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View Full Version : Cutting an internal blind keyway on lathe



.RC.
21st Sep 2016, 09:27 PM
Had to cut a 5mm internal blind keyway in 4140 about 25mm long in a 16mm bore

The cutter is simply a piece of steel I found that already had some HSS brazed onto the end. I had to grind the cutting end to size, of which I did on the surface grinder and also the tool and cutter grinder. The cutting end is square with the shank.

The cutter was then put in the lathe tool post and aligned so it was halfway above and below centre. The workpiece had a line scribed along it's length and some holes drilled, one for the keyway grub screw and another for the end of the slot.

It was put in the lathe and the line aligned with centre height. Then a simple matter of back and forward taking 0.05mm cuts at a time. It cut it quite easily. Was a lot easier then setting it up on the slotter.

I can get better pictures of the cutter in the sunlight if anyone is interested.

caskwarrior
22nd Sep 2016, 12:54 PM
Did you just put the lathe in backgear in the lowest range to prevent the chuck moving around? interesting setup indeed.

Thanks for showing the creative setup. Ralph

sacc51
22nd Sep 2016, 04:18 PM
I think it worth mentioning you need a decent size, robust lathe for this type of work, particularly if you intend doing a lot of keyways.

BaronJ
23rd Sep 2016, 06:41 AM
Odd isn't it when cutting a slot in this way is far more easy in steel than brass or bronze. After doing one brass bush this way, I made a hand slotting atachment that fastened in the tool holder.

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Steamwhisperer
25th Sep 2016, 07:51 AM
Impressive Richard, 16mm hole!! And blind to boot.
Did you machine a relief groove for the tool to clear?

Phil

.RC.
25th Sep 2016, 10:49 AM
Yes the middle hole is the relief hole for the keyway.

Here are some more pictures of the cutter. You will notice I made it to the HSS is fully supported, giving a much stiffer tool. Yet due to the roughly milled grooves the cutting edge still has clearance The only precision measured part of this tool is the cutting edge width.

Previously I have had the HSS fully clear of the shank, and often it would just fall off as the brazing let go.

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KBs PensNmore
25th Sep 2016, 01:14 PM
Thanks for the pics Richard. I think if the tip was silver soldered, rather than brazed, they would have held better? Would a tool shaped the same, be OK to use in a shaper??
Kryn