I have been constructing a new crosscut sled, and the thought came to me,
how close does this need to be to make nice joints...
Instead of using a square I cut the sides off an 8" square of birch
plywood, I then ripped a strip off the first side and measured the
difference with a dial caliper, and over 8" there is less than 1/128
difference, but that would be compounded over 4 cuts right?
So would you guys try to get it closer of just leave it as is?
I might try to get it closer but some times measurements can deceive or may
not be done accurately. Sawing technique can often render measurements
Use some scrap wood, make a frame and ask yourself, is that good enough?
Keep in mind that opposite parallel sides must be exactly the same length
also or even perfect 45's will not close properly. Use a stop to insure
same length "opposite" sides.
its kinda funny....but I was able to get it almost perfect, within a
needles width on the dial caliper, I would think that would be close
enough, but last night I had painstakingly straightend and squared the
bit that would become the main fence and after all that I managed to
install it with the wrong face to the saw....after switching things
around my test cuts came out much better....
In lots of situations, the precision of decent eyeballs and finger tips
is actually very useful for checks.
Thickness planer parallelism - plane a board, cut it in half, put
opposite edges together, rub the fingers over the meeting point.
Table saw blade or miter gauge/sled 90 degree accuracy - Cut a board in
half, flip one board, place the cut edges together and check for gaps.
If they don't work out, the calibration tools make recalibration easier
and faster than more test cuts, but the cuts are good enough for
in-service spot checks.
That is not what I was talking about, I'd be willing to bet that you would
find nothing wrong with my precision and or joints. It's that with years of
experience you learn how to achieve that with out having to use high
precision measuring tools with every adjustment.
Case in point, you bought a new Powermatic 2000 TS. If your measuring and
precision set ups on your old Delta saw were good why change saws? I'm just
saying that a precision measurement is not always the answer to a problem.
It sparked a spirited discussion; however, it clearly defines a few
In the data acquisition business, if you truly want an accurate
measurement, you make a differential measurement, not a single ended
Single ended measurements introduce instrument as well as people
errors into the measurement, something differential measurements
eliminate because they cancel out.
Using ANY measuring instrument to make a measurement is a single ended
Ask 5 people to make a measurement with a micrometer of vernier
caliper, and chances are pretty good you will get 5 different answers.
Set up a table saw, cut a piece, then break the set up.
Now reset the fence to the same dimension, cut a 2nd piece and compare
it with the first.
They will be close, but they will be different.
I submit your fingers are the best instrument for this measurement.
Biggest reason I know for "sizing" all the material for a job using a
single setting for the tool (Planer, table saw, etc) as the first step
in processing the wood.
BTW, you also do it all at the same time.
Weather conditions tomorrow will be different than today.
Lessons learned the hard way AKA: Expensive.
That would be my point. I am indicating that measuring will not always over
come techique and when you are talking a visible or invisible joint line the
technique problem may be so small that it could involve dozens of factors.
Including but not restricted to, is your table flat, is your stock perfectly
straight, are you working with soft or hard wood, is you blade "sharp", is
the surface of your table smooth, and the list goes on.
It certainly does it for me. Because we are not machines there will always
be some degree of imperfection with every cut. Measurements only get you so
close and if you were able to obtain the perfect setting your technique will
always add some degree of error from one cut to the next.
That is fine but if the precice calibration only corrects 10% of the problem
you need to learn how to make compensations to remedy the problem.
AND going back to my original points to the OP, dial calipers are good for
measuring and setting up equipment. The results of using that equipment is
not guaranteed to give good results when using wood as the material to
All of them if you can compensate, but for instance a precicely calibrated
saw will not eleminate tear out on the back side of a cut. There are other
factors to consider to minimise the tear out. Excessive tear out can ruine
a joint and technique can certainly minimize tear out. For instance when
cutting a 45 degree miter on your TS if you have the miter gauge clocked to
45 in a particular direction it prioduces a better/cleaner cut than if you
clock the gauge to 45 degreesin in the opposite direction. This all falls
into technique and no amout of precision will make both setting equal in
results on a consistant basis.
I couldn't agree more with everything Leon said, not the least being
to try it out to see for yourself.
You are talking about making a wooden device that you think will hold
tolerances to within one 0.0078125th of an inch. Think about it; a
wooden jig that will hold completely true through humidity changes,
temperature changes, techniques differences, movement of the sled in
response to different weight, density and size of material, etc.,
etc. Not happenin'.
Don't cheat yourself For dead bang spot on, buy a calibrated miter
Or... just use your miter saw. I for one have never understood the
folks that have to use their tablesaw for everything from precision
miter work for small pieces like building picture frames to making
raised panel doors.
Maybe its just me. I could see it on really large pieces I guess, but
even then... how often does one need a miter on a 12" board?
So why not eliminate the error you have control over (the original
calibration)?? Why settle for a sloppy calibration because you might
experience wood movement?
Error Total = Error in calibration + error from wood movement over time +
The 'error in calibration' can be eliminated completely w/o making a single
LMAO.... pretty hot issue, eh? I like it when someone replies to
their own posting.
You missed my point. You should always get your jigs, measuring
devices, etc. as close to perfect as you can.
We were talking about a >>WOODEN<< jig. In my experience, I have
never seen a usable wooden jig hold to perfect tolerance under all
conditions. Close, but not perfect. Obviously you feel differently.
To me, if I am to put a lot of time and effort into making something,
it needs to a design that can perform to the standards I want. Wood
can be a satisfactory fabrication medium for certain things, but not
repeatability of tolerances within a couple of thousands over a period
But since DCH didn't post what size board he was using, how do we know
what the table saw is the best tool for the job? What if he is
cutting 4" or 6" wide material? Should he be using a table saw and a
Certainly if that is the case, I would put any of my three miter saws
against his table saw and shop built jig. And for compound cuts, a
table saw is not even a consideration if I can get it under my miter
The milled aluminum and steel bed and fence calibrated with my
machinest's square are much more comfortable for me to rely on than
plywood, mdf, white glue,. hardwood, etc.
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