How Square Do Cabinet Parts Need To Be?

[minimal]

So what "tricks" do you all use to keep things as accurate as possible?

I don't know any, except never make two "dependent" marks at the same time, instead I mark & cut to the mark, then move on to the second one. This reduces the errors due to the kerf width, but if the angles aren't right there is no limit to how far off a linear dimension may be.

So, aside from "measure 3 times, with 3 different tools, then cut once" if you have any tricks, especially festool-specific ones, please speak them!

As for identifying errors visually, my motto is "if you can *see* it's off, it's *way* off".

Thanks in advance.

 

[Michael Kellough]

As for identifying errors visually, my motto is "if you can *see* it's off, it's *way* off".

Right. I meant if I can see that the wood doesn't fit the gauge perfectly.
Sometimes I can see that it's wrong as it sits all by itself. The missing inch tape measure bug got me the other day. Maybe it would have been better to be out the 1/32" that the poorly fitted tape measure hook causes but the part still would have been unacceptable and I might not have noticed it until assembly.

I use the biggest most precise square I can but I've given up using protractor like tools for laying out large (anything over a foot) mitered cuts. Instead I use CAD to find the locations of the ends of the cut line and then lay the guide rail on those marks. And, I keep the rubber strip freshly trimmed when the work has to be really precise.

 

[LaserGecko]

hadn't seen the Woodpecker square.  I will get it in and add it to my collection. $80 is a bit of a price but if it's square... 

John,

It's not just square, it's guaranteed to be square to within .001" for life.

Be sure to join their E-Club to get the weekly discount newsletter. I've been on it for years and they have put all of their tools on sale substantially at various times. They also have a bi-annual 10% off everything sale. I really want the 24" T-Square, but according to my records they're about due for the next 10% event.
http://www.woodpeck.com/tsquare24.html

I also really dig the MDF wall mount cases for their more expensive tools.

 

[Dave Rudy]

I've given up using protractor like tools for laying out large (anything over a foot) mitered cuts. Instead I use CAD to find the locations of the ends of the cut line and then lay the guide rail on those marks.

Michael,

Could you describe this more completely?

Thanks

Dave

 

[Michael Kellough]

I haven't found any protractor based tools that are both large enough and precise enough to be used for laying out large parts to my satisfaction. I often do odd stuff for artists and film making projects with different requirements than conventional cabinet making. In cabinet making consistency of the miter across multiple parts is often more important than the actual angle so I can make a custom jig that will guarantee the parts match, but when the specific angle must be achieved I design the part (if not the entire project) in CAD software to discover the X-Y coordinates of the ends of the line to be sure it is placed accurately.

I can confidently strike a square straight reference line which conforms to the CAD plan and then layout the coordinates for the miter measuring from that line. This is not unlike making a large square cut by constructing a graphic triangle with the dimensions of 3,4,5. I just use CAD to find out what odd numbers are required to construct my triangle. Then, with the WYSIWYG directness of the Festool guide rails I make the cut with a lot more precision than I could get with a protractor or bevel gauge.

 

[Dave Rudy]

Thanks, that makes sense

 

[CharlesWilson]

I just thicknessed a half dozen boards to 1/8". Now, if all I need is +-1/8"  tolerance, I could have just used a sheet of paper. That certainly would have been a lot easier.

Charles

 

[woodshopdemos]

If you have followed this thread, you may now be interested in the other dimension parallel cuts. That is a new subject and a new thread.

 

[hgporter]

If Wood published a tolerance of +/- 1/8" for a board thickness, it was either a mistake or it was for a noncritical piece (pen blank, backer board for a key holder, etc.) or it was a rough dimension. In all the issues I have read, I have never noticed Wood advocating blatantly sloppy techniques.

Phrases like "Perfectly Square" are meaningless. Perfection cannot be achieved, so acceptable tolerances enter in; what we often think of as perfection is sometimes costly to obtain. Tolerances permit us to quit when we are "close enough".

We rarely think of +/- 1/8 inch being close enough for anything, but consider something like the thickness of a board for a cross brace on a picnic table top. You wouldn't want the top boards varying 1/8 as you go across the table, but why spend a lot of time and money milling a noncritical brace?

Angular measurements are difficult to accurately layout by hand. (As an example, consider the task of aligning the tablesaw or miter saw for 45 degree bevel cuts.) Marking layouts with a protractor is difficult to maintain accuracy, because you are usually making relatively short lines and extending them across the workpiece. Imperceptible inaccuracy over a 3" surface becomes magnified as you project that layout over a two or three foot board.

For more critical work, engineers know to specify rise and run from a reference line (triangular measurements as someone alluded to earlier). This is where the 3-4-5 right triangle concept is used. Of course personal technique, width of lines on the "measuring rule", pencil thickness, etc, all effect the accuracy. (Where tighter tolerances are required, I choose a sharp knife over a sharp pencil.)

FOR EXAMPLE: To layout a 45 degree angle on a two foot wide board, measuring 24 inches along one leg, and 24 along the perpendicular leg and connecting the points generally gives the best way to layout angles. I routinely convert angles to triangle measurements and use this layout method rather than using my protractor. Since this post is getting long, if someone is interested in the geometric principles on how to do this, ask and I'll be glad to reply.

 

[cparson]

FOR EXAMPLE: To layout a 45 degree angle on a two foot wide board, measuring 24 inches along one leg, and 24 along the perpendicular leg and connecting the points generally gives the best way to layout angles. I routinely convert angles to triangle measurements and use this layout method rather than using my protractor. Since this post is getting long, if someone is interested in the geometric principles on how to do this, ask and I'll be glad to reply.

This sounds like a great method (especially since I don't yet have an accurate protractor) but I assume the accuracy of the angle diminishes with the size of the lumber?  Have you had any success with smaller pieces - say, 2-4" wide boards?

 

[Michael Kellough]

FOR EXAMPLE: To layout a 45 degree angle on a two foot wide board, measuring 24 inches along one leg, and 24 along the perpendicular leg and connecting the points generally gives the best way to layout angles. I routinely convert angles to triangle measurements and use this layout method rather than using my protractor. Since this post is getting long, if someone is interested in the geometric principles on how to do this, ask and I'll be glad to reply.

This sounds like a great method (especially since I don't yet have an accurate protractor) but I assume the accuracy of the angle diminishes with the size of the lumber?  Have you had any success with smaller pieces - say, 2-4" wide boards?

When the part is smaller than a foot or so marking errors can be more significant than the cumulative error of small measuring instruments so a machinist's protractor is sufficient. When the sides of a triangle get much larger than a foot, if your marking skills are good, you're better off using geometry. If you want to be really precise use large strong dividers set to length on Starrett rules.

 

[Dave Rudy]

I finally read the article.  I do not think that saying an 1/8" off is ok is a fair reading of what the author said.  The point he was trying to make is that the + or - for how close is close enough varies depending on the project, the particular cut or surface at issue, etc.  In some part of the discussion, the author indicated that it was required to be within 1/64" of the final dimension.  He also stressed at some points that absolute dimensions may be less important than that matching parts be identical to the others -- in other words, whether each side is 8" or 7-7/8" may be less important than that each side is the exact same length as the other.

Dave

BTW, the same issue of Wood referred to a 3-4-5 square for getting square crosscuts in sheet stock -- 
http://www.amazon.com/CH-Hanson-Squ...78-5051938?ie=UTF8&s=hi&qid=1179931920&sr=8-1