Broken tap in mast

[Red Horse]

Best idea is to use a demel as suggested. Drill out to next size for 1/4 tap. Mast sections are quite thin, i doubt a helicoil would work. you want a nice clean hole so you don't set up a stress riser. Use tap magic as suggested or diesel for a lubricant.

[GrowleyMonster]

Pounding the tap into the mast COULD work. It could also create small cracks in the area on the mast. The threads of tap and tapped hole will not let go to axial force very well.

The trick to using a small hole saw here is not using a centering but in the arbor, or using a broken off stub of a bit, or adjusting so that the central bit is shy of the holesaw teeth by the thickness of the mast plus protruding length of the broken tap... IOW you want only the outer saw part of the hole saw contacting the mast, and the broken stump of the tap is holding the hole saw centered. This will of course destroy that hole saw. Or maybe not. This, Milwaukee 5/16 in. Diamond Plus Mini Hole Saw-49-56-0507 - The Home Depot might work for you. It might even capture the tap and you won't have to fish it out with a magnet.

Having ran aluminum crewboats in my misspent youth, I can tell you that steel tools laying on top of often wet aluminum, especially if wet with salt water, is a recipe for electrolysis like no other. Eventually you will have a hole the exact shape of a broken tap. So if you pound it in, you need to get it out before very much time has passed.

Grinding it flush with a dremel and the 1/2" mini sanding drums and then coating with JBWeld or some similar epoxy immediately after grinding would be another option. Within minutes, aluminum will begin to form an oxide coating so get it on quick. Let it set, then smooth the surface with sandpaper. I use these sanding drums a LOT. They cut quick and are cost effective.

[catsketcher]

I broke a 6mm or so tap in my mast when I was making it. It was lying down on the ground at the time. I went and asked a friend what to do.

He came with a small punch and hammer and tapped it and worked at it for a while. In the end it shattered and we pushed it through. I then retapped the same hole. I may have gone up a size but I don't think so, I can't remember now.

I would give this technique a go first. Get somewhere where the boat won't move, in the marina would be good and get a nice bosuns chair. Get a good supply of swear words ready and try and break up the brittle tap before you start cutting.

It took Colin about 10 minutes to remove the tap. He knew what he was doing but it didn't seem like rocket science.

[Captsteve53]

Forget totally about trying to drill it out, normal hand taps are as hard or if not harder than drill bits usually around 60-66 RC (Rockwell range) and for non machinists that's damn hard (Tungsten is 68-72 RC and top of the range).

Previous threads re trying to break it up or smash it through the hole is in reality your only option at this stage(unless you can find a portable spark erosion machine?)

When re tapping try to use commercial tapping lubricant or at least kerosene which helps with Aluminium

Cheers Steve

[Blue Stocking]

Originally Posted by oleman

A broken tap in steel is bad, a broken small tap in aluminum is IMPOSSIBLE.
The aluminum galls around the flutes of the tap, an extractor of a #10 will not remove it. It will just break the drive pins.
The only real removal technique would be to remove the mast and take it to a shop with a milling machine and us a carbide drill and drill it out OR the shop could have an electric discharge machine that could remove it.
A common sense solution would be to drive it on threw and fish it out with a magnet or grind it off level with the surface and seal it from the weather.
Forget attempting to use the carbide bit in a hand drill you will immediately break the bit.

Exactly !! Many think that because aluminum is softer the ferrous, one can merrily crank a tap through the wall thickness. Nope, swarth fills the flutes and binds the tap. No more than a sensitive 1/8 rotation before backing off and clearing. Just spent 5 hours at masthead, 55 ft, drilling and tapping for a B&G wand.

[a64pilot]

Originally Posted by Guy

I think this is where the mast is going to break off and the whole rig comes down in a storm.

So if this were an airplane spar, you would remove the broken tap by what ever means that works, but you would not leave the parts and shavings in the bottom of the mast either. Then you would ream the hole to fresh metal, in this case 1/4"and fill it with a rivet. If the reason you were trying to drill the hole in the first place was to mount something, then go 1/4". With a 1/4" fastener you should use 1/4-28 not 1/4-20. 3 complete threads min.

Yesterday I went to see my mast that is down and being rewired etc. a hole had been added in it for spreader lights I want, well the hole looked like an angry rat had chewed it, I was horrified, the owner could tell from my expression, he said don't worry, I'll have them put in a grommet.
So I said the wire doesn't worry me, stress riders do, shouldn't the hole be deburred? I don't think he really understood the question, his answer was there is twice the thickness in this mast than is needed.
Still, a nasty hole bothers me.

[a64pilot]

Originally Posted by Blue Stocking

Exactly !! Many think that because aluminum is softer the ferrous, one can merrily crank a tap through the wall thickness. Nope, swarth fills the flutes and binds the tap. No more than a sensitive 1/8 rotation before backing off and clearing. Just spent 5 hours at masthead, 55 ft, drilling and tapping for a B&G wand.

Then there are those that put a tap into a drill for repetitive holes?

[model 10]

Originally Posted by a64pilot

Still, a nasty hole bothers me.

Then BS, make them do it right or do it yourself. It's your money, your mast and your ass if it breaks off.

[delmarrey]

I use to make lots of aluminum parts for computers years ago. Small taps use to break quite frequently. I used nitric acid to eat them out. I put a little clay funnel around the hole and filled it with the acid and let it sit overnight. Then see if I could move it the next day. If not, I did another day. Eventually the acid would eat enough to get it loose enough to extract it, or eat it totally away. If the acid tried to drain away I would also fill the spaces around the tap with clay.

Nitric acid eats iron ONLY! I've had a half gallon for years, now down to a quart in a special glass jug. I use it for cleaning up rusty spots on the boat, like around stanchion bolts and the likes. It only eats iron not plastic or paint. Stainless you clean then rinse with water. Keep it off your skin and especially out of the eyes.

[roverhi]

Haven't read the whole thread so this might have been mentioned. Use a Dremel with a thin cutting wheel to make a slot in the tap then use a flat screwdriver to turn the tap out. If you are careful will only nick the mast and may be able to use the same size fastener. Might want to overdrill the hole so there is no stress point to generate a possible crack.

If it weren't for the rust issue would be in the seal it off as best as possible and leave it in place crowd.