want to try veneering curved surface (Speaker box) with a vac press

[David R Jones]

Hi all, I think this is my first post, though I did join some time ago. I emailed Joe Woodworker the question below. He suggested I pose this here. I'm always doing something out of the norm, it's more fun that way... Here is the question:

<I need info on using a vac pump to veneer curved surfaces. Specifically speakers. I used contact cement before. Too bumpy. But i wrap the veneer right into the speaker itself (around the curves to the front where the speakers, or drivers, are in the black baffle) So the question is, can a "U" shape like this be veneered (sides and back) by letting the bag hug it inside and out as if it were a flat piece, except it is bent into a "U"? In the unfinished pic next to the one with stairs in the background you can see the veneer comes around from the back into the recess, and makes a pretty tight curve, gluing tight to the recess. I want to get a vac kit. It will doubtless need a mesh liner (or two?) and a good manifold to work. I have to rebuild the center channel (see pic attached in the second link with the big crack :() and want to do it right 8-) I would drive up to talk with you from Fairfax Va, but I don't want to get in your way. You sound busy...>

pics are here:

https://plus.google.com/photos/103557548946136147331/albums/5094533900960892913?banner=pwa

https://plus.google.com/photos/103557548946136147331/albums/5409383180300315505

So I am asking if anyone can see problems using a bag in this fashion. I will try a few flat things as practice first. I would get a vac kit with a venturi since I have an 60 gal. Husky compressor already. The vac press will be used to rebuild the center channel which obviously needed to be veneered with a backed veneer before finishing to prevent movement. All efforts to fix with Bondo failed to produce the desired result since the MDF is just fine grained oatmeal. The next try will be sealed inside an out with thinned shellac for penetration and then several heavier coats. Experience is the best teacher...

I case anyone just wonders why I want to do this, you only need to take a look at Sonus Faber Amati Futura (http://www.sonusfaber.com/futuraamati/en/)...:D:D:D Doing my own saves me over $34000.00!!

TIA for your consideration!

Dave Jones

[Steve Rozmiarek]

Dave, you want to veneer the inside too, or just the outside? I don't see any issues with it, except the u channel needs to be uniform. Any crossmembers, or blocking would give the bag a reason to wad up, or worse yet, break things. Keep in mind, that is a big thing, and getting it all prepped and into a bag will take some planning. Cool stuff though!

[Erik Christensen]

I don't see any obvious gotchas with what you are trying to do but it will be a challenge. Some thoughts -

1. the bag has to be wide enough to cover the exterior width around the entire curve plus enough extra so the side seams are not stressed
2. any interior members or blocking would be a concern
3. if you can do the glue up in stages it would be much lower risk - back first, trim, then 1 side then the other
4. only need mesh on the outside (veneer) side - if the interior has a few spots where the bag is sealed against the substrate who cares - nothing to press on the inside
5. before even thinking about spreading glue do some trial runs - does it fit in the bag, how hard is it to get in & sealed, then do a test run where you carefully draw a vacuum in stages - do things look OK? should you position it on its front or back (I'd guess back so you can manage the bag in the interior but your trial runs will tell you for sure)
6. by now you should know if you can pull it off and how many helpers you will need

good luck man - very cool project

[Jeff Duncan]

A couple thoughts, yes you can veneer that up no problem, no you cannot.....OK should not, use contact cement. You will need blocking of some sort inside the cabinet or else the vac could crush the whole thing. You will need to use a veneer "softener" to loosen the veneer up a bit for that tight curve. You probably won't want the full pressure of the vac, though I guess that depends on your system.....OK I wouldn't want full pressure on mine;) As for the center channel, you need to know why it failed in the first place. You can't really fix it without knowing why it failed. If you do know why it failed then once you account for that you should be able to bondo it and not have anymore problems. MDF is as stable as it gets in woodworking so if it;s done right you should be fine.

Lastly, (and maybe it's just me),you may want to consider editing your pics down a bit so we don't have to look through an entire album, (or two), to try and find what your asking us:o

good luck,
JeffD

[Steve Rozmiarek]

A couple thoughts, yes you can veneer that up no problem, no you cannot.....OK should not, use contact cement. You will need blocking of some sort inside the cabinet or else the vac could crush the whole thing. You will need to use a veneer "softener" to loosen the veneer up a bit for that tight curve. You probably won't want the full pressure of the vac, though I guess that depends on your system.....OK I wouldn't want full pressure on mine;) As for the center channel, you need to know why it failed in the first place. You can't really fix it without knowing why it failed. If you do know why it failed then once you account for that you should be able to bondo it and not have anymore problems. MDF is as stable as it gets in woodworking so if it;s done right you should be fine.

