Jointing Technique Help

[onocoffee]

I think I've lost the ball in the past two weeks.

I have a 5" benchtop jointer with helical cutters and it's worked great for what I've needed. Haven't used it in a couple weeks and something has happened to me. I can't seem to plane a flat joint.

I run the piece through the jointer for many passes and the "front" part of the piece gets planed down thinner than the back. This current piece is now 41mm thick on the forward end and 43mm on the rear end. I feel like I'm giving pressure on the front and then keeping it on after it passes the cutting head, but obviously I'm doing something very wrong.

Any thoughts on what I may have started doing incorrectly? Or could there have been something that i did the jointer to change it and create this issue?

Thanks!

 

[Vtshopdog]

Jointer should produce a flat surface, not necessarily uniform thickness.

Try running your jointed stock through a thickness planer with jointed side down and unmilled face towards the thickness planer cutters.

 

[smorgasbord]

True that jointers don't produce boards of uniform thicknesss, but a propertly adjusted and used jointer should not take a board that's flat and uniform thickness to something that isn't uniform thickness.

First thing to check is that the outfeed table is in-line with the top of the cutters in the cutterhead. Unplug the jointer and then a straightedge placed on the outfeed table should just graze the top of the cutters across the width. If not, break out the owner's manual and adjust.

The second thing to check is that the tables are co-planar. Typically, the cut depth is adjusted by moving the infeed table up or down. On some jointers, it's possible to adjust the infeed table to take 0 depth of cut - in other words, the top of the infeed table is level with the top of the cutterhead's cutters. If you can do this (or very close) then you can unplug the jointer, rotate the cutterhead so the middle is "low" and put a known straightedge on the infeed and outfeed tables. Using a raking light and/or feeler gauges, see how coplaner the two tables are. If they're not, adjust.

Note if you can't adjust the infeed table all the way up to the level of the outfeed table, you can still check by using thick feeler gauges under the straightedge on the infeed side. You want the same gap everywhere.

If the tables are aligned, then is the stock much longer than your infeed table, or are you trying to flatten a convex face? With a convex fact, the stock can rock as you feed it. With long stock, as new stock reaches the infeed table, that, too, can rotate the stock as you feed it.

Technique is simple: hold the board on the infeed table and feed. As you get enough material on the outfeed table, shift most of your pressure to the outfeed table - the idea there being that the flattened face registering on the outfeed table continues the flatness. But, for boards that don't hang off the infeed table that's not normally an issue. Yours being a benchtop jointer maybe hints that the longer stock needs some good technique.

 

[onocoffee]

Thank you guys. I will check those things.

I should have noted that I was running the rough sawn pieces through continuously because the back end (the 43mm) still had rough surface that hadn't been planed out = despite having run the piece through multiple times.

And I thought that I was practicing good technique by doing the pressure shift from infeed to outfeed side - but for some reason, the back end (the part still on the infeed) wouldn't plane - as though it was being held above the cutters by the outfeed side. Which is what (I think) led to the uneven planing.

I ended up giving more pressure to the back end so that it would contact the cutters and was able to get it flat, which I then ran through the thickness planer, but these last two days have been some strange jointing.

 

[Steve1]

A helical cutter-head is more tolerant of grain direction.
I sometimes alternate starting-end of the board.

 

[jeffinsgf]

Your symptom description sounds like your outfeed table is slightly higher than the cutterhead (normal cut at the start, then diminishing depth of cut as you continue to feed). Hold a straight edge on the outfeed table extending over the cutterhead. Rotate the cutterhead by hand. The knives should just kiss the straight edge. If it fails to touch at all, you need to lower your outfeed table.

So many things can go wrong on what seems like a simple machine. Tables not parallel will cut a curve instead of a line. Knives above table will cause snipe. Knives below table will cause a taper. Those are the simple ones. Then you get into the problems of the tables not aligned properly right to left to each other and to the cutterhead. Here's your can of worms. Do you have an opener, or would you like to borrow mine?