Firstly let me say that I am indebted to two member Robert and Woodbloke here without whose inspiration and help I possibly would not have undertaken this,
With the help of Rob and his mega throated bandsaw and drum sander he cut some oak into 2.5mm veneers for me.
You may recall this post from Robert viewtopic.php?f=26&t=1022 which I largely copied to make my vacumm pump.
I have also followed his improvised bagging methods which have work far better than I could have imagined so on my second run, I took photos and did this write up. I think Roberts original posts were lost when Woodhaven died.
Firstly I took some fairly heavy gauge polythene sheet cut from industial waste sacks (domestic bin liner are too fragile) enough to cover the workpieces twice with about 100mm to spare all round.
here with the substrate in place
and with the substrate removed to see the location of the vacuum pipe
My pipe is 6mm hard nylon and is curved due to it being supplied on a coil so I used masking tape to try and hold it straight.
I did two pieces with veneer on both sides in one go and cut another piece of polythene as an interveaving sheet to avaoid any risk of gluing the two panels together.
Here is one piece of book matched veneer taped ready for glue in the traditional manner.
I've not shown the glue application but I applied ordinary pva with a 100mm foam roller to the back of the veneer. I chose to apply to the veneer as my substrate is MDF and I wanted to minmise the risk of it swelling with the wet glue before I was ready to apply the vacuum pressure.
Here is the stack of 4 veneers and two substrates with the interleaving sheet place on the polythene sheet.
Now for the seal. run a bead of ordinary silicone sealant arounf three sides in a continuous run with an extra blob where the pipe goes in. Not that the smasking tape stops short of the silicone. and the bead extends at both ends a little to make sure there is enough on the fold.
some of the masking tape decided to let go as I took the photo but that was easily reapplied before applying the vacuum.
Now fold the upper half of the polythene over the top of the stack, gently form round the edges and then lightly press onto the silicone without deforming it much.
Switch on the vacuum and it soon looks like this
You can hear any slight leaks apply a bit of finger pressure or in extremis an extra squirt of silicone in the offending area.
Soon the vaccuum gauge looked like this and the pump switched off. I've not heard it come back on so no leaks!
I also lightly clamped the tube as it comes up from under the bench to remove any risk of the polythene being dragged aside
I recall some of my military colleagues saying "Preparation and planning prevents * poor performance"
Certainly applies here. Do some dry run practice first but it is very straight forward with a bit of preparation.
Thanks for reading
Bob