table saw blade alignment - close enough? - Woodworking Talk

duncsuss · 10-11-2009, 12:39 PM

A few weeks ago I posted asking advice on replacing the motor in a Delta Super-10 table saw ( Delta 34-740 TS / replacing motor advice please ).

I opted to pay the nearest Delta/PC/DeWalt repair facility to fit the new motor unit (which included the switch assembly and mounting brackets), as they asked only $66 for the labor. It was probably a good thing, as the mounting bracket had a minor flaw -- the hole milled to accept a pivot pin was a couple of hundredths out of round, and no amount of "encouragement" was going to get that pin installed. I would have assumed it was my error and could have spent weeks trying to make it work.

The eBay seller I got the motor kit from was fantastic -- he dismantled another kit he had on the shelf and shipped me a replacement bracket at no cost the next day. This one fit the pivot pin like a glove. I picked it up Friday, and the guy who did the repair gave me a 10-minute tutorial in measuring and adjusting blade alignment.

Now I've got it home, I measured it using a dial gauge bolted to a miter slot bar, testing against a dot on the blade that I made with a marker pen. At the rear, the dot on the blade is about 0.010" to the left.

Is this close enough? Should I even attempt to improve it?

One of the trunnion bolts is very difficult to get at (and seems to need a 15/32ths ring spanner, which I don't have) so before I take the skin off any more knuckles I wondered if it's worth it.

Thanks in advance for all your help.

Duncan

skymaster · 10-11-2009, 01:48 PM

If I understand you: .010 to the LEFT means closer to the miter slot and that is BAD , poor rips, burning cuts etc, plus just that much more likely to cause kickbacks. In a perfect world you want the blade within 2 or 3 thou to the slot and your fence away from the blade at the rear about 3 to 5.

knotscott · 10-11-2009, 02:07 PM

Duncan - I agree with Skymaster. "Close enough" is ok for table flatness, but for fence to blade alignment 0.002 or 0.003 is better. Your situation (pinching) is especially bad and can cause kick back...if you're going to be off, be off in the other direction.

duncsuss · 10-11-2009, 02:27 PM

Since I'm new at this my descriptions probably aren't accurate. Here's a photo:

Distance B is greater than distance A -- the back of the blade is 0.010" further to the left than the front.

The fence is going to be fitted to the right of the blade -- wouldn't this mean there is less chance of pinching than if the back of the blade were closer to the fence?

Either way -- I'll try to reduce the alignment error.

(Note: since I was measuring some distance above the table, the actual error is going to be greater -- perhaps 0.015" at the surface. Even more reason to try to fix it I suppose.)

Thanks!

Duncan

firehawkmph · 10-11-2009, 04:28 PM

Duncan,
Just for the heck of it, try a different blade. I know you put a dot on it and all, but it wouldn't take much to check. I would try a premium quality blade like a forrest, who guarantees minimum runout. Just a thought.
Mike Hawkins

M1911Bldr · 10-11-2009, 05:56 PM

If you're measuring and reporting .010, I take it you either have a dial indicator or caliper you're using to measure the slot-to-blade distances. I agree with everyone - do the adjustment and get it well withn .002. If anything, adjust so the blade is "relieved" by .001 at the back side. This will reduce pinch and give you better cuts as the up-cut won't be touching your work. While you're at it, make sure the table and blade are in the same plane (the table is "flat" to the blade). Tilt the blade to 45 deg. Measure the slot-to-blade distance again - after you've adjusted it with the blade at 90 deg. The measurements should be the same as for 90 deg. If they're not, your table is not "flat" to the blade. Shim the back or front to get the measurements the same- use the same size shims in both corners. If the measurement in the front is greater, shim the back and vice versa. Your method is coreect -0 using a dot to mesure to, by the way. You can "plagarize" any of Grizzly's cabinet saw manuals for pictures and instructions for all these measurements and adjustments. The manual for the G1023SL has excellent instructions.

duncsuss · 10-11-2009, 08:18 PM

It took a couple of hours, but I think I got it nailed to less than half a thou ... tap, measure, tap, measure, tap, measure, ooops overshot ...

