I’ve been spending some time recently checking the setup on some of my machines. When checking the the miter gauge on my table saw I’ve run into an issue. I’ve ripped a board to a width to ensure the edges are parallel to each other and designated one edge as the reference edge for testing and squaring the miter gauge. I use the reference edge against my miter gauge. The cut appears square using a 12” square (I’ve tested the square’s squareness) when checked against the reference edge however when I check from the other edge it is not square. On a narrow board of say 4” to 5” this isn’t noticeable however when using a 10” to 11” board it is really noticeable. I’ve tried several scenarios, re ripped, planed, flipped the board end to end and edge to edge. What am I missing here?
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Replies
If the mitre gauge slot is parallel to the saw blade, and the mitre gauge face is square to the mitre slot, the only thing I can think of is the fence is not parallel to the saw blade. If the fence isn't parallel you may be creating a wedge when you rip both edges causing one corner to be square and the other out of square after your crosscut.
(I edited this after you responded and I gave it more thought. I'm not sure a jointer would have made a difference. It has got me thinking though. One of the 3 things I mentioned has to be misaligned as far as I can see i.e. fence to blade, blade to mitre slot, or mitre gauge to blade).
Maybe someone else has other thoughts.
It's definitely solvable!
I don't own a jointer. I ripped both edges. I even hand planed one edge and used a machinists straight edge on it to verify and then used that edge against the fence to rip to a width again. To the best of my ability the fence is parallel to the saw blade as well as to the miter slot. Thank you for your input and I will check everything again.
The best way to determine square is the William Ng five cut method. By cutting the same board five times, you multiply the error by 5. So, check your miter gauge first (most likely to be a source of error). There are ways of determining if the blade is parallel to the slots, that's important, too. Also, when you check the blade against the slot, check against one tooth, then rotate the blade 180 degrees and check again. I had an out of flat blade that drove me nuts until I did that.
I agree with Ray2357. It is critical to check alignment and the first step is to unplug the saw. Then I start with the miter slot. To check miter slot to blade parallelism, I use a dial indicator and the kit from Woodpecker designed for that purpose. It is well worth the investment if you want to align your saw for the best possible alignment to the blade. the first step is to clean the miter slot until it is pristine with zero deposits along it's edges. Then elevate a blade known to be dead flat and raise it to it's highest elevation. Check the blade with a machinists square in multiple directions for flatness. Some use a stand mounted dial indicator and two parallels, all on a granite surface place to do this but a pro grade machinist square will be nearly as good. With the flat blade installed, and the kit's dial indicator you can adjust table to blade alignment by slightly shifting the table until there is no deflection from the dial indicator as it travels across the face of the blade. Once the table is truly parallel to the blade, you can check fence to blade parallelism. For this step it is not necessary to have a perfectly flat blade. Any reasonable blade will work. To ensure the fence is parallel to the blade, elevate the blade all the way up and select a tooth closest to the front of the saw or operator position, just slightly above the saw table. Measure the distance from this tooth to the fence. Then rotate the blade by hand so that same tooth is now at it's furthest point from the operator and again, nearly even with the table top, measure the distance to the fence and compare measurements. If they are the same then the fence is parallel to the blade. As Ray points out, this will eliminate any effect from even small amounts of blade distortion. Following this alignment sequence will ensure the miter slot and the fence are both parallel to the blade. For greatest cutting accuracy fence to blade parallelism needs to be checked every time the fence is moved as locking it down can cause a slight shift. Always, always, unplug the saw before making any of these measurements.
I have yet to find a miter gauge that will give truly square cuts on anything but small parts. As the parts get larger the drag on the table makes the M gauge flex or just drags enough on the table to skew the cut.
For crosscutting that matters you need a sled.
Second possibility is deflection when 'truing up" your non-referance edge. If you are just "shaving" the blade can deflect. Make sure you are taking a cut that leaves a nice solid cutoff and try it again.
MJ is on the mark. Don't expect much from miter gauge, especially factory gauges that come with small job site saws. There are aftermarket gauges that offer better performance but they still can let a work piece creep as its cut. For truly accurate crosscuts, especially on wide boards you have two options the crosscut sled that Lataxe loves to ridicule or his preferred solution a very expensive and space consuming sliding table saw.
I remove a quarter of an inch at a time. 1/8" blade width and 1/8" of wood. Is that enough?
I don't think it is the fence, because the effect of the fence being out of parallel is the blade cuts a wider kerf, but since the entire length of the board must pass thru the narrowest gap the board still ends up a consistent width. It may just have more saw marks, burning and be more prone to kickback.
I will go back to the basics.
How did you check your square? If you reference source is not true nothing else can be.
