Tool Tutorials #2: Frog and Cap Iron Adjustment Part 2 - The cap iron

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Blog entry by David Craig posted 10-22-2010 02:28 PM 13242 reads 1 time favorited 10 comments Add to Favorites Watch
« Part 1: Plane frog and cap iron adjustment Part 2 of Tool Tutorials series Part 3: When new blade appears too small for Grizzly G0555 bandsaw »

I have ordered 3 planes, so far, that were used. Of those three, only one didn’t arrive with the iron almost fully extended. I don’t see planes at garage sales any more, but when I did, I noticed the same thing. While the blade extension might seem like the obvious problem, one of the real underlying issues here is that the cap iron is not set right. The cap iron is another item on the plane that I think is overlooked, yet is an essential piece to successful plane operation.

Off the top of my head, I can think of three functions that this soft plate of metal provides. 1. It supports the iron and provides blade support for smooth cuts. 2. It separates the cut wood fibers away from the iron to keep the path free for the iron to continue its cut. The nice shavings that you see coming out of the top of the plane is pushed there by the cap iron. One of the other terms for the cap iron is “chip breaker.” 3. It sets the initial depth for your planing iron. The iron is connected to the cap iron which has a slot for mounting to the frog. Good retraction and extension of the blade depends on a correctly placed cap iron.

That is a lot of work for a flimsy piece of metal that gets so little respect :)

Lets start with support.

When I see a cap iron set too high on a plane iron, I can understand the logic. After all, the blade does the cutting, this piece of metal might interfere with the cutting edge or be obstructive, so the thought line is to move it out of the way. When this is done, you end up with a blade that takes too deep a cut and the unsupported iron will chatter up a storm. Think in terms of holding a chisel. We do not just hold on to the handle and push, we use one hand to hold the handle and the other hand to steady and guide it close to the edge. Woodcarvers, for instance, don’t end up with cut fingers because they keep their fingers too far from the blade. A cap iron works the same way, only it doesn’t usually end up in ER…

How close should it be set? Well that depends on the cutting operation. If you are attempting a very smooth cut, somewhere in the nature of 1/16th to 1/32 from the tip of the blade. Even if you are taking deep cuts, you really are not going to take much more than 1/16 off at a time. So even with a deep cut, I would not think the cap iron should be more than 1/8th from the cutting edge. The following pic is an example. This is from a plane I am fixing up for a friend.

Again, the importance is setting up a parallel cutting face, so you want to set the cap iron as parallel to the cutting edge as possible. This will reduce the amount of lateral adjustments you will have to make with the lateral adjustment bar, and it will provide more support to the cutting surface.

The next item that is crucial to support and to minimize chatter is spring. One thing that might not be widely understood is that the cap iron is a form of compression spring for the iron. The lever cap has a spring which compresses against the cap iron which also compresses against the blade. This compression keeps the blade or iron pressed tightly against the frog, but still allows easy depth adjustment. If there is no spring, then there is no compression and the iron is less firm against the frog and the pressure is more in line with clamping pressure which makes the blade difficult to adjust. When you screw the cap iron on the iron, you should feel a bit of a resistance and a bit of “spring.” You do not want so much spring that the iron is bending, just enough that you feel resistance when you push the two together. Too much or too little is easily remedied by putting the cap iron in a vice and pushing in one direction or another to add or decrease the resistance to the iron. You can do this with your hands and with little pressure. The metal is quite soft and pliable. This simple fix can reduce some issues with chatter.

Now lets move to the 2nd task of the three mentioned for the cap iron. Keeping debris and wood shavings clear for the cutting iron requires a tight fit between the edges of the cap iron and the cutting iron. Here is a side view of the two pressed together. Note the lack of light coming between the edge of the cap iron and where it presses against the iron.

If there are gaps between the edges of both irons, debris will catch and accumulate. This will reduce the iron’s effectiveness because more and more resistance will build. This also will cause chatter and the iron to rise above the board surface, preventing effective surface planing. If there are gaps, light work on sandpaper or a stone will flatten the cap iron edge and will help it sit more firmly. It does not take much as the metal is very soft and will flatten fairly quickly by hand.

