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Sunday, June 06, 2010

Weekend Rant: "Right Tool for the Job"

I am sure readers have heard the wise advice of "always use the right tool for the job", or some variant. It is advice well founded. Often using the "wrong" tool results in lots of frustration and/or poor results. But I submit there are jobs where there is no "right tool". I have discovered one of these in this weekend's project.

So, the job is to cut out an opening in your 3/4 inch plywood cored fiberglass deck. What is the single "right" tool to make the cut? Answer. There is none. The fiberglass will dull any toothed cutting blade in seconds (i.e. jigsaw or sawzall blade). Carbide grit blades work great on fiberglass and last a long time, but they wont cut plywood. In fact, carbide grit blades have a greater chance of setting the plywood on fire, due to heat from friction, before making any significant cut (don't ask me how I know).

So, what to do? Answer: use the "wrong" tool, and expect to ruin a number of blades in the process. But there is a way to go about it to minimize the tool cost:

  1. Go to the hardware store and stock up on toothed and carbide grit jigsaw and sawzall blades.
  2. Rough cut the opening just short of the desired opening size with a jigsaw and/or sawzall with a toothed blade. Expect to change in new blades a couple times. This gets most of the material out of the way and close to the edge of the desired opening where you want to spend time on detail.
  3. With a router and sharp rabbeting bit, carefully route out the plywood core. The router will fly through this easily. This gets the plywood out of the picture.
  4. Now, switch your jigsaw/sawzall to carbide grit blades. Cut the fiberglass even closer to the desired opening size as much as possible, without cutting beyond. It helps to have a plywood template cutout jig if possible.
  5. Repeat steps 3 and 4 as necessary to get closer to the desired opening size.
  6. Finally, trim the edges of the de-cored fiberglass with a router and trim bearing bit. Having a cutout jig here is a must unless you are quite good and freehand (I'm not). The blade on the router bit will be dulled here, so have a couple good quality bits on hand. The closer you can get with steps 3 and 4, the easier this step will be.
  7. Do the final rabbet of the plywood core to prepare for epoxy/resin fill of the edges.
There you go. One afternoon and a handful of blades later, you should have a nice cutout in your deck. Seems like a long process, but it will save cursing and frustration in the long term.

More on this later.


Colin said...

Your missing out on a fun tool to quickly remove the fiberglass. Crude but very fast. Pick up a cheap 4.5 inch electric grinder and a few cut off wheels ( the very thin ones for cutting off bolt heads. It will go though it like butter for the rough out. You will likely get the core too. If you drill some holes though to show the position inside the boat you can get it from both sides. Messy but very fast.

robert said...

Thanks for the idea! I do have a grinder and some cutoff wheels. Just never thought of using them on glass. Maybe that is the "right" tool.