Monday, March 23, 2015

Using marking gauges

If you ever uses one, you probably discovered that there seems to be a few way to buggered up a straight line and your lines may not be as crisps as you would have like.

First some basic maintenance
The head should be able to lock securely and square to the head, if it doesn't, you will never be able to uses it to its potential and it may earn flying lessons :-)
Refer to my earlier Marking gauges post to troubleshoot and evaluate various designs. If your antique gauge is missing its shoe, you will damaged the beam, make one. Especially if you feel you have to crank it down very tight to stop wiggles.

Notice the metal wing part sticking out from under the head? It is a loose shoe pad, shaped like a flattened U to stay put when loosening the head to move it. Its shape also prevent it from turning when cranking the screw. Often MIA in antique gauges, if it came with it.

Next take a hard look at the pin, cutter or pencil: they should be sharp, but their shape and position would also affect its use.
A conical pin, is going to scratch wood cross grain no matter what. Hint it is sometimes referred to as a scratch gauge, vs marking gauge.  Shaping that pin like I shown you earlier is how you fix that.

But that introduce, yet one more variable, the effect of the half cone shape on the gauge. It is acting like a wedge, either pulling the fence tight against the board or pushing away from it.

So what do you do? The short answer depends on what you are trying to mark and why.
The shoulder line should be straight, the V shape toward the waste area.
Marking the walls of a mortise, you would want the straight edge on the outside walls, but if you are now marking the matching tenons, ideally, it should be reversed.

Reverse for tenon, the straight wall should be on the inside.

Before you start flipping around those pins back & forth, you should instead invest or make, a few more, gauges dedicated to their function. If you happen to make the marks with the ramp side on the wrong way, don't sweat it, just be aware of where your true references surfaces are. But keeping the above information in mind will make your work more precise.

Using the gauges
First having taken the habit of establishing witness or joiner markings on you face and reference edge, make sure to always gauge (set the fence against) the reference edge.
They can be push away from you or pull toward you, but you should use a trailing motion, that is to say the gauge is slightly tilted up or down sideways (depend if coming or going) not straight across like a panel gauge. That's the reason for the top of our reshaped pin being like an arc, and the usual wear pattern shown on the gauge beam.

I replaced these pins years ago. That is about as much projections as I like for my pins

And just like using a marking knife, the biggest mistake is to try to make your final mark all at once. Instead, try 2, 3 marks. First one with a light touch, just to establish the cut, following ones (I always do at least 2) a bit stronger to deepen the mark. You will have less trouble following the grain that way .  Personally I prefer mostly to pull toward me, you get more control when working toward your core. Just remember to push the fence tight against the board, especially when the pin wedge shape is working against you.

Talking of mortise & tenons, they are usually centered on my stock. In order to find the center, just make a small mark from either sides, if you are centered, the marks will line up, if not, just remember that the offset is double the error. 

When marking my baseline for dovetails, I reach for my wheel type gauge, it is easier to roll over the board edges as I go around all 4 edges. It is also cutting cross grain all around, a task where wheel type excel. 

When marking tenons or mortise, I reach for my appropriately shaped pins on different mortise (or tenon) gauges.
Now you can start to understand why I have a "few" gauges :-) That and the fact that I like to keep them set throughout a project. Because you never know what you may have to redo or forget to do, before you change the setting...

The marking knife and marking gauges are what your cutting tools will follow next. May as well uses the mark left to our advantages.
Deepening the wedge side of the mark (don't touch that reference straight line, it's your finish shoulder) allow the saw to track straight across (called a 1st class saw cut) the ramp actually tend to push the saw against the straight shoulder. This also illustrate why the marks should be reversed for tenons vs mortise walls

Regardless of how ragged your cut, notice the sharp shoulder lines left. Easily cleaned up with a sharp plane to the exact shoulder lines. 
Understanding how to cut a crisp line and then using it to our advantages is what these tools are all about. When making or buying one make sure the head lock solidly, no wiggles, reshaped the pin if required and be mindful of the pins orientation.
Wouldn't that be easier to always use a cutting or slicing gauge instead of a pin type gauge? 
Not really, a thin knife edge will require more frequent sharpening, the modified pin last longer and we can better use the wedge shaped through to our advantage.

One last point, something rarely mentioned in the literature is the length of the pins sticking out. Too long they will chatter or tend to deflect and affect accuracy.  Too short the beam will experience more wear than necessary. So what is the correct length? That will depend on how you naturally tilt the gauge in use, so pay attention on how you use it and keep it as short as possible, while clearing the beam off your piece in use. Most gauges often come with the pin sticking out way too much. A long pin is nice for repeated sharpening, but it should be sticking out on top, not at the cutting edge.  Wheel types do not have this problem, the distance from pin to beam is fixed, even after numerous sharpening (we only touch up the flat back remember?) Use that distance as a starting point if you have both types. And remember you cannot have too many gauges.  

What about those measurements found on some beams? Oh please, we do not need yet another source of measurement errors! Set them to your tools, gauging blocks or adjust the fence until the mark is centered on the stock, no measurements involved in these operations! Just about the only time I will set my gauge with a measurement would be when using a panel gauge, and that is a slightly modified animal for its task.

Bob, gauging the snow in his driveway, wondering if its worth getting the snowblower out...


  1. Now you tell me not to do it all at once - after I figured it out for myself. I have yet to see Paul or anyone else do any marking in very long strokes at all. Why didn't I pay attention to this?

  2. Don't fret, nothing like learning the hard way, it sticks better that way :-)
    Bob, who has learned a lot doing it wrong for years...