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Brittleness of carbide saw teeth?

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Forum topic by Tog posted 09-17-2012 02:25 AM 893 views 0 times favorited 9 replies Add to Favorites Watch
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Tog

2 posts in 832 days


09-17-2012 02:25 AM

Topic tags/keywords: carbide blade sharpening damage tablesaw question

I just had a disturbing experience with a resharpened table saw blade and I’d like to know if my expectations are out of line or if it might have been damaged during sharpening.

I have a high quality 10” 40 tooth combination blade of a well known and highly respected brand. I’ve had it for about 20 years. It received light (hobby type) use for the first 10 years and has been unused, mounted on my saw for the last 10 years. (Finally got the time, space, and motivation to get my shop set up again after a move, career, etc.)

I sent the blade out to be resharpened at a facility recommended by the manufacturer. They replaced 2 teeth and resharpened the rest. I got the blade back and proceeded to mount it on my saw, doing what I always did in the past, which is putting a block of soft scrap wood on the back side of the blade to keep it from turning while I tightened the nut. While tightening, the blade slipped a couple of times, but I didn’t think anything of it. I didn’t think I was applying unusual pressure. When I was done, I noticed with horror that the two teeth that had slipped against the wood block were badly damaged. This wasn’t a failure of the braze; the carbide material itself was split down the middle; the back half was still attached to the blade and the front half had fallen off. (These were NOT the teeth that had been replaced.)

So I took the blade off and began examining the other teeth. I tapped each one lightly with a block of soft wood, about like you would tap someone on the shoulder to get their attention. With this light tapping, 3 more teeth split in the same way, right down the middle of the carbide.

I know carbide is hard but brittle, so it’s prone to chip and crack. When it slipped against the block while tightening, that was putting pressure on it in the opposite direction from the normal case when it’s cutting. That said, it still seems to me that these moderate forces shouldn’t be enough to actually fracture the carbide. Or am I wrong? Is C4 carbide really usually this fragile? Might the teeth have been damaged by improper sharpening (e.g. not enough coolant)?

I’m undecided about having the teeth repaired, not sure I would trust it again.


Tog


9 replies so far

View Loren's profile

Loren

7831 posts in 2402 days


#1 posted 09-17-2012 02:31 AM

I’d be inclined to suspect the sharpening shop of messing
it up. It is possible it was dropped by an employee or
in shipping. I have seen teeth break off easily after a blade
was dropped on concrete. Initially there was some chipping
but then teeth broke off when I worried at them.

My experience has been that resharpening doesn’t affect
the durability of the tooth.

-- http://lawoodworking.com

View Purrmaster's profile

Purrmaster

842 posts in 847 days


#2 posted 09-17-2012 07:25 AM

Could it be age? The expansion and contraction of the carbide over many years of use?

View Gshepherd's profile

Gshepherd

1689 posts in 955 days


#3 posted 09-17-2012 03:16 PM

Recently I had my 12in SLR blades resharpened. Installed it and started the saw and I could hear something was wrong. I just could tell by the tone of the blade some thing was not right. Double checked everything to be sure I didn’t install backwards, hitting on the caterpillar belt ect,ect…. All is well, so I cut a few pieces and was not satisfied and took it back the same day. Couple days later got it back, reinstalled and all is well. Reason was there were several teeth cracked and needed to be replaced. Found out his 16 yr old kid grinded the blade and was a newbie and he said it was probably dropped before sharpening, several teeth were replaced, resharpened, but it did not solve the ones that were cracked…. They did not charge for adding some new teeth and resharpening it.

-- What we do in life will Echo through Eternity........

View bondogaposis's profile

bondogaposis

2764 posts in 1105 days


#4 posted 09-17-2012 07:26 PM

Accept that the blade is a lost cause and buy a new one.

-- Bondo Gaposis

View MrRon's profile

MrRon

2991 posts in 1997 days


#5 posted 09-17-2012 10:23 PM

C4 carbide is not the same for all manufacturers. I used to sharpen blades years ago and never came across this problem. I don’t know what could cause the teeth to fracture as you described. I can only guess it’s something the sharpening service did to cause the subsequent failure. Only one possibility comes to mind; they used a very caustic chemical to clean the blade and that may have altered the chemistry of the carbide to make it more brittle. I would contact them and ask what they used to clean blades. One has to remember; sharpening services make their money from volume sharpening for industrial customers. They usually don’t put the attention into sharpening one blade for a customer as they would for a volume customer.

View Tog's profile

Tog

2 posts in 832 days


#6 posted 09-19-2012 02:52 AM

Thanks to all for the responses.

I hadn’t thought about the possibility that the blade might have been dropped sometime between the time it left my hands to the time it came back. I know I packed it well, and it came back packed well. I assumed the sharpening shop would have handled it with care, but who knows.

I’ve decided to retire the blade. Unless I had all the teeth replaced I’d be too nervous using it in the shop. Jittery nerves and sharp spinning things aren’t a good combination.

I’ll also be changing how I remount blades on the saw. No more wood blocks on the back sides of teeth; it’ll be a heavy rag and less force from now on.


Tog

View Moron's profile

Moron

4725 posts in 2647 days


#7 posted 09-19-2012 03:16 AM

Contrary to popular opinion, abrasion does not degrade carbide fast. Corrosion on the other hand is much faster at degrading carbide so its exposure to humidity, dew point even though it sits doing nothing can degrade the carbide to the point of junk.

a 20 year old blade from my persperctive has served its time.

Expensive is held within the wallet and just as an example, I pay upwards of 150 bucks for a blade on my circular saw and my miter saw blades can hit 200 a pop.

Carbide is not manufactured equally.

-- "Good artists borrow, great artists steal”…..Picasso

View pintodeluxe's profile

pintodeluxe

3574 posts in 1567 days


#8 posted 09-19-2012 03:57 AM

20 years, whether in use or knocking around the shop, is a good lifespan for a blade. Blade technology has changed in that time – better design to prevent kickbacks, anti-friction coatings,thin kerf etc.
Please don’t use a rag to hold the blade from spinning while changing blades. Try a bench dog blade loc.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View Dusty56's profile

Dusty56

11688 posts in 2442 days


#9 posted 09-19-2012 04:56 AM

I purchased a Forrest blade from my local Woodcraft store and brought it home all excited and anxious to put it to work. As I was peeling the special coating off of the teeth, bits and pieces of the carbide were coming with it.
By time I was done stripping the coating off , there were 6 broken teeth and several chipped ones. This was a factory sealed package no less ! There were no signs of external damage to the package. I was fortunate that WoodCraft took it back and gave me another one . It never cut as well as advertised so now I am wondering if there might be some other flaws with this second blade.

Just “snug” is all the arbor nut needs to be tightened. It’s not going to loosen up because it is threaded in the opposite direction that the blade spins : )

-- I'm absolutely positive that I couldn't be more uncertain!

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