Cutting Skin Fittings

steveej

steveej

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Good evening,

Thank god it's Friday.

Quick question on fitting new DZR skin fittings.......

Boat craned out today and I am off tomorrow to replace the original brass fittings from 15 years ago.

There are 6 in total and the plan is to cut them all out with a holesaw, prep all surfaces etc. then dry fit everything before getting the sikflex out.

Question.....all of the skin fittings seem much longer than those insitu. For 4 of them, space is restricted in the heads where they are all under the sink unit (heads in and out, plus sink and shower drain).

Would it be foolish to cut the skin fittings down? I believe I would knacker the thread? How would I repaire the thread.

Sorry if this is a simple question but I am not an engineer.

Happy Weekend
Steve
 
fit the backing nut right to the hull end of the thread.
cut the skin fitting,
tidy up the cut
remove the nut to clean the thread
fit to the boat.
fit the backing nut.
 
Your term 'cut them out with a hole saw' is a little worrying. Do this and you could well end with a hole that is too big for the new fitting. Why not just undo the nuts on the inside while somebody wedges a suitable tool inside the skin fitting from the outside to prevent it turning? Most skin fittings have a couple of lugs to hold a tool against. When you get them out you can measure the new ones against the old and cut to length. Use a file to clean the end of the cut thread and as already suggested make sure the nut is on the thread before cutting so you can take it off to clear the last bits of thread.

Yoda
 
yoda said:
Your term 'cut them out with a hole saw' is a little worrying. Do this and you could well end with a hole that is too big for the new fitting. Why not just undo the nuts on the inside while somebody wedges a suitable tool inside the skin fitting from the outside to prevent it turning? Most skin fittings have a couple of lugs to hold a tool against. When you get them out you can measure the new ones against the old and cut to length. Use a file to clean the end of the cut thread and as already suggested make sure the nut is on the thread before cutting so you can take it off to clear the last bits of thread.

Yoda
Click to expand...

don't worry, I have he right sized holesaws.
 
chewi said:
fit the backing nut right to the hull end of the thread.
cut the skin fitting,
tidy up the cut
remove the nut to clean the thread
fit to the boat.
fit the backing nut.
Click to expand...

Yes, I am hearing this from the father inlaw.........I'm just not sure I trust him.

he reckons 2 nuts on and some grease on the threads and to cut along the thread not parallell.
 
If you cut along the thread it will be a spiral cut from the end to the root.!

Cut it across at right angles to the axis, like the original.
 
chewi said:
fit the backing nut right to the hull end of the thread.
cut the skin fitting,
tidy up the cut
remove the nut to clean the thread
fit to the boat.
fit the backing nut.
Click to expand...

+1

This works for me too.

Funnily enough it was my father who showed me how this was done, especially the bit that involves using the nut to chase & tidy up the thread once the fitting has been cut to length.
 
steveej said:
don't worry, I have he right sized holesaws.
Click to expand...

Sorry but I do worry! I just don't see how from the outside you will get a hole saw to center and cut exactly down the threaded part of the fitting as you also have a flange on the outside. Better to just carefully grind off the flange and tap the remaining part inwards.

Yoda
 
yoda said:
Sorry but I do worry! I just don't see how from the outside you will get a hole saw to center and cut exactly down the threaded part of the fitting as you also have a flange on the outside. Better to just carefully grind off the flange and tap the remaining part inwards.

Yoda
Click to expand...

Have to admit I prefer to use an angle grinder too (very carefully). Usually I can lever the flange off with a large screwdriver (again carefully) and pull the rest through from the inside.

I've heard of quite a few people using hole cutters. I guess they must get a bit of wood and make a bung out of it to centre the hole cutter.
 
Leaving the nut on before cutting is the best method of keeping a usable thread but it's also possible to dress a knackered thread with a file if it's damaged. I find that filing all round at about 45° or less works well.
 
ghostlymoron said:
Leaving the nut on before cutting is the best method of keeping a usable thread but it's also possible to dress a knackered thread with a file if it's damaged. I find that filing all round at about 45° or less works well.
Click to expand...

Use 2 nuts ( preferably one of the old nuts on top) lock them together at the correct position so they do not turn..
Then cut down the face of the nut to give you a square cut. If you are a bit out use the face of the old nut as a guide to grind /file square. Then remove the 2 nuts & clean the thread .

For the second one turn the damaged nut ( if you have damaged it) round so you present a new square face to the cut.

If you cannot use an old nut use 2 new nuts & place a washer against the face first. It will tend to rotate but will give you a guide
 
rszemeti said:
Your chances of getting the holesaw to line up with the fitting are, frankly, zero.

Holesaws rely on the drill in the centre to locate them ...
Click to expand...

Using a holesaw is a common way of removing stubborn flanges, just knock a wooden bung into the existing fitting.
 
yoda said:
Sorry but I do worry! I just don't see how from the outside you will get a hole saw to center and cut exactly down the threaded part of the fitting as you also have a flange on the outside. Better to just carefully grind off the flange and tap the remaining part inwards.

Yoda
Click to expand...

I have successfully used an angle grinder for this, but from what I have read on here, the holesaw method is best done by jamming a piece of timber into the outlet (doesn't have to be an exact all round fit, but should be hammered in till flush), then find the centre geometrically and use this to centre the holesaw.
The use of a nut threaded on before cutting is commonly known to all metal workers who might want to shorten a bolt or cut a piece of threaded stud.
I'm not convinced that a skin fitting needs to be cut absolutely accurately at right-angles.......
 
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There is another way. Depending on the access inside, an angle grinder with a thin multi material disc can cut the nut off by going down one side at an angle. Much quicker than hole saws or grinding the outer flange off.
 
why would you need to cut them? there is a danger of damaging the hull. Undo the nut, and then heat up the fitting with a heat gun - sealant will get soft and you will be able to remove it by turning it left rigt left right with a pliers. That shouldnot be hard at all, at least that wasnt hard in my occasion. I dont understand why this method of cutting the fittings is popular since its so easy to remove them!
 
Akestor said:
why would you need to cut them? there is a danger of damaging the hull. Undo the nut, and then heat up the fitting with a heat gun - sealant will get soft and you will be able to remove it by turning it left rigt left right with a pliers. That shouldnot be hard at all, at least that wasnt hard in my occasion. I dont understand why this method of cutting the fittings is popular since its so easy to remove them!
Click to expand...

Most likely because you were lucky. Not all fittings come out easy. When i did mine i had to cut the inside off flush with the hull and then cut the rest into segments.
 
When I purchased my tub, part of the survey required service of all 13 seacocks under the waterline so I cut them all out. My favourite attack is to use a grinding disc to grind the outer flange almost all the way off then switch to a 40 grit flap disc to "sand" though the last gnats' appendage so not to damage the hull. Me and a mate did all 13 in a day, cleaned up the holes, primed & painted and new backing pads where necessary. Fitted all the new ones the following day.

It's generally not worth trying to undo them or pissing around in the bilges with power tools. Easy... grind off flange, knock in with hammer, clean and replace.
 
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