While machining the blade ramp isn’t hard, it is exacting and makes my brain hurt (screw this up and you don’t have a plane) so I thought I’d describe the process in a bit of detail. You can see the desired result over there —>
The 25º ramp dies in a 1/16” slot such that the blades hits the front wall. I do it this way because, after the plane is assembled, as the sole is lapped (to remove distortions and flatten), the mouth opens. If it starts at less than zero, I have room to do a nice job on the sole. After that, if I need to, I can open it the desired amount.
First order of business is to repeatability hold parts at 25º; the ramp and the infill need to have the exact same angle. The angle isn’t all that critical, being able to repeat it is. Angle vises are made for this kind of thing but I couldn’t find one (the ones I found are 90º out from what I need). So I made an angle block out of 1 1/4” aluminum, it is square to within 0.001” on all sides, long and wide enough to register on the mill vise and sole.
The ramp was roughed out with a big endmill (previous post) because from here on in, it is dinky cutters. In order to machine square sides into the slot, I’ll have to use a 1/16” cutter (which is fragile). Notice that slot isn’t as wide as the ramp. I don’t like lots of space around the blade. And it eliminates the need for those pesky blade adjusting set screws.
The drawing shows where everything is supposed to be. As you can see, things got shifted about 0.015” to the right. But, most importantly, the gap is close to the correct width (undersize by 0.009”).
I marked where the ramp should enter the sole and the front of the slot, knowing it was pretty unlikely I would be able to be dead on. I machined the ramp down to close to both the right height and the front line with a 3/16” cutter. Now for the “fun” part:: square ramp sides through the sole. It would have been easier to cut the slot at this point but I really didn’t want to move the part (I wound up removing the part anyway to add layout lines for the slot width and to recheck everything; hindsight, etc). I changed to a 1/16” cutter and painted on layout fluid. The fluid shows me where I have machined, which is important since I’ll have to go over the entire ramp as I won’t be able to get the cutter at the exact height needed. Evacuating the corners is tedious and you have to be really careful because you are taking big cuts with a little cutter. I overshot a bit because I only one shot to get this right (can’t get a file down there and re-jigging would just suck). Besides, I know from the drawing how much room I have.
Pop the part out, measure where the ramp enters the sole (first measuring photo above), subtract 0.2770 (the distance to the front of the slot) for where to cut the slot. Clamp the sole horizontal and cut the slot (I should have used a edge finder and indexed over but I just measured from the edge to the side of the cutter).
A small LED flash light is really nice when the mill is blocking the light and you can’t see the layout lines.
I used a riffler file to square the slot sides.
And yes! the mouth opening is a little under zero.
I thought about this process for a while and think I’ll change the order next time:
– Rough out the ramp.
– Cut the slot.
– Finish the ramp. Monitor progress by measuring from the front of the sole.
That should trade the “touchy feely” part of cutting the pocket for the my mills crappy z-axis (up/down) feed.
I’ve been trying to figure out if a split sole (two piece sole, cut at the slot) would make for a simpler build. Certainly, cutting the ramp is really simple. However, I suspect putting the sole back together (eg with a tongue and groove joint) and cutting the dovetails would add up to the same amount of grief. Plus, the “solidness” of one piece sole just appeals to me.
Machining aluminum: I have a Viper 1 1/8” carbide tipped router bit. I noticed that it is rated for aluminum so I tried it. It is awesome! Turning at 5k, metal just flew off the block (and half way across the shop, made quite a mess). I took 1/8” or so deep cuts because I wasn’t in a hurry.