Post by Sgian Dubh on Jan 13, 2008 23:47:26 GMT
A short while back on another forum someone posted his technique for veneering using drafting tape or drafting dots to join the prepared veneers.
I expressed some doubts about the suitability of using drafting dots for this task guessing that they might perform much like masking tape. Masking tape has the nasty habit of adhering too well to the wood and on removal tearing out the grain. It is also quite thick and, on soft veneers, I’ve experienced it leaving a depression in the veneer that’s difficult to remove without cutting through to the ground below.
I decided to give the drafting tape technique a go on a sample board. I used a piece of 12 mm MDF as the ground and used some offcuts of crown cut black cherry (Prunus Seritona) and radially sliced European beech (Fagus sylvatica) veneers for each face.
The rest is a photo essay of the job with comments here and there and a conclusion at the end. I’ve posted much the same on a couple of other forums, and here I simply post it as general information for anyone that might find it useful.
The following four images show the veneers cut with a laser line guided guillotine and the prepared edges taped together, the cherry with drafting dots and the beech using masking tape. I used PVA glue and applied it the ground on both faces to press the veneers in one go.
The panel is slipped into the veneer press. I used a heated hydraulic press for speed, although I could have used the vacuum bag press. Hide glue and a veneer hammer don’t work well at all with masking tape as the join ‘cramp’ and I doubt that drafting tape would perform any better. Both these methods are slower anyway and I was after speed.
The veneered panel gets high pressure heat treatment. The panel stays in the press for about 60 seconds: that’s all the time required for applying veneer with platens heated to 60ºC.
The bottom platen lowers to remove the panel. Normally I slip a sheet of plastic, like a cut up black bin bag, between the platens and the panel to prevent sticking. I didn’t have one handy so slapped a bit of paper towel either side, something I wouldn’t normally do as the paper gets imprinted into the veneer’s grain.
The veneer, the ground and the tape is hot when removed from the press, so you’d think tearing off the masking tape, next, or the drafting dot tape in the image after, wouldn’t cause grain tearout. It does in both cases even though I was very careful how I peeled back the tape. I was a little surprised to see the drafting dot removal caused more damage than the masking tape. However, beech is very hard, and the cherry joined with the drafting dots is a lot softer, so perhaps the tearing out of the grain in the cherry isn’t too surprising.
Glue bleed through on the beech veneer.
Some residual adhesive left on the cherry veneer from the drafting dot.
A bit of prep work is needed, so it's off to the 100 grit abrasive paper on the stroke sander followed by some hand sanding to 150 grit. After that a bit of carelessly brushed on shellac just to seal the grain.
In these last four images you can see the general colour and the bit of torn out cherry grain shows rather badly.
Conclusions. I was right to be sceptical of the efficacy of drafting dots used as a means to join veneers prior to gluing. They do tear out the grain on removal just as masking tape does, but I suspect it depends to some extent on the wood species. Neither the masking tape nor the drafting dots imprinted themselves into the wood. The masking tape I suspect was defeated by the hardness of the beech veneer beneath it. The drafting dots are thinner, so perhaps their ability to imprint deeply is compromised.
I shan’t be switching over to using drafting dots to join veneers on a regular basis, particularly for woods that can be ‘stringy’ such as European sycamore (Acer pseudoplatanus) for example or hard maple (Acer sacharum). I might use it for some of the harder tighter grained woods such as ebony or possibly some of the rosewoods. Slainte.
I expressed some doubts about the suitability of using drafting dots for this task guessing that they might perform much like masking tape. Masking tape has the nasty habit of adhering too well to the wood and on removal tearing out the grain. It is also quite thick and, on soft veneers, I’ve experienced it leaving a depression in the veneer that’s difficult to remove without cutting through to the ground below.
I decided to give the drafting tape technique a go on a sample board. I used a piece of 12 mm MDF as the ground and used some offcuts of crown cut black cherry (Prunus Seritona) and radially sliced European beech (Fagus sylvatica) veneers for each face.
The rest is a photo essay of the job with comments here and there and a conclusion at the end. I’ve posted much the same on a couple of other forums, and here I simply post it as general information for anyone that might find it useful.
The following four images show the veneers cut with a laser line guided guillotine and the prepared edges taped together, the cherry with drafting dots and the beech using masking tape. I used PVA glue and applied it the ground on both faces to press the veneers in one go.
The panel is slipped into the veneer press. I used a heated hydraulic press for speed, although I could have used the vacuum bag press. Hide glue and a veneer hammer don’t work well at all with masking tape as the join ‘cramp’ and I doubt that drafting tape would perform any better. Both these methods are slower anyway and I was after speed.
The veneered panel gets high pressure heat treatment. The panel stays in the press for about 60 seconds: that’s all the time required for applying veneer with platens heated to 60ºC.
The bottom platen lowers to remove the panel. Normally I slip a sheet of plastic, like a cut up black bin bag, between the platens and the panel to prevent sticking. I didn’t have one handy so slapped a bit of paper towel either side, something I wouldn’t normally do as the paper gets imprinted into the veneer’s grain.
The veneer, the ground and the tape is hot when removed from the press, so you’d think tearing off the masking tape, next, or the drafting dot tape in the image after, wouldn’t cause grain tearout. It does in both cases even though I was very careful how I peeled back the tape. I was a little surprised to see the drafting dot removal caused more damage than the masking tape. However, beech is very hard, and the cherry joined with the drafting dots is a lot softer, so perhaps the tearing out of the grain in the cherry isn’t too surprising.
Glue bleed through on the beech veneer.
Some residual adhesive left on the cherry veneer from the drafting dot.
A bit of prep work is needed, so it's off to the 100 grit abrasive paper on the stroke sander followed by some hand sanding to 150 grit. After that a bit of carelessly brushed on shellac just to seal the grain.
In these last four images you can see the general colour and the bit of torn out cherry grain shows rather badly.
Conclusions. I was right to be sceptical of the efficacy of drafting dots used as a means to join veneers prior to gluing. They do tear out the grain on removal just as masking tape does, but I suspect it depends to some extent on the wood species. Neither the masking tape nor the drafting dots imprinted themselves into the wood. The masking tape I suspect was defeated by the hardness of the beech veneer beneath it. The drafting dots are thinner, so perhaps their ability to imprint deeply is compromised.
I shan’t be switching over to using drafting dots to join veneers on a regular basis, particularly for woods that can be ‘stringy’ such as European sycamore (Acer pseudoplatanus) for example or hard maple (Acer sacharum). I might use it for some of the harder tighter grained woods such as ebony or possibly some of the rosewoods. Slainte.
