Window rebate cutting

[lordbell]

Hello there - newbie amateur here. I have bought an old house and am wanting to replace some old single glazed windows with double glazed panels. To enable me to do this, I need to increase the depth of the rebate to accommodate a 12mm double glazed unit + putty. The current rebate is only 15mm, so basically I need to cut away about 10mm of wood to fit the double-glazed panels into the window frames from the outside (obviously). I am thinking of using a hand-held tool to do this - but am not sure exactly what I need. As the windows are in situ (and are almost 200 years old), I'm not sure a router is going to be any good.

Has anyone got any idea of what I could use please? The routers I have found online almost all need to be used on a work-bench or alike. I have considered a tiny planer, even an old-fashioned hand held one, but that won't get me into the corners of the frames will it. The other option is to hand sand the rebates with some very coarse sand-paper. I have 18 to do in total, so not ideal.

Any help much appreciated please. Hope I have explained this well enough. Kind rgds and thanks in advance

 

[Chrispy]

Advice, don't do it, this is what secondary glazing is for.

 

[rdesign]

pictures would help . A router could possibly make a jig to go over the frame. but this will leave your corners not rebated but a sharp chisel and maybe a rebate plane.. a clifton 3:1 comes to mind with the front left off to get right into the corners.

this is a crap drawing but if you remover the single pane of glass and build a u out of mdf or plywood that will slide up and down the window frame you can mount ur router where it needs to be to extend the rebate with a straight cutter.

then just clean up the corners worth the effort in making a jig as u have 11 to do.

just an idea.... might work

 

[blackrodd]

Hello and welcome, I personally don't like the sound of you're proposal, Send some pics, but sounds like loads of work for next to no return.
Removing the glass held, no doubt by rock hard putty which in turn will play havoc with any cutters you intend to
use to extend the rebates, probably weakening the bars and just for 12mm of double glazing, Is, I would say, hardly worth the effort,
Secondary glazing would be the best bet, you can still get self build kits, and in my experience, Very good!
See what others say.
Regards Rodders

 

[AndyT]

If you do manage to do this, have you thought about the extra weight? If the windows are casements they are more likely to droop on the hinges. If they are sashes you will need heavier balance weights, probably lead instead of cast iron.

I agree that secondary glazing sounds a better idea.

 

[Mike.S]

I've also considered doing what you're proposing but decided against - as others have said it's unlikely to provide a good return (aesthetics/insulation) for the work/cost involved.

However, if you go ahead then consider: 1) 'stepped DG units' - these have a smaller inner glass pane that slips into the existing space of the frame (hide gap with beading), with a larger outer pane that can be puttied in to the existing rebate; or 2) rather than just deepening the rebate, cut out the full depth of the rebate (handsaw will get right into the edges) and fix new mouldings to the inside of each window casement to match existing (often available as standard ovolo or ogee shaped and in various sizes). This will also likely allow you to use thicker DG units with a wider more efficient space (nearer the 20mm optimal) - 12mm (3mm glass, 6mm space, 3mm glass?) seems hardly worthwhile.

Bear in mind also that 'warm edge' spacers often need wider rebates (not just deeper) to hide them for aesthetic and UV protection reasons.

Assuming it's heat loss (rather than sound insulation) you're concerned about then probably better to spend funds and effort on good draught exclusion measures.

 

[Jacob]

Don't do it. You will be wrecking some very good traditional joinery.
There are plenty of better solutions; draught reduction top of the list, then thicker curtains , secondary glazing, insulation, etc.
DG isn't that cost effective anyway - you would be better spending the money/effort elsewhere.

 

[PAC1]

I agree with all those who say Don't
You will be amazed the difference thick, lined and well fitted curtains make.

 

[Benchwayze]

+1 Don't. HTH

 

[Manny]

Did this on a mates window using a router - took 3mm off ( I advised him against it ). It sort of worked but looked odd. If you've not used to a router don't try it Mike.S suggestion No.2 would be better or secondary glaze. BTW using ordinary putty with D/glazed units is not advised.

 

[Ant-]

If the frame has to stay you could always make new sash's with the required rebate?

 

[Beau]

I have done it and worked fine. The customer did remove the sashes so I could work horizontally. Made up a simple frame so the router could bridge between the panes. Used a bearing guided cutter. Make sure remove all the glazing pins as I discovered router cutters don't like them :lol:

 

[ColeyS1]

What about pin an extra 10-20 on the front of the windows, certainly sounds easier than the routing option. Use some good 'sticks like 5hit' adhesive and ensure its all well painted/ sealed. Save yourself a load of hassle by running out some wooden beads

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