Cutting Curves in Marine Plywood

[ShagRock]

I'm looking for advice regarding tools and techniques for cutting 1/2" or smaller thickness marine plywood; particularly the long curves for planks in small boats and canoes. From reading this forum, there would appear to be lots of options, but which ones work best and maybe save some 'elbow grease'? There are jig saws, circular saws, pull saws, multi tools, etc. I could use some help in getting a better idea of 'best practices' from experienced boat builders.

ShagRock

[gert]

ruff cut with a circular saw; finish with a pattern bit in your router and a template (pattern) of the plank.

If the blade of a circular saw protrudes only 1/8 below the plywood it will easily cut a curve.

Whatcha building?

[TerryLL]

Skilsaw set shallow as gert suggests is the way to go. When I worked aluminum we cut curves in 1/2-inch plate with a skilsaw without difficulty. Plywood, no problem. Use a fine-tooth blade to reduce tear-out.

[Ian McColgin]

Up to 1/2" I use my Japanese pull saw as that give the cleanest edge and you can cut perfectly - no planing unless you have to put in a bevel later.

I am not good enough to use a shallow set rotary saw unless I tack down a guide batten first, and getting that offset correct to make the blade match the curve can be a pain, especially the extra radius if you're cutting an inside curve.

[MiddleAgesMan]

The key to making accurate cuts with a skilsaw is the location of the blade. My sorry saw has the blade at the right end of the arbor. Since I'm right handed this is the wrong side for me--if the blade was on the left I could see it better. You have to be a contortionist to see a blade located on the far side of the saw. I tried it and had to resort to making those long cuts with my Bosch jig saw.

[Bill R]

Ditto the Skilsaw with a fie tooth blade. The Bosch barrel grip jig saw will also become one of your best friends. Then there is the bandsaw, 14" minimum...

Careful- it is a slippery slope

[Hwyl]

I'm with the saw crowd, but I've seen people cut a template and use a router. Double the work and expensive, but if thats the way you want to swing.

[RodB]

A worm drive circular saw is good choice because the "gyro" effect of the motor and the blade being on different planes... allows lots of control as you cut along a line. The Makita Hyphoid is my favorite because of its lighter weight. This is one of the many tips I acquired from the designer/builder of my boat, www.tracyobrien.com.

Keeping the blade shallow, you can follow a line holding the saw with one hand. Just cut relatively close to the line, then use a low angle block plane to go right to the line... wallah! perfect panels.

RodB

[gert]

but I've seen people cut a template and use a router. Double the work and expensive

No it's not, this is the template (dead accurate-exact representation of plank)
http://farm1.static.flickr.com/175/370139331_9b6a081589_m.jpg

This plank was ruff cut with skill saw (trace template 1/4" oversize on stock) and finished with router & pattern bit; first plank is template for opposite plank so you need the pattern bit anyway.

http://farm1.static.flickr.com/178/370139334_aa5179dfea_m.jpg
Note the template is upside down so router (screwed to "sled") slides easily, sled is counter weighted with soupcan of lead.

[TerryLL]

Wow gert! That's the way I'll be doing it from now on. Thanks.

[epoxyboy]

A plain old handsaw works just fine - one of those thin flexy ones like a Stanley Jetcut or Bahco/Sandvik hardpoint. They are razor sharp when new (and so cheap you just get anther when they get blunt) and will go through 9mm (3/8") ply quick as - if its a canoe the ply will be even thinner. You can cut right to the line and the width of the blade means no wobbles in the cut. If you hold it at a about a 45 degree angle, there is minimal breakout on the bottom - though I am not really sure why people stress out about this. If its a stitch and glue boat, the sawn edges are buried in fillets and tape. If its lapstrake one edge is overlapped and the other is going to get all rounded over.
Plus, no saftey glasses, no earmuffs, no whining motor, minimal expense and you get a bit of exercise - and it really doesn't take that long!

Pete

[Cuyahoga Chuck]

It is possible to cut gentle arcs with a hand saw. It the saw is sharp and set properly it's possible to follow a line, straight or modestly curved, very closely without obliterating any of the line. For arcs you just bend the blade a bit in the direction you want to go. It did dull the saw as I went along. I think the glue lines have an abraisive effect on the teeth.
I use a 22 inch cabinet saw with 11 teeth per inch to cut our about 90% of the planks and bulkheads for my D4 S&G pram. The material was ¼" and 3/8" plywood.
That reminds me, I haven't resharpened that saw yet.

