PDA

View Full Version : Fabrication and Shop Techniques Pesky gaps in peened steel dovetails



Juan Hovey
12-09-2013, 2:42 PM
Hey, folks: I make dovetailed infill hand planes like the one below, and no matter how carefully I peen the tails and pins, I often end up with bothersome gaps where the steel just hasn't quite closed up.

I peen and file at least three times, often four, making every effort to mushroom the steel down into the joint, and I'm frustrated.

George Wilson suggested that I substitute precision ground low carbon steel for the 0-1 steel I'd been using for the base and sides of my planes, but even though low carbon steel is easier to work, I still end up with gaps in the joints that bother my eye.

Permatex Cold Weld and Loctite Weld, forced into the gaps and sanded over, improve things only marginally; they fill wider gaps (though not the narrower) but don't match the color of the steel when mixed half and half. Would it help to mix in more of the white hardener?

Are there better alternatives?

276675


Thanks in advance for any and all helpful input!

Brian Thornock
02-14-2014, 1:40 PM
I don't know all of what you have and haven't tried, but a domed pin punch of a fairly small diameter can help squish the metal into smaller gaps. Of course, you have made enough of these that this probably isn't news. Other than that, might you be able to warm the metal up slightly with a torch and then peen the slightly softened metal? This could introduce other stresses, though, which would have to be taken care of in the lapping stage, and I know how not fun that stage is with infill planes.

Juan Hovey
02-14-2014, 3:20 PM
Brian - Thanks for your note. I use a smallish pin punch sometimes to push metal into the corners of the dovetails, and I've used a small torch on occasion, though with caution. The solution, I've found, is to shape the tails and pins such that I start out with as tight a fit as I can manage and then make sure that I peen from the middle out, as it were pushing the metal into the gaps from behind. If you peen straight down into a joint, you can distort metal on both sides of the joint, but if you peen at an angle, hitting only the proud metal, you can direct its travel into the gap, filling it nicely. This takes practice, and every time I start peening, I have to remind myself to do it right. Here's a photo of my latest plane, with no gaps.
282485

george wilson
02-17-2014, 9:24 AM
Your work is getting better,Juan. I see you are using a different cap screw. Your handle should not get so slimmed down at the top. There is a "flattish" curve in the front of the hole near the top of the handle. I would not cut away the wood behind the plane iron. Your cap screw is bearing down on nothing but air behind the iron. That would tend to bend the iron convex and away from the bed behind it.

Are you using a cross pein hammer to peen your dovetails? You need to use a hammer that will force the metal to go TOWARDS the gap you are trying to fill.

A cross pein hammer squeezes the metal sideways at 90 degrees to the pein. You can use it to fill the sideways gaps,then turn it 90 to fill gaps above the dovetail.

It will never do trying to use any kind of filler in the gaps. Over time,the steel will change color,but the filler will not,and will stand out even more.

Get a cross pein hammer and study how it moves the metal. Blacksmiths know how to use different shape hammers to the best advantage. The cross pein is one of them.

Harry Strasil is a good blacksmith here on the forum. Why don't you PM questions to him about how to move your metal around? Are you leaving overhanging metal in BOTH directions: That is below the sole as well as sticking out from the sides? You need to have extra metal sticking out in both directions that you can squeeze out and fill the dovetails.

Juan Hovey
02-18-2014, 10:23 AM
George - It may be possible for the iron to bend away from the bed, but is it likely? The iron is 3/16-inch thick A-2 tool steel made by Ron Hock, and the chipbreaker is 1/8 inch thick. That's a lot of mass, for one thing - a lot of stiff mass.

For another, the iron is 7 inches long, the lever cap 3 inches long. That makes the distance between the tip of the cap screw and the lower edge of the lever cap something less than 3 inches, or substantially less than half the length of the iron. To be sure, the point at which the cap screw touches the iron is almost exactly the middle point of the iron, but the result, it seems to me, is that even though the lever cap exerts roughly equal force at two points - where the screw touches the iron and where the bottom edge of the lever cap does the same - it all occurs at and below the middle point of the iron.

I'm no expert on mechanics, but I suspect that if you want to distort only the lower half of such an iron, you must bring more force to bear on it than you're likely to get from the lever cap and screw.

Last but not least, although the function of the 1/8 inch hex screws passing through the sides of the plane is to eliminate lateral movement of the iron, the pressure they exert can only add to the downward force of the lever cap, keeping the iron both rigid and flat against the infill and the 1/2 inch steel frog riveted to the base of the plane just aft of the mouth.

When all is said and done, there is thus no more than about half an inch of "air" to worry about, and unless I'm missing something, I don't think it's cause for worry.

As to peening hammers, my dovetails tend to be small; most are about half an inch wide. I borrowed a cross peen hammer from a friend some months back only to find that the business ends of the head were wider than all but the one longish dovetail spanning the mouth of the plane. It didn't occur to me to look for cross peen hammers with narrower heads, but I'll do so now.

In any case, after lots and lots of practice, I've learned that if I leave about 1/16 inch of steel proud on both tails and pins and aim my ball peen hammer so that I'm pushing metal toward the gap, the gaps that gave rise to this thread are no longer a problem.