# how square should square be?



## sunnybob (Apr 3, 2015)

My never ending quest for flat square wood is progressing. very slowly I have to admit, but progressing.
anyway, now i have to ask if i'm on the same page as the rest of you.

i have a sliding table on the front of my router table, and have made a wooden jig that allows me to quickly clamp flat pieces to run them across the cutter to make flat sides.

So, i start with a 9mm thick flat piece of hardwood about 6" (150mm) roughly square,
i run the piece across the cutter to get a flat edge. By turning that wood once and repeating the cut, i get two sides at 90 degrees. but if i do all 4 sides, one from the next, i dont get 90 degrees at the end of it.

After a lot of trial, i realised I had to do 5 sides to get rid of any tolerances from the first cut.
I'm close, the final angle is ONE degree adrift, which means I'm a quarter degree out on each cut.
Without a complete redesign and lots of time and effort, my wooden jig is as good as I can get it.

Remembering my complete ignorance of this kind of thing, am I there yet? 
Or is it normal to get all four completely square?


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## Cherryville Chuck (Sep 28, 2010)

Obviously the closer the better. The main thing is if there are no gaps in any joints when you put your boxes together. If you can't see a problem then for all practical purposes there is no problem. If the 1/4* is causing a problem then instead of starting from square one and risking even worse results is it possible to shim some part of your procedure? The shim might only need to be a couple of thicknesses of paper.


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## Herb Stoops (Aug 28, 2012)

What happens if after you square the end if you use the same side to square the opposite end ,then run the other side? Like Chuck said a piece of paper or tape might correct the "problem", if it is a problem. Wouldn't be a problem for me. Maybe the "dial indicator guys" might have a solution.

Herb


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## DonkeyHody (Jan 22, 2015)

Well now you have opened a can of worms! I remember a recent discussion about whether dial indicators have a place in a woodworking shop. Some of us are hardly more than carpenters. If a cat can't crawl through the crack, it's close enough. Others are much more demanding, requiring joints you can't even feel. The way we get there varies from the artist who carefully planes a joint until it fits just right, to the technician who carefully sets up machinery to make "perfect" cuts every time. "Close Enough" depends on who you are and what you are building. It's not a destination, it's a journey. Your own definition of "Close Enough" will change as your skills progress. Meanwhile, just keep finding ways to get closer.


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## sunnybob (Apr 3, 2015)

The jig is like all my stuff, as basic as basic can be. No way to shim the leading edge without starting all over with a different design.

I thought a little while ago (while I was in the barbers chair) about reversing the wood after the second cut, I'm wondering if that will reverse the angle? if it did i would be dead on. I shall try that as soon as I can.

I have an engineering background which is why I'm trying for such close tolerances, but I've already learnt the hard way that wood moves about a lot.

The effect I really want to achieve is almost marquetry, where the box is made of different woods, and the floor has panels of different colour woods. this is why I am trying so hard for accuracy. Yes, I aim high (lol)


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## Ghidrah (Oct 21, 2008)

Sunnybob,

As soon as you said 5 turns it made me think of William Ng and his method for squaring TS sled fences. If I understand it right the process requires one to compound the error X number of times then measured with calipers. The error is measured over the length of the cut not at the vertex. If your calc of .25° at vertex is correct then at 6" sides, you are out of square opposite the vertex approx 13/512" + or -.


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## sunnybob (Apr 3, 2015)

ok, youve blinded me with science, where do i get a tape measure in 512ths? (G)
I reckon do two sides rotating the wood. The flip the wood and do the other two sides. i think that equals plus minus minus equals zero.


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## tomp913 (Mar 7, 2014)

sunnybob said:


> ok, youve blinded me with science, where do i get a tape measure in 512ths? (G)
> I reckon do two sides rotating the wood. The flip the wood and do the other two sides. i think that equals plus minus minus equals zero.


How is the sliding table indexed to the main table? As Ghidrah states, the 5-cut method is typically used for checking squareness of a sled, and it checked by measuring the "taper" of the strip left after the 5th cut. For your router table, where you're just truing up the edges of a piece of wood, the adjustment has to be made in the mechanism which locate the sub-table which slides past the cutter. Look at how this table is referenced relative to the cutter, and see if there is a way that you can make this adjustable, adding/subtracting paper shims is a good (low tech) way to accomplish this. I have an old Delta shaper where the wooden fences are shimmed to the table top with strips of playing card - I always meant to take it to work and have them skim it on the mill but never got around to it, the strips of card have worked for over 20 years with no problem.


