Cutting through fibreglass core decking suggestions?

[Peter Reynolds]

Hi,
I am replacing the forward hatch of my Seidelmann S299 and need to cut out the decking for the old hatch to enlarge the area for the new hatch opening.

Does anyone have suggestions on the right tool for the job? Handsaw or mini-grinder or recriprocrating saw?

Thanks all,
Peter

 

[Tim R.]

Peter, how thick is the deck there? Is it cored? How much bigger do you need to make the hole? I used a sabre saw to enlarge some portlight openings last year and that worked great. There was no core and it is 9/16" thick. I used wide blue painter's tape to protect the surrounding gelcoat from the saw foot.

 

[RichH]

Probably the best and most precise would be a Fein "MultiMaster" using a segmented cutting blade. Such will allow VERY precise cuts, especially if you use a 'guide' to rest the blade against as you're cutting. You will have very little 'trimming and sanding' after you cut with a MultiMaster.

http://www.jamestowndistributors.co...834&familyName=Fein+MultiMaster+FMM+250+Start

http://www.jamestowndistributors.co...ter+HSS+Segment+Saw+Blade+3-1/8+inch+Diameter

 

[Tim R.]

Multimasters are great but mine did not cut the 9/16" solid fiberglass very effectively.

 

[Peter Reynolds]

I believe there is wood core and the thickness is about 1"

 

[BobM]

I bought the cheapo Dremel version of the Fein for $100 to cut through my coaming. It worked fine and provided excellent control. Just make sure the blade is tight and the washer is in the correct orientation or it will loosen rapidly.

 

[Tim R.]

A sabre saw with a fine blade should work well then. Make sure you seal the interior with plastic around the opening you will be cutting. Otherwise the dust will get into everything.

 

[RichH]

Multimasters are great but mine did not cut the 9/16" solid fiberglass very effectively.

Adjust the amount of vibration to 'slow'. Dont let the blade get too hot and it will cut right through. If the blade gets too hot, the teeth will quickly anneal and rapidly lose their sharpness ... just like 'any' sawblade will. You can also spritz water into the cut groove to help cool the FRG. If any blade is smokin', youll quickly wear it out.

 

[Ross]

With a saber saw you can cut to your line. That is as precise as you need to get. Use bi-metal blades and if they get dull change them. They are consumables and aren't expected to last forever. Protect the inside of the boat from cutting dust. If you can tape a slack plastic sheet under the work area that will be good. Also as others stated seal all of your cut edges.

 

[Hermit Scott]

However you cut the hole take Ross's advice and tape a piece of plastic under the hole. You will literally have to take a hose to the inside of your boat to get all the dust out if you don't.
If the surface is flat, my favorite tool to cut fiberglass with is a router with a 1/2" bit. If you take the time to make a wood frame for a jig, the edge would come out looking so good you won't want to install the hatch and cover it up.

 

[philwsailz]

I agre about the precision edge a router gives, but wow, that is a wide kerf!!!!

To me it would be better to rough cut with anything, and then trim to "the line" with a router in a jig frame.

 

[Ross]

Since the hatch frame will cover the cut, the exact line of the cut is not very important. The opening must be large enough for the hatch and not so large as to make bedding the frame properly impossible.

 

[jibes138]

Use a circular saw, it will remove most of the cut really fast. Then use the fein or saber saw or router or a hand saw to cut out the corners. Also a rotozip would work for this as well, they have all kinds of attachments for various cuts.

 

[Sonya]

Hi Peter:

Safety thought, keep fire extinguisher handy, things tend to get very hot very fast and where there's smoke there can quickly be flame to follow, and fiberglass afire isn't easy to extinguish once it gets going....
Best of luck with your project.

Sonya

 

[Ross]

Sharp tools cut well, accurately and easily. If you have to start forcing the cut you probably have a dull tool and it is time to change. Sharp tools won't/don't overheat.

 

[BobM]

I'd pass on the rotozip

Use a circular saw, it will remove most of the cut really fast. Then use the fein or saber saw or router or a hand saw to cut out the corners. Also a rotozip would work for this as well, they have all kinds of attachments for various cuts.

I have one and that is a tool that loves to wander!

 

[Peter Reynolds]

Ok,
Here is what worked the best. I used an angle grinder and a metal cutting blade for the long straight cuts. It is like cutting through butter. I used the sabre saw to carefully do the corners! Thanks for the help.

 

[Chuckbear]

We cut the hole in our deck for a new hatch, see http://tinyurl.com/kor9vc
and we cut the hole with a Makita skill saw and a carbide blade. Finished the corners with a saber saw and a carbide blade. Chuck

 

[Marcia]

I used an inexpensive Dremil tool. Worked great and didn't leave me with a wide gap to fill.

 

[kendall]

I'll recommend the circular saw. Depth control is much better with it. (in case there's something inside you DON'T want to cut!) If you do adjust depth, mark the shoe so you know where the blade is for accuracy.
Mark out the cut, then use a hole saw for cutting out the corners, finish off with the circular.

Helps to have a helper hold the cut-out level when making the final cut, or tie it up so it doesn't drop in. If unsupported it may rip out some of the glass inside leaving you with an unwanted repair.

I prefer the porter cable saw-boss, works great for it. PC saws have the guide tube so you can direct the exhaust where you want it making clean-up a bit easier.

Ken.