Just a follow-up to describe my experience with the head alignment process...
I used bi-directional cuts with a S4S 1"x5" pine board to evaluate the pivot tilt.
My starting point with no shims yielded a thickness difference between the top and bottom of the cutoffs (double sided) to be around 0.136".? This implies that a pivot offset of about 0.068" would be required (half of the measured difference).
Here is part of the aftermath
Next, by using different shims between the table and the board, I found that a 0.082" shim provided a 'straight' vertical cut.? As recommended, I did multiple cuts with each setting in order to be able to average the measurement.? Since the distance from one edge of the table to the other is about 6.5" and the length between the pivot supports is more like 5", I decided that I needed to scale the 0.082" accordingly.? So I proceeded to make a new pivot shaft that lowered one end by 0.082 * 5" / 6.5" ~= 0.065".? Note that this is pretty close to the initial estimate based on un-shimmed cutoff measurements.
Here is the new shaft:
After installing this shaft, I did some more test cuts.? Although much better, I felt like I needed to go a little further.? The difference between top and bottom of the cutoffs went from 0.136" to 0.022".? Based on this, I re-machined the shaft to increase the offset from 0.065" to 0.080".? Unfortunately, this went too far.? My difference between top and bottom changed from 0.022" to -0.022".? I guess I really need to split the difference with the offset.? I should have declared victory with the first offset...? It was really good enough.
At this point, I'm going to just leave it alone and see what happens with metal cuts in real material.? It is clear that one cannot strive for perfection out of these machines and I think I have reached the point of diminishing returns.? On to other upgrades like a better vertical table and adding the longer vise jaws...
Some lessons learned:
- I did change the gearbox oil (used the Redline).? For my gearbox, it seemed like 200 ml was a good amount.? I used John's suggestion of propping the front legs of the saw up by 3 1/2" (using a 2 x 4 with the saw in the horizontal position.? 200 ml rose to a level where it was just about to spill over the lower edge of the open gearbox.
- I was disappointed in the wood cutoff measurement technique.? I felt like the behavior of the wood may not be representative of how the machine will cut metal.? Perhaps averaging multiple cuts helped but it seemed like the grain of the wood was affecting the path of the blade in a non-random way.? I did ease the blade through the wood by gently lowering the head over the course of maybe 15 seconds.? I used a pine board which has a fairly loose grain.? Occasionally there was a knot and I could see that the knot definitely had an effect so I would avoid them.? All in all, I did not feel like I got a reliable reading even with some averaging.
- In lowering the blade side of the pivot (by .065" to 0.08") it was clear that there was not enough play in the opposing pivot support.? It was not possible to lower it even this 'small' amount without either flexing the pivot shaft or placing undue stress on the opposing pivot.? So, I wound up using a reamer to widen the opposing pivot support enabling the proper amount of shift on the blade side of the shaft
- I drilled and tapped the blade side pivot block and used a setscrew to tighten the new shaft.? And of course removed the original bolt that secured the shaft to the frame because that is now the new pivot point.
- Once the blade side was lowered, the new position caused the plastic blade guard to touch before turning off the machine.? It still works but the final 1/8" of the cut is flexing the plastic guard and affecting the down pressure of the saw.? I still have to work on a better solution for this.
- I am not confident that it is 'right' based on the behavior I saw with the wood cutting, but it is certainly good enough to stop tinkering for now.? If it turns out that I overshot the desired offset, then I will add a little metal tape under the modified shaft to bring it up a hair rather than make another shaft.
- During this process, I captured a lot of details in a spreadsheet to keep track of test conditions and results.? I found it useful to avoid getting mixed up as I went through the process.
- The head is heavy and awkward and I struggled to get the pivot shaft in and out while trying to balance / position the head.? It has to be positioned just right in order to get the shaft in and out without getting stuck.? I hesitated to use a drift because I did not want to force it, risking damage to the pivot blocks.? Two people would have made this easier.
Thanks again for all the insight gained through the amazing people in this forum !!-Tom
