520 Fence Is Not Square to the Table Surface

[rlkeeney]

I'd feel confident buying used but understand your reluctance. I'd also demand a refund if I got a fence that wasn't square to the rails.

I have had this fence for several years, or I would send it back. Until this came up, I never thought about checking if the fence was square to the table.

I probably will buy a used fence, but I need to convince myself that I can't fix this one first. When I do buy one, it will be put under strict scrutiny.

The top of the 520 fence is roughly 3 inches above the table so, assuming I still no how to do math, each 0.005" of gap is about 1/10 of a degree out of square.

In my case, it would be doubled. I make two passes, putting the opposite side against the fence for the second cut.

[DLB]

FWIW I shimmed my fence using a feeler gauge (aka thickness gauge) under the left infeed end pad. A shim thickness of around 0.012" to 0.018" seemed to produce a result approximating the OP's first picture. Somewhat to my surprise, I found the rear clamp made no discernible difference. I also measured that out of square condition with my Wixey, which indicated the fence was out of square by 0.2 degrees. (The Wixey has a published accuracy of +/- 0.2, so take that with a grain of salt.)

In the spirit of 'no such thing as a dumb question,' are those four bolts that hold the extrusion to the main casting tight?

This suggests to me that the problem could be solved or masked by either shimming the right side pad or removing material from the left side pad. I'm not suggesting this, just putting it out there.

- David

[rlkeeney]

In the spirit of 'no such thing as a dumb question,' are those four bolts that hold the extrusion to the main casting tight?

The bolts are rock solid. Not a dumb question. It's the simple obvious things that can bite you.

This suggests to me that the problem could be solved or masked by either shimming the right side pad or removing material from the left side pad. I'm not suggesting this, just putting it out there.

I was able to get the fence square by applying several layers of blue tape to the right pad. It is not a permanent fix, but it is a proof of concept. I have some aluminum tape coming that I am going to try for a more permanent fix.

While applying the tape and testing for square, I discovered that my fence sides are bowed in slightly in the center on both sides of the t-slot. Is this normal?

[chapmanruss]

Robert K, the sides bowed in is not normal and may account for the twist you described.

Continuing this here from My Growth Rings for those who may not read both sites.

As Robert H posted on MGR he found out after contacting CS getting the pads seated all the way in fixed his problem and likely would correct Robert K's problem here if it wasn't for the bowed in sides.

Hopefully others who come across this problem of the fence not being square to the table surface will find this helpful. This only applies to the Pro Fence of the Mark V 520 and Mark 7.

[DLB]

... As Robert H posted on MGR he found out after contacting CS getting the pads seated all the way in fixed his problem ...

I don't really understand, maybe because I've never had it apart. Was he referring to the pads that the main casting (Fence Base) ride on, between the casting and the rails? Were there any pictures? The SS parts breakdown doesn't show the pads I'm referring to being separately available.

I do have one 520 fence with a very slight outward bow. The high spot is just under the T-slot on both sides and runs the full length of the extrusion. If I rock my straight edge down, I can get a 0.003" thickness gauge between the fence and straight edge at the top. So the high spot is probably half that number.

- David

[rlkeeney]

@DLB
The pads are on the main casting. They are not shown in the parts breakdown; they are not shown, so I assume they are part of 518419 (217). There are photos of the other fence with the pad extended on my growth rings.

My fence is straight along the bottom edge. All I had ever done with it was rip it until now; otherwise, I would never have noticed it. My jig was made to ride on the fence and was not square to the table. While troubleshooting this, I found the problem was not with my jig; it was with my fence.

[rlkeeney]

I squared my fence to the table by using layers of aluminum tape on the low pad. This makes it usable for 99.9% of my needs. If I locate a fence in excellent condition, I may buy a new fence. So far, I have not found one I like. I'm not going to buy one that is dinged up, and for sure not one that has been hit with the saw blade. I emailed Shopsmith support a few days ago about parts availability for the fence and received an email asking which parts I needed. I sent them the extrusion part number, but I haven't heard back.

Shopsmith 520 Rip Fence Shimmed With Aluminum Tape

2026-04-26 07.21.30.jpg (187.36 KiB) Viewed 18512 times

[dusty]

Pardon me, please for being a skeptic.

Have you fixed the problem or just compensated for it. Are you certain that the casting (the part to which the pads attach) is properly attached to the aluminum fence extrusion.

Another thought. The reference surface appears to be the front rail but is the rail correct for this mearurement. I would think the table top (unless you have diligently aligned the rails to the table top.

[dusty]

Now that I look at this I realize I have a similar situation but only a new fence can change my situation. My aluminum extrusion is not square. Not terrible but not perfect.

My fence is many years old but I thought it had been well cared for. Not the case. Let your finger tips be the judge. I find many rough spots that could have an impact on precision. The to the degree that it would effect most work that I do but someone striving for perfection would be seriously disappointed.

I am curious. In the latest picture posted (with tthe alumium tape) -- how did you measure to determine that the pads are now in the same plane and perpendular to the table surface or rails.

[rlkeeney]

Have you fixed the problem or just compensated for it.

Compensated obviously.

Are you certain that the casting (the part to which the pads attach) is properly attached to the aluminum fence extrusion.

The screw are all locked down tight. What else could it be?

The reference surface appears to be the front rail but is the rail correct for this mearurement.

No, the rail is not being used for the reference. The fence is out of square with the table top down its full length on both sides.

I would think the table top (unless you have diligently aligned the rails to the table top.

Even though the rails appeared perfectly aligned, I loosened all the screws and reset them using two jigs.

The fence has a slight dip (dent) about six inches long on the left side, centered on the t-slot.

None of this has any noticeable effect on ripping. I discovered the problem when I made a jig that straddled the fence and had two problems. The jig slid perfectly down the first few inches of the fence, but became progressively tighter as I pushed it toward the back of the fence. While I was troubleshooting this issue, I discovered that the jig was square to the table when sitting on the table, but not square when on the fence. I checked the fence, and it was not square to the table. When I checked the pads on the fence, one was higher than the other. Both pads are tightly seated. It took several layers of aluminum tape to get the fence square to the table, but this does not fix the dent.

My conclusion is that the previous owner either dropped the fence or damaged it in some other way I can't imagine. There is a very slight dent in the fence along with a tiny twist. I checked the fence again using my Starrett straight edge because, while writing this, it occurred to me that I had not checked for the dent on both sides. The dent is on both sides and a bit more on one side than the other. It is as if the previous owner clamped something tight on the fence to bend it like that.

So what do? Forget fence-straddling jigs for now. Keep an eye out for a used fence in excellent condition, and hope Shopsmith comes through with parts.