Help - Mitres opening up & underpinning big carved obech

[blaisehall]

Hi,
I'm new to the forum and I've only been framing professionally for a year. I'm learning as I go and making loads of mistakes! I've got two problems which I could do with some help with if anyone can.

1. I made a frame on Monday, painted it and then (inadvertantly) left it on a storage heater over night. The mitred corners have opened right up and have massive cracks in them now. I don't mind that I can't sell it. What's really worrying me is - should I not be keeping all my mouldings in an unheated, drafty barn/workshop. Will they open up like this one has when my customers get them into their centrally-heated dry homes?

2. Every time I underpin big carved obeche (is it called a spoon-shape?) moulding it comes out nice and tight at the back but open a crack at the front (where it really matters). It isn't that the Morso needs adjusting - the angle is 45 degrees ok (it's a nice fit at the back). Is there a trick to this?

I use a Morso and a Cassese underpinner.

Cheers,

Blaise

[Roboframer]

Blaise - firstly ....... Welcome.

Secondly - well - later, but for now, just 'Welcome'

[blaisehall]

Thanks for the welcome. It's good to know there are other framers out there. I've been reading a few of your posts and you certainly know your onions.
Blaise

[Spit]

should I not be keeping all my mouldings in an unheated, drafty barn/workshop. Will they open up like this one has when my customers get them into their centrally-heated dry homes?

Wood is a natural material, and will absorb moisture like a sponge in excessively damp conditions - when it then gets warm & dry in 'normal' conditions it will shrink. You should keep mouldings in reasonably 'normal' conditions.

Have you considered building a 'warm room' within the barn? Spend a couple of hundred on making a dry, warm area could save you many times as much in the long run.

Every time I underpin big carved obeche (is it called a spoon-shape?) moulding it comes out nice and tight at the back but open a crack at the front (where it really matters). It isn't that the Morso needs adjusting - the angle is 45 degrees ok (it's a nice fit at the back). Is there a trick to this?

The morso does need adjusting by the sound of it. The left hand fence needs a tiny adjustment - trouble is, I can't remember if it is forwards or backwards. Get some 3x1 or 3x2 and try it both ways, you'll soon see.........

[blaisehall]

That's good to know. I didn't know it was quite that absorbant. I'm surprised I haven't had any customers complaining of cracked frames. The idea of a warm room is a good one, but I have another barn with heating that I can move the all the mouldings to. It will be a pulaver but it sounds like it's essential. I'll do it tomorrow.

I wouldn't have guessed it was the Morso - I'll have a fiddle with it tomorrow. Other mouldings seem ok though. I fing the big carved obeches a bit of a fiddle to pin. The underpinner doesn't hold them properly and seems to almost force the pieces apart as it pins.

Thanks for the advice, it's much appreciated.

Blaise

[Spit]

I wouldn't have guessed it was the Morso - I'll have a fiddle with it tomorrow. Other mouldings seem ok though. I fing the big carved obeches a bit of a fiddle to pin. The underpinner doesn't hold them properly and seems to almost force the pieces apart as it pins.

That's because the cuts are more than 45 degrees each. Try pulling the left fence backwards by a millimetre or less at the end - see if that improves it. If it makes it worse, push it in a little. It really only needs tiny movements!

Use a good quality square to make sure your underpinner is configured properly as well.

[blaisehall]

[quote="Spit"]
Use a good quality square to make sure your underpinner is configured properly as well.[/quote]

At the risk of looking even more stupid - what's 'a good quality square'?

Blaise

[Spit]

BTW The errors will show up more in bigger mouldings. When setting up your morso, use as big a piece of wood as you can fit in to test. Make up a couple of short pieces, and pin them. If you have your underpinner fences right, it should show whether your morso needs aligning.

[Spit]

A set square - like this http://www.screwfix.com/prods/61849/Han ... re-6-150mm

[kev@frames]

just adjust the left fence, not both.

[blaisehall]

Thanks very much.

[prospero]

I fing the big carved obeches a bit of a fiddle to pin. The underpinner doesn't hold them properly and seems to almost force the pieces apart as it pins.

Some profiles are tricky to pin. Sounds like the top pressure pad is bearing down at a different point to the hammer, in which case you will get lifting as you describe. Don't rely on the lateral clamps to hold it. A neat tip that works a treat on some mouldings (reverses in particular) is to make a short reverse-mitred chrevron with scraps of the same section, that is with the inner sight edge on the 'outside'. Place this face down on the corner to be pinned. You then have a flat surface for the pressure pad to bear on and the corner is held down with an even pressure all over.

