Underpinning - How?

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Woodypk
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Underpinning - How?

Post by Woodypk »

Ok,

So this is a bit embarrassing but I'm not sure how to get really tight miters with the under pinner and I'm hoping someone can offer some advice.

I've got a basic underpinner - the CS79 but every time I try to pin my small oak mouldings, it seems to not pull together the mitres.

I've tried both soft and hardwood Vnails and neither seem to produce the results I get by using a stanley band clamp. With the clamp, there is Zero gap. It takes some aligning in the vertical plan but I've had a bit of practice at this now and they always look pretty good. But it's time consuming and I only have so many clamps...

Here's the really embarrassing bit - I then take the frames to the underpinner to put in a nail once the glue is dry just as a back up in case the frame is ever dropped or knocked, so that it would at least not fall into pieces, even if the mitres did break. Is this totally unnecessary? I know how strong wood glue is and that in normal use conditions, the nail offers no additional strength to the frame, I've only ever done it for the reason mentioned above.

I cut my mitres on the Morso but I've never been shown how to make frames, or underpin and I feel like I might be missing a trick here.

One thing I've wondered while using the underpinner is how much force should I use to press the mouldings together i.e manually closing the mitre gap up before pressing the pedal? I've never been shown how to use an underpinner so I've maybe got my technique wrong? Can technique go far wrong with an underpinner?

Any suggestions of methods that I can have a go at would be kindly received, tested and reported back on.


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Re: Underpinning - How?

Post by vintage frames »

There's nothing wrong with any of the efforts you are making to join your mouldings.
The problem comes with trying to join oak.
As you know it is a very hard wood and will not displace easily to allow in an under-pinner wedge. Hence it will force out the mitre as you try to get it to accept a steel wedge.
Yes, you can hold together the mitres as strongly as you need - nothing wrong there - I never understood the need for under-pinner side clamps.
But the only successful way to join oak is to use a band clamp. They're cheap. Buy lots if you have to join lots.
Glue is only successful if allowed to dry under pressure.

If the glue were to break the frame will need the additional support of a 'cross nail'.
Use the nail as a drill bit to make a pilot hole before hammering in the nail.

If needs be, countersink the nail with a punch and fill with oak coloured filler.
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Re: Underpinning - How?

Post by Woodypk »

I'm not sure how this ended up on a second version of my thread...

But thanks so much for the reply, Vintage.

As mentioned, I don't mind the clamping method, it always had given me superior results. I just wasn't sure if I was doing something wrong.

I make these particular frames as premade, and so to build a stock of them I can only glue as many frames as the amount of clamps I have.

Would you still recommend putting the V nail in every time like I have been doing or rather pin the mitre, punch and fill? Even if the frame has been glued and the glue has fully cured would you still recommend this?

I try to stay away from pinning frames on the edges as I like both the face and edge to look neat. The back, not so much as you often don't see it.
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Re: Underpinning - How?

Post by vintage frames »

I only posted on your second identical topic as I didn't want to be associated with the other contributor.

You can underpin after the glue has cured, if you like. You might still have a problem getting the wedge well in.
I always use a cross-nail.

Try not to worry too much about the frame sides.
Do a splendid job on the frame front and no-one will ever notice the sides.
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Re: Underpinning - How?

Post by Justintime »

After failing many times and an ever growing customer base for 30-40 at a time skinny oak frames I invested in a second hand Hoffmann MU2 dovetail router which meant I could do them all in a morning, without screaming. I feel your pain! A pneumatic underpinner is much better suited to joining oak with it's strong front clamps and pressure from below, I still use the Hoffmann though. At one point I found a way to glue clamp and join on a foot operated with the clamp still on, tricky but it worked. That was with a FrameCo expensive metal clamp, that I assumed was necessary at the time.
I agree with Dermot, nailing is a tried and tested and a traditional method that I don't think anyone could complain about. I have had it demo'd using a bench vice to hold one stick, glue pilot and pin. Quick and effective. We have a lot of old framed work come in for new glass after a drop or an upgrade of materials. 99% of them have loose corners, which without a nail or wedge would have fallen apart years ago. I am always amazed how long work can hang on the wall with such loose mitres, wiggly fixings, just masking tape holding it together on the back...
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Re: Underpinning - How?

Post by Gesso&Bole »

I use a lot of skinny oak mouldings, and like Justin I have invested in a Hoffmann which is the perfect tool for the job.

Before I had the Hoffmann, I used my underpinner (pneumatic) to put one small wedge in each corner (Usually a 7 or 10mm) then used a Bessey strap clamp to get all the corners perfect, then used a headless pin gun to cross pin (again pneumatic) near the top. I have got 4 strap clamps, and by the time I've got the next batch ready the glue has dried.
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Re: Underpinning - How?

Post by Woodypk »

When using the hoffman, do you specify the depth of the cut and then insert the key and flush cut to length? Is that how the machine works?
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Re: Underpinning - How?