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## DaninVan (Jan 1, 2012)

Wouldn't doing the 'do 1 side then flip and do the opposite side' simply give you two pairs of parallel sides? Basically a parallelogram with the corners not necessarily at 90deg?

This is reminding me of my SiL working with me doing the new 2x2 spindles on his back porch. I wanted to do the center spindle then use a 2" spacer to set the adjacent ones consecutively going in both directions away from the center. 
Nope. Apparently that's not accurate enough; he had to do each one by measuring top and bottom to a 32nd" ....zzzzzzzzzzzzzz


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## sunnybob (Apr 3, 2015)

Tom, you might be on to something there. Its a very basic system with wooden slats sliding between two ally rails. i always push the unit towards the cutter to take out the very minor slop in the slider. I could just about get a thickness of paper on the front edge of the rail which might tip the whole sled enough.

Dan, TWO sides, not one.
Cut one side, then use that as reference to cut side two. This now has a quarter degree angle. use side two to cut side three. This now has a half degree angle. Flip the wood top to bottom and do side four, this has removed a quarter. do side three again, and your back to 90 degrees.

Thats my theory, based on nothing more than hope. i shall try to prove or disprove it tomorrow morning, but we are going away for 3 days, so it depends what time the packing is finished.

Ordinarily, I would agree that this is very small potatoes, but i want to match five different shapes into one box base, so I'm testing myself.


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## DaninVan (Jan 1, 2012)

We may be talking at cross purposes,Bob?
What Herb suggested tries to avoid the cumulative error factor.
Router Forums - View Single Post - how square should square be?


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## sunnybob (Apr 3, 2015)

That seems to be what I meant, but said a different way. I've always had problems visualising in 3D. i can make it, but I cant draw or "see it" without having my hands on it.


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## tomp913 (Mar 7, 2014)

sunnybob said:


> Tom, you might be on to something there. Its a very basic system with wooden slats sliding between two ally rails. i always push the unit towards the cutter to take out the very minor slop in the slider. I could just about get a thickness of paper on the front edge of the rail which might tip the whole sled enough.
> 
> Dan, TWO sides, not one.
> Cut one side, then use that as reference to cut side two. This now has a quarter degree angle. use side two to cut side three. This now has a half degree angle. Flip the wood top to bottom and do side four, this has removed a quarter. do side three again, and your back to 90 degrees.
> ...


Firstly, you need all the slop out of your guide system and then you need a second fence at 90° to the initial guide. In essence what you're trying to do is mimic a jointer/planer. You start off by truing up the first edge, but just rotating the part and using the 3rd edge as reference will only give you a trued edge that's parallel to edge #4, you haven't cut it square to edge #1. As Dan said, if you start with a parallelogram with no square corner, your set-up is not going to correct the starting condition. If you have the second fence and put side #1 against it, then side #2 will be at 90° and so on. Think of squaring a block on a jointer - flatten side #1 and then, with side #1 against the fence, machine side #2 at 90° to side #1. At that point, you normally switch to the planer and make two (or more, depending on material removal) passes with face #1 and then face #2 against the table - this makes #3 parallel to #1 and #4 parallel to #2, and everything is square because you started with faces #1 and 2 at 90°.


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## Herb Stoops (Aug 28, 2012)

DaninVan said:


> Wouldn't doing the 'do 1 side then flip and do the opposite side' simply give you two pairs of parallel sides? Basically a parallelogram with the corners not necessarily at 90deg?
> 
> This is reminding me of my SiL working with me doing the new 2x2 spindles on his back porch. I wanted to do the center spindle then use a 2" spacer to set the adjacent ones consecutively going in both directions away from the center.
> Nope. Apparently that's not accurate enough; he had to do each one by measuring top and bottom to a 32nd" ....zzzzzzzzzzzzzz


Get him a dial indicator for Christmas,Dan.

Herb


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## Ghidrah (Oct 21, 2008)

Sunnybob,

I don't think there is a usable tape at that range outside of a microscope, but if you want to drive yourself mental, calipers is the closest you're likely to get. 

Degrees = (A/R) • (180/PI) 

This can be worked both ways to find "A" or "degrees" the only constant is (180/PI) which is rounded out to = 57.2957795 = 1 radian. To me, at best this a mind exercise, to actually measure "A" or Degrees accurately is worse than watching paint dry or a golf tournament or my oldest playing an RPG.

