Lapping chisel back

[Washy21]

My first post on this forum sought to understand how I had made my waterstone badly concave. I learned from that experience and the great replies, but the chisel that I used to do that damage: Marples 25mm also seemingly suffered as well. I have been trying — for a very long time — to lap the chisel back but can't get the edge flat (see picture). I have tried float glass and various grit papers and then moved onto the course waterstone, but it is when I get onto this stone that I feel I can not get the whole back flat. The picture is not great but as you look at it in the photo the top left appears shiny and doesn't seem to be affected by the lapping efforts.

Anyone any ideas on how I can remedy this and get the chisel back flat and am I correct in saying that the chisel is 'dubbed' ?

 

[carlb40]

Have a read through this

flattening-chisel-backs-with-lapping-film-t68506.html

And have a watch of these.

http://www.workshopheaven.com/tools/Sha ... video.html

Probably easier to see it done than explain

 

[Washy21]

Have a read through this

flattening-chisel-backs-with-lapping-film-t68506.html

And have a watch of these.

http://www.workshopheaven.com/tools/Sha ... video.html

Probably easier to see it done than explain

Many thanks. The topic in the first link is interesting. It tells me that some people feel that lapping backs is pretty much not required, or at least, not something to obsess about. Still, at the moment it's bugging me.

 

[carlb40]

I know that feeling. Everyone is different. I myself like to lap the back of the whole chisel, yes i know there is no point. But i like shiny things :mrgreen:

 

[Washy21]

I know that feeling. Everyone is different. I myself like to lap the back of the whole chisel, yes i know there is no point. But i like shiny things :mrgreen:

I can see why it could easily become and obsession. :roll:

But for me I kind of just want to know that the tool is good to go. In this case the continued lapping is having no effect and I'm not sure why that is.

 

[carlb40]

Best thing to do if you want to lap the back of the chisel. Follow the example shown in the video. Use your diamond stone. Draw the chisel back say 10 times from roughly 25 - 30mm in from the edge of the chisel. Then see how it looks. Pop a pic on here for comparison

 

[No skills]

I dont know how large the waterstones are but I guess they are a fair bit smaller than the piece of glass you were using?? is it possible you are having difficulty putting even pressure on the chisel when its on the stone and its not staying flat??

Just a thought.

 

[Washy21]

Many thanks for the replies.

Of note is the manner in which the tutor in the video handles the operation: very precise and slow. Additionally, I don't have lapping film but I do have a course DMT Diamond stone. Here is a picture which shows about 25 vertical strokes on the diamond stone. The scratch pattern is evident but the corner is still looking dubbed. I have also included a diagram, which whilst exaggerated, shows the areas that I can't seem to touch in the process.

The other point of note is that from the front the bevel on the chisel dipping down from right to left.

 

[Jacob]

I know that feeling. Everyone is different. I myself like to lap the back of the whole chisel, yes i know there is no point. But i like shiny things :mrgreen:

I can see why it could easily become and obsession. :roll:

But for me I kind of just want to know that the tool is good to go. In this case the continued lapping is having no effect and I'm not sure why that is.

Because it's good to go whether lapped or not. Just a quick sharpen is all you need, if all you want to do is use it as a chisel.
No need to worry about the straightness of the edge it won't make a haporth of difference in use. But you could try to compensate for it each time you sharpen - but don't go mad removing metal - waste of a good chisel!

 

[Washy21]

I know that feeling. Everyone is different. I myself like to lap the back of the whole chisel, yes i know there is no point. But i like shiny things :mrgreen:

I can see why it could easily become and obsession. :roll:

But for me I kind of just want to know that the tool is good to go. In this case the continued lapping is having no effect and I'm not sure why that is.

Because it's good to go whether lapped or not. Just a quick sharpen is all you need, if all you want to do is use it as a chisel.

Hi Jacob,

I want to use it as a chisel but it will be used in delicate work on guitars and I guess this is why this whole flatness issue is bothering me. The bottom line I guess could be to ask the question: Do I need lapped chisels (not necessarily polished like mirrors) in order to work on fine detail woodwork such as guitars — or is it a complete waste of time unless the backs are so badly convex or concave ?

 

[carlb40]

After 25 strokes on the diamond stone that is a good result. Another 25 strokes or so would probably get rid of that low spot on the left as we look at it.
The videos were for reference, the sharpening medium doesn't matter. As long as you get them sharp, that is what matters.

As to the bevel, that could be one or two things.
1st from manufacturer it could be slightly thicker on one side than the other.

