Thursday, June 16, 2016

Project #4 - Birch Bark Handle for a Puukko Blade

Since I have worked on the Projects 1, 2 and 3 more-less in parallel and also had the blades sent for HT I wanted to try something else in the mean time. Already before I started I got a few ready made blades (mostly for puukko knives). So I have decided to take a simple Polar whittler puukko blade and try to make a handle from birch bark. My Iisaki Aito also has a birch bark handle and it proved very comfortable and practical as it offers a great grip.

The Design:

This part was pretty straight forward and I though so will be the execution. But I underestimated all those little details that can go wrong when you do something for the first time :)

Basic components
  • Polar carbon 80mm blade with HRC 59
  • 5mm thick brass bolsters
  • 0.8mm thick fibre spacers
  • birch bark
  • 1 cm tick piece of stabilized wood
The tools
  • hacksaw
  • DIY bevel grinding jig & permanent marker
  • DIY clamp for the gluing of the handle
  • knife, scissors
  • bastard (cut #1) and medium (cut #3) files
  • needle files (round and flat)
  • wood glue (Titebond III), slow curing epoxy (min 60 minute)
  • hammer
  • sanding paper (120, 180, 240, 320, 400)
  • degreasing stuff (acetone or similar) and pure alcohol


Basic parts and tools.
Birch bark

Since one of the most important materials was the birch bark, let's start there. From some youtube videos I had an idea how to clean the bark and how to cut small pieces. I expected to make a lot of mess (and I did), but I did not expect it to be such a hard work. The devil was hidden in the fact, that contrary to knifemakers from Scandinavia who would use fresh birch bark, I could only buy one that was already dry. I actually bought the bark from 2 different sources and got 2 very different types of bark (one apparently older and very thick, the other much thinner with smoother surface)

I started to clean the birch bark with bare hands as I have seen in a video before, but since it was rather hard I put on a gloves. 15 minutes later I was having pain in my both thumbs so I moved to scraping the upper layer of the bark with a knife. This worked better and it looked like I am on the right track.

Cleaning the birch bark with a knife.

Once I was nearly finished with one about A3 sized sheath I noticed that on a side there was a split in the bark - about 1/3 of the total thickness from the surface and it went relatively deep. So I pulled on it and large part of the surface came off in one piece - with a much smoother surface underneath. I realized that I need to remove all that relatively thick layer. That went much faster than scraping the bark with a knife and left me with much cleaner bark.

After the thick upper layer was removed from the bark the underlying bark was much smoother.

So I continued in a similar manner with some more of the bark. It took me in total around 2 hours to clean and cut to pieces bark for the whole handle. Once I had enough cleaned bark I have cut it in 3x4 cm pieces altering the orientation for every other row, so once glued on the handle the orientation of the structure in the bark would be perpendicular in every two subsequent layer. This is recommended for better mechanical stability of the handle.

After that I punched holes (with a leather puncher and 4.5 mm large hole) and tested the pieces on the tang of the knife to avoid problems once I will start gluing.

Bolsters (yes, more than one)

The next logical step was to make a bolster which I decided to cut out of a 5mm thick sheath of brass rather than using some pre-formed one. The requirements are simple - it should have a nice tight fit around the shoulders of the ricasso and the tang of the knife.

To get the cutout for the tang I have drilled 3 holes with a small drill bit (I think it was 3mm as the tang was 3.5mm thick) and then I used first a thin round needle file to connect these holes, followed by a flat needle file to shape the opening to a final fit.

Connecting the drilled holes with a thin needle file.
I did file the shoulders of the blade so that they are lying on the same line (otherwise there would be gaps between the shoulders and the bolster)

Bolster #1:

Here I did the mistake of not preparing the tang properly. The important point is to make sure that the width of the tang at the place where the bolster will sit is the most thick of the whole tang, so that when testing the fit while filing the opening in the bolster you do not get stuck too soon and then have the opening too wide for the final position. I was too fast and the bolster had gaps around the tang.

Bolster #2:

With the fresh experience I was much more careful. I did the opening just as large that I would have to peen the bolster in place (last few mm of the tang). But before I would do that  I wanted to finish the shape and front side of the bolster, as this would not be possible once it wold be in place.


Testing the fit while working on the tang opening.

But since I did not want the bolster to have sharp corners, I decided to invest more time and round the front face.  After about 15 more minutes I was rather happy with the result. No perfectly symmetrical, but I though OK for the first knife. Then I sanded the bolster up to 400 grit which gave it a rather nice matt finish.


Bolster shaped, but not polished/sanded yet.

To get the bolster to its final position I have used a block of wood with a hole drilled in the middle and than a steel pipe and a hammer to peen the bolster in its final position. I started to get a good feel about this project :)

Peening the bolster in the final position

However that did not last long - first check showed a very obvious mistake I did. When rounding the front face of the bolster I did not measure how wide the blade was (both on the spine and choil side) and got a really bad looking result.

Obvious mistake - the heel of the knife is sticking out after I rounded the bolster.

Bolster #3

With the lessons learned from first 2 bolsters I decided to make one more. I made it a little larger so that I would not run into same problems as with the bolster #2. I also went with much less rounding this time. I also filed the opening on the bolster a littler large on the back side as this would make the peening a little easier.

Bolster #3 was designed a little larger than #2

Drilling the holes.
Filing the tang opening.

Once I got a good fit I started to shape the bolsters.



Left to right: Bolster #1, #2 and #3

The birch bark handle

Once the bolster #3 was in place I could continue with the handle. Before I would start with glueing I would degrease the tang and the bolster. To be on the safe side I used a 5 minute epoxy and filled in the small void between the bolster and the tang. Once that cured I could finally proceed with the handle.