[RFNK]

Gert, let me guess ... you ran a batten along an existing line or `next' plank and a batten along the opposite line or `other' plank, then you joined these bent battens with little girders (Gerters) to hold the bent battens' shape. Is that right? If so, how did you fasten the little girders - hot glue? tacks? staples? The whole thing looks brilliant to me but is this the process? Rick

[dguidry]

What happened to using the old method of ticking points off the frames with a compass onto an apporximated plank. Very accurate.

[Canoeyawl]

I have always used the tablesaw.
Cut almost to the line, finish with a plane.

[James McMullen]

The one advantage with using a fast cutting tool like a skilsaw or a router is that it allows you to completely screw it up in microseconds, whereas a slower, more controlled tool like a jigsaw with a block plane to follow requires a lot more time and effort to totally bungle your cut. Think efficiency, my friends!

[Ian McColgin]

I cut it twice and it's still to narrow.

Really, the nice sharp Japanese pull saw will handle the arcs and follows the line easily if you learn to breath out though your mouth so's to blow the dust off the line.

[ShagRock]

Firstly, thanks to so many of you for helping out with this!:) To put my response in perspective, I'll mention that I helped build a few wooden boats in Newfoundland using a carvel method on hot-water bent ribs; but that was years ago and never with plywood. I'm starting a one-off experiment with a sailing canoe discussed under another thread http://www.woodenboat.com/forum/showthread.php?t=91946&highlight=shagrock/htm (http://www.woodenboat.com/forum/showthread.php?t=91946&highlight=shagrock)

Routers and band saws are not practical because I'm not involved in any detailed woodwork (mostly house framing, decks, gazebos, sheds etc.) I have an old jig saw, but it's the least used tool I own. I was going to add a Bosch 1590evsk jig saw to my kit, but after reading all the above, I might reconsider - I'll leave that one open. Based on all your advice, I could add several new items for the boat project at less cost than a new jigsaw, but some may have a different opinion on that:
1) Thanks for all the skilsaw tips - that's invaluable information for a novice plywood user. I have one and will buy a fine tooth plywood blade. Any suggestions as to best blade or are all brands equally as good?
2) Handsaws have always been a favorite and I am handy at cutting to a fine line. I need a new one as it is. Pete mentioned the Stanley Jetsaw and I have found their 11pti Sharptooth to be good. I'm not sure how they compare?
3) I purchased a Japanese 17pti pull saw a couple of days ago. There's a nice 'selection chart' at the Okako Z-saw website. I studied that to familarize myself, as I've never used one. On the advice of a cabinet maker, I chose a 'utility' type that also cuts pvc and other stuff. I was told plywood is rough on saws, so an expensive one for dovetailing natural wood is overkill.
4) Rob mentioned a block plane and I have one. However, I saw a light weight 3 1/2" Bosch electric plane on clearence sale in a nearby store. I used an electric before on wood planks. Will it be equally as useful with plywood?
5) dquidry noted the use of compass for lofting and probably not to difficult to get used to. That's probably more accurate than just using a tape measure and crosshair points.

James - could your clarify what you mean?

ShagRock

[ccx2]

I cut it twice and it's still to narrow.

Really, the nice sharp Japanese pull saw will handle the arcs and follows the line easily if you learn to breath out though your mouth so's to blow the dust off the line.

Ha Ha , sounds like some of my work, goodun Ian:)

[Mike Redmond]

Good morning,I'm a newbie here.Bought a Japanese pull saw about a tear ago,they are fantastick.They will cut a very thin kerf(saves a bit if you cut a sheet of ply in 3 16" sections)wish I had heard of them years ago.I have used it to cut the bow curve for a Jon boat it worked great.Just have to get used to the idea of pulling on the saw tough..Mike R

[RodB]

To reinterate... its a cinch to use a left bladed worm drive circular saw to cut along a gentle curved line with tons of control. A sidewinder standard circular saw with a carbide blade can, if your not careful, self steer and mess up the cut... a hyphoid saw like the Makita is so easy to control... so set the stock atop a few 2 X 4's and just cut along the line, its so efficient and quick to make the cut and then use the low angle block plane to go right to the line... if the curves are too severe in some areas to use the circular saw, then use a hand saw (pull saw ) or a jig saw in those areas. With a sharp carbide blade, I have always been able to get very clean cuts with this method, I much prefer to use my hyphoid (worm drive) circular saw to any jigsaw if the curve is not too drastic.

