Shopsmith Forums

I'm checking to make sure my saw is square to the world and have run across something I don't understand.

My miter slots are square to the blade to less than 0.003" (smallest feeler gauge I have). I've confirmed this via several measuring methods. My miter gauge is 90 deg to as absolutely close as I can get it.

When I do a crosscut using the right miter slot, the cut is dead square - both on the "work" side of the cut and the "waste" side. If I then flip the board end over end and move it to the other side of the blade so that I'm using the left slot but still have the miter gauge contacting the same edge of the board, the cut is a degree or two under 90 deg.

The slots are parallel. I'd think if the error were in the miter gauge then I'd see it using either slot. But only in one side? I don't see how what I'm getting is possible.

Any thoughts? Thanks!

----Later----
SPOILER: please read the thread for the full diagnostic process but it ended up being a combo of user error and a loose miter gauge pivot screw

The board could be slipping along the miter gauge to account for the degree off. Everyone holds the board differently when working on each side of the blade. This difference could allow the board to creep especially if you normally work on the right side of the blade. On the right side of the blade, you have to prevent the board from slipping to the left into the blade. You may not even be aware of unconsciously pulling the board slightly to the right to prevent this creep. But when switching to the left side of the blade it would allow the board to move into the blade causing the cut to be out of square.

HopefulSSer wrote: ↑Wed Nov 17, 2021 10:55 am The slots are parallel.

I guess I would challenge this statement above. Are you assuming that both miter slots are exactly parallel to each other? Or, did you measure them exactly parallel to each other? I only work off of the right miter slot myself. I think I have seen past posts on this forum that indicated it is very difficult to impossible to get a perfect alignment of the main table, i.e. having both left and right miter slots to be perfectly aligned with the sawblade, at the same time. Hopefully others will comment here who know more about this.

RFGuy wrote: ↑Wed Nov 17, 2021 11:15 am

HopefulSSer wrote: ↑Wed Nov 17, 2021 10:55 am The slots are parallel.

I guess I would challenge this statement above. Are you assuming that both miter slots are exactly parallel to each other? Or, did you measure them exactly parallel to each other? I only work off of the right miter slot myself. I think I have seen past posts on this forum that indicated it is very difficult to impossible to get a perfect alignment of the main table, i.e. having both left and right miter slots to be perfectly aligned with the sawblade, at the same time. Hopefully others will comment here who know more about this.

To the limit of my ability to measure, they're parallel. I also ran across this page:
https://www.shopsmith.com/mediawiki/index.php/Table
...which says they're cut at the same time with the same arbor.

Perhaps the table has become distorted over time. But is so the difference is very slight -- smaller than I would think would cause the degree of out-of-square I'm seeing. But maybe?

thunderbirdbat wrote: ↑Wed Nov 17, 2021 11:11 am The board could be slipping along the miter gauge to account for the degree off. Everyone holds the board differently when working on each side of the blade. This difference could allow the board to creep especially if you normally work on the right side of the blade. On the right side of the blade, you have to prevent the board from slipping to the left into the blade. You may not even be aware of unconsciously pulling the board slightly to the right to prevent this creep. But when switching to the left side of the blade it would allow the board to move into the blade causing the cut to be out of square.

I'm using the trigger-grip lock thingy on the miter gauge with one hand and holding it tight against the face of the gauge with the other so I doubt the board is shifting. And the error is pretty consistent suggesting that that it's not slippage (I'd think the error would be more variable). Plus I find doing that is a little more awkward for me using the right slot vs the left, but the right is more accurate. But perhaps there is some unconscious thing going on.

One variable I have not controlled for is runout in the blade, but I would think all that would do is make the kerf a little wider.....

(FYI when measuring the slots for parallel I measured on the blade using the same tooth front and back. And then double-checked against the sanding disk).

Another thing it could be is that one miter slot could be slightly larger in width than the other one. Keep in mind the Shopsmith miter bar is an older design. More modern miter bars utilize multiple nylon rings or metal springs to take up the "slop" in the miter bar slot to keep it tracking true. Many of us tighten the screw in the middle of the Shopsmith miter bar, but that is not the intended purpose for that screw. So, it could be that you adjusted the Shopsmiter miter gauge bar to fit well in the slot on one side, but the other side may be a bit looser. You may want to check for this by inserting the miter bar in both slots and check if there is excess "slop" on one side. Just a thought.

RFGuy wrote: ↑Wed Nov 17, 2021 11:35 am Another thing it could be is that one miter slot could be slightly larger in width than the other one. Keep in mind the Shopsmith miter bar is an older design. More modern miter bars utilize multiple nylon rings or metal springs to take up the "slop" in the miter bar slot to keep it tracking true. Many of us tighten the screw in the middle of the Shopsmith miter bar, but that is not the intended purpose for that screw. So, it could be that you adjusted the Shopsmiter miter gauge bar to fit well in the slot on one side, but the other side may be a bit looser. You may want to check for this by inserting the miter bar in both slots and check if there is excess "slop" on one side. Just a thought.

That's a good thought! It's an old table and it wouldn't surprise me if one slot is worn more than the other

I tend to agree with Brenda that the most likely explanation is that the work is probably slipping/being pulled into the blade. That can happen even with the pistol grip.

One thing I'd be curious about is what happens if you keep the miter gauge in the right slot the entire time and flip the board end for end after making the initial cut? The reason I ask is when you flip the board end for end, while you have the same edge against the miter gauge, you've now put a different face on the table. If the original face was flat and square to the edge against the miter gauge but the second face isn't, it might introduce some small errors especially. But, again, my money is on Brenda's explanation.

Make sure the headstock, table, and quill locks are tight. The quill lock, in particular, should be the very tight version of hand tight. And also check for end play in the spindle with the quill locked. I try to move the spindle in and out using either that aluminum knurled cap or any arbor. Watch for movement where the color contrast is high at the headstock side of the aluminum knurled cap. Movement of any of these is more or less the same as movement of your stock along the face of the miter gauge, and may look like an angle error.

What method are you using to align your miter gauge? And can you check that by seeing how that same method looks from the other slot? I'm thinking the 'book' method may create an error for the other slot.

- David

The OP states the same side of the board is being lined up on the miter gauge. I'm curious why the end over end change in the first place. Why isn't the board and miter gauge simply moved to the other slot to make another cut without any other change? I would also hold the board against the miter gauge with my hand to make sure it isn't moving, not just using the pistol grip hold down.