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Techtchr
04-23-2003, 11:23 PM
I was asked to make a part for an old Banjo. Original parts are NA, and aftermarket replacements are not the correct size. As you can probably guess, the part not only has to be functional but "pretty". I will probably chrome or nic plate when done.

Imagine a piece of right angle steel bent into a 12" diameter hoop. The angle is aprox. 1/2" on a leg and 3/32 thick. Picture a top hat or a flange type shape. The machines I have to work with are a 10" SBend lathe, O/A Torch, Mill drill, band saw.

I thought of trying to have someone bend a piece of angle for me, But the pretty part of the equation didn't seem right. I also thought of doing this out of multiple pieces and welding or silver soldering together. I also thought of spinning this shape out of a piece of sheet stock, but my lathe is too small. May be able to borrow a friends though.

Any fabrication techniques would be greatly appreciated.
Thanks,Matt

Thrud
04-24-2003, 01:40 AM
Matt

It would have been bent and then roll formed. Heavy brass is easy enough to form and can then be silver soldered into an actual hoop. Polish it up and laquer it or have it Chromed - should look spiffy!

It could be cast to shape, but I do not think that is the way it was done - too much work. It could also have been beaten to shape as a silversmith would do.

DR
04-24-2003, 10:40 AM
The part was probably made using drawing dies. One stroke of press, blanked the ring and formed at the same time. Fairly expensive dies designed for each specific part.

There are ways to cobble up some simple dies to do this on a onesy-twosey basis. See the Bonny Doon Engineering website. They make presses for jewelry and other small objects. Their techniques could be adapted to make what you need. You would need some kind of hydraulic press, the dies could be made on your lathe.

Mike Burdick
04-24-2003, 11:50 AM
Matt,

With the tools you have make a small three roll bender. Groove or flange the rollers (depending whether the angle's flange is toward the inside or outside) a little larger than the thickness of one leg so the angle will have a nice flat bend when rolled. The top roller can have a bolt head welded to it for turning with a ratchet and needs to be adjustable (up and down) in order to get the correct radius. The bottom two rollers need to be fixed in location but capable of rolling....you get the idea.

If you make a nice roll bender you'll also find many other uses for it in your shop.


[This message has been edited by Mike Burdick (edited 04-24-2003).]

Dave Opincarne
04-24-2003, 07:29 PM
I'd opt for soldering or brazing and put my effort into cleaning up. Silver solder in sheet form would seem ideal.

-Dave

Techtchr
04-24-2003, 08:15 PM
The top hoop is just a big ring. The bottom hoop which is the one i need to make is the right angle shape. Due to the extra decorative holes cut into the flange on similar after market hoops I'm guessing they were stamped out in some way. I know I can make this part, I just don't want to do it the long way when I could do it quickly.

Thrud, I contemplated brass, but due to the fact that the bolts that hold the banjo head attach to this bottom hoop, I didn't think the brass would be structurally good enough, but I didn't take a magnet to the other hoop to see if it was a ferris metal or not. Will check it out. Brass would be easier. Thrud/Dave,
The silver solder idea is one I had thought of also. I'm good at polishing and making things look spiffy. ooooh shiney http://bbs.homeshopmachinist.net//smile.gif

DR. I've seen the bonney doone site a great idea. Have to borrow a hydraulic arbor press. I think I'd have to borrow a larger lathe to do the dies though. Was trying to stay with my own machines.

Mike, it's 8:00pm here, and I've been at school since 6:30. Brain Drain. The roller idea was one I'd had in the back of my brain for other projects, but I've never done it before, and never knew how to get started. Going to have to read your post a couple of times before I fully understand. I'm taking rt. angle stock and bending it into a hoop with three rollers right? Place in a triangular spacing with two rollers as guides, and one drive roller? (slip roll type arrangement?)How do you adjust tension for stock thickness and diameter? Ellipse on the roller shaft?

Thanks for all of your replies. As usual you've been of great help.
Regards, Matt

Mike Burdick
04-24-2003, 10:01 PM
Matt,

The rollers have a right angle groove cut into them so that one leg of the angle iron has a place to fit, the other leg will be flat on the roller.