Mike >> I have another blade, I'll try that too. Guess I could spring for a new one -- do Forrest price their blades reasonably? I'm not looking to go cheap, but let's not forget that I'm a newbie at this (there's no point buying expensive if all I'm going to do is ruin the blade by doing something stupid).

M1911Bldr >>

Quote:

make sure the table and blade are in the same plane

I'm not sure I understand this concept ...

As I see it, the first alignment I did was to get the blade parallel to the table slot, with the blade at 90 degrees to the table surface.

If I tilt the blade to 45 degrees and the blade is no longer parallel to the table slot, what would I adjust? It's a direct drive motor (the arbor is the rotor shaft). There are 4 trunnion bolts which attach a mounting bracket to the underside of the table -- these are what I had to loosen to allow adjustment in what I've done so far. I guess there are other bolts that attach the motor housing to the trunnion, but I don't like the idea of digging that deep into the works.

Thanks again --

Duncan

woodnthings · 10-11-2009, 09:10 PM

Quote....While you're at it, make sure the table and blade are in the same plane (the table is "flat" to the blade). Tilt the blade to 45 deg. Measure the slot-to-blade......."
The table and the blade will never be in the same plane. The blade will be at 90 degreees to the table (when adusting the trunnions or arbor to be parallel to the miter slots) or at somewhere between that and 45 degrees to the table. I've never heard of measuring to the blade at 45 degrees to check parallel to the miter slot, but that doesn't mean that's a bad thing, just there would be no way to correct for it if it were out. If the blade is within tolerance at 90 degrees it should be also at 45 degrees. If not, there is a major machineing issue with the arbor, in this case motor shaft.
If there is a better explanation of this condition please let us know, as I am missing something here.

bill
Some of this high precision issue is so much straining for gnats while swallowing camels. I think that's how it goes?

Here's my ideas on this topic:Tablesaw blade alignment with miter slot

knotscott · 10-11-2009, 09:12 PM

Duncan - What kind of blade is on the saw now? It looks fairly serious to me, like maybe an Infinity Combomax or CMT combo blade, which are both very nice combo blades....the Combomax is THE best 50T combo blade I've tried to date. A Forrest WWII is an excellent blade too, will set you back ~ $75-$100, and isn't necessarily much better (if any) than what's on there if it's one of the two I mentioned. A sharpening would be < $20 if it's dull.

duncsuss · 10-11-2009, 09:26 PM

Quote:

Originally Posted by knotscott

Duncan - What kind of blade is on the saw now?

It says: Freud LU84M - diameter 10" - Z50 HM ... N.MAX 7000 ... combination blade ...

This came with the saw when a friend gave it to me, I never really thought about it.

duncsuss · 10-11-2009, 09:41 PM

Quote:

Originally Posted by woodnthings

This confused me also

That's a relief ...

It's been a few years since I did any 3-d geometry, but I think the blade and table top are each in their own plane, which intersect in a line parallel to the miter slot when properly aligned. I can't figure out what would make that line of intersection change its angle with respect to the miter slot.

To me it seems like adding equal amounts of shim to both left and right rear (or left and right front) trunnions is functionally identical to raising or lowering the blade.

I think adding equal amounts of shim to both front and back right (or left) trunnions would be identical to cranking the angle adjustment wheel.

Regards,

Duncan

knotscott · 10-11-2009, 09:59 PM

Quote:

Originally Posted by duncsuss

It says: Freud LU84M - diameter 10" - Z50 HM ... N.MAX 7000 ... combination blade ...

This came with the saw when a friend gave it to me, I never really thought about it.

The LU84 is a nice blade too. Just give it a good cleaning with some degreaser spray, hit it with a brass brush, and see how it does for you. If you get a lot of burning, raggedy cuts, and a lot of resistance then have it sharpened.

woodnthings · 10-11-2009, 10:04 PM

I think you've got it! Also the stops for the 45 degree tilt and 90 degrees should be adjusted while you've got your toolbox out.

