Engineer genius required snapped stainless bolts

[rolesyboy]

Moderators- please delete if this post is not allowed

I have an old jet ski which has sat in my garden unloved for the last 4 years so now I need to sort it. The engine was removed and two of the stainless bolts sheared in the captive nuts. Trouble is they are in a fibreglass hull. Any engineering geniuses on here able to offer any suggestions for removal. There is little to hang on to, I tried drilling but the drill won't centre and heat is a no-go in a fibreglass hull.
Thanks in advance. Mark

[rich@minispares.com]

mark

I would say either some high quality sharp drills in sizes small enough to both centre and take the smallest amount of material out each pass (which will keep the heat down)

or

admit defeat and reglass the captive nuts back in!


stainless grabs like hell on nuts and bolts, so can be a swine to get out

[mk1]

Probably not what you want to her, but I agree with Rich's second option.

Dig the broken captive nuts out & re glass some new ones in.

M

[Ronnie]

Drill a smaller hole on center if you can (not important and use a tungsten or similar burr to open to root dia, depending on the dia of the bolt it should be possible to (if done well) to remove the old threads like a helicoil, and at least try to expose a couple of the top threads to start your tap. We have to do it all the time at work sometimes as small as 6mm as Rich said inco and stainless bolts are prone to binding.

[mk1]

Centering on a broken bolt in something as wobbly as GRP can be "challenging" though.

Without bragging I am pretty good at drilling out & re tapping bolts that Rich has snapped But Stainless into GRP would be tough

[GraemeC]

If you can get a ball shaped burr just smaller than the bolt, you should be able to grind the surface to a nice bowl sharp that will help centre a drill.

[rolesyboy]

Wow, thanks folks. I thought I might get lynched by the Mk1 mafia for that request. It must be Christmas.
The big challenge is centering a drill bit in a bloody awkward spot (twice!!) I do like the suggestion of a small ball shaped burr to get a start on it. Failing that I will have to re-glass the captive nuts in (which I have never done before)
Many thanks.

[Goldbrocade_62]

Can you blow compressed air on it or dribble cold water on it to keep it cool while drilling it

[captain]

Can you blow compressed air on it or dribble cold water on it to keep it cool while drilling it

Sensible question

[smithyrc30]

Did you try a centre drill? You will need a carbide one for stainless but they wander much less than a conventional twist drill.

One of these:
http://www.ebay.com.au/itm/SOLID-CARBID ... SwAYtWGP4L

High chromium stainless hardens if you drill it part way through and let it cool, you have to get the cut done it one go otherwise you will take the edge off an HSS drill when you try to finish the cut.

[pad4]

sit a nut on it - weld through the hole into the stud and spanner off

[smithyrc30]

sit a nut on it - weld through the hole into the stud and spanner off

Captive nut in fibreglass????

[pad4]

Hey it was 3 ish in the morning and id had a few

pad

[rolesyboy]

Tut, tut...You just cost me a jet ski Paul.
"alcohol, the cause of, and solution to, all life’s problems.”
~ Homer Simpson

[mk1]

I really like that ball shaped burr suggestion. I think it would work, just depends on how much it would cost I guess.

M