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  1. #1
    Join Date
    Nov 2006
    Location
    Ireland
    Posts
    84

    Default First attempts at wood threading.

    I wanted to make some wooden threads so I read a number of articles online, including IanW’s excellent tutorial on making larger threads in a progressive fashion with a single point cutter in a wooden tap, but the consensus seems to be that a metal tap is needed for small threads. The tap seems to be the key ingredient, lots of articles, youtube videos and even a Woodwright episode online about making screw boxes if you have a tap, but a home-made hand-filed metal tap (I don’t have a metal lathe) seemed a step too far.


    I have a use for a small thread, ¾ seemed a good compromise between strength and versatility, so I looked online at some of the sources for metal tap kits.


    The reviews of wood threading kits on supplier sites can be very confusing. People either say they’re rubbish or wonderful. Also some of the comments can make the process seem very complicated, describing difficulty getting a square result or citing a need for straight grained hardwood species which have been immersed in oil for some time prior to cutting


    I bought one of the Taiwanese threading kits


    1bought threading kit.jpg
    and after my first attempts can now understand why reviews vary so wildly.
    The tap and screw box are just two, albeit essential, parts of the process of making a usable wooden thread. There are another two elements to get correct in the process.


    Firstly, you probably won’t buy dowels suitable for threading. The screwbox needs a round dowel consistent in size. So to get my dowel starting stock I had to make two other tools.
    I needed a rounding plane to give consistent correctly sized stock. A very simple construction, just a pencil sharpener on steroids.
    I had O1 steel left over from making plough plane blades so I made a dedicated blade but there are examples online using anything from plane and spokeshave blades to a clamped chisel.
    However to make the rounding plane I needed a tapered hole so first I had to make a taper reamer.
    Lots of examples online showing reamers being made using a bit of spring steel from an old saw blade. It looks easy in some of the examples, score the steel, bend it in a press brake and the blade snaps cleanly along the scored line. I don’t have a metal bender so I clamped the scored line between two bits of angle iron held in a vice. It did not snap cleanly (to say the least) when bent over but the tears were all on the waste side and I could file it to shape.
    2mangled saw b.jpg


    Size wise the wooden holder for this tapered blade was at the limit of my small wood lathe and my wood turning skills aren’t great, all I’ve ever made are knobs and a few tool handles. Fortunately the wooden tapered holder doesn’t have to be that accurate, it’s just a support for the tapered blade.
    3reamer and rounder.jpg



    I could now consistently produce correct sized dowels. Running bought dowels through the rounding plane was an eye opener, the variation in shavings showed just how oval and inconsistent in size the bought stuff could be.


    As a first test I ran some 21mm pine dowel through the rounding plane to get consistent round ¾ stock and turned some threads with the screwbox, using a quick spray of some mineral oil as lubricant. Consensus online seems to be that Linseed, Tung or other wood finish oils as recommended in the threading kit instructions can dry and gum up the cutter, better to use mineral oil.
    Then I drilled a 5/8th pilot hole in another bit of pine with a brace and bit, using a square set upright as a guide. Turned the tap into the hole, again keeping it square by eye against a guide. Result was usable threads, a bit of tear out on the pine treads but it screwed up ok and the threads were perfectly adequate, for long term use I’d probably harden them up with some brushed on CA super-glue.
    However the alignment was out of square. Eyeballing the pilot drill and tap square against a guide clearly didn’t work for me.
    4 not square.jpg


    So the second extra essential element is some way to hold the drills and tap square.


    My drill press doesn’t have the depth or throat capacity to easily use it with large wooden stock but I have had success at drilling square smaller drill sizes using a cheap plastic guide collar holding metal bushes.


    I made a similar type square guide for the large threading bits using some pieces of offcut ply. I needed three sizes, 5/8 for the pilot hole, ¾ for a thread clearance hole and then a tap guide with a lower ¾ hole to hold the tap and a top ½ hole to hold the shank.
    I laminated a couple of bits of ply to make a 30mm deep lower support, then some spacers and a thinner top. The bottom has to be thick enough to engage with the top of the tap taper.
    I drilled completely through for all holes using the plastic square guide against the bottom reference face. First using a long 5mm drill in the guide and then opening out the holes 1mm at a time with successively larger drill bits. One of the low cost local supermarket chains does occasional weekly specials on tools and I’d snapped up some own-brand large drill bits, the standard jobber type which self-centre in an existing hole.