Maybe you have one of those digital angle gizmos for this. I've got one but I haven't check my settings yet. The old tri square seems close enough. but I will double check it, but if I find a discrepancy then what.....

too much knowledge can be dangerous!

bill

duncsuss · 10-11-2009, 10:13 PM

thanks for these suggestions

Quote:

Originally Posted by knotscott

The LU84 is a nice blade too. Just give it a good cleaning with some degreaser spray, hit it with a brass brush, and see how it does for you. If you get a lot of burning, raggedy cuts, and a lot of resistance then have it sharpened.

duncsuss · 10-11-2009, 10:19 PM

Quote:

Originally Posted by woodnthings

Maybe you have one of those digital angle gizmos

Nope -- so far I've managed to get by with a tri-square, combination square, and a couple of draftsmans squares (45 and 30/60). If I ever start doing compound miters maybe a digital wotnot would be handy.

Thanks -- now I have to go start a new thread for a question on a different subject

M1911Bldr · 10-12-2009, 04:57 AM

The adjustment I'm referring to is to ensure the table surface and the trunnion mitre pivot shaft are both in the same plane/parallel to each other. See pages 40-41 here: http://cdn9.grizzly.com/manuals/g1023s_m.pdf
You shim the front or back of the table/trunnion mounts to "tilt" the table/trunnion orientation so the blade is still parallel to the mitre slots when it's at 45 deg to the table. If this is out, you'll get the same pinch or drift in mitre cuts as you had in square cuts. This doesn't have anything to do with the 90 and 45 deg stops, its to make the trunnion pivot and table parallel. It's the trunnion pivot that moves when you adjust blade angle that I'm referring to (the one oriented fore-aft on the trunnion). If it's not parallel to the table surface, the blade will skew as it's angle is changed for mitres. Here's another reference to this:
Archive for the ‘Trunnion Alignment’ Category

Trunnion Alignment

Monday, June 16th, 2008 What

Just because you align the blade at 90 degrees doesn’t mean it will stay that way when you tilt it to 45 degrees. On most table saws, the entire blade carriage rides in semi-circular tracks called “trunnions”. The blade is tilted as the assembly travels along these tracks. The “axis of rotation” for the blade tilt mechanism is supposed to run along the surface of the table where the blade comes through the table insert (throat plate). This way, the table insert won’t interfere with the blade even when it’s tilted. However, inaccuracy in machining, or stress relief in the castings often causes this axis of rotation to shift so that it no longer runs along the surface of the table. So, as the blade is tilted, it gradually gets out of alignment with the miter slot. Fortunately, this process should only be required once for the life of your saw.

Why

The following symptoms are common when making bevel cuts on a saw when the trunnions are not properly aligned:

Burning of the cut edge
Board wandering away from the fence during a rip cut
Sawdust being thrown up at the operator
Kickback

These are the exact same symptoms that occur for normal (90 degree) blade alignment. If you see any of these symptoms when you tilt the blade (making bevel cuts), then you need this procedure.

How

First, make sure that the standard blade alignment (blade at 90 degrees) is accurate. Then, tilt the blade to 45 degrees and check the alignment.
The measurements

The best way to do this is to tilt the dial indicator as shown in the photo above. The most accurate readings always result when the plunger of the dial indicator is at right angles to the surface being measured. Use the same method that was described for standard blade alignment - mark a dot on the blade and take all measurements with the stylus of the dial indicator on that spot - rotating the blade as necessary. The error measured in this step will represent a combination of horizontal (90 degree) and vertical (tilt axis) misalignment. If you don’t perform the standard 90 degree blade alignment accurately, then it will influence your readings when the blade is tilted and invalidate the procedure.

Measurements can be made with the dial indicator horizontal as shown above but I don’t recommend it. Many sources of error can creep into your readings making them inconsistent and very frustrating. The dial indicator will have a tendency to lift during the measurement process so be sure to check that the jig remains flat on the table. Since the dial indicator is not perpendicular to the surface being measured, the readings will be exaggerated by 1/cos(45). This turns out to be equivalent to the vertical (tilt axis) misalignment so no further correction is needed.

