Aligning a Sliding Table Saw Carriage
I learned a long time ago that my expensive Starrett gauges and straight edges don't mean crap if the cut is still bad. So after I use the precision measuring stuff, I put a TCG blade on and fire up the saw. I clamp a 2" wide piece of melamine to the cross cut fence and listen to the sound of the teeth as it passes back and forth. I mean to say that I will make the cross cut, then pull the table back and forth, listening to the sound at the front and rear of the blade. I set my slide to be perfect with no toe-in. Just to make sure I do this with the out rig table set in the forward position (panel cutting) and in the middle position (for cutting door parts to length). I have a good saw so it has always been the same no matter where I lock the out rig table. I also set the table about .1 mm higher than the iron saw table.
From contributor N:
You might want to check the owner's manual for your saw. Mine tells you to set the sliding table so that the back of the blade just clears the cut edge of the work.
From contributor E:
I have an SCM slider that is real close. The method I used was a master plate in place of the saw blade with a dial indicator clamped in the carriage groove. I hope contributor M can comment on this, because I still see saw marks on the panel edge and am not sure how I might correct that.
From contributor M:
I had a master plate before that I used on my Unisaw. I wish I still had it. Like I said before, the proof is in the cut. If you are not getting the cut you want, adjust as necessary.
As for toeing in for clearance at the back of the blade, here are the problems I see. The rip fence must be perfectly parallel to the slide table's movement. If it is not, your stock will be forced in or out as it moves along the non-parallel fence when using it as the reference. If you set the slide to have clearance at the back of the blade, and set the rip fence parallel to the slide, you will have a problem when ripping off the rip fence without the slide. The blade will have the opposite toe, causing tear-out on the top of the panel. When ripping lumber, this condition will cause kickback. When processing panels, the offcut should be just as perfectly cut as the piece on the slide. If you favor the slide by toeing in the blade, you will cause your offcut to suffer as it will hit the back of the blade more than the front. This can cause really bad cuts when crosscutting long parts where there is a lot on the fixed table.
It is true that you will get a better cut on the sliding table if you give a bit of clearance at the back of the blade, but the penalties are too much in my opinion. And the saw marks don't matter anyway.
As for using a dial indicator, I think it is overkill. I have a Starrett "last word" test indicator. I think it shows .001 mm resolution. I used it before with my Master plate. Now I use a scrap strip of melamine and my ear to hear the alignment. If I wanted to toe in the slide I would just listen for that as well.
Toeing the slide also messes with the scoring blade because you are running the panel over it in a strange angle. I can't easily explain the effect, but if you draw two perfectly aligned lines on a paper to represent the scoring and main blade, then draw another line at a 15 degree angle to the blades representing the toed-in slide, you will see that the scoring blade ends up having to be shimmed wider than the blade. This causes weird alignment issues with the rip fence as well.
I can't see saw marks on my melamine panels (particleboard doesn't generally show any at all), but I do see them when ripping and straight lining lumber. I can see nearly the exact same pattern whether ripping off the rip fence or straight lining with the slide. I figure this means it is dead straight. The marks are about half and half from the front and back of the blade.
Blade quality is a big deal. If you have a couple of bad teeth or a warped blade, the marks will be a lot worse.
I am sure there are others with better methods, but I would look to the Europeans and see how they do it. American shops are more used to cabinet saws and they tend to use sliders differently. The Europeans have been using sliders a lot longer and they use them for everything.
From contributor D:
The easiest way I have found through the years is a five sided cut. Using a 3/4 x 4 x 8 sheet, start at an 8' side and rotate the sheet, cutting about 1/4" off each side. Once all 4 sides have been cut, your 5th cut will be an 8' side. Cutting about 1/2" off, then break the dropoff in half and place them together on the 1/2" face. Whatever the runoff is from end to end is how far your travel carriage is off. From there adjust fence accordingly.
From the original questioner:
To be clear, the 5 cut method is the best way to align the carriage fence. The problem here is to align the sliding table itself parallel to the blade.
I agree that perfectly parallel is the way to go. Scoring is one issue. Second is the fact that the two sides of the saw should work in conjunction with each other. (A reason to calibrate the rip fence and carriage fence measure perfectly.)
If you are ripping 12 inch strips from a sheet, the first cut is the dust cut on the table. The second is a cut combining sliding table with rip fence pulled back. The third is the same, as is the fourth. The fifth cut to finish the fourth piece will be a cut only on the rip fence with the rip fence extended.
Now crosscut those strips into pieces 30 inches long. Pull the rip fence back and set it for 30. Push the piece against the carriage fence and cut the first piece, then slide it over to cut the second. The third piece would be dangerous to cut with the short side against the rip fence, so turn the cut edge around and cut it against the stop on the carriage. All these operations are compromised if the fences are not all completely square and parallel to each other.
From contributor G:
I think contributor M' s method is correct and the only thing I would add is to use a dial indicator when moving the slide so you can see how much you have moved it. If you moved it .010 and it was too far, you can move it back .005. This will save some time, as the amount that you need to move it is quite small.
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