Best raker profile for a CBN/ABN grinder wheel.

[KiwiBro]

There are differing views on this and much like the OEM's I suspect, there's a level of compromise involved when not knowing the conditions of use, including the wood being cut.

I'm setting up a dedicated grinder for rakers and seriously considering a Dinasaw ABN/CBN wheel to be made to my profile specs. Trouble is I can't decide on the specs and am thinking I might just copy a Stihl raker profile. It has a near continuous curve with what seems to me to be not much initial wood contact area at the top of the raker - which I fear might lead to digging into the wood and higher friction in soft wood than I'd perhaps like - but perhaps there's a trade-off between allowing the raker to sink into the wood to smoothen out the rocking of the cutter and the 'feel' to the user, and the extra friction if it sinks too low being unnecessary and undesirable. But it's Stihl so who am I to argue with that?

Either that or a flat profile on the wheel with a round at one end and then I will adjust the grinder tilt angle to get the final angle of the top of the raker. This gives me some flexibility

There are quite a few deep thinkers in this forum topic so I thought I'd throw this one open to the panel for feedback. At a few hundred dollars I can't really afford to stuff this up.

Any help appreciated.

Thanks in advance.

 

[BobL]

I can't see how a single curve stone profile is going to work. As the raker wears at some point the grinding wheel is going to start grinding away drive links. You will need a different stone profile depending on the raker depth.

This is why folks with grinders sometimes do them flat but this is not as good because this creates a bump on the front edge of the raker which generates extra friction which means getting out a file so you might as well file em full stop.

You are dead right about the curved raker digging into the wood but this is exactly how the raker is supposed to work - the cutter grabs, then the raker digs into the wood rocking the cutter back so it can take more bite which forces the raker into the wood more so that it can bite a bit more . . . . . This biting and rocking happens until the chain tension builds up so much that a chip is torn (not cut) from the wood. Flat rakers means less rocking means non-optimum chip formation.

More significant than the raker depth is the angle between raker cutter edge and wood.
The diagram in the top left is the one I mean.

The things that grinders do well ie generate identical cutter length and raker depth, are actually not as important as is made out. Unless these are way out I have stopped filing cutters to the same length and rakers to the same depth and just get the raker angle right to +/- 0.5º and all is good. It makes hand filing a little easier not having to worry about these unecessary parameters.

I can't see how that constant angle can be assessed and generated consistently with a conventional grinder. I have though about building my own grinder (I like building machines) - maybe now that I am retired I'll give a

 

[KiwiBro]

BobL for president!

Thank you Bob.

Your contributions have to be one of the best things about AS.

Keeping a consistent cutter angle the red line shows where the raker would end up when the tooth is on it's last legs.

The top of this raker relevant to the drive link will vary on the chain and the pitch; .404 could get interesting

The grinding wheels are approx 145mm or so, OD. The raker is offset from the drive link by construction (it's riveted to the side of it), and sometimes far moreso by design (Sthil splay their rakers out).

I'm wondering, if on the few chains that are on their last legs, the natural offset of the rakers, plus the curvature of the grinding wheel equals only a few times where the wheel will be digging into the drive links (and possibly the top of the tie straps if these aren't set down just a tad from the top of the drive link). I'm thinking maybe it wouldn't be so bad as to not try shooting for the continuously curved raker profile?

Then there are the safety chains with bumper links and all sorts of flotsam to throw a spanner in the works. It may be these would be more challenging because the curve of the wheel could end up cutting through some of these if the wheel is not a flat profile. There's some weird types of these bumper drive links. Some I think it wouldn't be too much of a problem, other's it could be a nightmare.





View attachment 282694

 

[BobL]

I'm wondering, if on the few chains that are on their last legs, the natural offset of the rakers, plus the curvature of the grinding wheel equals only a few times where the wheel will be digging into the drive links (and possibly the top of the tie straps if these aren't set down just a tad from the top of the drive link).

Good point - maybe come in a little sideways rather than directly down?

Then there are the safety chains with bumper links and all sorts of flotsam to throw a spanner in the works. It may be these would be more challenging because the curve of the wheel could end up cutting through some of these if the wheel is not a flat profile. There's some weird types of these bumper drive links. Some I think it wouldn't be too much of a problem, other's it could be a nightmare.

I wouldn't worry about these. If you can get conventional chain working that would be interesting enough.

