A stab at something new

I started with a blank of 1.2510 tool steel. For those of a left pondian persuasion, that’s O1 tool steel. This comes in 500mm long precision ground bars. The one I started with is 20mm wide by 2mm thick.

The first step is to paint it blue… Yes I know in wood work paint usually comes at the end of the process, but in metal working, it’s closer to the beginning.

A coating of blue dykem (layout fluid), allows me to use the scribe I made (my first lathe project).

Marked up, it goes in the band saw and I lop off the unnecessary material. This makes it a lot easier to work on. The next task is to mark where I need to drill two holes. For this I take advantage of the fact the makerspace has a surface plate with height gauge. But I need to set the height. Normally this would be done with gauge blocks, but being an idiot, I left those at home. Fortunately I have some a gauge pins I keep at the space, and in there there’s a 10mm pin.

Crude, but it works.

Next we go to the drill press.

Next up I cut two brass pins from a length of 5mm brass rod. Then I cut another two, as I cut the first pair the wrong length… something something measure twice… These get deburred on the belt sander. In the woodworking part of the makerspace I run a peice of ash left over from the marking gauge project through the table saw. This results in a 5mm thick by 44mm length of ash (fraxinus excelsior). This I then cut into 4 20mm by 100mm scales. The scales are taped to the steel bar, and a drill bit is used as a transfer punch. Drill the holes out on the drill press. Line them up on the metal. Thank myself that I cut an extra pair of scales, and drill these ones out. This time making sure the hole is in the right place. I now have all the parts I need.

Now I have a decide how to cut the angled section of the blade. One of the great things about the makerspace is it has a wide variety of excellent tools. Many of which could be used to achieve what I want to do. I tried the metal band saw first, but couldn’t find a good way to get it to cut the 30° angle. Which is actually 60° as far as the mitre saw is concerned. But the saw only goes upto 45°. For a brief moment I ponder using the belt grinder. It’s next to the mitre saw. But I decide that while it would work, it would be madness. However, under the belt sander are boxes with multiple angle grinders, one of which has a cut off disk fitted. I’ve never used an angle grinder before, so this seems like a good time to have a go. It cuts nice an easily, but the waste piece flies off into the dark corner of who knows where. Hadn’t anticipated that. I now have a jagged edge. I could neaten it up on the belt grinder. But hey, I got a machine shop. To the mill!

While I used a protractor to mark it out, and am using precision ground stock. The reality is that for this project, the angle of this cut. Doesn’t really matter that much. I line the workpiece up in the vice just by eye. It’s close enough. Then with an end mill, I tidy up the edge. Things are starting to take shape.

I take the opportunity to grind a bevel on the big pedastal grinder. I can now do a test assembly, and see how it will work. This made me realise that when trying to sharpen it, the handle scales are going to be in the way. So I lop off a little bit, and round the corners.

That’s everything I can do at the workshop. For the next stage, the tools I need are at home.

While steel is quite hard in the grand scheme of things, this steel isn’t as hard as it could be, and in it’s current state, it won’t hold an edge very well. I needs heat treating. Fortunately 1.2510 steel is a relatively forgiving steel to heat treat. The hardest part was actually setting everything up on a tiny balcony, and in the Kitchen,.

On the balcony I made a hearth on top of a log from insulating firebricks. It’s quite late in the evening, so I also set up a pair of makita work lights so I can see what I’m doing. I could heat treat the steel as is, but it’s likely to leave a scale on the steel that is not as nice to look at. An easy way round this is a flux of Boric acid. The steel is wrapped in a cage of stainless steel wire, then covered in a paste of boric acid mixed with Isopropyl alcohol. Place this on the hearth, add a thermocouple to my multimeter. And it’s time to cook this cookie…

My blow torch is relatively small, but I don’t need to heat treat all of it. I only care about the pointy end. So I focus the flame there. The… green… flame…

and I melt the thermocouple… oops.

Then the borix acid starts to melt. It forms a glassy glaze over the knife. Keeping the blade nice and clean.

