Chris Schwarz's Blog

Get a Flat Frog Sandwich

Reader Tim Williams writes: I have a number of old Stanley planes that I’ve spent a lot of hours cleaning and refurbishing. I’ve read multiple places about how when tuning up a plane, it’s a good idea to flatten the mating surfaces of the frog so the iron beds well, with lots of contact, to avoid chattering.

However, I find that whenever I take a flat iron and attach a chipbreaker to it, the tension of the chipbreaker on the iron puts a very gentle curve on the iron. So, when I attach the chipbreaker and iron to the frog, there’s a very slight gap under the middle of the iron (just enough to see light through if I hold it up to a light). I’ve tried loosening the bolt holding the chipbreaker and iron together to reduce the tension, but if I loosen it enough to remove the tension, the iron slides against chipbreaker.

 On one plane, I’m using a Hock chipbreaker. It mates more fully against the iron and doesn’t curve the iron, so it appears to bed better on the frog.  Finally, I’ve not really used these enough to notice much chattering.  Should I even be worrying about this?
 
What’s happening here is that you have too much curvature in your chipbreaker. When you cinch down the iron, it bends to match the shape of the breaker. There are several solutions to this: You can remove some of the curvature in your chipbreaker. Place one end of the breaker in a vise and push against it gently. It will bend easily. Then try again.

Another solution is to replace the iron with a thicker aftermarket iron. This is always a good idea. The thicker iron will resist bending. Or you can replace both the iron and chipbreaker, which is what I like to do with vintage handplanes that I am going to use for high-tolerance planing (jointing or smoothing).

The bigger question is if the bending is even a problem. It depends. With some forms of planes (such as infill planes) the lever cap puts so much pressure on the iron and breaker right up by the mouth that it doesn’t matter if the iron ouches the frog or not.

In Bailey-style planes, the more contact you get between the frog and iron the more stable the whole assembly will be and the less likely that bad things will happen, such chattering or the plane going out of adjustment while planing.

When I set up a Bailey plane, what I shoot for is a flat sandwich of frog, iron and breaker, as shown in the photo above. That works best.

- Christopher Schwarz

P.S. Our RSS feed has been bockety this week. If you like this post, you might also like my post earlier this week on how to understand the system of bench planes which is here.

3 thoughts on “Get a Flat Frog Sandwich

  1. Christopher Schwarz

    Actually, I’d say that mating is perfectly acceptable and will allow high-tolerance planing. The more common problem is that the iron bows the other way (in the middle) — pulling away from the frog near the frog screw.

    Chris

  2. Andy Saemann

    I agree with Tom Henderson – I see poor bedding between the frog and iron at the business end of the assembly. This is one reason why so many people like modern bevel up planes – they require MUCH less skill to setup correctly. Try tightening your lever cap screw until the iron beds on the frog. If this doesn’t help, take your own advice, Schwarz, and upgrade to a thicker iron.

  3. Tom Henderson

    Looking at the photo, it appears that the blade has pulled away from the frog for the bottom half an inch or so. Isn’t this exactly the issue that Tim Williams initial post suggested?

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