Grinding questions

[mitch8]

I've heard that the golden rule in machining is to go from large to small in your chip size
http://www.sandvik.coromant.com/us/...cutting-strategies-for-mold-machining-US.aspx
But I was wondering if the same principle applies to belt grinding. What I mean is that if I'm trying to thin the edge on a blank but not the spine should I lead with edge or trail the edge?
Thanks again
Mitch

 

[Brian.Evans]

I'll chime in. I will hazard a guess that most makers grind edge up (edge leading). Some grind edge down (trailing). I grind edge up.

Mark your centerline, grinder a 45 degree short little bevel to almost the center line. Walk the grind lines up the blade a bit at a time. It's harder to type than show.

 

[mitch8]

I think I can see what your saying.
What is the benefit of the process you just described?

 

[mitch8]

I usually forge the edge down quite a bit if that makes a difference.

 

[IrishSteel]

I agree with medicevans. When I grind, I grind edge up so I can see how thin I'm making the edge and so I can see if I'm keeping the bevel symmetrical. With the spine up I would have no idea just how thin I'm going and would have to check it every few passes. You can do it either way but most people seem to find edge up easier.

 

[quint]

I think I can see what your saying.
What is the benefit of the process you just described?

The main benefit (besides the edge up or down which is preference, I do mine edge up) is that if you grind a angle like that it allows you to only cut a thinner portion of the side of the blade. Then when you grind the next step your only grinding another short portion of the blade. This keeps you from grinding the entire side of the blade at once. It helps with control and allows myself to grind alot better over all.

I do it like this because I grind freehand right now (sometimes use the bubble jig) since I dont have a tool rest setup on my NWG I built. One of these days. When doing it freehand and grinding in steps like this it helps alot.

 

[raylaconico]

Grinding edge up is the best way IMO. You can see the edge as you're grinding so you see what you're doing.

 

[Fred.Rowe]

This thread was originally posted in 2009. If you have not seen it previously it contains some good food for thought.
Progressive grinding assures that as you grind up the blade the abrasive will make contact with the peak left by the last grinding angle. The steel is removed faster each time the angle of approach changes.



I used a 4 inch by 2 1/4inch by 5/16 inch section of planer blade for this demonstration.
The first picture shows the blade section, end on, before it was ground.

The second and third pics shows the grind on the left side of the blade using an angle of approach of 10 degrees.

The forth picture shows the results of switching to a 5 degree angle of approach. The grind moves up the blade and moves to intersect the edge that was ground at ten degrees.

This next picture shows the grind at 4 degrees angle of approach, the grind moves up the blade and moves to intersect the edge.

I jumped from a 4 degree angle to an angle of 2 1/2 degrees, relative to the belt surface, to show the amount of grind line change caused by changing the angle of approach by 1 1/2 degrees.

The last picture shows the grind at the 2 1/2 degree grinding angle.
As you can see the grind has gone completely across the 21/4 inch blade section.

The straight edge shows the ground side to be perfectly flat across the ground bevel.

When you grind blades by degrees, two things will happen, one is the grind goes faster because you are grinding across the high points left by the previous angle of approach. The second is you will end up with a perfectly flat bevel.

So whether you want a flat scandi grind blade, ground at 12 degrees or a wide chopper, three inches across, ground @ 2 degrees we are all looking for the same results, flat even bevels.
If you have questions send me a pm, happy to answer any questions you might have.



Happy grinding, Fred