How to straighten bent 8mm metal shaft accurately on the cheap, DIY Tantillus 3D printer.reprap

I purchased some cheap 8mm shafting from China and it all turned up bent so I came up with a simple but accurate way to straighten them quickly with low budget tools. I used a DTI (dial test indicator) and some skateboard wheels and bearings.
Results were as good as plus and minus 5 microns. The worst case was plus and minus 10 microns. Way good enough for a 3D printer

[@Robonza]

Thanks, I worked out the reason this works so well. It's because the wheels flex and add compliance to the bearings. This means the shaft can deform in a relaxed way. I had some friends come over and do their Tantillus bits too.
I just need to get a my heated bed finished now!

[@tastymacification]

Exactly what I needed to know. Except I don't have any of the items your using.

[@thusarix121]

Ryan Walker,you, i like you

[@cristian_prundeanu]

Thanks mate. Exactly what I needed.

[@hauptuhrdotnetblog6700]

Very interesting. Yesterday my clock fell on me. The invar pendulum with a 7KG bob fell towards me hit my head and bent slightly. Clock now won’t run. Not happy Jan. It’s a much longer rod but this could be the solution. Thank you.

[@j_sazabi6637]

Very nice. Thanks for sharing!

[@keithrobinson5594]

Great tip many thanks

[@blvck_mvgic]

Did the same but without a DTI, just rolled my bent bars on the table and marked the flexing point with a pencil, then pried the bars carefully and slowly to the point they didn't look bent and rolled nicely.
Thank you.

[@Robonza]

Nice! that works too if you are not after super precision

[@booboo699254]

If you have a granite slab or a sheet of mirror, that works well... I used a sheet of very thin paper as a filer guage.

[@KamalAliJacksonMS]

Perfect. Thank you.

[@TheCumulusClimber]

great tip, thanks.

[@stjiu]

Great method, glad to know it. Thanks heaps. :-)
This is not too bad, i bought a cnc kit from CNC Fusion in USA, their ballscrew is bent for about 2mm over the lenth of about 400mm and worst, the bearing housing is not squared to thr axis. I supposed they can do better than china made part.

[@marklimbrick]

I have a slightly bent 8mm shaft, 400mm long. 0.25mm centre gap when placed on flat plate. Cannot get linear slides to run smoothly when fixed to carriage. Used three wooden wedges (half clothes-pegs) as a sandwich between wood boards. In a big metal vice, I can deform up to 10mm+, but the shaft will not take up a permanent correction. If these shafts are in any way through hardened chrome steel? (it may be possible even though from Ebay). I've had no problem bending wrought iron angle and mild bar into exact curves. I'm considering that this bar will just snap at some point, it's behaving like a pretty good spring at the moment.

[@Robonza]

Tricky, if its no good maybe try harder and if it does break then no loss. You could try annealing it. Heat it up really hot and cool it really slowly, this should make it easier to bend.

[@marklimbrick]

Thanks, put so much bend in it the wooden wedges crushed. Now it is straight enough. So it is probably a really good through hardened and tempered chrome steel shaft. Tougher than my expensive spanners.

[@meljazz]

would this work for 2mm thick rods?

[@JayZoop]

Is this mainly for gradual bends of a rod, vs maybe a kink in the rod??

[@Robonza]

It will work on a simple curve but if you got a kink it is probably too damaged

[@elobiretv]

Thats the same sort of thing people use to straighten arrows.