Last time we got our iron worked up and ready to go to work. However, the iron can’t work on its own. It needs a chipbreaker. What for? Well, in my estimation, 2 things. First, the chip breaker lends structural support to the iron. It basically acts as a spring stiffener to the pretty thin tool steel the iron is made of. The 2nd job of the chipbreaker gives it its name. It breaks the chips, or more appropriately to planing wood, it controls the shavings. It helps to create consistent shavings by guiding the chip off the cutting edge and directing it back into a curl. In a nutshell, the chipbreaker (more properly called the cap iron according to many) forces the wood to fold back on itself “breaking” the continuity of the wood fibers. That is key to a well-performing plane because it aids in the prevention of tearout.
A well tuned chipbreaker is essential to making a bailey-pattern plane perform consistently well IMHO. On clear, straight grained, cooperative woods, it’s not that noticable. Get some tight-grained figured wood with changing grain direction though and you’re likely to find out quickly if your chipbreaker is shaped and set properly.
I recently was cross-grain planing some White Oak with a jack plane. The plane was clogging every few strokes and the task was terribly frustrating. Eventually I ended up removing the chipbreaker and going through the process I’m about to describe. It turned out that while I had created a good fit between the chipbreaker and the iron when I rehabbed the plane, I hadn’t undercut the edge of the ‘breaker enough and it was causing me much pain. The difference in plane performance after correcting the problem is night and day.
So what exactly is our objective when we work on the chipbreaker? 3 things:
- We want an absolutely air-tight fit between the iron and the leading edge of the chipbreaker.
- We want ONLY the leading edge of the chipbreaker to make contact with the iron.
- We want the top of the chipbreaker to be able to control the shavings coming off the wood.
The following illustration from an article on WoodCentral shows how we want our chipbreaker set on our iron:
The article linked above is a worthwhile read on how to prepare the chipbreaker and set it on the iron. The following is how I do it.
Enough background, let’s get on it!
Here is our chipbreaker. All we have done to it up to this point is rust conversion.
There is significant pitting on both sides of the chipbreaker leading edge. That’s not ideal but I believe we can make it work just fine with a little elbow grease.
The first thing I want to do is to make sure the back part (above the “hump” at the leading edge) is relatively flat on both sides. Mostly we don’t want burrs or raised areas and we want to make sure it doesn’t have a twist in it. If there is some twist, you can most likely straighten it in a vise. You may have to hammer it a bit on an anvil but this steel isn’t hardened like the iron and can be “bent to our will”. No twist in this one and in the 9 or 10 planes I’ve rehabbed, I’ve only had to straighten 1 out.
I start with a fine mill file and file down the burr raised at the threads.
Now I stroke the flat area on both sides on some wet/dry paper. We don’t need this to be polished at all, just want to make sure it’s decently planar and doesn’t have any raised areas.
The bottom side, shown above, is pretty flat to begin with. The top side, shown below, has a bit of a hollow and pretty bad pitted area.
I work it on my coarse diamond stone a few strokes just to smooth it out. This isn’t necessary, I just like to make it smooth.
I’ve also dyed the leading edge up on the top. This is where I’ll move to next. It doesn’t really matter whether you shape the top or bottom of the leading edge first. You’re probably going to end up working them more than once anyway ;-p
We want a “knife-edge” in contact with the iron. Objective #1 we stated says we want a tight fit but according to #2 that fit has to occur only at the leading edge. Essentially, we want to hone an edge here. I’m going to start with about a 10 degree bevel on the front.
The exact angle isn’t critical and I don’t use my Wixey box to hone it. I just wanted to give you an idea of what the angle I’m grinding looks like :-) You can hone it at a shallower angle. I’ve just never seen any real advantage to it so I basically just want a polished edge with some slope. For now, I’ll work it only on my coarse diamond stone just to grind a small bevel back about 1/32-1/16 inch. You can go further if you want but I like to leave as much material as I can. Plus I’m lazy so I like to remove as little as necessary.
I grind enough to make sure there’s no pitting in my bevel edge. I’d rather not have any pitting right behind the bevel either but I don’t think it’s going to be practical to avoid it on this guy. I am going to take it to the belt sander and gently grind the rounded part to smooth it as much as possible though. I’m careful not to hit the bevel I just created on the sanding belt. If I were a smarter fella’, I would have gone to the belt sander first…
Now let’s turn our attention to the bottom side. First I’m going to grind a flat that’s slightly undercut. You can see that I’m going to let the part right behind the rounded section set flat and grind the leading edge just enough to clean it up. I do this part on wet/dry paper because I don’t want to grind the area that’s resting on the granite down. The intention here is just to clean up where our bevel will be to make sure there isn’t any pitting we’ll have to grind out.
We should be okay but, I am going to take a half-round file and get rid of that pitting behind the ground flat.
Now onto the diamonds. We’re going to hone an edge just like we did with the iron and polish both bevels up through the fine diamond stone. See how all of my plates set above the plywood top the same amount?
That way, I can let the end of the part rest on the plywood and will be grinding a consistent angle across all 3 stones. Both bevels are small so I just work them on the medium then the fine. It only takes a few strokes on each to roll up a wire edge.
Sorry, this picture is kinda crappy. But I think it’s sufficient to give you an idea of what our leading edge that contacts the iron looks like.
Below are pics of the top and bottom bevels at this stage. The edge isn’t as bad as it looks in the pictures (I didn’t remove the burr from the fine stone yet) but it’s not great either. The pitting that was present on both sides of the ‘breaker has taken its toll. Ideally, I would grind back until I could get a “perfect” edge. However, given the extent of the rust that was on this guy, I’m afraid we would remove too much material. I think this edge is good enough and I don’t think it will hurt the plane’s performance. If I find out differently after I get it in use, I’ll have to re-evaluate.
