I have a handful of moulding planes: a pair of hollow/round, a few beading planes, as well as a few joinery planes such as a dado, rabbet, and shoulder plane. The joinery planes are no problem to sharpen, and the beading planes and hollow plane gave me little problems, but the round plane was more difficult than I thought it would or should be. I was able to flatten the back easily enough (which any woodworker on Earth should be able to do), but I could not get a consistent edge on the bevel.
Just the other day I watched a video posted by Paul Sellers on sharpening moulding plane irons that opened my eyes and shed a lot more light on working with these sometimes tricky planes. I’ll post a link to the video, as watching the video is far more clear and concise than my explanation would be. But I do want to add that during the course of the video Sellers mentions that moulding plane irons were far less polished and refined than a bench plane or chisel would have been. Sellers states that the higher angle of the plane coupled with the profiled nature allowed the irons to have less than perfectly flattened backs and relatively unpolished bevels. My previous conclusion was less scientific, because I always felt that moulding plane irons weren’t as highly sharpened and polished because they are more difficult maintain, and the woodworkers who used them just didn’t have enough time to spend on sharpening to such a high level. A chisel or bench plane iron can be maintained and honed in a matter of just 30 seconds, a mouldiing plane iron takes longer no matter what anybody says.
I’ve only personally worked with/handled a few dozen or so traditional moulding planes, and I can say that every one of them had an iron that at best needed a good deal of work, at worst needed a medic. I can also say that at the very least a few of those planes were only owned by one person, so it’s not as if they were all just passed down to half a dozen people who were progressively worse at sharpening. So while my conclusion may be off base, the proof is in the iron, and some of these irons were not well-sharpened. If you don’t believe me, believe Paul Sellers, who probably handles more vintage moulding planes in a week than I will in my lifetime.
Nonetheless, I tried Sellers suggestions, and I did get the round plane to work. I did not sharpen past 600 grit sandpaper or 1000 grit water stone, so I don’t have a truly refined edge yet. I will go to 8000 grit and then the leather strop, but I am going to do that when I sharpen my carving chisels so I can sharpen/hone everything all at once. So if you are having issues with sharpening moulding plane irons, I highly recommend watching this video.