Radiusing a cap-iron?

[Jelly]

I just dug out and fettled a Footprint No. 5 as a jack/scrub for a friend who's planing down a wide table top glue up which is a little bit in wind... (Also lent him a big woodie panel plane, and No.4, along with doing a quick "how to session on tge techniques and process forplaning a wide surface flat).

I put a fairly harsh (maybe 6¾") radius on the blade which was ok, but in order to get the setup right, needed to get the cap iron further down... I plonked it down on the tool rest flat and ground the profile of the iron onto the (nice thick accommodatin, flat) mating surface, then went to re-grind the angle of the chip breaker on top, which was where the fun started; long story short, the shape of the cap-iron makes it surprisingly easy to take off more material than you really want to, and I had to go back further than planned, as well as taking metal off the mating surface to get it fitting nicely.

Is grinding the profile by taking off all material with the cap-iron held freehand (not on the tool rest) at the desired angl right from the start, a better approach for this, or is it just a pig of a job, where past a certain radius you'd be better off just making a form and hot-bending the correct shape of cap-iron with the desired radius?

 

[D_W]

The cap iron should remain straight across unless the sole of the plane isn't flat. Or more plainly, the cap iron should match the profile of the sole if the purpose is to break chips.

Prep should be the same for all planes, freehand grind a radius profile that terminates around fifty degrees at the edge. This radius is relative to the thickness of the cap iron and not the width.

Old caps can be filed if they are in rough shape and there is a lot of work to do.

 

[D_W]

I should add to this, once someone used a picture of the cap iron on a gutter plane to convince me that cap irons should match the profile of the iron (they never do in an old plane with a flat sole). Of course, a gutter plane is expected to cut a similar depth cut along the width of the cut because it is cutting a profile. A jack plane, fore plane, etc, is cutting a thicker chip in the middle and none at the edges. There is no need to radius the cap iron because it will be set based on the thickest part of the chip, and it will have to remain above the sole of the plane at any set or the cut will become too difficult to push. As the shaving thickness tapers to nothing away from the center of the cut, the distance to the cap iron should be less, anyway (and it is, of course), as the thinner part of the chip won't need as long of a distance to the cap to be held down and successfully severed.

It is perfectly acceptable on a highly radiused iron for the cap iron to protrude past the end of the iron when set close, as mentioned, the cap iron itself will never go below the sole of the plane, so any iron that is shy of the cap iron will never be in the cut to begin with.

If you ever see advice to modify the cap iron to follow the iron profile on a plane with a flat sole, please disregard it as quickly as you've read it.

 

[David C]

David,

I have a 5 and 51/2, both with slight camber.

The C/Bs were shaped to match.

What problem do you anticipate?

I have found none.

David Charlesworth

 

[D_W]

David,

I have a 5 and 51/2, both with slight camber.

The C/Bs were shaped to match.

What problem do you anticipate?

I have found none.

David Charlesworth

With slight camber, no problem, and certainly no benefit. Even if poorly done on more radical camber, the part modified may never be in the cut - other fitting problems may occur since most have cap irons some relief behind the edge, though.

I'm not sure what benefit there is to modifying things where no benefit is to be had. Problems could arise with beginners doing it, too.

For something like a gutter plane or a hand rail plane where the surface is a finished surface and intended to be cut quickly, the matching profile would be very useful.

 

[woodbrains]

Hello,

If you gently camber your plane iron, and want a cap iron to actually give a cap iron effect, of course it should conform to the radius. But the camber should only be slight, most people tend to put far too much camber on their irons. For a smoother it is almost imperceptible. So a cap iron effect is possible with a straight across cap iron, but a radius set to match a cambered blade might be better and certainly won't do any harm. For a jack, blade camber can be more pronounced and a cap iron which conforms to the radius is helpful at reducing tear out on cranky grained wood at the dimensioning stage will save lots of effort later. I can't think how a cambered jack can have a straight cap iron set super close at the centre and not have it flush or beyond the cutting tip at the edges, which would cause shavings jamming between iron and cap.

