520 Extension Table/Fence issue

algale · Post by **algale** » Sat Jun 23, 2012 9:34 pm

I removed the front rail. There is roughness at the bottom of all three bosses that may be causing one or more of the spacers to cant outwards at the bottom thus pushing the fence out of alignment. Anybody remember what there bosses look like. Here's the video: http://www.youtube.com/watch?v=YtBondA1Rhc

reible · Post by **reible** » Sat Jun 23, 2012 9:48 pm

Hi,

Is this a shopsmith purchased upgrade/new machine purchase or ebay/cl type of situation?

Ed

algale · Post by **algale** » Sat Jun 23, 2012 10:08 pm

Measurement error: In the last video, I said the center spacer that holds the fence rail away from the table was only 0.001 narrower than the left and right spacers. This was NOT correct. The center spacer is actually 0.007 narrower than the spacers on the left and right. Whether this is causing or contributing to the error, I do not know.

algale · Post by **algale** » Sat Jun 23, 2012 10:41 pm

Ed,

Here are some answers/responses to your questions:

reible wrote:
Mark a tooth tip and use that tip to align the main table. I have no problem getting within .002"/.003".

I just re-checked and the slot to blade alignment is 0.003 (I actually mark a spot just inside the gullet with a sharpie]In your case I would now go to checking the rip fence. Again using the miter gauge. [/QUOTE]

Too late for that. The rail is off. But the videos showed slot to fence alignment was within 0.001 -0.002. [/QUOTE]

reible wrote: I would think selecting at least 4 locations and locking the rip fence in position and verifying you can lock it in position on both sides of the blade and have it lock with in .005" is a good point to be at.

I checked numerous spots all along the main table. It was 0.001-0.002 all all along the main table. Everywhere else it was visibly inaccurate as confirmed in the videos.

reible wrote:Speaking of the rip fence, unless there is a good amount of clamping force applied by the clamps they are not going to work well. When you lock the front lever it should square up the fence, the back clamp is only to make sure it stays in position. You can adjust the clamps but only a small bit at a time. It is also good to lubricate them where the levers cam.

Clamping force was quite adequate. In the video the fence doesn't move because I have already squared the fence head to the fence before locking the front fence lock. The fence did not move when locking the rear fence lock either. You can hear from the squeak it could use some lubrication.

reible wrote:I would also check the extrusions, especially where the tubes go it. I have one that is a bit off from being square and have heard of at least one other person having had the same problem, shipping/handling damage??. Visual inspection of all parts is worth the effort, so add that to the list.

Not sure where the squareness of the end of the extrusion would impact any of this since the ends of the extrusions don't reference anything but I have noticed no problems with the outsides of the extrusions. I have also examined the inside of the main front fence extrusion and it has no defects that are visible.

reible wrote:Is this a shopsmith upgrade/new purchase or ebay/cl type of situation

I bought this used off of CL from the original owner who was a machinist. It was very lightly used.

Thanks for your interest.

Al

algale · Post by **algale** » Sat Jun 23, 2012 10:58 pm

[quote="JPG40504"]Perhaps it is time to attempt to discover things which do not align correctly two parts at a time. This may be more difficult, but start with the front main table rail and a tube. Insert the tube and secure it oriented as you would if you were going to attach an aux table. Using a straight edge(longer than the combination square) determine if the tube is indeed parallel to the front outer surface of the rail. Repeat using the same tube oriented as before but secure it to an aux table(only) and again check for parallel to the front outer surface of the aux table rail. Look at the spacing between the extended part of the tube and a straight edge held tightly against the rail front surface. If parallel the spacing should be constant along the total extended portion of the tube.

To put some perspective on this, that 1/16" deviation front to rear of the fence to the grooves is 1/3 of that across the front rail.(0.020") Bear in mind any 'vertical' differences will be the result of the 'bowed' tube.

This needs to be done on both the front and rear rails.

Come back with some observations.]

Not ignoring you here, JPG, but basically events sort of over took this. I think the front rail was not parallel to the front edge (it was not perpindicular to the sides) and removal of the fence showed two potential problems: (1) the center spacer is 0.007 narrower than the left and right spacers and (2) there is a rough spot on the casting bosses where the spacers go. The spacers (or some of them) may have been partially sitting on this rough spot, causing the spacers to be canted. As you point out, small errors in rail alignment can cause big fence alignment errors.

Before I do anything further, like shimming the center spacer or trying to file off the rough spots on the bosses, I would like some feedback from the forum on how to proceed.

Thanks,

Al

Ed in Tampa · Post by **Ed in Tampa** » Sat Jun 23, 2012 11:44 pm

I think you found the problem. If the front rail was canted (not parallel) to the main table and you adjusted the fence to be parallel to the saw/miter slot. And assuming the fence rails on the aux tables are parallel to their respective tables when you put the fence on the aux tables it would be skewed (crooked, not parallel to the grooves).

Now how to fix it. First I think there is a problem with the spacers if the middle spacer was .007 shorter than the two on the end and you tightened the fence rail it would have been bent U shaped in the center. That would cant both ends. However both ends would be slanted differently. So the fence adjusted for one side of the miter slot should be off if placed against the other miter slot.

The roughness on the boss could be the problem but I would think in this case the problem would be on the left. If fence rail was slanted with the left side further out and you adjusted the fence parallel on the main then it would be off to the right on aux tables.

I would check the fence rail both the back and front to make sure it wasn't bent or slightly damaged. Then I would do what ever it took to mount perfectly parallel to the front table edge and perfectly 90 degrees to the miter slot. Then I would adjust my fence making it parallel to the miter slot

Then I would recheck my aux tables. I would expect them to be perfect also.

Somebody mentioned the back rails and I think you eliminated them when you checked the fence just using hand pressure against the front rail. Back didn't come into play when doing that.

I think you are very very close to solving the problem. First thing Monday I check the parallelism of the fence rails to the respective table they are connected too.

As I said in the past I went through 3 main tables before I found one I could live with and it was nothing to write home about.

JPG · Post by **JPG** » Sun Jun 24, 2012 12:30 am

I believe shimming the main table rails is going to be your 'solution'.

A caveat is to be sure to maintain the front rail to rear rail spacing.

Measure the three aux tables to determine a likely correct spacing dimension. Pick a good measuring location on the front and rear rails of all 4 tables or preferably the table front/rear bosses.

You have determined the front main table rail is not perpendicular to the slot, do check the rear rail as well.

After having determined the 'correct' spacing, you should be able to determine if the PO machined the main table front and rear bosses.

Assuming all the aux tables bosses share the same front-rear spacing, the main should be likewise. If not and the main table has been modified, the standoffs will need shimming to both make the rail perpendicular to the slot and the front rear spacing as well.

I will attempt to measure my 510 tables and will report back with the 'results'.

JPG · Post by **JPG** » Sun Jun 24, 2012 12:47 am

If the correct front boss surface to rear boss surface dimension is not 22", it is very close! I looked at all three aux and the main early 510 tables and a later 510 aux table that I have.

I measured the boss to boss dimension, not the table edges which are tapered.

dusty · Post by **dusty** » Sun Jun 24, 2012 6:06 am

My main table measures 22"x17". The 22" measurement is boss to boss. Otherwise the table measures 21 7/8"; the bosses are 1/16" thick.

I was able to measure seven spacers. They measure .314" +- .001".

[ATTACH]17820[/ATTACH]

algale · Post by **algale** » Sun Jun 24, 2012 8:57 am

dusty wrote:
I was able to measure seven spacers. They measure .314" +- .001".

[ATTACH]17820[/ATTACH]

My left and right spacers were .314. The middle spacer was .307.