Tapping a radiator

foresthillsjd

in moving all my radiator vents to the lower position on the radiator, I realized most of my radiators just have a dimple where the vent is supposed to go.  I have a 1/8 tap, size R bit, cutting oil, variable speed drill.  What do I need to know?

mattmia2

Might use a couple sizes of bits and work your way up. Try not to get the oil in the system, enough of it could cause the boiler to surge. Maybe wipe it off with a rag then some solvent when you are done and use it sparingly. Be gentle withnthevtap and reverse it to clear the cutt8ngsvevery half turn or so. If it starts binding reverse it at least 1/4 turn and go in some more. You dont want to break the tap off in the hole, they are hardened so they are fairly brittle. A few spare bits is a good idea too. Maybe get to near the final size with a common fractional drill then ream it to the final size with the r drill.

JUGHNE

You are lucky to have the dimples.
Easier to drill and tap the cast iron than doing the same on a steel plug that is a 100 years old. IMO

Having a "T" handle for the tap helps insure tapping remains perpendicular to the radiator.
A bit of an angle is very amplified when screwing in an air vent.

ethicalpaul

Try for perpendicular, but if you must be off, make sure it's sloping slightly down toward the radiator and not up toward the radiator

foresthillsjd

@JUGHNE like this kind of handle? https://www.amazon.com/Starrett-93A-T-Handle-Tap-Wrench/dp/B0006J4DNK/ref=asc_df_B0006J4DNK/?tag=&linkCode=df0&hvadid=312407216551&hvpos=&hvnetw=g&hvrand=11626338296323225898&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9004400&hvtargid=pla-434687592209&ref=&adgrpid=62201427276&th=1

delcrossv

foresthillsjd said:

@JUGHNE like this kind of handle? https://www.amazon.com/Starrett-93A-T-Handle-Tap-Wrench/dp/B0006J4DNK/ref=asc_df_B0006J4DNK/?tag=&linkCode=df0&hvadid=312407216551&hvpos=&hvnetw=g&hvrand=11626338296323225898&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9004400&hvtargid=pla-434687592209&ref=&adgrpid=62201427276&th=1

Yes, exactly.

JUGHNE

You need to check the size of the square shank on your tap.
Perhaps the General set shown below your ad would suffice.
You just need it for a few uses.
(at least the sizing guide is made in the USA)

The Irwin fixed handle is good but 12.25 long, you need at least 6" of swing area.

ethicalpaul

But don't buy the starrett one unless you hate money

Here's the 1/8" NPT tap: https://www.amazon.com/Drill-America-POU1-8NPTW-DRILL/dp/B01M4RXY21/ref=sr_1_3?crid=16ZB96QSSOZSF&keywords=1/8"+tap+npt&qid=1642180330&sprefix=1/8+tap+npt,aps,77&sr=8-3&th=1

I found and bought this metric set some time ago that mysteriously contained 1/8 NPT but it's no longer available...maybe there's a duplicate one out there: https://www.amazon.com/gp/product/B00AHV3DWY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Jells

Semi-pro machinist here who just tapped 3 today. I found the best way to square it was to start the tapping with the drill till it stalled, then switch to a handle. Much easier to square a drill, and my biggest T handle wasn't large enough for the tap, I had to use a clamp on handle.

Don't bother drilling in stages, but grinding the cutting edge of the bit flat to a 'zero rake' works very well with cast iron (as well as plastic), it doesn't grab. The idea is to scrape not 'dig in'.

I was doing 'main vents' on the top floor rads, installing a vent right above the spud to speed the clearing of the riser but not affect the speed of the rad. We'll see, but the riser line I did this to a few years ago is the one that heats consistently.

Hap_Hazzard

I agree with @Jells, but another technique that works is to hold the tap in the hole by pressing on the end of the T-handle with your left thumb and rotating the arms with your right hand until you get the first few threads cut. Then the rest is easy. Also, a little grease on the flutes of the tap will catch most of the chips. You need to take it out and clean and re-grease it several times because you're threading a parallel hole with a tapered tap, so you make a lot of chips.

foresthillsjd

@Jells that’s super helpful.  I dont have a grinder. Would an approach like this using an abrasive stone work? (I’ve copied it with time stamp to the correct part of the video)

https://m.youtube.com/watch?v=pAngKHIZgyA&t=54s&pp=2AE2kAIB

Jells

foresthillsjd said:

@Jells that’s super helpful.  I dont have a grinder. Would an approach like this using an abrasive stone work? (I’ve copied it with time stamp to the correct part of the video)

https://m.youtube.com/watch?v=pAngKHIZgyA&t=54s&pp=2AE2kAIB

Yup, that's it exactly.