Darryl Keil Last Activity 2025-09-09 11:09 AM
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Jim Clement

Posts: 18

Joined: 2007-03-06
Location: Seattle

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Subject : Flexible caul -alternative to gum rubber
Posted : 2007-04-02 8:40 AM
Post #33722

In his veneering video, Paul Schurch uses "a heavy grade of canvas" rather than Daryl's 1/16" gum rubber as an upper caul to press down marquetry made of differing thickness veneers. Anyone have experience with this, or with other methods?

By the way, Schurch video #2 (actually a DVD) on marquetry is being released April 18. If it is anything like #1 it should be very helpful.


 
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Brian Gray

Posts: 339

Joined: 2004-01-21
Location: Sandusky, OH

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Subject : RE: Flexible caul -alternative to gum rubber
Posted : 2007-04-02 9:44 AM
Post #33723 - In reply to #33722

I've studied with Paul a couple of times, and I've used his heavy canvas method. I've also worked with Julie Godfrey and Silas Kopf...they use roofing rubber.

I've never heard of gum rubber - Darryl...can you speak more on this? What is it, and where to get it? Different from roofing rubber?

In any case...the whole purpose of this layer is so that if you have any veneers that are not identical thicknesses, this layer will allow the pressure to be applied evenly across each piece...especially marquetry and intricate pieces and details.

That being said, I would think that a rubber product would work better for this application than canvas. Rubber would have more elasticity to equalize pressure better than canvas (I would think).

That being said, I used Paul's canvas method for a couple of years until I worked with Julie and Silas and went with the rubber at their recommendation, and I never had any kind of failure with the canvas.

On the other hand, Paul has created some of the most amazing work I've ever seen and he has obviously had great results with the canvas.

My thoughts are that both will serve the purpose. However, perhaps rubber, because of it's elasticity, is the way that I'll lean.

Someone here on the forum mentioned a while back that they use styrofoam for this purpose. I think that they were using styrofoam insulation sheets. And this makes perfect sense, as well. The press would smash the styrofoam until it reached full pressure, and should equalize everything on various thicknesses.

I've never tried the styrofoam method, but it seems to me that it should work fine, as well.

And thanks for the reminder on Paul's new video. I'll get my order placed!


 
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Darryl Keil

Posts: 1455

Joined: 2003-05-22
Location: Maine

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Subject : RE: Flexible caul -alternative to gum rubber
Posted : 2007-04-03 12:44 PM
Post #33727 - In reply to #33723

Jim and Brian,

Jim, I have never used canvas so I really cant comment on how it compares to gum rubber. I would think the gum rubber would have more ability to accommodate thickness variation but there may be some good reason for the canvas I'm not aware of.

Brian, I switched to the natural gum rubber after one of my students turned me on to it. I like it much better than the neoprene rubber as its a softer durometer. I get it from the local rubber supply house. You should be able to find it from whoever sells rubber hose and sheet products in your area. Try some, I think you will really like the results.

Sincerely
Darryl Keil


 
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Trosey

Posts: 7

Joined: 2004-12-20
Location: Texas

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Subject : RE: Flexible caul -alternative to gum rubber
Posted : 2007-04-04 9:28 AM
Post #33731 - In reply to #33722

I have had very good luck using 40 mil PVC shower pan liner. It is readily available from plumbing supply houses. I have found that it is comes in 4'and 5' width(just tell them how long you want it). Cheap, approx 50 cents a square foot. Easy to cut with either scissors or a knife. Reusable and protects the bag from glue damage and/or sharp corners.

HTH

Trosey


 
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mike mcnerney

Posts: 87

Joined: 2003-07-17
Location: ottawa ontario

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Subject : RE: Flexible caul -alternative to gum rubber
Posted : 2007-04-19 8:01 PM
Post #33778 - In reply to #33731

I don't do enough of this & I may be missing something but I thought that was what you used the plastic screening that you sell for. but maybe you need that over the rubber. I have recently band sawn some 10" poplar & I did not have access to a thickness sander so some of it is thicker than it's bookmatched piece right at the joint. So is the rubber the way to go?
with or without the plastic screen on top?
thanks
mike


 
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Darryl Keil

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Joined: 2003-05-22
Location: Maine

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Subject : RE: Flexible caul -alternative to gum rubber
Posted : 2007-04-19 8:23 PM
Post #33779 - In reply to #33778

Mike,

What I call "EvacuNet" is the plastic screening that is meant to be a platen substitute, (the base board with the grooves in it" not for uneven thicknesses.

