What's goin' on here...Jointer woe.

[Timothy Robinson]

So I watched a few youtubers sharpen their planer/jointer blades and I can shave with my plane irons so fI thought I'd give it a go. I settled on a 45 degree X-jig with allen screws to hold the knives IMG_1502.JPG
I sharpened the three HSS 'delta' knives on abrasive paper down to 1500 grit and the edges were fine with a slightly rolled edge. I flattened them on 1000 grit and there were no flat spots. They cut like scalpels. But on the first use, I was truing up another bit of the oak from which I made the jig and this happenedIMG_1501.JPG Is it possible to get an HSS knife too sharp? is the metal not hard enough to survive a knot in red oak?

[Andrew Hughes]

I would guess that your oak knot was very hard. It also could be your knives are lower grade of hss.
The pic look like the knives were trying to cut through some very dirty wood.
My official guess is the hss very low grade.
Good Luck

[Rod Sheridan]

A knot can fracture carbide cutters and chip or roll over the edge of a steel knife.

The variables are the knot, and knife material as Andrew mentioned....Regards, Rod.

[Mike Kees]

a suggestion for good quality HSS knives. 18% Tungsten or T1 . I buy from my local sharpening service,they cut whatever length I need from appropriate width and thickness stock. This steel is so much better than the cheap knives that come in most machines . It will cut nicer surfaces and last far longer between sharpening.

[Bradley Gray]

I have all my J&P knives back beveled. This makes for more of a scrape cut that is better on figure and lasts longer.

I would send them to a sharpening service for the back bevel grind, then resume your sharpening method.

https://www.google.com/search?q=back...XY5DBNfV7J9lM:

[Mel Fulks]

Ops want a good vote count ! Subject has been covered well,so if Gramma votes with you ...good knives will be bought !

[Warren Lake]

Mel has been preaching steel quality for a while which is good. Oddly knives I got from an auction for one machine are the 18 percent tungsten. Be nice to be able to check previous knives from old machines to identify what type each steel is.

I have no interest in back bevel on a plane iron or machine knives. I knew a guy who had two molding companies and he put a front bevel on his knifes, he said on some woods having that extra bevel will machine cleaner than honed razor sharp knives. ter. Having a second bevel works well as long as the knife is sharp and there is enough relief cut on the heal so its not hitting the wood. You can both hear it and see the wood skate around on the jointer if that is the case. Last time I had shaper knives done it was a Weinig trained guy and he put a second bevel on everywhere he could I guess to make the edge last longer. Ive done fine with no bevel and if hollow ground makes it very easy to hone.

[Mel Fulks]

Warren,I think real high speed steel came in about 1890--1900. I know that they found out pretty early that 18 percent tungsten was the optimum number. This is just a guess but I'm thinking the junk knives
came in right after the value of the good stuff was well known.

[Timothy Robinson]

I would love to have such a service available locally. I can't even find anyone to sharpen my saw blades.

[Mike Kees]

I actually have two different places to get stuff sharpened or buy saw blades ,jointer and planer knives. They are both one hour away in Lethbridge ,we go there nearly every week so not a big deal.

[peter gagliardi]

What was the original knife angle? Did you make it steeper or shallower as measured from the knife cutting face? If shallower, that might be part of the issue.
It is my experience that hardwood knots do not generally present themselves as very much harder than the surrounding straight grained wood- tougher, not harder.
Softwoods however can have a huge hardness differential- especially Spruce and Hemlock- enough to crack a knife even.

[Randall J Cox]

Don't know what blades I have in my jointer or planer (but I have had both sharpened-straight HHS blades, no carbide) but I do run smallish knots through somewhat routinely. I always spritz the knot with water, let it soak in a couple of min before running them through. Softens the knot just a tad but not very deeply, if I have to run through again, I spritz again. Been doing this for years with no issues. Read about this trick in a woodworker mag way back when. And I always make sure to clean any water off the cast iron tables for obvious reasons. Randy