Storing bent laminations

[n0legs]

Morning all.
Pretty much as the title, how do I store them before the next stage ?
Do I clamp them all together or do I just put them somewhere safe ? It might be a few weeks before I can continue with them.
They are Meranti glued up with cascamite.
Should I put some sacrificial finish on them to help keep their moisture content stable ?
All suggestions and advice welcome, thanks in advance.

 

[custard]

The workshop I was in that did the most laminating either stored them in the original former or made simple jigs that would hold them and prevent spring back, their thinking was that Cascamite type adhesives actually take a long time to dry completely and the workpiece benefits from some support during this period.

 

[n0legs]

The workshop I was in that did the most laminating either stored them in the original former or made simple jigs that would hold them and prevent spring back, their thinking was that Cascamite type adhesives actually take a long time to dry completely and the workpiece benefits from some support during this period.

Hi Custard, well they've been in the former for 12 hrs each so I'm hoping the glue is dry.
So would it be best for them to all go back in the former for storage when I've finished the laminating stage ?
Or could I just wind some clamps onto them ?
Thanks for the help.

 

[Phil Pascoe]

I've not done much lamination, but I wouldn't presume any glue used in a stressed situation to be dry for at least two days.

 

[n0legs]

I've not done much lamination, but I wouldn't presume any glue used in a stressed situation to be dry for at least two days.

Yes Phil I'm thinking I may be being a bit hasty.
What I've seen and read gives the impression when the glue's set get on with the next set. The cascamite says it takes 6 hrs to set, and the leftover glue is before that.
Might re-evaluate, thanks for the advice.

 

[Bradshaw Joinery]

Cascamite should be dry withing a few hours if its 15 degrees+ and dry. doesnt take long for the left over in a pot to set solid.

Storage, i can only guess at storing them with their own weight working with the way youve bent them, to try and counteract the memory of the wood?

 

[n0legs]

Cascamite should be dry withing a few hours if its 15 degrees+ and dry. doesnt take long for the left over in a pot to set solid.

Storage, i can only guess at storing them with their own weight working with the way youve bent them, to try and counteract the memory of the wood?

Thanks Olly, I now have a plan.
I'll make a far simpler MKII former for storing them on.
I'll stack them on top of each other and keep them still with one of my ratchet straps. I think that should do the job.

 

[Sgian Dubh]

Morning all.
Pretty much as the title, how do I store them before the next stage ?
Do I clamp them all together or do I just put them somewhere safe ? It might be a few weeks before I can continue with them.
They are Meranti glued up with cascamite.
Should I put some sacrificial finish on them to help keep their moisture content stable ?
All suggestions and advice welcome, thanks in advance.

If you're using a non creeping adhesive such as urea formaldehyde (Cascamite) or epoxy resin to do the glue up, once the glue has cured there's really no need to put bent laminations in a holding jig. In over forty years I've never done it, nor seen it done in any of the workshops I've been involved in. I, or we've simply pulled them out of (or off) the former and set them to one side ready for the next phase. Obviously if there's quite a few of them you stack them up neatly, but that's about it in terms of storage. You may be getting confused with steam bent forms which are quite commonly put into holding jigs for a few days after the initial bend has been achieved.

I wouldn't even bother putting on a finish of any sort if it's going to be weeks before you next get to them. A finish good enough to effectively limit adsorption and desorption of water vapour over a period of weeks is going to be something much more substantial than a bit of polish gashed on carelessly, and would involve a much more rigorous routine.

I'd simply put your laminations somewhere safe, and ideally in a similar sort of environment to that planned for their end use, presumably somewhere inside your house might do (under a bed, store cupboard, etc?), assuming these items are intended for internal residential furniture of some sort. Slainte.

 

[custard]

The workshop I mentioned that stored laminations in "holding jigs" was the Edward Barnsley Workshops. Their argument was that building up laminations using many thin lamina, means that you're introducing a relatively large amount of water back into the timber with any water based adhesive such as urea formaldehyde. Therefore it's not creep that motivates their approach, but concern about timber movement as the wood itself re-dries. Obviously you wouldn't have this issue with epoxy, because there's no water involved, but the Barnsley policy was to avoid epoxy with laminations where possible because the glue lines are that bit more pronounced.

Personally I wouldn't pretend to know who's right in this debate. I did a fair amount of laminating before and never noticed any movement after the initial spring back on releasing from the jig, but that was using much thicker lamina. At Barnsley they'd often be 1.5mm or less, and it's rational to expect any problem of timber saturation to be more severe with thinner stock. In any event, knocking together a holding jig takes all of ten minutes and I'd rather invest that time than see many hours of work rendered useless.

 

[Sgian Dubh]

custard, the reasoning behind the Barnsley workshop's for using holding jigs doesn't add up for me. Whilst it's true that water based adhesives add moisture to the wood I don't see how a holding jig will have any beneficial effect once the glue has cured. Whilst it's true that the water that's been added to the wood will work its way out again as the wood dries thus leading to a risk of warping, e.g., cup, bow or winding, I can't see any utility in an insubstantial quickly assembled holding jig that simply holds the laminate in the intended curve. It surely won't have any useful effect on the cross grain movement of the wood, which is the main direction that warp takes as wood changes its moisture content in response to the environment. In any case, if the laminates are made up of random grain patterns (very common) then they are all fighting each other after the cure of the glue, and the structures rely upon the glue to hold it all in its desired shape. It's quite common in laminate work to make up extra parts to allow for rejection of some at a later stage, e.g., make twenty six or seven laminated chair parts to get enough for twenty four chairs.

