Chain Filing Angles

[openspaceman]

5 minutes ago, 5thelement said:

Have you got a stone to re-profile the grinding disk? 
I have only used a grinder to reshape and sharpen harvester chains, I would have to reshape the disk occasionally to get the desired result in the cutter.

I can see the reason for dressing the stone for getting the gullet right but the top cutter is ground with the flat bit of the disc.

 

BTW while not a great user of a grinder as I sharpen my chains on the bar for speed my chief gripe with people who use them grind too much, too heavily and burn the chain.

[Mick Roseblade]

8 minutes ago, 5thelement said:

Have you got a stone to re-profile the grinding disk? 
I have only used a grinder to reshape and sharpen harvester chains, I would have to reshape the disk occasionally to get the desired result in the cutter.

Yes, I lost the one that came with the grinder, but I have one that came with a Tormek grinder. I haven't had to use it yet though. I check with my profile gauge from time to time and so far so good.

[Mick Roseblade]

3 minutes ago, openspaceman said:

I can see the reason for dressing the stone for getting the gullet right but the top cutter is ground with the flat bit of the disc.

 

BTW while not a great user of a grinder as I sharpen my chains on the bar for speed my chief gripe with people who use them grind too much, too heavily and burn the chain.

Yes that's how I see it, As for burning the chain, I used to use a spray bottle to squirt a bit of water at the disk to help cool it. However I don't bother now, I am just more careful not to take to much at a time. 

[5thelement]

8 minutes ago, openspaceman said:

I can see the reason for dressing the stone for getting the gullet right but the top cutter is ground with the flat bit of the disc.

 

BTW while not a great user of a grinder as I sharpen my chains on the bar for speed my chief gripe with people who use them grind too much, too heavily and burn the chain.

We would always finish the harvester chains off by hand file after using the grinder for exactly this reason. 
The grinder was largely used to uniform/resize the damaged cutters rather than sharpen them.

 

[SimonHS]

Are you using the right thickness grinding wheel for the chain?  The wheel should cut on its rounded face, giving a grind that looks the same as filing, and not on its flat side.  Grinding too deep will also cause the hook to be straight rather than rounded.

[openspaceman]

2 minutes ago, SimonHS said:

Are you using the right thickness grinding wheel for the chain?  The wheel should cut on its rounded face, giving a grind that looks the same as filing, and not on its flat side.  Grinding too deep will also cause the hook to be straight rather than rounded.

Yes it cuts on the front face as it  passes the top cutter but the locus of the piece of grit that cuts the angle is a straight line, , so the top cutter has a flat angle. The side cutter angle and gullet are determined by the depth of cut, angle  to the tooth  and radius of the wheel.

[Mick Roseblade]

1 minute ago, SimonHS said:

Are you using the right thickness grinding wheel for the chain?  The wheel should cut on its rounded face, giving a grind that looks the same as filing, and not on its flat side.  Grinding too deep will also cause the hook to be straight rather than rounded.

I am using the recommended disks in the grinder handbook. I have 2, one for .325 chains and one for 3/8 chains, I am deliberately setting the depth stop low enough to get the gullet and give me a flat grind to the top plate (just). I know this will distort the hook a bit which is why I was playing with the grind angles to try to find the best compromise. Whilst it may not be technically correct, I just want it to work for me.

[Woodworks]

43 minutes ago, SimonHS said:

Are you using the right thickness grinding wheel for the chain?  The wheel should cut on its rounded face, giving a grind that looks the same as filing, and not on its flat side.  Grinding too deep will also cause the hook to be straight rather than rounded.

I dont think thats quite true. Got some pictures of my cutters off a grinder in this thread and thats the recommended grinding disk for that chain. Doubt a 4.8mm thick disk would even fit on the grinder let alone a 5.5mm one.

 

Edit. From F R Jones 

• 1/8 – 3.2mm wheel fits: 3/8″ low pro, .325″, 1/4″
• 4.7mm wheel fits: 3/8″, .404″

 

Edited July 31, 2021 by Woodworks

[Mick Roseblade]

Just out of interest I thought I would get the calipers out and measure my disks and files. 

Interesting result.

Disk 1 3.3mm

Disk 2 4.6mm

Both disks as supplied by Oregon with the grinder.

 

3/16 -4.8mm file actual measurement 4.6mm

7/32 -5.5mm file actual measurement 5.4mm

 

Given those results, even if you used the grinding disk horizontal (which you obviously can't), using the recommended disk will always either give you a shallow gullet or a flat grind on the top plate and distorted hook.

You could use the 4.6mm disk on the .325 chain but then you run into other issues.

So I come back to my point about finding the right angle and depth for the best compromise.

Edited July 31, 2021 by Mick Roseblade
Correction

[SimonHS]

I had another look at this.  I'm using an old model Stihl USG.  The radius on the stone is offset, not symmetrical, which is like a form tool for grinding chain.  It cuts like a thicker wheel.  I've attached an excerpt from the USG manual, but it's not very clear even if you zoom in.

 

The wheel is 3.8mm thick and the radius is 2.4mm offset to one side, so it cuts like a 4.8mm thick wheel.