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Discussion Starter #1 (Edited)
Hi all,

I'm using a precision engineers square to check a planed board for flat and square. I've laboriously set the knives in the cutter head, checked tables are parallel, etc, etc.

When using the square should there be..... no visable light..... at all, how square is square, does perfection exist?

I'm an aspiring wood worker..... not a metal working engineer.... machining tolerances.

Using the square, is very close too, good enough or does it need to be..... exactly, exactly precise?

Thanks.
Peter https://amymaytrust.com/
 

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Peter, in my opinion, it depends on what you're doing and how tolerant you want to be. Keep in mind that it also depends on the size of the machinists square you are using. As an example, if you are using a 6 inch square and have 1/64 inch out of square, that deviation will grow as your square gets longer. Having said that, you are working with wood, which will change with temperature/seasonal changes, so, I try to get it as square as possible then late nature takes it's course. You aren't machining parts for the space shuttle.
 

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John
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Peter
Perfection is What We all aspire to, the honest truth is i have never made it happen, i believe most woodworker will tell you that with every project mistake where made the art is correcting them so only you know!
Wood is constantly moving
 

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As Vince noted...depends on what you are doing with the board. If you are concerned about the face, if it doesn't rock, it's good enough. Maybe you're making a door panel or sorts...?

If we were discussing the edge AND you are going to join it to another board, then you would want a greater level of precision but your square should be more than good for checking square. The less light, the better...but if you see light at one end of the square compared to the other over 3/4" or so then I would say it needs a bit more work. Again, depending on the application.

Your flat board is good enough if it doesn't rock corner to corner...

Use it soonest out of the planer to make sure nature doesn't take its course...
 

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Hi all,

I'm using a precision engineers square to check a planed board for flat and square. I've laboriously set the knives in the cutter head, checked tables are parallel, etc, etc.

When using the square should there be..... no visable light..... at all, how square is square, does perfection exist?

I'm an aspiring wood worker..... not a metal working engineer.... machining tolerances.

Using the square, is very close too, good enough or does it need to be..... exactly, exactly precise?

Thanks.
Peter https://amymaytrust.com/
Hello Petter; So what method are you using to set your knifes? Also, do you have a good technique on the jointer? Getting lumber square and flat is hard to do. If you are a little out here and a little out there they mount up into big errors. I try to do the best I can but it isn't ever good enough.
 
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Discussion Starter #6 (Edited)
Peter, in my opinion, it depends on what you're doing and how tolerant you want to be. Keep in mind that it also depends on the size of the machinists square you are using. As an example, if you are using a 6 inch square and have 1/64 inch out of square, that deviation will grow as your square gets longer. Having said that, you are working with wood, which will change with temperature/seasonal changes, so, I try to get it as square as possible then late nature takes it's course. You aren't machining parts for the space shuttle.
Thanks for replying Vince,
This is the combination ( up and over ) surface planer, thicknesser I have which has a 3 knife cutter block.
Is a sweet machine.... as long as it does its job properly.

https://www.axminster.co.uk/axminster-trade-series-at107pt-planer-thicknesser-ax954318

The piece of timber I was checking for square I was given and checked for square when I got it and seemed preety close to that. I faced it and then edged it, repeating several times then checked.
I'm using a new Empire combination square set to measure 5.5 inches, the Empire combination square has a reputation for accuracy. I also checked using a SOBA precision tools engineering square 6 inch one, BS standard 939 grade B Accuracies less than 0.001" deviation per inch over the entire length of blade.

The board is 22 inch long x 5 inch wide. Across the face of the the board I can see a very fine slither of light towards the center of the board. I can pass a 0.1mm feeler through this gap. Towards the edges of the face no feeler gauge will fit.
Checking the edge itself, which is only about an 1/2 inch thick. Along parts of the edge, just on the right hand side of the edge, I can just about pass a 0.5mm feeler gauge but not a 1.0mm feeler gauge.

I checked the timber on the iron table of the table saw, couldn't detect any rocking movement whatsoever.
So does that all mean I get 10 out of ten, gold star and top of the class? :)
Primary use of surface planer ( jointer ) at the moment) is for surface planing rails and stiles for interior, exterior house doors and making the various sections to make up my replacement windows.
Thanks people.
 

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Discussion Starter #7
As Vince noted...depends on what you are doing with the board. If you are concerned about the face, if it doesn't rock, it's good enough. Maybe you're making a door panel or sorts...?

