Just wondering if anybody has good and ideally repetitive hands on experience of this sort of work and is a position to provide some tips regarding the practicalities? All feedback appreciated.
I'm getting ready to glue up some 125 x 40mm x 2,200mm long laminations in beech to make the top for a heavy bench. Similarly in shorter lengths for legs etc.
Most use one of the usual modified PVAs and they are convenient - but I'm not terribly keen because of the risk of creep and their less than fully waterproof nature. (despite the claims...)
Thinking of using the new West G-Flex 650 flexible-ish epoxy - basically because standard epoxies while waterproof are not reliable on timber in circumstances where the wood may move due to significant changes in moisture content. They also often require filling to keep them in the joint.
Epoxy adhesives are waterproof and get a very good bond on most woods, but the wood cells adjacent to the bondline which are partially filled with it can become brittle and can fail if there is a lot of movement. Epoxies get used by home aircraft builders for example but are not certified for commercial aircraft use on timber for this reason in the US.
Epoxies are widely used in boat building, but timbers are normally sealed with a coat of the epoxy all over to avoid this risk.
The G-Flex 650 data suggests that it by virtue of being flexible avoids this problem and contact with West's tech support in the US backs this up - they publish test data which says that it holds up on a variety of woods cycled from almost fully dry to saturated with water.
The handling of the stuff is where it gets interesting. G-Flex 650 is about the thickness of honey (a bit thicker at 65 deg F) and can be filled to further thicken it if needed - but this hopefully will not be required on what will be tight and horizontally oriented joints. There's a thicker filled 655 version but this likely contains silica (?) which could be very hard on cutting tools.
It's very slippery and laminations will move about under the clamps unless located. (biscuits?) One positive is the 40-50 min pot life - although this is temperature dependent.
Too much epoxy squeeze out is expensive, a terrible (the very moderate word I first used got censored by the system - bloody hell!) to clean up and is best kept off clamps etc. - so lots of plastic sheeting and well controlled/'just right' application quantities are adviable.
Epoxies don't like temperatures much below 70 deg F so a reliably heated workshop is advisable at this time of year - they will set well below this but don't develop their full properties. They require only sufficient clamping to close the joint, too much pressure can cause dry joints. The other side of this is that there needs to be enough epoxy in the joint to ensure that the surfaces are well wetted.
It's important not to handle the stuff - to use gloves etc. The hardener can trigger skin problems and even potentially serious immune reactions etc in some.
I've lots of experience of handling epoxies in moulding and small adhesive applications, but not in this sort of scenario - and it's clearly important to figure out an effective working regime in advance. Hence this thread.
The critical steps are probably (a) to guarantee accurate alignment of the laminations (to minimise the requirement for flattening, and to result in flat side faces from which squeeze out can be wiped of with a scraper before it sets), and (b) for cost and convenience reasons to perfect a spreading technique which consistently applies just enough resin to give a good joint but no more.
Some trials on other jobs (laminating up blocks from birch ply) suggest that the West (1/8in?) finest notched spreader used at right angles puts down about 2.3ml per 25 square centimetres or a bit less. A notched spreader so far seems the best option by which to get accurate control of the coating. This is probably a bit more resin than is ideal, but tilting a notched spreader reduces/adjusts the quantity put down.
A look inside some test laminations even suggests that if using this preader it may be enough to apply the epoxy to one surface (if it is flat/planed) using the above spreader - although it is often recommended to wet both surfaces before assembly.
There's a YouTube video of a well known (I think) Australian maker laminating curved table legs (which he seemingly makes regularly) - he seems to use a spreader with no notches and is very sparing in his use of adhesive but does coat both surfaces.
Cost is a factor and it would be easy to add say 30%+ unnecessarily - so getting this right is important.
Thoughts?
I'm getting ready to glue up some 125 x 40mm x 2,200mm long laminations in beech to make the top for a heavy bench. Similarly in shorter lengths for legs etc.
Most use one of the usual modified PVAs and they are convenient - but I'm not terribly keen because of the risk of creep and their less than fully waterproof nature. (despite the claims...)
Thinking of using the new West G-Flex 650 flexible-ish epoxy - basically because standard epoxies while waterproof are not reliable on timber in circumstances where the wood may move due to significant changes in moisture content. They also often require filling to keep them in the joint.
Epoxy adhesives are waterproof and get a very good bond on most woods, but the wood cells adjacent to the bondline which are partially filled with it can become brittle and can fail if there is a lot of movement. Epoxies get used by home aircraft builders for example but are not certified for commercial aircraft use on timber for this reason in the US.
Epoxies are widely used in boat building, but timbers are normally sealed with a coat of the epoxy all over to avoid this risk.
The G-Flex 650 data suggests that it by virtue of being flexible avoids this problem and contact with West's tech support in the US backs this up - they publish test data which says that it holds up on a variety of woods cycled from almost fully dry to saturated with water.
The handling of the stuff is where it gets interesting. G-Flex 650 is about the thickness of honey (a bit thicker at 65 deg F) and can be filled to further thicken it if needed - but this hopefully will not be required on what will be tight and horizontally oriented joints. There's a thicker filled 655 version but this likely contains silica (?) which could be very hard on cutting tools.
It's very slippery and laminations will move about under the clamps unless located. (biscuits?) One positive is the 40-50 min pot life - although this is temperature dependent.
Too much epoxy squeeze out is expensive, a terrible (the very moderate word I first used got censored by the system - bloody hell!) to clean up and is best kept off clamps etc. - so lots of plastic sheeting and well controlled/'just right' application quantities are adviable.
Epoxies don't like temperatures much below 70 deg F so a reliably heated workshop is advisable at this time of year - they will set well below this but don't develop their full properties. They require only sufficient clamping to close the joint, too much pressure can cause dry joints. The other side of this is that there needs to be enough epoxy in the joint to ensure that the surfaces are well wetted.
It's important not to handle the stuff - to use gloves etc. The hardener can trigger skin problems and even potentially serious immune reactions etc in some.
I've lots of experience of handling epoxies in moulding and small adhesive applications, but not in this sort of scenario - and it's clearly important to figure out an effective working regime in advance. Hence this thread.
The critical steps are probably (a) to guarantee accurate alignment of the laminations (to minimise the requirement for flattening, and to result in flat side faces from which squeeze out can be wiped of with a scraper before it sets), and (b) for cost and convenience reasons to perfect a spreading technique which consistently applies just enough resin to give a good joint but no more.
Some trials on other jobs (laminating up blocks from birch ply) suggest that the West (1/8in?) finest notched spreader used at right angles puts down about 2.3ml per 25 square centimetres or a bit less. A notched spreader so far seems the best option by which to get accurate control of the coating. This is probably a bit more resin than is ideal, but tilting a notched spreader reduces/adjusts the quantity put down.
A look inside some test laminations even suggests that if using this preader it may be enough to apply the epoxy to one surface (if it is flat/planed) using the above spreader - although it is often recommended to wet both surfaces before assembly.
There's a YouTube video of a well known (I think) Australian maker laminating curved table legs (which he seemingly makes regularly) - he seems to use a spreader with no notches and is very sparing in his use of adhesive but does coat both surfaces.
Cost is a factor and it would be easy to add say 30%+ unnecessarily - so getting this right is important.
Thoughts?
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