drilling and tapping cast iron

[Battis]

I have close to ZERO experience with drilling and tapping. I have an old steam radiator - the threads that the side vent screws into are gone. I want to drill a larger hole and tap threads. Any hints or warnings about drilling and tapping cast iron?

[OS OK]

I've drilled and tapped lots of machinery with cast side frames, cast is soft...be careful starting the tap, you can wiggle the tap and ruin the top threads pretty easy. Hold vertical, hold steady and apply pressure to get the tap started until it can pull it's own way through.
I use a 50/50 mix of 'anti-seize and motor oil' for all taping needs except aluminum...go slow, turn the tap incrimentally in 1/8'th turns as you advance...if it starts feeling difficult, back the tap out, clean the shavings off then relube it and start in again.

It's no big deal...just go slow and when your done, you'll wonder why you were so concerned.
After a few, you'll find yourself using a variable speed drill motor to drill & tap...(you can bust a tap easily though, they are super hard and brittle!)

[Battis]

Good info. Thanks. At least the hole is already there - I just have to enlarge it.

[OS OK]

Make sure that you know the proper size drill bit for the tap size you use.

[Ballistics in Scotland]

There is a lot of variation between cast irons, but yours was chosen for one of the most demanding jobs it is used for, and one of the demands was being drilled and tapped the last time. It shouldn't be a difficult job.

Do you have the plug or fitting that used to be there? There are various ways it might have made the seal. It could have been a tapered pipe thread, which you can replace with a larger size. It is supposed to make an adequate seal without any kind of sealing compound, but if inconsistency of tooling dimensions or porosity in the metal causes leakage, it will be the kinered that drips, not floods you out. Just dismantle, dry it off, and apply a sealant rated for long service at that temperature.

Then there are straight threads, sealing by a washer or O-ring in either of two locations. The one I would hope not to see is at the bottom of the hole, which is partly closed by a flange. For this you would need a plug or second tap to start the hole, and a bottom tap to take the threads close to the bottom. Actually you can get by with one tap of any kind if you will only use it once, by tapping as deep as it will go, and then grinding back the chamfered tip.

A much easier one is the fitting which seals on the outside, with a washer which remains visible between the radiator and a flange on the outside end of the fitting. You can convert the former style into this. But make sure the washer is hard and thin, or it will be squeezed out of the joint.

[Battis]

I have the vent that was there - new vents have the same size threads. The local hardware store told me the size drill and tap that I need for that vent or a new one. One of the questions is whether or not there's enough "meat" left for the new, larger bushing.
Parts to do it myself with no guarantee of success are less than $50. The plumbing & heating company that I use will charge me (probably) $150 - $200 to try it, with no guarantee of success. I figure that if I try it and it doesn't work, I can JB Weld the vent in place - the problem will be if that vent ever has to come out again.

[bbogue1]

I'm throwing in my 2 cents worth. I've been in the position a few times in my life where I had to drill and provide threads to attach something to an engine block. I cleaned out the hole by drilling a hole and put a helicoil in there. Each helicoil has a size hole it likes best. Is this a viable application in a radiator?

[Battis]

Someone mentioned a helicoil today (he works with pipes at nuclear power plants) but all I could do was stare at him with a dumb look. When it comes to plumbing, I'm like a housewife in the 50s. June Cleaver...
I just bought the drill bit, tap and bushing, and the store is going to loan the tap handle to me when I'm ready. If I mess it up, at least I'll have a larger hole for the JB Weld.

[JimB..]

Normal warning about enlarging holes, I find it easy to bugger them up with a hand drill, especially larger holes.

[country gent]

Drilling it out and tapping to a larger size shouldn't be a problem if there is room in the casting for the bigger thread. You can do this with a hand drill you need to be very steady and solid doing it. A drill cutting one size bigger may want to grab. Another trick is a second set of eyes back and watching the drill to maintain true alighnment as this is hard to see while running the drill. Put a nice chamfer on the hole before tapping, this helps the tap to start straight and true. Use a good cutting fuid on the tap and turn 1/8 turn and back up. One nice thing is cast iron is it dosnt normally form long stringy chips. Clean hole often with canned air or an air compressor. On a tapered pipe thread depth is important to seal check often and make sure it has the right left to form the seal.
Threads can be made removeable with JB weld easily. Just like bedding a rifle coat the part with 2-3 coats of wax and let dry. This is a release agent and the JB Weld sticks to t not the part. Done right threads with JB weld are 100% not the normal 75%-80% so they are snug fitting. This works well for things that arnt disassembled a lot.
I have done thread for powder measure stands like this with JB weld and its a good snug fit. Wont take the same torque as steel threads but it works and allows for a simple timed thread. Be sure and let the epoxy cure fully for several days before use. Most epoxies cure to use in 24 hours but may gain strength over several days after that also. We had a epoxy at work that cured in 24 hours but didn't reach full strength until 7 days time. If you go the JB weld clean the area good with solvent and heat after to burn oils and other things out of the cast iron.