If we were discussing the edge AND you are going to join it to another board, then you would want a greater level of precision but your square should be more than good for checking square. The less light, the better...but if you see light at one end of the square compared to the other over 3/4" or so then I would say it needs a bit more work. Again, depending on the application.

Your flat board is good enough if it doesn't rock corner to corner...

Use it soonest out of the planer to make sure nature doesn't take its course...
Thanks Nick see my reply to Vince.
 

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There was a lot of discussion about this a couple of years back. Some folks were striving for accuracy close to a couple of thousandths of an inch. But that's metal working levels of accuracy. but warm it up or cool it down and its thickness changes.

So many methods of wood working, many standard bits of construction are designed to allow for changes. But there are a few things that really matter. For example, having the blade angle as close to a perfect 90 (or 45, or any specific angle required). Get a Wixey digital angle gauge (about $30), which you set onto the table, set the zero, then turn it and put it on the saw blade. Adjust the blade until you get an exact 90 or whatever you want. That makes your cuts square at least,

Wood expands across the grain so things like table tops require a little wiggle room. You can buy hardware that lets the top expand and contract. Or you can afix one edge with screws or pegs, but on the other side of the top, you can cut a short groove in the base so a fixed screw into the top leaves room for the the top to slide a bit with expansion. The base won't expand noticeably since the side rails run long grain relative to the top. When a long grain connects to cross grain, you have to accommodate the expansion. So the technique used is more important than the accuracy.

Picture frames (I make these for my artist wife) must have a perfect 45 degree angled cut, and the lengths of the top and bottom, and one side and the other, must be exactly the same (or as close as you possibly can get it. To do the length cut, you have to use a stop block on whatever "fence" you are using so the piece is cut identically. So here, the accuracy of both the angle and length is really important. But even here an tiny error of a few thousandths is almost inevitable. So you wind up using a tiny bit of filler to fill in any gaps. (Usually have no more than about 1/10th mm of a gap because I use a special "gillotine" tool machined to an exact 45 and 90 degrees. So in this case, the tool is important. If you choose a really good miter gauge and fit it snug to the miter groove cut into the saw, you can get good mitered (angled) cuts. Well, if you also set up your saw blade to be parallel to the miter slot within 3 or 4 thousandths of an inch, then you line up the fence with the blade, but have the far end set about 3-4 thousandths of an inch out from parallel to the blade so you don't trap the workpiece and make it kick back at you.

I guess I'm saying you want your tools set up as close as possible to perfectly, then the wood will be cut with enough accuracy to make your project assemble OK

If you are careless in setting,say, the angle of the blade, you may find you can't glue two pieces together and have them stick. Don't drive yourself crazy with accuracy of the wood, but get it close as you can and it will be good enough. Perfect just isn't possible in woodworking.
 

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Discussion Starter #9
Peter
Perfection is What We all aspire to, the honest truth is i have never made it happen, i believe most woodworker will tell you that with every project mistake where made the art is correcting them so only you know!
Wood is constantly moving
Cheers John.
 

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I guess I'm saying you want your tools set up as close as possible to perfectly, then the wood will be cut with enough accuracy to make your project assemble OK
Yep. Sometimes close enough is good enough, and you just can't get better than that.
 
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Hello Petter; So what method are you using to set your knifes? Also, do you have a good technique on the jointer? Getting lumber square and flat is hard to do. If you are a little out here and a little out there they mount up into big errors. I try to do the best I can but it isn't ever good enough.
Lowered the infeed table down. A furniture maker helped me out, by giving me a planed piece of timber, to use the moving forward ruler method x 5mm on both sides of the outfeed table, being sure same movement on both edges of the outfeed table and adjusting so same movement which I did. Machine knives have springs underneath, released lock nuts used the machines jig to set the height of knives to cutter block. Jig is like in attached images . Mine is one with red arrow and looks very similar and used in the same way as the one with the cir clips on the end. On my old jointer I tried using a one way multi gauge TDC method as well as moving ruler method. Old planer wasn't up to it, so upgraded to a more professional job.

With new planer I was struggling quite a bit to set the knives up correctly in the cutter block, later I found I could lower one side of the outfeed table so I got same movement using ruler method on both sides of outfeed table.

I think the Axminster engineer who advised me about setting the knife height correctly, thought I was getting a bit obsessive with the accuracy, come precision part of things, this is what he told me. Perhaps I still have some overlap, on getting the timber precisely square.

" I tried one last time earlier today. I lowered the outfeed table so could get the ruler to move by 4mm.
Knife three moves the ruler by 4mm, knife two by 6mm and knife one by 2mm. I didn't bother to check the movement at the other end of the block as would have had the same inconsistent results. "

This is what he said.