If you were able to physically and accurately mark out .25 degrees, (I can't, I think even my Exacto tip is too thick)


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## tomp913 (Mar 7, 2014)

Bob,

I understand that you're making smallish boxes, and trying to square up the individual pieces and cut them to size on the router table. I think that there's a way to accomplish this without any elaborate sliding fixture, assuming that you have a fence and enough room on your router table to the FRONT of the bit to accommodate the size part that you need. Starting with pieces cut roughly to size and not square, you need a way to get two edges 90° to each other, and I think that this will work. Starting with edge #3 against the fence, take a skim cut on edge #1 opposite to it. Now you need a fixture - just a piece of plywood, a little narrower than your finished size and with a fence at 90° to the length screwed to it. Put the workpiece on top of the plywood fixture, and with edge #1 against the fixture fence, run it past the table fence taking a skim on edge #2 - edges #1 and #2 are now perpendicular to each other. Take the fixture off, adjust the table fence to give you the final size and take two passes, one with edge #1 against the fence and the final one with edge #2 - the part is now square and to finished size. If you attach the fence to the fixture with screws, you can adjust the fence while making test pieces until you have as accurate a 90° angle as you need - you should have an accurate square in your shop that should let you get pretty close for a first try. The explanation is a little involved, but it's really pretty simple - the way it works is because the router table will always give you parallel surfaces, the trick is just to get two of the surfaces perpendicular first before cutting to the finished size.


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## Herb Stoops (Aug 28, 2012)

Ghidrah said:


> Sunnybob,
> 
> I don't think there is a usable tape at that range outside of a microscope, but if you want to drive yourself mental, calipers is the closest you're likely to get.
> 
> ...


I agree with Ghidrah.

Herb


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## Ratbob (Apr 6, 2015)

Ghidrah said:


> Sunnybob,
> 
> I don't think there is a usable tape at that range outside of a microscope, but if you want to drive yourself mental, calipers is the closest you're likely to get.
> 
> ...


Not sure what arc length (A in your drawing) has to do with this problem. It's simply a matter of scale. A 0.25* error from 90* will result in less than 1/32" across 6", in most cases acceptable. If you extend that error to 6' the error is now greater than 5/16" which is unacceptable.


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## mgmine (Jan 16, 2012)

Think of it this way, how perfect were the joints used by craftsman in the 17th century? They were using hand tools yet everything looked perfect. I can't picture what a 1 degree error would look like but I'm sure that once you change anything at all on your saw (such as a new blade) this one degree is going to change somewhat. Even raising or lowering the blade will change things.Or for that matter a piece of wood that is surfaced differently will ride through the saw differently. I put a square on the cut piece and if I don't see light I call it square.


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## Quillman (Aug 16, 2010)

Checking squareness with squares is folly.
Squares are indicators not measuring tools.
Precisie parallelism and squareness measurements require sophisticated measuring tools
and conditions. If rough meaurements in a foot or so of material show errors
on the order of the meaurement error (i.e. using a rule to 1/32" allows meaurement only to the nearest 1/32") it might be more prudent to get on with the project.

Just 10' of angle error (1/6 of a degree) will produce a 1/32" error in parallelism/foot.
Cancelling that error, x rotating the work against the saw fence 5 x, is a rediculous practice.
Chasing that kind of error with measuring tools to 1/32" is a waste of time. Moreover, without a lens, you cannot read a rule to 1/64"ths, a common scale interval.

Jigs and fixtures, on the other hand, do require precision.
If you must chase a mil (.001") do it with your fixturing.
If your jigs are screwed up, all the cuttings from those jigs will be a guess and x-golly.
Controlling squareness, straightness and parallelism demands more than ordinary
equipment. Took me > 4 months to design and create a rectangle maker.
With its sleds I can hold .001"/24" of parallelism in wood, plastic and aluminum.
Squareness requires a special calibrated x-cut sled. You don't want to go through
that much hell for a dining room table top.
Just cut, mill, assemble, don't worry , be happy.


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## DesertRatTom (Jul 3, 2012)

This is why they invented jointers. Make sure the outfeed table is the same height as the cutter at its highest point. Use a Wixey to set the fence 90 to the table. This gives you the flat, square edge you need to start with. Now use the planer to flatten one surface butting the known straight/90 edge to the fence. 

