How to cut out a hatch opening

[Triton106]

I have never really learned how to properly cut out a hatch opening even though I have done several in the past. The results are invariablly less than satisfying, primarily due to the lines not being as straight as I would liked even though most of the time I use a straight edge as a cutting guide for my sabre saw. The other issue is that the cutting edge is not always perfectly perpendicular to the hatch board. When the corners are not rounded it is just a pain to have to drill sevel holes to enable the sabre saw blade to start the cut (I always mess up every time I try to save time by making plunging cuts).

I am about to cut out a large hatch opening in the cabin sole approximately 12" by 48" to install a stainless steel water tank. Since my sole is teak and holly (1/4") surface on top of the original fiberglass (approximately 3/8") I expect the total thickness to be at least 5/8". I would appreciate some tip for making a simple and straight cut easily. Does it make sense to use a sabre or a circular saw?

[Tim]

Are you planning to use the cutout portion as the hatch when all is said and done, or fill in the space with a new hatch?

[Hirilondë]

Consider Tim's question first. Then the following: You may want to consider cutting the teak out in a hole of one size and the fiberglass out in a hole about 1" to 1 1/2" smaller. This will give you a lap joint when you either re-install the cut outs or make new pieces to replace them.

As to the actual technique for cutting I like using my Fein Multimaster. I have succeeded in cutting a hole in a bulkhead such that the hole became a door opening, and the cutout became the door. It took quite a while to make the cut accurately, but the effort was rewarded in a door with matching grain and color and a perfect fit. This might very well be a viable option for your sole.

And like any precision work, careful lay out is essential. And to carefully lay out you need to know the size of your tank, the exact location of your bilge space, the size of your replacement hatch if a purchased item and any other parameters that will effect the job. If you are making the replacement hatch or just filling in the sole afterward, then you can build to the hole.

[Quetzalsailor]

Certainly do-able. Obviously easier in the comfort of your shop, and at a decent working height.

I've done such things with the intent of using the cut-out afterwards in order to maintain the grain appearance. It's obviously much easier to do the work when you're making the part since you will have designed the thing so that you don't have to plunge cut as much. Makes gluing up more of a chore, though.

I would never use a sabre saw for the purpose since the withdrawing stroke of the blade lifts chips unpredictably. You can, if you dare, use the sabre saw from the back and steer it by watching from the front - works fine on smallish stuff where you can hold and guide adequately.

I use a hand-held radial saw and I clamp edge guides to the work. I plunge cut with the saw's guide against the edge (of course). I use a new blade with the finest teeth - a veneer, or plywood blade. It will be the thinnest, too. Cut slowly since heating will cup the blade and cuts will strongly tend to be curved; there's precious little set to the teeth on such a blade. Stop just shy of the sharp corners and free the cutout with a sharp handsaw. Since the handsaw will be even thinner than the radial blade, you should be able to cut well between the intended finished edges, both inside and out. Don't let the cutout drop out and tear things.

Alternatives include framing the cutout with trim on both the opening and the cutout. This would give you protection for the raw edges of the veneer and the wood grain going in a less damage-prone direction. This also would give you some wood to waste, but you'll still have to end up with perfect cuts.

Hirilonde is bang-on, as usual. Think through what locates the hatch in the sole, and what holds it flush.

[Tim]

Two notes:

1. Whether or not a sabre saw chips out the top veneer depends largely on operator technique and proper blade selection. Choose a fine blade to minimize or eliminate this problem. For that matter, there are also downward-cutting blades available that reverse the teeth, though I don't much like these for some reason.

2. Tape works well to not only mark your line clearly but also protect from chipout. Also, many jigsaws have little inserts that fit in the table (base) to close off the opening around the blade, greatly reducing chips even with the wrong blade.

You have to use whatever tool you are comfortable with. Not everyone is comfortable with (or owns) every possible tool, so use what you know, no matter whether it works as well for others or not. Your jobs have to work for you.

Me, I'd use a jigsaw. I do, all the time, and I am used to and comfortable with it in a wide variety of situations. This tool works for me, but your results may vary. To start a cut without plunging, or without a huge hole, I often drill 2 or 3 inline holes with a drill bit of the same diameter as the saw blade, right on the cut line, connecting the holes to create a blade-sized slot from which you can start your cut.

Your cut (with a jigsaw) will be slow going because you have to cut through wood and fiberglass together; the right blade for fiberglass is not the right blade for the wood, so this means you'll be cutting slowly and probably burning up and dulling many blades.

If you can possibly make the cuts separately as Dave mentioned above, that would be ideal. This will depend on how your teak is secured to the fiberglass--I am guessing this may not be possible in your situation.

Lesson learned: it takes careful thought and planning to avoid having to cut into finished surfaces to do something that would have best been done beforehand. Keep this in mind as you go forward with the work you are planning.

[Triton106]

Thanks very much Tim, Dave, Quetzalsailor. Really helpful advice and ideas. I priced the Fein Multimaster a couple of times and although I love the versatility of the tool I cannot afford it. So, I will proceed with my basic sabre saw with tape over the seam and real fine blade. I do plan to reuse the cutout for hatch cover but Quetzalsailor's idea to trim out the edge of the openning and cover is very classy and could bail me out if I should fail to execute a straight cut the first time.

[Hirilondë]

I do plan to reuse the cutout for hatch cover but Quetzalsailor's idea to trim out the edge of the openning and cover is very classy and could bail me out if I should fail to execute a straight cut the first time.

It isn't just a good cover up if your cuts don't come out perfect, it isn't just classy either. It is good protection for the edge of the plywood, both from moisture and chipping.

[Quetzalsailor]

I have not had Tim's fortune in not lifting chips with a sabre saw. My 40 year old Craftsman is quite prone to it and I long ago left it in dad's shop. The real cheepie is so sloppy that it's only good for drywall. Unlike older sabre saws, my Porter Cable 543 has a circular motion as it strokes; this is a nice feature and with good blades is much better.

I have not had satisfactory fortune with taping to prevent chipping. It is a useful method for retaining the chips for later re-adhering.

Another technique which I've used with some success is to cut through the veneer face or the top face of the piece with a sharp blade. Cut right along the line and saw a short distance back from it. Any chips smaller than the knife cut will be stopped at the cut.

Of course, unfortunate grain direction will foil care, as will poor adhesion in cheaper plywood that's common these days.

It's not just veneered goods that would benefit with grain ends covered with trim. Quetzal has 5/8" thick Teak and Maple sole boards. The ends after 40 years are occasionally chipped and I've managed to reglue just a few.

I would think that even a veneer banding across the end grain would have a benefit worth the effort. Just the act of saturating the end grain with an adequate adhesive would be a major gain. There has got to be a range of veneer/trim thicknesses that are more effective than others. If there is significant moisture change in the wood, precious little hope can be had for retaining the veneer/trim in place. That's why fine antique desks, some tables, and good breadboards are breadboarded.