When to 'sub - frame'

[+Rafe+]

-ooop must have hit TAB on the keyboard and posted a bit early.

Hi all,

Out of curiosity, who here has set rule for using a sub - frame when creating a larger framer. What is the combination that requires the use of one?

I have always been a bit uncertain and more than likely over engineered frames.

For example - A1 size artwork, float mounted with 35mm margins and framed in Lion L001 Ash wood frame, I would add R&H A345 sub - frame.

Just a curious enquiry, obviously it also depends on the thickness of the main frame too but I am guess folks who produce larger volumes of work might have a better 'rule of thumb'?

Have a good day

[+Rafe+]

...No that was the preview I saw ... COFFEE!

[Not your average framer]

I don't think that it is very meaningful to try to suggest any hard and fast rule for when a sub frame would be necessary. Not all situations are the same and not all framers would necessarily decide to add a sub frame in the same situation. It's also is not particularly by the overall size of the frame. For instance, I sometimes will use a sub frame on a narrow moulding, because some customers insist on the narrowest possible black frame around a reasonable large artwork and a really wide mount. I have to agree that there are times when this can look particularly effective, but it can be a difficult decision to make!

Not all frames are greatly suited to accommodating sub frames. It's an unfortunate fact the some frames are a bit too flimsy to be able to securely screw in to the support the sub frame. A sub frame is not going to contribute any meaningful support without being possible to adequately secure it in place. I don't necessarily use normal sub frame mouldings, sometimes I need something that is less visible when in situe and this can mean a lower profile made from a stronger wood type. It is not unknown for me to cut down a piece of Ash moulding to make a lower profile sub frame and even perhaps with a bit extra width to increase the available strength.

I'm maybe not a particularly normal case as I have various woodworking tools like a table saw and a surface planner, so I may have options which not everyone has. Part of the point that I am making is that it's o.k. for each of us to use our own judgement, for when a sub frame is needed and how we will do that with whatever we wish to use as a sub frame. It is even possible to chamfer the sub frame to reduce it's visibility, when the frame is hanging on the wall. Another option that I sometimes use is to add a spacer frame behind a mount and treat that as part of the frame, with a smaller backing board fitting inside of this additional frame. I already make stacked moulding frames, so this sort of comes fairly naturally. The only difference is that this inner frame needs to be removable, in case the glass ever needs to be replaced.

Don't get too hung up about this! It's a judgement thing, just trust your own judgement and it will be alright. There have been times that customers don't want sub frames fitted, because they are trying to save money and in those cases, if I feel strongly about it, I tell them that I won't stick my label on the back. This usually causes them to stop and think!

[prospero]

It's largely a matter of intuition. A ½" thick frame on the 36x24 frame with glass - deffo.

If it seems a bit weak and weedy - subframe.

I made a bathroom mirror 48x36 with 10mm Beech moulding. Hefty subframe. With a bit of ingenuity you can
make a cleat system whereby the whole weight is taken on the top rail of the subframe. Or, affix the hangings
to the subframe. Either way removes any stress from the frame. For a really strong subframe don't mitre it. Use
half-lap joints. I do this a sneaky way by using 8mm pine cladding with the 'tongue' ripped off. You can then form
the joints with minimal woodworking and the laminated build makes it very stable.

This one is a bit extreme, but you get the idea....

bigmap004.jpg (18.05 KiB) Viewed 2007 times

[+Rafe+]

Thanks both. You have clarified what I a have been doing, possibly I might be a bit overall cautious.

Prospero I've seen your posts about that sub frame before, its quite a thing and more so know that it was for a 10mm frame. The final piece must have been impressive!

Just interested to know as I my experience isn't anywhere near as experienced as most on here and I don't want to be seen as ripping clients off adding on a cost that might not be needed.

Thanks again

[prospero]

Actually, that subframe pictured was 6ft(ish) square and was more to keep the back firm than strengthen the frame.
The outer frame was strong enough in itself. But I could have put a diddly frame on it and it would have worked.

Thing is, you have to have the outer moulding quite deep to swallow the depth of the subframe. It's a different matter
if you're using a narrowish frame with an 8mm deep rebate.

** One way is to use a stout back (2.5 MDF?) and rivet the d-rings to the back. This way the weight is taken completely
off the frame and it only serves to hold the glass/thing/back together. In effect, the back becomes the subframe.
The tails of the rivets need covering with something like aluminium tape lest they rust. If you use a good wet tape to
cover the back that negates the tendency for the glass to pop out if handled incorrectly. Slightly half-arsed method, but
if push comes to shove......

[Justintime]

I used to think "belt and braces" meant someone had overdone the work, until a carpenter friend told me that belt and braces was standard practice.
Our job is to foresee any future issues and to remove the possibility. If I have a valuable and heavy piece I will always "over-engineer" it.
Have you seen the way some customers handle the work once they leave the shop??

[Not your average framer]

A possible alternative can be to have a thicker backing board and chamfer the edges of the board to make the board a lot less visible. Quite often I will just secure the backing board in the usual way, using framers points. I don't much like the Fletcher Terry rigid points because they don't seem to penetrate as well as the semi rigid tabs. I like the Alphamacchine semi rigid tabs because they seem quite strong and springy and keep the backing board held in place really solidly.

I have a pneumatic gun which I use for bendy tabs, but I use a manual Fletcher flexi tab gun which happily takes the semi rigid tabs if you grind away the little ridge inside the magazine, which is intended to stop you using non Fletcher Terry tabs. I have two suitable Fletcher Terry tab guns and two suitable Eletrrotech Flex-04 tab guns as well. If a gun is going to develop a problem at any time, it will probably happen at a bad time so I like to have a spare gun handy, just in case. I don't like some other makes of flexi tab guns as many of the cheaper ones don't tend to fire the tabs tight to the backing board.

Sometimes a more substancial backing board is enough to steady some frames up enough.