Glowy molten goo…

Testing the steel with a magnet tells me when it’s hot enough. If the magnet sticks. MORE FIRE. Eventually the magnet does nothing, and it’s time to quench.

The O in O1 steel stands for oil. 1.2510 is an oil quenching steel. There are lots of fancy quench oils available. But I opted for rape seed oil. For two reasons. I can buy it at the supermarket, and in the words of Quinn Dunki, makes the workshop (well balcony in this case), smell like french fries. It requires two hands and lots of care to do the quench, so no photos (sorry). Quenching the steel makes it really really hard. But it also makes it very very brittle. If I dropped it now, the workpiece would shatter. To solve this, it needs to be tempered. Fortunately 1.2510 steel is really easy to temper, requiring just a couple of hours in an oven at 200°C, plus an extra hour for every 25mm of thickness. At 2mm thick, that means just 2 hours.

Once quenched, and the work piece has cooled down to about 150°C, it goes into the oven. Two hours later when the timer beeps, I take it out and let it cool on a fire brick.

The boric acid glaze disolves with boiling water. A little light scrubbing with an old toothbrush later, and we have one hardened and tempered blade!

Next step. Sharpening.

I fire up a box set, and get to grinding the edge on a diamond plate.

The bevel was put on with a grinder, with no jigs, just guessing at an angle. And… it’s… um… multi facetted…

It takes a long time, working back and forth on the 300 grit diamond plate. Slowly working the edge until I’m mostly there.

It’s most of the way there. But as there’s still work to be done, I don’t want to keep cutting myself, so I’ll leave the final sharpening for later.

Back to the workshop, and it’s time for some mountain dew…

I took about 150 microns off on one side with the surface grinder to make it look pretty. Unfortunately the combination of the heat treat, and general manufacturing process of the steel has filled it with stresses, and as I grind it, some of those stresses are released. On the second side, it all goes to pot. Because of the mountain dew coolant, I don’t realise it until it’s too late.

-adult language in progress-

Oh well. If I clamp it together, am liberal with the epoxy, and with the pins as extra reinforcement. I can recover everything I’ve done. Something I hadn’t really understood before I started making tools like this, is that the holes in the knife handle scales that are pinned, don’t typically have parrallel sides, but instead are tapered. Then when the pin is peened, the metal moves to fill the cone shape hole, and hold the scale in place. I have a simple tapered hand reamer to cut the taper in the holes in the wooden scales.

The workshop is 11°C, however the epoxy needs to be above 20°C to cure properly. Fortunately, a 3d printer can be abused to make a drying chamber. Set the print bed to 25°C, and “cook” for an hour.

Once out of the 3d printer… I take the assembled knife over to the anvil, and with a ball peen hammer, start to peen the pins to fill the holes. One side goes absolutely perfectly. One pin of the other side goes great. The other… well as the brass moves out to fill the hole, it blows out the end grain of the wooden scale. Oh…

-Adult language in progress-

Deep breaths. I mix up some more epoxy, fill the crack, and clamp it back together. Back in the 3d printer it goes for another 20 minutes. Hopefully it will all hold, and if anyone asks, the crack… um… adds character…

It’s finally time to head over to the belt sander to tidy everything up. I start at 80 grit, taking off all the epoxy squeeze out, fixing the slight alignment issue with the scales and the blade. Round off the corners… chamfer the edges (to seperate us from the animals).

And it’s done! all that’s left now is to add my makers mark. Add some finish, and give it the final sharpen.

The finish is 2 coats of danish oil. But I’m left with an issue of how to let the finish dry, in the end a pair of 1-2-3 blocks bolted together, act as a clamp to hold the handle end out in space while the finish dries.

Left over night for the finish to fully cure. I can release the bolts, and admire what I’ve made.

It’s not perfect. The blemishes and imperfections give it… character. But on the whole, I’m happy how it came out. At 150mm long, it’s quite short for a marking knife, but I don’t think that will hinder it’s use. It’s comfortable to hold, nice & sharp, and the steel doesn’t flex.

I’m calling this one a success.