How to tell if a saw blade is sharp?

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Sorry if this is on topic. :-)
I suppose I could just google it, but here goes...
There was a 10" Delta 60 tooth on this table saw and it was covered in all kinds of gunk and baked-on sap or something. I cleaned it all off and scraped off every tooth individually.... yeah, I was bored and there was a good CD on. :-)
Is there a way to tell if a saw blade is still sharp enough or needs to be sharpened? Is there a tried and true testing technique? Or is it as simple as just trying it and seeing if it cuts clean, smooth and fast?
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-MIKE-

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I'm not aware of an official method, but I would make a cut with it, then switch to a known sharp blade, and make another cut from the same stock. You should be able to feel if it's sharp or not.
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Mike wrote:

Look at it closely -- if it's sharp just like a blade the tooth edges and corners will be crisp and not rounded. Carbide, of course, isn't quite a sharp initially as HSS but general precept still holds.
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I pretty much go by the quality of the cut or if I feel it slowing down.
If that is the original Delta blade that came with the saw, it may cost more to sharpen than to replace it but a good sharpening make a difference. I send mine to Ridge Carbide and they come back perfect. http://ridgecarbidetool.com/sharpening.php?osCsid 684552e408e89ecf0af6aab3043a2a $15 for your blade, plus postage.
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Ed Pawlowski wrote:

http://ridgecarbidetool.com/sharpening.php?osCsid 684552e408e89ecf0af6aab3043a2a
That's a great price, Ed? How much was shipping?
This blade is a Delta 35-7646. Looks to be a hundred dollar blade that can be had for 40 bucks. :-)
It's thick, flat, and the tips seem to be pretty thick... meaning I guess they have plenty of room to be sharpened.
There's a sharpening shop, close to me. If they are as cheap as your place, I may take all my blades. From what I hear from the guys at Woodcraft, a properly sharpened blade cuts better than a new one.
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First blade is $9, ea additional is $1, but five blades is free shipping.
I sent a DeWalt blade from my miter saw that was in rough shape from cutting laminate flooring and it came back better than when new.
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Ed Pawlowski wrote:

I called a place here in town (where I bought my lathe) and their prices are pretty much the same as that place.
Do I assume that the process is automated somehow and will have great results? Don't know.
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-MIKE- wrote:

Yes and no...like (almost) anything else, there's art behind the science and skill besides simply bolting a blade to a sharpening mandrel.
Good places will true the blades before sharpening (where the most skill is) and repair damaged teeth, etc., etc., ...
OTOH, a sorry place may well end the life of a blade permanently (or at least w/o expensive retrofitting).
If I don't have specific knowledge via folks who've used a service that I trust to know when they got a good result, I'll start w/ a blade I won't care too much if it does come back in bad shape before I'll trust them w/ the good stuff.
Ridge Carbide is one I've used as well that I will concur is good--there's another closer to us in Tulsa I'd have to look up specifically I use generally that's also excellent.
Forrest will sharpen/repair/retune other blades besides theirs as well. About the same price as others for basic sharpening, but if you've got a sweet blade, can't beat them for making it sing best tune it possibly can if they work their full magic on it. It'll cost some extra depending on what they do so I don't waste it on inexpensive blades that aren't going to benefit...
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Yep, that's it. Some (high-end) tools can log the torque on the motor and the total energy usage so you can look for the watt-hours per foot of cut, or the force on the teeth, but mostly you make a fast cut on a bit of scrap and figure it might be dull if the motor complains.
Slow cuts or unstraight bits of wood will not be good tests.
The cut (remember, cut it FAST) should not look polished; that polished look is the first sign of a dull blade.
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whit3rd wrote:

That's great info.
Not to second guess you.... well, yeah, I guess I am.... :-) Where did you get that info? Experience?
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If you see the blood before you feel the pain, then it is still plenty sharp. Otherwise have it sharpened right away.

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SonomaProducts.com wrote:

I know that's true with razor blades. You don't know you're cut until you feel some piece of your clothing get wet.
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I'd put it on the saw and make a test cut...
If it cuts clean and doesn't bind, go with it..

mac
Please remove splinters before emailing
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-MIKE- wrote:

Ask it to do partial differential equations ...
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Tim Daneliuk wrote:

When it cuts you, you say, "Ouch, that smarts!" badoomp-chink! Tip your waitress.
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Tim Daneliuk wrote:

Yeah, right. Mine can't get past determining whether a solution exists. I guess only half the circumfrence is sharp...
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HeyBub wrote:

The problem of where the blade begins and ends is known to be NP-Really-Hard...
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Scientifically they photograph the top and sides and measure the radius of various sides in microns.
As a rule of thumb, if you think it might be dull then it is.
I am going to second Whit3rd. Not sure how he got his data but he is correct. The only thing I would caution is that a very clean cut is different from a polished cut. Remember you are cutting fibers in wood. You want a very sharp, even edge to sever the fibers cleanly instead of pulling them out and stretching. A dull blade will pull the fibers out, stretch them and leave a fuzzier surface. A duller blade will pull the fibers out and the next tips will run over the pulled out fibers and polish them.
Wood fibers do have certain amount of pullback or snap back but not a great deal. It is best to clearly sever the fibers. This is a lot easier to see when you cut a chunk of hemp rope with a very sharp knife, a dull knife and a really dull knife. Cutting natural wood is a lot like cutting hemp rope as far as the behavior of the fiber is concerned. It is just much more obvious with hemp rope.
As to how I go my data. I manufacture top end, custom saw blades. We work with Forintek http://www.forintek.ca/ and have done research for and with hundreds of mills plants and saw shops over the last 28 years. You can see some of our research at www.carbideprocessors.com.
Having said all that, your question is extremely good. How to determine sharpness is always a question in research. There is no single, definitive way to determine sharpness. I mentioned edge radius above. If you are cutting brittle materials you with something such as an ATAF (alternate top / alternate face) with a high ATB (alternate top bevel) you will want a separate determination for point sharpness and well as edge sharpness.
Finally different materials also help determine how well a blade will cut irrespective of sharpness. A cermet 2 tipped blade has a much lower coefficient of friction then carbide and will cut better than a carbide blade with an identical edge.
Tom Walz
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Thomas Walz wrote:

Great stuff, Tom. Thanks.
I don't know if this group has a FAQ, but that should go in it.
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-MIKE-

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wrote:

Cut a small piece of cabinet-grade ply. If the cut edge is clean and not hairy, chances are good you got a sharp blade. The gunk is most likely from cutting sappy wood, perhaps pine.
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