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  1. #1
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    Default Make a kerfing chisel

    In 2011 I posted an article on a kerfing chisel, a tool used to deepen the kerf in half-blind dovetails.





    The idea for this came from a method used by Tage Frid, who used either a scraper blade or, as I viewed in a video, a section of bandsaw blade. The kerfing chisel was my effort at making a specific tool, rather than buggering up a prized scraper blade.


    In the years since, I am aware of two similar tools, the first was by Ron Bontz and the second by Rob Cosman. Both are shaped like saws, complete with brass backs and scraper plates. They do the same thing.


    Over the years I have received many queries how to make a kerfing chisel, and this posed a problem since I had made it from a steel gardening trowel/spatula. These can be difficult to find. I have been thinking of other ways to make this easier for anyone interested in rolling their own. This is what I came up with ...


    At the moment I am testing out a few different sizes ...





    Top is Jarrah and bottom is Hard Maple.


    A few others ...





    The parts include a scraper blade (these are 0.03" thick). I was curious to see whether this would create a problem when dovetail saws have a 0.026" kerf (0.02" plate plus 0.003" set, which is considered "fine"). A ferrule is made from brass tube.





    Turn the handle, and then saw the slot for the blade using a bandsaw. Place the handle on a V-jig to hold it steady. Ensure that the shaft matches the depth of the ferrule (so that is bottoms out against the end of the handle). Epoxy everything together.


    So why is a kerfing tool so useful that it warrants being made into a specialised tool?


    Here is a half-blind pin board socket being sawn. Note the diagonal angle, which leaves half the socket ...





    This is where the kerfing chisel is used: First clamp the ends of the pin board. The edge of the blade is squared (not bevelled like a chisel), but it has the potential to split or cleave a board. The clamp helps prevent this.





    Tap the blade into the kerf, to full depth, moving towards the boundary line a little at a time - be especially careful with the outside kerfs, where there is less support.





    I have been doing this for a decade and may have had 2 or 3 splits in all this time, mainly from being careless.


    When chopping into the socket, the deepened kerf will make it easier to split out the waste ...





    The blue tape makes it easier for older eyes to see lines ...





    Cleaning out the waste is significantly easier ..





    Removing waste leaves clean sides to the sockets ...





    This is saw-to-saw cut ...





    Regards from Perth


    Derek
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

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  3. #2
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    Default

    Derek

    I have never had the use for one of these, but they look wonderful. You could use old saw plate (back saw or panel saw) of a suitable thickness if you don't have scraper blades or don't wish to cut one up.

    I realise that you are never going to wack the bejesus out of this tool because of the potential to split, but as you are using the gennou would it benefit, and maybe look even more appealing, to have a top ferrule too. I think I am a little prejudiced in this regard as I always feel that chisels without a top ferrule look "unfinished," but I concede that it is quite unnecessary on a paring chisel, for example.

    Lovely job and great investigation into the subject. How many have you made in the quest? It looks like at least five and maybe six.

    Regards
    Paul
    Bushmiller;

    "Power tends to corrupt. Absolute power corrupts, absolutely!"

  4. #3
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    Default

    Quote Originally Posted by derekcohen View Post
    In 2011 I posted an article on a kerfing chisel, a tool used to deepen the kerf in half-blind dovetails. Over the years I have received many queries how to make a kerfing chisel, and this posed a problem since I had made it from a steel gardening trowel/spatula. These can be difficult to find.

    At the moment I am testing out a few different sizes ...
    Another very informative post; thanks!

    The tool you converted in your original article looks like a plasterer’s cornice tool; if so they are readily available from all hardware stores. The one I linked to from Bunnings is available in 13, 16 and 19mm widths and are all $14 each. Saying that; your scraper blade version is much simpler to make as the cornice tool needs a belt sander/linisher and a fair bit of care when thinning the blade.
    Nothing succeeds like a budgie without a beak.

  5. #4
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    Quote Originally Posted by Bushmiller View Post
    Derek

    I have never had the use for one of these, but they look wonderful. You could use old saw plate (back saw or panel saw) of a suitable thickness if you don't have scraper blades or don't wish to cut one up.

