Planes with movable fences, such as plows and rabbets, have two major defects.
1. In wooden-bodied planes, the fence can be tricky to adjust parallel to the tool’s skate or sidewall. An out-of-square fence can create some horrific results on your wood.
2. In metal planes, it’s difficult to secure the fence so it doesn’t slip. Even if you apply all your strength to the thumbscrews or collets, the fence slips too easily for my taste.
Part of this problem is caused by the tool, and part is caused by the user. When plowing deep grooves, it’s all too easy to tip the tool slightly at the bottom of the groove. If you tip the plane, the leverage against the fence will make it slip. Almost nothing will stop it.
One solution to these two problems is simple: Don’t use fenced planes. Or use planes with fixed fences only – such as standing rabbet planes.
If you aren’t willing or financially able to go down that route, I’ll offer a different solution that I have encountered in several other shops.
It will make you cringe. But here goes: Tighten the fence on your metal planes with pliers. Yes, this will mung the collets or thumbscrews, but it works.
Case in point: Last week I forgot to tell students in my class in North Carolina to tighten the fence with pliers. About half of them had the fence slip. This week in Washington state, I remembered to mention the pliers. And none of the fences slipped.
Sadly, I also use pliers on the depth stop to prevent it from slipping.
I apologize in advance to anyone who puts the pliers to their plane. Your tool will be uglier for it. But your work will be prettier.
— Christopher Schwarz