Shopsmith Forums

At this point in the discussion it might be good to take a few measurements. First measure the distance between the inside edges of the miter slots at several points along the path of the slots. Then do the same for the outside edges of those slots. The measurements should be the same, right? Then measure from the inside edge of each miter slot to several points along the blade. These should be the same also, right? But, I would expect them to show some variation, based on the results the OP is seeing in his cuts.

Majones1 wrote: ↑Thu Nov 18, 2021 10:15 am At this point in the discussion it might be good to take a few measurements. First measure the distance between the inside edges of the miter slots at several points along the path of the slots. Then do the same for the outside edges of those slots. The measurements should be the same, right? Then measure from the inside edge of each miter slot to several points along the blade. These should be the same also, right? But, I would expect them to show some variation, based on the results the OP is seeing in his cuts.

For deviations in the miter slots to translate into deviations in a cross cut the miter slot deviations would have to be very noticeable.

If there is no differences in those measurements I believe there are only two variables left, the miter and the human.

dusty wrote: ↑Thu Nov 18, 2021 10:39 am
For deviations in the miter slots to translate into deviations in a cross cut the miter slot deviations would have to be very noticeable.

But what other variables are there?

Majones1 wrote: ↑Thu Nov 18, 2021 10:41 am If there is no differences in those measurements I believe there are only two variables left, the miter and the human.

Hmm there's a thought. Perhaps I should take myself out of the picture and recruit someone else to make the cut to see if they get the same results. I have a friend whom I think would be happy to oblige....

Is the 5 cut method usable with a miter gauge? I've only seen it discussed in terms of a crosscut sled alignment?

Atleast some version of it to accentuate the error on either side.

http://valleywoodworkers.org/wp2/wp-con ... Square.pdf

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There is at least one more variable, wear on both the miter slot and the miter bar. One would be more than the other since it might be used a lot more. I know my right side slot gets used more.

I wouldn't get too worked up over the geometry paradox until you test a different blade.

I had a similarly mysterious issue with my Makita track saw. If I made a continuous through-cut down the track in MDF, I'd get a slightly banana-shaped cut that bowed away from the track by about 1/32". But if I made a light skim cut, the kerf was straight, and positioned right next to the track where it belonged. Plunge-cut through cuts were also right where they should be. I got these results with a like-new Makita factory blade, both before and after a thorough cleaning.

After eliminating all other variables I could identify, and doing some web research after that, I suspected some sort of weird blade dynamics. As in maybe a standing wave that literally shifted the cutting plane. So I replaced the Makita blade with a Festool blade, and the results were tremendously better, to the point that I'd have never noticed any straight-line deviation unless I was looking for it. And then I tried a Forrest blade with a slightly thicker plate. The Forrest cut dead straight, to within my ability to measure it.

Now in your case, it's not obvious why guiding on a different miter slot would change the results. But the sort of blade dynamics that I suspected on my track saw are vibration-induced. So anything that affects vibrations and resonances (which is just about everything) could potentially affect the results.

There's a semi-mysterious (to me) process in circular saw blade manufacturing called tensioning the blade. The plate is hammered so as to expand the metal radially, creating desirable internal stresses that improve the blade stability. As I understand it, this is largely a manual process, and I suspect that it wasn't done properly on my Makita blade (despite marketing claims that it was "expertly hand-tensioned").

The feedback from Dennis made me think of something. When you are doing these crosscuts, are you just using the main table by itself or do you have the connector tubes inserted to anchor the main table to the aux table? It might be worth repeating those cuts with connector tubes in and locked. The reason that I say this is that I was surprised how much table flex there is with the main table when I attempted to align it with my Woodpeckers Saw Gauge 1.0 and my MasterPlate reference surface. I couldn't get reliable results until I used connector tubes anchored to the aux table (viewtopic.php?p=279255#p279255). Why it might be important here is that when pushing through a crosscut on the right miter slot, the miter gauge is more or less over the main table support posts, but when pushing through a cross cut on the left miter slot, you are pushing the miter gauge through the slot further away from those posts - perhaps putting sideways pressure on the table. As I recall, I think I could get a few thou difference/play in my main table when it was by itself, but this mostly disappeared when I had connector tubes in and locked. This might explain why you are seeing different results in one slot versus the other.

RFGuy wrote: ↑Thu Nov 18, 2021 12:20 pm When you are doing these crosscuts, are you just using the main table by itself or do you have the connector tubes inserted to anchor the main table to the aux table? It might be worth repeating those cuts with connector tubes in and locked.

He has a Greenie with a 500 style table. And that means it's even less stable than the newer table systems. There is a trunnion holding up the front of the table but the back is supported with a much smaller bracket on a pivot pin. Any movement of the table on those supports would skew on two axis and take the cut off 90º. If that is the case it should be evident on the face of the cut which would not be perpendicular to any of the four sides and possibly not flat. But I doubt that is the case.