Lastly, (and maybe it's just me),you may want to consider editing your pics down a bit so we don't have to look through an entire album, (or two), to try and find what your asking us:o

good luck,
JeffD


Jeff, as long as the bag evenly gets into the center channel, it will not crush. Maybe you were looking at one of the pics that looks like there is a void at the back. I think that is how it is laid out? Anyway, as long as the vacuum is on both sides of the form, or speaker housing in this instance, it won't crush it. I wouldn't worry about too much pressure much either, but I am at 4500 feet.

[David R Jones]

Dave Jones


Jeff, as long as the bag evenly gets into the center channel, it will not crush. Maybe you were looking at one of the pics that looks like there is a void at the back. I think that is how it is laid out? Anyway, as long as the vacuum is on both sides of the form, or speaker housing in this instance, it won't crush it. I wouldn't worry about too much pressure much either, but I am at 4500 feet.

Thanks, everyone. I have to get the kit and then build it. And yes, there should be no inner members, just the U so the bag can suck up to the entire inner surface and will not crush things. I want to use if not full, most of the pressure. I'll just have to very carefully do the cross members afterwards.
Erik, those are good considerations. I get it that the bag needs to be wide enough not to stress the veneer that hangs over the edge, or stress the bag itself. As far as why the assembly cracked, it was hurried into use for the family gathering on a Thanksgiving. It wasn't completely sealed, and not veneered at all on the sides, and the cumulative shrinkage across 38 or so exposed edges loosing moisture thru the winter popped a crack at the weakest point which would be the middle of the 3/4" section. That is why I think I will wash coat with some shellac, heavier coats, and get to a hard smooth outside before roughing the outside a little and then mock up, then glue up. Sounds good any way.:cool:

Sorry about the albums instead of pics. When I do get into the good part, I'll post pics..

[Jeff Duncan]

Jeff, as long as the bag evenly gets into the center channel, it will not crush. Maybe you were looking at one of the pics that looks like there is a void at the back. I think that is how it is laid out? Anyway, as long as the vacuum is on both sides of the form, or speaker housing in this instance, it won't crush it. I wouldn't worry about too much pressure much either, but I am at 4500 feet.

Good point Steve! I wasn't thinking about the bag going fully into the cavity but that would certainly eliminate that issue. And if that's eliminated than he shouldn't have to worry about applying full vacuum.

JeffD

[Kevin Jenness]

I think you may have a hard time getting a bag to conform to both the inner and outer surfaces of this form, but the mockup will answer that question. If it is not possible, you can insert a bladder into the cavity, connected through the vac bag to ambient air pressure, thus supporting the box from inside, or insert temporary bracing with a face panel to prevent the bag from being torn up by the bracing. It's not clear what the radius is on the corners, it may require pretreatment of the veneer as Jeff said. You might benefit from Darryl Keil's advice; he has done a fair amount of complex curved vacuum veneering. You could post your query on his forum at vacupress.com. He carries the bladders, and has a couple of excellent videos on the subject of veneering with vacuum.

I would be concerned about gluing to a shellaced surface; testing is in order.

[David R Jones]

I think you may have a hard time getting a bag to conform to both the inner and outer surfaces of this form, but the mockup will answer that question. If it is not possible, you can insert a bladder into the cavity, connected through the vac bag to ambient air pressure, thus supporting the box from inside, or insert temporary bracing with a face panel to prevent the bag from being torn up by the bracing. It's not clear what the radius is on the corners, it may require pretreatment of the veneer as Jeff said. You might benefit from Darryl Keil's advice; he has done a fair amount of complex curved vacuum veneering. You could post your query on his forum at vacupress.com. He carries the bladders, and has a couple of excellent videos on the subject of veneering with vacuum.

I would be concerned about gluing to a shellaced surface; testing is in order.

Thanks, I will certainly look at Darryl's site. the shellac is for sealing. thin coats to sink in to the mdf, then before any glue, the outside would be roughed up with 120 or 180. but your caution to test first is good. Maybe Darryl or even Joe WW would have guidance there. Pretreatment was done with the earlier effort with contact cement and worked surprisingly well. Hope a bladder is not needed. Hopefully poly will suckup tightly to all surfaces.

Thanks again all, once I get the pump and familiarize myself with the basics, I'll find out..:cool::cool: