setting angles on table saw accurately
jcutrer
| Posted in Power Tools and Machinery on
i have a delta 10″ contractors saw-i don’t trust the 90 & 45 degree settings on the saws scale & i don’t trust my settings-i am looking for dedicated 90 & 45 degree precision squares to use to set the blade-does anyone know where i might find these and/or does anyone have suggestions & recommendations as to an easy & foolproff method setting blace angles with confidence-thanks for any help 7 suggestions
Replies
JCUTRER,
There are several ways to do this.
1. Buy a machinst's square - Grizzly (www.gizzly.com), Woodcraft, Lee Valley.
2. get a plastic drafting square (they are dead on). at an art supply store.
Use 1 or 2 to measure the angle of the cut with the saw table as the flat reference . . .
or . . .
3. Don't use either mechanical square, and get at least TWICE the accuracy. Here's how:
Prepare 2 test pieces - Two, 2' long fir 2x4s will do. Joint one surface of each to be the reference surface. If the faces of the 2x4 are already acceptably flat, omit jointing.
With the saw at its "90 degree" setting, rip a sawblade-thick cut off each piece, keeping the reference surfaces down flat against the saw table.
Keeping the reference surfaces of each piece on the flat saw table, bring the cut surfaces against each other. Only if the blade is precisely at 90 degrees will the 2 cut surfaces "kiss" from bottom to top, with no light visible between them. If the blade is not at 90, the difference will be magnified by a factor of 2 and either the bottom or top of the cut surfaces will touch, but not the other. Adjust the blade and cut both pieces again until they touch from bottom of cut to top. Then, and only then, the blade will be exactly at 90 degrees to the table surface.
You will then have 2 pieces with a precise right angle relationship between the reference face and the cut face (they will be exactly square between those two faces. Set one aside for the next step.
Set the saw at "45 degrees." Rip two test pieces, using a good face of each as the reference surface against the saw table. Place them together with their reference faces flat on the saw table so that the cut faces form an upward "V." Place the square piece from above between them in the V. Any deviation from 45 degrees will be magnified by a factor of 2. If the square piece doesn't fit into the V exactly, adjust the saw and repeat.
Rich
Edited 8/26/2002 4:35:41 PM ET by Rich Rose
> ....
Set the saw at "45 degrees." Rip two test pieces, using a good face of each as the reference surface against the saw table. Place them together with their reference faces flat on the saw table so that the cut faces form an upward "V." Place the square piece from above between them in the V. Any deviation from 45 degrees will be magnified by a factor of 2. If the square piece doesn't fit into the V exactly, adjust the saw and repeat.
.....
I didn't spawn the thread, Rich, but appreciate the explanation. Do you have any other (equally as obvious once explained) for a bonehead trying to set a perfect 30 degree angle for ripping?
Dennis in Bellevue WA
[email protected]
Dennis,
I can't think of a good solution for 30 degrees. You could cut three pieces which should "stack" to 90, but that would be messy and would probably introduce a lot of error. Maybe someone else who has served some time in a machine shop has a "trick" for setting 30 (and prolly 60) degrees.
Rich
Rich-
FWW had an article some time ago on making a Sine Bar to do accurate measurements of blade tilt. Maybe someone else has a reference handy.
> ....You could cut three pieces which should "stack" to 90, but ....
Duhhh - I told you it would be obvious (hehe)
Actually, I've been using a 30deg. bit in my router table. Not terribly pleased with the finish of the cut so I'm experimenting using the saw. I think the proof of the pudding is in the eating - take some scrap, rip 6 pieces @ 30 deg ea. edge and see if they close into a hexagon. Divide error by factor of 12. (!) Guess that means wait 'til the shop cools off and the metal shrinks enough to move the arbor that small amount (grin)
Dennis in Bellevue WA
[email protected]
Rich-
I couldn't find a reference for a sine bar. But here are some other thoughts:
Is there any reason to think that the motion of the tilt is not linear in angle? If it is linear, then, once you've established the 0-deg and 45-deg points, shouldn't a linear scale between them be as accurate as you want? Make a bigger scale; make a longer pointer.
If you really want to set an accurate 30 degrees (or 17.3 or 41.7) make a large right-angle triangle of plywood or plastic or whatever's handy. Use as large a hypotenuse as is tolerable--24" ought to be fine. Make the short leg of the triangle equal to the sine of the desired angle (0.5000 for 30 degrees) times the hypotenuse (exactly 12" in this case, or 0.2974 x 24 = about 7-1/8" for 17.3 degrees). This is what a sine bar does, but the sine bar is adjustable.