Take the square out of the equation. Mark the leading edging of the board you just ripped parallel, cut off a 6-8" piece using your miter gauge. Now stand the board on edge on a known flat surface with the leading edge on top, you tablesaw is probably good, then take the cut off and stand it on edge with the leading edge on the bottom, butt the two pieces together. If there is no gap the board is square and the problem lies with your square. If there is a gap adjust your miter gauge and test again until you eliminate the gap.
Once you have eliminated the gap check your square to verify it is accurate.
I laid the 'handle' of the square to the left against the reference edge of my board and struck a line. I then rolled the handle to the right and struck a line near the first. They line up.
That method is okay but not perfect. The thickness of a pencil line can vary as well as the human eyes ability to judge the line is inherent with potential error. Seeing light through a gap of a square can be less than the thickness of a pencil line.
Is there another way to check the square for true?
You can true a board in the manner I described or use a high quality known reference square. There are manufactures who certify the accuracy of their squares, Woodpecker, Starrett, Blue Spruce, Bridge City and others all certify their tools to within thousandths of an inch.
I had a 12 inch combo square that was perfectly square sometimes and slightly off other times.
Turned out the head was warped!
It was only square if the wood was wide enough to span the hollow area of the sliding head.
Not saying that's what's happening to you. But it's something to check.
Mike
On the 8th day a tablesaw sled was made; a jointer (hand or powered) is assumed when you start trying to get square parts ;-)
For testing square, I use a set of machinist's reference squares I got from igaging. They don't get used for anything else - not for marking or other work. Just for checking the other squares and setups. They are more than good enough for woodwork.
I have been quite surprised by how small a difference in the mitre bar can be detected. a sheet of thin paper between the bar and stop is more than enough to throw it off square detectably.
The most likely explanation for the OP's problem is that the cuts were not parallel to each other. This is a problem as it is the main purpose of the saw. Possible causes include - an uneven or irregular reference edge against the fence, a twisted board, operator error (not holding the board firmly against the fence) or (maybe) the fence not parallel with the blade.
The best way to test square is the 5 cut Ng method using MDF - a 10 inch square is best.
I agree with the sentiment from MJ and esch that a mitre gauge is not really for accurate cuts. They can be tuned, but by then you could have made a decent sled.
I 'spose it's about time to close this up but I thought I would let you know what I've been using to test with. As stated previously the saw is a Dewalt contractor's style using the original fence with and without a baltic birch auxiliary fence. I have an Incra Miter 1000 SE miter gauge and a Jointech Smart Miter JSM-48 style sled. I've used two Stanley and one Wood River combination squares and one Kapro 353 Ledge-It square. My results are consistently the same. Measuring against the reference edge it appears good but when measured against the opposite edge it is out of square. If the square(s) are square I would expect it to register good both ways or out of square each way. Even if the square were not square I would expect it to be out on each registration. I do want to thank each and every one of you for your replies and suggestions. I do appreciate the input. My best guess at this time is that I'm not really getting my boards truly parallel on the edge cuts but at this point I'm not quite sure how to resolve that so I guess I start over. And although I've built and used homemade miter sleds in the past and not really cared for them I think I'll probably go back to one and try it again after I've resolved my 'parallelism' issue.
Once you design, build, and adjust a new TS sled, you’ll look back and wonder how you made-do for so long with so little. Enjoy the voyage!
Sort'a makes you wonder how anything ever got made, "Back in the Day(s)", of Hepplewhite, Chippendale and all them other po' folk who struggled with poor lighting, [comparatively] inaccurate tools and no 'lectricity. Don't it?
[Hint: "Fudge" was not for just dessert, it was also served with "Finesse".]
John Townsend didn't work to .001 tolerances?
I don't obsess about tolerances. It's wood, and pretty much every surface sees a handplane after a power tool.
When I check for square, I crosscut the widest piece I normally use. I put the side that was against the fence against a straightedge, and strike a line along the cut edge. I flip the piece face down, with the same edge against the straightedge, and check the cut edge against the line. If it matches, I'm square. I don't need a micrometer or calipers.
Most crosscut are 6 inches or less. Many larger pieces are things like a tabletop that overhangs, and .1 inch squareness would be adequate for that, never mind .001
Reading this and something really stands out. Keep in mind I am a mechanical designer, not a machinist but I have worked with them for years and understand the basics of precision measuring.
" I’ve ripped a board to a width to ensure the edges are parallel to each other and designated one edge as the reference edge for testing and squaring the miter gauge. I use the reference edge against my miter gauge. .......when I check from the other edge it is not square."
ASSUMING the square is accurate and you are using proper technique, there is only one answer. The boards edges are not parallel. That is the only way it would be square on side and not the other.
This assumes the square is accurate. Edges are strait and clean. No chips under the square when measuring.
Most people have more than one square in the shop and when in doubt I check with several of them and compare the results. Recently discovered my favorite was not square.
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