Sorry, but I still don´t understand that statement. A thin layer of Epoxy to remain in the joint? Of which joint you are talking about: the joint of Epoxy and wood?
That's okay - we'll poke away at it until you do understand! ;-)
All that I was trying to point out is that most glues (like Titebond) work best with a close-fitting joing - two wood faces that meet nice and flush with one another - when they are clamped together, you want significant clamping pressure and most of the glue to squeeze out. With epoxy, you want just the opposite - the two faces of wood to be bonded together need not fit together perfectly (in fact better is the joint is a little rough or jagged) and when you clamp, the clamps are just to hold the two wooden faces in position - not to apply pressure to squeeze the epoxy out - you want to leave some epoxy in the joint between the two wooden faces to be bonded.
What does it mean for practice? Should I first apply a little bit of Epoxy to the wood, let it become hard, and then apply the Epoxy with the filler?
No. Read on the West System web site about their two-step bonding process:
Two-step bonding
1. Wet-out bonding surfaces-Apply a neat resin/hardener mixture (without fillers) to the surfaces to be joined (Figure 9). Wet out small or tight areas with a disposable brush. Wet out larger areas with a foam roller or by spreading the resin/hardener mixture evenly over the surface with a plastic spreader. You may proceed with step two immediately or any time before the wet-out coat reaches the final cure stage.
2. Apply thickened epoxy to one bonding surface. Modify the resin/hardener mixture by stirring in the appropriate filler until it becomes thick enough to bridge any gaps between the mating surfaces and to prevent "resin-starved" joints. Apply enough of the mixture to one of the surfaces, so that a small amount will squeeze out when the surfaces are joined together with a force equivalent to a firm hand grip (Figure 10).
Thickened epoxy can be applied immediately over the wet-out surface or any time before the wet-out reaches its final cure. For most small bonding operations, add the filler to the resin/hardener mixture remaining in the batch that was used for the wet-out. Mix enough resin/hardener for both steps. Add the filler quickly after the surface is wet out and allow for a shorter working life of the mixture.
3. Clamp components. Attach clamps as necessary to hold the components in place. Use just enough clamping pressure to squeeze a small amount of the epoxy mixture from the joint, indicating that the epoxy is making good contact with both mating surfaces (Figure 11). Avoid using too much clamping pressure, which can squeeze all of the epoxy mixture out of the joint.
4. Remove or shape excess adhesive that squeezes out of the joint as soon as the joint is secured with clamps. A wooden mixing stick with one end sanded to a chisel edge is an ideal tool for removing the excess (Figure 12).
Make sense?
I hope this helps you.
Terry Farrell
----- Original Message -----
From: Gregor _
To: Pianotech List
Sent: Saturday, May 10, 2008 5:05 AM
Subject: RE: Epoxy Bass Bridge Repair
Sorry, but I still don´t understand that statement. A thin layer of Epoxy to remain in the joint? Of which joint you are talking about: the joint of Epoxy and wood?
What does it mean for practice? Should I first apply a little bit of Epoxy to the wood, let it become hard, and then apply the Epoxy with the filler?
Gregor
----------------------------------------------------------------------------
From: mfarrel2 at tampabay.rr.com
To: pianotech at ptg.org
Subject: Re: Epoxy Bass Bridge Repair
Date: Fri, 9 May 2008 15:57:38 -0400
Some adhesives like Titebond are not very good at filling gaps. They perform best with a tight-fitting joint and minimal glue left in the joint. Epoxy and many other adhesives is gap filling and you want at least a thin layer of epoxy to remain in the joint - doesn't have to be much, but you don't want a perfect fitting joint and then apply high clamping pressure. With epoxy you want a loose fitting joint (or roughened up surfaces) and minimal clamping pressure - clamp pressure is not to "clamp" as such, but rather simply to hold pieces in place.
Terry Farrell
----- Original Message -----
From: Gregor _
To: Pianotech List
Sent: Friday, May 09, 2008 11:49 AM
Subject: RE: Epoxy Bass Bridge Repair
Terry,
what do you mean by "you need to leave some epoxy in the gap. You don’t want to epoxy-starve the joint."?
I found a source for Western System Epoxy handy repair set including that filler here in Germany. Good to know, I will try it perhaps one day, but not with that Kawai. I told the customer to ask a collegue who has 7 pianotechs working for his shop: 4 on master level, 2 with certificate of apprenticeship and one apprentice, and they have a huge workshop. I don´t do repairs with woodwork anymore, just tuning, small repairs and selling pianos. But in this case it probably would have been easier to order a new brigde from Kawai which fits perfectly without any adjusting: just installing and it fits.
Gregor
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From: mfarrel2 at tampabay.rr.com
To: pianotech at ptg.org
Subject: Re: Epoxy Bass Bridge Repair
Date: Fri, 9 May 2008 08:57:04 -0400
Epoxy repairs for a situation as you describe can yield very good results. Sometimes the crack opens up a fair bit – you’ll want to clamp it back into position – not to clamp in the traditional sense, but rather to simply position the parts in their original orientation – you need to leave some epoxy in the gap. You don’t want to epoxy-starve the joint.
I use West System epoxy resin, hardeners and fillers:
www.westsystem.com My favorite for a cracked bridge is #404 High-Density Filler and using the West System two-step bonding procedure described on the West System web site. The following is from the West System web site:
404 High-Density Filler
404 High-Density filler is a thickening additive developed for maximum
physical properties in hardware bonding where high-cyclic loads are
anticipated. It can also be used for filleting and gap filling where maximum
strength is necessary. Color: off-white.
You can either push the bridge pins into the uncured epoxy, tidy up and be done with it, or, for a neater, more exacting job, you can epoxy the gap and then drill bridge pin holes after the epoxy hardens. I have found that if cosmetic considerations are not paramount, I apply the epoxy, clamp together until the wood is close to original dimension, clean off epoxy squeeze out (acetone) - at that point you will be able to see the outline of the original pin holes - push pins in place - the wood will have been drawn together enough to hold the pin in its original position - and then level off and clean up the little bit of epoxy that squeezes out of the holes as you push the pin in place. Wait a day or two for the epoxy to completely cure, go back and install bass strings.
I've done this repair numerous times with great success.
And of course, on a nicer piano where the budget allows, new bridge and/or new cap is preferred.
Terry Farrell
----- Original Message -----
From: Gregor _
To: pianotech at ptg.org
Sent: Friday, May 09, 2008 5:13 AM
Subject: Epoxy Bass Bridge Repair
I crawled the archieves but I did not really find what I was looking for: does Epoxy work even for bigger gaps?
I wanted to tune a Kawai CE-11 upright yesterday but the bass bridge looked horrible: a long gap which affected 9 notes. The gap started at the upper pin row and the pins were vertical. Some strings rattled at the pins. The gap expanded up to 4 mm above the upper pin row. I did not try but I could imagine that I could have pulled out some pins without using pliers.
First at all: I never worked with Epoxy. My first thought was to pull out the pins, fill the gap with epoxy and drill new holes for new pins. Could that work or is such a gap too much for Epoxy? The bridge is made of one piece of wood, no cap.
I was shocked about such a gap in a Kawai from 1992 (no grey market import): no floor heating, no air con and no heater near by the piano. And I don´t live in an area with huge differences in the climate. Very strange. That damage is a pitty because everything else in this piano was in a pretty good condition. But making a new bridge would be definitely too expensive including transports from the second floor into a workshop and back to the customer.
Gregor
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