I favor making an accurate scale.
P.S. If you use the 7-1/8" approximation in the above example, you'll get 17.27 degrees rather than 17.3. Big deal for a tablesaw!
Edited 8/26/2002 7:28:43 PM ET by Donald C. Brown
I bought a set of two plastic drafting triangles; one is 45‹-45‹-90‹; the other is 30‹-60‹-90‹. I haven't checked, but I wonder whether triangles with other "specialty" angles (e.g, 22.5‹) might be available as well, maybe on special order?". . .and only the stump or fishy part of him remained."
Green Gables: A Contemplative Companion to Fujino Township
I use 1/16" plexiglas for making my squares, because after you scribe the lines with either a sharp scribe or an exacto knife, you can break it exactly on the line by snapping it down over a sharp edge.
If you want a 30' and 60' square, just lay out an equalateral triangle (all three sides the same length), then find the center of one side and connect it to the opposite corner. This gives you a 30',60' and 90' of any size you need. With a little care, you can get accuracy of under 0.010".
As for the 45', just lay out a perfect square (exactly equal diagonals), and join the opposite corners. With careful scribing, you have a 45',90' and 45' to the size you need.
Good Luck, Bob.
As you all have indicated, there so many ways to carefully set up a piece of equipment. The two "special" angles of 90 and 45 are the only ones that I am aware that are self referencing, and, with an amazing degree of accuracy set up the saw without reference to any "outside" measurement. BTW the technique is not limited to table saws. Similar logic sets up radial arm saws, jointers, bandsaws, etc.
Rich
Edited 8/26/2002 10:29:18 PM ET by Rich Rose
Rich -
30deg setting:
Flatten one each on two workpieces. Plane the other sides to exactly parallel. Rip each piece at a 30deg setting on the saw. Using, say, the right hand piece of each rip as the workpiece, toss the cuttoffs. Flip one of the workpieces as you would for a square setup. They should close perfectly otherwise the discrepancy is twice the amount of correction on the machine - same as with a 90. (??)
A guy on the job suggested that today but I didn't have time this evening to test it out. Will try tomorrow.
Dennis in Bellevue WA
[email protected]
Dennis,
"Plane the other sides to exactly parallel."
There's the necessity for reference to another measuring system (tool). Doesn't meet the test of self-referencing. It's just as accurate to simply compare the cut to a reference 30 degree triangle.
Rich
> .... Doesn't meet the test of self-referencing.
Oops - forgot to read the rules.
Dennis in Bellevue WA
[email protected]
Dennis,
Agree with all the posts here - I've learnt another few ways to do this.
Here's another way
Start by cutting both the ends at the 30 degree nominal cut. Put both cuts together, should create an angle of 60/120 degrees.
Now, use both your drafting triangles. Use the 45/45/90 to establish the 90 degree cut and then butt the 30 degree angle against it = 120 degrees. Now proceed as previously.
Cheers, eddie
I once suffered lots of grief by assuming that the plastic squares in art stores are accurate. Finally I visited half a dozen local art stores and testing a dozen squares, from the cheapest to the most expensive, and found none that was even close to accurate.
In each store it was the same experience. I'd ask the salesperson for the drafting triangles and casually ask whether they were accurate. Disdainfully, he or she would assure me they are. "Mind if I check?" I would ask. Scowling, the salesperson would stand beside me as I found a flat vertical surface, set the base of the square against it and placed a sheet of paper under the square. I'd scribe one ostensibly 90 degree line with the square, flip it over, and scribe another one. Every time the lines were significantly out of alignment. With a speechless salesperson looking on, I'd return the triangle to the shelf and leave the store.
I'm telling you, this happened each and every time. Never did I find a square drafting square in an art store. Nor did I find a square square in any local woodworking store. I would give great betting odds that the 45% side of the triangles were no more accurate than the ostensibly right triangle.
It was in this forum that someone opened my eyes to the possibility of making your own square and fences using techniques similar to those Rick describes here. Those techniques allowed me to make a table saw sled that is perfectly square to the blade, and I routinely set up my radial arm saw in the same way.
Besides the fact that drafting squares aren't really square, they introduce the possibility of error that the "manual" method does not. But in any case, I'd be very leery of using drafting squares for anything but drafting.
it's always been my experience that the drafting triangles are right on, also. i'll have to check mine when i get home...
Mark,
I have an orange drafting triangle. The kind that pipes light hitting the flat face out through the edges so that they look like they're glowing, and throw illumination on the work. (I love such things)
It's square. It's 18" on the square sides. No name on it.
I've never had one that wasn't square. But that's no testimonial. I don't think I've had more than 2 or three in my life.
Rich
the easiest way to test the accuracy of your drafting (or other) triangles... remember pythagoreans theorem? "a" squared plus "b" squared equals "c" squared.
for those who need a refresher, the two sides that make up the 90 degree angle are "a" and "b". get the length of each, square them (multiply them by themself) individually on a calc and add them together. hit the square root button, and whalla. there's your long side's length. if it doesn't add up, it ain't square, and your angles are in the air. if it adds up properly and both sdes "a" and "b" happen to be the same length, congrats! you have a 90-45-45 triangle you can rely on.
the trace and flip method is good, too, but there's room for error. like if the square slides when you're tracing it, or if you move your hand ever so slightly perpendicular to the edge your tracing, the thickness of the square will shift your line as your pencil levers on it.
both my post (brand name) 90-45's are perfect, as is my 90-60-30.
Take all your triangles up to the kitchen table or someplace that's nice and smooth and flat. Lay your best Starrett rule down on the table and place your triangles back-to-back along the rule. That checks the 90's against the 90's.
Dennis in Bellevue WA
[email protected]
Dennis,
Yes, that's the best way, but two triangles checking to be square is not definitive. Each MAY be out just complementing the other. If 3 all match to each other, all three are perfectly square.
Rich
the trace and flip method is good, too, but there's room for error. like if the square slides when you're tracing it, or if you move your hand ever so slightly perpendicular to the edge your tracing, the thickness of the square will shift your line as your pencil levers on it.
And there isn't room for error in measuring the sides of a triangle? To notice the odd tenth of a degree deviation from 90 degrees, you'd have to measure the sides to 0.001 inch accuracy (that's accuracy, not precision). What do you use to make your measurements?
Rich,
I would bet (a little) that the edge of your orange drafting triangle really is glowing. I've had one like that for many years; it's a good tool. A fluorescent organic dye is probably added to the plastic, and when blue or green light hits it, it converts part of the energy to orange and radiates it all directions, including out the edge. From your description and the fact their imprint on the plastic tends to wear off quite quickly , my guess is your's is a Staedtler. About 15 years ago I checked a bunch or triangles and found theirs consistently accurate, other brands less so. Even the well known graphics arts brands produce clunkers. I tried to buy a good see-through rule in the largest graphics dealer in the Hartford, CT area, and not one of their ruler brands agreed with any of the others, causing the salesman's entire belief system to crumble. Some brands don't produce any rulers with inches of the correct length, but some of those cheap grade-school rulers, with the holes for loose-leaf rings and a pencil groove, agree with a Starrett under 3x mag. The peak of the bell curve for quality control is normally at zero error, so if you make enough quantity, many will be on spec essentially by random chance.
Jim
Jim,
Yes, it certainly does fluoresce, now that you have described it. I believe that the light coming out the edges is from "total internal reflection" and is the same process which permits fiber optic strands to transmit light from one end to the other without losing any out the sides.
And I believe that it IS a Staedtler.
Rich
I use an adjustable triangle available at any drafting supply store. Set any angle you want. Quite accurate. Art
I just use a speed square.
TDF
I'm surprised some vernier adjustments aren't available on woodworking machines. Especially on machines that are often used by more then one operator. The machine gets adjusted to exactly how one person reads the scales. Anyone else comes along, and if they just stand differently while making adjustments it's off, the machine accuracy becomes operator specific. A vernier scale would be exceptionally useful on a compound miter saw for carpenters.
Don
Don,
I use the handwheel position on my saw as the "vernier scale". I view the angle pointer as the course scale and the handle position on the handwheel as the fine scale. I put a piece of masking tape with a line indicating the handwheel position for 90, and another for 45. There is still potential for error due to parallax, but not nearly as much compared to trusting the protractor scale. There is also the issue of backlash, but that small error can be almost eliminated by making it a rule to always approach the final setting from the same direction each time.
