JBL 4343 restoration, progress and quite possibly a lot of question along the way

[macaroonie]

One thing to remember is that due to the larger diameter of the cutter for a given rotational speed ( RPM ) the blade speed will increase. There is always a sweet spot cutter speed , mostly depending on the material and also the rigidity of the tool system. You will most likely want to run at a lower speed than normal with that big cutter , that's if your motor is equipped to do that.

Since the profile is end-on to the sheet and since the remaining profile has a sharp 45 deg point that you want to preserve intact I suggest that you either register your work piece to a sled that is jigged to run across the cutter. Ie. no fence.

or

Use a fence at the other end of the workpiece , no fence at the cut edge. You will need to rig up repeatable stops or marks to get your sizes to repeat ( sides , tops all the same )

Go back to the build thread I posted ages ago

http://www.audioheritage.org/vbullet...l=1#post181001

Footnote : Those canteen tables with a steel frame and a formica top can be found at the reclaim places for pennies. Plenty of area to work with and a good surface. It's usually laminated to birch ply.

[DingDing]

Mac: The Triton has variable speed and recommended speed settings depending on the diameter of the cutter, but it didn't take account for the material density. I guess you just need to work some things out by experience.

Good ideas about the canteen tables and the sled. The reclaim places are far away from where I live and IKEA ships so I'll see what I can find. I saw a guy who built a sled that attached to his custom fence when doing the horizontal cut. Would be ideal for bigger panels.

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Have been experimenting a little today.



The blue is two coats of RAL5007 matte finish on one coat of primed MDF. It's a little less deep than the blue which was on and has a little more gray to it. The picture doesn't quite capture the color of the objects, but I think this color will work very well.

The left piece of walnut was laminated on using contact cement. I think there was something wrong with the cement as it would not stick to the paper backing properly and was impossible to distribute evenly on both surfaces (MDF). Was impossible to get rid of the uneven buildup no matter how much pressure I put on it. It was probably a problem with the contact cement or it was just a poor product. If it had distributed evenly it would have been a good choice for smaller projects which should be done as fast as possible. The sample is also oiled with two coats (will do more) of some cheap teak oil I had sitting. Going to get better oil which brings out more of the red color.

The right piece was glued on with some PVA glue I had by putting on two thin coats and letting them have a rubbery consistency to the touch. Used an iron and a scrap piece to add pressure along the grain. This method was preferred but took longer. Will practice some more with bigger pieces until I do the speakers and will use Titebond II and not what I have, because I know it works over time.

So all in all a good experience with the wood glue iron method. Saeman made a very good post of his insights a while back. Here they are again for anyone who may want to try this.

saeman's words and takeaways

For what it's worth, here's a few comments on problems I have encountered.

1. I have used paper back veneer, bubble free and phenolic backed veneers. Paper backed is the easiest to work with as it is thinner material. Phenolic backed resembles formica in overall thickness. It bonds well but since it is thicker it's harder to make sure there are no voids or bad bond spots.

2. I have talked a lot about buying some kind of commercial heating iron and never have. My wife's clothes iron works great and she hates to use it anyway. Her current iron used to be teflon coated but I've worn patches of the teflon off pressing veneer.

3. Temp setting is about 1/3 of max for most household irons, or about 160 degrees max. Too much heat and you will melt and puddle the glue under the veneer - TROUBLE - if this happens you need to turn the heat way way down and slowly dry the glue again. All you need is enough heat to re-activate the glue to allow both glued surfaces to bond (just like two surfaces coated with comtact cement.

4. Going over the veneer with a hot iron is not enough. More pressure is required to ensure a solid bond. Heat about 1 square foot at a time and immediately (while the surface is still damn hot to the palm of your hand) roll over that area with a 4" veneer roller applying all the pressure you can. Roll slowly and listen for any crackling sounds. Roll with the grain and then roll side to side against the grain. If you hear crackling it indicates that the veneer is lifting. Heat - roll - heat - roll, until there is no crackling to be heard. After doing the whole surface go aroung all edges again. Let that panel/side sit for several hours and then trim off excess veneer. Then go over the whole surface again slowly with the roller and listen for any crackling. After sitting for a while if the bond is not good it will lift. If this problem occurs hit it with the heat again. I have always used Titebond II and have heated and reactivated as long as two days after laying the veneer.

5. After you have trimmed off excess veneer - take your thumb and fan the entire edge (like you would shuffle thru pages in a book or a deck of cards) and listen for spots where the veneer is loose around the edge. Heat and roll any you find.

6. Bubbles under the veneer usually happen when too much heat is applied. With some practice everyone using this method will find their own settings. Not enough heat and your veneer will be crackling under the roller until your supper is cold. TOO MUCH heat will melt the glue and quite often cause bubbles. If you have a bubble that persists, it can be sliced open using a thin blade modeling knife. Let any trapped air escape, roll the hell out of it and apply less heat in that area to get a bond.

7. Applying the glue - I apply 2 (sometimes 3) coats to each surface using a 4" paint roller. Most veneer manufacturers recommend a 6 to 8 mil glue coating between veneer and substrate. If you skimp and apply only one coat you'll some day, after a big change inhumidity, find your veneer lifting from the surface. Titebond II turns clear when it's dry to the touch. When the first coat is dry you can apply the second/third coat. You can wait as long as a couple of days to apply your veneer but I have had the best results after waiting just an hour or two after the last coat is dry. It will appear dry but you will be able to penetrate the glue with your finger nail and it will feel a bit like a hard rubber surface. If you wait a day or more the glue will be HARD and even though heat will reactivate and bond, I have gotten the best results with the rubber like surface.

That's a lot of rambling and babbling but maybe my techniques will help some of you achieve the results you're looking for. I've had a lot of frustration doing veneer work but have worked out the bugs and have been getting good results.