Why does aggressive chisel prep make such a big difference?

[John C Cox]

Hey guys,

TLDR: If you are having problems with poor chisel performance - try aggressively flattening the backs and working the bevels on coarse PSA sandpaper before you write them off...

21 chisels in... 19 have seen large improvements in edge holding and cutting wood after aggressive back and bevel prep.. 1 worked fine with minimum prep. 1 was a dud and was exchanged for one of the 19 that saw significant improvement.

Why? Why does this make such a big difference in performance?

Prior to this - I was never one to advocate aggressive back flattening or really going at the bevels.... Just clean up the back enough so there was a bit of polished chisel at the bevel... Sharpen up the bevel and go..... But I was also unhappy with chisel performance... The edges would roll or fold when paring spruce end grain - and certainly when chopping mahogany and cherry end grain... And I just couldn't get good work out of them.... Obviously I must have gotten bad chisels...

I was puzzling over how many Youtubers and fellow Creekers could get a lot of work out of So many chisels yet somehow I couldn't...

Well.. I stumbled into grinding the heck out of the backs of a set of Two Cherries that seemed like they all had humps in the back.. And the more I ground - the better they cut... When I stopped - they really go through wood like crazy...

So I tried the Aldi chisels that were marginal - they wouldn't pare spruce... Wouldn't chop mahogany... Same thing - aggressively flatten the backs and work the bevels on 100 grit PSA and now they do... Same bevel angle as before - now they cut....

Same for Woodcraft green handle chisels, Wood River socket chisels, and my Pfeil...

19 chisels.... All saw major improvement... All cut very well now without edge trauma.....

The new Marples was the only one that passed the same tests without major prep... Go figure....

What's going on here guys? Why - with a range of $7/set through $45/each - all see huge improvement with very aggressive back and bevel prep vs "standard" prep...

[Bill Houghton]

The cutting edge on a tool is the meeting of two surfaces at an angle. The closer the surfaces are to flat and straight, the more likely the meeting point will be an actual edge. And, the more it's an actual edge, the longer it's likely to last. Plus, a lot of people find that new chisels are imperfect in their temper for the first 1/8" or so. Plus plus, a flat back will register on the wood more accurately.

Why do you have so many different bench chisels? Were you frustratedly seeking chisels that would cut better than what you were seeing?

[Stewie Simpson]

I had a close look at the backs of 2 sets of vintage W.M Marples Firmer Chisels that I purchased from the U.K a number of years ago. None of them have totally flat backs. All showed signs of their original concavity until you get to an 1" to 1 1/2" from the cutting edge. At that point they appear to straighten out. Those that have seen more constant use over the years (based on their remaining length) also showed signs of being slightly toed up within this same area.

[John C Cox]

That's a beautiful set of chisels you have there.

[Jim Koepke]

21 chisels in... 19 have seen large improvements in edge holding and cutting...

Why do you have so many different bench chisels?

Some might say 21 is just getting started. There are likely that many in my drawer of 'beaters and loaners.'

Getting back to aggressive chisel preparation makes some sense. All but a few of my chisels were purchased second hand. Many of them needed work on the backs to remove rust and pits.

Maybe someone knows more about the metallurgy of heat treating and is it just the bevel area that decarbonizes?

jtk

[lowell holmes]

Since Harvey came through, I have not seen my leather chisel roll full of chisels. I will look for them tomorrow in the plastic tubs full of my tools.
As to why chisels need to be prepped for use, they need to be mirror flat on the backs and scalpel sharp. They do not come that way,
You should be able to create translucent shavings with a chisel. See the link below.

https://www.wikihow.com/Use-a-Chisel

[Stanley Covington]

Buy right buy once.

I grew up in a very frugal home. My father was the youngest of 8 children born to plasterer in a desperately poor part of the US during the second year of the 10 year Great Depression. Eating at his father's house was not guaranteed some days. Dad worked as a carpenter and cabinetmaker. We did not buy new things when I was a child. The first new woodworking tool I owned was a Disston saw I bought from Monkey Wards when I was 21 to make furniture from discarded concrete formwork lumber for my wife and baby. My point is that the virtue of buying things used, repairing them, and getting by was ingrained into me as an infant.

It can be fun to buy beaters and refurbish them. It feels good to make useful again something that was unused, unappreciated, and practically discarded, especially when it cost less than lunch. The frugal gene I inherited from my father smiles every time. But as the years raced by, I came to realize that a few high-quality tools that don't need to be fixed are a better investment of time and money than buckets of run-down chisels that were mediocre even when new.

