filling countersunk screws prior to veneer

I am an experienced in wood working, but I have mostly worked with solid wood. When I have used veneer, it is in the form of veneer plywood... used for table-tops and as the panel in frame-panel cabinet doors. Speaker construction is somewhat different than normal cabinetry (obviously).

I am planning a project using 20mm (3/4 inch) Baltic birch plywood, and there will be many countersunk screws on the outside of the cabinet due to the bracing. Before I veneer the outside of the cabinet, I assume I must fill those screw holes and sand flush so that the veneer has a smooth flat face to bond to. I am using peel-and-stick veneer.

What is the recommended filling material? spackling compound (used in gypsum board / drywall construction)? automotive "bondo" body putty? I can think of several materials which might work, but what is the best practice ?

Jim
 

TMM

Member
2007-09-01 8:37 am
Australia
Another +1 here for automotive body filler.

Epoxy would also work, but is softer so is more difficult to sand (it 'gums up' when sanding due to the heat generated). Auto body filler is usually polyester resin with some filler material to make it thick and so it sands better.
 
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pkitt

Member
2009-02-24 12:32 am
I first used wood screws, then biscuits, but for quite a few years now I've used dadoes and rabbets with the added benefit of everything going together squarely.
Paul

In my Basszillas there is extensive bracing and no metal fasteners. As an experienced woodworker you should be able to cut dadoes and rabbets without problems. Optionally you could use biscuits or dowels, neither of which requires drilling on the exterior surfaces.

Building the BassZilla Platinum Edition - Fall 2012
 
Automotive body filler is fine. No need to use a specific wood filler as the patch won't show. Before applying the vener and after filling the holes I would seal the wood surface, lightly sand it and seal again. It will reduce moisture show through and give the veneer a better bonding surface.

I used veneered chip board for some disco speakers.
Worked great until one night going into a gig they got wet.
The chip board just swelled up and fell apart at the ends.
Lesson learned, plywood from now on.
 

Galu

Member
2018-04-17 6:50 pm
^ Did you not use the iron-on edging tape to protect the raw chipboard edges, along with a couple of coats of varnish Nigel?

That describes the home made cabs I used for my very first disco - guaranteed to be beer and lager proof!

P.S. I used wood screws, but from the inside.
 
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^ Did you not use the iron-on edging tape to protect the raw chipboard edges, along with a couple of coats of varnish Nigel?

That describes the home made cabs I used for my very first disco - guaranteed to be beer and lager proof!

Yes I used the iron on strips on the tops but not the bottom of the box.
Explains why.
 
So to bring an old thread back to life...

I tried many of these methods, just to see which was easiest. The method I like the best is to counterbore the screw hole at 3/8" diameter, then glue in a small section of 3/8 dowel. I cut the dowel rod into 1/2 inch sections on my band saw, and then after gluing I cut them flush with an oscillating multi tool. Then hit is with 100 grit paper before veneering. This proved faster, easier, and less trouble prone than filling the holes with paste or glue or goop.
 
I want to mention another method.

Keep in mind we are talking about situations where internal bracing needs to be secured with a screw from the outside of a cabinet wall. I am using the "highly braced" cabinet technique which avoids structural damping but instead uses extensive bracing to drive resonant frequencies above the excitation region of music/film soundtracks. Cabinets like mine have a LOT of internal bracing.

Most of the bracing can be clamped in place, or secured with a dado cut. However, there often arises a situation where the most straight forward approach is to use the humble screw.

So this final method I want to mention is to use an exposed temporary screw. This procedure is common in boat building, but I have not seen it used very often in furniture or cabinet construction: A pan-head screw and a fender washer are used as a clamp while the glue dries. After the glue has fully cured, the screw is removed. The small hole that remains can be filled with a drop of glue, lightly sanded, and veneered over. This method can be applied anywhere there is an adequate glue joint, but no good way to achieve clamp-up with typical clamps.
 
A reason you don't see some of these suggestions in furniture/cabinetmaking is the word "telegraphing". You learn to not penetrate any surface if it will be either veneered or paint/lacquered. There is always a good chance that any surface imperfection/repair will eventually show up in the finished surface. Dowels on end don't contract lengthwise at the same rate as the surrounding material. Result is round dots under the veneer which you can then do nothing to correct.


Best to exhaust all other methods before going through the face.You can just as easily add a screw block to the end of an interior brace and fasten that to the interior side of the cab wall(s). No need to create additional, time consuming, finish prep on the exterior.