Flattening jointer fence

[David Utterback]

The fence for my Jet 8" jointer is 0.012" out of flat along its length yet is square to the beds along this dimension. The defect occurred within the last 12 months after 6 or 7 years of use. (There are gremlins in my shop! I am certain.) It is difficult to edge joint boards.

I have a piece of 3/4" thick granite that is about a foot longer than the fence. My plan is use coarse wet r dry emery cloth on the granite surface which will be clamped to the top of my workbench. The surface will be checked for flatness using a Veritas straight edge that is about the length of the fence. If this does not work, it will be off to the machine shop for surface grinding.

In the meantime, I may make a temporary fence with MDF and BB plywood so I can finish my project. Any suggestions or disapprovals?

Thanks!

[Rick Lizek]

I've fixed many a fence by removing the fence and putting blocks under each end and using a small jack to put pressure on the middle and pushing it down about twice the amount it's off and it typically will spring back to 0 deflection. There is a small amount of bend in the cast iron. For twisted fences I clamp one end down to a sturdy bench an clamp a sturdy board to the other end and twist it slightly past where you want it to end up. You will have to repeat it several times to get it where you want. I learned this technique from the regional sales man from powermatic. I spent over twenty years of being a professional tech and did this on many fences. Worked like a charm.

[Mark Wooden]

+1 on what Rick describes- Powermatic actually published the information for use by the owners of their machines.They recommended putting the fence on two 2x4 blocks and standing on it. Cast iron moves and they knew it.
One of the issues that many Asian machines have is they don't allow the castings to 'age' for a few years before they machine them. Your fence developing a bow after a while isn't unusual and can be remedied.

[Chris Fournier]

+1 on what Rick describes- Powermatic actually published the information for use by the owners of their machines.They recommended putting the fence on two 2x4 blocks and standing on it. Cast iron moves and they knew it.
One of the issues that many Asian machines have is they don't allow the castings to 'age' for a few years before they machine them. Your fence developing a bow after a while isn't unusual and can be remedied.

No one ages cast ion for years any more, it would cost too much to hold the inventory and technology/metallurgy has long since shown that proper production processes and post casting treatment will eliminate casting stresses.

The 0.012" along the length of a fence should have absolutely no bearing on our ability to joint an edge, not even one little bit.

[Keith Weber]

You said that the fence is square to the table along it's entire length. If that's true, it really shouldn't affect your cut. When you face plane, you don't really even need to use a fence, so 0.012" of out-of-flatness will have zero effect on your cut. When edge jointing, you could, in theory, have a curved, but vertical fence, and as long as your board maintains contact with that fence throughout the cut, you should end up with a perfect 90° edge on your board. The only time, in theory, that it could adversely affect your cut is when you've got the fence tilted at an angle. Even then, at 0.012" of out-of-flatness over the entire length of the fence, I doubt that you would even be able to measure any variance in the angle. Now 0.012" of twist is a different story, and would have a small effect on the board when edge jointing.

If the "curve" in your fence is to the left as viewed from the infeed table, you could put some shims between the fence and its mount if the design of the allowed a place for you to do that.

[Mark Wooden]

No one ages cast ion for years any more, it would cost too much to hold the inventory and technology/metallurgy has long since shown that proper production processes and post casting treatment will eliminate casting stresses.

The technology may exist, but very few use it.....

[Al Launier]

You said that the fence is square to the table along it's entire length. If that's true, it really shouldn't affect your cut. When you face plane, you don't really even need to use a fence, so 0.012" of out-of-flatness will have zero effect on your cut. When edge jointing, you could, in theory, have a curved, but vertical fence, and as long as your board maintains contact with that fence throughout the cut, you should end up with a perfect 90° edge on your board. The only time, in theory, that it could adversely affect your cut is when you've got the fence tilted at an angle. Even then, at 0.012" of out-of-flatness over the entire length of the fence, I doubt that you would even be able to measure any variance in the angle. Now 0.012" of twist is a different story, and would have a small effect on the board when edge jointing.

If the "curve" in your fence is to the left as viewed from the infeed table, you could put some shims between the fence and its mount if the design of the allowed a place for you to do that.

My thoughts exactly! As long as the face is flat it would follow the fence square to the knives resulting in an edge square to the fence.

Well said Keith!

[Robert Engel]

Fugetaboutit......it won't affect your ww'ing at all.

[jim mills]

Those that say do nothing are correct, but if your genetic make up is like mine, that defect drives you nuts, and takes your focus off the task at hand. I have a powermatic jointer that had the same problem. I did exactly as you describe...used granite and sandpaper. Took alot longer than i thought it would. I ended up doing alot of the work with a ros, then used dykem (sp?) On the granite to mark the hogh spots and then sanded them off. Kind of a "hillbilly hand scrape" if you will. Turned out real nice, and i feel a lot better about the jointer.

[Don Jarvie]

Unless it affects the wood where a joint is off then fix it. If this was metal work then maybe but wood moves so don't bother.

[M Toupin]

+1 on what Rick describes- Powermatic actually published the information for use by the owners of their machines.

What Mark & Rick said.

Page #8 http://vintagemachinery.org/pubs/655/2789.pdf

(http://vintagemachinery.org/pubs/655/2789.pdf)Mike

[David Utterback]

Thanks for the feedback! Jim has pegged my personality type and I will continue "homemade" remedies before going to the machine shop. The one I used last year for my band saw table should cost less than $100.

I only weigh 170# so standing and even bouncing up and down did not make any change in the fence. I have had it under clamping pressure for well over 24 hours using my biggest deep throat Bessey clamp. No change observed earlier today even though the face is deflected 1/8" or more when clamped.

The PM manual (Thanks, Mike for the link.) says that you will be able to feel the fence "give." That has not happened. I was wondering about minimally peening the back of the fence to give it a little more encouragement. If not resolved soon, I will try the grinding on the granite surface.