I've been filing for a little while now, although I've never been an apprentice before. Before I had a lathe and mill, I had files and hacksaws and made do. I learned a few things early on:
- A good solid vise is important. It is also important that it be mounted on a bench at the right height for the work you're doing. I have 7 vises in my shop, 3 of which are used for filing. The biggest and lowest one (a nice Charles Parker vise) is below my elbow height so I can lock my arms to my body and use my legs and body weight to lean into a roughing cut; this one is for when I need to remove a lot of material. My Prentiss vise is mounted at about elbow height so I can use my arms in a natural stroke without tiring too much. My Wilton bullet vise is mounted high and is used for fine, light work. It is mounted high so I can see where my file is touching the work.
- It is important that you know how your body and arms move. Each of us has a stroke, a natural angle when we move along our own lines of movement. You have to figure out what yours is and use it. You also have an effective stroke where you can control the angle of the file; go beyond it and the file will tip. Know what your effective stroke is.
- Related to the above, I tend to level the top of the work on my big vise because I use my body to move. On my mid sized vise and smaller vise, I tend to put the top of the work with the farthest end tipped slightly down because my stroke makes me dip at the end of the stroke. I'm sure other folks do it different but this lets me file flatter.
- You have to see what you're filing in order to file it. More specifically, you have to know where you want the file to cut. Sometimes you want to hit the whole surface, sometimes only in one spot, and sometimes you want to hit one spot at an angle. Learn to see where you want the file to cut and then learn to put the file there.
- The way you hold a file matters. Grabbing a handful of handle and nose works for rough work when you're removing a lot of material but it doesn't work when doing fine work. Learn to grip with the last three fingers of your hand and then learn to guide the angle of the file with your thumb and forefinger; this is how you make the file cut at the angle you need it to cut. The lighter the work, the lighter the touch at the front of the file.
- I tend to stroke at right angles to the cut of the file's teeth. This seems to cut better for me than using a lot of downward pressure. The harder I bear down, the less flat the surface gets so I try to avoid excessive pressure and I let the file cut. Pretty sure this has to do with bending the file with pressure but I admit that sometimes pressure is what's needed, especially when roughing ugly.
- Listen to NortonDommi and learn to drawfile and learn which file to drawfile with. This is important because it allows you to sight along the top of the work and the file at the same time. There are times when you have to get the work flat and drawfiling will help you do that quickly. A single cut bastard file and a clear idea of what needs to be taken down will get the work flat really fast when drawfiled. A double cut file, used with a fine touch, will help you fine tune a surface and produce a nice finish.
- Practice, practice, practice. And understand that perfection is not going to happen but tolerances will allow you to get really close. I'm guessing that nobody produced a 1" square, +/- 0.0000", apprentice or journeyman, but within 0.005 - 0.010", yeah, that can be done.
I made a knurling tool with zero clearance between the side plates and the arms. In order to get the arms to move freely but with no discernible side play, I drawfiled the inside of both plates. Got her done in a few minutes ... because of the 40 years of filing that went before.
Stick with it and it will come. This is a skill that is all but dead nowadays but in a hobby shop, yeah, we filing!
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