    I realise that you are never going to wack the bejesus out of this tool because of the potential to split, but as you are using the gennou would it benefit, and maybe look even more appealing, to have a top ferrule too. I think I am a little prejudiced in this regard as I always feel that chisels without a top ferrule look "unfinished," but I concede that it is quite unnecessary on a paring chisel, for example.

    Lovely job and great investigation into the subject. How many have you made in the quest? It looks like at least five and maybe six.

    Regards
    Paul
    Hi Paul

    I have been doing a little experimenting with plate thickness, and so far it seems that this does not make any significant difference.

    Most saw plates are 0.02” thick. Then add 0.003 - 0.004” each side for the set of the saw, and you end up with something closer to 0.03” than 0.025”.

    Then there is the accuracy of sawing to the line - how close can you get? Are you within 0.003 of the line, or less. In other words, are you changing the socket size? I do not think so.

    Plate thickness will affect how easily it cuts into the wood. However, this is affected by how big a bite one takes. That also is determined by the hardness, and brittleness, of the wood.

    I measured some of the cabinet scrapers in my collection. They were mostly greater than 0.03”. Paint scrapers from the big box were greater than this, and some have used these successfully.

    Bottom line: at this time I would argue that a blade up to 0.03” is fine.

    With regard to a top ferrule, ideally, when striking the kerfing tool, saw or chisel style, you want to use a steel hammer. The energy from one is better focussed than a wooden mallet. I added a ferrule to the Kerfing chisel I made a decade ago, and have been using since. I use Japanese chisels a lot, and copied this style. The kerfing chisel in this article is being used sans-ferrule. These are all hard woods: Jarrah, Hard Maple (USA), and some type of Cassurina, the name of which escapes me at this time. I have been using a 225gm gennou, and not seen any signs of damage to date. (I have not used the saw style kerfing tool in many years, and I wonder how these hold up - plus there is less area to hit).

    Regards from Perth

    Derek
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

  6. #5
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    Quote Originally Posted by Bushmiller View Post
    Derek

    ....You could use old saw plate (back saw or panel saw) of a suitable thickness if you don't have scraper blades or don't wish to cut one up.

    ....

    Regards
    Paul
    Further to this Paul, the panel saw plates I have looked all have steel in the thickness of 0.35 or greater!

    Incidentally, the steel I have used is HSS.

    Regards from Perth

    Derek
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

  7. #6
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    Quote Originally Posted by derekcohen View Post
    Further to this Paul, the panel saw plates I have looked all have steel in the thickness of 0.35 or greater!

    Incidentally, the steel I have used is HSS.

    Regards from Perth

    Derek
    Derek

    I was going to point out that in fact saw plate thickness varies quite a bit and is primarily dictated by the length of the saw (this extends to back saws too). I didn't because you mentioned the absolute thickness you had found was not critical. A panel saw can be as low as .025" (18" or 20" saw) but will be up to .039" for a full size 28" saw. Even that is not hard and fast as there is some variation between manufacturers and indeed between their best models, which probably have a taper grind so something else of which to be wary, and their budget models without any taper grinding and would be more suitable for your purpose.

    Incidentally, I don't think the set would have too much bearing in this instance, as I don't think the teeth would be used.

    The HSS would most likely be a superior material, although again, maybe not critical for this purpose. I was just suggesting a cheap alternative that can be picked up almost anywhere for very little or may even be lying around the workshop.

    Regards
    Paul
    Bushmiller;

    "Power tends to corrupt. Absolute power corrupts, absolutely!"

  8. #7
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    I have been using a cheap paint scraper from the BGS for a number of years. I cut the ears off it to give parallel edges, one to hit with a hammer and the other to do the cutting. For me this style, based on copying the Tim Rousseau card scraper/gents saw idea, is a lot easier to set in place using the convenient handle, is not too long like a discarded gents saw would be and seems easier for me to align vertically over the cut than a longer handled chisel style.

    It doesn't look anywhere near as pretty as Derek's though.
    Franklin

  9. #8
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    Derek, I remember the first time I saw Frid's method of extending the saw cuts for half-lapped tails (as you said, he just grabbed the nearest card scraper). That was at least 40 years ago & I'd not long discovered card scrapers (still one of the best things I learnt from reading FWW!). So I thought I'd give this method a try, rushed into the workshop & grabbed a bit of scrap & proceeded to cut a set of half-lapped D/Ts. I split both corners off the first board I tried tapping the scraper into, partly because I'd picked on a very splitty bit of wood & possibly mostly because I took way too big "bites" as you've warned aginst. Disappointed & discouraged, I went back to doing it the way we were shown at school, just carefully chopping out the waste after making the diagonal saw cuts.

