Accuracy of knife making.

D

Don the Diver

Joined
Jan 2, 2019
Messages
4
Trying my hand at making knives for relaxation I was wondering what other blade smiths work too in respect of tolerance.
In my current project I am trying to work to around about plus/minus 0.1mm, is this overkill or the norm?
 
Better this thread relocate to the knife maker's discussion forum - shop talk, maybe ask a mod to do this
 
Don the Diver said:
Trying my hand at making knives for relaxation I was wondering what other blade smiths work too in respect of tolerance.
In my current project I am trying to work to around about plus/minus 0.1mm, is this overkill or the norm?
Click to expand...
That's +/- .004". Plus or minus four thousandths.
That's pretty tight for fabrication. Normally, that would be sent to a machine tool. A good fabricator could do it easily enough.
Necessary?.....
 
Yea pretty tight. How are you measuring .1mm ? There's a good chance you aren't actually consistently maintaining less than 4 thou.

Unless you're a machinist with metrology equipment and the necessary machines in which case you'd be fine maintaining 4 thou.
 
What specifically are you measuring?

Even on production parts in a professional manufacturing environment. Not all dimensions are important.

Most will use the decimal point as a ref for how important the dimension is.

12.0" would maybe be + or - .030"
12.00" would maybe be + or - .015"
12.000" would probably be + or - .0005"
12.0000" would probably be within .00005" (5/10 = half a thou)

So...... not EVERY dimension is important to Me.

So far, I'm only making Fixed blades, and bte is my most checked with an actual instrument.
The rest get a scale, or a tape measurer.

Or really to be honest. I use my eye and hands Most.
I feel A lot of what I'm doing, almost think I could do it blind.......

-probably the reason they look the way they do ;/
 
Crag the Brewer said:
What specifically are you measuring?

Even on production parts in a professional manufacturing environment. Not all dimensions are important.

Most will use the decimal point as a ref for how important the dimension is.

12.0" would maybe be + or - .030"
12.00" would maybe be + or - .015"
12.000" would probably be + or - .0005"
12.0000" would probably be within .00005" (5/10 = half a thou)

So...... not EVERY dimension is important to Me.

So far, I'm only making Fixed blades, and bte is my most checked with an actual instrument.
The rest get a scale, or a tape measurer.

Or really to be honest. I use my eye and hands Most.
I feel A lot of what I'm doing, almost think I could do it blind.......

-probably the reason they look the way they do ;/
Click to expand...
.00005 is the ten millionth colum. So that would be 50 millionths.

.0005 is 5 tenths

.005 is 5 thou
 
shinyedges said:
All good, when it's time to count zeros you know it's getting small. Few people understand what it takes to actually work to such tight tolerance, it's a huge pain in the rear lol 🤣
Click to expand...
Depending on what it is..... I agree.

Someday when I start designing, and making my own folders all my old gauges will come in handy.....
Except I'll even be MOre blind then.

On the topic at hand, I've been meaning to get a nice magnifying lens for looking at my edges.
this Should be a good reminder for me to do such.
 
shinyedges said:
All good, when it's time to count zeros you know it's getting small. Few people understand what it takes to actually work to such tight tolerance, it's a huge pain in the rear lol 🤣
Click to expand...
Tollerance stack is something I often have to deal with, too
And even still, we don't necessarily want too tight of a fit, in areas with epoxy, or sliding actions, etc.
If it's a pressfit, there is no room for the adhesive.

That is where understanding good design comes into play.


A good saying I like to use here (and elsewhere) is....... "We are not building watches"
 
Crag the Brewer said:
Tollerance stack is something I often have to deal with, too
And even still, we don't necessarily want too tight of a fit, in areas with epoxy, or sliding actions, etc.
If it's a pressfit, there is no room for the adhesive.

That is where understanding good design comes into play.


A good saying I like to use here (and elsewhere) is....... "We are not building watches"
Click to expand...
Agreed not everything needs to be to the thou or less. Reading prints made by engineers with little experience surely makes programmer/machinists scratch their heads.

I programmed/machined for dod contractors making all kinds of things out of all kinds of materials on 40/50 taper horizontal and vertical mills and 5 axis lathes. Some loosely toleranced, some ridiculously toleranced. Min and max material conditions, intended use for the part, what they want and what they write on the print don't always jive.
 
shinyedges said:
Agreed not everything needs to be to the thou or less. Reading prints made by engineers with little experience surely makes programmer/machinists scratch their heads.

I programmed/machined for dod contractors making all kinds of things out of all kinds of materials on 40/50 taper horizontal and vertical mills and 5 axis lathes. Some loosely toleranced, some ridiculously toleranced. Min and max material conditions, intended use for the part, what they want and what they write on the print don't always jive.
Click to expand...
I once worked with a young engineer who had all his dimensions to three decimal places, Always, which made them plus or minus .005"

One worker made a part of his, complained the next day. It took some time to make, and measure accurately. It was a over 16 foot long piece of aluminum.
Machined within .005"
it was only a rail to keep people from walking under another structure. It could of easily be off 12 inches and it didn't matter.

He just kept that as his default setting for dimensioning. I had to yell at him.
 