If you have resawn some solid wood there is no need for rubber or any other cover sheet, just let the bag press your poplar directly. Only commercial veneer really needs the rubber sheeting with a caul on top.

Sincerely
Darryl Keil


 
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Brian Gray

Posts: 339

Joined: 2004-01-21
Location: Sandusky, OH

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Subject : RE: Flexible caul -alternative to gum rubber
Posted : 2007-04-19 10:54 PM
Post #33780 - In reply to #33779

just to piggy-back on Darryl here...

The rubber or canvas serves a totally separate purpose from evacunet, or even wax paper or plastic sheets.

Evacunet - makes sure that the air is evacuated from every little area of your project. No trapped air bubbles.

Wax paper/plastic sheet - creates a barrier so glue will not adhere to areas that you don't want it to (the bag, another lamination, the platen, etc).

Rubber/Canvas - allows the vacuum bag to get even pressure on uneven thicknesses of veneers.

If you lay down a solid caul on a pattern of veneers where the veneers may be of slightly different thicknesses, then the caul will press hard on the thicker veneers, but not put much (if any) any pressure on the thinner veneers. The rubber or canvas will fill the gaps on top of the thin veneers, and apply pressure.

So like Daryll said...if you have resawn your own veneer, chances are that all of the veneers came from the exact same tooling, so they will be of exact thicknesses...no need.



 
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tvsp

Posts: 11

Joined: 2006-02-10
Location: OH

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Subject : RE: Flexible caul -alternative to gum rubber
Posted : 2007-04-20 7:36 AM
Post #33781 - In reply to #33780

I have been pressing olive ash burl to plywood cylinders (for musical drums) and have been not using a caul or any kind of sheet overlay; this has been working well for me getting excellent seams (on my 2nd pressing) more so than when I was using a sheet of vinyl between the bag & veneer. So I'm confused what the reason for any overlay sheet is when pressing only one thickness of veneer.
Attached file : 2393.jpg (33KB - 222 downloads)



 
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Darryl Keil

Posts: 1455

Joined: 2003-05-22
Location: Maine

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Subject : RE: Flexible caul -alternative to gum rubber
Posted : 2007-04-22 10:33 PM
Post #33782 - In reply to #33781

TVSP?

A caul for commercially cut raw veneer serves a couple of purposes.

One, this veneer can sometimes wrinkle when the glue make contact, especially when using white and yellow glue. A rigid caul will level this out under most circumstances.

Second, when veneer is slightly wavy and you press directly against the bag, the low points of the veneer will make contact with the substrate seconds before the higher points do locking the veneer in place before it has a chance to level out. Now, as the bag applies more pressure the high points are driven down with no where to go which ends up causing another form of wrinkling.

Its not that these conditions will happen in every case but enough to make using a caul a smart strategy. For curved work bending ply's make good cauls.

Although I still use cauls for curved work whenever I can it's not as critical as with flat work, hence the fact that you have not had any problems with your drum shells. If you did have a bubble you could massage it down with a block of wood or small wallpaper roller in most cases.

Sincerely
Darryl Keil


 
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tvsp

Posts: 11

Joined: 2006-02-10
Location: OH

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Subject : RE: Flexible caul -alternative to gum rubber
Posted : 2007-04-23 6:46 AM
Post #33783 - In reply to #33782

I see. I have been flattening my veneers 1st, plus using Unibond 800 the 1st contact probably isn't that critical. I thought that maybe a caul was to prevent the veneer from 'tearing' or being pulled apart on a curved surface if there was a buckle or ripple in the bag as it's being pulled down.


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