[454PB]

Cast iron is tricky to drill because it tends to "grab" the drill bit. It helps to use some kind of lubricant and take care to control the speed of feeding the bit into the cast. For tapping, go slow, clear the hole and tap frequently, and use a good lube. Surprisingly, the Lee resizing lube woks very well as a tap lube.

[country gent]

We would grind production drills with a little less relief and a small flat on the face edge for cast iron, this help stop the grabbing and improved the finish. Sometimes a small change in geometry makes a big difference. The droills were ground closer to what you woulduse in brass than steel.

[Ballistics in Scotland]

The helicoil system involves a sort of steel spring. But the wire isn't round. It is a sort of diamond section, forming a thread on the inside to take your bolt (in this case your vent fitting), and on the outside to screw into the hole you have tapped oversize. Usually it requires a tap in a special helicoil size.Yolentyu can see plenty of pictures on eBay, and since it has been around a while there are probably copies under other names.

It might be very good for your job. But I can see three possible snags:

I don't believe they make helicoils for tapered pipe threads.p

They won't seal on the threads alone, and I am doubtful even about sealant in that application.

They might be stainless steel, but I am doubtful about the sort of light plating, in this application, which would be fine in engines etc.

They might be usable with a system that seals on a washer, especially at the bottom end of the hole, so that the steam or water doesn't actually reach them.

[NyFirefighter357]

I am a heating technician, is this a steam or hot water application? Before you drill it out try a chase tap and re-tap the hole. You might be able to put a close tapered nipple and coupling in tight and add your "vent". Vent inplies steam system, if so it's only holding 1-2lbs pressure. If you have to go up a size it shouldn't be a problem & it will drill easily but do not use oil on the bit or tap use soap. Seal the treads with Teflon you'll be fine. H/w system only holds 15lb max 30psi before relief valve blows. Heli coil will work too. Message me if you want to discuss further. Jay

[Rusty W]

I've had better luck w/these. http://www.timesert.com/

[frankenfab]

Drill to 80 or 90% thread if using a hand drill.

JB weld cann also be amazing, depending upon the stress load it will receive.

[MaryB]

I have filled bad holes with JB weld, drilled for the original size tap thread, tapped it back to original and had it last 25 years... did it on a friends hot water radiator system. Make sure to use acetone or similar to degrease the hole well before filling.

[Battis]

It's a steam system. Right now the vent is held in place with Teflon tape wrapped around the vent's threads. It's not in there tightly but it's holding.
I was all set to drill the hole earlier today, but decided to turn off the radiator at the valve in case I messed things up. Yeah, great idea. I turned the round valve and it snapped off. I used a pipe wrench to turn the body of the valve but it's frozen in place. So, the radiator is on, as it has been for a long time, but I'd still like to be able to turn it off, which probably means replacing the value fixture. I called my heating contractor and they can be here...in a week. I called another company but they haven't called me back.
Anyhoo- I've been heating with wood since 1984 so it's no big deal, though I do like that steam heat. I'll leave it as it is, with the vent held in place by the tape, until the contractor gets here. I might swap it out with another radiator from an unused room.
Thanks for all the advice and tips. Believe me, I read and re-read each post. Chase taps, Time-serts, JB Weld - it's all stewing in my brain.

[Ballistics in Scotland]

I am a heating technician, is this a steam or hot water application? Before you drill it out try a chase tap and re-tap the hole. You might be able to put a close tapered nipple and coupling in tight and add your "vent". Vent inplies steam system, if so it's only holding 1-2lbs pressure. If you have to go up a size it shouldn't be a problem & it will drill easily but do not use oil on the bit or tap use soap. Seal the treads with Teflon you'll be fine. H/w system only holds 15lb max 30psi before relief valve blows. Heli coil will work too. Message me if you want to discuss further. Jay

Ah, this counts as advice from the horse's mouth. Most of us have been talking about threads and materials. All I know about steam is about engines, with loose fittings flying across the room.

That low pressure does make thread chasing and/or epoxy more convincing. I like the look of the Timesert system too, if it is available in a size to fit the vent.

[Battis]

I had thought of using JB Weld or another epoxy to hold the vent in place - now that I know there's only 1-2 lbs of pressure, I'll definitely try that. The fact that the vent is being held in place with only Teflon tape puzzled me - now I know about the low pressure. And, I never knew how strong JB Weld actually is.
Sawzalls, duct tape and JB Weld - the universe's gifts to homeowners.