Joining large box section mouldings

[Not your average framer]

For some unknown reason it seems that large box section mouldings in softer woods often cannot be relied upon to be of uniform height throughout a length of moulding, or between two lengths, even when they were supplied packed together. This problem does not appear to be restricted to just lower priced mouldings, but even happens with the likes of Enrique Lopez.

As a result, I have developed the following method to overcome this:

I place a piece of 2mm MDF under the softwood pressure pad on my underpinner. The MDF is larger than the pressure pad so than there is no chance of marking the moulding. The result being that the underpinning process forces the two pieces of moulding to line up flush at the front face and any slight variation appearing at the rear face is easily hidden by the tape on the back.

These height variations are usually very small, perhaps 0.5mm, but they still show if you don't do something about it.

[Roboframer]

Very timely thread Mark!

A few weeks ago I ordered just one length each of 5 of Nielsen's Loft range - plus the matching spacers/fillets/call them what you will.

The loft range is VERY expensive - just simple deep rebated profiles with the matching spacers, but they are all veneered - in real Teak. Beech, Wenge, whatever and really do look the biz.

I ordered a length of each of those 5 rather than opt for the free corner sample set of the whole range so as I could make some complete frames as props - corner samples are not enough to show the potential.

Aaaaaaaaaaaaaaaaaaaaaaaanyway - I had your problem - my underpinner clamp helped but I would never have let an actual order go out with the end result.

My solution to the problem otherwise would have been the phone and I'll be showing my rep the 'props' I have made and letting him know, in no uncertain terms that if this happens 'for real' it will be the second, and last time.

You shouldn't have to mess about correcting things that should simply not be happening - your supplier should.

[Not your average framer]

Hi john,

I have a bit of a theory about this problem - I can't prove it, but it's just speculation by me. I wonder these mouldings do in fact start out being machined to be exactly the same, but due to the fact that they absorb any humidity in the air they change dimensions slightly after leaving the factory.

Obviously the grain and qualities of the wood varies from one piece to another, so they don't all chance dimensions to the same degree. The resulting changes would be more obvious on larger moulding profiles, because for the same percentage variation the actual variation would be greater if the profile is larger.

[Roboframer]

Dunno about that Mark,

If that was the case we'd be seeing the problem in width as well as height - if I turn a 3" wide moulding on its side it becomes a 3" deep thing.

How would we sort the problem over a 3" width?

Ring Ring!

Rest my case m'lud!

[osgood]

If that was the case we'd be seeing the problem in width as well as height - if I turn a 3" wide moulding on its side it becomes a 3" deep thing.

It's just that you don't notice a small difference in width. There are plenty of mouldings where pieces are not exactly the same width, but the difference is not as easily seen.

The difference in height is easily noticeable due to the fact that if the tops (especially flat tops) are out by one two or three thousandths, it can easily be felt with your fingers.

I like Mark's idea and will give it a try, but I use another method. When the tops are not level, I use a leaf out of a set of feeler gauges after the joint is together. The leaf (usually the 3/thousandths) is placed under the half of the joint that is lowest and very close to the joint, then I place one of the harder nylon bungs on top of the joint and use my FBH to bang down on the bung. I check after each bang to see if the top of the joint is level.

It works a treat and levels the tops without damaging the moulding.

CAUTION: It might damage soft mouldings, but then they are easy to move a little with your hands anyway.

[Merlin]

Thank God for FBH's and FBS's

What would we do without them. Precision engineering !!!!

[Not your average framer]

Dunno about that Mark,

If that was the case we'd be seeing the problem in width as well as height - if I turn a 3" wide moulding on its side it becomes a 3" deep thing.

How would we sort the problem over a 3" width?

Ring Ring!

Rest my case m'lud!

Hi John,

Yes, I think we get the same problem with the width too! However, we all get used to lining the two pieces up before joining to minimise the effect. Sometimes a little camouflage and touching up may be required, but with a little care it all looks o.k. Being on the outside edge helps a lot, but the front of the moulding is often another matter.

The difference is that when it is a height problem and a softer wood moulding, by using a softwood pressure pad both pieces are forced down flat onto the underpinner and thats how they get joined. Whereas, inserting a little piece of MDF allows the insertion of wedges to force both pieces of moulding against the MDF. By doing this the higher of the two pieces fixes the height of the MDF and the less high of the to mouldings is forced up to met the MDF.

[Roboframer]

What is this 'MDF' ?

[Not your average framer]

What is this 'MDF' ?

Hi John,

MDF is that horrible stuff which many of us don't like using, but we all have a little bit tucked away somewhere. This is because it still comes in handy such as for gluing to cheapskates canvases when they won't pay to have it framed properly.

And you are preaching to the converted - I stock Artcare foamboard which is used as my prefered backing board.