Handy holes

 

At some time or another everyone has to drill some holes in their boats whether it be for cables, hoses or some other thing. There are a bunch of ways out there to do it, but in truth all too often boat owners and boatyards pick up and use the first drill that they can lay their hands on.  The two shown above are the cheap spade bit on the left, and what is known as a forstner bit on the right. Both are intended, and were designed for wood but that is where the similarity ends. The spade bit. even when new and sharp, does an ineffective  job as it does not so much cut as scrape. The forstner bit on the other hand  probably cuts the best hole you can get - in almost any material other than metal. If possible every hole should be backed up on the underside with some scrap to prevent tearout which is especially noticeable with the spade type bit.

The picture below shows a three quarter inch hole that I had to drill yesterday through a plywood bulkhead using a forstner bit.  I think you would agree that even from the picture you can see that it is very clean and neat.

A forstner bit does work on fiberglass, but like the spade bit produces clouds of dust as the complete hole is reduced to waste, so when you go up to a 2 inch hole things start to get a very dusty and nasty. When working with fiberglass I like to use a proper hole saw as it only cuts out the perimeter.  It does a great job for not too much money  and will even produce a neat cut out when not backed up on the waste side.

 
It can be a pain in the neck sometimes trying to remove the disc that gets stuck inside the saw, but I have found that the 5 inch diameter saw is great for making plywood discs from scraps that can be used as backing plates to through hulls and sea cocks. Just coat them with epoxy before installation and they last for years. One final tip and that is to only buy the hole saws and other expensive bits as you need them. You can buy kits but you always end up paying for sizes that you will rarely if ever need.  Avoid those cheap hole saws from the dollar store.  The teeth are too fine and will burn up on the first hole.  Save your money - they are junk!

Comments

[Doug]

I haven't tried a forstner bit on the boat yet, being a big fan of hole saws. I'll have to add a select few to my bag...

I did want to share a handy tip that I learned from a friend. Used when you need to enlarge an existing hole with a hole saw I've used this technique on the wire port in an aluminum radar arch and for making enlarged component holes in a fiberglass dash.

Using a hole saw of the proper size cut a hole in a piece of plywood (I've also used 2x4 stock). This is now your guide/template. Secure the template in position (screw it down, clamp it, whatever works for the situation) and using the same saw and some care you can cut your new hole without needing to rely on the pilot bit. This has saved me from a great deal of aggravation and sanding with a dremel tool!

[Bill Parks]

I only own one Forstner bit so I often have to make do with spade bits. One trick I've learned is to just drill through until the pointy thing on the spade bit breaks through, then flip the piece over and finish the hole from the other side. The result is a nice clean hole.