Straightening a Jointer Fence

      A discussion of high-tech, low-tech, and caveman-tech methods for making a bowed cast-iron jointer fence straight again. September 27, 2008

My Delta DJ-20 jointer fence has a bad bow. It's 5"x36" and is out 1/32" over its length. I noticed it after owning it for a couple of years. Back then it was 1/64". Neither of the 2 local machine shops had surface grinders large enough to flatten it. Their milling machines did not have enough travel to hit the whole length in one pass. Now I have to get it fixed. Do I need to get it surface ground or can I have a machine shop CNC mill it flat?

Forum Responses
(Solid Wood Machining Forum)
From contributor J:
Don't know about the machining part, but I do remember years ago reading about being able to bend the cast iron tables and fences back into shape. Check with the guys over at OWWM - they may have some good tips for you.

From contributor R:
You can bend cast iron somewhat. I've tweaked a fair number of fences this way over the years as a machine tech. You might try pricing a new one. Might actually be cheaper than having it ground. I have a specialty grinding shop in my area that I've used to blanchard grind jointer fences and tables. It takes more for the setup than the actual grinding. They have very powerful magnetic tables and the part must be shimmed carefully or the magnet will pull it down and after grinding it can be worse than it was. Whatever works! You might try gluing some ply to the surface and face jointing it and putting some laminate over it. Cheap and have done it a few times for my more frugal clients.

From the original questioner:
I placed a chunk of plywood at the ends of the fence and gave it a couple of precision stomps with my foot. Then hit a few times with a mallet. It took about 10 minutes. It's as straight as ever. It makes me think I might have whacked it awhile back when moving shops.

From contributor B:
Bet you didn't! Cast iron machined green most likely will not remain straight. Its internal stress would be enough to cause it to warp. The cheaper they make these machines, the more problems occur.

From contributor F:
As long as the fence is 90 degrees to the table along its length, you do not need to worry about its straightness. We had to move the infeed table on our DJ30 to make it 90 degrees to the fence when we bought it, and it has stayed there ever since.

From the original questioner:
I would assume that it was a little green when they ground it (I'm sure they didn't let it sit around aging for 6 months after the pour). It's also a very out of balance chunk of metal. Having a straight fence helps to take the twist out of rough boards. It also helps a bit when you try to make 3x3 square stock. When edging 3/4" boards it doesn't make much difference. That's why I wasn't concerned for so long.

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