This will offend some, but for others like me who have already passed through the collecting phase and just need to get the job done, dammit, quality and usable condition at the time of purchase are more important than cheap price and scratching the tinkering bone. I have dozens of old chisels I bought at flea markets, yard sales, and antique stores that I spent a lot of time and effort fixing. It was satisfying for the moment, but looking back and realizing that all but a few of those chisels were nothing to brag of even when new, and that I use only one of those chisels now, and that the rest will all end up back in flea markets after I die, I can see it was a waste.

Many will read these words and scoff. But remember them 30 years from now.

Buy right, buy once.

[Jim Koepke]

But as the years raced by, I came to realize that a few high-quality tools that don't need to be fixed are a better investment of time and money than buckets of run-down chisels that were mediocre even when new.

Did purchasing and rehabilitating an old tool help you to earn the funds to purchase a better tool?

During my early years of woodworking, if my purchases were limited to buying only high end tools, nothing would have been purchased. Some of the lesser tools have helped me to earn income. Some were purchased to be rehabilitated and sold to earn more money to purchase better tools.

No two people have the same financial or time considerations.

jtk

[Stanley Covington]

Did purchasing and rehabilitating an old tool help you to earn the funds to purchase a better tool?

During my early years of woodworking, if my purchases were limited to buying only high end tools, nothing would have been purchased. Some of the lesser tools have helped me to earn income. Some were purchased to be rehabilitated and sold to earn more money to purchase better tools.

No two people have the same financial or time considerations.

jtk

Point taken.

[Lasse Hilbrandt]

John, if I understand you right, your point is that the whole back of the chisel needs to be completely flat ? I thought it would be enough with a cuple of centimeters that are closest to the edge ?

[Derek Cohen]

Lasse, that is not what John is saying, if I understand correctly. It is his thread - I will leave it to him to explain.

Regards from Perth

Derek

[Pat Barry]

John, how much steel are you actually removing? I suspect it can't be very much if you are just doing this by hand on sandpaper. It would take quite a lot of effort to remove much steel by hand with that method. I suspect that it's just a few thou.

[Derek Cohen]

Hey guys,

TLDR: If you are having problems with poor chisel performance - try aggressively flattening the backs and working the bevels on coarse PSA sandpaper before you write them off...

21 chisels in... 19 have seen large improvements in edge holding and cutting wood after aggressive back and bevel prep.. 1 worked fine with minimum prep. 1 was a dud and was exchanged for one of the 19 that saw significant improvement.

Why? Why does this make such a big difference in performance?

...

John, are you going by a different name on another forum?

I don't think that others here are getting what you are trying to say, that is, by grinding back the chisel back, the steel that remains is harder than the outer surface that was removed. And that this enables the edge retention to significantly improve. Is that correct? Will you say why?

Regards from Perth

Derek

[John C Cox]

I don't think that others here are getting what you are trying to say, that is, by grinding back the chisel back, the steel that remains is harder than the outer surface that was removed. And that this enables the edge retention to significantly improve. Is that correct? Will you say why?

All I am saying is that all of them cut better when they got past some "threshold" of chisel prep... It was very noticable - both on the stones and on wood...

As to the cause of it... I am not convinced it is specifically decarb... For several reasons... Patrick makes good points in the other thread about alloys used to reduce decarb problems... I noticed the same thing as he mentioned in my backyard chisel experiments... There was no noticable decarb layer to deal that persisted beyond simple adequate flattening and sharpening... I had no decarb problems even with a Mapp gas torch..

And I am not convinced it is from "Flattening" the back.... I think flattening the back has a side effect on whatever was hurting edge durability.. But I doubt "Flat" is the cause of better performance....

What I did notice last night is that when I re-honed the bevel on my Worksharp - the problem came back when chopping mahogany and eucalyptus - though not when paring mahogany, spruce, or eucalyptus end grain.....

Although it's nowhere near the extent of previous - it still feels like I went backwards somewhere.. It could just be my expectations, though.....

Do you guys prep separate chisels for chopping? If so - how? Is it possible that a finely honed and polished edge performs worse chopping than a fairly coarse edge?

[steven c newman]

Might be be more to do with the angle of the bevel....chopping takes about..30-35 degrees, paring is around 20...and 20 is not good for chopping..too thin.