25° Grinding Jig.
Here is a jig to set the angle on a grinder. It can be made for any angle.
My grinder is an 8” machine with the standard tool rest. The wheel is a Norton 3x 46 grit
When adjusting the tool rest for a specific angle you need to take into account two things, the diameter of the wheel and the thickness of the blade.
As the diameter of the wheel becomes significantly smaller, it will be necessary to make a fresh jig (the operative word is “significantly” since a little decrease in diameter is not important).
Each time the jig is used, it must account for the thickness of the blade. This is done by placing the blade on the tool rest, and then the jig on top of the blade.
Tighten the tool rest setting once it is set up as in the picture.
Making the Jig
The dimensions are not relevant and may be made any size you want. The jig in the picture will grind a 25-degree hollow on an 8″ wheel.
Use a blade with a known bevel angle (say 25 degrees).
Set the jig so that it will create a hollow at the middle of the bevel. To test this, use a Black Sharpie and colour the bevel. Place the blade on the rest and – with the power off – move the wheel back-and-forth to create a slight scratch pattern. Adjust the rest until the scratch is in the centre of the thickness of the bevel.
Retract the blade on the rest until it no longer touches the wheel. (you may want to clamp it here so that it does not move while creating the jig).
Place a block of wood on top of the blade and hollow grind that. This will give you a template to reproduce that angle.
Do another for 30 degrees (and any others you wish).