Next, Wixey the table saw blade 90 to the table, and use any of several methods to make certain the blade is parallel to the miter slot. Use any type of gauge you prefer to make sure the fence is perfectly parallel to the slot, or slightly skewed at the outfeed end by up to 4/1000ts. Now cut the second edge of your piece with the known flat edge of the workpiece against the fence. Depending on the quality and condition of the blade, and any run out, you will be getting about as square a piece of wood as your equipment will deliver. Yup, your tools are a factor here. This, by the way, explains why buying a high end aftermarket fence is on so many of our wish lists.

Check out any of the used table saw books you will find in abundance on Amazon, any one of the good ones will guide you through the setup process.

Errors introduced by the saw alone will drive you nuts because until the saw setup is absolutely perfect (impossible), you are going to have slight variations. Yes, you want to eliminate as many errors and inaccuracies as possible, but if you have done all the above, then you are at the limits of your tools. Even slight changes in how you feed the wood into the blade will cause slight deviations. Heck, bearings wear over time and introduce errors as well. I prefer dial gauges for setting up, they help get you as close as is possible with the tools you have and they don't have batteries that are dead every time you try to use a digital gauge. Stop driving yourself nuts. If wood projects turn out great, you're doing fine. Wood moves. 

I agree with Quillman that pursuing perfection on jigs is critical, yet still, if you make anything perfect, I suggest you have had a happy accident. Consider "flat" tables on a table saw. They are NEVER perfectly flat. Relax, make boxes, enjoy the process and replace or repair any tool that is messing you up. Buying only top grade saw blades helps as well.


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## DaninVan (Jan 1, 2012)

*?*



tomp913 said:


> Bob,
> 
> I understand that you're making smallish boxes, and trying to square up the individual pieces and cut them to size on the router table. I think that there's a way to accomplish this without any elaborate sliding fixture, assuming that you have a fence and enough room on your router table to the FRONT of the bit to accommodate the size part that you need. Starting with pieces cut roughly to size and not square, you need a way to get two edges 90° to each other, and I think that this will work. Starting with edge #3 against the fence, take a skim cut on edge #1 opposite to it. Now you need a fixture - just a piece of plywood, a little narrower than your finished size and with a fence at 90° to the length screwed to it. Put the workpiece on top of the plywood fixture, and with edge #1 against the fixture fence, run it past the table fence taking a skim on edge #2 - edges #1 and #2 are now perpendicular to each other. Take the fixture off, adjust the table fence to give you the final size and take two passes, one with edge #1 against the fence and the final one with edge #2 - the part is now square and to finished size. If you attach the fence to the fixture with screws, you can adjust the fence while making test pieces until you have as accurate a 90° angle as you need - you should have an accurate square in your shop that should let you get pretty close for a first try. The explanation is a little involved, but it's really pretty simple - the way it works is because the router table will always give you parallel surfaces, the trick is just to get two of the surfaces perpendicular first before cutting to the finished size.


Tom; i may be missing something(?)...
Are you suggesting runing his material between the bit and the fence?
I thought that was a serious infraction? (Trapping the material between the fence and the bit).
I still don't have a RT so not something I'm likely to encounter, but I think_ I need to be aware of the ground rules._


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## tomp913 (Mar 7, 2014)

DaninVan said:


> Tom; i may be missing something(?)...
> Are you suggesting runing his material between the bit and the fence?
> I thought that was a serious infraction? (Trapping the material between the fence and the bit).
> I still don't have a RT so not something I'm likely to encounter, but I think_ I need to be aware of the ground rules._


Dan,

I read in an Incra book that it was OK to have the part between the fence and bit as long as the feed direction resulted in climb cutting, and that appeared to me to be essentially what @sunnybob was doing based on his description. On further research, I see that this is NOT the correct way to do things, and I sincerely apologize for suggesting it.

Moderator - is it possible to remove my posting so that nobody tries to do what I describe?


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## Ghidrah (Oct 21, 2008)

Ratbob,

Degrees and (A/R) are variable, "MY" example uses a 6" radius, any radius (you) choose can be plugged into the formula. (2 • 6 • π/4= "A"= .25 of C) .25% of a circumference with a 6" radius is 9.42477* = 90°. Add or subtract from that number, "A" and you + or - 90°. Change the length of "A" and you change the angle of degrees at the vertex. 

The length of "R" is irrelevant, the length of "A" is relevant to "R", "C" and whether it equals 90° or not.

