Filing the Mouth on a Cast Iron Plane

by Robin Frierson

This article first appeared as a thread on theWoodNet woodworking forum. It was compiled and reproduced here for easier public consumption. All Text and Images are the property of Robin Frierson.

Here are some photos I shot showing my procedure for mouth filing, the procedure having been told to me by some knowlegable plane tuners over on the old Badger Pond Hand tool forum. I dont know how to post the photos into the message, perhaps someone else can later, but here they are with an explanation to follow:

Photo #1 shows the tools. First thing I do is place some tape on the inside of the frog as the file can remove some japanning. I use smaller 6in swiss files in three different smoothness grades. I also use some custom made sanding pads cut from tempered hardboard. In fact you could simply skip the files and use the sanding pads. Make them the exact width of you mouth, usually a little larger than the blade and then use sanpaper attached with spray adhesive. I rip them out of 1/8 in hardboard. I usually finish up with 600 grit for a very smooth mouth.

Photo #2 shows how I position the plane, sole up, in the vise with lights both above and below the plane so you can see how your progress goes. Dont clamp too tight or you will distort the sole. Remove the plane as your work and check your progess with the hand lens. I sometimes take a little more metal off inside the corners as there is where I usually get clogging. You also do not need to bring the bevel all the way to the sole, you may want to stop just short of the sole and bring your sanding block up to 90degrees. I sometimes worry if its too thin at the sole it could later chip.

Photo #3 shows the filing block being placed on the plane sole. I cut a piece of wood with a 15 degree bevel and square it to the sides. I put the bottom of the block just even with the mouth to start. If you need to remove more material just scoot the block back a little. Best to start with it even with the mouth and then move it back later if you need to. The block allows you to place your file or sanding block(the hardboard with sandpaper) against the block and maintain a consistent bevel. Stop often and check your work.

Photo #4 shows me squaring the block against the side and then later attaching it with double stick tape or spray adhesive.

Photo #5 gives a side view of the block showing the bevel.

Photo #6 shows the sanding block placed against the filing block. At first, till you get the bevel started, it may not rest against the block until you get some material removed. If using a file take care to not touch the rear mouth area or the sides of the inside as you can wear through the tape. I have gone over to just using the sanding blocks, making up several with different grits. BTW, they also work well for final sanding of the frog face and rear sole, to make one continous bearing surface.

Photo #7 shows how a file can be placed against the filing block.. I use a hand lens to check my progress. Another method is the simply scratch awl a line on the sole and do it by hand, but I prefer using the wooden filing block as it makes it easier.

You may notice the paper shim on the frog of my # 4 1/2. I have placed them on some planes to reduce the vibration and hopefully mimc the action of a wooden infill. You simply cut one out and use spray adhesive to attach it to the frog face and then wax it so the blade slight freely across it. I use paper cut from file folders or you could use thin veneer. I think it helps some, but it could be just the placebo effect. Any questions?


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