Sometimes laminates are made up of sequential layers, either flitches of knife cut veneer (0.6, 1 mm, 1.5, 2.5 mm thick, etc) or thick laminates (~4- 12 mm thick) ripped from a thick section of wood. Here the grain does match throughout the laminate thickness, and the usual guidance in my experience has always been that if the wood was true and stable prior to creating the laminates, there's a very good chance it will be satisfactory after the laminates are reassembled in order to create the bend(s).

I've never bothered making a holding jig for laminate bends, but they're useful for steamed bends. Incidentally, epoxy (slow set) is king for some laminates, especially complex ones using several male/female formers, or compound free bends that include things like twisting made without a former - the hour or so of working time is vital for success in such cases. The one big problem with most urea formaldehyde glues is their very short working time, usually only about ten minutes, which is not enough if you have a big laminating job, many leaves, and some tricky formers to get in place and suck up tight with clamps. You just can't get the glue on quick enough, get the lot in the formers and clamped up in the ten- twelve minute window. I've seen a lot of people try to do it against my advice over the years, and I've seen many laminate failures because people thought they could work a lot quicker than they actually could. Slainte.

 

[custard]

The one big problem with most urea formaldehyde glues is their very short working time, usually only about ten minutes, which is not enough if you have a big laminating job, many leaves, and some tricky formers to get in place and suck up tight with clamps. You just can't get the glue on quick enough, get the lot in the formers and clamped up in the ten- twelve minute window. I've seen a lot of people try to do it against my advice over the years, and I've seen many laminate failures because people thought they could work a lot quicker than they actually could. Slainte.

I'm puzzled. UL39 adhesive mixed with 15% UH191 hardener gives over 3 hours of open time at 20 degrees C. And even Cascamite gives an hour of open time.

 

[Sgian Dubh]

I did say most urea formaldehyde types have a short working time. The stuff commonly called Cascamite may have an open time of about an hour (pot life if you like), but once you start applying it to wood you only have something like a 10 or 12 minute 'working time' at ~20°C to spread the glue, align the parts and apply the pressure. From the moment you start applying the glue until the moment you you walk away from the finished job having tightened the last clamp, you've got, at most, fifteen minutes, and even that's pushing it: ten or less is better. If you're still trying to get pressure on half an hour after you start the job failure is almost guaranteed. I've seen far too many failures because workers haven't followed guidelines such as those I've outlined, e.g., bent laminations that simply fall apart when they're taken out of the clamped up formers, or out of the vacuum press.

Off the top of my head I can't recall the working time for UL39, and I'm really guessing that because of its longer open time its working time might also be two or three times longer - I could be completely wrong with that. Slainte.

 

[n0legs]

You may be getting confused with steam bent forms which are quite commonly put into holding jigs for a few days after the initial bend has been achieved.

I wouldn't even bother putting on a finish of any sort if it's going to be weeks before you next get to them. A finish good enough to effectively limit adsorption and desorption of water vapour over a period of weeks is going to be something much more substantial than a bit of polish gashed on carelessly, and would involve a much more rigorous routine.
.

Hi Richard, yes that's what my point of reference is from. I was reading about steam bent and my concern was, that I couldn't find the answer for elsewhere, did the same apply for a bent glued lamination.

With regards to the temp finish idea, the wood is at a stable 8% (well my moisture meter says it's 8%) MC. The wood has been stored in the same place before machining, after machining and after being formed into the curves. It's only away from this spot for 12 hrs, give or take 30 minutes. It can't stay in this place forever, the good lady won't be best pleased. So I got thinking before I move it should I "seal" it with something whilst it lives in another place in the house.
I'm kind of vary after my circular table top went **** up.

I'd rather invest that time than see many hours of work rendered useless.

Hi Custard, that's exactly what I was thinking.

Anyhow guys thanks for the input.
As an update all the laminations and curve forming have been completed. They've gone well, I'm very pleased.
To clarify, they are made of 7 layers 4 mm thick, they are not massive. The curve isn't huge either, just a gentle curve of 875mm.
4 mm gave a nice flexible thickness that bent easily around my former.
So far none of the 3 that are out of the former have moved, they are not being held in any way at the moment. They're just safely stored in the house. I've got to go release number 4 at midnight.
I was going to use the former as a holding jig but I'm not sure at the moment what to do. I can store them safely out of the way in the house, in the former they might be more of a storage issue.
I'll try and post some pictures tomorrow for those interested.
Thanks all.

 

[Sgian Dubh]

I was going to use the former as a holding jig but I'm not sure at the moment what to do.

Well, based on what I've already said, you'll be able to surmise I wouldn't bother with either a holding jig or using the former as a jig. I too have a project on the go now with laminated American cherry parts, four arcs that are each a half a circle's circumference with a 390 mm inside radius, therefore quite tight each made out of 12 layers of 2.5 mm cherry.

They haven't seen the former since they came out of the vacuum press three weeks ago, nor a holding jig. I just move them about as needed, to work on them, get them out of the way in the work area, or stack them up for storage. There have been no problems so far, and I expect none to develop. Familiarity developed over the years with the process, materials, and the way the end results behave has led me to develop a certain amount of confidence in what to expect. Slainte.

 

[n0legs]

Familiarity developed over the years with the process, materials, and the way the end results behave has led me to develop a certain amount of confidence in what to expect. Slainte.

That's the bit I lack :lol: I will get there though.
I'm not going to clamp or restrain them in anyway, gotta' stop dithering someday and my mind is made up. The first one is now 4 days out of the jig and there has been no movement except for the initial spring back.
To hell with it, really living life on the edge now :lol:
Thanks Richard

 

[n0legs]

Here they are. Over length at the moment though.
I'm really happy with the way they turned out, this was a first for me.