2nd It could be uneven/ out of square sharpening.
The latter is why i use a jig. To keep things square and true

But not everyone likes/ uses jigs

 

[Jacob]

...... Do I need lapped chisels (not necessarily polished like mirrors) in order to work on fine detail woodwork such as guitars

Try it either way and see. I'd think not (within reason) unless, as you say, the backs are badly convex or concave, in which case choose another chisel?
It's a good idea to practice on a lot of scrap. See if you can tell the difference between one sort of chisel finish and another?
Also if you want to make guitars it's a good idea to get stuck in making them and not waste your time tool fiddling! It's only with practice that you will find out what you really need in the way of tools and sharpening etc.

 

[CHJ]

Regarding the very corners of the blade, one thing that can affect the 'flatness' of the surface is the removal of metal from the bevel sides.
If the steel has any adverse stresses in it then the very corners can continue to move toward the bevel side as support metal is removed, in most instances in a working tool to a degree of no consequence at all, but if attempting to maintain within lapped flatness levels you may never remove them.

Also be prepared for a tool to move as the shop temperature changes, even holding a blade in the hand or using it will cause it to change dimensions, whether in the plane you are trying to 'improve' or not is a matter of chance, what appears flat one day may be otherwise the next.

Washy21 wrote:
...... Do I need lapped chisels (not necessarily polished like mirrors) in order to work on fine detail woodwork such as guitars

I doubt Stradivarius had anything other than a hand forged tools sharpened on a sandstone grinding wheel.

 

[Washy21]

Regarding the very corners of the blade, one thing that can affect the 'flatness' of the surface is the removal of metal from the bevel sides.
If the steel has any adverse stresses in it then the very corners can continue to move toward the bevel side as support metal is removed, in most instances in a working tool to a degree of no consequence at all, but if attempting to maintain within lapped flatness levels you may never remove them.

Also be prepared for a tool to move as the shop temperature changes, even holding a blade in the hand or using it will cause it to change dimensions, whether in the plane you are trying to 'improve' or not is a matter of chance, what appears flat one day may be otherwise the next.

Washy21 wrote:
...... Do I need lapped chisels (not necessarily polished like mirrors) in order to work on fine detail woodwork such as guitars

I doubt Stradivarius had anything other than a hand forged tools sharpened on a sandstone grinding wheel.

Brilliant replies thanks. After another hours work I think I made a breakthrough with the low spots reducing significantly.

Stradivarius' tools look primitive in the context of what's available today. How on earth did he do it without lapping film, diamond stones and grinders ? (hammer)

 

[Jacob]

.....
Stradivarius' tools look primitive in the context of what's available today. How on earth did he do it without lapping film, diamond stones and grinders ? (hammer)

He spent more time making things, getting practice in, instead of tool fiddling!

 

[Washy21]

.....
Stradivarius' tools look primitive in the context of what's available today. How on earth did he do it without lapping film, diamond stones and grinders ? (hammer)

He spent more time making things, getting practice in, instead of tool fiddling!

Words of wisdom. Cheers

 

[Jacob]

.....
Stradivarius' tools look primitive in the context of what's available today. How on earth did he do it without lapping film, diamond stones and grinders ? (hammer)

He spent more time making things, getting practice in, instead of tool fiddling!

Words of wisdom. Cheers

Well I don't know about that but how on earth did he do it without lapping film, diamond stones and grinders ? is a bloody good question which more people need to ask more often IMHO!

 

[carlb40]

.....
Stradivarius' tools look primitive in the context of what's available today. How on earth did he do it without lapping film, diamond stones and grinders ? (hammer)

He spent more time making things, getting practice in, instead of tool fiddling!
Well I don't know about that but how on earth did he do it without lapping film, diamond stones and grinders ? is a bloody good question which more people need to ask more often IMHO!

Maybe he had a Stradiveritas lapping plate? :mrgreen:

 

[Washy21]

.....
Stradivarius' tools look primitive in the context of what's available today. How on earth did he do it without lapping film, diamond stones and grinders ? (hammer)

He spent more time making things, getting practice in, instead of tool fiddling!
Well I don't know about that but how on earth did he do it without lapping film, diamond stones and grinders ? is a bloody good question which more people need to ask more often IMHO!

Maybe he had a Stradiveritas lapping plate? :mrgreen:

I believe he had Strada 'various' secrets as well =D>

Anyway, I've managed to get it flat on a piece of float glass and a course stone (purchased circa 1824) and I don't think I will be polishing the back to mirror like. I will post some pictures later.

 

[Dodge]

Well I don't know about that but how on earth did he do it without lapping film, diamond stones and grinders ? is a bloody good question which more people need to ask more often IMHO!

The biggest question that hasn't been asked though is if diamond stones and lapping film etc had been about in the days of Stradivarious and Chippendale would they have been using them rather than the other primitive sharpening tools available - I'm sure they would have moved with the times the same as current users are using equipment which is available to them now.

The same as i'm sure they wouldn't be cutting their wood by hand if they had access to powered bandsaws and table saws to make their lives easier.

After all why are we all driving around in cars rather than sticking with the horse and cart???