(Working backwards when .25° is known)
.25°/ 57.2957303364*(= 1 radian, is result of 180/ π) = .00436330366* (is result of A/R) • 6 (6= R) = "A"=.0043633266" = approx 13/512". 

.25° angle @ 6"Ø = + or - .0043633266 of 9.4247779605. The tedium occurs when (° or "A") is unknown.

P.S.
A/R, fixing error in "A"
"A"= .0261799612*= approx. 13/512"


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## Nickp (Dec 4, 2012)

DaninVan said:


> Wouldn't doing the 'do 1 side then flip and do the opposite side' simply give you two pairs of parallel sides? Basically a parallelogram with the corners not necessarily at 90deg?
> 
> This is reminding me of my SiL working with me doing the new 2x2 spindles on his back porch. I wanted to do the center spindle then use a 2" spacer to set the adjacent ones consecutively going in both directions away from the center.
> Nope. Apparently that's not accurate enough; he had to do each one by measuring top and bottom to a 32nd" ....zzzzzzzzzzzzzz


I'm with you, Dan...I do the center and go left and right with a spacer. But I don't let anybody else do the center spindle... 

...can't let go of everything...


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## tomp913 (Mar 7, 2014)

I spent a lot of years talking to customers about a product that had a misalignment capacity of 0.5° which was simplified to an offset of .008 in/in, much easier to discuss. For the 6" part having an angle differing from 90° by 1/4°, the vertical leg would be off by, in round numbers, .024". If you cut two test pieces using the same set up and put them back to back, the cumulative error would be .048", a pretty obvious deviation. I think that most woodworkers work to much tighter tolerances without realizing it. Think about checking the set-up on your miter gauge; the usual test it to cross-cut a piece, flip it edge for edge and check for a gap between the cut ends, Adjustments are then made until the gap is close enough to satisfy the user, and much less than 1/4°.

Using the same criteria, think of a pantry cabinet 30" wide x 84" tall - if the corner angle is off by 1/4°, the corner-to-corner dimensions will differ by .246" (if I did the math correctly) - I certainly wouldn't be happy with a cabinet that far off, and shoot for the diagonals to be identical within the thickness of the tick mark on the tape measure.

I cut my cross-cut my cabinet panels with a track saw that has an attached (adjustable) fence that works like a T-square, and made a fixture to set/check the setting. I used a piece of birch plywood and laid out a perpendicular to the base edge with trammels and then attached a strip of aluminum to the plywood. Checking the angle on the track takes a few seconds, and the fixture gives me consistent accurate 90° crosscuts.


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## Ghidrah (Oct 21, 2008)

Tomp913,
I agree, the longer the line the easier it is to see especially when near other vertical linear objects. When I was framing regular I could see a 1/4" out of plumb in 8' to 10', not in the horizontal. Our eyes are geared for the vertical. However speaking of trim only regardless of the length of a side, a .25° error off 90° is invisible for a piece of trim 2.5" to 6" wide


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## tomp913 (Mar 7, 2014)

Having been born with strabismus - surgically corrected initially when I was a toddler but the condition returned. I had my last (and I do mean last) operation 8 or 9 years ago at which time they discovered that the inside muscle in both eyes had become detached from the eyeball. The surgery corrected the condition for a short while but the eye has since drifted again and at my age I'm not willing to give them another try. Long term, this has resulted in the condition where I can't consciously focus with both eyes at the same time and wind up focusing primarily with my right (dominant) eye but can still see out of both eyes. Really stumped the MVA until my surgeon filled out a certificate for me - I have poor depth perception and can't judge vertical very well, at least relatively close up.

I agree that the end of trim being off by 1/4° is probably not noticeable unless it butts up against another piece of trim - for example, the ends of the apron off by 1/4° wouldn't matter, but you would see a gap where the side casing butted against the stool.


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## Cherryville Chuck (Sep 28, 2010)

tomp913 said:


> Dan,
> 
> I read in an Incra book that it was OK to have the part between the fence and bit as long as the feed direction resulted in climb cutting, and that appeared to me to be essentially what @sunnybob was doing based on his description. On further research, I see that this is NOT the correct way to do things, and I sincerely apologize for suggesting it.
> 
> Moderator - is it possible to remove my posting so that nobody tries to do what I describe?


Tom I can delete it if others think it is necessary but an explanation of the problem might be more useful. 

