You are looking at a simple, but very effective jig for making angled cuts with a hole saw. This is the brainchild of Cory McMahon of Triton Marine. We were in the process of installing a fresh water pick up for the new air conditioning cooling system when Cory suggested this to Chris Martin.
This jig is made by drilling a pilot hole through a block of wood, and then making a cut with the hole saw in question.
You then use double sided carpet tape to position the jig. Now, when you begin to make your cut with the hole saw it is held in line by the block of wood.
Because you are cutting a circle on an angle, in this case 45-degrees, the cut out is oval shaped. This plug is from the engine room bulkhead which also forms the aft end of the fresh water tank. The inside, after almost seven years, is shiny and clean.
With the installation of an updated air conditioning system we are plumbing the aft fresh water tank to be used for cooling the condenser coils. We want the pick up for the pump to be right on the bottom of the tank, thereby minimizing the amount of water that needs to be carried. The 45 degree angle allows the tank penetration to well above the highest point of the bilge in normal operation. We are expecting both more efficient an d quieter operation from this new Marine Air gear.
Posted by Steve Dashew (December 11, 2011)
December 12th, 2011 at 10:53 am
A jig or “external pilot” is also useful for holes perpendicular to the surface where the material at the center is absent (enlarging an already existing hole) or otherwise inadequate to support a pilot bit. There’s a half inch hole in my hull where the pitot tube for the old knotmeter was installed. The location is perfect for a garboard drain, but the drain requires a one inch hole and the existing hole is too large for the quarter inch pilot. Cut a piloted hole in a piece of scrap wood to make a jig, and in less than a minute I’ll have a hole of the proper size.
How did you make the angled jig – block the board up under a drill press?
December 12th, 2011 at 10:49 pm
The block of wood was held at the correct angle in a vice and then cut with the ole saw to make the jig.
December 12th, 2011 at 12:11 pm
You had mentioned in a post about one of the FPB64s that they were trying to use the fresh water tank instead of pumping raw water for an air conditioner. It must have worked. How many btus can you shed for how many square feet of tank/hull bottom this way? Will you be able to connect the cooling tubes right to the hull bottom or will you need to keep some water in the tank for heat transfer?
December 12th, 2011 at 10:53 pm
Hi Daryl:
Yes, this system of using hull tank water for cooling the condensers does work. We have the data per unit of area, but I think we will keep that under wraps for a while. And to be clear, this is using internal tanks for cooling. The approach ins Wind Horse is a little different than the FPB 64s.
December 12th, 2011 at 12:17 pm
If you don’t have a band saw and need to make an angled cut on a tube you can use the hole saw at an angle to mark the tube or even use it as a jig and cut along one side of the block of wood.
December 13th, 2011 at 6:38 pm
The guide-block-hole-saw-jig works great too if for some reason you don’t want the pilot whole. I’ve used it when I have had to drill partially through the material without damaging the opposite face, and also when what I’m after is the plug itself, as a patch, usually. First make the jig, then remove the pilot bit before cutting the plug. If you have the entire hole saw assortment you can usually make a plug and a hole that match up if structure, and not aesthetics, is the goal. ( shop people won’t like that idea, but us field carpenters can’t carry EVERYTHING with us )
December 16th, 2011 at 7:58 pm
This is almost the way we do it here. The difference is that we drill the hole square through the block and then cut the block on the angle we need. You then put the cut face to the tank or whatever. This means that the holesaw has no chance of jumping out of the guide block when you start drilling.
Great tips. Thanks again for the link to those who are doing.
Ken