Now we move to the last. Most of the problems with depth adjustment will be resolved when the cap iron is placed the correct distance from the cutting edge. When setting the depth, let common sense prevail. The goal of the plane, even when roughing, is to build up a smooth surface. Taking off only 1/16th at a time seems like a small amount when rough flattening but consider the fact it would only take 4 swipes to knock it down a quarter of an inch, and that is with just the jack or scrub plane. There is still the matter of joint planing and smooth planing which will remove even more surface area. You will eventually get a feel for what works best for each type of wood and task you are performing. I usually start out with the blade just barely felt past the iron and adjust from there.

Thank you all for the reading. I hope some of this information can be put to use to help someone gain more confidence and enjoyment out of the work of planing with much less frustration. I frequently look up tips and how tos from this site. My hope is that I can pay it forward some and provide equally useful information.


-- There is little that is simple when it comes to making a simple box.

10 comments so far

View canadianchips's profile


2632 posts in 3532 days

#1 posted 10-22-2010 04:41 PM

I am with you one this. You explained it very well. I do think the most common mistake is trying to take too much material off with one pass. As you mention start small and adjust accordingly !

-- "My mission in life - make everyone smile !"

View JimDaddyO's profile


623 posts in 3614 days

#2 posted 10-22-2010 05:03 PM

Following along….just bought a bunch of oldies I am restoring so I can use them.

-- my blog: my You Tube channel:

View jockmike2's profile


10635 posts in 4781 days

#3 posted 10-22-2010 05:10 PM


-- (You just have to please the man in the Mirror) Mike from Michigan -

View Dennisgrosen's profile


10880 posts in 3650 days

#4 posted 10-22-2010 05:41 PM

another good blog from you David :-)

take care

View steve71's profile


29 posts in 3331 days

#5 posted 10-22-2010 07:12 PM

talk about good timing, i was just looking @ my old stanley last night. thanks for the great info.

View mafe's profile


12135 posts in 3624 days

#6 posted 10-22-2010 09:51 PM

Fine blog.
Thank you.
Best thoughts,

-- MAD F, the fanatical rhykenologist and vintage architect. Democraticwoodworking.

View stefang's profile


16803 posts in 3869 days

#7 posted 10-23-2010 12:09 AM

Great blog David. I especially liked the tip about bending the cap iron in the vise.

-- Mike, an American living in Norway.

View Broglea's profile


687 posts in 3625 days

#8 posted 10-23-2010 02:17 AM

Right on and very informative. I’ll need to go check my #3 as it does chatter too much. Thanks!

View David Craig's profile

David Craig

2137 posts in 3643 days

#9 posted 10-23-2010 01:38 PM

Thanks for the kind comments all. I have learned much on this site and if I do happen to learn something, I try to share as well :)

-- There is little that is simple when it comes to making a simple box.

View Jim Bertelson's profile

Jim Bertelson

4268 posts in 3699 days

#10 posted 10-26-2010 04:47 PM

Finally got all the way through this in an unhurried manner. My focus this last weekend was getting those two new shop projects finished and published. Sometimes publishing to LJ’s is half the fun.

I am on call this coming weekend, and I find I usually do not get anything useful done around the shop. I don’t like the beeper or phone going off while I am working, like with a glueup, or one of the big saws. I actually did cut myself once when the beeper went off. Occasionally I get some design work done, I might try working on the No. 4 a little, but usually a call weekend is written off.

I don’t think I ever read much organized stuff about planes, until I started reading your blog here. The timing is right. Everything I knew about planes I remembered from junior high shops. I set the cap iron instinctively just like you described. Most of the time I get pretty good shavings, but the blade needs a real workover. I think a total tuning will bring this plane up to standards for most work for my shop.

I have the miter arms for the super sled to do, I think one is already done. Once those are done, the shop is in good enough shape to make my computer cart for the office. It is already designed. It will be made of edged plywood. Better construction is not indicated for the surroundings there. But I need to get some decent plywood, so next week I will start the hunt for a vendor.

Thanks again for the blog… is a good way to learn about planes in bite sized pieces…......


-- Jim, Anchorage Alaska

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