working with mahogany crotch veneer
#30
  Re: RE: working with mahogany crotch veneer by mr_skittle (I did a test run las...)
I always veneer both sides of a panel at the same time.  That keeps the moisture in balance so the panel stays flat. I use Weldwood Plastic Resin Glue most of the time, although I can't seem to find it anywhere at the moment.  Fortunately, I still have a pail.  If I couldn't get PRG I'd use Unibond 800 or West Systems epoxy.  I only use shop sawn veneer and Better Bond and other aliphatic glues aren't rigid enough.  I learned that one the hard way.  

There's no need to use cauls for vacuum bagging.  I use a piece of Melamine on the bottom.  I put a piece of plastic window screen on top of the Melamine a layer of sheet plastic on top of that and then and lay one layer of veneer on that.  The veneer is cut to be the same size or slightly smaller than the substrate.  I apply glue to one side of the substrate, either Baltic birch or MDF, flip the substrate over onto the bottom layer of veneer, add the glue to the top side of the substrate and then place the top layer of veneer on top, and secure the registration of the veneer layers and substrate with blue tape in a few places.  Another layer of sheet plastic goes on top and then another layer of window screen.  Then I slide the Melamine carrier into the vacuum bag, close it up, and turn on the vacuum.  The window screen assures that the vacuum reaches every sq mm on both sides of the panel so even if there's a low spot in the substrate or veneer the veneer is still pressed tightly against the substrate with no chance of bridging.  

I trim the panels to final dimensions after the parts come out of the vacuum bag.  If you start with panels at their final dimension then of course your veneer needs to be larger than the panel and that means you need to use a top caul to prevent the bag from cracking the veneer where it hangs over the substrate.  The other issue with that approach is that you have to clean up the glue squeeze out with a router, etc.  By trimming the panel to size on the table saw after vacuum bagging you don't need a top caul and it gets rid of the squeeze out with no extra work.  No top caul also allows you to easily put parts of different size into the bag at the same time.  

John
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#31
  Re: working with mahogany crotch veneer by mr_skittle (I've gotten in a lit...)
Thanks for sharing your expertise, John.

I never considered skipping the top caul but after thinking about it, I get it. I actually started thinking of that last night when I saw a video with a guy just using a 1/4in piece of plywood for the top caul. I thought, "well that's not rigid enough to do its job." At that point, I questioned what its job actually is.

The issue I have with gluing both sides at once is with the distinct concern of bleed-through with the crotch veneer. The product I'm using suggests letting the glue sit on the substrate for 5-10 minutes before applying a crotch veneer. The open time of the glue should allow me that wait time on each side and still have no problem getting it in the bag with time to spare. I'll have to think on that one. The other reason I'm hesitant to do both sides at once is fear of a bad glueup on the first one. I have 5 sheets of veneer and need 4. That gives me one chance for failure. I'll probably end up veneering each side ASAP. That is to say, the second side of veneer will be on within an hour of the panel coming out of the bag. And then the panel will be put into the frame ASAP after it comes out of the bag. I'll move as quickly as possible to avoid warp.
How do you know you're learning anything if you don't screw up once in awhile?

My blog: http://birdsandboards.blogspot.com/
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#32
  Re: RE: working with mahogany crotch veneer by mr_skittle (Thanks for sharing y...)
If you are super concerned about bleed thru hide glue might be a better choice.  It's been used for forever, can be cleaned off the face if it does bleed thru, and is no problem under traditional finishes.  Liquid hide glue works fine in the vacuum bag.  

You're only using the crotch veneer on the show side, correct?  If so, I'd veneer both sides at the same time.  Whatever you lose is lost but cheap stuff on the back side is of little consequence.  

John
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#33
  Re: RE: working with mahogany crotch veneer by jteneyck (If you are super con...)
(11-22-2021, 01:04 PM)jteneyck Wrote: If you are super concerned about bleed thru hide glue might be a better choice.  It's been used for forever, can be cleaned off the face if it does bleed thru, and is no problem under traditional finishes.  Liquid hide glue works fine in the vacuum bag.  

You're only using the crotch veneer on the show side, correct?  If so, I'd veneer both sides at the same time.  Whatever you lose is lost but cheap stuff on the back side is of little consequence.  

John

While I am concerned about bleeding through, I don't know if I should be. I had zero evidence of it on my test run. I just have a general feeling of worry because this crotch veneer is overshooting my skill level. I've done some really simple veneering before with paperbacked stuff and the like, so I felt comfortable with the decision to go this route, but I didn't realize that mahogany crotch is one of the more challenging veneers to work with. 

I'm actually going to do the show veneer on both sides. The panels are for a hybrid wardrobe/dresser that has 3 drawers on the bottom and two doors on top. Overkill? Maybe, but it's for my 9yo daughter so it'll be in my house for another decade and with her forever. I think overkill is appropriate here.
How do you know you're learning anything if you don't screw up once in awhile?

My blog: http://birdsandboards.blogspot.com/
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#34
  Re: working with mahogany crotch veneer by mr_skittle (I've gotten in a lit...)
The panels are done and there were no issues to speak of. I'm really happy that it's over and now I have the experience for next time. The Ultra-CAT glue worked good and not a drip bled through. I did one sheet at a time, so there were 4 separate glue-up events. I know I could have done it in just 2 glue-up but I was just being really careful and paranoid. I used a piece of 3/4in MDF as the bottom platten. I layered the veneer on the substrate, then a piece of nylon screen, a piece of plastic sheeting, then a 1/4in piece of MDF ply on the top. Then into the bag for 4 hours.

I can't say enough how helpful it was to do a sample piece with some cutoffs of the veneer. I was able to test for bleed-through, work with the glue some, and see a finished result. One of the sides of the sample ended up having some failed glue spots so I was also able to see what that looked like and figure out how to avoid it.

The panels have 2 thin coats of shellac so far and the frames are still raw. The doors will get two more coats of shellac and then 2 coats of lacquer. Each subsequent coat of finish seems to bring out the figure of the crotch. I'm really excited to see them all done.

   
How do you know you're learning anything if you don't screw up once in awhile?

My blog: http://birdsandboards.blogspot.com/
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#35
  Re: RE: working with mahogany crotch veneer by mr_skittle (The panels are done ...)
Those look great; well done.  Kind of reminds me of a chest X-ray.  

John
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#36
  Re: working with mahogany crotch veneer by mr_skittle (I've gotten in a lit...)
Well worth the time invested.
Looks great!
Gary

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#37
  Re: RE: working with mahogany crotch veneer by jteneyck (Those look great; we...)
(11-27-2021, 03:35 PM)jteneyck Wrote: Those look great; well done.  Kind of reminds me of a chest X-ray.  

John

Ha, my wife said the same thing but she's looked at thousands of radiographs. I can see it, but that's not where my mind goes.
How do you know you're learning anything if you don't screw up once in awhile?

My blog: http://birdsandboards.blogspot.com/
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#38
  Re: working with mahogany crotch veneer by mr_skittle (I've gotten in a lit...)
The doors are all done now. I'm pretty happy with how they turned out. Next time I'll look into some grain filling on the show face of the panel. There are plenty of noticeable spots in the finish from imperfections in the veneer. All I did to finish it off was to use some paste wax on the lacquer. 


   
How do you know you're learning anything if you don't screw up once in awhile?

My blog: http://birdsandboards.blogspot.com/
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