Good luck,

RodB

[TerryLL]

This is the tool, unless you work in an unheated shop and need the exercise to warm you up, then use a handsaw. Actually, I built my first two boats with hand tools, a long but very rewarding and educational experience. No regrets.

http://i325.photobucket.com/albums/k365/TerryLava/P1010010.jpg?t=1233437318

[David G]

I always use a jigsaw. It works fine, and it's what I'm used to. However, the slickest tool I've seen used for this purpose is a corded trim saw. Not a cordless saw, because swinging an arc is hard work for a motor, and uses up a lot of battery quickly - something that's already an issue with these particular cordless tools. You can turn a tighter corner with a trim saw (because of the small diameter blade) than with a regular skilsaw. Lighter, and handier as well. It also swings a fairer curve than a jigsaw in most hands. Really the perfect compromise, I think. I don't own one, and am used to the jigsaw at this point in my career, so won't be buying one... but I'd certainly recommend one. They're handy for lots of other boatwork and house projects also.

http://www.skiltools.com/en/AllTools/Category/Product/default.html?pid=HD5510&cid=192162

And, on the question of blades: I get mine from my regular wholesale supplier. But if you don't have a local guy, lots of folks rave about these blades from Matsu****a:

http://www.duckworksbbs.com/tools/saws/index.htm

[pipefitter]

Circular saw here as well in both aluminum and wood. Finished to the line with the belt sander, held at the angle that best fits the curve. A good eye with the angle grinder and the right grit will also do a nice job.

[eastern270]

I use the circular saw also with the blade bearly protruding below the plywood. Cut close my line and finish with a belt sander. Great idea you have there for templates. I would imagine you could use your template to finish with a router and trim bit. Good luck.

[boylesboats]

A worm drive circular saw is good choice because the "gyro" effect of the motor and the blade being on different planes... allows lots of control as you cut along a line. The Makita Hyphoid is my favorite because of its lighter weight. This is one of the many tips I acquired from the designer/builder of my boat, www.tracyobrien.com.

Keeping the blade shallow, you can follow a line holding the saw with one hand. Just cut relatively close to the line, then use a low angle block plane to go right to the line... wallah! perfect panels.

RodB

That make sense
A worm drive circular saw is good choice because the "gyro" effect of the motor and the blade being on different planes...

[boylesboats]

I cut it twice and it's still to narrow.

Really, the nice sharp Japanese pull saw will handle the arcs and follows the line easily if you learn to breath out though your mouth so's to blow the dust off the line.

You cut it twice :eek: no wonder it's still too narrow..

[paladin]

Thanks Gert....saved me the trouble of trying to explain it......

[Philip Maynard]

When I was cutting plywood sheathing for arch top windows with a circular saw, an electrician said "how do you cut curves with that" I said "curved blade" and he did a double take and took a 2nd look at my saw.

[bruce w]

i just use a old disstons hand saw a nice narrow thin blade taper ground it will work a inside curve ,i have seen them on ebay going for little money ,sad when you think that when they were first bought they proberly cost a weeks wage.

[spirit]

The Festool Jigsaw with a carbide-tipped blade gets very close and smooth.

[dguidry]

No it's not, this is the template (dead accurate-exact representation of plank)
http://farm1.static.flickr.com/175/370139331_9b6a081589_m.jpg

This plank was ruff cut with skill saw (trace template 1/4" oversize on stock) and finished with router & pattern bit; first plank is template for opposite plank so you need the pattern bit anyway.

http://farm1.static.flickr.com/178/370139334_aa5179dfea_m.jpg
Note the template is upside down so router (screwed to "sled") slides easily, sled is counter weighted with soupcan of lead.
On looking at this method again, I can't help but wonder if the stress on the template created when you lay it flat might skew the pattern enough to create errors in the template???

