520 Extension Table/Fence issue

algale · Post by **algale** » Sun Jun 24, 2012 9:28 am

The consensus is to try a shim first, which has the benefit of being reversible. Before I got too tired and went to sleep last night, I did quickly remount the front rail to see if the rough spots on the bosses interfered with the spacers. I do not believe that they necessarily interfere. The rail can be mounted with the rough spot acting almost like a shelf that the spacers rest on but without it affecting the distance between the spacer and the main table or spacer and rail. While it looks like it can be mounted like this, however, does not mean it WAS mounted like that. It still is possible that one or more spacers was being canted by the rough spots on the bosses. I am curious whether my bosses are unique in having this rough little shelf at the bottom.

Getting back to the spacers, I have measured and remeasured and there is simply no getting around that that the center spacer was definitely 0.007 narrower than the left and right spacers (the left and right spacers are 0.314 and match what Dusty got on seven spacers he measured). So we will see if that was the real source of my problems after I experiment with shims and report back.

Also, for those brave souls still following along, I put my blade of Starrett square on the rail back and front sides of the front rail and it appears to be perfectly flat; in other words, I do not think the front rail has been permanently bent out of shape as a result of the too skinny spacer in the middle.

Thanks for the contributions of everyone who has responded.

dusty · Post by **dusty** » Sun Jun 24, 2012 9:43 am

If you pulled the front rail in by .007" in the center it would definitely have some effect on rail alignment but what I envision is inconsistent with what I believe your video shows (relative to being out of square).

At any rate, it does appear that shimming of the front rail has some good chance of resolving your problem.

Maybe a sanity check is in order. How about leaving out the center shim and checking for square?

Ed in Tampa: I think we would have gotten here eventually but yours was a good and timely input. I was fixated on the front rails of the small tables.

JPG · Post by **JPG** » Sun Jun 24, 2012 10:54 am

Ed was the first to say so, but thinking that the main table rail was not perpendicular to the slot was a too far remote possibility that was too easily disregarded(by me anyway). That was a mistake!!!:o

FWIW .314 sounds like 5/16" + plating.

It may have been interesting to have measured the fence to left slot parallelism.

If the center short spacer is skewing the rail, the skew would be opposite on the other side and the fence misalignment 2x what it is on the aux tables(in the opposite direction).

However the rail was observed to be straight, so the shorter spacer is still a mystery!

It will be interesting to see if the back bosses are 'modified' and if the back rail is skewed.

Since the aux tables appear to be consistent with each other, we could assume they have not been modified but do need verification since yer boss description was not that they were flat!

At this point I would not assume ANYTHING about the main table etc.

Of most interest will be the spacing between each of the three front-rear pairs (22" - ?) and the squareness of each three boss set to the slot.

algale · Post by **algale** » Sun Jun 24, 2012 10:57 am

Ok. I have shimmed the front rail center spacer the required 0.007 and as far as I can tell, the front rail is now perfectly perpendicular to the miter slots (which after all is the key measurement and far more accurate than measuring against the uneven surface of the table edge. The rear fence already was perpendicular.

I put the fence back on the main table hoping to see a major change, but he revised results are a little underwhelming. Previously you will recall the dial indicator read "0" at both ends of the fence. Now, putting the fence back on the newly shimmed front rail, I am getting +0.002 at the outfeed end of the fence. In other words, removing the fence, shimming the center of the fence and reattaching everything has shifted the fence alignment on the main table by only .002 inches. I could try readjusting the fence, bringing it back to perfect and placing it on the extension tables to see if this made a difference but I know 0.002 isn't going to correct the obvious problems I am seeing when the rip fence is transferred to the floating or extension tables.

Back to the drawing board. I am going to investigate the rails/spacers on the auxiliary tables.

New video:http://www.youtube.com/watch?v=8qBD4Y8MLJo

pennview · Post by **pennview** » Sun Jun 24, 2012 11:02 am

One thing you might want to check is whether the three bosses on the main table are on the same plane. Perhaps the fence is true enough to use for checking or possibly a decent level will show if there's a reason for the shorter spacer. You could also check how the bosses line up with the bosses on the auxiliary table.

JPG · Post by **JPG** » Sun Jun 24, 2012 11:09 am

pennview wrote:One thing you might want to check is whether the three bosses on the main table are on the same plane. Perhaps the fence is true enough to use for checking or possibly a decent level will show if there's a reason for the shorter spacer. You could also check how the bosses line up with the bosses on the auxiliary table.

This(and the plane perpendicular to the slot) would be the objective of any shimming. Add 22" from the rear bosses as a third objective.

Methinks the machinist PO attempted to tweak the table(s) to align them and failed!

dusty · Post by **dusty** » Sun Jun 24, 2012 11:14 am

pennview wrote:One thing you might want to check is whether the three bosses on the main table are on the same plane. Perhaps the fence is true enough to use for checking or possibly a decent level will show if there's a reason for the shorter spacer. You could also check how the bosses line up with the bosses on the auxiliary table.

This is somewhat off topic except that I checked the bosses on my tables only because of this thread. My tables have bosses that have been milled in two different fashions. With either style, the pad where the spacer rests is 1/16" proud of the table side.

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JPG · Post by **JPG** » Sun Jun 24, 2012 11:36 am

So maybe the PO did not tweak after all!

Maybe this is one of Ed's rejects!:D

algale · Post by **algale** » Sun Jun 24, 2012 11:48 am

Well, the shimming of the front rail did accomplish one thing. There is no longer a catch when I move the square between the main table front rail and the floating table front rail. Also to the extent the floating table grooves are properly parallel to the grooves/miter slots in the main table, the front rail of the extension table is not perpendicular to the grooves in the floating table (this is also true of the extension table). Looks like I'm in for a Shim-Fest. Or is it a Shim-Dig?

I added a video to show what talking about.Check out this video on YouTube:

http://www.youtube.com/watch?v=rKeIqKj7 ... ata_player

algale · Post by **algale** » Sun Jun 24, 2012 9:46 pm

Spent several hours today trying to get things aligned to no avail. For the time being I am out of energy and ideas.