'3mm' Groove in Sash Window where Glass is inserted into

[AnalogKid]

Hi...
Some of the Sash's I'm renovating have a 3-4mm grove on one edge of the wooden sash (Blue line pointing to groove)
(Top edge of the bottom sash'

The other 3 edges of the sash, are the standard 'rebate' where putty would be placed (and the glass window pushed into this bed of putty'
(Red arrow pointing to rebate)

I've had to remove the glass from the window and will replace it with 4mm glass

--The groove is too small for 4mm glass
-- It could possibly be routed / and then chiselled out

But is the best idea to route / cut away the wood, and expose a full and continuing rebate around all 4 sides of the sash
(where I have the red crosses, showing the wood to be removed - but those red crosses would go 'all the way' along the edge where they are currentyl marked

 

[paulc]

Can the frame be disassembled ?
Running the strips though a table saw would give you a nice clean slot. The alternative is to route with a biscuit cutter (or maybe a t-slot), but you would need to finish off the ends with a chisel if the frame can not be disassembled.

 

[CliffordPope]

The upper edge of a lower sash doesn't normally have provision for rebate plus putty - the glass slides upwards into a groove instead. This would have been sufficient width for the original glass.
I've never really understood the reason for this convention - perhaps just to give a narrower less obtrusive profile?

 

[Feltwell]

You're trying to solve a problem that isn't there in my opinion.

If you need to increase the width of the slot in the bottom of the top rail then do so, but much easier to put in glass that fits.

For the rest of the window just bed the glass on putty (or putty replacement sealant, which I prefer now) on the rebate, then face up with more putty or sealant on the outside. It's how the windows were made and has been fine for over 100 years!

I'd strongly advise taking the sash with you into the glaziers when getting the glass, they'll then cut it to suit. Rebates can be narrow and frames off-square.

 

[CliffordPope]

Also it's a handy frame for carrying the glass home with you!

 

[AnalogKid]

I've possibly made the wrong assumptions
--I had thought 3mm glass in windows was either not available or not allowed?

Also
--my prior preferred option was not to widen the grove, but to remove the wood entirely, so there are 4 'rebate edges rather than 3

CliffordPope - I'm unable to fathom the reason either

I'll certainly be taking the sash's in to the Glazier for cutting.

 

[AnalogKid]

I spoke too soon. Some of the glass is 2mm thick

 

[Cubist]

I spoke too soon. Some of the glass is 2mm thick

Thats commonly referred to as 'picture glass' and was typically used for that purpose. However, it was also frequently used in older houses. Its still available in the UK and used for greenhouses as it is cheaper and lighter more readily.

3mm (1/10 inch) glass is/was widely used in the US for Storm Windows, mounted either on the outside or inside of a window-frame that was installed earlier in the buildings life. The purpose being to provide extra protection from strong winds and improve insulation - the origin of double glazing I suppose.

Im still trying to fathom the purpose of the rebates in your frames though.

 

[88v8]

Sliding box sashes?
If you put in thicker = heavier glass, you'll need heavier weights or the windows will not stay open/shut.
One can buy makeweights that sit on top of the existing weights, if there is sufficient height in the boxes.

Ivor

 

[AnalogKid]

Sliding box sashes?
If you put in thicker = heavier glass, you'll need heavier weights or the windows will not stay open/shut.
One can buy makeweights that sit on top of the existing weights, if there is sufficient height in the boxes.

Ivor

I've picked up a roll of roofers lead so I can roll some make weights around an 8mm piece of dowl for the new 6mm sash cord to pass through. Estimates so far show approx 2lb needs to be added to each sash weight based on weighing empty sashes and calculating weights for 3mm or 4mm glass.

So far I can see all the weights appear to be original and have never been adjusted, though there are mixed 2mm,3mm and 4mm pieces of glass in various sashes (indicating various repairs over the years)

 

[Feltwell]

Much easier to use makeweights, and they're less likely to "hang up" - catch on each other as the weights pass each other as you open and close windows - especially if you get the ones with a conical top. If you've got "feathers", free floating thin bits of wood in the sash box between the weights, so much the better.

No need to be too precise on weights, just make the top sash so the weights are 1/2 to 1lb heavier in total than the sash, and for the bottom one they should be 1/2 to 1lb lighter than the total sash weight. If you've 2 or more panes of glass in a sash it's important they are the same thickness so it's balanced left to right, otherwise it will just twist & jam all the time.

 

[AnalogKid]

Thankfully the feathers are still in place.
I was heading down the mighton connical makeweight path, but wasn't sure of the final weight of some of the sashes.
(Whether I can rescue some of the 2mm glass or need to replace)
As I urgently need to get one window back in (out of 4 windows that have been removed) I thought ”rolling my own” weights might be the easiest ”initial option”

I hadn't realised the importance of balanced left and right panes in the same window, but realise that part of why our sash have never slid easily.

I'll be borrowing your brass screws and cups for the staff beads if I may, as I am sure next summer I'll want to touch up/tune up the windows.

Ps...appreciate the shopping list you put together in one of your older posts.

It made a useful guide when hitting the mighton, readiseals sites