Transom Fitting Hole Saw

[Nasher]

Hello All.

The skin fitting/Bung I’ve brought for my transom is just under 26mm OD.

All the hole saws I have, or can find, jump from 25mm to 30mm although I believe a flat wood-boring bit of 28mm is available if I can find one.

Firstly does anyone have/know of a 27/28mm hole saw? Or Imperial equivalent?
Because I only have decent access from the outside, if the reach isn’t enough for 2+ inches of Marine ply and Fibreglass I’ll have to stop and break out the plug before continuing.

Or, has anyone used a Flat blade type wood-boring bit for Fibreglass? Does it splinter too badly?
I obviously want to bung a load of Sikaflex around the fitting before fitting, but really only wanted a 27mm hole, so I could shave a bit off either side of the 28mm tool.

Help.

Nasher.

[jwalker]

Originally Posted by Nasher

Or, has anyone used a Flat blade type wood-boring bit for Fibreglass? Does it splinter too badly?

Nasher I've used them often. They are a bit crude but they work OK. Rock the drill a bit. They tend to get a ring of fibreglass stuck on the point. They do splinter when you burst through. I usually try to go in from the second side once the point is showing through. If you can get one, the type which have a wee ear on the end of the blade make a nice clean cut before the rest of the blade chisels out the centre. These blades are normally soft enough to sharpen them with a file so you can make an ear onto and ordinary flat one.

[codprawn]

Do a test cut first - I doubt the 25mm or 30mm will cut exactly on size. MAYBE they will cut slightly under or oversize - worth a try. Wouldn't it be possible to use a small drum type sander or roughing bit to enlarge the hole slightly?

Screwfix do a 29mm if that helps.

[kwil]

Had the same problem, hole borers are not usually deep enough, so I used a Forstener bit they are usually used by kitchen fitters to mount hinges etc in chip board but it worked fine.
Heres a picture of the bit.

[AndrewH]

Nasher

Just found this that claims to have a 2" deep 26mm diameter hole saw. Don't know how deep your transom is but if you use JW's suggestion and go from either side you should be able to get through a 4" transom

http://cgi.ebay.co.uk/7-pc-2-HOLE-SA...QQcmdZViewItem

Hope this helps

Andrew

[Nasher]

Thanks all.

I'll try a 25mm one I have to see how big it actually cuts, But I think its 25mm

I did see the Forstener bits, but could only find expensive sets available, and only with the usual 25mm and 30mm.

The Flat Wood borers I saw had the ears on the end, but the 28mm ones were out of stock, I'll try to get one and slim it down by a mm or so.
Unfortunately I can't go in from both sides as mentioned because of the small bilge well in front of the transom.

If all else fails I'll try opening up a 25mm hole with a sanding tube, but 2+ inches of fibreglass and marine ply will take a time.

Codprawn - Screw fix have opened a trade counter today just around the corner from work.

Andrew - In my experiance those multiblade hole saws are quite useless for anything more than a few mm thick. Thanks anyway.

Nasher.

[Hightower]

Don't do anything yet mate!

I'll have a look at work tomorrow for something in the 28/27mm range.

I've got a 29mm diameter one here if that's of some help. If not wait till tomorrow evening and I'll check.

[jwalker]

Originally Posted by Nasher

Unfortunately I can't go in from both sides as mentioned because of the small bilge well in front of the transom.

Get someone to watch you and when the bit begins to come through, stop. Take the bit out of the drill, put it into the hole on the inside and turn it with a pair of grips. It's a bit of a guddle but not too difficult. Turn it until the ears cut a groove deep enough to make the connection into the main hole.

[Endeavour]

i have a 27 and a 29mm. They are made by starrett who make just about every size...

http://www.lawson-his.co.uk/scripts/...%20Hole%20Saws

these guys are quick on the delivery too

[Endeavour]

Just read this article again. These holesaws are only about 30mm deep so u will need to break out the plug before continuing all the way.....

[crusoe]

Nasher.

If I was cutting a hole in the transom I would use the 25mm flat bit. If possible either cramp a piece of timber or wedge it on both sides to where your drilling from. These flat bits are ok but are very crude and have a habit of juddering and creating an elyptical hole. On the side the bit bursts through you can save a lot of damage by using the timber block.To enlarge the hole by 1mm dia simply get a short length of brush stale cover it with a length of course emery/abrasive cloth push it in and out a quite few times. Job done Its always easier to make the hole bigger than it is to make it smaller,seal the cut out with salt water proof silicone etc and fit your bung.

[yoyo]

Drill a small pilot hole first and then you can drill halfway from both sides with your hole saw, this will help to stop any splintering on the outside faces of the transom. If the hole is a little small I have used a round file for finishing to get the exact size.....It works for me.

[Nasher]

Thanks all I'll figure something out now.



Nasher.