The 'hoop' is formed by putting down pressure on the material that is placed between the other two rollers. This will induce a slight bend and, when rolled, this continious bend will form a perfect 'hoop'.

I don't have the ability to post a sketch but a metal roller is very simple to make. I have even seen people make them using an ordinary bench vice.

Paul Alciatore
04-24-2003, 10:15 PM
Just a dumb thought, but you did mention that there are some similar hoops available, just the wrong sizes.

Could you get one that is just slightly larger and cut a small piece out to bring it to the corect diameter. Then silver solder or whatever to rejoin the loop. An overlapping or staggered (Z) joint would make it stronger. Two slightly smaller ones may also work but would require pieces and two joints - more work.

darryl
04-24-2003, 10:33 PM
If you roll one per suggestions, use a longer piece than needed, say 4 ft. Roll about 400 or 450 degrees, so it becomes an overlapping coil. What you want is to have to stretch it out slightly to achieve the proper diameter hoop. Then mark the overlapped ends for cutting, removing some metal from each end to come to the final length. This way, you get rid of the incongruous bends at the ends of the piece, and will have a smooth curve at the junction, as well as around the hoop.

WJHartson
04-24-2003, 10:52 PM
Have you tried "ODE Banjo Company" for the parts. They have lots of parts available. When I built my Banjo I got the parts from them.

The brass ring would have the structural strength needed to tighten the head. There is not that much tention on the head of a banjo. The screw lugs are used to evenly tension the head over the tone ring. The multipal clamps spread the load out.

You could make the part by bending and angle and using a stretcher to form the ring. I assume that the leg of the angle is out. If it is in use a srinker.

Hope this helps.

Joe

Stepside
04-25-2003, 10:02 AM
I have built a three wheel roller as described--Everthing considered it should work for the hoop. It is correct that you need to roll more than 360 degrees as there is an unbent part on each end of the stock. I use the roller for curved to gates and fence pieces as well as rose arbors. Very usefull tool as mine will roll up to 2 inch square tube.
I have also built a "bonny-doone" press. It would take some serious tonnage to build the described part.
If I were to build the part I think I would build a hammer form out of MDF or similiar material. You should be able to spin all the hammerform parts on your lathe. I would probably take several steps of hammering and annealing to get the desired shape.

Techtchr
04-27-2003, 07:14 PM
Thanks again for the great replies. The shimming of an oversized hoop is somthing I hadn't considered. Sounds like a good idea. When I get the time I will build the rollers, as I've had other occasions to use such a device. I would like to get into building ornamental Iron. Hammer form and spinning was one of my initial favorite ideas, but the lathe capacity is a problem. I am glad the brass will be OK, as I'm much more familiar with working brass in the ways described than steel. I was gone all weekend for training. When I get back on the banjo project I'll let everyone know what I did.

Thanks, Matt

DR
04-27-2003, 10:09 PM
[QUOTE]Originally posted by Stepside:
(snip)I have also built a "bonny-doone" press. It would take some serious tonnage to build the described part.


I see some one else has a hydraulic press for forming metal.

The maximum tonnage to draw form this part is easy to figure. The max tonnage is always less than the tonnage required to shear the equivalent material. The shear tonnage would be pi * 12 * 3/32 * 35000 or around 61 tons. If you started with a ring of material rather than a round blank I think the tonnage would be significantly less, probably half or less than the shear tonnage.

shorty
04-29-2003, 08:12 PM
How about a drum head ring from a set of drums?? Try phoning "Drums Only" in Vancouver Canada. They make their own line of drums called "Ayote" (after Doug Ayote)
the might be able to steer you to whoever fabs their rings for them and then just order the size you need....I realize this takes out all the fun of fabbing a piece but.... http://bbs.homeshopmachinist.net//smile.gif

brunneng
04-29-2003, 08:22 PM
For an idea of how simple the roll formers can be made check out this little one at micromark:
http://www.dxmarket.com/micromark/products/81356.html

Man, if I ever run out of projects I can pull out their catalog of mini-tools and I can make that, and that, and that, etc...

They also have a sweet little bender to copy:
http://www.dxmarket.com/micromark/products/82819.html