Underpinner Issue

[RobM]

We're getting into some expert detail now! I'm going to keep this up my sleeve and try it as I get more experience with the underpinner.

The main thing when underpinning is to get the top clamp pressure directly over the wedge insertion point.
I use a wooden triangle of wood faced with cork and wrapped in clingfilm. To prevent hardened glue building
up on the cork I wrap it in clingfilm which can be easily changed.

It's an extra operation to place the triangle but it does allow you to get pressure on just the right point. You don't
always need it, it depends on the underpinner and the moulding. Very good for deep scoops.

* I always like to pin all the outer wedge positions first and the (changing the top clamping if necessary) and then
do the inside. There is a good reason for this from an engineering standpoint but I won't go into it just now...

[RobM]

The top clamp pad needs adjusting - okay, I'll try this.

Cheers, Mark!

An incorrect or badly set top clamp pad results in the moulding lifting whilst the wedge is being inserted.

Mark

[RobM]

I'm enjoying all this debate over wedge positions and getting a little insight into how approaches differ.

All good discussion.

It's a fine point but I'll try to elucidate....

If you have cut the angles spot-on when you come to the last corner there should be a small gap between the
faces. When you push them together it 'cinches up' the whole frame. The three other v-nails act a fulcrum points
and the joints will all be super tight. Desirable for a good glue bond. That's if the v-nails are near the outside.
But... if they are toward the inside then the tendency is to pull the other joints apart at the back, the fulcrum points
being in a different place.

Imagine this... Pin a frame with no glue with the wedge positions on the inside. Stand it on end and try to deform
it sideways. You can. But pin on the outside and you can't.

As I say, a fine point but a good principle.

[JKX]

The “bung” needs to hit the moulding before the hammer pushes up the v nail

Regards density of the “bung” for soft or hard woods, they will probably be different colours
Cassesse is yellow (soft) and green (hard)

[Justintime]

I would strongly recommend getting hold of the instruction manual for your underpinner. You'll be amazed at how much instructional information it holds for setting up, using and servicing the equipment.