In normal table routing (with the bit only partially exposed by the fence) feed direction is from right to left because of the spin of the bit. Feed direction is opposite to bit spin. What many newbies don't realize is that when the wood is between the fence and the bit that feed direction is reversed. Left to right is now opposite bit spin. 

If you are using the table normally and you feed the wrong direction, i.e. left to right, you climb cut and the router bit starts to self feed but also pushes the wood away from the fence at the same time. The wood may get thrown but probably not far. What is more dangerous is that your hand may get drug into the bit.

If you have the wood trapped between the fence and the bit and you feed right to left you will be feeding in the same direction as the bit spin and the wood will self feed causing it to be ejected at very high speed with the possibilities of breaking a bit and bending the armature on the router plus possibly dragging a hand into the bit. Proper feed direction would be from the other direction. However, if you start feeding from left to right and the wood wanders away from the fence the bit will catch it and throw it back at you and at very high speed.

There is a you tube video I've seen where Bill Hylton does this operation to prevent chip out on something (sorry, can't remember what the job was anymore) but he put a fence on BOTH sides of the wood so that it really was trapped. If you do it that way then it is no longer dangerous. But to effectively trap it like this the board already needs to be parallel to stay tight between two fences, so it would not be a wise method to use to true something up.

If this isn't clear to anyone reading it then please speak up.


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## Herb Stoops (Aug 28, 2012)

Charles, a few years ago I was making some lattes screens for a persons deck and it was a simple 2X2 cedar frame dado-ed out with 2' wide lattes panels fitted inside the frame. 
So when I was running the 2X2's thru the router to route out the dado, the first one I was feeding right to left and about 2' into the cut,the router bit grabs the 2X2 and shot it out the other side. So I set up feather boards and fed the next one thru from left to right and it went good so did the rest that way. So now whenever I do dado's on the router table I feed left to right, but I make sure that I use feather boards so they can't reverse direction.

Herb


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## DonkeyHody (Jan 22, 2015)

Chuck,
Thanks for the clear explanation. I've always heard not to trap the wood between bit and fence, but I never really thought about why.


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## Jerry Bowen (Jun 25, 2011)

Bob,

Truth is, there is no such thing as "perfectly square", same thing, no such thing as perfectly parallel lines. Of course your question about how square is square enough is legitiment as the world that we live with is such that square enough is what we seek and live with. I suspect that the project or application will dictate the degree of perfection that is required.

Your question, IMHO is a very good one especially in the context of wood working. My "Guarenteed Square" six inch square is guaranteed to be squard within .001", which means that it is reasonable close to being square enough for most applications, but is not truly "square". You have to really be a "nit picker" like I am to spend much time thinking very long about such things, I'm sure that this trait that I have is a curse or a blessing.

Jerry


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## Cherryville Chuck (Sep 28, 2010)

Herb Stoops said:


> Charles, a few years ago I was making some lattes screens for a persons deck and it was a simple 2X2 cedar frame dado-ed out with 2' wide lattes panels fitted inside the frame.
> So when I was running the 2X2's thru the router to route out the dado, the first one I was feeding right to left and about 2' into the cut,the router bit grabs the 2X2 and shot it out the other side. So I set up feather boards and fed the next one thru from left to right and it went good so did the rest that way. So now whenever I do dado's on the router table I feed left to right, but I make sure that I use feather boards so they can't reverse direction.
> 
> Herb


I was was listening to a podcast of one of Fine Woodworking's editors and he talked about mistakenly feeding the wrong direction in a similar case to yours Herb. He was cutting a dado in a piece and the dado was wider than the bit so 2 passes were needed. He cut the first one which went fine as the forces on each side of the bit balanced out. On the second pass he moved the fence closer to the bit and automatically started feeding from right to left as we normally do. But when he moved the fence closer he was cutting with the inside edge of the bit instead of the outside edge like we normally do. When you do that you are feeding with the spin of the bit and the bit took the wood and launched it. Had he routed the first pass with the fence closer and then moved the fence farther away from the bit for the second pass he would have been fine.

This is one of the reasons I encourage newcomers that the basic rule is to feed against the spin instead of trying to remember all the variations. Feeding against the spin is the simplest way to analyze for correct feed direction.


