Using an underpinner - or not...

[RogerC]

Just a general topic for discussion rather then a specific question, but thought I'd throw it out there.
We've only been framing about 6 months (as a business service), but picked up a Gielle underpinner with our Morso.
My initial, naive view was just buy moulding, cut with Morso, then glue and underpin to make the frame.

In fairness, this works a lot of the time. But sometimes the join isn't great and we have to re-do.

Recently I've been experimenting with glue & band clamps, then pin when dry. Or just putting in a single wedge, then adding more when the glue is dry.

Just wondering what technique most use for 'general' framing, and what types of frame require a different method of assembly.

And yes Jo/Alec, this is on the list when I see you later this month...!!!

Thanks in advance.

[Chris_h]

I cut, glue and underpin straight away. Don't really have time and space for band clamps. I think the problem with underpinning after the glue is dry is that you can weaken the joint from the already set glue.

When I started I remember a big change to the improvement of my joins with an underpiner was getting the wedges in the correct place, with the right amount of pressure for different mouldings.

[Tudor Rose]

And yes Jo/Alec, this is on the list when I see you later this month...!!

Absolutely, we will have a look at your machine set up and how this is working for you. You will get arguments either way from people who swear that their version is the right way to do it! Personally we glue and pin, adding band clamps if we feel it is necessary. But we can discuss that a lot more when we see you.

[pramsay13]

The point of underpinning is to hold the join in place while the glue dries, to save the need for clamping.

In theory this would allow you to do 5 or 10 frames at a time, but it would be unusual and awkward to have that amount of clamps sitting.

My worry about letting the glue dry first and then pinning would be cracking the glue bond.

The only time I add clamps is after using the glue and underpinner, and it's a taller moulding that needs help to keep the top joined.

[prospero]

In my experience with underpinning (about 40 years) it's not good to add more pins after the glue as set.

It's all about getting the top pressure in the right place - that is getting the top pad over the insertion point.
Easy on a flat moulding, but on a moulding with a high back and placing a v-nail near the inside you have the
pressure offset which can cause the joint to rise and divide.
I have made many little gizmos to place on the low points of the join to make sure the pressure is applied in the
right place. Another good trick is to cut a small corner of an awkward moulding but mitre it 'wrong way round'.
This corner is placed on the corner to be joined and it gives a flat area for the top pad to bear on. The pressure
is spread equally over the join regardless of the v-nail position.

Some mouldings are just not underpin-friendly, but there usually is a workround.

[JFeig]

What is the reason for the need to "rework" the joining process? My assumption is that the frame corner joints are not holding and thus cracking.
What is the "drying time" between the frame joining and the installation of the art?

With a background in woodworking, the mitered joint is well documented as the weakest joint that be used. Adding additional "V" nails after the fact produces a shock wave that can crack that joint.

The number of "V" nails and their placement is a case by case decision based on the size and profile as well as the type of wood of the moulding.

[NTG999]

I started a thread titled Understanding underpinners and received a lot of helpful advice, part of the reason was to help with the purchase of a new machine. I tried plenty before purchase and IMO the difference between a basic machine and a 'deluxe' machine is significant, the opinions I came to were that a pneumatic machine is better (especially with harder woods) because it punches in the wedge as opposed to levering it in with a foot operated machine, good also when stacking wedges and a machine that clamps the moulding so the join can be inspected before underpinning is a real plus.
My advice would be to try better machines and then consider if they are worth it; I definitely think they are

[JKX]

I started with a manual underpinner, it was "OK" until it came to most harwoods and some deep rebates where stacking was required. Upgraded to pneumatic and what a difference, but still not very happy stacking in some mouldings and it only took up to 10mm wedges.
Then I upgraded to a CS200, with automatic pressure sensors and the rebate clamps from hell and that was great, what you saw, clamped, was what you got, joined!

I tailored my moulding selection with each machine and eventually showing over 2000 samples, I'd say you could go with nothing else if you wanted. However, gven my time over I'd get a Dustin straightaway, plus maybe 16 mitre vices - (the serious ones, not the blue Stanley ones), at least 4 band clamps and an assortments of other clamps like sash clamps, spreader clamps etc etc.

One thing I did (and still) have that was very useful for some problematic frames and boxes, was a pocket hole jig.

[vintage frames]

What's a Dustin?

[JKX]

[prospero]

On wide mouldings (2"+) on biggish frames I like to put a biscuit in. It makes what is a simple butt joint into
a Mortise and Tenon and make joining easier. The different in the strength of the corner is significant.
I've tried breaking biscuited corners by hand and it's very difficult.

I'm on my 7th box of 1000 biscuits.

[Justintime]

Cut, underpin with glue then strap clamp. Over half of my work is clamped after. The tighter the join while curing, the stronger it will be. Glues like Titebond are generally stronger than wood once cured. If time is an issue, a half hour/hour of clamping is sufficient, overnight is best.

[red]

i glued my guitar neck which had snapped off at around a 80 degree break with titebond.
that was 10 years ago and still as solid as ever. the neck is under huge tension,
im sure much more than a mitred frame?

[JFeig]

i glued my guitar neck which had snapped off at around a 80 degree break with titebond.
that was 10 years ago and still as solid as ever. the neck is under huge tension,
im sure much more than a mitred frame?

Yes, but your project is a "scarf" joint and not a corner mitered joint. Most glues are stronger than the wood itself.

[RogerC]

Thanks all for your input & thoughts.
I originally, and naively!, assumed the underpinner would be a magic wand. Of course not - just another tool to be used in the right circumstances!
The learning continues...

[JKX]

I’d say it was the best for most circumstances, but the small print would be you get what you pay for with - brackets on - you have to speculate to accumulate - brackets off

!