Engineers square or Machinist Square

[leehljp]

I have made my dado circular saw and am having problems with precision alignment. The first L- Square guide I made was about a degree off and I didn't notice until I made some dado cuts for shelving in a 2 board shelf with the dado in the end boards. Being persnickety as I am, I made a second set of wood L-Square guides. This time, I clamped my carpenters square onto my wood L-square guide and even checked squareness with my Woodpeckers 9 inch square. As best my eyes could tell, it was aligned perfect. At this point, I screwed the just glued L-Square together. Still in alignment as best I could tell.

But when I cut the 2 dados into two end boards to accept the shelving, they were off about 1/16 from each other on the outboard side. Not bad but not perfect. That means on dual 6 ft high end boards for shelving, there is no telling if I will have even more alignment issues or not.

What is the most precise? Machinist square or Engineers square? My understanding is that a Machinists square is generally more heavy duty simply because of its use. Not sure if that is true or not, or if it affects the precision.

I need at least 6 inches, prefer 9" but if I could find a 12" I would be happy. I would also like for it to be within .0005" square. At least 1/4" or 6mm thick. Steel, but Aluminum would do.

Might be expensive, but this would be a welcome addition to my tools if I could count on this being precise.

The L-Square below shows my purpose. The dado in the bottom of the L is my alignment guide; the left side is my guide. With this, all I have to do is set the alignment dado and clamp the left side alignment guide to the board and I clamped the right side to make sure it is/was square. I need to improve it by about 1/2 of a degree or maybe 1 degree. The back end of the cut was almost 1/16" off from the line marked. I am not sure where my error is occurring.

The marked line squares with my Starrett square from both sides; The L shows being square. but both boards, after being cut, show up as being off by the same amount. It was not enough to keep me from using them on the second set of end board cuts, but I didn't like the "not perfect".

I have considered that I am "drifting" or that the Dado in a circular saw is doing what the router mount in the BT3x00 does if not lock down - the vibration causes it to move.

I am trying to cover my bases to figure this out, and starting with a perfect square.

Ideas?

[Jim Frye]

12" Speed Square? It's what I used when I made the shelving unit for my shop. I was guiding a router, but the application should be the same. The web inside the square provides good clamping area.

[LCHIEN]

.0005, Half a thou, out of a 12" square is .002 degrees. by simple trig. How did you pick .0005? Out of a hat?

Maybe your requirements are not really that tight. Do you want to pay for that kind of accuracy?

For a 6 inch square, 10 thousandths is about 0.1 degrees.

You said the dado was 1/16th off at the end (I'll assume a 12" wide board)
then that angular error is 0.3 degrees.

Another question I have, if you cut parallel dadoes with the same square they should be parallel regardless of how accurate they are angle wise to perfect 90.
Since they are not parallel and off by 0.3 degrees I have to assume you did not apply the squares consistently.

So are you really chasing the right rabbit? A more accurate square I don't think sounds like your problem.

[leehljp]

.0005, Half a thou, out of a 12" square is .002 degrees. by simple trig. How did you pick .0005? Out of a hat?

Maybe your requirements are not really that tight. Do you want to pay for that kind of accuracy?

For a 6 inch square, 10 thousandths is about 0.1 degrees.

You said the dado was 1/16th off at the end (I'll assume a 12" wide board)
then that angular error is 0.3 degrees.

Another question I have, if you cut parallel dadoes with the same square they should be parallel regardless of how accurate they are angle wise to perfect 90.
Since they are not parallel and off by 0.3 degrees I have to assume you did not apply the squares consistently.

So are you really chasing the right rabbit? A more accurate square I don't think sounds like your problem.

I saw one machinist square somewhere that was .0003 and somewhat expensive. SO Yes in a way, picked it out of a hat. I had a "registration" triangle square some years ago (in Japan) and can't find it now and it was much more precise than the run of the mill HD/Lowes triangle squares. Those are ok for general run of the mill construction, but I do like to measure with precision when possible.

if you cut parallel dadoes with the same square they should be parallel regardless of how accurate they are angle wise to perfect 90.