[blaisehall]

A neat tip that works a treat on some mouldings (reverses in particular) is to make a short reverse-mitred chrevron with scraps of the same section, that is with the inner sight edge on the 'outside'. Place this face down on the corner to be pinned. You then have a flat surface for the pressure pad to bear on and the corner is held down with an even pressure all over.

A great tip. Thanks.

[MITREMAN]

Hi Blaisehall,
Thats a good tip from Prospero I have used it many times myself, another quick way depending on the moulding profile is to use a small triangle of 1/4 plywood say 8-10cm lay this on top of the moulding this will stop the bung marking softwoods and give it a even platform for it to hit on and distribute the pressure evenly (reducing the pressure, can help to if you are using a machine via a compressor).
Just going back to your cutting and joining?

Lets assume you have made your underpinner fences square as already advised

1; Check your blades make sure they are ground correctly and fitted correctly (Know burr, know snagging, hollow ground, know grinding of the front edge or overlap of the blades where they meet ?

2: As start point when adjusting fenches of a Morso,pull back the blades and place a straight edge along the two fenches and also along the bar on the right hand arm (the one with the measuring scale), they must be in line (parallel ), to start with.
Then cut a flat wide moulding or timber of at least 7cm wide into a small frame with a postage stamp size hole, you only need to hold it togeather to see the results,this will accentuate any gap problems if everything is ok, know adjustment is needed.
If there is a gap at the front, adjust the left hand fence only backwards
If there is a gap at the back, adjust the left hand fence fowards

Note; Never move the right hand fence
You only need to move the fence approx 1/4 of the total gap of one corner, adjust about a 1mm at a time (loosen the left fence to finger tight tap with a rubber mallet retighten recut and test the joint and continue
untill perfect.
It will take some getting used to but you will get there.
Once you have it right you could score a line against the rear fence this will give you a starting point if you have to adjust again. always check after putting on new blades (check there is know burr on the blades first)

MITREMAN

Any problems with blade grinding
Contact www.framersequipment.co.uk Look for the link on blade grinding facts. They also sell squares and straight edges.

[prospero]

A little refinement on MITREMAN's triangle. Get a thin cork floor tile and cover one side. Good when you have to pin a moulding with a sharp top.
A chrevron made from approx 3/4" flat moulding (also cork lined) is handy for clamping odd mouldings where there is a steep slope and the pressure pad can't reach without marking the side of the slope.

I also make frame bumpers with cork tiles, but that's another story.....

[MITREMAN]

Nice one Prospero,
"Great minds think alike"
Try this, I used to get fed up with using the trangle on large runs,On-off on-off
So I cut a triangle from 1/8 alumium drilled and counter sunk a screw into the rubber bung (which i bought a spare for) and covered the alumium trangle base over the screw hole with Upholstery rubber glued on with evo-stick. ("oh dear that's not conservation tactics" tidy the bung up on a grinder.
Also you can cut down rubber bungs to allow for taller profiles and grind them to a shape, like when using a moulding with beveled slope towards the site edge, you can gride a slope to fit the contours of the profile.

"Build a bridge to take the strain"


MITREMAN

[Not your average framer]

I'm not sure if we have established what's going on here! You say that the mitres looked fine at first, so exactly where are the mitres opening?

On the inside of the frame?

On the outside of the frame?

Or all along the front surface of the frame?

Also do I understand that this is only a problem on this particular moulding? If so is the moulding much bigger that ones that you normally use? Where are you placing your wedges? How much of the thinkness of the moulding is fully secured by wedge penetration? How much glue are you using in each mitre?

While we are waiting for your answers, here's a tip to be going on with!

Where I was trained I was told to always underpin the thickest part of the frame first. I've not heard it elsewhere, but it's a good tip to follow with difficult mouldings.

[MITREMAN]

Hi Blaisehall,
Good points by NYAF , we need to see the exact problem to help you better, why not post some photo's so we can all have a look, one of the cross section of the moulding used (include the ref and manufacter), one with the joint problem and one corner that you have broken open to expose the wedge position.
Some good tips on moulding storage from the boys/girls out their,I have a few to, let you know later when i get a bit more time.

MITREMAN

[prospero]

blaisehall. Meant to ask......What glue are you using?

[markw]

Prospero just beat me to it , are you gluing the joints? If you have a good joint then it really shouldn't open unless the wood was really damp - although force drying it isn't going to help.

The other factor that can cause problems is the dreaded snot wood - you generally notice this when cutting as the back of the moulding often just breaks away - sometimes the whole moulding just wont cut clean - when you get this soft sappy wood your not going to get a joint that holds.