Putty Hacking Knife

[AnalogKid]

I've watched various videos etc, and each person uses a hacking knife differently.

One approach is the blade edge knife is perpendicular to the glass and the blade is hammered 'between' the (for example) bottom wood rail and putty

The other (less common approach) is where the knife is almost parallel to the glass and 'hammered' between the glass/putty interface

The bad drawing shows 'two positions' for the hacking knife

Is there a 'right' way - or are both methods correct

 

[AnalogKid]

PS: I should add, I hope to save every pane of glass (if possible)

 

[Cubist]

Ambition is a fine thing but sometimes.... the bridge is too far.

Using the knife at right angles to the pane risks the blade penetrating under its edge and stresses the glass when levering the putty out. However, in my own experience most broken panes result from leverage applied when trying to release the glass from the inner putty bed in the frame rather than the outer fillet. Nevertheless I always work with the blade parallel to the glass if I can but thats rarely completely possible.

 

[Cubist]

Oops, forgot to mention. With wooden frames glaziers will often 'pin' the glass in the frame and putty bedding using metal staples or even panel pins - another good reason to work parallel to the pane.

 

[Feltwell]

From what I can see of your picture - neither is right!

You should have the knife sticking out at 90 degrees from the glass and frame, and gently hammer it's point along the bottom of the putty, where it joins the frame - so your hammer blows are always parallel to the face of the glass. Watch out for glazing sprigs (little triangles of steel holding the glass in) or panel pins as Cubist says.

 

[Feltwell]

Like this, if you're right handed and were hacking out right to left - so you're actually hammering down and across, to make the knife point bite into the hard putty initially, then so the edge of the angled knife blade follows the edge of the wood - but the hammer blow never puts any force *into* the glass:-

 

[88v8]

If the putty is well adhered, soften it with a soldering iron.
Don't touch the glass ....

Ivor