Given the above and Donald C's (not the same person I assume?) suggestion of interpolating between settings, it should be feasible to get intermediate angles accurately, going by the number of turns on the handle. Since the worm gear, the rack teeth and the radius of the rack in the angle adjustment mechanism are all uniform, it has to follow that the angle adustment is linear. This is just an analysis, not backed by experience- have to try it sometime.
Rick
Rick,
It's a good idea. I've used tape before as a reference when having to do multiple operations repitiously. Since the relationship is linear or 1 to 1, if the screw threads and the rack is consistent, every turn of the wheel should be accurate also. Thanks, I'll give it a try.
BTW, Don and I are not the same posters.
Don
I have the 30 degree proof worked out. It requires one test piece, 2 cuts. It is self referencing.
I'll try it out in a little while when I get home from work.
Rich
jcutrer, if you're not interested in getting a new mitre gauge (i highly recommend incra) then there is another way that will give you extremely accurate results. get your self a set of angle plates from a machinist supply house. you don't need to get starrett, imports will do just fine as even they are accurate to within a few seconds of a degree. you can get a 45 45 90 and a 30 60 90 set for 52 bucks canadian at KBC tools. you can call them at 1 888 kbc tool (and no i don't work for them)
Here's a method for determining that the saw is accurately cutting at 30 degerees. It requires only one test piece. A 2 x 6 seems to be a comfortable size. Length is arbitrary.
Set the saw to "30 degrees." Prepare the test piece with one of the 6" surfaces jointed flat as the reference surface (face 1). With face 1 flat on the saw table, rip the piece approximately down the middle of its 6 inch dimension, resulting in two pieces: A, with a "30 degree" cut and; B, with a "60 degree" cut. If A is more or less than 30, B will be less or more than 30 by the same amount. Put B aside.
Rotate piece A so that the newly-cut face (face 2) is down on the table and rip again so that there are "30 degree" angles at each end of face 2.
The test piece is now an isosceles triangle with the vertex between side 1 and side 3. If the original cut was less than 30 degrees, The acute angles will total less than 60 degrees, the vertex angle will be greater than 120 degrees, and piece B will be greater than 60 degrees.
If the original cut was greater than 30 degrees, the acute angles will total more than 60 degrees, the vertex angle will be less than 120 degrees and piece B will be less than 60 degrees.
Place piece A with side 1 flat on the table. If the original cut was less than 30, the angle between side 3 and the table will be less than 60 degrees. Piece B, with its reference side flat on the table will not fit under piece A because its angle of cut is greater than 60.
If the original cut was greater than 30, piece B will fit under side 3 with a gap twice as great as the cut error plus the cumulative error added by the second cut.
If piece B exactly fits, you're done. If not, adjust the saw according to the direction of misfit and cut another piece. The pieces will fit without a gap only when the cut is exactly 30 degrees.
Rich
Edited 8/29/2002 2:17:59 PM ET by Rich Rose
Edited 8/29/2002 2:19:58 PM ET by Rich Rose
I agree with Rich, get some drafting squares. They're accurate and cheap. The 30 degree setting is no problem, since they not only make 90/45/45 squares, but also 90/60/30.
Jeff
I use a machinists universal bevel. It's a protractor with a vernier scale. Grizzly sells a rather lousy dial version, the fine gears and dust don't mix well, but Enco, MSC and others carry vernier models. It's pretty easy to get within 1/12 of a degree. Yes, they're more expensive than drafting squares but one tool will work for any angle and should last a lifetime. I probably used mine five times today one setting I needed was 59 3/4º which gives me 1/4º for fitting at the toe end of the angle I was working. I makes things a little easier for me to get a perfect fit. I just went to the shop and measured my drafting triangles and they, even the cheap ones, were dead on.
Right now MSC has an import universal bevel for $59 and Enco has a better one made by Fowler for $77.95. Both are listed in their current sale catalogs. If I were ordering, I'd get the Fowler because it has a better magnifier. If anyone needs catalog numbers or contact information let me know.
Regardless of which tool you are using, if it is thin like a drafting triangle, you must make sure that you are measuring with it 90 degrees to the blade, and 90 degrees to the saw table, any tilt or variation off of 90 degrees, and it doesn't matter how accurate you device is. I like to set my blade as close as I can get it, then use other methods discusssed here to verify the accuracy.
I would rather be mountain biking.
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