I’m very old school, the folders I’ve made have involved little measuring equipment, rather parts are made to fit one another by hand.

dOJYjfV.jpg


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fJtkvMs.jpg


Just for fun, I didn’t make many & this was probably the best.
I still have it.
 
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Crag the Brewer said:
I once worked with a young engineer who had all his dimensions to three decimal places, Always, which made them plus or minus .005"

One worker made a part of his, complained the next day. It took some time to make, and measure accurately. It was a over 16 foot long piece of aluminum.
Machined within .005"
it was only a rail to keep people from walking under another structure. It could of easily be off 12 inches and it didn't matter.

He just kept that as his default setting for dimensioning. I had to yell at him.
Click to expand...
Some engineers can't get it into their head that part of their job is to design parts to be cost effective. I can't count the times I heard that to machine to +/- .005 or even +/-.0005 all I had to do was to "press a button".

We once had an engineer tolerance a 5" plus hole to a bore tolerance... tenths. Turned out it was an access hole to reach through. The bigger the hole, the harder to achieve bore tolerances.

Since I do have Autocad experience, I would explain how to go back and easily change pertinent dimensions to a different decimal place. Always surprised them how the "stupid machinist" knew that.

They asked a mathematician and an engineer what two plus two was.
The mathematician said, "Four".
The engineer said, "Four, but better make it five to be sure."
 
davek14 said:
Some engineers can't get it into their head that part of their job is to design parts to be cost effective. I can't count the times I heard that to machine to +/- .005 or even +/-.0005 all I had to do was to "press a button".

We once had an engineer tolerance a 5" plus hole to a bore tolerance... tenths. Turned out it was an access hole to reach through. The bigger the hole, the harder to achieve bore tolerances.

Since I do have Autocad experience, I would explain how to go back and easily change pertinent dimensions to a different decimal place. Always surprised them how the "stupid machinist" knew that.

They asked a mathematician and an engineer what two plus two was.
The mathematician said, "Four".
The engineer said, "Four, but better make it five to be sure."
Click to expand...
They don't teach Engineering in college to become an engineer..... After school, it usually takes a good number of years before they Get It.

They think a one inch plug will fit into a one inch hole.
It does on CAD.
They aren't taught what it means and takes for a slip fit, a press fit, Tolerance stacks.......
They don't take into account IF it can actually be assembled and serviced.
All those little details.
Then of course Cost.
 
shinyedges said:
Yea pretty tight. How are you measuring .1mm ? There's a good chance you aren't actually consistently maintaining less than 4 thou.

Unless you're a machinist with metrology equipment and the necessary machines in which case you'd be fine maintaining 4 thou.
Click to expand...
Thank you for your response. I am very lucky, I design and build underwater vehicles and because of this we have our own factory complete with lathes, mills etc and of course a whole range of inspection equipment. I myself, after some fifty year of turning experience, work to to plus/minus 0.1mm on regular systems and 0.05mm for O-Ring seals.

I think I will relax the tolerances a little bit say, 0.2 to 0.3. Thank you once again.
 
Don the Diver said:
Thank you for your response. I am very lucky, I design and build underwater vehicles and because of this we have our own factory complete with lathes, mills etc and of course a whole range of inspection equipment. I myself, after some fifty year of turning experience, work to to plus/minus 0.1mm on regular systems and 0.05mm for O-Ring seals.

I think I will relax the tolerances a little bit say, 0.2 to 0.3. Thank you once again.
Click to expand...
Ah, makes sense on the tolerances! Very cool.
 
Crag the Brewer said:
What specifically are you measuring?

Even on production parts in a professional manufacturing environment. Not all dimensions are important.

Most will use the decimal point as a ref for how important the dimension is.

12.0" would maybe be + or - .030"
12.00" would maybe be + or - .015"
12.000" would probably be + or - .0005"
12.0000" would probably be within .00005" (5/10 = half a thou)

So...... not EVERY dimension is important to Me.

So far, I'm only making Fixed blades, and bte is my most checked with an actual instrument.
The rest get a scale, or a tape measurer.

Or really to be honest. I use my eye and hands Most.
I feel A lot of what I'm doing, almost think I could do it blind.......

-probably the reason they look the way they do ;/
Click to expand...
Thank you for your reply. I think you are 100% correct regarding tolerances that not all are important. My post, as a complete novice, was just to understand what the typical tolerances are. The knife I am making will be a work knife to back up my standard diving knife. It is more important that it cuts through fishing line and other junk that is so common underwater these days than the tolerances.
 
Hand work or machine work? Folder or fixed blade?

For machine work, +/-.005 is pretty standard. For fits on a folder you might want to do as much machining as possible and/or keep tight tolerances. For a fixed blade, not so much.
As said, required tolerances would vary as to what the part does.
Part of Lean Manufacturing is Design For Manufacturing.
Design parts to make them as cheaply as possible as long as they do what they need to do.



'Course, tight tolerances only came about when mass production became the norm. Guns, steamboats, other machinery was made for years with hand fitting. You just couldn't replace parts without hand fitting. When I first started machining, there were still old legacy machines being made and repaired with castings and crackerjack assemblers/fabricators scraping parts in with red lead. Done a little of that myself.
 
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