Table Saw Blade Alignment

      Advice on keeping a table saw blade parallel to the fence, and some general observations on accuracy and tolerances. October 25, 2006

Question
I have a Delta Unisaw. I frequently check for the blade being parallel to the miter slot. I like to check it with the belts off the pulley for ease of rotating the blade, etc., and this way I can get accurate results less than .001. The problem arises when I put the belts back on and tighten them. Once I tighten the belts, the blade falls out of alignment by .01. I can get accurate results by tuning with the belts on, but what is causing the difference in alignment when the belts are on vs. off? Possibly my pulleys are out of alignment?

Also, it seems that my saw is out of alignment often enough that I have to check it every few weeks. I like to keep no more than .003 out of alignment but it does not take long for it to get beyond .003. Does anyone have suggestions for keeping saws aligned for longer periods of time?

Forum Responses
(Solid Wood Machining Forum)
From contributor S:
I would say the first thing you should check on is bearing wear. With the belts off the arbor pulley, spin the arbor and try to feel for any hesitation, spots that turn harder or even grinding, etc. If you don't notice any of these traits, grab the arbor and try to wiggle it - put the indicator on the arbor while you do this and watch your needle. If you notice anything other than a smoothly rotating arbor or if your indicator registers movement when you try to wiggle the arbor, it is time for new arbor bearings. Now if you rule out bearing wear, I would say that your problem is being caused by the deflection of the arbor mount under the load you're putting on it when you tighten your belts. You may be putting too much tension on your belts. Many people have a tendency to put more tension than necessary on a belt. As long as you're not getting slippage during operation, you're going to be okay (believe me, you'll know it when a belt slips - it stinks up your whole shop). If de-tensioning doesn't help, then I would say that you have no choice but to align the saw with the belts on.

When I check the alignment on my saw, I use a "master plate" instead of a saw blade. This is basically a machined and calibrated plate of aluminum that you bolt on in place of the blade - this way you don't have to worry about pitch on the blade or running your indicator onto the carbide. You can buy it from Amazon.



From contributor D:
When it's all said and done, the post above basically says "stop taking the belts off so much." Excellent advice, especially about the plate.

It's woodworking machinery - .01" is overkill. Sure I know where you're coming from, wanting supreme accuracy, but if it's that close, you've probably got the best one ever made.



From contributor J:
Which way is your saw going out of alignment? Once you have set the blade at 90 to the top and parallel to the miter gauge slot, it should not move, barring running into the saw with a cart! Is the alignment with the fence going off? If so, it's your fence and not the saw. Also some good advice in those previous posts, especially about overtightening the belts. If you're trying to get more accurate than .01 on your tablesaw, you're in the wrong profession. Not that being accurate is a bad thing, but at those tolerances, you'll spend all your time tuning machinery and not making money.

And although I have not tried to measure, I would guess a typical thin kerf blade will flex more than .003, thereby defeating the quest for super accuracy. Not to mention the tendency for most of the materials we work with to move after being machined. If after all this, you still want more accuracy, the Unisaw is a good machine, but there are certainly better ones out there. Just have to decide how much is the accuracy worth?



From the original questioner:
What machines do you recommend that are better than the Unisaw? I have a Forrest WWII blade that is less than .002 runout. I think that .01 is not very accurate at all. Making inset doors with a 3/32 reveal all the way around would be next to impossible with a 0.01 difference in blade from front to back.


From contributor G:
Maybe take a look at a CNC system for that kind of tolerance... or outsource the doors you need to make.


From contributor J:
If your blade were .001 out from front to back, it would not change the size of your work piece from front to back. If your blade is .001 closer to the fence at the front of the blade, the back of the blade will not contact the work piece, therefore it will not affect the dimension. If the blade is .001 closer to the fence at the back of the blade, you may get some burning of the work piece. You would also be more susceptible to kickback. But either way, your work piece should still be parallel coming out.

If your work piece, i.e. stiles and rails, are coming out not parallel, it may be that the work is pulling away from the fence as it goes past the blade. I may be wrong, but I don't believe it's the blade being out. Another thing which may help, though, is a 5" blade stabilizer.

As for tolerances, that is something we all have to find a balance with. I do try to keep my work pretty tight, but if a 30" tall overlay door is off by just over 128th from top to bottom, well I'll admit I can live with that. I'd split the difference so it's only .005 on each side, not easily visible. For your inset doors, if you still can't get the saw true, you could knock that off with two passes of a well tuned hand plane.

By the way, I'm still using my 1954 Unisaw, and although I occasionally think of upgrading, I have to admit it's a great machine.



From contributor G:
Big difference in Uni quality from 54 to the 80s, 90s quality.


From contributor D:
Contributor J is right - it sounds like the fence. Wood moves. And guess what? Metal does too. Temp change can affect metal enough to detect measurable differences, especially when you're looking at thousandths, etc. Not saying that's what is happening - I'm just saying ease up. Better is great, but a 64th is a respectable goal in woodworking. And 99% of humans can't see less than a 16th.


From the original questioner:
Thanks for all the advice. I build cabinets on the side for some extra cash, but I've only been doing it for a year. I'm pretty good with overlay doors, but my inset doors are not working and I'm getting frustrated figuring out what the problem is. I'll take everyone's advice into consideration.


From contributor J:
Contributor G, you're right about that! I just replaced the original 1h.p. motor on my saw about 3 years ago, and believe me, this machine was well used when I got it. I wonder if the 2h.p. Leeson I put in there will last as long? It's certainly not noticeably more powerful than the old 1 horse. Sorry to go off topic, but I do miss that old Delta quality.


From the original questioner:
Why has Delta quality diminished? What brands are better than Delta?


From contributor J:
I think a lot has to do with the competition from overseas. I personally think the Powermatic 66 is one of the best 10" saws on the market, but you pay for it. I think for many years Powermatic and Delta were pretty close in quality. For some reason Delta seems to be catering more to the hobbyist workers, and Powermatic is focusing more on professional shops. I looked at Delta's 12" jointer this weekend at the ww expo and it was pretty rough looking. If not for the color, I would have thought it was a Grizzly! Other tools like their bigger radial arms are still pretty well built, though. I guess you really can't go by the name anymore, but actually have to check out each individual machine. Just so you know, I'm not trying to bash Delta; I own quite a bit of their machinery and it works well.

If you are going to start looking to upgrade, I would check out the Powermatic 66, and I've also heard good things about the new Sawstop saw. But I personally don't think it's going to make much difference for a small shop. If you get it set accurately, you should be fine. You don't need the best machinery to make nice work. I would love to get the 66 myself, but my Unisaw still works fine and there are so many other things to spend my money on.



From contributor G:
Take a look at the Extrema 10'', pretty good machine.

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