Post by Justintime »

You set up where and how deep you want the key to go and plunge route it. Then glue it, hammer in the key and trim it.
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Re: Underpinning - How?

Post by Justintime »

That's an interesting point that Jim made about the time to glue and clamp. I use Titebond 3, which recommends 30 minutes for it to go off, no stress for at least 24 hours and it should be fully cured in a few days. It means that if pinned/underpinned before clamping, it only needs to be clamped for 30 mins, allowing you to get a lot more done in a day. When I started framing I used to leave them overnight, which slowed things down considerably on volume orders (and was totally unnecessary :Slap: ). I can highly recommend Brummers Interior wood filler in Natural Oak, once waxed it blends perfectly into the wood.
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Re: Underpinning - How?

Post by vintage frames »

Up to this I've been religiously clamping my glued frames overnight.
But now I see that I really only need to leave the clamps on for about 30min.
I checked on the Titebond website and they confirm that as long as the clamping has been tight, the glue has cured enough to be released after 30min.
Many thanks to Justin and Gesso&bole.

On an aside, many years ago the only place you could source Titebond was from a luthiers supplies. That spoke volumes in itself.
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Re: Underpinning - How?

Post by prospero »

I do the same as Dermot. One shallow wedge near the inside just to hold it in place and then you can cross-nail
near the top with good old hammer and pins and punch - or a pneumatic headless pinner if yo have one. I haven't.
I always drill a pilot hole. That's for narrow , deep mouldings. As for clamps, band clamps are fine but there are always the
old-school spring clamps which are quicker than a strap but do leave a slight 'divot' which has to be made good. But
if you are filling the nail holes anyway it's a minor job. When I started off underpinners were a relatively new thing
and every framer had a few sets of spring clamps. I use Brummer Stopping (many shades available) which when sanded
flush is virtually invisible.

For Oak mouldings that are not deep you can use wedges. I prefer the std soft wood ones. Don't try stacking them though.
I've never really taken to Hard Wood wedges as they never seem to give a tight join. One thing to watch out for when pinning
Oak (or any other dense wood) is the top pressure pad. Use a hard one. You need more welly when trying to push a wedge in
and there is a tendency for the top of the join to lift and separate before the wedge 'bites' if there is any give in the pad.
If the corner is held down very firmly the corner will be tight.

I have been known to drill a few tiny holes in the miter faces of Oak if if particularly hard. The reasoning being that it provides
a better key for the glue. Whether makes the join stronger I've never really tested . :roll:

The Hoffman key system is great, but you need to use it enough for it to pay for itself.
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Re: Underpinning - How?

Post by Woodypk »

It’s interesting you say about using a hard pad. The pad on my underpinned is soft and pretty worn now.

I noticed a thread had appeared about hacks with framing machinery and it was mentioned about using some Perspex as a hard back but doubling up as a window to check the mitre. This is genius and I’ll definitely be trying this.
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Re: Underpinning - How?

Post by Fruitini »

Any ‘give’ in your equipment will have a detrimental effect on your mitres when joining oak. A soft pad will almost certainly be causing you issues. The Perspex hack might improve things but if the pad is soft there will still be some give. I’m not sure what underpinner you have but is it possible to operate without a pad at all and have the plate come down directly onto the Perspex creating a much firmer hold?
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Re: Underpinning - How?

Post by Woodypk »

I’m using a CS79 so I’ll try removing the pad and giving it a go.
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Re: Underpinning - How?

Post by fusionframer »

I took off my pads too, but i glue gun a bit of thin felt, (baize) on. So go give like a soft pad, but protects denting timber. Easy enough to remove a stick new ones if you get glue over them.

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Re: Underpinning - How?

Post by prospero »

For years I used a triangle of ½" thick wood. (plywood is fine) with a piece of 3mm cork fixed to it. The cork came
off a floor/wall tile - not sure you can still get them. Cork is firm enough not to compress too much but softer than the Oak
so as not to mark it. Slight pain having to manually place the triangle, this works well as it also spreads the pressure.
Also handy for moulding that have a narrow raised highpoint. You cam position it above the wedge insertion point on
the inside of deep scoops to apply the pressure where it's needed. :wink:

** I wrapped this triangle in Handywrap so it can be changed easily when it gets gunged up with glue residue.
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Re: Underpinning - How?

Post by Not your average framer »

It's interesting that narrow oak frames were mentioned. I use a 13mm x 13mm square oak moulding, it tends to open a little at the corners and I need to fill the gaps will PVA glue and sand away and swelling with my bench top belt sander. This causes some of the saw bust to get in to the glue and help to colour the glue to match the moulding. Frames which are made from this moulding are quite popular, most are usual kept as natural oak colour, but they also make really nice narrow black frames as well. I only ever use these for bespoke framing.
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