 

[KiwiBro]

Good point - maybe come in a little sideways rather than directly down?

I think I'll have to play with a normal wheel and various profiles before committing to an ABN/CBN raker wheel, to see what can and can't be done.

Another thing while looking at rakers, the rakers that Stihl use are stamped first then bent out. Because they are bent out, they are not running perpendicular to the top of the cutter, thus the top edge of the raker is not parallel with the top of the cutter. This has the effect of promoting one side of the top edges of the raker higher than the other, which I'm guessing leads to more penetration into the wood. How many people file their rakers so that the top of the raker is parallel with the top of the cutter, or do they file them perpendicular to the face of the raker so that one edge of the top of the raker is higher than the other?

We are probably talking 9/10ths of bugger all I guess but have you tried both ways and noticed any difference?

Here's an image of the side, swiped from the great images in your first reply, with my attempt to show what I am talking about about the top of the rakers on Stihl chain.

View attachment 282729

 

[R DeLawter]

I think I'll have to play with a normal wheel and various profiles before committing to an ABN/CBN raker wheel, to see what can and can't be done.

Another thing while looking at rakers, the rakers that Stihl use are stamped first then bent out. Because they are bent out, they are not running perpendicular to the top of the cutter, thus the top edge of the raker is not parallel with the top of the cutter. This has the effect of promoting one side of the top edges of the raker higher than the other, which I'm guessing leads to more penetration into the wood. How many people file their rakers so that the top of the raker is parallel with the top of the cutter, or do they file them perpendicular to the face of the raker so that one edge of the top of the raker is higher than the other?

We are probably talking 9/10ths of bugger all I guess but have you tried both ways and noticed any difference?

Here's an image of the side, swiped from the great images in your first reply, with my attempt to show what I am talking about about the top of the rakers on Stihl chain.

View attachment 282729

bump

 

[Philbert]

I think I'll have to play with a normal wheel and various profiles before committing to an ABN/CBN raker wheel, to see what can and can't be done.

I think that that is your best route. Different brands and models of chain have different depth gauge profiles. So unless you are committed to a specific chain, you might not enjoy the benefit of that special wheel. But using a conventional wheel will let you try out a few profiles.

There was related thread about making an ABN/CBN wheel for square ground chain. Not until you have to commit to something fixed do you start to think about the advantages of being able to change your wheel profile. - http://www.arboristsite.com/chainsaw/229210.htm

Philbert

 

[KiwiBro]

I think that that is your best route. Different brands and models of chain have different depth gauge profiles. So unless you are committed to a specific chain, you might not enjoy the benefit of that special wheel. But using a conventional wheel will let you try out a few profiles.

There was related thread about making an ABN/CBN wheel for square ground chain. Not until you have to commit to something fixed do you start to think about the advantages of being able to change your wheel profile. - http://www.arboristsite.com/chainsaw/229210.htm

Philbert

Thanks Philbert. The only way I'm goig to be able to justify the costs of these wheels is if I start sharpening for others. That is quite a can-o-worms in that I don't have the experience to know all the different chains that would usually come my way under such an arrangement. commercial guys - no problem -it's most likely chain I've seen or used. Homeowner saws - well I've seen some crazy looking safety chain and suspect that's just the tip of the iceberg.

Will probably stay with normal wheels and play with profiles until gain more experience and get a better idea of the types of chains that might present themselves.

I think a square grinder is going to be out of my budget at this stage but thanks for the thread reference. I've a read and filed it in my head for 'when the time comes'.

 

[imagineero]

Get yourself a silvey raker grinder. It is to the CBN/ABN raker wheel as the gatling gun is to the revolver.

Shaun

 

[KiwiBro]

The Silvey that is going out of business (if what I've read is correct)?

 

[Philbert]

. . I think a square grinder is going to be out of my budget at this stage but thanks for the thread reference.

Get yourself a silvey raker grinder. It is to the CBN/ABN raker wheel as the gatling gun is to the revolver.

The Silvey that is going out of business (if what I've read is correct)?

I wasn't trying to steer you to a square grinder, or even a dedicated raker grinder - was just trying to share the considerations that another A.S. member was going through in considering a custom made ABN/CBN wheel.

There have been rumors and a thread about Silvey going out of business. I spoke to one of the people there a month or so ago, and he stated that that is not a certainty.

Philbert