Fixing the tools to fix the car

[MM54]

Yesterday while working on de-rusting the Chevelle, my (very lightly used) cheap (Kobalt) air cutoff tool decided to stop making torque - it went from fine to barely spinning and stopping if you touched the wheel to anything. Shortly afterwards, my nice IR die grinder (very heavily used) started acting up like it's got a bad bearing, it'll be fine then jam up, then be fine, etc. Bad day for my air tools.

Today, after some after-work christmas shopping, I tore into the cutoff tool. It came apart like any other (rotary) air tool, but my first clue as to the problem was when I pulled the motor out of the casing and was greeting by a tiny roll pin, just hanging out in there.

After a few moments trying to figure out where the heck it came from, I figured it out and simultaneously figured out what probably caused the loss of power. If you don't know how an air motor works, this next paragraph might will not make sense.

The rear plate of the motor, visible above, contains the inlet port, and the exhaust is on the sides. The rear plate is keyed to the body of the motor with... a roll pin. After investigating for a while, I found the front plate (see below) also host to a hole where the roll pin should fit - but why would it matter with the ports on the rear/sides? The front plate is also keyed into the body of the tool. This means that when the roll pin fell out, the whole motor rotated within the housing, misaligning the inlet port on the motor from the port on the body, and venting most of the inlet air straight to exhaust.

After figuring out how it should be aligned, with some cussing, I drove the tiny little roll pin into its hole. Hard.

After oiling (because in these the oil essentially is all of the internal seals) and reassembly, a quick test confirmed that it is now working properly, and possibly better than it ever has before, making me wonder if this pin fell out a long time ago, and it just took until now for the motor to shift in the housing enough for it to stop working.

If I have time tomorrow I'll take the die grinder apart. I doubt I'll find as simple of a fix therein, and based on the whole "time" thing I might give a cheapo die grinder a shot, since apparently a $100 one only lasts a couple hundred hours... I'll take a 50-100hr out of a $15 one I can grab locally for the sake of making progress on the car.

[jminer]

Good luck with the die grinder. Glad you were able to fix the first one, I’ll admit most modern tools have gotten cheap and good enough I just buy the cheap one if it’s not something I’m going use a ton. Ryobi battery tools and Kobalt back when I still used air tools.

[MM54]

@jminer Thanks. I got this cutoff tool a while back on clearance and was never very impressed with it, only would use it when absolutely necessary for clearance reasons.

The die grinder on the other hand I use whenever possible since it's so much more precise and overall practical than getting out the angle grinder for a task. The die grinder has hundreds of hours on it, yet acted up on the same day as this cutoff tool which had probably half an hour on it. Hopefully I can fix it. If not, a replacement at the plastic hell is $15 and a 5 minute drive

[Shop-Teacher]

@mm54 Well done! Air tools are something I know jack squat about.

[mocamino]

@mm54 This is 200-proof Oppo. And quite timely. I was using my cutoff tool (a cheapo Campbell Hausfeld) just the other day and experienced the very behavior you described here. I figured I was buying a new one (and still may). But your excellent post just told me how I may revive the old tool.

[VincentMalamute]

@MM54 Thanks for posting this. No, I have no idea how an air motor works. And I guess I'll keep buying the cheapo air tools.

[rctothefuture]

Part of me regrets always taking tools back to swap them out when they fail, as I'm sure the fixes are as easy as this.

Then again, a shiny new tool (from warranty) is just as rewarding in some cases.

[VincentMalamute]

Question: What is the difference between a die grinder and a cutoff tool? I have both and they look the same to me.

[MM54]

@rctothefuture said in Fixing the tools to fix the car:

Part of me regrets always taking tools back to swap them out when they fail, as I'm sure the fixes are as easy as this.

Then again, a shiny new tool (from warranty) is just as rewarding in some cases.

If this was under warranty from somewhere local, I'd have swapped it out too! I have to wonder how long it'll be before one of those roll pins comes out again, doesn't seem like a good design for something likely to vibrate and undergo a lot of temperature changes.

@vincentmalamute said in Fixing the tools to fix the car:

Question: What is the difference between a die grinder and a cutoff tool? I have both and they look the same to me.

A lot of people put cutoff arbors on a straight die grinder. My preferred die grinder is a right angle one, which makes it more ergonomic for most tasks but there are many straight ones (which are more "normal"). In terms of the difference, I think a cutoff tool will sometimes have a larger motor for a little more torque, and they come with a guard.

[VincentMalamute]

@MM54 so arbor mostly. Maybe torque. I forgot the guard.