"The difference in height of the blades is amplified in the distance the straight edge moves across the bed.
I mentioned in my previous email the scale you are working to (0.10mm is roughly 5mm of travel) therefore;
1mm of travel on the straight edge is about 0.02mm so the height above the outfeed table you have is around 0.04, 0.08 and 0.12mm. This will work fine, the material will grow or shrink a lot more than that depending on the weather.
Setting the machine this precisely is a bit like setting your car tyres so the O of Goodyear lines up with the valve for balancing purposes, not necessary."
He also said timber would move fractionally as fed through the machine.
My feeding method I'm using is hand over hand, light pressure. I think I'm doing it quite well.... though I dread to say.... but not perfectly :)
 

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Discussion Starter #16
There was a lot of discussion about this a couple of years back. Some folks were striving for accuracy close to a couple of thousandths of an inch. But that's metal working levels of accuracy. but warm it up or cool it down and its thickness changes.

So many methods of wood working, many standard bits of construction are designed to allow for changes. But there are a few things that really matter. For example, having the blade angle as close to a perfect 90 (or 45, or any specific angle required). Get a Wixey digital angle gauge (about $30), which you set onto the table, set the zero, then turn it and put it on the saw blade. Adjust the blade until you get an exact 90 or whatever you want. That makes your cuts square at least,

Wood expands across the grain so things like table tops require a little wiggle room. You can buy hardware that lets the top expand and contract. Or you can afix one edge with screws or pegs, but on the other side of the top, you can cut a short groove in the base so a fixed screw into the top leaves room for the the top to slide a bit with expansion. The base won't expand noticeably since the side rails run long grain relative to the top. When a long grain connects to cross grain, you have to accommodate the expansion. So the technique used is more important than the accuracy.

Picture frames (I make these for my artist wife) must have a perfect 45 degree angled cut, and the lengths of the top and bottom, and one side and the other, must be exactly the same (or as close as you possibly can get it. To do the length cut, you have to use a stop block on whatever "fence" you are using so the piece is cut identically. So here, the accuracy of both the angle and length is really important. But even here an tiny error of a few thousandths is almost inevitable. So you wind up using a tiny bit of filler to fill in any gaps. (Usually have no more than about 1/10th mm of a gap because I use a special "gillotine" tool machined to an exact 45 and 90 degrees. So in this case, the tool is important. If you choose a really good miter gauge and fit it snug to the miter groove cut into the saw, you can get good mitered (angled) cuts. Well, if you also set up your saw blade to be parallel to the miter slot within 3 or 4 thousandths of an inch, then you line up the fence with the blade, but have the far end set about 3-4 thousandths of an inch out from parallel to the blade so you don't trap the workpiece and make it kick back at you.

I guess I'm saying you want your tools set up as close as possible to perfectly, then the wood will be cut with enough accuracy to make your project assemble OK

If you are careless in setting,say, the angle of the blade, you may find you can't glue two pieces together and have them stick. Don't drive yourself crazy with accuracy of the wood, but get it close as you can and it will be good enough. Perfect just isn't possible in woodworking.
Hi Tom and thanks for the detailed helpful reply and tips. I have a magnetic angle gauge for setting the saw blade 90 to the table.
 

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Pat Warner pointed out once there is no such thing as perfection. It's like dividing 1 by any other number. It will never equal zero. What you are after is a measurement that is so small a deviation from perfect that the difference is meaningless. And that varies according to your circumstances.
 

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Discussion Starter #18
Pat Warner pointed out once there is no such thing as perfection. It's like dividing 1 by any other number. It will never equal zero. What you are after is a measurement that is so small a deviation from perfect that the difference is meaningless. And that varies according to your circumstances.
Thanks for the input Charles.
 

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It's all about how it goes together . . . When you fit your boards together, are you satisfied with the way they fit? If so, you're plenty accurate. If not, you need to tweak something. I promise you that no one will ever check the flatness of your boards with a feeler gauge after it leaves your shop. And if you check it yourself two weeks from now, you'll get a different result than you did today. But a sloppy joint rarely gets better with age.
 
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It's all about how it goes together . . . When you fit your boards together, are you satisfied with the way they fit? If so, you're plenty accurate. If not, you need to tweak something. I promise you that no one will ever check the flatness of your boards with a feeler gauge after it leaves your shop. And if you check it yourself two weeks from now, you'll get a different result than you did today. But a sloppy joint rarely gets better with age.
Thanks.
 
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