Trust my protractor?

[Silvan]

I bought a stainless steel protractor. You've probably seen the like. It has a scale engraved onto a rectangular piece with a moving rule that ends in an angle indicator marking. I don't have the manufacturer in front of me, but it was made in the USA, and it seems to be a well-made little tool.

I attempted to use this thing to see if saw blade is really set at 90 to the table, after doing my absolute best to dial it in using my square. It came in at 89+ on one side, and 91- on the other side. I checked my square, and it came in at 89+.

I checked two other squares, and both of them came in at 89+ too. One is Johnson combination square, another is a Stanley combination, and the last is a Stanley, um, whatever you call an L shaped piece of metal kind of square with no moving parts.

So do I trust the protractor or the squares? All were made in the USA, and all have been well-treated.

If I go buy a Starret (sp?) or comparable anal $BIGNUM square, will it read

90.0 on this protractor?

[Dave Balderstone]

It's pretty easy to check a square.

Scribe a line. Flip the square. Does the line match?

djb

[Bay Area Dave]

what Dave said, Michael.

scribe the lines and see if they overlap along their entire length.

dave

Dave Balderst> >

[B a r r y]

I had a General that fits that description, and it was WAY off!

Barry

[John Grossbohlin]

I'd forgo the "questionable" tools all-together. Why not just cut a board that is close to the maximum depth of cut in thickness and after the cut flip one of the pieces over, butt the cut ends up against each other while they lay on the table, and see if they match up square... if they don't then the blade isn't perpendicular to the table. Since the maximum depth of is typically a bit over 3" on a 10" saw it shouldn't be too difficult to see any deviation from square. I suggest running a pencil line down the length of the board on one side to help keep track of the flip.

John

[John Grossbohlin]

I see I left a word out... classic case of reading what I thought I wrote instead of what I actually wrote! ;-)

John

[Lew Hodgett]

Why bother? Life is too short to clutter it up with a bunch of toys IMHO.

(BTW, my sail boat also reflects this simple approach to life.)

A square miter gage and a piece of scrap plywood is all that is needed to determine if a saw blade is square with the table.

Extend the blade to full height, stand the plywood on edge (vertical) and make a cut using the left table slot.

Rotate the piece 180 degrees, put the miter gage in the right table slot and run the plywood thru again centering the first cut over the saw blade.

The sides of this double cut are now parallel indicating a square cut or they are not parallel indicating adjustments are needed.

Works for me, YMMV.

Lew

[KYHighlander]

Get one of those 30/60/90 plastic triangles, you know the one you had to have for shop class. My shop teacher required we learn 6 weeks of drafting before taking us into the machine shop. Probably the best and most useful class I took in school and I'm not even referring to the woodworking skills he attempted to teach me.

KY

[Bernard Randall]

That's what the professionals do. View it with a light behind the cut.

Bernard R

[Leon]

Exactly... I seldom use a square at all.

[Unisaw A100]

The biggest, best and most $BIGNUM square you'll get from Starrett is the Builder's Combination Square.

it will set you back $300ish but it's a fine tool. (Don't Ask Me How I Know This).

Smaller heads for the standard blades (combination square) are available and are precise but you'll need a jeweler's loupe to use them (1) but will have a smaller blade and body.

(1) I have a little 8X loupe I got at a camera store that lives in my square drawer.

UA100

[Doug Miller]

This method presumes that the edge you're holding the square against is straight. Unless you know that it is, you can't trust the results. :-)

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

For a copy of my TrollFilter for NewsProxy/Nfilter, send email to autoresponder at filterinfo-at-milmac-dot-com

[Doug Miller]

Yep, I have one like that too. The markings are a bit too wide to permit it to be truly accurate.

Neither. :-)

Probably not -- but that will be the fault of the protractor, not the square.

If you buy a Starrett, you will never regret it (not after the initial shock, anyway). And you will never have to worry about this again, either. If the Starrett says something is square, it's square. Same goes for Incra.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

For a copy of my TrollFilter for NewsProxy/Nfilter, send email to autoresponder at filterinfo-at-milmac-dot-com

[George]

Outcome based woodworking.

Once I got the outcome I wanted, I checked my squares against the blade. Both turned out to be right on, which I sort of thought they were, because when set on a flat surface, there was no light between the uprights.

I can now use them if I want to to check the limit screw on the saw for 90.

[Bernie Hunt]

Silvan,

Don't confuse made in the USA with being accurate. There are many POS items made in the USA. The same way there are many highly accurate items not made in the USA.

Use the draw two lines method other have mentioned here. Us a marking knive to get a very thin line and see which one lines up.

About every 6 months or so, I get out all my squares and make sure they still agree. I have a couple of fixed squares that I use for setup in the shop and they get banged around sometimes, So I check them against the square that stay in the toolbox. If everyone agrees, them I'm good. If there is a disagreement, then I use the double line method to find out who got bent.

I also recommend that you check your rulers against each other. I got some hook rules one time that were 1/16" off. Not back unless you plan on doing some fine woodworking, hahaha.

Bernie

[Silvan]

Hafta take a pass. I just got the bill from my wisdom teeth. They estimated $700 short.

Too bad surgery isn't like car repair. "Book says $1300, and I'm not paying a penny more."

(It came to $2,000. OUCH! It's a lot of money to spend to get someone to torture you. It would have been cheaper and far less painful to hit myself in the nuts a couple good times with a sledge hammer.)

[David Hall]

Now, how does he know if his miter gage is square? Somewhere along the road you need at least one square that you are comfortable is square within your tolerances. The scribibg a line on a board with a known straight edge method proves squareness sufficient for my tolerences. Of course, a $2 plastic 30/60 drafting square is commonly recognised as quite square. One of these can be used to test that protractor at

90, 60 and 30 degrees.

Dave Hall

[John Crea]

Frankly, I would trust a archetect's triangle to be closer to true

90degrees than most of the junk out there in the hardware stores/borg, and it is a WHOLE lot cheaper and lastly if it get dinged/damaged, it doesn't hurt too much to toss it and buy a new one

For an alternative, there are machinist's SQUARES for under $20 that will let you know if it is square or NOT, just won't give you a read out of the actual angle

John

[Dave Balderstone]

Yup.

Yup.

[Bob S.]

Doug,

Legit question - not jerkin your leg on this one or baiting you and I agree with your statement below about not regretting purchasing Starrett.

I own one, it's the off-the-shelf, $70 square and the certificate says it's accurate to within .002" over the length of the 12" blade. So maybe it is square and maybe it isn't but certainly close enough for my woodworking use.

So the question is - if you care to respond:

If it is off by the full .002" (max allowable error) and I haven't checked it yet, then what would that equate to in degrees from being square (90°)? This assumes the blade is .002" wider/narrower at one end, which is possible but probably unlikey.

Bob S.