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So, my car has a bad case of the eccentric bolts being rusted solidly into the rear toe arm. Best practice repair is sawzall through the bolt where it goes through the outer bushing, then pop the bolt head from the mount, throw away the old toe arm (with eccentric bolt solidly rusted in side) and replace the whole arm assembly (and bolt). I reckon that I should be using cutting oil as hardened steel is going to take awhile. Cutting oil is nowhere to be found in the local big box stores (employees have said that they get a LOT of requests for it though). Can I get away with something like WD-40 or will I just end up lighting it on fire and causing myself even more problems? I've heard of people doing this procedure dry, but it can eat a whole pack of blades that way.

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migrated from Mar 13 '14 at 21:42

This question came from our site for contractors and serious DIYers.

So, my question about cutting hardened steel goes to mechanics just because these bolts happen to be on a car? That seems like a bad move. What about people looking for advice about hardened bolts in other applications? The answer will be the same. I really think this should have stayed in DIY. – Brian Knoblauch Mar 13 '14 at 21:52
I would think you could use some 0W20 engine oil, but I'm not a machinist. Also, ensure you are using a fine toothed sawzall blade. Just my suggestion and not really an answer. – Pᴀᴜʟsᴛᴇʀ2 Mar 13 '14 at 22:22
Yeah, I picked up a pack of 6", 14 TPI blades. I think that should be fine toothed enough. – Brian Knoblauch Mar 13 '14 at 22:58
Yup, that's what I'd use. WD-40 would be too light and would catch things on fire, I'd bet. Though, if enough was used, it probably wouldn't be an issue. – Pᴀᴜʟsᴛᴇʀ2 Mar 13 '14 at 23:05
@Paulster2, truly. Fire bad! – Bob Cross Mar 14 '14 at 23:56
up vote 3 down vote accepted

According to this Wikipedia article, WD-40 should probably work good. It also says to stay away from multi-weight oils (due to the detergents and other factors), but single weight oils should work just fine (like SAE10 or 20, if you can find them). According to the article, there are four things which cutting oil does for you:

  • Keeps the workpiece at a stable temperature (critical when working to close tolerances). Very warm is OK, but extremely hot or alternating hot-and-cold are avoided.
  • Maximizes the life of the cutting tip by lubricating the working edge and reducing tip welding.
  • Ensures safety for the people handling it (toxicity, bacteria, fungi) and for the environment upon disposal.
  • Prevents rust on machine parts and cutters.
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I've got a whole big monster can of WD-40 that came with my house, and I don't use WD-40 for anything else, so I'll (carefully) give it a shot! I also have since run across a video of Chip Foose advocating WD-40 as cutting oil. – Brian Knoblauch Mar 14 '14 at 19:33
@BrianKnoblauch ... Chip is the man. I'd say go for it and not worry too much. Just keep it wet and lubed. – Pᴀᴜʟsᴛᴇʀ2 Mar 14 '14 at 19:35
As a followup, WD-40 didn't cause any problems. We couldn't keep a good flow in the location so it was a drier cut than we wanted, but no issues encountered. Had to stop multiple times to let the saw and blade cool. Total of 3 hours and 10 blades to cut 2 bolts, but it's done (the cutting anyways, unfortunately I have AWD which parts aren't available for so now we need to get spacers made to make a FWD replacement part fit)! :-) – Brian Knoblauch Mar 24 '14 at 10:57

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