vacuum press woes

[dave323]

Hi,

Wondering if anyone else has had any similar problem using a vacuum press to this and can give me a pointer on what I am doing wrong as clearly something is not right.
I am laminating plywood strips together to make my pieces thicker in places. For some reason my laminations are not getting properly stuck together.
After removing from the vacuum bag and the glue has dried I can peel the strips apart and obvoiusly have not bonded.
I have read if your laminations are not closing up then you need to increase vacuum but I am already using above the stated 25Hg.
I am using tight bond 3 glue and it is going off ok, temp here is about 15 degrees which is fine for this glue so this is not the problem.
I am getting 25Hg with the vacuum pump which seems to be the desired level from reading online.
I have tried another vacuum pump and pulled 27Hg and still have the same problem so I feel this maybe is not the problem either.
For my bagging I am using thick polyethylene sheet which I have made into a bag. I know the 2 main materials used are vinyl and polyurathane but I read online you can use virtually use anything?
I have seen a guy on youtube who seems to be sucessful in using a pond liner probably very similar to what I am using for a bag.
Ok so thats 2 possible problems, well if my vacuum dial is reading way off (which I doubt) or the vacuum bag material is somehow not right.
So on to the bagging proceedure. I have a joe woodworker venturi vacuum system (you can search that online) I am using the method provided on his site for laying out the wood.
I have an 18mm MDF backer board with cuts in the back face to allow the flow of air all over it to escape to the vacuum pump. Then I put the work on the inside face of this board and another board on top again with the cuts on the outsideface to allow air flow. This assembly then all goes into the vacuum bag. Sealed with tape..
Have also tried not using the top board, just using the plastic bag pulling down on top, which gave the same results.. the laminations were not properly stuck. I should give these boards the proper names the bottom baord is called the platen and the top board the caul I believe.
The strange thing I find about all of this is I can't find any information online about anyone else having a similar problem with joining wood with the vacuum press. All seem to be doing it without issue =) Any advice appreaciated.

 

[Steve Maskery]

How long are you leaving it in the bag for? Do you keep the pump running or switch if off once the pressure is reached?
S

 

[Richard S]

How old is the glue you are using, could the frost have got to it?

 

[dave323]

Thanks for the fast replys,
The work is left in the bag for a hour or more with the pump cycling on and when I take it out it has dried at least mostly and importantly I cannot bounce/ shift the 2 laminations, then I let them dry but the problem is the bond is not right. They peel apart even 24 hours later. I suspect things have not gone well just looking at the join. It is mostly fairly tight looking but the occational gap/void between the 2 laminations gives me a suspicion that its not right which is confirmed when I test the join. Il try an leave a test piece in for longer to rule another thing out but I suspect that is not it.
The glue should be fine the bottle is only a year old and has not been left out in the winter as I read its not good to let it freeze.

 

[marcros]

if you can peel the strips apart, that suggests to me that it is a glue issue. I would start with replacing that element.

have you tried the glue on a flat piece of scrap, perhaps with light, medium and strong clamping pressure?

 

[Steve Maskery]

+1
I don't use Titebond myself, but assuming that one hour of clamping is what it recommends, I'd try a different bottle of glue.
S

 

[dave323]

macros, good idea.. I have used this glue before but not for months. Will test this out and post back I suspect it should work with the normal clamps.
Its funny though I thought tightbond gave a really strong bond it seems it does not stick well unless pieces are forced together well. (which is wierd as the vacuum press should be doing that!) anyway off to test the glue normally with clamps. Will be gutted if the glue is the problem, its a 1 gallon container only opened a few months ago and not used much yet I thought I was being careful storing it, I may have left if in the attic for the start of the winter season but not for long.

 

[Peter Sefton]

I would say it’s a glue issue, sounds to me like the glue has skinned off before coming under pressure. The venturi system can be slow to pull down and all PVA type glues need to be assembled quickly.

I would use UF glue or epoxy resin in preference to Titebond or PVA

Or
1 If you stay with Titebond 111 make sure the workshop is not to warm when applying glue
2 No cross breeze across the glue line
3 Work quickly
4 Possible more Glue on both surfaces
5 Don't rush to take it out of the press I would leave it 3 hours.

And if all else fails come on one of my laminating courses :wink:

Good luck cheers Peter

 

[custard]

I've used Titebond for vacuum laminations, it's not my first choice but it worked okay. But I've also had terrible problems with Titebond that was too old or that had been stored in frosty conditions.

I followed up with Titebond and there are batch numbers on each bottle that they can cross reference to give you a manufacturing date. I seem to remember them saying that they don't give a use by date because the storage conditions are critical. I came away from that with the conclusion that Titebond is a really terrific glue range, but you need to be ultra picky about how you buy it (big retailer with fast stock turnover) and how it's stored, and storage includes the carriage company who might leave it in an unheated warehouse on a January night in Scotland!