Before I started I made a simple clamp from 3 pieces of wood and two 50 cm long threaded rods (10mm size) and some screws.

Blade with bolster in blade in the clamp ready for the gluing of the handle.

Before I continued I have used 2 needle files to keep the pieces of bark organized and in the right order.

Ready for gluing.

I have used 2 different glues for gluing. Titebond III (II would be also fine) between the birch bark pieces and slow cure (90 min) epoxy to fill the void between the bark and the tang. It was a rather messy process. Once I was nearly finished it turned out that I have too few birch bark pieces prepared. I have simply clamped what I got and let it cure until the next day. I would then prepare a few more and finish the gluing.

Note: The knife handle could actually be made completely without glue. Just stack all the pieces, put on the the end cap and peen the tang over. Then take the knife and put in an oven set to 80 - 100 °C (cca 176 - 212 F) for half an hour. At this temperature the birch bark will release its natural tar that after cooling will seal the bark. You do not need to worry about messing the heat treatment of the blade as this temperature is too low for that. You can find more details HERE I will try that approach next time.

To give the knife a little spin I added ca 1cm thick piece of stabilized wood (I had some left overs) and on top a brass end cap.

Important - before fitting the end cap I would file the end of the tang (which is not hardened and this easy to file or saw) to round shape such that it would just fine the hole drilled in the brass end cap. Later once the glue cured the tang will be cut so that just a few mm stick out and mushroomed with a hammer to secure the end cap. Later after sanding the end of the handle it turned out that I did not do a particularly great job with the peening, but since the handle was also glued with epoxy it will hold well.


Handle curing after all parts were glued.

I have put a piece of plastic foil between the edd-cap and the vise.

Once the handle was cured I have proceeded with sanding it to shape. I used my brand new 1x30" belt sander and 40 grit Klingspor belt. Since the birch bark is rather a soft material this was proceeding rather fast, but the fine, light dust was everywhere. It was so bad, that I actually stopped sanding and only continued once I got an industrial vacuum cleaner that I attached directly to the belt sander which improved the situation dramatically.

Just few minutes of sanding - still a lot of material to remove, but the dust was EVERYWHERE.
So, once the vacuum cleaner was attached I have continued to send the handle to shape. I have used Norton Blze 60 grit (mainly because I was lazy to swap belts after I was grinding bevels of a different knife). It was a little slower, but I did not want to hurry too much as once you grind too much material away, you can not put it back. I was checking on the process continuously - comparing to the handle of my Aito and simply taking the handle in my hand to see whether it offers a comfortable grip.

In particular I was careful around the bolsters. These are made from brass which has excellent heat transfer abilities and so could yield overheating that part of the handle and damage the Epoxy. Also - grinding too fast or too hard could yield uneven transition between the hard brass and soft birch bark, since the birch bark is much softer than the brass.

In total it took me around 90 minutes to ground the blade to shape.  Since the handle has a simple shape (oval in cross section and barrel-like profile) I kept sanding the all sides and tested the handle in my hand until it felt right. Had I not tested it regularly I would have probably ended up with a handle that would be too large. I kept sanding with the #60 belt until I was happy with the shape. Then I rounded the most 'corners' that were left and with nearly zero pressure put a uniform finish on the bolsters.


Vacuum cleaner is attache - the sanding may continue.

Slowly getting closer to the final shape.

Handle ground to shape and carefully smoothed out with the #60 grit belt.  (I used different belt than the one shown)

Handle finishing.

Once the handle was shaped with #60 belt I continued with Sait 7S #120 and with the smooth & soft 3M Trizact A45 (cca grit #400). This was all very light work - especially around the bolsters. I have rounded the butt a little more and flat sanded the bottom of the handle on every belt to get a uniform finish. I have just touched up the edges of the bolster so that it would not feel sharp in hand.

Once the sanding was done I gave the handle 2 coats with Tung oil which gave the handle a very nice feel and lovely contrast. Seems like the Tung oil works well with the birch bark.

First coat with Tung oil.
Lessons learned

Again - quite a few mistakes and little things that I picked along the way of this project:
  • Do not hurry when making the bolster. Thin the tang such that it slightly tapers (left/right and top/bottom) - that will allow you to get a tight fit and minimize the risk of voids between the tang and the bolster.
  • Make the bolster a few mm larger in all direction to have enough material for the taper.
  • Before you start gluing the handle have EVERYTHING prepared and clear your bench so you minimize risk of tipping things over and such. 
  • Use slow cure epoxy - in particular if you use 2 types of glue at the same time, it will take you easily 30+ minutes to assemble the handle and you do not want to put yourself under pressure.
  • If something goes wrong mid-way - do not worry. Clamp the part you have done as if the handle was finished, let it cure till the next day and then continue. Happened to me and you can not see it on the result.
  • Before you will start finish sanding the handle - test the abrasives/belts you plan to use. Some will loose some grain when fresh and that may get caught in the soft birch bark. You do not need much grinding power, so do not worry to use belts that are partially worn out as those are less likely to 'stain' the handle.
  • Go really slow when finish-sanding the handle. Once you got up to about #240 grit use some soft fine belt (the 3M Tricazt series is excellent) - that will make it easier to get smooth finish on the bolster.
  • Use some sort of oil on the bark handle. Tung oil worked nicely, but other would certainly do. You could as well use a mix of mineral oil and bee's wax (this mixture is often called 'board butter') and re-apply if the handle starts to feel dry.


Finished knife







The fit of the tang is not quite perfect - there is a little gap.

Next to my trusty Iisakki Aito.



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