Help! Drilling holes in fenders

[Stadtline]

Hello,
I was wondering whether anyone can help me with this!
I have bought D-section fender/rubbing strake and need to drill/cut holes of around 12.5mm. Cutting holes at teh top of the D and on the base will allow me to pass bolts through to secure to the hull.

I have tried traditional drill bits, but this makes a mess as the fender "gives" and the resulting hole is not clean at all.

Has anyone had a similar experience and found a solution to purchasing a suitable cutter?

Many thanks!
James

Use a hollow tube with OD sharpened. Silicon oil for lube. Make something like a gasket punch but allow room for material thickness and a means to get material out (like a hole saw but without teeth or if you can accept a little roughness, just use a hole saw) I have heard people try freezing first but that would make for an unruly snake! Would you mind elaborating about how you are going to attach to hull? Typically, one would run screws strait into the boat through an aluminum bar acting as a washer inside the "D" (it's kinda tricky to get it all lined up right with correct hole sizing throughout). If not feasable, fender washers at every screw but don't get too tight and get them all equally tight to not deform rubber. Use rubber plugs you cut out to fill holes, glue in place with color matching 5200. Most of the time, for "D" rubber, black.

[troy2000]

Originally Posted by mark775

Use a hollow tube with OD sharpened. Silicon oil for lube. Make something like a gasket punch but allow room for material thickness and a means to get material out (like a hole saw but without teeth or if you can accept a little roughness, just use a hole saw) I have heard people try freezing first but that would make for an unruly snake! Would you mind elaborating about how you are going to attach to hull? Typically, one would run screws strait into the boat through an aluminum bar acting as a washer inside the "D" (it's kinda tricky to get it all lined up right with correct hole sizing throughout). If not feasable, fender washers at every screw but don't get too tight and get them all equally tight to not deform rubber. Use rubber plugs you cut out to fill holes, glue in place with color matching 5200. Most of the time, for "D" rubber, black.

Might work better to sharpen the ID of the tube instead, if you have a round file or stone small enough to do so. And as Mark says, be sure to use lube.

[welderbob]

we use to use a flat spade bit. the type carpenters use. You may want to use a plastic strip (1/4" starboard?) inside the "D" rubber. Over time the S/S bolt will eat thru the aluminum strip.

[alan white]

They make hole saws that small. Use the thin-wall type, which is usually cheaper anyway.

[Stadtline]

Thanks for the advice. Will have a look at all options and have a go! Thanks again!

[gonzo]

A sharp spade bit is cheap and works great.

[alan white]

Spade bits do require a material that is solid enough to keep the pilot centered.
Also, the bits also are prone to grabbing suddenly in certain situations. If a wood backing is used to support the pilot point, spade bits are, as said, quick, cheap, and effective.

[Stadtline]

Thanks for the posts...will get one of each and give them all a go.

Thanks again!

[Submarine Tom]

I've never done it but a soldering iron comes to mind.

Avoid the fumes.

-Tom

[Stadtline]

I went out and bought a spade bit at 12.5mm as it was the easiest to source and it has worked perfectly! The pointed bit located well and helped make a clean cut by providing a pilot.

The fender I have is quite rigid. Softer versions may not give the same success in case anyone else has a go. But definetely worth a try on a bit of offcut and the spade bits are only a pound or so!

Many thanks for all your posts

[hoytedow]

Originally Posted by mark775

Use a hollow tube with OD sharpened. Silicon oil for lube. Make something like a gasket punch but allow room for material thickness and a means to get material out (like a hole saw but without teeth or if you can accept a little roughness, just use a hole saw) I have heard people try freezing first but that would make for an unruly snake! Would you mind elaborating about how you are going to attach to hull? Typically, one would run screws strait into the boat through an aluminum bar acting as a washer inside the "D" (it's kinda tricky to get it all lined up right with correct hole sizing throughout). If not feasable, fender washers at every screw but don't get too tight and get them all equally tight to not deform rubber. Use rubber plugs you cut out to fill holes, glue in place with color matching 5200. Most of the time, for "D" rubber, black.

Perhaps you can quickfreeze the drill locations on the spot just before drilling by applying dry ice, being very careful, directly to the target.

An idea worth trying (I will, next time I do this). If I wanted the whole thing cold, I could take it outside! It's not "Florida cold" - but it is cold! Everything's crunchy/squeaky here tonight...