Re: Entire head coming down at an angle?
|
Hi Tom You're correct that the blade is square to the saw table, even when it's moving in a non-square arc due to the pivot shaft not being parallel to the saw table, but you have forgotten about the set of the teeth. The set enables the cut surface to accurately?mirror the movement of the blade without deflecting the blade body as implied by your drawing. I agree that the gap between blade and setsquare is an accurate?representation of the tilt of the pivot shaft and the saw table BUT you will find (as I did when I tried it way back) that measuring the gap is way more difficult than it seems. The most inaccurate part of the measurement is assessing?the 'feel' of the feeler gauge between the upper end of the setsquare blade and the sawblade, as the blade will perceptibly deflect with?very little pressure leading to over measuring and hence over correction.?? Cutting test pieces from the S4S timber allows the following benefits - repeatable production of test-pieces
- standardized measuring with a micrometer or digital caliper
- the test piece is produced by actually cutting something (not an inference from a secondary related process)
- It is very very sensitive, allowing you to creep up on the point where the pivot shaft becomes parallel to the saw table to an accuracy of 0.002" difference between each end of the test piece 4" long (0,05mm in 100mm) where saw? manufacturers?consider? 0.012" in 4" to be 'effectively square'
Can I suggest an alternative to measuring the gap between the blade and a set square: - Find a feeler gauge?set from which you can remove the leaves (Mitutoyo and others do one with a thumbscrew tightening the friction between the leaves)
- Stack appropriate leaves under one end of the S4S timber to tilt it, at the edge of the saw infeed table (which end depending on which way the pivot shaft is tilted), until the test pieces?saw off parallel as measured with the micrometer or digital caliper??
- The angle is then the stack height over the distance from where the S4S timber is tilted.
- When you think you've got the stack thickness correct, cut about 3-5 more identical test pieces to verify that its correct (always take 10sec+ to make a cut in wood or the teeth gullets overload and it cuts in a curve)?
- To? find the amount that must be removed from the pivot shaft, multiply the stack height by the distance between pivot shaft ears on the base casting, divided by the saw infeed table width??
Effectively it is the same measurement you propose but made in a repeatable fashion. In fact?this can be turned?into a quick and dirty fix - fixing an equivalent thickness of metal, to the stack height, in that place with double-sided?tape (the tape I used was 0.003" thick in itself?and must be accounted for). This works for lengths of stock to be cut that are greater than saw infeed table width. Worked?for me until I got the time to fix it for good - jv??
Good Evening,
I know it has been a while since addressing this topic, but I just bought a used Grizzly G1010 4x6 and I wanted to align it before starting to use it.
I spent a LOT of time reading through this forum and I want to compliment all of you on the excellent work you have done here.
I am specifically interested in the vertical alignment discussed here, and especially John's paper:
"Fixing vertical squareness or Worn pivot bearings on a 4x6 Bandsaw v2.pdf"
This paper is excellent, and I have discovered that my table is very smooth and flat.
But I do have an issue with the pivot not being parallel to the table (to the tune of around 1/16").
While learning about this, I made a simple CAD model shown here:
If you look at this model from the front (facing the vise wheel), it looks like this...
(you can see as the blade goes up, it remains perfectly square, always aligned with the engineer's square):
Now, if I look at the same view, but with a tilted pivot...
the blade travel moves away from the square (by around 1/8" in this illustration):
I love the way you guys have come up with to fix this by machining / filing the pivot pin.
There is one thing that bothers me however, and I would like to get your opinions...
The issue relates to the technique of using the 1x4 S4S test board to determine the necessary offset for machining.
If you look carefully at the blade path with and without an offset, you get this:
 ?
Notice that with the tilted pivot, the blade drifts to the side (1/8" in this example), but it is important to note that the blade itself is always vertical.? This is because everyone (rightly so) adjusts the blade guides so the blade is vertical.? What this means is that when you are doing a test cut, the blade will want to cut vertically (as all good band saw blades do), but it is drifting to the side because of the tilted pivot.? Doesn't this mean that the test cuts are not really correct and may tend to be curved or otherwise inaccurate?
It seems to me that it might be better to not use test cuts because of this effect, and rather, just measure the gap between the blade and the engineer's square over a 5" distance (which corresponds to the pivot bearing spacing).? This measurement seems more direct, simpler and is not subject to any error from a blade that is being forced sideways by the tilted pivot during the test cut(s).
When I try to correct this I will start with a new pivot shaft, and the beauty of this technique is that nothing is being modified with the saw (other than adding a grub screw) so if a mistake is made, it is easy to revert back to the original setup.
Does you agree with me that this sideways drifting has an impact on the accuracy of the test cut method of measurement?
-Tom
|
John Vreede