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## DesertRatTom (Jul 3, 2012)

tomp913 said:


> Having been born with strabismus - surgically corrected initially when I was a toddler but the condition returned. I had my last (and I do mean last) operation 8 or 9 years ago at which time they discovered that the inside muscle in both eyes had become detached from the eyeball. The surgery corrected the condition for a short while but the eye has since drifted again and at my age I'm not willing to give them another try. Long term, this has resulted in the condition where I can't consciously focus with both eyes at the same time and wind up focusing primarily with my right (dominant) eye but can still see out of both eyes. Really stumped the MVA until my surgeon filled out a certificate for me - I have poor depth perception and can't judge vertical very well, at least relatively close up.
> 
> I agree that the end of trim being off by 1/4° is probably not noticeable unless it butts up against another piece of trim - for example, the ends of the apron off by 1/4° wouldn't matter, but you would see a gap where the side casing butted against the stool.


Regarding strabismus: Too bad you did all that surgery. The results are very poor from surgery, less than 17 percent of patients recover full binocular vision. But there may still be a way to eliminate it. Get the book "Fixing My Gaze" by Susan Barry. I work with the kind of eye doctor she talks about that do non surgical correction of strabismus. It has a far better success rate, but multiple surgeries make it more complicated because every time thy separate the muscles from the eyeball, they destroy some of the cells that tell the brain where the eyeball is positioned. Get the book. Dr. Barry is a professor of neurology at Mt. Holyoke college who had infant strabismus and multiple surgeries. She had it fixed for good when she was middle aged. Have met her several times at doctor meetings. Very down to earth, and she explains the neurology in a really clear way.


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## Jerry Bowen (Jun 25, 2011)

DesertRatTom said:


> Regarding strabismus: Too bad you did all that surgery. The results are very poor from surgery, less than 17 percent of patients recover full binocular vision. But there may still be a way to eliminate it. Get the book "Fixing My Gaze" by Susan Barry. I work with the kind of eye doctor she talks about that do non surgical correction of strabismus. It has a far better success rate, but multiple surgeries make it more complicated because every time thy separate the muscles from the eyeball, they destroy some of the cells that tell the brain where the eyeball is positioned. Get the book. Dr. Barry is a professor of neurology at Mt. Holyoke college who had infant strabismus and multiple surgeries. She had it fixed for good when she was middle aged. Have met her several times at doctor meetings. Very down to earth, and she explains the neurology in a really clear way.


Tom,
The biggest part of my vision proble, or so we believe at this time, is due to my optic nerve having been crushed due an accident when I about three years old. Not much can be done to correct the damage that was done, or so I am told, but thank you for your concern.

Jerry


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## RainMan 2.0 (May 6, 2014)

Jerry Bowen said:


> Tom,
> The biggest part of my vision proble, or so we believe at this time, is due to my optic nerve having been crushed due an accident when I about three years old. Not much can be done to correct the damage that was done, or so I am told, but thank you for your concern.
> 
> Jerry


Jerry I sure wish they'ed make bigger strides with this promicing looking stem cell research . I pretty much need a whole new body 

Jerry are both optic nerves damaged ? You have close to the same vision in each eye ?


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## Herb Stoops (Aug 28, 2012)

Cherryville Chuck said:


> I was was listening to a podcast of one of Fine Woodworking's editors and he talked about mistakenly feeding the wrong direction in a similar case to yours Herb. He was cutting a dado in a piece and the dado was wider than the bit so 2 passes were needed. He cut the first one which went fine as the forces on each side of the bit balanced out. On the second pass he moved the fence closer to the bit and automatically started feeding from right to left as we normally do. But when he moved the fence closer he was cutting with the inside edge of the bit instead of the outside edge like we normally do. When you do that you are feeding with the spin of the bit and the bit took the wood and launched it. Had he routed the first pass with the fence closer and then moved the fence farther away from the bit for the second pass he would have been fine.
> 
> This is one of the reasons I encourage newcomers that the basic rule is to feed against the spin instead of trying to remember all the variations. Feeding against the spin is the simplest way to analyze for correct feed direction.


Tom you are right in instructing fellow woodworkers the correct way to use a router table. I am not contradicting that. I was just just relating an experience I had Dadoing. and how I overcame it. 
Dadoing on a router table is sort of dicey, the bit is buried all way around in the wood and it has to be guided by the fence, thus trapping it between the bit and the fence. 
Hand routing is different as a straight edge/jig is used with the base of the router or bushing riding against it. This seems to me a safer way to dado with a router. Still have to route against the rotation of the bit. Narrow stock is hard to hand route and seems like the best way in on the table saw or router table. I have seen carpenters score the dado cut on the table saw then route them on the router table also with a smaller bit, when they didn't have a T/S dado set.

