Making KL parts

[Tony Russell Davis]

Here's a one for the engineers. I have made and fitted an additional KL to my Mullen but didn't have to make the bellcranks as I already had two spares. They use parts similar to the ShoBud pattern, but with an open sided slot that slips onto the side of the hex crossrod and closes with a grubscrew. This avoids having to take the crossrod out and slide the parts on from the end (which involves removing many other parts too). Many guitars use a similar system, but with square, not hex, rods.
Problem - how would you cut the slot with a "hex" end? I made one on a metal-cutting bandsaw by repeatedly cutting down to the "V" mark and removing the waste between the saw cuts, finishing off with a small file (tedious and difficult to get the facets true and flat). I have some machines available to me (inc. milling machine and lathe) and thought I could get a milling cutter with a 120degree point, then simply cut from side to side - job done! But such things (seemingly available in US) are not in any of the engineering catalogues in UK.
Any ideas? Tony.

[Bent Romnes]

Tony, the only way to get around that problem is to have a milling cutter made to the shape of what you want milled out. I was told that this is what Mullen did

[Tony Russell Davis]

Hi Bent - I too figured that was the way to go, but I can't find a cutter that shape. So - any ideas as to how to make one, or where to get one in UK will be welcome. Or any workaround that gets the job done differently? T.

[bob adams]

What material are you using for the bellcrank Tony?

[Tony Russell Davis]

Got some decent aluminium Bob.

[bob adams]

Ok,

Drill an 8mm hole at the centre of the hex aperture, (it is 8mm isn't it?) get yourself a piece of stainless hex, (if you're stuck some sealer/silicon guns use it) cut a piece about 4" taper it and then drive it through the 8mm hole, pass it through a couple of times, needs a good vice, steady hand and thumb protection! but trust me it will work just be very careful to get the flat of the hex horizontal and square!

[Tony Russell Davis]

Thanks Bob - that's a home-made "broach" isn't it? I have read about that or similar but commercially made broaches also seem only to be available in US, so I've never seen one. I'll get on making one asap. The US hex rods are 5/16in flat to flat, which is 8mm, near as dammit. I'm pretty sure that 8mm hex (or even 5/16) will be lying about in some of my boxes masquerading as allen keys or the like.
I have the impression that the tool described will crush or distort the aluminium into a hex. Do you think it might be useful to cut a few gaps, ringing the tool, to allow it to also cut/scrape material from inside the hole as it passes through? I also wonder if I can rig up an arbor press with a bottle jack to push rather than bash the tool through.
Bob - you got my brain back into gear - thanks!
Tony.

[Will C]

Apart from my pm to you, Tony, I did wonder about broaching too, but feared the broach would be as hard to get or make as the cutter. Bernard Curnow, who built some decent steels, was a toolmaker. I wonder what he would make of this little to-do?

Will C

[Tony Russell Davis]

Broach.jpg (6.64 KiB) Viewed 6042 times

So here's the home made 5/16in broach, tapered to go into a 8mm hole - made from an allen key. The nicks on the edges of the hex are made with a dremel cutting disc and angled to act like saw teeth on the aluminium. I've not used it yet because I'm busy working on a device to push it through, rather than bash with a hammer. Just wanted to show off the new tool. Tony.

[Will C]

Nice work, Tony. I've been thinking: might this approach work better if you start with a circular hole, then broach it into the hex shape, then remove the "side" to create the "open sided" hex recess? This would avoid the tool wandering as you do the broaching. You could use the drill press to force the broaching tool through the hole, n'est-ce pas?