Brass Rod Bender for Banjo Hooks

This is bender specifically made to put a very tight radius bend in 5/32″ brass rod for banjo hooks. The original design was modified from this:  http://www.micromark.com/universal-bender,8229.html  but required a few revisions to get the desired result. Finally, when I was able to force the rod into a tight radius bend, some would crack. I learned that they needed to be heated with a torch before bending, but don’t have to be bent while hot.

The key difference between this and the little universal bender (besides less “slop” and tighter-tolerance fittings) is the movable round die is a “cam” that can be pivoted (with a 3/4″ wrench) and forced tightly against the stationary die while the bend is being made.

This was also my first exercise with hardening O1 tool steel. There are tons of guides on line covering this topic so I won’t go into detail here. Having the working surfaces hardened may not be necessary for bending brass but I wanted to play with O1 steel and this was pretty forgiving applications for a first try. It went quite well.

IMG_5702

Here are the parts

Base plate cut from 3
Base plate cut from 3″ x 3″ x 0.25″ angle iron
Top plate cut from 0.375
Top plate cut from 0.375″ thick stock with 0.75″ square block  TIG’d on and tapped for the clamp screw.
Sliding block
Sliding block
Sliding block mounted with retaining screw
Sliding block mounted with retaining screw
Top plate mounted to base plate with 0.25
Top plate mounted to base plate with 0.25″ thick spacer plate and 0.5″ dowel pin inserted
Bending arm
Bending arm from 0.25″ bar. Has a 0.375″ block TIG’d on to support the dowel pin. Two holes were drilled but only the hole nearest the pivot was used.
Stationary die with 45 and 30 degree
Stationary die with 5/32″ diameter troughs cut 0.030″ deep in the clamp surface. Made from 1″x 0.5″ O1 steel bar and hardened. This can flipped over to use either the 45 degree or 60 degree side.
Movable eccentric cam die with 5/32
Movable eccentric cam die with 5/32″ diameter groove cut 0.030″ deep. Made from 1″ diam O1 steel and hardened.
Hardened face for sliding clamp. Hardened O1 steel .
Hardened face for sliding clamp. Hardened O1 steel .
Setup prior to bend
Setup prior to bend. What’s not shown here is that the base plate is supposed to be clamped in a vise.
All bit in place. The round movable die has hex flats for a 3/4
All bits in place. The round movable die has hex flats for a 3/4″ wrench so that it can be rotated with force during the bend to keep the rod tight against the stationary die.

Here also is a link to a CAD file on Onshape (a web based CAD tool). You may have to sign up to see it, but it’s free and is not a bad CAD tool. This file is not exact in that it doesn’t show threads in holes, nor the detents in the clamp pieces that hold the rod, and maybe some other small things forgotten.

Onshape – Rod Bender

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