Yes, but only if I don't get the facing boards turned around or backwards before cutting, at which point they will "x". At my age . . .
I did that on the first pair. That is a problem of the inexperienced - or just plain dumb thinking by an otherwise "knows better" but didn't put mind in gear (me) as I was more interested in getting it done than thinking it through.


I THINK I know where I messed up. It wasn't my square in the OP, it was the yellow clamp on the right side. I pulled the clamp tight to hold it in place and squeezed too tight, probably compressing the wood by a minuscule amount, throwing the perfect alignment off. The other side was clamped by a hand clamp.

IF this is what happened, it is a matter of technique for me to fix it. Thanks guys

BUT I STILL WANT A GOOD MECHANIST SQUARE!

[leehljp]

I ordered this one from Woodpeckers.

https://www.woodpeck.com/mft-layout-assembly-square-19.html

I am OTC when it comes to precision angles. I hate 1/2 degree or even 1/4 degree off. Cheap Thin blade vertical squares engineers squares with thick base that are available from HF can distort a degree when clamping 2x4 or 1x6 sides. I found that out. I will see how good the Woodpeckers unit is. It is beefy, so it should stay accurate.

[LCHIEN]

OTC? Over the counter?

You mean OCD? Obsessive compulsive disorder?

That square looks very solid.

[leehljp]

Loring: Yes, OCD. I don't know if it was my spell checker or my brain, or my fingers that did that. We often blame the spell checker or brains not thinking but honestly, I have found my fingers often click a letter out of sequence or inadvertently. My neurologist told me that my pseudo Parkinson's / Essential Tremors makes for reach/touch to be off from what my mind wants. I mentioned to him once that I felt I had a mild form or dyslexia but he dismissed that.

Interesting thought Off / Topic from the OP - I do find that my fingers press the wrong keys at times that I am not aiming to press, - kind of like a dyslexic reading letters transposed in their mind. I know how to spell words, but when fast typing, I watch my fingers press certain keys in reverse order that I am thinking, repeatedly. Old age is not for sissies.

I have a form of dyslexia in hearing. When I was learning Japanese, What I heard and what was often said (in the learning stage) I heard certain 2nd and 3rd syllables before the first. When I recorded the sounds of teachers and then played them back in slow motion, I heard differently; when sped up to normal speech, again I heard the 2nd or 3rd syllable first. Knowing this helped me think and overcome the dyslexia until my mind finally settled on the right order. It was frustrating but it helped and taught me to listen for the context, and focusing on context taught me cultural understanding in ways that normal learners missed.

The above paragraph is what often happens in my fingers as I type. My mind thinks one thing, but my fingers type something else, unless I type slowly.

[capncarl]

I see where engineers square are 0.001” per inch of length whereas machinists square is no greater than 0.0002 in/in. Whatever that means, I have a couple of sets of machinist squares they stay cooped up in my toolbox so they won’t get damaged, lot of good that does me! I’m always afraid they will get dropped or knocked off the table. This way when my kids sell all my stuff someone will get a 40 year old like new set of Starrett squares for $15.

I can deal with my dyslexia but I have a hard time dealing with computer induced dyslexia…. Spell check/ auto correct…. When I miss spell something and it pops up several replacements and I pick one. Later on when I proofread, how da heck did that get there, a totally different word than I picked was in its place.

whick set of woodpeckers squares did you order?

[leehljp]

The WP layout and assembly square: https://www.woodpeck.com/mft-layout-...square-19.html Thinking of getting a 1281 square to go with it.
I had a registration square very similar to the woodpeckers that I used to square up my BT3000 in Japan. I put it up after every use and did not use it for anything else. I can't find it now but I thought I used it once when I got back. I have a few tools that I used to keep separate from everything else too, . . . but at my age, I have decided it is time to get more use out of them!