    Our teacher showed us how many cabinetmakers over-cut the sides of the sockets to make it easier to remove the waste (something I've since seen many times on old furniture), but made it clear to us he thought that was sloppy workmanship, & I easily accepted that, being naturally fussy about neatness in my work. Over the years & after many D/Ts, I've gotten pretty quick at doing them this way, but I suspect the choice of wood has a lot to do with it - crisp-cutting woods like Qld. Maple are just so much easier to chop out cleanly than woods like Jarrah.

    So, much as I'm tempted to make a kerfing chisel just for the fun of making it, I think I'll sit this one out Derek, I reckon I can coast to the finish-line doing it the way I've become used to. But perhaps my main reason for resisting is to avoid having yet another tool on the bench! I'm getting more & more like my dad as I approach my dotage - he used to complain that he spent more time looking for the tool he just had in his hand a few minutes ago than using them. I reckon I'm up to about 50/50 now, & climbing......

    Cheers,
    IW

  10. #9
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    Avoiding any discussion on what style of half blind kerfing tool is superior, I will just post a couple of photo's of the kerfing tool I made back in June 2018. Its designed to be struck with a wooden mallet.




  11. #10
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    Hi Stewy

    That looks beautifully made. Can you say something about the construction: steel used, thickness, how it feels in use?

    Regards from Perth

    Derek
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

  12. #11
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    UPDATE ON THE CONSTRUCTION OF THE KERFING CHISEL, ABOVE:


    There are two important features to consider if you plan to build a kerfing chisel.


    1. The first is that thickness does influence the process and outcome. The thicker the blade, the more effort to pound it into the wood. More importantly, if you are one to saw to the line, using a blade wider than the saw kerf will widen the socket, and the result will be a loose fit. Of course, if you do not saw to the line, then there is simply more effort involved.


    Over the past week, while building 10 drawers, it has been apparent that a thin bladed kerfing chisel is significantly easier to use. There is much less effort involved with, say, a 0.024” blade versus a 0.030” blade.


    2. The second issue is that it is not enough to simply epoxy in the tang of the blade. The blade is subject to much lateral forces, and eventually will come loose. In order to prevent this, the ferrule/mortice/blade needs to be pinned. I used 2mm diameter mild steel nails. Since I have been making blades with stainless steel (see picture for source of SS scraper blades), the drill bit of choice is one made from tungsten carbide.








    Regards from Perth

    Derek
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

  13. #12
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    I don't understand why this is better than a stiff putty knife with a sharpened edge.

  14. #13
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    Quote Originally Posted by Bill Houghton View Post
    I don't understand why this is better than a stiff putty knife with a sharpened edge.
    1. The putty knife will have steel that is excessively thick. This will enlarge the kerf and be difficult to drive in).

    2. A sharpened edge will act like a chisel and cleave the board into pieces.

    3. The small area if the kerfing chisel does not obscure visibilty and makes it easier to position where you choose.

    Regards from Perth

    Derek (who has been using a kerfing chisel for 10 years)
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

  15. #14
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    Derek and Planemaker, Ill be making one of your kerfing chisels for sure!

    A few days ago, I just HAPPENED to stumble over this.... an interesting kerfing chisel here on Tab #3 there is a video....

    131891338_1743794215782197_1977576938733727685_n.jpg

  16. #15
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    Evan, that looks like a kerfing "tool" (not chisel) made by Rob Cosman, or modelled on his. He brought his out a few years back. No one makes it in a chisel format - I understand why after experimenting with suitable blades. The saw-style is easier to make. I have also read of a few who converted cheap gent saws.

    I am obviously biased (!) but I think that the chisel style is easier to use (the narrower blade offers better visibility and easier positioning). I had a saw style about 8 years ago, which was sent to me by someone on a member of one of the US fori.

    I look forward to hearing about your experiences and opinion of each style.

    Regards from Perth

    Derek
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

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