Help with square

[Laurie Brown]

Ok, I have been pondering this for over an hour and feeling like I'm in the Twilight Zone or something....

Below is a sample piece of board. I was trying out my new saw blade and wanted to see how well it cut.

http://www.aerth.org/Downloads/board1.jpg


Looking at this picture, the lower right corner of the board with the red square is square, as checked with my Swanson Speedsquare. I have checked that my fence is parallel to the miter slot, and to the blade using a ruler to measure the distances in mm. and the speedsquare.

Now, IF the corner with the red square really IS square, then if I rip this piece along the opposite side in the direction shown, then the corner with the blue square should be square after the cut, right?

The problem is, the corner with the blue square is NOT square after I make the cut. It's noticeably off within the 6" span of this piece of sample wood, compared to the other corner. The only way I can think of that this could happen is if the fence somehow bows or moves when making the cut? I have a Delta T2 fence on my hybrid, and I can set the fence and push on it all over and don't see any movement. So I'm at a loss to figure out what's going on, or if I'm just crazy. ;)

[Prashun Patel]

Two dumb questions:
1) Did you check the alignment of the blade relative to the fence at the front and the back of the blade?
2) Are you in any way twisting the board when it's coming off the blade? That is, are you tight to the fence all the way thru the cut?

And one super-dumb question:
1) Is the bottom of your test piece straight?????

[Lee Schierer]

Unless you have really keen eyes, measuring with a ruler is not going to get you close enough to solve your cut problem. I would suggest a dial indicator. You can purchase one from Harbor freight for less than $20. Make sure your miter gauge fits snug in the slot, no side to side play. Attach that dial indicator to a block of wood with a wood screw so it can't move and clamp the block of wood to your miter gauge. Raise the saw blade all the way up and measure the root of a tooth near the front of the table. Mark that spot with a pencil, rotate the blade so your marked tooth is at the back of the table and check the reading agian. You should get this reading within .005" or less. Then lower the blade and move the fence over near the miter gauge. Check the alignment of the fence to the miter gauge slot. Again you should be able to get within .005 without a lot of problems. Closer to .000 is better, but not essential.

Most likey you will find your blade is at an angle and this is pulling your wood out of parallel during the cut. You will most likely also find your fence is out of square and possibly not flat along the length.

Also Speed squares are designed for general carpentry work and are not precision insturments. A good combination square (Starrett) or a rosewood cabinet makers square would be a better tool. http://images.rockler.com/rockler/images/12938-01-200.jpg Plastic drafting triangles are surprisingly accurate for their cost and work well for seting the blade at 60, 45 and 90 to the table and for setting the miter gauge angle.

You won't regret the investment in tools.

[keith ouellette]

Measure across the top and the bottom and see if you made a parallel cut first. If everything is tuned right and you have one straight side when you run it through the saw then the side you cut will be parallel with the side that was against the fence.

Are you sure the side that you ran against the fence was perfectly straight?

make sure the saw blade is perfectly parallel with the fence and the miter slot.

making a square isn't as easy as many people think.

[Jeff VandeZande]

Laurie,
I think Lee is right about tools and I think your piece is not actually square.
Try this, unplug the saw, raise the blade and slide the piece thru as you did for the cut.
The saw blade tips should just touch the piece all the way thru. If they do your piece is parallel and if it checks square from one side and not the other - you got a dud square.

[Jack Ellis]

I have several combination squares. The only ones that are square are the Starretts. The next best one has an aluminum ruler and a plastic head! All of the others are probably acceptable for carpentry but not for precision woodworking. Engineer's squares are also good for this sort of thing, even thought their principal use is in metalworking.

Another tip. If you use a try square or cabinetmakers square like the one shown in Lee's photo, don't make the same dumb mistake I did, which is to assume the outer edges are square just because the inner edges are square. They probably are not!

[Laurie Brown]

I obviously need better measuring tools. ;)

I've been looking at those Starretts on Amazon, but there are so many of them. Which one is the best one? What's the difference between the forged head or the cast iron head?

[Lee Schierer]

I obviously need better measuring tools. ;)

I've been looking at those Starretts on Amazon, but there are so many of them. Which one is the best one? What's the difference between the forged head or the cast iron head?
I'm not sure it makes a lot of difference. The forged head is probably stronger and less likely to break if dropped. I have this one:Starrett Combination (http://www.amazon.com/Starrett-C33H-12-4R-12-Inch-Combination-Square/dp/B00002254K/ref=pd_bbs_sr_1?ie=UTF8&s=hi&qid=1235607136&sr=8-1)

For checking large assemblies I have an antique carpenters framing square that I checked once with a coordinate measuring machine (CMM) at work and determined it was within 0.1 degree of 90 inside and out. Many of the stamped metal ones you see now are off by a degree or two but can be adjusted with a bit of work.

[george wilson]

The forged head is hardened. Unless the cast iron head has been used to death,it would be fine for you. the trouble with combination squares,which is the type of square you are talking about,is that they will get out of square from being slid along the blade,and wearing.

The best type square to use when squareness is critical,is a fixed beam machinist's square. I do not mean the cheap import types.they may not be too accurate. I bought a set of SPI squares for the shop before I retired,fom MSC co. They are imports,too,but they were pretty decent. I suppose a bit more quality control was used because of the name. SPI means Swiss Precision Instruments. Th name belongs to MSC-Manhattan Supply Co.,now. the SPI products are made in various places from USA to China. You don't have to buy a whole set,but unless you want to spend $100.00 or so on a Starrett 6" square,I suggest the SPI.

[Rich Engelhardt]

Hello,

I've been looking at those Starretts on Amazon,
As have I.
Try ebay.
Lot's of Starrett and/or Browne and Sharpe for good prices.

[Larry Edgerton]

Laurie

The first thing I do when I get a new employee is take their Swanson speed square and throw it in the trash. I don't allow them on the job, they are just not accurate enough.

And then there is the Estwing hammers........

[Laurie Brown]

Laurie

The first thing I do when I get a new employee is take their Swanson speed square and throw it in the trash. I don't allow them on the job, they are just not accurate enough.

And then there is the Estwing hammers........

LOL! Ok, then what do you use? ;)

[Ralph Okonieski]

It took me a long time to purchase a set of engineers squares but they are one of the most frequently used tools now. My set only goes to 6 inches so I use a good framing square for the larger stuff. A set of engineer squares can be had for maybe $30-60 depending on number in set and whether on sale.

[Wes Grass]

Quick check for square. Stand the piece up on it's 'fence' side on a flat surface, like your table saw, and place the outside of your square blade against the 'square' end. If it's not square you'll see a gap at either the top or bottom. The gap will be twice the error.

[Larry Edgerton]

LOL! Ok, then what do you use? ;)

If you think that is funny, you should see their face when I throw it.:)

If I had to have just one square in my shop it would be my Mitatoyo 12"combination. I use it to check miters, as a depth gauge, as a center finder,as an oddangle measure, as a scribe, and occasionally as a square. A Starrett would be just as good.

There is a confidence that comes with the crispness of a good square, you will find it when you have one, and you will know what I mean.