Herb


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## Jerry Bowen (Jun 25, 2011)

Herb Stoops said:


> Tom you are right in instructing fellow woodworkers the correct way to use a router table. I am not contradicting that. I was just just relating an experience I had Dadoing. and how I overcame it.
> Dadoing on a router table is sort of dicey, the bit is buried all way around in the wood and it has to be guided by the fence, thus trapping it between the bit and the fence.
> Hand routing is different as a straight edge/jig is used with the base of the router or bushing riding against it. This seems to me a safer way to dado with a router. Still have to route against the rotation of the bit. Narrow stock is hard to hand route and seems like the best way in on the table saw or router table. I have seen carpenters score the dado cut on the table saw then route them on the router table also with a smaller bit, when they didn't have a T/S dado set.
> 
> Herb



Herb
When setting the Incra Jig to do to joinery work, one of the first steps is to get the bit set at the proper distance from the fence so tht it cuts a dado dead center. Once done, all of the cuts will be collective will be centered on the workpieced when cut. Because of this, I have learned and have never had a problem cutting dados on the router table. One needs the correct diameter bit and as pointed out, if the first cut is not wide enough you "ALWAYS" move the fence away from before making the widening cut or cuts as required. 

I have never needed to cut a dado with a hand held router but it looks to me at first blush that it could be a "BUG A BOO" to me.

Jerry

Jerry


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## Jerry Bowen (Jun 25, 2011)

TheCableGuy said:


> Jerry I sure wish they'ed make bigger strides with this promicing looking stem cell research . I pretty much need a whole new body
> 
> Jerry are both optic nerves damaged ? You have close to the same vision in each eye ?


That's an interesting question, in that the doctors have always used the term "nerve" singular implying that there is only one nerve. I assum that there is only one but don't know. 

This sure makes me wonder now that you have asked, UMMMMM.

I see no difference in the vision of my eyes. I so know that recently the vision in my right eye is beginning to worse than my left, but only recently. I notice now that if I work up a sweat, either when walking or working in the shop that the nearly blinds my right eye but it clears up when I stop perspiring and the sweat in my eye is dried up.

It's my central vision that is impaired which means that see pretty well with my peripheral vision. When, for example I look at my dog in my peripheral vision, she is pretty clean, but when I try to look directly at her she disappears. This problem is remedied when the light is cut down with dark glasses and say glasses plural, one pair won't do the job for me.

Jerry


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## sunnybob (Apr 3, 2015)

Wow, I certainly started something here, didnt I?

I've been away for 3 days so am just catching up.

The original cause of this question, was that I was trying to make a decorative base involving a square of indian rosewood surrounded by beech, inside an octagonal trinket box. because the rosewood is central in the design, i wanted all edges square to each other. When i finished and put a metal square to two of the edges, there was a small error which I felt was within bounds, but when I put the square on the third corner of the 4" square piece, there was enough daylight under the far end of the metal square to easily slide a credit card through. Not acceptable.

I shall rethink the jig I'm using, and possibly make another with improved clamping of the piece.
As always, all your suggestions have been helpful (even if the mathematical ones went waaaay over my head (lol)


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## tomp913 (Mar 7, 2014)

DesertRatTom said:


> Regarding strabismus: Too bad you did all that surgery. The results are very poor from surgery, less than 17 percent of patients recover full binocular vision. But there may still be a way to eliminate it. Get the book "Fixing My Gaze" by Susan Barry. I work with the kind of eye doctor she talks about that do non surgical correction of strabismus. It has a far better success rate, but multiple surgeries make it more complicated because every time thy separate the muscles from the eyeball, they destroy some of the cells that tell the brain where the eyeball is positioned. Get the book. Dr. Barry is a professor of neurology at Mt. Holyoke college who had infant strabismus and multiple surgeries. She had it fixed for good when she was middle aged. Have met her several times at doctor meetings. Very down to earth, and she explains the neurology in a really clear way.


That sounds like an interesting book - I see that it's available on Amazon for Kindle so will buy a copy. The surgeon who did the operation didn't believe in post-operative exercises/therapy, whereas my optometrist was very insistent that they should be a required part of the process (an interesting situation as the optometrist is his FIL), maybe part of the reason that I didn't follow through with a second surgery.


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