Aligning the fence

heathicus · Post by **heathicus** » Sun Jan 06, 2013 8:59 pm

I was working on alignment today and found my fence needed adjusting (500). I know the screws on the left and right side of the base should not be used for alignment, but I was unable to do so without them. The base had a pivot point in the middle of it and would wobble. Without using those set screws, I could not stabalize the base.

Did I do something wrong? Is my base just damaged? What is the real harm in using those set screws to stabilize the base?

rpd · Post by **rpd** » Sun Jan 06, 2013 10:13 pm

heathicus wrote:I was working on alignment today and found my fence needed adjusting (500). The base had a pivot point in the middle of it and would wobble. Without using those set screws, I could not stabalize the base.

Did I do something wrong? Is my base just damaged? What is the real harm in using those set screws to stabilize the base?

I think this link may have the answer to your problem. Mark V Rip fence fix.

heathicus · Post by **heathicus** » Sun Jan 06, 2013 10:32 pm

I don't think that's the issue. That describes a problem with the part of the base that contacts the top of the bar. I believe my problem is with the part of the base that contacts the side (front) of the bar.

edflorence · Post by **edflorence** » Mon Jan 07, 2013 12:08 am

heathicus wrote:I was working on alignment today and found my fence needed adjusting (500). I know the screws on the left and right side of the base should not be used for alignment, but I was unable to do so without them. The base had a pivot point in the middle of it and would wobble. Without using those set screws, I could not stabalize the base.

Did I do something wrong? Is my base just damaged? What is the real harm in using those set screws to stabilize the base?

I need to go back and review the proper procedure in PTWFE, but fwiw, over the years I have often succumbed to the tempatation to swing the fence a little bit one way or the other to get it aligned by using those screws and can report no problems. Can't really see how it could get you in trouble.

JPG · Post by **JPG** » Mon Jan 07, 2013 3:26 am

edflorence wrote:I need to go back and review the proper procedure in PTWFE, but fwiw, over the years I have often succumbed to the tempatation to swing the fence a little bit one way or the other to get it aligned by using those screws and can report no problems. Can't really see how it could get you in trouble.

The reason it 'gets you in trouble' is that it concentrates the force of aligning the fence to two 'spots'. With those screws fully retracted, the forces are spread over the entire width of the 'base'.

Heath: Question is, what is making it 'pivot'?

edflorence · Post by **edflorence** » Mon Jan 07, 2013 1:05 pm

jpg;

OK, that makes sense. I can see that spreading the stress over a wider area is preferable to concentrating it on a couple of points in terms of a general principle. But I am talking about swinging the fence extremely small distances with the screws, so not a lot of force is involved. Still, I grant the point.

I did go back and review a couple of editions of PTWFE as well as the instructions that came with the fence and other than the admonition to be sure the setscrews are in the retracted position when aligning the fence, could find no other reference to them. So what are these screws there for? I seem to remember this subject cropping up before on the forum, but the substance of the discussion escapes me.

heathicus · Post by **heathicus** » Mon Jan 07, 2013 1:37 pm

If I understand it correctly, they are for those rare times when you WANT the fence to be skewed. Such as "jointing" or edge sanding with the disc sander. See: http://www.shopsmith.com/academy/discsa ... x.htm#edge

JPG · Post by **JPG** » Mon Jan 07, 2013 2:01 pm

[quote="edflorence"]jpg]

It is not the force from adjusting them, but the force from clamping the fence to the table. I would never consider adjust those screws when clamped.

Back in the old days (before the conical sanding disk) edge sanding was done by intentionally skewing the fence(back side away from the disk) and feeding the workpiece from the rear. The fences of that vintage had a single screw on the right side of the fence base for that purpose.

FWIW it is 'mentioned'(albeit very briefly) in all 5 versions of PTWFE that I have.

Why newer versions of the fence have a second screw on the left side is a mystery to me(I suspect someone at SS did not understand what you have just read and 'assumed' they were for fence alignment). I am not comfortable with that! Stupider things have happened though!(band saw table upgrade:rolleyes:)

The 510 fence went back to a single screw, but that second screw made it into the bandsaw and 500 upgrade(I think) fences.

heathicus · Post by **heathicus** » Mon Jan 07, 2013 2:14 pm

While we're on the subject, let me make sure I correctly understand the locking mechanism on the fence.

As you turn the lock knob, the front of the fence locks in place. A tab compresses against the bar on the table holding the fence base solid against that bar. If everything is correct, the set screws are fully retracted and the fence should be square with the blade (and miter gauge slot). As you continue to turn the knob, a tab at the back of the fence squeezes against the back side of the table which holds the back of the fence in place and keeps it from deflecting from side pressure.

Right?

On my fence base, after the front of the fence is clamped, but before the back of the fence is fully clamped, if both set screws are fully retracted, the base will swing slightly side to side. It's not stable until the back of the fence is fully locked, or the set screws are extended.

I'll have to investigate more thoroughly why that is, but it will probably have to wait until the weekend.

JPG · Post by **JPG** » Mon Jan 07, 2013 2:23 pm

heathicus wrote:While we're on the subject, let me make sure I correctly understand the locking mechanism on the fence.

As you turn the lock knob, the front of the fence locks in place. A tab compresses against the bar on the table holding the fence base solid against that bar. If everything is correct, the set screws are fully retracted and the fence should be square with the blade (and miter gauge slot). As you continue to turn the knob, a tab at the back of the fence squeezes against the back side of the table which holds the back of the fence in place and keeps it from deflecting from side pressure.

Right? Correct!

On my fence base, after the front of the fence is clamped, but before the back of the fence is fully clamped, if both set screws are fully retracted, the base will swing slightly side to side. It's not stable until the back of the fence is fully locked, or the set screws are extended.

I'll have to investigate more thoroughly why that is, but it will probably have to wait until the weekend.

Sounds a lot like #2 this thread!

I looked at all 4 500 fences that I have, and none of them have the 'hump'.

A close look at how the base aligns with the table rail reveals the following.

The rail is flat(parallel to the table top?)on the top edge and has a bevel on the bottom edge.

The fence base has a flat(humpless) surface that rests on the top edge of the rail.

The fence base has a beveled surface that contacts the bevel on the rail.

All those surfaces are smooth and straight(hopefully).

In the middle of the fence base is the clamp 'finger' which pulls the fence base towards the rail when tightened.

That clamping action and the beveled surfaces pull the fence base down tight against the rail upper edge and wedges onto the rail lower beveled edge. The clamp also pulls the fence base into and down on the table rail where the fence base needs some clearance to the outer corner of the rail.

A cause of rocking side to side has got to be one of the beveled surfaces not being straight(or bumpy?) or the corner of the fence base that the top edge of the rail rests against/on is funky.

I believe that hump(#2) interferes with that corner fit.