building form maintainance

[patrick corry]

I have a traditional building form for a wood/canvas canoe onto which I will shortly begin bending ribs. The form is of unknown age, though relatively new, presumably 10 years old or so. The 3/4" x 3/4" strips with which the form was built have dried over time leaving the galvanized metal strips ever so slightly loose, or away, from the body of the form. Those galvanized strips were, of course, fastened at the center line and near the inwale position and since they haven't changed length they now stand a bit proud of the form surface.

Should I release the strips at the inwale end and re-fasten so they are tight to the form? And also, after removing (sanding off) the surface corrosion, should I varnish the entire form to inhibit future corrosion? I'm concerned a bit with having the few spots of rust transfer to the ribs which will be hot & moist when in contact with the metal.

Thanks for your thoughts.

 

[Andre Cloutier]

Hello Patrick, bit of a judgement call in terms of what is considered loose. Bands tight to the form will give the best shape, and just as important will limit the bounce of the rib when struck to clench the tacks, which could give a less than desirable outcome. maybe take a picture to show how loose they are. Not a huge deal usually to tighten them, depending how they are fastened. If the galvanizing is now rusted, you can sand and varnish, or even lay clear packing tape over the steel before bending, or both. More varnish never hurt any forms, lol. You will get staining on the wood though based on your description if used as it sits - ask me how i know. best of luck,
A

 

[patrick corry]

Maximum 'stand-off' from the surface of the form is no more than 1/4", mostly less. Central rib brace is omitted for clarity.

 

[Michael Grace]

It seems unwise to count on those bands to get a good clinch on your tacks. Can this be rectified? Is this, as you suggest, because the form has dried and shrunk, or is it because the form isn't fair? If the form does have a smooth, fair curve in the bottom of the canoe, one approach would be to remove all screws beyond the center of a given band, then start by adding screws to hold the band down in the high spots, then work outward toward the rails. Just a thought. You've got the best insight by having the form there with you.

 

[Rollin Thurlow]

Yes, it would be wise to remove all the steel bands; Plug all the screw holes from the steel bands; Give the hull a good sanding to smooth out any rough edges and maybe add some filler to any low spots; Give the form a couple coats of varnish; On the underside of the old bands, file down the metal around the screw holes that will keep the band from laying flat; Reinstall the bands holding them as tight as possible to the form; apply two coats of varnish to the steel bands and a bit of tape over the heads of the screws.
Its a bit of extra work but the canoe hull will be so much better.

 

[patrick corry]

My thanks to all of you who have replied. In my original thinking, my concern was for the final shape of the ribs and hadn't really considered the facility of clinching the planking tacks. I see now that that would have been the greater concern. That different perspective is why I posed the question.

Now that Mr. Thurlow has weighed in... after all, this form is of his Atkinson Traveler design... I value the detail of the replies and the level of work which must be done to preserve the form and it's function. The form was well made by a gentleman in Ohio, and was faired correctly with voids filled where necessary to give a good shape. Once I am done with the build I hope to donate the form to a teaching group, perhaps a school vocational arts program or a wood/canvas canoe building program where it can benefit a greater number of people.

One last question: What is the preferred method of securing the metal strips to the form? In the attached pictures you may notice that some of the drywall screws used are not fully flush with the surface of the metal. Would nails be a better alternative, such as ring shank drywall nails which have a very thin head? If bugle-headed drywall screws are OK, how should the metal be drilled and prepared best to allow the screw heads to be flush with the metal. It would be a shame to pull the hull off the form and find dozens of phillips head impressions on the inside of the ribs!!

Thanks gentlemen.

I found that a ratchet strap around the entire form and rolling table will hold the metal tightly to the form everywhere.

Here, note the displacement from the original fastening location when the metal is held tighter to the (perhaps shrunken) form.

And finally, an example of the screw head proud of the metal surface. This is common in many spots.

 

[Andre Cloutier]

wow that’s loose. Forget the strap, one screw at the rail won’t hold it all tight. Ring nails on the edge will keep them flat and tight. My forms, esp my wanigan forms are done this way. Only a screw at the rail after all band is flat. I’ll see it I can get a picture

 

[Rob Stevens]

Comme ca.

 

[Andre Cloutier]

Well, that looks familiar lol

 

[Todd F]

Had to look up the translation for Comme ca. All good now!