Shopsmith Forums

Is not the 'middle' the point at which the bend radius is smallest? i.e. is the gunwale not straighter towards the ends? IIUC putting the scarf joint in the middle places it at the most stressful location.

JPG40504 wrote:Is not the 'middle' the point at which the bend radius is smallest? i.e. is the gunwale not straighter towards the ends? IIUC putting the scarf joint in the middle places it at the most stressful location.

Hmmm. I think the upward sweep at the bow and stern may have the smallest radius but you raise an interesting point.

algale wrote:I'm getting ahead of myself here, but...

I have some black walnut in 6 and 7 foot lengths that I would like to use but I would have to scarf three pieces together to get the necessary length. This will put the two scarf joints closer to the ends of the canoe and under more stress than a single scarf in the center of the canoe.

I assume epoxy/microfiber glue will be stronger than the wood itself, but I'm not sure if I'm asking for trouble.

Anybody got any views ?

Thanks,

Al

I don't have a lot of experience with actually making scarf joints, the strippers I built did not require many, so factor that in when considering my two cents here...but, from reading and from making lots of other types of glue joints, I believe that if the scarf bevel is shallow enough, on the order of about 6:1, a good tight fit and clamped securely then the resulting joint will bend pretty much the same as if it were a solid piece. I just this week read in John Brooks' book "How to Build Glued Lapstrake Wooden Boats" that in his planking plywood any bevel longer than 6:1 produced noticeable flat spots. At 6:1 the plank bends into a fair curve. Given, then, that a properly scarfed gunwale will act like a solid piece I am not sure I can see that there will be more stress created by multiple scarfs or by the location of the joints.

The sweep of the sheer in both horizontal and vertical directions on a canoe is pretty mild and I would guess that making the gunwales up out of three pieces instead of two would be OK, providing the scarfs are done neatly. If the stem ends of the gunwales don't want to take the vertical curve you could consider edge gluing a second strip to the gunwale for a couple of feet at both ends of the boat and then cut out the shape of the vertical curve to match the sweep of the rest of the gunwale.

Per the the book I am using to build the Slow Boat, I have applied a sealer coat of epoxy (tinted with sanding dust) to the outside.

In addition, while the sealer coat was still tacky, the book called for reinforcing the stems by applying a 4 inch wide strip of fiberglass and wetting it out with clear epoxy.

I found cutting these fiberglass strips left many, many loose fibers on the cut edges of the cloth. Has anybody got any tips for minimizing loose fibers when cutting the fiberglass?

In addition, while applying clear epoxy over these reinforcement strips and squeegeeing off the excess, some of these loose fibers pulled away from the cloth.

I removed the stray fibers I saw while the epoxy was still wet, but as the epoxy makes the glass transparent, I missed some. After it all had cured, I sanded the sealer coat and the stem reinforcement strips per the instructions in preparation for applying the first full layer of fiberglass. As I sanded, the shapes of the stray fibers that I missed revealed themselves.

Even when sanded smooth to the touch, the fibers have left behind whitish "ghosts" or trails in the sealer coat. I am hoping I don't need to sand these ghosts out completely before applying the next layer of fiberglass and that if I simply sand the ghosts smooth they will disappear when the next layer of glass is applied and wetted out with epoxy.

Thoughts?

algale wrote:Has anybody got any tips for minimizing loose fibers when cutting the fiberglass?


Thoughts?

The problem with cutting cloth, as you discovered, is the ragged and unbound edges that fray and shed. One way that is recommended to deal with this is to cut the cloth "on the bias", that is, at 45 degrees to the weave of the cloth. I have tried this but found that there still was too much loose fuzz. The best way is to purchase a roll of fiberglass bias tape, which is not only bias cut but has a selvedge or stitched edge along both sides. It has been many years since I bought any but as I recall it was easy to find a source for a roll of 4 inch wide tape. All the problems with loose fibers should disappear with the tape.

Hope this is helpful.

PS Thanks for the project update.

Are you using Mat or tape. Tape comes in 4" wide rolls. Only cutting is the length. Sharp shears cut cleanly. Avoid mat unless it is unsized (no wax) with epoxy resins.

I just did a quick Google search and found that Jamestown Distributors has the glass tape with both edges woven in widths from 2" to 12". Looks like it should be just the ticket.

Personally, I don't like tape because the finished edge, while it doesn't fray, does cause a quite a lump on its own.

I prefer to cut the strips myself as follows. Start by pulling a strand or two out across the cloth. If it's wide this can be a little frustrating at first but once you get the hang of it .... not so bad.

It is worth while because it gives you a path to cut parallel to the strands. Once your strip is cut off pull the last couple of strands away from each side and each end. What you are left with is a nice straight piece of tape with a longish "fringe" on all sides. It will apply without losing any strings unless you are really rough with the squeegee.

When you 'glass with epoxy, apply the cloth dry and smooth out all the wrinkles. Then apply the epoxy carefully from the center out to the edges, keeping all wrinkles ahead of you.

Good luck and have fun.

Thanks for the responses, Ed, Tenbears and Shipwright. Looks like there are advantages and disadvantages to using tape. To answer your question, Tenbears, I'm using woven cloth.

I don't think either solution (tape or pulling fibers to get a straight cut line) will work for the next piece of fiberglass I need to cut, which is a piece that covers the "football." The area is way too wide for tape and it has no straight edges to use Shipwright's trick. It is placed down dry, and then a full sheet covering the entire hull is laid over it. Both are wet out at one time. I'm hoping the inevitable loose edges on the football shaped piece will be less prone to coming out because they are under the full sheet, which should protect them from pulling from rollers, brushes and squeegees.

Incidentally, I didn't see any advice or views about the other question in my post (about the ghosts in the epoxy the strands left behind)? Do I sand down until smooth only or do I need to sand them out completely down to bare wood before applying more glass/epoxy?

algale wrote:Thanks for the responses, Ed, Tenbears and Shipwright. Looks like there are advantages and disadvantages to using tape. To answer your question, Tenbears, I'm using woven cloth.

I don't think either solution (tape or pulling fibers to get a straight cut line) will work for the next piece of fiberglass I need to cut, which is a piece that covers the "football." The area is way too wide for tape and it has no straight edges to use Shipwright's trick. It is placed down dry, and then a full sheet covering the entire hull is laid over it. Both are wet out at one time. I'm hoping the inevitable loose edges on the football shaped piece will be less prone to coming out because they are under the full sheet, which should protect them from pulling from rollers, brushes and squeegees.

Incidentally, I didn't see any advice or views about the other question in my post (about the ghosts in the epoxy the strands left behind)? Do I sand down until smooth only or do I need to sand them out completely down to bare wood before applying more glass/epoxy?

From my experience with fiber glass the white ghosts as you call them will disappear with the next layer of resin. What you want is smooth and enough resin to make cloth disappear.
Too many try to squeegee to much resin off and the matting remains visible and detectable to the touch.

I say all of that with this in mind every time I fiberglass I use gel coat or a tinted resin topcoat. I have never gone for a clear resin only finish. So since everything underneath is covered I was only concerned about smooooooooth.