[OP]
Contributor
According to Rob Cosman a handplane blade is twisted if while applying a small micro bevel to the backside the grinding ends up showing a triangular shape. If that is correct it seems to me that whatever effort is put into making the edge flat all is lost when putting on the chip breaker and fastening the assembly onto the plane. In other words, wouldn't the assembly of the blade and chip breaker take out the twist?
Contributor
Maybe the answer to this problem is to not "apply a small micro bevel to the backside."Originally Posted by Steve Mathews
Results speak louder than any expert. If the chip breaker mates up properly with the blade while not clogging with chips and makeing good shavings, then it doesn't matter so much what is going on between the blade, chip breaker, frog and lever cap.
If there is a problem, then something may need being done.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)
Contributor
I'm not quite following the "small microbevel to the backside" part. It is common to put a secondary bevel on a plane blade as it gives the edge a little more strength and also makes it easier to sharpen. A back bevel is normally to increase the cutting angle on a bevel down plane and I'm not sure why one would put one on a bevel up plane in any circumstance. So I'm not really clear on why one would put a microlevel on the back of the plane blade.
Not to expert-bash, but Cosman is also the guy that basically said in a video that #4 planes were really only for women and petite men, which I found somewhere between ludicrous and offensive, in addition to completely false. I sometimes wonder how these people get to be "experts".
Contributor
Ignoring the wisdom of a back-bevel..., I'm confused about what "twisted" means here. If it means ground crooked, i.e. not straight and square, then yeah the ground area will have a triangular shape. If it means the iron is not itself straight and flat, like a twisted board, then you have an entirely different problem to solve.
[OP]
Contributor
In this case "twisted" means not flat, like a twisted board. The blade definitely moves when pressure is applied to the corners when sitting on a granite surface plate. I placed the blade on the magnetic chuck of my surface grinder and was able to flatten out the twist temporarily but it sprang back when removed.
A back bevel is used and recommended by many accomplished woodworkers besides Rob Cosman. Lie-Nielsen demonstrates it in their sharpening videos. It seems like a good idea but the complication of the twist I'm experiencing has me stumped. BTW, the blades involved are out of #7 and #5 1/2 bench planes, both Lie-Nielsen products.
[OP]
Contributor
The blades in questions are out of #7 and #5 1/2 bench planes, both bevel down.
Contributor
Easiest way to determine whether a plane blade is "twisted" Plop it down on a flat surface....see IF it will lay flat......
[OP]
Contributor
See my comment(s) above. It does not lay flat.
Contributor
The iron itself, or the assembled unit....?
Contributor
The double iron assembly is flexible enough to rest flat on the frog once installed. I'd be sceptical of the extra tricks promoted by the internet gurus. LN customer support is renowned, if your blades are twisted call them and they should be able to resolve your problem.
(i believe Rob Cosman claimed that all those no. 4s were meant for children in shop clases)
[OP]
Contributor
Just the blade or iron itself. I'm communicating with LN now but nothing is settled yet other than they guarantee flatness within .0015", which it is not.
Contributor
Considering how thick those LN blades are (too thick some would say) I have no idea how one could get bent in normal or even abnormal usage. Were they bent from the factory?
[OP]
Contributor
It's my understanding that once the blades or irons as some have put it are machined the steel is heat treated. I believe Lie-Nielsen uses A2 for their blades. The heat treating process has the potential of warping the part if not done properly, especially when relatively thin. Then grinding is done if necessary. If the part is warped in the heat treating process it could remain that way even after surface grinding when held in place with a magnetic chuck. The chuck has a tendency to conform the part being held to its flat surface.
Rob Cosman, I think rightly states in at least one of his sharpening videos that blades have a tendency to come out in one of 4 flavors; 1) completely flat, 2) convex in shape, 3) concave in shape or 4) twisted. Flavors 1 and 3 relative to the surface that needs to be flat are the only ones that can be adequately dealt with in sharpening. Actually, one that is twisted can work if not too bad.
That's my take in all of this so far. It would be interesting to hear back from those experienced with heating treating.
Member
I'm puzzled, because Cosman advocates David Charlesworth's "ruler trick". Is it possible that his statement was of the nature of "...too much of a back bevel will cause X, Y Z..."? For what its worth, though I watch Rob Cosman on You Tube and like his approach, I do not use "the ruler trick", mainly because for the type of wood I work, I have not needed it.
I like Bandit's suggestion: lay the blade on a surface plate to see if it lays flat! Also, is there some confusion here, as to what the back of the blade is? Maybe better to refer to one side as "the bevel side" and the other as "the flat side"?
If the thunder don't get you, the lightning will.
[OP]
Contributor
I don't understand your first question. Please elaborate if possible.
As for laying the blade on a surface plate to see if it's flat, that was mentioned twice before. I did that and it was not flat. On a LN #5 1/2 and #7 there is only one side a back bevel would placed on the blade, the side facing the chip breaker or "flat side" as you put it.
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