Blades and Frogs

[Jim Koepke]

You can make a blade bend further away from the middle of the frog that way by increasing the cap-iron's preload, though only to a point as the cap iron is quite weak relative to the blade. You can't go the other way without decreasing the cap iron's preload, and that causes other problems such as jammed shavings at the blade to cap-iron interface.

I must be lucky in finding the sweet spot of cap iron tension.

Here is something of mine from before David Weaver posted about setting the chip breaker:

http://www.sawmillcreek.org/showthre...ker-to-Jointer

Scroll down to post #27 & #28, Chips Ahoy or is that a Cap Iron?, for a little bit about cap iron tuning.

jtk

[bridger berdel]

I'm sure that someone somewhere has mated a stayset cap iron with a Miller's falls lever cap. Seems like that would be about the max you could do in the "total bedding" arena. I doubt it would make a whole lot of difference in the performance of the plane but it might make for a nice solid "feel".

[Rob Lee]

(snip)
Given that reality, I question whether it's even desirable to have the blade in contact with the frog along its full length, as opposed to having the normal forces distributed more towards the cutting edge. LV's design choice looks increasingly sensible as I think about this more deeply.

Hi Patrick -

Our planes are designed with a line of contact along the mouth, and a locus (more than just a point) of contact on top of the adjuster. The blade "bed" (or frog, if the plane has a frog) is machined to ensure clearance.

We think trying to get two surfaces to mate perfectly is a mug's game.... and have gone for predictable, repeatable, and controllable geometry.

Just as a three legged stool is stable, the line and point approach ensures we have contact where we want it.

Cheers -

Rob

[Ray Selinger]

What Rob Lee didn't mention is with the Vertas replacement blade and cap iron, you have a pretty healthy chunk of steel.Bowing shouldn't be a question.

[Patrick Chase]

What Rob Lee didn't mention is with the Vertas replacement blade and cap iron, you have a pretty healthy chunk of steel.Bowing shouldn't be a question.

IMO it isn't really a problem with Stanley blades either. Those designers knew what they were doing way back when, and sized the blades adequately.

As I said earlier, this is one of those things that you shouldn't even look at unless you have a specific problem that you're trying to fix. If you know anything about metrology then you will *always* be able to find a gap somewhere, and you will chase your tail endlessly and quite possibly make matters worse [*] if you try to fix it. I think that's what Rob meant when he referred to "a mug's game".

[*] As I said in another post, I think that from a functional perspective you want the pressure at the iron<->frog interface distributed toward the cutting edge of the blade. If you strive for "perfect mating" in the middle then you will necessarily sacrifice some pressure at the ends, and that may hurt you.

[steven c newman]

Gaps? What gaps? This is a Millers Falls No. 11 I have been using on the latest project..
IMAG0004.jpg
Do you see any gap? As with 99.9% of the rest of my planes in the shop. Have had a few come through....that something else was causing the "gap"...like a badly fitted lateral lever sticking up too far, or not sitting in the slot that was made for it.

[Ray Selinger]

Steven if you pull off that nice lever-cap, lift the cap-iron/ blade out and put the edge of a 6" rule on the blade of the cap-iron/blade, you'll see the gap. It doesn't even have to be a good 6" rule. Does it matter? that's a different story.

[Patrick Chase]

Steven if you pull off that nice lever-cap, lift the cap-iron/ blade out and put the edge of a 6" rule on the blade of the cap-iron/blade, you'll see the gap. It doesn't even have to be a good 6" rule. Does it matter? that's a different story.

Steven showed us a Millers Falls for a reason - it has a 3-point lever cap, which means that the straightedge check isn't conclusive.

In any case you can't diagnose gaps in an assembly as complicated as a plane from a picture or any other form of direct visual inspection. Apply an extremely thin coat of marking grease (something like Prussian Blue) on the underside of the blade, install it, and see where you (don't) get transfer. I guarantee that you will be shocked at the percentage of the area that's actually in contact, even with an MF lever cap. Even that is a conservative way of measuring since the marking fluid won't be zero thickness. There are more involved ways of detecting smaller gaps, but this will do for now.

Note also that gaps are unlike horse shoes or hand grenades: Close doesn't count.

[Stewie Simpson]

Mr Bailey was a fairly switched on guy. He realized that a metal bed is much more susceptible to chatter than a wooden bed, and the best way to address that issue was to use a thinner blade that would allow the cap iron to add additional tension. We are of course talking about a period where a 4 point contact was considered ideal. The use of a thicker blade is a fairly contentious approach if its aim is to reduce chatter. The use of a 3 point approach as Mr Lee mentioned makes for perfect sense. As a side issue, theirs a very good reason that tapered irons for a wooden bed have a slight concavity to their underside.

[steven c newman]

Anyone is free to come to the Dungeon Shop and verify the lack of gap. I also used a lot of Stanley planes....which are also gap-free.

So, come on over, bring whatever you need to test the lack of a gap.

[Patrick Chase]

Mr Bailey was a fairly switched on guy. He realized that a metal bed is much more susceptible to chatter than a wooden bed, and the best way to address that issue was to use a thinner blade that would allow the cap iron to add additional tension. We are of course talking about a period where a 4 point contact was considered ideal. The use of a thicker is a fairly contentious approach if its aim is to reduce chatter. The use of a 3 point approach as Mr Lee mentioned makes for perfect sense. As a side issue, theirs a very good reason that tapered irons for a wooden bed have a slight concavity to their underside.

Lee Valley uses a two-area approach - a linear patch across the leading edge of the frog, and a "locus" (Rob's term) that's roughly semicircular at the adjuster.

In any case we finally agree on something: That approach is basically ideal. Everything in between doesn't matter so much.

[steven c newman]

Hmmm, I am not from Lee valley. Went back down to take a picture or three of the Stanley planes...
IMAG0001.jpg
Stanley #5
IMAG0002.jpg
Stanley #6c,T-10
IMAG0005.jpg
Stanley, Made in England #4


All lay on the frog with no gaps.......IF you take the cutters out of the plane, they will curve a bit. Curve is on the frog side of the irons, away from the chipbreaker. Yet, when I place them back on the plane...no gaps. Either it is "magic" or the frog has been fettle correctly. I can not even slip a piece of paper between the frog and the iron.
IMAG0003.jpg
Close up of the #6c's frog.

Magic?

[Kees Heiden]

Once upon a time I did a little test with an old Stanley that appeared to have no gap between frog and blade. I took a very thin piece of paper and put it under the blade, sticking out on one side. Then I installed the blade assembly and fiddled with the lever cap screw until the piece of paper was clamped just so I couldn't move it. Then I took a very heavy shaving and while I took the shaving I could easilly pull out the piece of paper.

This shows that allthough the fit might look tight, the blade bends enough under planing pressure to create a gap nonetheless.

[Ray Selinger]

So it's worth while filing the frog face, not to get a full contact rather so the machining mistakes (Stanley and their machining of green castings) don't interfere with the contact at the bottom.

I think,for a while in the '80s, Lee Valley sold an English made plane with a hinged lever cap under their Lee Valley name.

[Patrick Chase]

So it's worth while filing the frog face, not to get a full contact rather so the machining mistakes (Stanley and their machining of green castings) don't interfere with the contact at the bottom.

Yeah, if you have a plane wherein the blade doesn't bed at the bottom then IMO that's worthy of intervention. I'd still say to rely on performance rather than on inspection to determine how much work is necessary though.