sharpening

[agg221]

I have just spent ages on a 26" full chisel that someone had run on a badly worn bar

 

Would that be mine by any chance?

 

Alec

[spudulike]

Would that be mine by any chance?

 

Alec

 

Hi Alec

 

No - sorry it wasn't, yours was in reasonable condition compared to the other chain!

 

Yours fell in to the poor hook and one side of the chain wearing the cutters out and the other side remaining sharp - all down to a bar with too much chain roll and over sharpening on one side of the chain.

 

You should find the bar is now in good fettle and the chain is as sharp as the day it came out of the factory.

 

Think this discussion is like one on religion, almost impossible to prove one way or the other and to be honest - the end result is down to the skills of the technician rather than the method used.

 

Let me know how you get on with your chain and bar, and the 66 Magnum once it is back with you:thumbup:

[treequip]

If you heat steel and quench it, it goes from soft to hard, if you heat hard steel and let it cool slowly it goes soft, try heating a spring and quenching it - it will probably shatter if you compress it!

 

The terms to read up on are hardening and annealing!

 

Yes the terms are hardening and annealing and you can add tempering since you mentioned springs, we will get to that in a moment.

 

Annealing ferrous metals like saw cutters requires heating then cooling over time. Non ferrous metals can be quenched from hot and will still anneal but ferrous materials wont, they must be cooled slowly or the result is hardening. Thin objects like cutters air cool quickly and this has the same effect as quenching.

 

The analogy of springs is a bit spurious because springs are made of steel of a different composition. It is much higher in carbon and that makes it brittle. Springs are tempered to give a balance of hardness and ductility, hearing and quenching removes the temper and allows the naturally brittle nature of the material to exhibit.

 

So much the metallurgy, here id the acid test. Take a chain and over heat the cutters with a chain grinder, now try it with a file, it will skate off the cutter because the cutter is now hard.

[skyhuck]

If you heat steel and quench it, it goes from soft to hard, if you heat hard steel and let it cool slowly it goes soft, try heating a spring and quenching it - it will probably shatter if you compress it!

 

The terms to read up on are hardening and annealing!

 

I have just spent ages on a 26" full chisel that someone had run on a badly worn bar - all the cutter tips were buggered - had to take about 1.5mm off each cutter - it took a while on a grinder and think I would have still been sharpening if I had been using a file.

 

Not saying it can't be done but not a 5 minute job - not by me anyway - how badly damaged is "badly damaged"? Mine was a real mess!

 

Clearly you have never tried to hand sharpen an over ground chain, or even a tooth that has hit steel and been heated.

[18 stoner]

a well maintained grinder used by someone who knows what they are doing is quicker and easier and gives a near factory sharp finish.

 

Do you not try and achieve a better than factory sharp chain?

 

Semi chisel low profile chains on a 14" bar are a different can of worms to a 26" full chisel.

 

Why so?

 

when done by people that understand the technicalities of sharpening chains.

 

A bit derogatory and big headed dont you think?

[spudulike]

Clearly you have never tried to hand sharpen an over ground chain, or even a tooth that has hit steel and been heated.

 

No, cos I use a flippin grinder that is set up right and the wheel hasn't got glazed up from over use:thumbup:

 

The grinder WHEN USED CORRECTLY and set correctly will grind such a chain.

 

I do 90% of my chain sharpening in a workshop as I service and repair saws rather than use them professionally, if I used them out in the field then I would probably use a file much much more and I think this is why the two trains of thought!

 

Anyway - this isn't helping the original question of why the guy in the original post God bless him, isn't getting a cutting edge that works - perhaps we should be talking about file size, cutter angle, hook and raker depth, perhaps we should be sending him links of the Stihl and Oregon guides on how to sharpen a chain, what about different manufactures of file - I gather Vallorbe are good but havent used them - just used Stihl and they seem good............................ what about a few pictures to assist the bloke - if you cant hand sharpen or understand what you are trying to achieve then a grinder won't help anyway - I can post some good and bad pictures of grinder and hand sharpening if hat helps!

 

Hope the original poster is still reading - try looking at this: -

OREGON Maintenance Manual

&

http://www.stihlusa.com/information/STIHL-Sharp-Advice-Saw-Chain-Guide-Bars.pdf

 

Isn't a helping hand better than bitching about this as I am sure both methods work fine when done in the correct manner!

[spudulike]

Some pictures of chain sharpening

 

1) Badly ground chain with overheating, note the roll of metal around the top of the cutter and on the side of the cutter - not one of mine!

 

2) A cutter on the same chain now hand sharpened

 

3) One of my chains freshly ground

[agg221]

This definitely doesn't help the original poster, but may help with the explanation as to what happens when steel gets hot.

 

I can't find the specific grade(s) of steel used for chainsaw chains, but it will inevitably be a fairly high alloy steel, probably a fair amount of chromium, and is also likely to contain a reasonably high carbon content.

