How to tell if a bit is worn out?

[Stropping Young Lad]

Hi all. This feels like a stupid question, but how can you tell if a bit is worn out? I have a few old axe heads I was thinking about fixing up and using, but I wanted to make sure the bit metal isn't too worn down. Honestly, I can't tell the difference by looking at it.

Can anyone explain this?

 

[Square_peg]

If it doesn't look worn out then you're probably fine but there are two way to know for sure if you've still got hardened steel left to work with.

1) Soak it in vinegar for 24 hours. This will reveal the quench line from the the original manufacturing. Then you'll see how much hardened steel you have left.

or

2) Take a file to the top or bottom of the axe starting at the eye and working your way to the bit. You'll feel the metal getting noticeably harder as you move away from the eye and inch or so. When you've done the vinegar soak you'll see that the file test corresponds very precisely with the revealed quench line.

 

[Stropping Young Lad]

Okay. It looks old, but I’m not sure I would be able to tell the visual difference between worn and not warn without a brand new example sitting next to it.

I’ll try the vinegar bath. It’s got a deep black patina right now, so maybe it’s hiding the quench line. (The axe I’m working with is a Kelly True Temper Vulcan Double bit, by the way)

 

[nickzdon]

I always pay attention to the toe of the bit, which is the upper tip of the cutting edge. It should extend out further from the handle than the bottom tip (the heel). Toes get chipped often from striking the ground, and then have to be filed back to eliminate the chip. This gives the toe a big rounded curve. Also, improper sharpening will accentuate the curvature of the bit over time; these axes I tend to avoid purchasing or restoring.

The axe on the right is an extreme case of toe loss. (photo pulled from the 'bay)

 

[Stropping Young Lad]

Ah, good tip. I'll have to check out my axe heads when I get home.

 

[Stropping Young Lad]

Well, the Vinegar bath really made a difference. Unfortunately, I still don't see a quench line. The toes and heels of the bits are about in-line.

I might put this one aside and work on my flint edge instead. I just really can't tell.

 

[nickzdon]

Post a pic. We'd be interested to see it.

 

[Stropping Young Lad]

Will do. I'll post a pic later on tonight, I'd appreciate any help.

 

[Stropping Young Lad]

Alright, let's see if this works...

 

[Square_peg]

The toes are heavily worn on that axe. Just the same, you've probably got close to an inch of hardened steel remaining.

Even if the the vinegar doesn't show a quench line the file will still tell you for sure how much hardened steel you've got left.

 

[Stropping Young Lad]

Okay, thanks for the help. As long as it's useable, I'm happy. This is the first axe I've tried to fix up, so I don't need perfect. Especially since I didn't pay much for it.

 

[cooperhill]

I think overall you'd want to take some of that roundedness out by focusing on filing back the center some. Here's one that I did that kind of shows the progression.