Friday, March 1, 2013

V4.9 - Make sure your Jointer is flat

So, we were talking about our little friend, the Jointer last week. We went over some of its basics and what it can do. Thinking maybe this week we’ll just outline some of the ‘care and feeding’ of it.

Like we said, the jointer is just “two flat tables, with a rotating cutterhead between them”. A simple and not very complicated machine, but oh so much it can do for you. In order for it to perform at its best, there are a few things that you need to pay close attention to. One thing is those tables I mentioned. They need to be nice and flat AND they need to be nice and flat. I know, that sounds weird, right? Here’s the thing: each table needs to be nice and flat… and the whole machine needs to be nice and flat also.

A couple of tools that are a must when making sure that your jointer is ‘nice and flat’, is a machined steel straight edge and a set of feeler gauges. The bigger your jointer is, the bigger your steel straight edge needs to be. A short straight edge can be used to check an individual table, but to check the whole table surface, the straight edge needs to be at least three-quarters as long as the whole jointer. In other words, if your jointer has an overall length of 6 feet, your straight edge ought to be 4 feet long. Here’s why. When checking an individual table, first you would use a ‘ladder pattern’. You’d lay the straight edge on the table surface-just inside the edge of the table-and use the feeler gauges to determine if the surface is within the manufacturer’s flatness tolerance. Do one edge and then the other edge (these are the rails of the ‘ladder’). Then take the straight edge and lay it across the table in several spaced out places (these are the steps of the ladder) and check the flatness there.

The last check for an individual table is an X pattern. This is done just as it sounds. Lay the straight edge from corner to corner on the table surface and then do the same from the other corner to other corner. If these flatness checks turn out good, each table is ok.

Then comes the fun part – checking the full machine. The checks are done the same way, but the straight edge is placed one the entire jointer surface, after you have raised the infeed table to be level with the outfeed table.

What this check will tell you is if both tables are in a proper ‘plane’ with each other. If they are not, your tables may be nice and flat, but you will never get a successful joint because your board will come out twisted.

Send your questions or comments to: and we’ll see what we can do to help you.

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