In order for our chipbreaker to work properly, it needs a “spring” in the fit with the iron. I lay the part flat on my granite plate to make sure that with the ends in contact there is light showing underneath.
Not much is there? Well, it’s time for the rubber to meet the road. Let’s put this guy on our iron and see what she looks like!
Well, that’s just not good at all! Never seen this before. I’ve had fits that were just barely touching but this one’s not touching anywhere at all across the full width. I suspect that while this plane sat rusting away in someone’s barn/garage/shed/basement over the years that the oxidation has eaten that leading edge back.
No worries though! We can fix ‘er up. We probably should have checked this first and done the following steps prior to grinding our bevels. We’re likely to introduce some twist into the part when we bend it so the edge isn’t parallel to the back of the piece. Oh well, live and learn…
Like I said earlier, this steel is pretty cooperative. I’m just gonna clamp it in a vise with the rounded portion just below the jaws and pull on it a bit. If my bend is 1/2 way between the threads and the leading edge, it should minimize the effects of any twist we introduce.
We can see the effects of just a little one-handed persuasion:
This actually ended up being too much bend. I was afraid it would be too much stress on the threads so I put it on an anvil and gave it a single whack in the center of the high point with a ball-peen hammer. That made it just right. Sorry but I didn’t take any pics of that. I think you can imagine it though ;-)
So now let’s test the fit with the iron again shall we?
Sorry for the pic quality but it shows exactly what we want to see – single point contact only at the front edge.
The next process is where you really want to make sure you get it right. It can make a huge difference in how your plane will perform. We said our first objective was to have an air-tight fit with the iron. Well, we don’t. I tried and tried to get a decent pic showing the light coming between the 2 pieces but couldn’t do it. You want to hold this up at every angle and turn it every way and make sure you don’t see ANY light between the two. You’d be surprised at how thin a gap wood shavings will find their way into.
When I tune this fit, I just not where my gaps are and then grind the bottom bevel a bit while putting pressure down on the high spots. Then I check the fit and repeat until the fit is right. In lieu of that though, since it’s hard to photograph the gaps, I’m going to use dye and print the fit like we did when we fit the frog to the base.
I lay a thin coat of dye down on the iron and lay the ‘breaker straight down on top of it (I don’t lay it over from the side like it appears in the picture). Then I press straight down, hard, on the threads like it would be clamped in reality.
Then I pick the chipbreaker straight up. I don’t want to roll it or shift it to avoid false dye transfers. The line of dye removed from the iron shows more clearly in pictures where the contact areas are.
What it doesn’t show though is that we don’t have enough angle on our bottom bevel. If we look at the dye transfer on the chipbreaker edge, we see that the back of our bevel is making contact when pressure is applied.
We don’t want that. If we could be confident that the entire bevel was in contact, then it would be ok. However, if the very leading edge gets lifted even slightly, chips will have a path of ingress and will work their way under. Trust me.
So, let’s re-grind our bottom bevel. Rather than re-grinding the whole thing, I worked it a few strokes on the fine plate with pressure concentrated on the high spots according to my dye print which meant I pressed down just left of center. That will help my fit at the edge. But I still need to make sure that the leading edge is the only part of the bevel making contact. Rather than regrinding the entire bevel, I hold the part at a much steeper angle and just work off a clearance bevel behind my main bevel.
Now re-check the fit. The pic isn’t real clear (sorry) but my clearance bevel was good. Only the sharp edge made contact. I still don’t quite have solid contact all the way across though.
I gave it a little more work on the fine diamond. This time I check it after each stroke on the stone to be sure I only remove the dyed areas. Just 3 strokes did it. When checked again, I can see not even a hint of light between the two parts. Like a dummy, I forgot to do a final print to show the fit. Guess you’ll have to take my word for it ;-)
After I get a good fit, I give both bevels a few swipes on my leather strop with some green compound to make sure my wire edge is gone. I fit the chipbreaker on the iron like it will be set when I fettle the plane. I set the edge of the chipbreaker back about 1/32” from the cutting edge of the blade. For a smoother, I set it closer – about 1/64” and for a jack or a scrub that will be used for dressing raw stock, I set it around 1/16” or more depending on blade camber. Many set theirs much closer than I do. I just don’t see it as necessary in general. I have moved it much closer on occasion though with a smoother on really gnarly grained woods. It does help with tearout. The article I linked near the beginning of this post goes into much greater detail than I will here.
Below, we can see that after working the bottom bevel and tuning the fit, I only have a little bit of the top bevel left on the left side of the ‘breaker. A little bit should be enough though, if not, I’ll find out when I start using this plane and fix it then.
Et voila! We have finished with our iron and chipbreaker. We have a nice sharp cutter and a tight-fitting ‘breaker. In spite of some extensive pitting present on both pieces, I think we’ll have a perfectly good functioning cutter when we get right down to it. The pitting in the chipbreaker and the fact that the iron is shorter than than the chipbreaker aren’t ideal. But I don’t think those issues will cause any problems in the plane’s performance. We’ll find out in a few days for sure.
We’re almost done. :-)) Next time we’ll put our plane all back together and finish up the work on the main body. After that it’s just a matter of fettling.
I plan to wrap up in 2 more segments. If I’ve left out any details you’re curious about, let me know in the comments. If there’s enough interest, I may add an extra entry to address things that didn’t get covered in the main process.
Thanks for checking in! I hope to get one more entry posted this week and wrap this up early next week.
-- Kenny, SW VA, Go Hokies!!!