how to straighten drill rod?

Brute style old school...

Find something hard and flat like a chunk of train track or plain heavy steel.

Does not matter except it needs to be flat and heavy.

Simple energy transfer here...

You need a medium sized ball peen hammer as well.

Simply roll the round over the flat and the bow will feel obvious as a high spot.

Hold it such that it is "up" then gently tap the highest spot with the FLAT of the hammer a couple taps and roll it again.

It takes a lot of taps and the bow will move as you are causing stress relief as well as other actions

It will get real straight in not too long and the force of the taps need not be such to dent the rod.

Hold it against the flat material and if the flat stuff is fairly heavy the energy of the tap is reflected back into the round.

Straighten drill bits and bolts this way.

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If you need a 12" straight bar for use as a reference, I would suggest using a larger diameter. For that length, 3/4" as a minimum. Even if you can straighten the 3/8"bar, it takes very little force to deflect it.
 
Hi RJ,
this bar is going to be used on Sherline mill annd lathe. A .375 bar will fit up the spindles and a 3/4 inch won't. my interest is in dertimining runout in Sherline's tool holders and the collet system I bought. And this is more or less just idel curiousity.
 
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When MSC has free shipping you can get a 1.25 ft. Thomson linear shaft 5/8dia. for $13.00. JR49
EDIT: just read your post above, a .375" bar will be even cheaper
 
This how we straightened 1/2" turbine pump shafts, these were 10-16 feet long. put a set of v blocks on the floor and use an indicator to locate the high spot, rotate it to the top and press down on the shaft. Determining the amount of force and how far to deflect the shaft is a learning experience. We sure didn't whack them with hammers and such. We could get the shafts within .001 pretty easily. Determining where the bow is the hard part, if it is bowed the whole length it's a lot easier then having a kink in one area.
 
Hi JR49. I checked Thomson's shaft spec for straightness. They say .001 per foot when it leaves the factory. I'll report back, where my 36 inch is right now amnd how close I get it. I guess I'm assuming that the very small bow in it is distributed over the entire length and not here and there.

EDIT: after finding that MSC will sell a .375 x 12 inch Thomson shaft for less thjan $10, it looks like getting a couple of these is probably the best idea. It certainly isn't very challenging to inidcate any offset one of these might have and take it into account when I use it for appraising the geometry of one of my setups.
 
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I finally got a setup which could give me some hint of the amount of wow in the .375 drill rod.

Amazing. It was all in the ends. I set it in two v-blocks set about 24 inches apart and was unable to see any deflection at all using a .0001 graduated test indicator. I thought it wasn't touching the rod, but it was and 24 inches of the middle of the rod is so straight and round that it is beyond my equipment to detect any variation. It looks as if I can get two 12 inch straight (really straignt) rods out of this, or maybe better a 6 inch one and a 12 inch one. I haven't tried cutting them, but expect I'll have to grind through them with a cutoff wheel and then maybe clean up the ends.

This rod was bought from Grainger BTW and was not advertiesed to be all that special. I think I paid $7.50 for it.

Post Mikey edit: I found that this rod could be easily cut with a HSS cutoff tool - no sweat ... but some oil.
 
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I took an old printer from the dump. I was told they all have a rod straight to a few tenths. They were right. The rod is about 5/16 x 12 inches and dead nutz straight.
 
For future reference, modify a knurling tool by replacing the knurls with bearings or make a similar tool. Mount it on your tool post and center it up. Put the end of the rod in a collet or chuck and capture the other end in a cap with a fairly deep center drill on the other end. Use center in tailstock to support the cap and rod. Put lathe in lowest speed. With spindle turning, bring the roller tool up to the middle of the shaft and gently advance it, pushing the shaft over center. Check your dial or DRO, then back the tool off and check shaft. Advance tool again a little more than the first time. Back off and check again. Rinse and repeat until the shaft is running true.

Warnings: Only works on bowed stock, not kinked.
Use common sense, don't try this on a shaft that is big enough to overload your crossfeed screw.
 
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