Making Rope Knurls



This is a bit of fun playing with Knurls, using knurls and trying to produce the old vintage design look
is very difficult as a homebrew keymaker, as you are rather limited to knurls that are available to buy
and the day of fancy knurls off the shelf is long gone unless you are prepared to pay megga bucks to have
one made, One of the knurls loved by old keymakers was the "Rope" knurl, which I set out to make
below, Now you must remember I am NOT a machinist, I have no training on doing this, just a few clues
on the internet, and my usual trial and error approach, and these are my very first homemade knurl wheels so be
kind when judging them hi!! the concave rope knurl produces a lovely all round domed
knurl on the end of an adjuster, you can fudge a knurl like this by making a dome and flat knurling the top of
it, but it don't look good on close inspection, to make the correct one you need a tool called an "Indexer" all it is
is a sort of vice that holds a small piece of circular metal and can rotate it is a number of steps, which you fix
to your milling machine, days gone by they were very expensive, and still are but the good old Chinese as usual
have made an "economy" version, ( 40 on Ebay) not the greatest in quality but does the job.
first of all you get a piece of steel bar and cut a rounded slot just under the required size, then fit the bar into
the indexer, taking a fine 90 degree cutter you proceed to cut slots down to the bottom of the main slot, you can see this
process in the pics below. on the left the Indexer fitted to the mini mill which is set at 40 degree cutting angle
and on the Right you can see the cuts on the wheel progressing as the indexer advances, here it is set to 72 cuts


 




When you have cut all the way around you drill a hole in the centre clean up the cut edges and mount it in
a knurling bar and use it as you would a normal flat knurl, Except you have to realise you are
knurling a dome!  so you obviously have to make the dome on your adjuster before you can knurl it :()
Below Left you can see a finished cut and the bar is in the lathe ready to be parted. And Right you can see
a selection of completed knurls which have been parted and hardened ready for use.



These days it seems the 90 degree cutters needed to cut a rope knurl wheel are no longer made, but instructions (as always)
are on the web on how to make one, and below you can see the one I made, it only has two cutting edges but it does the job and it has
been case hardened, these can also made on the indexer, so that accuracy can be maintained.



Below a typical rope wheel and result of the cut on brass



Below is a rogues gallery of knurl impressions, some better than others, and the homebrew tools, the small one is the
latest, I intend to use it to make some small fine cuts..

And below a very fine cut on a deep rope magnified up, this is a 40 degree angle with 72 cuts on a 12mm diameter.
about as fine as I can get it, this is pushing the envelope for me, I can't even see the cut without a magnifying lens.
Great fun...




Getting the shape and cut of the rope image from the wheel can be quite complicated and all are different
Here below is a perfect 15mm Dia wheel, 4mm thick with a  .5mm deep cut of 3mm wide, 60 cuts at an angle of
30 degrees per cut !!  all of which are adjustable when being made, And to make this one wheel involved
128 different operations, a mistake in any one means the scrap bin and start again (been there many times)
on average I should say at the moment for every good knurl there are three failures for one reason or another
They are tricky things to make :()
Two many cuts and the brass won't clear leaving a blurred image, two few cuts and it loses the resemblance
to a rope, to deep a cut and it loses symmetry, to shallow and the image is to faint and so on...
Also to get 60 cuts on a manual indexer you need to uses the vernier scale, inserting the locking pin anticlockwise
at positions 0, 6, 2, 8, 4, and back to 0, repeated until you arrive back where you started, this represents 360 degrees
divided by 6 and you have to get it RIGHT, lose concentration and insert the pin and cut in the wrong location
and its scrap bin and start again :(