 

Carbon is soluble in iron at high temperatures, forming a phase (atomic arrangement) called martensite. This occurs at different temperatures for different alloys, but is in the region of 600degC (dull red). For ferritic steels, you can test this as a magnet sticks below the martensite transition temperature but not above.

 

Carbon is not soluble in iron at low temperatures. If you cool slowly it precipitates out, leaving a soft ferritic iron phase. If you cool quickly (quench) however, there is insufficient time for the phase to transition, leaving a 'locked in' martensitic phase. This is glassy hard, and way too brittle to hold an edge, even if you can get one on it.

 

You want a trade-off between brittle and hard - more of the latter, less of the former. Conveniently, transition from martensite to ferrite is non-linear, i.e. if you gently heat the quenched steel up, you lose brittleness faster than you lose hardness (the process of tempering). This leaves steel in an optimised state for the application - higher tempering temperature means greater loss of hardness in exchange for more toughness.

 

The usual function of the additional alloying elements such as chromium is to increase hardness and hot-working properties. Chromium has an additional function in that it forms chromium carbide by reaction with the carbon. This is extremely hard (and brittle) but being in a dispersed form within the iron matrix it doesn't make the overall material excessively brittle. Other alloying elements such as manganese increase hot-working properties, i.e. make the alloy less sensitive to losing properties with heat.

 

So what does this mean? Well, when a chain component is made it will first be quenched, then tempered to the right hardness. If you overheat it a little bit in grinding/filing you make it softer as more carbon is precipitated out to revert to the ferritc phase. Overheat it a lot (glowing dull red) and you re-form martensite. This will quench as it's a thin section, leaving glassy hard unfileable material. So, the former is softer, the latter is harder, both are bad!

 

So the only option is to leave it in the temper condition it was made to, by filing it gently, or grinding it gently, to stop it overheating.

 

I have no idea if this helps, but at least it's something I know about!

 

Alec

[treequip]

This definitely doesn't help the original poster, but may help with the explanation as to what happens when steel gets hot.

 

I can't find the specific grade(s) of steel used for chainsaw chains, but it will inevitably be a fairly high alloy steel, probably a fair amount of chromium, and is also likely to contain a reasonably high carbon content.

 

 

 

Alec

 

Thanks for that Alec, it’s an excellent description of the metallurgy involved.

 

It might not help the OP but the only thing that is going to help is practice and best under an expert eye. It will however help people understand how a cutter works and as such is a worthwhile exercise.

 

The need to be able to field sharpen with nothing more than a file means the chainsaw world employed little lateral thinking in this one.

 

Hard cutters would probably need grinding which would make field sharpening a nightmare so with the exception of specialty chains like tungsten carbide the cutter is designed to be sharpened with a file.

 

The cutter body is a pretty soft steel, it files freely and is reasonably malleable, if it hits something hard at speed it’s not uncommon to bend a cutter. The “cutting edge” to coin a phrase is the few microns of chrome plating on the top edge of the cutter to give it durability. If you scrape a chain on stone and remove the chrome the cutter won’t hold an edge.

 

Clearly removing a hard metal like chromium with a file would be near impossible so file sharpening removes the body from under the chrome which flakes away leaving a good durable edge. This way you don’t need anything more than a simple round file (and a good technique) to field sharpen a chain.

 

Andy

[agg221]

Thanks Andy,

 

With your additional information we're getting close to a full picture here.

 

The use of a hard coating introduces another factor, in that not only is it hard, it is also stiff, and brittle. If you put it on a soft substrate, the substrate can't support the load on the surface in use, so it deforms, resulting in cracking and delamination of the coating. The best analogy for this is the way ice on mud behaves when you tread on it.

 

This means that although the steel doesn't have to be hard enough to retain a cutting edge, it still needs to be left hardened enough to stop the coating from cracking off. My understanding is that chainsaw files are left harder (less annealed) than ordinary bench files as the underlying steel on the chain is still pretty lightly tempered. Some file makers (e.g. Vallorbe) actually make very high grade files which are left hard anyway, but their main market is precision instrumentation, such as clocks and watches, where the steel is left hard on the pinions.

 

If I'm correct, then heating the steel even fairly modestly, to the point where you start to see colouration on the chromium plate, will mean softening of the underlying steel and the plating will no longer be properly supported. If you heat it to red, the plating will start to form chromium carbide with the carbon in the steel (in addition to the quenched martensite). This is structurally analogous to tungsten carbide, and comparably hard, so it's no surprise that the surface on a seriously overheated chain is unfileable!

 

It's also worth considering that filing is a cutting action, while grinding is a wearing action. Cutting is less likely to generate frictional heat, so probably less risk of damaging a chain. That said, grinding is commonly used for precision sharpening of machine tools for a reason, so it's probably as simple as personal preference as to which set of skills you prefer to learn.

 

Alec

 

If you