A heavily cambered iron used for hogging off lots of material, as would a scrub, I would not camber the cap iron as it actually is only required for depth adjustment of the Bailey type plane.

Mike.

 

[D_W]

It should not be cambered too conform to the blade camber unless the sole of the plane is also radiused with the blade camber. This should make sense. You will not have a strong shaving at the edge like you do in the middle, and the fact that the cap iron is close to the edge of the blade will make no difference because the shaving won't be thick enough to cause it to resist. In a pure technical sense (which shouldn't be necessary, you cannot find any shortcomings in use of a straight-across cap), not cambering the cap is superior. The projection of the iron at various distances from the center is in tune with the shaving thickness at each point.

If you camber the cap iron, you have a shaving multiple times as thick at the center as the edge, but the cap iron distance is the same for the varying thicknesses. That makes no sense.

I'm not sure why this one has legs so much as it does. The very best outcome that you can hope for is that you're wasting your time.

Match the cap iron to the profile of the sole.

 

[thetyreman]

I'd imagine without a grinding wheel it would take literally hours of constant sharpening non-stop lol not even worth thinking about, it would be one hell of a workout.

 

[AndyT]

I'd imagine without a grinding wheel it would take literally hours of constant sharpening non-stop lol not even worth thinking about, it would be one hell of a workout.

I think it's not as bad as all that. A cap iron is normally mild steel, not hardened, and could be reshaped in a few minutes with a file. Bending the tip so it touches all the way across would be more of a challenge.

However, I'd say D_W is right, and if the sole of the plane is flat, the edge of the cap iron should be straight.

Curved cap irons are only needed on gutter planes (convex edge) and forkstaff planes (concave edge).

 

[bugbear]

Curved cap irons are only needed on gutter planes (convex edge) and forkstaff planes (concave edge).

Getting a good (shaving proof) fit on a forkstaff plane cap iron is quite an interesting and time consuming exercise.

I think making a Witchet(*) would have been quicker.

BugBear

(*) other names are available

 

[David C]

Just to add to the gutter plane example, I followed Alan Peters advice and converted a few wooden jack planes into hollowing planes. (Convex in width).

These had their capirons shaped to the same curve as the blade. They were very useful and performed well.

They had significant camber.

As Mike said, my bench planes (used largely for squaring edges or finishing) with very little camber, have shaped capirons so that the edges do not project past the edge for ultra close settings.

best wishes,
David

 

[ED65]

A jack used in the old way, or any other plane used for roughing, should not have the cap iron radiused to match the cambered edge just as D_W has stated.

As he says, think about what you want the shavings to be like and it should be plainly obvious why not. The plane will work better if the cap iron doesn't match the curvature of the edge, but if you're doubtful of the advantage do a direct side-by-side comparison and find out the right way.

 

[D_W]

Just to add to the gutter plane example, I followed Alan Peters advice and converted a few wooden jack planes into hollowing planes. (Convex in width).

These had their capirons shaped to the same curve as the blade. They were very useful and performed well.

They had significant camber.

As Mike said, my bench planes (used largely for squaring edges or finishing) with very little camber, have shaped capirons so that the edges do not project past the edge for ultra close settings.

best wishes,
David

It doesn't matter if the edges of the cap irons overlapping the cutting edge. They cannot physically get in the cut as the cap always resides in the plane - never does any part of it go below the sole.

 

[woodbrains]

Hello,

For there to be any cap iron effect, the leading edge has to be set 0.3 mm from the cutting edge, certainly not more than 0.5 mm. If the camber is greater than this, either the cap iron is set back more than will yield any effect, or the cap iron is set over the edge of the iron near the sides. It just doesn't seem right to me, that a little work with a file should be omitted to raduis the cap iron, when it makes things into a much more sensible arrangement. Probably 10 mins work, and the cap iron effect is preserved right across the cutting edge and it looks a lot better, too. If the iron is radiused so much that hanging the cap iron over the edge is necessary, then the full width of the blade is not being used, which is pointless. Either camber less or use a narrower plane.

Mike.