    5square jig.jpg 5a square.jpg


    With the rounding plane and square guide I was able to make threads and nuts which screwed up square.


    My choice of mineral oil brand as a thread cutting lubricant might be a bit unusual. All I had at the time was WD-40. I’ve always cleaned my tools with WD-40 and never seen any problem with residue having an effect on finishes.


    I took a 20mm “hardwood dowel” – the only description when I bought it at a local DIY superstore, unspecified wood type which could be anything but looked similar to some ash I’d previously used.
    Sprayed WD-40 liberally on this 20mm dowel just before cutting - no prolonged oil soak, it reduced to size and cut satisfactory threads without tearout.


    6square.jpg threaded hardwood dowel


    Also a lot of comment online says that it’s a one-shot attempt with a screw box, you can’t go back and increase the length of thread on a dowel because the second cutting attempt could start at a different point, destroying the already cut threads.
    I found I could drop an already threaded rod into the top of the Taiwanese screw box and turn it anti-clockwise. It’s easy enough to feel when the already cut thread drops into place at the cutter, then turn clockwise as normal. The pine thread example above was cut in two sections, the first inch and a half as my first test and then extended just to see if that was possible.




    7complete threading kit.jpg complete threading kit
    My final ¾ threading kit, a complete threading process needs some way to ensure correct sized dowel stock and something to hold the drills and tap square.

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  3. #2
    Join Date
    Mar 2004
    Location
    Brisbane (western suburbs)
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    Default

    An excellent post, Jim! You've highlighted the bits that dogged me when I started out. I gave up on the traditional threadbox very early-on, partly because of my incompetence in setting it up again after sharpening the cutter & partly because we have comparatively few woods in Oz that thread well with them The router method is noisy & messy but fast & reliable for threading longer screws & it can handle any wood you are likely to feed to it as long as the bit is sharp. With our bone-hard woods, a carbide bit is almost essential, ordinary HSS bits will dull after after a metre or less of cutting & start chewing your dowel up instead of threading it.

    I think it was a very good move to make yourself the "rounder box" straight up. I turn my screw blanks on the lathe - I used to turn heaps of chair spindles so turning screw blanks was not a big challenge, once, but these days I don't turn regularly & find it takes far longer to get a clean blank than it once did. Been meaning to make myself a "rounder" for yonks, so maybe the time has come.

    The taps that come with those kits are tricky to start straight, alright, the 3/4" tap I have is probably identical to yours. The lead-in is too short, which allows it to slew in the pilot hole, but after a bit you get used to them & I can usually start mine straight (on a good day). The "nut" wood can be virtually anything, I've not struck a wood that won't take internal threads (across the grain!) well. In fact, I deliberately select a softer wood for handscrew jaws so they are less likely to mar the work being clamped. I've had a few screws chip or lose a few turns of thread (due mostly to faults in the wood) but so far have never stripped a wooden nut.

    I usually don't use any fluid with my smaller metal taps, but boiled linseed can certainly help ease larger metal taps (>1 inch) through hard woods. I've also not had any success using oil with the "primitive" tap. There is little provision to clear the swarf with these & the oil just forms it into a thick paste that clogs things quicksmart.

    Wood for screws needs more careful selection & it was searching for suitable woods to make handscrews that sucked me into the wood threading business far further than I'd ever intended. In your part of the world you may be able to get hold of Apple or Pear wood reasonably easily, which are among the best-threading woods I've struck. My 'test' for how a wood will take threads is how it peels on the lathe, if it peels in long ribbons, it's a pretty good indication it will make very clean threads. We don't have many of those sorts of hardwoods here, which is one reason I went to the router method early in my career. It's about the only thing I use a screamin demon for these days!

    So, in a week or two, you are going to have a wall full of these, eh? 3_4 handscrews.jpg


    Cheers,
    IW

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