Thread: Movement in shop made ply doors

The body rests on my basses are all one direction grain with about a 3ft radius curve, very stable. Mine are 5 ply.

Originally Posted by Ball Peen

The body rests on my basses are all one direction grain with about a 3ft radius curve, very stable. Mine are 5 ply.

Thanks Bill,

I considered making them 5 ply, but am concerned about the open time of the glue. 5 Ply has four surfaces to be glued up, and 3 ply only two.

What glue are you using to bond the veneers together?

John, mine are only 170mm x 520mm. Tightbond, and I have to go like the clappers! Resorcinol is slow enough for an early morning session but you will have black lines.

Use a sponge paint roller and tray to speed things up. Isn't plywood laid with the grain alternating to prevent creep?

Originally Posted by Chris Parks

Use a sponge paint roller and tray to speed things up. Isn't plywood laid with the grain alternating to prevent creep?

I always use a sponge roller on big jobs, but open time is still limited.

Not worried about dimensional changes due to seasonal humidity, so I hope I can run the grain in one direction so the edge remains pretty.

Fine Woodworking recently ran a video feature making a small curved front wall cabinet.

With this they made a bending form to be able to generate all of the face components (2 doors and 5 drawer fronts) in one run then cut the various components out and sized them. Their steps were basically.


Laminate a curved front substrate by vacuum moulding 2 or 3 layers of bending ply over their bending form.

Mark and cut each face component undersized (to allow for edging)

Cut and apply edging that is sourced from the same board as the face and back veneers to each component and trim flush front and back but leaving oversize top, bottom and sides.

Vacuum mould slightly oversized front and back veneers to edged substrate one component at a time.

Trim finished components to size to fit the appropriate openings. The trim process is working front and back veneers and the intermediate edging simultaneously.

This technique gave them vertical edgings that matched the face veneers with virtually invisible glue lines, however the top and bottom edgings were noticable because the veneers were endgrain and the intermediate edging was face grain.

I suspect that you could probably do your doors by pre edging a suitable flat substrate and then veneering face and back. From the look of your image, I doubt that either top or bottom edging being face grain would be a visual issue as they appear well above or below normal line of sight, however you could possible make those edgings in end grain if you thought it worth the effort. I think FW used one of the Titebonds as adhesive, but not sure at the moment but could check and report back if you are interested.

Hope this is usefull

Thanks guys,

I now have some more ideas to think about as I contemplate final design.

Until recently I'd have assumed that to get good stability in ply panels (such as I intend to make for the doors for this unit) that an odd number of veneers was required. I recall my dad telling me as a kid that ply always has odd numbers of veneers ... and so it seemed to be ... until recently. Whenever I bought ply it was 3, 5 or 7 ply.

I bought a 17 mm ply panel from Bunnings a while ago. What struck me was that it had an even number of veneers. Judging by the fact that the inner two veneers have grain running in the same direction it seems that two pieces of 8 mm three ply have been glued together and sanded back to 17 mm. So it is a six ply.

So, as I make up these doors, should I stick to the old rule my dad taught me (always use an odd number of veneers, and ensure they are balanced around the centre veneer) or do I have options?

Hi John,
My thinking would be that for a ply sheet to remain stable and flat that there will be an odd numbers of plies, for a 3 ply, the outside plies will balance each other against bow/curve while the center ply prevents the dimensional change of the outer plies, of course the outer plies does this as well for the inner.

For a made up board/piece from leaves/plies where dimensional stability is given the same consideration as we might give to solid timber I don't think it matters wether the leaves are odd or even when the grain runs all the same direction, of greater concern will be the radius to be formed, the timber used to form the plies, the final thickness, glue used and glue up time, springback.

Here's a few pics of what was to become a curved apron, I wanted 19mm thick so first up I went for 6x3mm thick plies, (18mm plus one for veneer), all cut from the same board and then glued back together, 3mm bent OK for the radius, although thinner would have given me less springback but more glue faces to glue up and maybe a different glue choice and on it goes...
Vic ash leaves.jpgleaves in the former.jpg



Pete

Originally Posted by pjt

Hi John,
My thinking would be that for a ply sheet to remain stable and flat that there will be an odd numbers of plies, for a 3 ply, the outside plies will balance each other against bow/curve while the center ply prevents the dimensional change of the outer plies, of course the outer plies does this as well for the inner.

For a made up board/piece from leaves/plies where dimensional stability is given the same consideration as we might give to solid timber I don't think it matters wether the leaves are odd or even when the grain runs all the same direction, of greater concern will be the radius to be formed, the timber used to form the plies, the final thickness, glue used and glue up time, springback.

Pete

Pete,

Thanks for that ... it pretty much confirmed my thinking.

As matters transpire, SWMBO decided yesterday that she wanted flat doors. However, this info has been stored away for future use. I have a bee in my bonnet about making a tall, narrow cabinet where the bottom edges of the doors bend and flare a little ... like the hem of a skirt.

Cheerio!

John