Adjusting the Depth:
First, slightly loosen the large brass lock knob. Then, adjust each depth adjusting screw in turn to move the blade to the desired position. These adjustments are done while holding the plane upside down and sighting down the sole from the front of the plane. It is important to have your eye in a direct line from the bottom of the plane. Then, relock the large brass lock knob.
Please note: Unlike conventional planes, backlash is taken up by finishing your adjustments retracting the blade.
You might think there is zero backlash because there is only 1 threaded connection in a straight line between the frog and the depth adjusting screws. However, for the screws to turn, there must be some clearance between the threads. This, then, accounts for the tiny amount of backlash. As previously said, it’s always more precise to do your final adjustment retracting the blade.
Adjusting the Mouth Opening:
I will start by saying that I never adjust the mouth opening. Therefore, the frog is always seated back against the wood bed. This is my recommendation for users also. The main reason for moving the mouth opening is to help fight tearout. This, however, is only minimally effective. Adjusting the chipbreak gap is much more effective, and doing this on a ‘Blum’ plane is very easy and quick.
However, adjusting the mouth opening is easy. Just loosen the large brass knob, and insert a small shim behind the frog, from the bottom of the plane. This can be as simple as a matchbook cover or similar. Snug up the brass knob and then adjust the depth screws. Then tighten the large brass screw.
On a traditional double iron, the chipbreaker is the piece that sits on top of the iron. On a Blum plane, the chipbreaker is not a separate piece, but is the leading edge of the frog. This is much easier to use and doesn’t require any of the fiddling and precise fitting of a traditional chipbreaker. On a ‘regular’ double iron, the iron must first be ground perfectly square. If not, the chipbreaker can not be set really close ( where it is most effective ), because it won’t match up with the iron. The second issue is that the back of the blade must be flat and the chipbreaker must fit against the back perfectly. This is especially critical when setting the chpbreaker very close to the edge ( small chipbreak gap ). Otherwise, chips will jam underneaath the chipbreaker and all planing comes to an immediate halt. The third issue is that the chipbreaker must be ‘sprung’ just right to give the proper pressure at the leading edge so no chip can ever get underneath it. The screw holding the chipbreaker to the iron might be 2-3″ from the front of the iron. The fourth issue is that the leading edge of the chipbreaker must be ground at the proper angle to be the most effective at holding the chip down to be sheared by the iron. On some planes, this is not ground right, so the chipbreaker is much less effective than it could be. This is probably because some makers still believe the chipbreaker is only there to just stiffen the iron!
On a Blum plane, none of those issues come into play. The blade is easily lined up with the chipbreak edge. The bottom of the frog is ground so the blade contacts it evenly. The back-up iron gives direct pressure so no chips can get underneath, and the leading edge is ground at the proper angle to give maximum effectiveness. Also, the depth doesn’t need changed to reset the chipbreak gap nor does anything need to be removed from the plane.
Adjusting the Chipbreak Distance:
You can leave the depth right where you were cutting, or, to make it easier to see and manuever, you can lower the frog below the sole about 1/8″. Re-lock the large brass lock knob.
Loosen the 3 screws on the bottom just enough so things move easily. Use a small, straight screwdriver to move the blade out, and use your fingers to move it back in. The rare earth magnets in the frog bottom will hold the blade in place during adjustments. Move to the desired distance. Use a phillips screwdriver to then move the back up iron to just at the back of the bevel of the blade, being careful not to move the blade. Tighten the 3 screws and re-adjust the depth.
What is the ‘Right’ Distance?
The best answer I can give is that experience will give you your answer. Most old texts said to move it ‘as close as possible’ for fine cuts in difficult woods, and move it ‘farther back’ for heavier cuts. One old book said to move it to 1/100 th of an inch for swirled grain. That’s .010 ( ten thousands of an inch ). I move it closer than that for difficult cuts. The problem is that measurement of the chipbreak gap is difficult at best. You can use a feeler gauge or a calipers. Since this is done ‘by eye’, the best thing to do is look at the distance and compare it ‘by eye’ to a standard such as a feeler gauge or caliper gap. You won’t have to know any measurements to set it, but it does help when learning to have something to go by and compare to.
The closer the chipbreaker is set, the harder the plane will be to push, so its use needs to be somewhat discretionary. If you are jack planing with a heavy cut, and there will be more cleanup with a smooth or fore plane, you don’t want the chipbreaker set so close as to make it more difficult to push. Experimentation is the key. Happily, your ‘Blum’ plane has the easiest to set, most reliable chipbreaker on the market, so moving it should become part of your planing regimen. It will greatly expand your planing abilities.