 

[D_W]

Don't do it, there's no reason to, you can't put the filed part back on and you're oversimplifying the scenario by comparing what's going on with a straight blade to a cambered one.

The set on a cap iron, by the way, is dependent on shaving thickness. I'm sure I set the cap iron off on the fat side of 0.5 mm on a try plane when using it to dimension. Even that plane which has greater camber than my smoother, no camber on the cap iron. And the stakes are greater there because there are abutments and wedge fingers to fight off. Never a jam up, never any significant tearout.

I guess I'd put it this way, if you want to file your cap iron, go ahead and do it. If you advise people to file a radius onto their cap iron, you're on the wrong side of correct and you should wait to instruct people until you're telling them not to put a radius on their cap iron - unless the sole of the plane is not flat. Then the cap iron profile should match the sole for good performance.

There are plenty of things that I don't know well about woodworking, but nobody understands cap irons better than I do or has thought more about them. Perhaps Warren Mickley has thought more, I guess - he's been using one to eliminate tearout for 40 years and has thought quite a bit about them, but that's probably about it.

I have had this argument many times over the last four years, and for the most part, I have heard back from people when they realized that radiusing the cap iron makes no sense. That includes planemakers.

Do it yourself if you'd like, but please don't advise other people to do it or that it makes sense. I am being a bit heavy handed, no offense intended, I have just seen this substandard setup advised too many times.

Also, we never actually use the full width of an iron, especially if we're trying to do efficient planing. Firstly, we don't want the tracks in material, and second, camber gives us cushion for lateral adjust and makes the plane much easier to use (we never have the issue where the extreme right or left of a plane is in a heavy cut while the other side is not). When we use a jack plane, quite often half of the iron or a little more is in the cut. The harder the wood, the less off the full width we have in it.

 

[Beau]

Think I might try this myself. Only use a slight camber but can see it makes perfect sense to camber the capiron enabling all of the blade to be used before resharpening. Think some care will be required as my cap iron has fair bit of relief on the underside but a bit of carful work should be able to sort it.

 

[D_W]

Good God, it's hopeless.

 

[Sheffield Tony]

I'm struggling to understand why, if you are using a plane with a heavily cambered blade, you'd be fretting about tearout. If you're using a scrub plane, you'd be planing across the grain and worrying about hogging away material as quickly as possible. You don't even need a capiron, let alone a closely set one.

 

[D_W]

I'm struggling to understand why, if you are using a plane with a heavily cambered blade, you'd be fretting about tearout. If you're using a scrub plane, you'd be planing across the grain and worrying about hogging away material as quickly as possible. You don't even need a capiron, let alone a closely set one.

The cap does make for a nicer working jack due to the fit of the cap iron and iron assembly to the wedge (at least when they're new or in current use and everything is tight). You're exactly correct about the work. It is the next step after the jack where the cap iron saves the most labor/effort/time.

Even if one prefers to work with the grain (as is suggested by some old texts) rather than across it when doing jack plane work, you still try to work in the direction of the grain and leave the cap iron set back a fair amount.

What seems to be getting missed here is that the far left and right of the iron should never be deep enough in the work such that you'd modify the cap iron (something you can't reverse, and something you never see done on old planes). The idea of trying to "use the whole iron" is something that is appealing until you try it and realize that working with the iron cutting somewhere other than the middle of the plane offends your craftsman's sense and makes it harder to do reflexive accurate work (unless the work is occurring exceedingly slowly - that wouldn't be reflexive). On other forums, the idea of this creating more economy in iron life is often brought up, but there are very few who will threaten iron life with parsimony in sharpening.

 

[Beau]

If there is an ideal spacing from tip of blade to capiron and you like to use a cambered blade why would you not want a cambered capiron to match the blade? I use a 5 1/2 plane for most work and it has a nice wide blade. I don't set it to cut it's whole width but just a part of it at a time. I then adjust the angle using the lever from time to time to use another part of the blade as one part dulls. Having an even spacing from capiron to tip of blade seems entirely logical and don't why I have not tried it before.