagine we do have some place that tests them. We have some of the larger welding and gas supply chains in the area and I'd imagine they are capable but will call before assuming too much. 

The hoops will be textured. I'm not sure how much texturing I'll do but I'll definitely do some. 

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24 minutes ago, Michael Cochran said:

Will have to find a way to get a more even cut if I go that way. My cutoff saw cuts at an angle coming down and I haven't figured out how to fix that as yet.

Inside the box:

Find out why the cutoff saw is not cutting straight and fix the problem.

 

Outside the box:

Find the angle of cut the saw is creating. Shim or adjust the stock being cut so the saw now has a 0* angle finished cut.

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What type cut off saw is it? Which direction if it drifting? This is just a matter of correct set up or a dull blade. Easy fixes.

Frosty The Lucky.

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It's a no name 10" sliding compound miter saw. It comes down with the blade tilted slightly to the left on the top of the blade. I looked at the adjustment for the tilt and I have it locked in the furthest upright position it will go. When you go to adjust the angle on the top end the saw tilts counter clockwise which is the direction the blade is already leaning. I haven't taken the time to investigate and zeroing adjustments that may or may not be on this saw. I know when it was given to me it came out of a fab shop and it was well used. 

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Forget the marks, use a square to adjust it with in both planes. The angle marks on power saws are notoriously off, even the high dollar ones.

Here I thought you had something that needed experience reading and expertise setting like a band saw.  Just because I have to do the song and dance with mine now and then. The trick is reading a band saw, sometimes a bit of dirt will dull teeth on one side of the blade making it pull the other direction. Yeah, into the sharp side, the teeth pull as they bite. 

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Another suggestion, make your rings as a continuous spiral around the mandrel, like a big spring.  Gives you leverage from the straight stock & you only have the initial flat on the start where the end is clamped.  The rings will come out almost the same size that way.  Cut 'em apart afterward.

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4 hours ago, aessinus said:

Another suggestion, make your rings as a continuous spiral around the mandrel, like a big spring.  Gives you leverage from the straight stock & you only have the initial flat on the start where the end is clamped.  The rings will come out almost the same size that way.  Cut 'em apart afterward.

If I had a mandrel large enough that would be an excellent idea. 

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12 hours ago, Michael Cochran said:

If I had a mandrel large enough that would be an excellent idea. 

I've used an oxy/acetylene safety cap; just kept sliding it through the coil.

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