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Re: Mysterious shift in saw alignment

 

You've got it MarkK. Moving the 'Pivot' (as its called) casting (#121) is what has made?your switch hit the?base casting and why it no longer cuts square horizontally.?
As I've said many times, the heart of a 4x6 (or any horizontal /vertical bandsaw with a hinge in the middle) is the axis of the turning of?the pivot shaft (the centreline of the hinge, which here-after I'll call the pivot axis).?You figure the effect of every adjustment in relation to the pivot axis. The pivot axis is fixed immovably in the base casting but almost everything?else has some freedom of movement in relation to it.?
To cut perfectly square, both horizontally across and vertically down through, the work, the workpiece has to be parallel to the pivot axis? in both plan?view?(looking vertically down) and front elevation (looking across surface of the vice table from the front of the saw)??AND?the blade body (the 1/2" bit above the teeth) has to be square to the pivot axis?in both plan view and front elevation.??
Let's?look at horizontal squareness?first, because this?is where your?switch hitting the base casting came from:
Horizontal squareness?comes from looking at the workpiece and blade in plan view only.?
  1. Getting the back of the workpiece parallel to the pivot axis is easy to set by moving the fixed ice jaw and clamping it when it's parallel.This needs to be set parallel as good as you can get it (certainly better than 0.008" (0.2mm) difference in distance from the?pivot shaft to the front face of the vice jaw at each base casting pivot shaft ear). I re-bushed the pivot on the fixed vice jaw and pinned it in this position, (with a taper pin through the vice jaw into the base casting), because you NEVER have to move this again in a properly setup saw cutting square. This returns it to the identical parallel position each time after doing an angle cut.??
  2. Getting the blade square to the back of the workpiece is more difficult.? This is primarily set from the joint between the the pivot arm casting and the sawframe?(your piece #121 and the sawframe at the back left hand side of the saw).? Slide the pivot?arm casting forward in relation to the sawframe, and when you tighten the bolts the sawframe will pivot left and the switch hits the base casting.? The angle between the blade and the back of the work tightens so this is the way you move it when the angle between the back of the workpiece and the horizontal cut face of the workpiece is obtuse (>90deg). Slid it the other way?of its an acute (<90deg) angle.? ?To get horizontal squareness exact you need to be able to micro-adjust the slip across this joint and the best way is with Rick Sparbers adjustment bolts per the picture attached.? You can get additional adjustment range from this joint by filing?or machining out the bolt slots in the pivot arm.?
  3. Horizontal squareness is also affected by the adjustment of the clearance between the blade side guide rollers ONLY IF you have eccentrically adjustable rollers?on the inside of the loop of the blade.? This is annoying so I've changed the inside rollers on my machine so they?rotate on concentric mounts, to remove this adjustment.??
And that's it for horizontal squareness, there are no other adjustments?built into the?machine that affect horizontal squareness.? I have a saw where the pivot axis was bored 'not square' across the base casting at the factory, and this has been a real mission to correct, but generally this is OK in most saws

Vertical squareness is a whole other ballgame that doesn't concern?your problem, but basically looks at the parallelism?of the bottom of the workpiece (essentially the surface of the vice table) and the squareness of the blade body to the pivot axis in front elevation only. The squareness of the blade body is just an adjustment, but the parallelism of the vice table to the pivot is built into the machine at manufacture and is very often wrong (upto 2 out of 3 depending on mnfr. I'd guess) and is a major problem to fix. One of the contributors to this is the base casting warping and twisting after machining while it sits in its box (or in your shop), as Roger describes, but the major one is poor machining at the factory that?Mark2 and Howard talked about.? These 2 have to be corrected BEFORE you pin the fixed vice jaw to the base (the 'properly setup saw' caveat in point 1 above). - jv





On Sat, Mar 19, 2022 at 4:50 AM Mark Kimball <markkimball51@...> wrote:
Last night I had a thought about what _might_ have happened, but I need to confirm it.? I remembered that I had? tipped my saw over to open up the gearbox and replace the gear oil (I supported it with a plywood plank at the right height).? This would put some sideways rotational force on the frame, and in the right direction if something in the support arm assembly was loose.? The bed casting isn't all that rigid either so there could have been some flex in there that caused something to shift..? One observation that supports my theory is that, while I was able to adjust the blade guides so the saw cuts pretty square in the vertical plane, the blade clearly is misaligned on the horizontal plane (and the direction is consistent with my problem).....and it WAS properly aligned at one point.

To be more specific, I'm talking about part #121 in my owner's manual for the HF #93762 bandsaw.? There it's called the "left pivot" but it also has been referred to as the "support arm".? The left end of the pivot shaft passes through it and on mine it's secured by a grub screw in the support arm.? Two adjustment/fixing bolts attach it to the frame and the support has two slots in it to permit adjusting the frame so it is horizontally square to the pivot shaft.

More later....

Mark

Adjustment screws in pivot arm.jpg

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