Understanding underpinners

[NTG999]

Hi all, I started back in the framing business last year with the 2nd hand equipment, I am now thinking of upgrading my underpinner; currently I am using a basic Framers Corner foot operated unit. I would like to understand more; with my underpinner it seems if I inadvertently leave a small gap then the UNI wedge goes in and the gap remains, it is my hand pressure that seems to determine how tight the joint is, (unless I glue first). Reading manufacturer info and watching demo videos they seem to claim the wedge pulls the joint tight, I don’t totally follow that unless during the action the wedge is somehow stretched and then pulls back?
I’ve been looking at the Cassese machines and uncertain if the pneumatic machines are identical to the manual or is just, they take less effort? They also have machines that only use Cassese cartridge wedges, I quote “recognised today as the best on the market” or some use UNI wedges
I don’t mind spending but I don’t want to make a bad purchase, thank in advance

[Gesso&Bole]

Generally, with a manual underpinner, you must pull the joint tight with your hands, and then hold it still, whilst pressing the pedal with your foot. To insert multiple wedges you will normally have to move the moulding you are joining backwards and forwards.

Pneumatic machines generally have clamps that hold the moulding tight whilst the wedge is inserted automatically. Some pneumatic machines are designed to join quickly, some have more options to adjust the joint before joining. ie factory type framing vs bespoke framing. Top of the range pneumatics will have multiple clamps, adjustment to the 90 degree fence, and the moulding will stay in position whilst the wedge block will move underneath to different positions as required.

Having said that, there are some manual underpinners with clamps, and some pneumatics without.

I would go for a pneumatic if the following apply

1) You can afford it
2) You want to join ash/oak regularly
3) You find it hard to hold mouldings tight in position
4) Bad knees
5) High volume

Do wedges pull the joint together? Only if you have got a good join I suppose. The Alfamachine power twist wedges are my preferred.

[Justintime]

Pneumatics don't compare to foot operated. I was reasonably satisfied with my Cassese CS88 and still use it mostly for joining spacers etc. The Cassese 486 Ultra I now have has adjustable fences which is really useful. It is way over specced for a low volume bespoke framer like me, but I have absolutely no regrets! It's a game changer.
A friend of mine had the Framers Corner underpinner and their guillotine. She swapped them in as soon as she was able, she had nothing good to say about either of them.

[prospero]

The v-nails are very cunning. They are actually slightly flared so when they go in they try to follow a
parallel track but in doing so the faces of the joint tend to be squeezed together. It's the wood that 'stretches'
or more accurately 'compresses'. I'm talking minute deflections here, but significant.
If you try normal v-nails on very hard wood (oak?) you can get v-nails splitting. This is why there are special
*'Hardwood' v-nails with parallel edges and a different cutting edge. (Personally, I don't like these).



* The term 'Hardwood' is misleading. It refers to timber from deciduous trees are in no way denotes the actual
density of the wood. Some Hardwoods are very soft. Some Softwoods are very hard. It's purely a Botanical term.
Hard Wood is one thing, Hardwood is something else.

** Some people will tell you differently but never pre glue a joint, let it set and then underpin. Always pin while
the glue is liquid. It's the glue that makes the joint strong. The pins only serve as an internal clamp and continue
to protect the joint and prevent catastrophic failure. (Failing to bits )

*** btw. I've always used a non-pneumatic underpinner. Less to go wrong at the wrong time. Only consider an air-powered
machine if you have good reason to do so.

[Justintime]

Out if interest @prospero,which underpinner do you use?

[prospero]

At the mo, a Cassesse CS88.

[NTG999]

Thanks for all the replies; excellent info - as always.

[NTG999]

Ref this

** Some people will tell you differently but never pre glue a joint, let it set and then underpin. Always pin while
the glue is liquid. It's the glue that makes the joint strong. The pins only serve as an internal clamp and continue
to protect the joint and prevent catastrophic failure. (Failing to bits )

I see the logic and have used both before and after 'glue dry' underpinning, one thing I do notice is that; to date I haven't seen an underpinning video with any glue about, and how does this work with Polcore? I've read lengthy posts about glue choices on this forum but if 2 pack mitre mate type is used it will be dry before pinning. I have noticed pretty much every Polcore frame I have received for re-framing is never glued

[prospero]

Most Poly moulding, it has to be said, is used on frames that are at the bottom end of the market. Price is the issue.
So if an operation can alos be removed from the process it makes a huge difference in cost.
You can underpin only and the joint will appear sound but it's nowhere near as strong as a glued one. It will likely start
to gap after a few years. It depends what level of quality you are working to.

As for glue/let set/pin, to me that's the silly way round in my philosophy. The pinning process is quite a violent one and
great force is involved. In some circumstances it will weaken/break the already-set glue bond.