[gert]

Apparently not :)
http://farm4.static.flickr.com/3018/2561671359_a8bc573f9e.jpg

A legitimate concern, and all later templates, as they got narrower got many more "gerters". The ribands are 1/2 X 1 solid (the 1" representing the land) with 1/8 ply "gerters". The plywood was definatly harder to bend especially on her stern end. I do believe there was a slight difference but this is boat building not 4 decimal place rocket science.

This (image below) is the origin (to me) of the method for boat building. I originally saw it on a "This Old House" episode where the counter top guy showed up with a bundle of 1/8 X 2 ply strips and a hot melt glue gun.

This is Albert Strange's "Wenda"
http://farm1.static.flickr.com/6/6626781_5f1da1cee3.jpg
And if it was good enough for that beauty, by a pro, who am I to question?

The template is tweaked to be fair before the cross pcs are glued on; then when the first plank it routed said plank is further faired with a block plain before it's used as a template for the opposite plank.

Planks #6, apx 24' long:
http://farm3.static.flickr.com/2221/1533947881_a578885a49.jpg
there's 800 lf of 1/2" thick curved plywood edges on this boat, hence the power tools.

ps
I cut the lands with the "Tom Hill jig" but using a router with a 1" cutter instead of a block plane - sweet & consistent.

Power tools are for getting you thru the tedious repetitive stuff that causes tennis elbow, and quite frankly, they can be more accurate.

[kenjamin]

My circular saw was bolted to my West System Scarffer so I cut all my planks for my Caledonia Yawl with my Makita cordless circular saw. It did go through the batteries but the accuracy was great and there was no cord to hang up as I was doing the cut. I have three 18 volt Li ion batteries so didn't do much waiting for batteries to charge. The three batteries and my charger kept up pretty well with my power requirements but 3/8" was my thickest ply. It was 7 pile Sapelle ply, however, and hard as a rock!

[Canoeyawl]

Sorry Shameless plug :D::)

Reminder... by signing up to post on this Forum, you've agreed to make nice, and pages and pages of rules the greedy lawyers wrote. It all comes down to:

Don't be rude.
Don't sell stuff or services.
Don't post inappropriate pictures.
Don't whine at the Admin. He hates that.
Don't create a new user to come back in if you were temporarily or permanently banned. It's bad Karma.

[David G]

Chase,

I'm sure your heart is in the right place. There's nothing wrong with guerrilla marketing. It's just that - in fairness to all the business owners who come here - no one is allowed to use this forum to advertise (other than in the most innocuous and tangential ways). That's just the rules. Good luck with your biz!

Cheers,
David G
Harbor Woodworks

[Chan]

Middle ages man, I find that interesting because I'm right handed and find left arbor circular saws difficult to use.
I don't know if they still make them but porter cable used to make a nice 6" corded circular saw, "trim saw". I use one all the time for cutting shingles and woven corner shingles.
If investing in a saber saw I would recommend the trigger style as opposed to the barrel grip. The barrel type has an inconveniently located on off switch, and it's either on or off as opposed to a trigger with a finger.
Either way most of the saber and circular saws are the same machines marketed under different brands, ie. bosch, dewalt, ryobi, exception being maybe makita, but I never liked blue japanese tools.
Cutting a curve with a circular saw I would set the depth to just barely cut through the stock, less than an 1/8" deeper.

[ShagRock]

Another question I have relates to cutting for in-line edge joining as in plywood planks for stitch and glue versus right angle joining as in building boxed in seats for a boat where filleting might be used.
1) Is is best to cut planks such that a small gap is left for the epoxy to fill?
2) If plywood planks are fastened (say to three ribs/bulkheads in small canoe), could then the planks be cut to a 'tight fit" and glue used instead of epoxy?

[RodB]

Another question I have relates to cutting for in-line edge joining as in plywood planks for stitch and glue versus right angle joining as in building boxed in seats for a boat where filleting might be used.
1) Is is best to cut planks such that a small gap is left for the epoxy to fill?
2) If plywood planks are fastened (say to three ribs/bulkheads in small canoe), could then the planks be cut to a 'tight fit" and glue used instead of epoxy?

