Any tips on how to straighten a 1/4" bent rod?

I've got a couple older newall scales/rods for a dro. They are bent enough that they wont slide freely thru the reader. OK at some points there are small kinks that completely stop the sliding. In some spots when it starts to bind I can twist it and it will slide again, which wont work when every thing is clamped on my tool and cutter grinder.

I've tried to roll on a flat table and tried to bend down the high spots. I've tried to start at one end and work towards the otherside. I'm not having any luck.

I've been thinking of trying to put the rod in a long vee block and pressing at the high spots and rolling.

I'm going to call the local archery shop tomorrow to see they can straighten arrows.

Thanks in advance.

Rosie

Rosie,

If I remember correctly the Newall units actually are a hollow tube with balls inside. If this is actually how they are made I would think that a bent rod/tube would not be repairable.

Stuart

For a job like this I would spin the tube between centres and use a dial indicator to check the runout (AND the phase angle of that runout) at regular stations along the item.

Regarding the phase angles, pick the worst runout and 'rotate' the other angles to reduce that worst one to zero. Think of that runout as lying in the xy plane.

Then remeasure the runouts, in a 'near enough' way so that, for each runout, you record one component on the xy plane, and one on the xz plane (at right angles to the former)

These values can then be used to prepare two drawings (just on graph paper, doesn't need to be fancy) showing the bent shape in plan (xz) and elevation (xy)

Exaggerate the y and z axes ten or one hundred times in comparison with x (like the gradient profile of a railway line)

This will show exactly where the bends are along the tube, and also show their 'character', such as how localised they are.
Armed with this (and with the 'x' direction clearly marked on the tube) you should be able to decide how close or far apart the V blocks need to go in respect of each kink.
Put some thin rubber on the faces of the V blocks so they don't mark the tube, and push (say in a drill press) with something equally padded, at the apex of each bend, in each of the y and z directions,

If, in some cases, the apex of that particular bend is in the same place for both y and z components, just rotate it to find the high spot, and press in that compound direction, until the tube has minimal runout when spun in the blocks.

If it's bad, you may need to remove the balls (the act of pressing them out may help push out a few kinks) and fill the tube with cerrobend (low melting point alloy)

I've not done this repair with a Newall, so I'm only assuming it is possible to strip the balls out without scrapping the unit.

The archery shop idea is a good idea. They have little straightening jigs with dial indicators on them to gage how far you are bending them.

Like this - Arizona Archery

I would remove the balls. Find a close fitting size drill rod that will go past the kinks such as they are. Use a lead hammer to beat the tube on top of the wrinkle, lessening the kink. Then step up to the next size drill rod that will pass and hammer it some more. After that, then you can do the final straightening. This could make it slightly larger than it should be, so then take the tube and pull it through a round die to reduce it and tighten it back up.

Allegedly the correct calibration of Newall scales is depends on having the correct preload on the balls inside the tube. Removing the balls, or even straightening the tube, may affect things. Whether significantly or not is another matter.

Clive

Just a note from the archery(was on pro circuit for 10 or so years)side,once you've straightened a cpl thous. arrows you kinda get the hang of it.No kidding,you can get a much better feel starightening by hand because the aluminum will let you know when its "back home" or straight.This feel isn't there when you use the jig.The jig takes longer,consequently we almost always do it by hand/eye.

The arrow jig's biggest asset is in showing how the placement of support rollers affect the straightening action.IOW's the bend don't always have to be equal distance between roller supports.By its use you'll learn,hopefully sooner than later,bends aren't usually symetrical.

Wood arrows are straightened similar to straightening steel beams and such.Albeit Fred Flintstone'ish,we use an section of antler and rub the backside of bend creating heat which if you hold your mouth just right,works like majic.BW