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Wood Butcher

Leveling cracks with pillar method

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I've seen the pillar method employed many times, and understand (I think) that the wedges are used to alter the outside shape, so that the arching still flows, and there is no dip at the crack.

With the pillars so close together, how do you choose to level complex cracks and prevent the two halves moving out of register when gluing?
Are interlocking pillars the only way, or can there be other methods?
Must a cast be used, or it can be done without?
Are clamps vertically over the crack to be avoided?

A successful dry run is one thing, but once glue is introduced, things can start to slide a little.

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A common method is to do a dry run, mark the insertion level of the wedges where the arching comes out correct, and use those markings when reinserting the wedges after glue is applied.

As far as vertical alignment is concerned, when a crack is enough off 90 degrees that it will inevitably slide upon clamping after glue is applied, there are various strategies for inserting vertical jack screws etc.

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Wedge cleats can be helpful for leveling as well. The cleat is made so it fits on one side of the crack and overhangs the other. You can then make a wedge to slide into the overhanging part of the cleat and level the crack.

I’ve heard of the jack screw method David Burgess suggests and am intrigued by it, just haven’t tried it. 

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1 hour ago, Wood Butcher said:


Are clamps vertically over the crack to be avoided?

 

I sometimes use vertical clamps between the pillars. And glue long cracks in shorter sections.

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1 hour ago, Wood Butcher said:

It seems there is a lot going on all at once, and that a lot could go wrong too, if not careful.

Are you all introducing the glue from the varnished side?

Yes, the key is to be tidy, well-organized and patient. Not really my strongest points, but I do try my best in this context. As David Burgess said, you should number and mark the wedges after clamping up and adjusting everything dry. I use plastic tile spacer wedges, which are quite handy. I introduce the glue from the varnished side, working under a fairly gentle heat lamp to give a bit more working time. As I said earlier, working in short sections (and not moving to the next one until the previous one is dry) helps to keep things under control. If you do this, take care to wipe off the excess glue in the right direction!

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Thank you for the replies so far. I was wondering how it was possible to keep things level, with everything on only one side of the plate. It really sounds a skilful repair.

I only tried it once before, but it became disastrous. I had used paper separators to make removing the pillars easier after the crack was glued, but when gluing the crack, managed to pop off several of the pillars tightening the clamps :rolleyes:

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21 minutes ago, Wood Butcher said:

 

I only tried it once before, but it became disastrous. I had used paper separators to make removing the pillars easier after the crack was glued, but when gluing the crack, managed to pop off several of the pillars tightening the clamps :rolleyes:

Yes, that's a really bad idea. They need to be firmly glued :)

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I'd suggest practicing by taking a ~2mm thick piece of spruce, breaking it, and pillaring  it back together.  Then you can make it more challenging by breaking, planing the two sides at an angle so they want to slide when glued and clamped together. The wedged overhanging cleat method that TVB described can work well for that. It can also sometimes be useful to have two people applying the pillar clamps and wedges, to get everything in place before the glue gels or sets.

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I'd add that it helps limit slippage to orient the clamping plane of the pillars, as much as is reasonable, to the angle of the crack in the plate.  If the crack runs too far off 90 degrees, pillars and wedges may not be the most advisable approach.  Also, if vertical clamps are used between the pillars, I try to remove them as soon as possible after the glue gels, as otherwise the clamping pressure can cause a slight depression at the crack due to the expansion/contraction caused by the glue. Carefully heating the crack (from the unvarnished side) after assembly is often helpful as well (to make sure the joint is as tight as possible... you'll often see very small beads of glue rise to the surface of the plate at the  crack).

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1 hour ago, Jeffrey Holmes said:

Carefully heating the crack (from the unvarnished side) after assembly is often helpful as well (to make sure the joint is as tight as possible... you'll often see very small beads of glue rise to the surface of the plate at the  crack).

Another method to re-liquify glue after everything is in place and to make sure the joint is as tight as possible is (with clean and dry varnish) lay saran wrap (plastic film) over the area of the crack and then place a wad of paper towel or cloth that has been sitting in your glue pot water bath over the just glued area, that has been squeezed to remove excess water.  I then remove the plastic, remove any residual glue and re-check everything.  This method is pretty quick and effective.

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3 hours ago, Mark Norfleet said:

Another method to re-liquify glue after everything is in place and to make sure the joint is as tight as possible is (with clean and dry varnish) lay saran wrap (plastic film) over the area of the crack and then place a wad of paper towel or cloth that has been sitting in your glue pot water bath over the just glued area, that has been squeezed to remove excess water.  I then remove the plastic, remove any residual glue and re-check everything.  This method is pretty quick and effective.

Like that Mark!

 

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8 hours ago, Jeffrey Holmes said:

Like that Mark!

 

Thanks Jeff.

It's an offshoot from my vacuum bagging methods for dealing with very difficult bias cracks or torn areas.  I've put entire plates under warm running water to re-liquify glue while encouraging things into position.  Not a method for impatient people, but it can yield excellent results, or perhaps interesting catastrophe.
Some day...

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17 hours ago, Mark Norfleet said:

Thanks Jeff.

It's an offshoot from my vacuum bagging methods for dealing with very difficult bias cracks or torn areas.  I've put entire plates under warm running water to re-liquify glue while encouraging things into position.  Not a method for impatient people, but it can yield excellent results, or perhaps interesting catastrophe.
Some day...

:) As I recall, patience is not an attribute in which you are lacking!  

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I've developed a clamp and procedure for this that works very well. The shop made clamps using hardware that costs apx  $0.25/clamp plus scrap maple two drill bits and one tap.

I use plastic covered rare earth magnets instead of clamps because they are light weight and  clamping pressure is only vertical (no torquing from clamps). The plastic prevents scratching and glue does not adhere to it.

Magnet clamps can be a little tricky to control. I 'park' the magnets alongside the cleat then slide them in place, lifting the one that goes over the cleat. If you get the magnets too close they tend to 'jump' out of control.

I dry clamp everything, checking the alignment with a straight edge across the crack, glue the cleats in place then after the glue has dried apply glue to the warmed varnished side. 

 

Glad to answer any questions. 

Oded Kishony

20140528_144332.jpg

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I use this flanged nylon knurled screw and a brass version with the corresponding tap. The lower screw is used to pull the clamp together, so the hole on the left is slightly oversized to allow for some degree of movement and the opposite side is drilled through and tapped. The upper part, drilled and tapped on one side, is used to spread the clamp.IMG_20180321_175858938.thumb.jpg.bc59e09e19402b527895c2f1071c9f93.jpg

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This photo illustrates how you can use this clamp to align a crack that has a 'step'. Notice on the right side of the crack is a narrow wedge that pushes against the screw shaft effectively pushing down that side of the crack.

To glue the pillars in place I put a dab of thin hide glue with my fingertip on the surface, let it dry a bit and use ca glue on the pillars that are surfaced with paper (I use 3x5 card paper).

Oded

 

IMG_0046.JPG

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