Making an M18x1.5 thread cleaning tap

[MrWhoopee]

M18x1.5 is probably not commonly available. Get a 3/4 grade 8 bolt, cut off the threads, turn and thread, gash some "flutes" in it and go use it. Don't mess with trying to heat treat it. It's probably not necessary and would likely make the "tap" softer. You're not cutting threads, just cleaning them out.

 

[ChazzC]

M18x1.5 is probably not commonly available. Get a 3/4 grade 8 bolt, cut off the threads, turn and thread, gash some "flutes" in it and go use it. Don't mess with trying to heat treat it. It's probably not necessary and would likely make the "tap" softer. You're not cutting threads, just cleaning them out.

Available from McM, and you only need to buy one: M18-1.5 x 40mm G8.8 around $13 including shipping.

 

[ChazzC]

If the bung is stainless (the only way to build an exhaust system) then a chaser might really make a mess of things- use a tap. If it's steel or cast iron, it'll be fine. You're going to want to use sensor-safe anti seize for certain if chasing removes any passivation to save trouble down the road.

If it got hot enough to mess with the threads, any passivation is toast and he’d need to do an acid treatment afterwards to restore it.

 

[twraska]

I screwed up the other day working on my Bronco project. I welded in a O2 sensor bung to my header reducer and got it a little too hot. The threads look ok but have kind of a mill scale look to them. I could probably force the sensor in, but I would rather clean up the threads.

So, my plan is to make a cleaning tap. I'll turn some stock to M18x1.5 and then mill 3 slots length wise and then heat treat. Since I have never did any heat treating before (I'll watch some YouTube first) will it distort the threads? The other thing is, I'm not sure what I have for stock, will 12L14 work? Other than that, I probably only have mystery metal. Or maybe a larger US bolt that I could turn down.

I don't think it will take much to clean up the threads, maybe even turning an M18x1.5 and a couple slots would do it without even hardening.

I’ve had good luck just cutting some grooves in the threads on a grade 8 bolt.

 

[MrWhoopee]

Available from McM, and you only need to buy one: M18-1.5 x 40mm G8.8 around $13 including shipping.

Yes, I was thinking about the suggestion to use a bolt.

 

[ChazzC]

Yes, I was thinking about the suggestion to use a bolt.

A bolt is what I found:

 

[MrWhoopee]

A bolt is what I found:

View attachment 490915

Once you pay shipping it's cheaper to buy the tap from Amazon.

Amazon.com

 

[Just for fun]

Well, I had to look up passivation. And yes, I would say that the passivation is probably toast.

The exhaust system is just mild steel.

Thanks for all the tips. The Bolt thing would work I'm sure, if I could find one locally. So far, no joy finding one locally.

If I can't find a bolt locally or if making one doesn't work, it would be cheaper to weld in a new bung.

Off to the shop.... I'll report back later.

 

[Just for fun]

Success!

I cut an M18x1.5 in a piece of mystery steel, cut 4 slots in it with a cut of wheel. And twisted it in with a pair of vice grips, LOL. It worked, I'm able to twist in a plug all the way by hand.

Like I said it didn't need much, just a little touch up.

Here is what it looked like before I cleaned it up. It doesn't look any different now.

 

[WobblyHand]

Made something similar to chase printed threads in an uncommon size. Wasn't worth buying a tap for it. In my case, I single pointed the thread on the lathe and then used my mill to cut some grooves or channels. Spent a bit of time clearing the swarf and burs attached to the edges of the threads, but it came out fit for purpose. More than good enough for occasional use.