Blog: Test For Accuracy By: John Heisz

With my knives freshly sharpened, I thought I would do some test cuts on the planer to see how consistent the thickness of cut was across its width. This was more to satisfy my curiosity as to how accurately it was cutting, not because this is something that was particularly important to me – my use of this machine has been more for smoothing wood out, ready for sanding, as opposed to planing something down to a precise dimension.
So, I ran a 2″ wide piece through on the left side, measured it then ran it through on the right side. To my surprise, the planer was also cutting on the right side – not promising. I measured it and found nearly 50 thousandths of an inch in the difference! I started to investigate.

The first thing I checked was that I had put the knives in correctly. The alignment tool for this planer is ok, but could be better and mistakes can happen. I found that the knives were indeed installed properly.
The next thing I did was look at the machine to see if there was any adjustment on the platen. I couldn’t see any.
I then looked at the mechanism that raises the cutter head / motor assembly – two lead screws on either side and four guide posts, two on each side. I wondered how the lead screws were connected and looked underneath. There was a metal pan that I removed, exposing this:

Two sets of nylon bevel gears and a shaft to link the two lead screws. At that point it occurred to me that the head assembly may not have been set up properly in the factory, and I decided I would attempt to make some adjustments.

I figured that the left side had to come down by more than .04″, so I removed the screws that hold the shaft retainer on:

I could then lower this gear, disengaging it from the other one. I turned the lead screw gear one tooth and re-engaged the shaft. This would lower the cutter head down on the left side by some amount. I had to do this several times (four or five teeth, I lost correct count when I messed up and went backwards once), to lower the cutter head to where both sides were equal. Incredible.

It is not outside the realm of possibility that these gears somehow jumped a tooth over the two years I’ve owned this planer, since there is quite a bit of slop between them. One tooth I could see, but four? Or five?
Anyway, it works well now – something like 3-4 thousandths of an inch deviation across the width of the cutter head, which is pretty darn good in my book. Trick is, will it stay that way?

After my ‘adjustment’, I marked both sets of gears, just so I’d know at a glance if something had moved:

I used a black permanent marker to put indexing dots on each.

The assumption would be that this type of tool was made and setup for some measure of reasonable precision, from the factory. Of course, this might be their acceptable tolerance – within 50 thousandths. I guess the lesson is to not take anything for granted, especially with economical tools. If you are at all concerned with precision, check it out beforehand.