Your Mill as a Key Cutting Machine
Posted: Fri Mar 22, 2013 11:14 pm
Hello all, long time no post. I’ve discovered a neat trick for my small mill and thought I’d share. It makes a dandy key cutting machine.
Recently, I work for a real estate company that rents properties. When a tenant moves out, the locks must be changed right away. We use Schlage locks on our properties, so all info below pertains only to Schlage C keyways (the common 5-pin configuration). When rekeying a lock, you can choose any particular pin combination that suits your fancy. The new key is usually cut with a key cutting machine, or a key punch. I’d sold my key cutting machine years ago, not thinking I’d ever need it again. But rather than buy another, I gave cutting keys on the mill a shot, and it works really well. I think it’s actually more accurate than a key cutting machine, because when I rekey the lock to match the cut key, the pins are dead-on where they should be at the shear line…no adjustments necessary.
Just a couple things are needed. First, a 90 degree countersink, 3/8 in diameter. Purchase one that comes to a point (Enco sells none, but McMaster-Carr does). Then flatten that point ever so slightly on sandpaper. The flat is .035 on a from-the-factory key. I widen mine a bit more than that to .055 so I have a little more leeway if I’m not exactly precise on where the pins are cut on the X-axis. (The cut on the X-axis can have some "slop." The Z-axis can have almost none.) See the modified countersink below...
Next, you need a parallel that’s a few thousandths narrower than the key blank. You probably have a nice narrow parallel set. I didn’t, so had to make my own…what a pain to machine something so thin.
Next, I follow this process: Clamp the key in the vise with the bow to the left. Dykem the key. Edgefind on the shoulder of the key and zero the X axis, then center the quill (CCW .100 for my .200 edgefinder), then CW .007 to adjust for backlash (unique to my machine), and zero again. Now move .100 away from the shoulder of the key. Inset the keycutting bit. Crank the Z-axis up to .000 on the scale. Now lower the quill to lightly contact the key (which you’ll recall is now positioned .100 to the right of the shoulder). Remember the tip has been flattened, so this direct contact is OK, you'll not cut anything or damage your bit (the key blank is brass, anyway...no worries). Clamp the quill. Move the X-axis from .100 to .231, the correct L-R placement for the first cut. Move the Z-axis to the appropriate depth for the cut, and move the vice in the Y axis to make the cut.
All you need now are the Z-axis depths that match Schlage pins, and the various X-axis locations (which are .156 from each other, starting at .231). Here’s my cheat sheet.
Feel free to ignore the column headed “Seig X3” because an X3’s Z-axis is graduated in .0005 rather than .001 like a respectable mill, so on an X3 you always have to remember to “double” the cut depth. I also have a column for Schlage pin sizes, and “Key Area” refers to the area you pinch between the bottom of the cut and the bottom of the key when you measure a cut with calipers or a mic.
Here's a shot of a key that allows you to compare the mill-cut profile (in back) to a factory cut key (in front). On the back key, the last two cuts (at tip) are made on the mill. Notice mine are slightly larger at the base (as I wanted, for greater tolerance). The larger base would limit having a very deep cut next to a very tall cut. I probably could not cut a 0 cut or a 1 cut next to a 9 cut with my wider base. But such variances are frowned upon anyway, being very hard on the lock.
The last step is to file the "peaks" that are between the cuts...all they do is add wear to the lock, so I generally soften them. This allows the key to slide in and out easily, and greatly reduces wear on the lock's springs.
Suggestions for further improvement appreciated.
Recently, I work for a real estate company that rents properties. When a tenant moves out, the locks must be changed right away. We use Schlage locks on our properties, so all info below pertains only to Schlage C keyways (the common 5-pin configuration). When rekeying a lock, you can choose any particular pin combination that suits your fancy. The new key is usually cut with a key cutting machine, or a key punch. I’d sold my key cutting machine years ago, not thinking I’d ever need it again. But rather than buy another, I gave cutting keys on the mill a shot, and it works really well. I think it’s actually more accurate than a key cutting machine, because when I rekey the lock to match the cut key, the pins are dead-on where they should be at the shear line…no adjustments necessary.
Just a couple things are needed. First, a 90 degree countersink, 3/8 in diameter. Purchase one that comes to a point (Enco sells none, but McMaster-Carr does). Then flatten that point ever so slightly on sandpaper. The flat is .035 on a from-the-factory key. I widen mine a bit more than that to .055 so I have a little more leeway if I’m not exactly precise on where the pins are cut on the X-axis. (The cut on the X-axis can have some "slop." The Z-axis can have almost none.) See the modified countersink below...
Next, you need a parallel that’s a few thousandths narrower than the key blank. You probably have a nice narrow parallel set. I didn’t, so had to make my own…what a pain to machine something so thin.
Next, I follow this process: Clamp the key in the vise with the bow to the left. Dykem the key. Edgefind on the shoulder of the key and zero the X axis, then center the quill (CCW .100 for my .200 edgefinder), then CW .007 to adjust for backlash (unique to my machine), and zero again. Now move .100 away from the shoulder of the key. Inset the keycutting bit. Crank the Z-axis up to .000 on the scale. Now lower the quill to lightly contact the key (which you’ll recall is now positioned .100 to the right of the shoulder). Remember the tip has been flattened, so this direct contact is OK, you'll not cut anything or damage your bit (the key blank is brass, anyway...no worries). Clamp the quill. Move the X-axis from .100 to .231, the correct L-R placement for the first cut. Move the Z-axis to the appropriate depth for the cut, and move the vice in the Y axis to make the cut.
All you need now are the Z-axis depths that match Schlage pins, and the various X-axis locations (which are .156 from each other, starting at .231). Here’s my cheat sheet.
Feel free to ignore the column headed “Seig X3” because an X3’s Z-axis is graduated in .0005 rather than .001 like a respectable mill, so on an X3 you always have to remember to “double” the cut depth. I also have a column for Schlage pin sizes, and “Key Area” refers to the area you pinch between the bottom of the cut and the bottom of the key when you measure a cut with calipers or a mic.
Here's a shot of a key that allows you to compare the mill-cut profile (in back) to a factory cut key (in front). On the back key, the last two cuts (at tip) are made on the mill. Notice mine are slightly larger at the base (as I wanted, for greater tolerance). The larger base would limit having a very deep cut next to a very tall cut. I probably could not cut a 0 cut or a 1 cut next to a 9 cut with my wider base. But such variances are frowned upon anyway, being very hard on the lock.
The last step is to file the "peaks" that are between the cuts...all they do is add wear to the lock, so I generally soften them. This allows the key to slide in and out easily, and greatly reduces wear on the lock's springs.
Suggestions for further improvement appreciated.