 

[dave323]

Peter, thanks for the tips. I do have the problem when using this glue its going off too quickly, which is a real nuisence. I do try and add more glue to stop it drying. I have done test pieces which I can get in the bag and evacuate in 3 or 4 mins and still the ply can be seperated. I have some evo stik hopefully thats a urea formaldehyde glue will try it tomorrow. That one actually has been left out over winter as I did not really care for it, doh. Got to get this working asap for a project, silly me.

 

[Chrispy]

Hi Dave
I've used an old rubber vac bag with a pump using pva glue and I find with veneer even after 2 or three hours, when removed the veneer is very damp so although the glue may have started to set the fact that it's sealed inside a plastic bag I think must slow the setting/ curing time right down so when you said you leave yours for only one hour makes me think you need to give it longer.

 

[Peter Sefton]

I am not sure which Evo Stik you have Uf (Cascamite) glue should be powder mixed with water or powder mixed with resin, this like all glues will suffer from frost damage and shelf life is important.
I would also sand all surfaces before gluing and then ensure the surfaces are dust free, is the ply good, is it oily?
Good luck tomorrow

 

[marcros]

i would buy the glue by the litre and keep it nice and fresh. probably works out cheaper than chucking some away because you dont trust it, and far cheaper than having to redo work.

 

[Peter Sefton]

i would buy the glue by the litre and keep it nice and fresh. probably works out cheaper than chucking some away because you dont trust it, and far cheaper than having to redo work.

+1 for that

 

[dave323]

Its birch ply not oily, did not realise these glues could be so fussy. If all else fails at least I can epoxy this project
Are there any other tests one can do to determine if a vacuum press is working properly?
I do slightly wonder if the very thick bag I am using could be the problem as its 1200 guage polyethylene. (10x thicker than a standard vinyl bag) From what I can gather this should only be a concern if you are doing curved work.

 

[dave323]

I can confirm the glue has had it, the clamped piece has the same issue. It was probably damaged before I even got it. It was delivered on a frozen winter morning I took the delivery on a monday so it may have been left with the courier over the weekend. Oh well you live and learn. Hopefully its just the glue then and my vacuum setup is fine. Will epoxy this one and look into getting some UF glue. Any recommendations?
Thank you all and what a great forum. =D>

 

[Steve Maskery]

For gentle curves I've used ordinary PVA and never had a problem. But for anything challenging, or which needs a longer open time, I'd use Cascamite every time.
S

 

[Sgian Dubh]

for anything ... which needs a longer open time, I'd use Cascamite every time. S

I wouldn't. Urea formaldehyde glues generally give you no more than about ten minutes from the moment you start applying the adhesive to the moment you walk away because the job is fully clamped. If time is an issue, which is commonly the case with large complex laminations, a sensible adhesive choice in my opinion is a slow set epoxy resin-- you get about an hour to work before you have to call the glue-up done. Several brands are available such as West System's range, but they are expensive, eg £150- £200 for a 5 litre kit, including a colloidal thickener, or similar. Slainte.

 

[Steve Maskery]

That's interesting, I've not found it so quick. According to the data sheet:
http://www.polyvine.com/index.php?option=com_content&view=article&id=112&Itemid=184&lang=en
it has a gel time (I am assuming that is the same as open time) of 1-2 hours at 20 deg C

I wouldn't expect an hour, and I've never glued up anything extremely complex, just some tight bends from time to time, but I've never found that I'm running out of time.

+1 for West, though, although -1 for its price.
S

 

[Sgian Dubh]

Steve, I think the gel time might be the same as the pot life. In other words if it's starting to gel in the pot it's past the time for its use. I may be wrong, but I suspect that's the case.

I find in use that when it's applied to the surface of something that's being veneered, or laminated, that if the glue shows signs of becoming dry on the wood surface before you can bring the parts together and get the pressure on there's more likelihood of failure. This is avoided if the job can be achieved in ten minutes as I said earlier. I have seen successful glue ups when the job has taken longer to get together, eg 20 minutes or so, but I've also seen more failures, especially when the job takes longer still. I really don't like using urea formaldehyde glues, or most other normal wood glues, if I can't get the job together in that ten minute time frame.

There are wood glues out there with longer open times, eg, liquid hide glue, and some of the extended open time PVA or aliphatic resins. But if an hour or so is needed, as in the case of complex laminations, eg, many laminates to make up the thickness, a few switchback like bends in the same plane, and laminates that include things like twisting as well as bending, I think the only real option is an epoxy resin with a slow acting catalyst and a filler to get it all together, assuming a temperature of about 20ºC. Slainte.