Porthole Hole

[BOATDOC]

It would seem to be a simple job- cut a round hole 6" in diameter for a porthole. I would like to hear how others have approached this task and what they have learned in the process.

Thanks

[Jay Greer]

Leave clearance of 1/16" around the diameter for expansion and contraction of the wood sorrounding the port light spigot. This will prevent splitting of the cabin sides at a later date. A ply wood guide templete will allow you to router cut the hole using a straight bit with a bearing. If clearance will not allow for the router body then a boring bar can be used to scribe the hole followed by using a key hole saw, I like the Japanese saws that cut on the pull. The hole can then be cleaned up with a rasp or curved spoke shave. All of this is much easier if the sides are cut in the shop prior to assembly
JG

[BOATDOC]

Assume we are cutting the hole in the finished hull- perhaps not a flat surface. Above the waterline, through 1"to 1.5" planks. (I am sorry but I am not familiar with how a boring bar is used.)

[Wild Wassa]

" ...perhaps not a flat surface."

Well spotted Skipper.

That's what I've been working on today. Repairing a porthole that was cut into a concave surface. I made an architrave in the cabin, so that the hatch will sits flat when I reinstall it (Two holes to fix and not much fun). It sounds like it would not ever happen but people actually do it without thinking ... and people like me repair their lack of forward thinking.

It certainly is a good warning.

Warren.

[Dan McCosh]

After the hole is cut, the edges should be well sealed. It's a common place for checking to begin.

[Jay Greer]

Sorry to mention the boring bar with out an explanation. I am speaking of a circle cutting guide bar for a router that is center mounted. This will only work if one is working on an area that provides sufficient clearance. Another way but a bit difficult to control is to use a hole saw with a guide rod and a hell of a secure lever arm on a half inch drill motor. The technique is to not go the full depth but to cut first from one side and then the other, marking the wood to almost a full cut but finishing by hand with a key hole saw.
Can be very touchy if you have not done it before!
JG

[Dave Fleming]

Are you folk talking about a 'flycutter'?

Single cutter on a bar with center bit held in Drill Chuck.

[PeterSibley]

Are you folk talking about a 'flycutter'?

Single cutter on a bar with center bit held in Drill Chuck.
and a very easy thing to stuff up if not used in a drill press., the results can be unpleasant all round....

[Lazy Jack]

I would probably use a hole saw to drill a series of large holes around the parimeter of the porthole...if the planking is thicker than the depth of the hole saw set the pilot bit deep so that it pokes through to the inside, then you can follow the hole back through sawing from the inside to remove the 'puck'. I would then use a sabre saw with a long blade or a sawzall to connect the holes and remove the block of waste wood, then flatten the peaks between the holes with a chisel. The next weapon of choice would be a coarse sanding drum mounted in a drill, use the largest diameter drum that will fit the porthole, then sand the edge down to the final dimension. A luan template of the opening fastened temporarily in place would be better than a pencil line becase it wouldn't keep disappearing under the dust from the sanding drum.
Thats how I'd start...

[Lazy Jack]

... by the way, I've never done this before...

[Rich VanValkenburg]

I had to cut portholes in Sonja's new cabin sides. I used a cheap, adjustable hole cutter that lets you set the diameter you want. It's a bit that's really meant for a drill press, but I used a 1/2" chuck drill motor, heavy gloves(in case it all got away from me), and a good grip. It's not the type of hole cutter that gives you a second chance in case you mess up. I had two cuts to make for each port, the outer diameter of the brass trim ring(these were 3/8" deep and were just the limit of the rabbet that I had to finish by hand), and the inner hole that went right through. I've got a photo that my wife took and I can scan this and send it to you. I don't get into photoposting much since I'm back to having a slow dial-up connection.
A round hole saw was too expensive and I wasn't able to find one in the diameter I needed.
Here's a link to a similar bit. For doing what you want, BE CAREFUL. This thing can be a bone breaker if you lose concentration. http://www.dremel.net.au/prod1995.htm

Rich

[JimConlin]

There are hole saws available up to about 6". Minor increases (but not reductions) of the size if the hole can be done with a router. Start with a rabbet bit and follow with a tromming bit.

[Jay Greer]

Are you folk talking about a 'flycutter'?

Single cutter on a bar with center bit held in Drill Chuck.

No, I am talking about using a hole saw. Using a fly cutter is asking for trouble! Even with the hole saw, the problem is that, often the saw will bind in the cut and torque the drill motor--scary! A good bit of insurance is to screw a block on to the waste section of the cut to give a deeper guide for the extended length pilot drill that the saw has down it's center. I also use a longer than usual pipe handle on the drill motor. This saves me from breaking my wrists if the hole saw binds in the cut! I drill from both sides to avoid break out.
JG

[Dave Fleming]

I most certainly was NOT suggesting using a 'fly cutter' for the job.
Jes' trying to clarify things in my own fuzzy mind.