Replies

1. 
   HowardAcheson | Jan 10, 2011 11:40am | #1

   You can certainly make your own jig that can run in the miter slot.  Many do.

   Here is the low tech, low cost way to align a tablesaw that I learned maybe forty years ago and use to teach to my students.

   Make 3/4 x 3/4 x 12" hardwood stick. Drill a hole somewhat centered in one end and insert a brass #8 x 1" round head fine thread machine screw about half way. UNPLUG THE SAW.  Raise the blade completely up. Clamp this board in your miter gauge (if you determine that there is some slop in your slot to miter gauge, use a playing card to take up the slop) so the screw head just about touches the blade at the front. Now rotate the blade by hand and determine which tooth is the closest. Adjust the screw in or out until it just touches this tooth. Mark this tooth. Rotate the blade so the tooth is now at the back of the table and move the miter gauge/stick assembly to the back and see if it touches the marked tooth to the same extent. If it doesn't, adjust the trunnion (if a contractor saw) or the tabletop (if a cabinet saw) until it does.

   For a contractor saw, first use a small c-clamp on the rear trunnion and cradle to keep the assembly from moving.  Then loosen the two rear trunnion bolts and one front trunnion bolt.  Slightly loosen the other front trunnion bolt and use a stick to tap the trunnion until the blade and screw lightly touch.  The blade does not move directly around the center so you will need to repeatedly go back to the front of the blade, readjust the screw, and then again measure the back. Be sure to check after tightening the trunnion as the trunnion frequently moves when being tightened.

   For cabinet saws, loosen the bolts that hold the tabletop and tap one corner until things come into alignment.

   The same adjustment gauge can be used to set the fence parallel to the miter slot.  Slide the miter gauge to the front of the table and move the fence over to the screw head and insert a playing card between the screw head and the fence just so you can move the card as it touches both the fence and the screw head.  Now move the miter gauge to the back of the table and see if you have the same feel when you insert the card.  I like my fence absolutely parallel--if you want to have a slight opening to the fence, you can easily estimate the opening by adding a thickness of paper to the card.

   I always show my students with a dial gauge that their adjustments are within .001 - .002.

   You can also use the same gauge to measure blade runout by using a $5.00 feeler gauge.

   Finally, after you are satisfied with the above adjustments, check the position of the splitter to make sure it is exactly in line with the blade.

   Bottom line, there is no need to spend more than the $0.05 for the brass screw.

2. 
   RalphBarker | Jan 10, 2011 05:10pm | #2

   one approach

   Here's mine

   
1. 
   PenobscotMan | Jan 10, 2011 06:13pm | #3

   That's a very elegant jig.  I'm guessing the second picture shows the gadget that fits in the slot to achieve a tight sliding fit.  I will look for that -- maybe Lee Valley?  Or did you fabricate it?

   What  I've done so far is to screw a piece of steel to the wood fence of my miter gauge and then attach the indicator with a magnetic  base.  There is quite a bit of slop in the gauge, but by pressing to one side I can get measurements repeatable to within .001 or so.  With this system I figure I am within about .003 of perfection.

   The key step is to get a tight fit in the miter gage slot.

1. 
   RalphBarker | Jan 10, 2011 06:30pm | #4

   Yes, the bar on the bottom was from the jig parts array at Rockler, as I recall. The screw pressure adjusts the tightness of the fit in the miter slot.

   In practice, however, I find that I, too, have to press the jig to one side of the slot to get any consistency. If the jig can move, there's enough slop to appear on the dial indicator, throwing off the readings.

   Some of the commercial units don't actually drop into the miter slot, but rather ride on the two upper edges. I'm now wondering if that might be a better design approach.

1. 
   PenobscotMan | Jan 10, 2011 07:09pm | #5

   Move and tighten?

   Your jig gizmo looks like the attachment on a featherboard.  By tightening the knob, the jig locks in the miter gauge slot.  But as you say, if it's loose enough to slide, it's loose enough to give inaccurate readings.  Now I'm wondering -- if I tighten it down at the front of the blade, take a reading, loosen it to slide it to the rear of the blade, tighten it down again and take the second reading -- are those two readings in the same line relative to the miter gauge slot?  (One way to check this would be to take repeated readings at the same point, between loosening and tightening steps.)

   Rockler sells for less than $20 replacement miter gauge bars that have adjusting screws in the sides to take out the play.  That might be the answer.  I'm guessing the the purpose-designed indicator-holding jigs have something similar.

1. 
   RalphBarker | Jan 10, 2011 08:14pm | #6

   calibration

   Little spring-loaded roller bearings on the outboard side of the miter bar would be neat. ;-)

   But, I had my left arm calibrated, so I can exert consistent pressure (5.0001 lbs) against the jig as I move it along the miter slot. ;-)

2. 
   PenobscotMan | Jan 11, 2011 04:28pm | #7

   Arm calibrated within 1/10000 of a pound, Wow!

   Now that is real precision.  Here is what I ended up doing:  screwed the indicator to a piece of wood, clamped the wood to the miter gauge, tried to get the bar tight in the groove, made measurements fore and aft.  Looks good within .003, close enough for government work, as they say.

   I do wonder how much this matters -- we are cutting wood, not machining metal for the Space Shuttle.  If you took all of the machine set-up advice in the woodworking magazines, you would never have time to make anything.

   Thanks for the advice.

3. 
   RalphBarker | Jan 12, 2011 11:24am | #8

   obsessions and compulsions

   "I do wonder how much this matters . . ."

   Yeah, we do tend to be a little OCD-ish about these things. On the other hand, square is square, and unsquare becomes obvious pretty quickly. And, while being within 1/64" is pefectly OK for the finished piece, it only takes 1/128" for that table saw to put a wooden stake through your heart. ;-)

3. 
   hammer1 | Jan 13, 2011 09:18am | #9

   I use a simple straight edge. The extended length magnifies any discrepancies over a longer distance.