I'll just comment on #1 ... the diagram below shows a typical method to join panels... with one radiused edge for a nice flat joining of the panel edges... The fillet will fill the gap and allow a nice radiiused surface for the biaxial cloth to follow. The biax is the strength of the joint...

http://i40.photobucket.com/albums/e239/Prestoboat/Misc%20boats%20etc/Doublebottomcross-section-ste.jpg

Oh yea, I forgot... if you are working with ply panels... it is much easier to move a saw (circ saw) than the enitire sheet of ply.... There is no simpler easier system of accurately handling ply panels than the Eurekazone "smart table" and their circular saw base and smart guide... www.eurekazone.com I cannot imagine ever using a table saw for ply panels again... unless one has a 52" fence and outfeed tables etc already set up in the shop specifically for this. Festool also has a great saw guide that works with their marvelous plunge saw... The Eurekazone systems is the most bang for the buck and can be used with any circular saw... The smartguide can be used with integral clamps or with a foam tape on its bottom surface... so you can just lay it down on the stock and it will hold position nicely. The smart guide has a plastic insert that you cut initially with the saw on its base...which shows EXACTLY where the saw will cut...and the plastic accessories that attach to the saw base prevent any ripout or splintering ... a smooth clean cut like you get on a table saw with a zero clearance throat plate... This is a dandy system for handling plywood.

http://i40.photobucket.com/albums/e239/Prestoboat/Misc%20boats%20etc/smartguide.jpg

RodB

[RodB]

Heres a great link showing some of the great ideas from Eurekazone...


http://eurekazone.com/gallery/ez-woodworking-inventions

[ShagRock]

RodB - thanks much for the disgrams on joining plank edges and your reference to the Eurekazone. On the latter, this looks like a great system for straight cuts, but not sure how it handles curing curves? It would be really neat for transporting to work site or out to the backyard as opposed to lugging around a table saw setup! Some further queries:
1) Will it allow easy cutting of say 45 deg bevels?
2) Can it be used to rip strip planks from a a piece of 2 x 8' stock? and if so could it be shifted ahead or to opposite end of a long plank say 16' long to achieve the same result?

Cheers:)
ShagRock

[RodB]

The Eurekazone system allows cutting a bevel... pretty simple. Listen, the inventor of the Smartguide has a system that will allow you to almost never use your table saw. Check out the website and look at the variety of tasks you can do with their system. Its truly amazing. The all around ease of handing ply panels sold me.

As far as cutting strips... you can bolt the smart guide 50" segments together and make a longer one... but I don' think Dino, recommends longer than 12 feet for maintaining a very straight edge... (150 inches with three 50" guides). It would be quite simple to take an 8 foot or 12 foot straight edge of theirs and shift it forward and continue the cut... making sure it is aligned with the first cut. They have a repeater device that attaches to the saw base and allows you to do the same width cut over and over.

Most folks buy the 100 inch setup and have two 50" guides that can be connected when you need to cut longer than 50 inches. I also have the shorter 25" guide for cross cutting. I may, someday buy an extra 50" guide and keep two of them bolted together permanently so I can always handle the 8 foot cut on ply without any messing around.

I think the easiest way to cut strips on very long stock is with a circular saw jig base specifically set up for the strips you desire... but you need to build a nice long narrow table for the stock to sit on. Of course this shelf/table can be simple or quite elaborate... depending on your needs. Note:.... Its much easier to move the saw than the long stock and with a thin kerf Matsu****a blade, you will be cutting perfect strip planks for a very long time.

This is the easiest way to cut strips on long stock... IMHO

http://www.home.earthlink.net/~durgerian/id5.html



http://i40.photobucket.com/albums/e239/Prestoboat/Misc%20boats%20etc/cutting_strips.jpg

http://i40.photobucket.com/albums/e239/Prestoboat/Misc%20boats%20etc/stripjig.jpg

http://i40.photobucket.com/albums/e239/Prestoboat/Misc%20boats%20etc/sawstrips.jpg



I still think the worm drive saw (my choice is the Makita hyphoid) allows the most control in cutting ... I use it alot for general cutting and I can freehand close to a line so easy. ITs the cats meow for cutting out stitch and glue panels... ie., following very close to the line. Of course, I use a normal circular saw with the smartguide system... With the worm drive saw... with shallow blade depth, you can cut gentle curves. Also, as mentioned above, a corded trim saw with a smaller blade is a cool tool for a bit stronger curves... but I prefer the worm drive cause is just so darn easy to control with its gyro effect. I guess it depends on exactly the type of cuts you are doing and the quantity.

Good luck,

RodB