Make a note of the change in reading between your two measurement points as well as the direction of the change. In this case it’s about 0.006 inches and it’s higher at the trailing edge of the blade. To determine the vertical (tilt axis) component of the misalignment, multiply the measured error by 1.414 (the square root of 2). The result, 0.0085″, is the amount of tilt axis error influencing the misalignment of your blade. When measured with the dial indicator horizontal, the reading is a little more than 0.008 inches. Correcting the error will involve inserting some shims and you will need this information to calculate the proper thickness of the shims and where to install them.

woodnthings · 10-12-2009, 07:33 AM

Quote:
9.

Tilt the blade to 45° and repeat Steps 1-5. If
the blade is still parallel to the miter slot, continue
on to the “Miter Gauger” instructions.
Otherwise, continue with the next step.
10.
If the blade was parallel to the miter slot at
90° but not at 45°, the table will need to be
shimmed with metal shim stock. The shims are placed between the table and cabinet over each of the four table mounting bolts "

I understand this idea, but it doesn't come across as the exactly the same as what you stated above, so I inserted the statement in parenthesis.

Quote "You shim (between the cabinet and trunnion mounts) the front or back of the table/trunnion mounts to "tilt" the table/trunnion orientation so the blade is still parallel to the miter slots when it's at 45 deg to the table."
The trunnions have a rotational axis. but no actual shaft and what this is saying is that the axis must be parallel to the table slots or during a 45 degree rip the blade will be "canted" or not in alignment, causing burning etc.

Great photo explanation and that's a awesome set-up for the dial indicator. From Grizzly or who makes it?

Thanks, bill.

M1911Bldr · 10-12-2009, 08:38 AM

I apologize for being too general in my description. The idea is to get the trunnion pivot for mitre tilt- the imaginary shaft that runs through the trunnion mitre mechanism from front to back and along/through the slot in the table insert) - and the table parallel to each other. I guess you could refer to this as the trunnion "sagging", either in the front or back, under the table so the pivot isn't aligned with the table's surface. When you set the mitre slot/blade alignment with the blade at 90 deg, you're adjusting the orientation between the slot and the arbor/blade. When you measure and adjust the blade at 45 deg, you're actually meauring to see if the trunnion pivot "shaft" (there is no actual shaft, just the center of the trunnion pivot mechanism) is running truly parallel to the table's surface. In Duncsuss's case he'd shim where the trunnion bolts to the bottom of the table (equal shims in either the two back corners or the two front corners), since the trunnion's mounted to the table and not to the top of a cabinet. The dial indicator setup is from "tablesawalignment.com." I made my own using a 3/4" wide piece of 5/16 aluminum bar. Dial indicators are CHEAP and worth ten times their price in setting up shop tools. They're the ONLY way to properly set/adjust fences jointer knives, mitre guages, planer knives and parallelism, etc etc etc. You can get a dial indicator and a magnetic base for about $25.00 at Grizzly, Enco, MSC and Harbor Freight.

duncsuss · 10-12-2009, 11:52 AM

... I think

First I'll check to see if the blade remains aligned at 45 degrees -- if it does, I'll save myself the headache of trying to figure out what might have gone wrong if it had gone wrong.

If it isn't aligned at a 45 degree angle, then I'll have to study the workings of the tilt mechanism to see how many different places a shim could be introduced and what the effects might be. The design of this saw seems quite different from the cabinet style Grizzly, and from the normal contractor style saws. The front and rear trunnions are very close together -- about 4 inches apart, nearer the front than back of the table.

I like that alignment jig ... here's the one I made myself from a spare miter bar, a scrap of wood, and a dial gauge I bought from Rutland Tool for about $10:

Thanks for persevering despite me being slow on the uptake --

Duncan

M1911Bldr · 10-12-2009, 09:23 PM

Great jig! Just be sure to keep it "pressed" down to the table so the dial indicator doesn't skew while you're measuring to the blade. I think, the way you described how your trunnion is mounted to the underside of the table, that if you have to adjust anything, you'll add shims between the trunnion and table at the same bolt locations you loosened to adjust mitre slot/blade parallelism. You'll shim either the front two or the back two mount points so you effect the parallelism between the table surface and the axis that the trunnion pivots on to set blade tilt. I wouldn't use the "dot" up on the tooth. You might be getting into the "tooth set" area. I stay right at the bottom of the gullets, on the disk of the blade itself.