Hot melt glue - some advice please

[FrenchIan]

Hi, I've never used the stuff before, but it might help me out.

I'm still making end-grain coasters, by taking slices off a log (at the moment, spalted hornbeam) and cutting them square. I want the finished article to be slim (say, 0.7cm), so I'm cutting slices at 1cm and sanding them down. The problem is that they tend to warp at that thickness, making a lot of work to sand them flat again (hornbeam is amazingly hard.....). I have a static belt sander for the rough work, but mainly use sheets glued to glass, Scary-Sharp style, and it's hard going. Also wears down my fingertips...

So, here's the idea.

I cut the blanks at 1.5cm, and leave them to acclimatise. Those that warp, I sand flat on the belt sander. Then, using hot melt glue, I stick them along a plank of 18mm MFC, butting against each other. On each side of this long row, I screw (from below) small battens of softwood. These are there to provide some side support to the blanks, but mainly to give the thicknesser feed rollers something to grip.

Then, I feed this through the thicknesser (with new blades set to a fine cut each time). To begin with, it'll be the battens that get planed, but then it'll be the blanks. Once all the blanks have a clean face on them. I take them off, reverse them, and finish planing to the thickness I want. A bit of light sanding (no bandsaw marks to remove, now!) and bobs your uncle!

WILL IT WORK??

Cheers

 

[Chrispy]

Hot melt glue is quite thick and messy. it would stick your tiles down but unevenly, and if you could prise them off again in one piece I think the glue will leave a stain like mark.

The thicknesser bit is wishfull thinking, it will probabily smash the tiles to bits.

Can you cut the blank nearer to the finished thickness to start with and do away with so much sanding, perhaps glue or fix the log to a board to hold it steady while you band saw it with a nice sharp blade.

 

[marcros]

could you rout out a recess for a piece of stable board to go into- you dont have much thickness to play with, so say 4mm mdf- and glue that in as a strengthening piece? even a piece of metal if necessary.

alternatively, cut it thicker and let it warp, as you say, then use a block plane to level it off, possibly even reslicing it to near finished thickness after it has moved.

 

[FrenchIan]

@Chrispy, I was afraid the glue would leave a residue. Plus if it's liable to disintegrate when I plane it, that's not good.

I can't cut it more closely to size, as it warps after I cut it. I need some way of removing this warping, hence my idea of cutting oversize.

@Marcos, I'd prefer to keep the wood slices fairly simple. I could try cutting them very thin (say 5mm) then gluing pairs back-to-back. A bit like plywood - that might stabilise it a bit?

Plus, I may try the second method - cut oversize, leave to warp then resaw flat again. Definitely possible.

Thanks, guys

 

[CHJ]

As Chrispy says the thicknesser idea will not work, the blades will be trying to chop end grain and the loads at best will just smash the blanks, at worst you will at the same time wreck the blades.

What are you using to slice them, can you improve the sawn surface finish.

If your stock is fully dried I would expect to be able to slice them off within a millimeter of finished size and just lightly sand the surface.

This is some dry Cherry I have just sliced within the last half hour.

And the other side after a quick rub by hand with 180grit paper.

Similar slices that are lying on my bench left over from a job a couple of months ago have not warped significantly.

 

[beech1948]

CHJ beat me to it.
The cause of the warping is probably due to moisture present in the thin blank so the first step is to ensure that the material you are cutting from is dried fully. I have never cut such oysters myself but I assume that you are cutting from branch stock. Maybe try to cut a piece say 200mm long and put it in the microwave. A technique used by some turners. I don't know for how long you might need to microwave but maybe ask in the turning section.

Good luck
Al

 

[Chrispy]

Are you making these one at a time or in batches? if the latter I can not see why they are warping, even if the wood was very green to start with, so long as you let the air get to both sides the same and you sand both sides the same without one side getting hot, put it this way if you treat both sides the same it wouldn't know which way to warp would it? (but it will split )

 

[FrenchIan]

Thanks, guys.

OK, the idea of putting it through a planer sounds like a no-no. Pity.

@CHJ/Beech1948, the log is trunk wood, not branch. Also, I think it's dry. These are logs that I've bought for firewood, and it's normally seasoned for 2 - 3 years before it's sold. Possibly it's dry to barn standards, but not to house standards? Maybe I should bring the log into the house for a couple of weeks before I slice it.

@CHJ, possibly if I left then as rounds (oysters?) they'd stay stable, but I'm cutting squares out of them before I start the finish sanding. I suspect that may allow some stresses to appear as warping. As for the quality, ex-bandsaw and pre-sanding, it's reasonable but could be better. The trouble is, end-grain hornbeam is HARD, so even a "light sanding" is a lot of work.

@Chrispy, my jig will handle a piece that's 165mm long. so I get 12 - 15 slices each time. I square them off, then stack them in the house for a few days. Curiously, only some warp (but they're all prone to splitting....)

I'll try drying the next log to house standard before I slice it, and see it that helps.

Thanks for all the ideas, guys.

Cheers

 

[beech1948]

Thanks, guys.



@CHJ/Beech1948, the log is trunk wood, not branch. Also, I think it's dry. These are logs that I've bought for firewood, and it's normally seasoned for 2 - 3 years before it's sold. Possibly it's dry to barn standards, but not to house standards? Maybe I should bring the log into the house for a couple of weeks before I slice it.

If dry to barn standards about the best they could be is around 20% moisture content. Usual MC for in house use is say 8% and maybe a little/little more.

So drying down from 20%+ to say 8% is going to take a few weeks. A way to judge if you have no moisture meter is to weigh the wood, then keep weighing at say 2 week intervals or more frequently and you will see the moisture reduce.