Parting off blade

... One evil, but easily overlooked, gotcha when parting off with tools held in QC or 4 way tool posts where the cut axis is significantly offset to the tool post fixing is the significant twisting force on the whole assembly...

​My QC tool post is a Bison clone of the Dickson type, it came with a hole drilled through for an anti rotation pin which removed any possibility of tool post 'twist'...



I also set it up & drilled another blind hole in the top slide to allow the QC holder to rotate to 45*.

George.

Such pins are indeed very effective but they do fix the angle(s) of the tool post relative to the top slide axis which many folk find limiting. There may also be an understandable reluctance to drill hole(s) in the top slide.

The gotcha of course is that simple clamping down is "usually fine" and such movement is inevitably due to the extra force needed to overcome (or not as the case may be) a hang-up in progress.

It gotcha-ed me three time in over thirty years. But the real cause was not appreciating the extra slippy-ness and penetrative powers of the lubricant in synthetic coolant over old style suds.

Changing / improving things being the classic way to get gotcha-ed. Cue tearful "But it used to work!".

Clive.

Perhaps I'm lucky but up till now I've had no problems parting off on my Myford S7 with quite a small HSS blade, 1.4mm wide x 9.5mm deep mounted a rear toolpost, but if parting a diameter greater than say 16mm I do start with only a small amount, say 4mm of tool sticking out of the holder and then move it further out in stages, is this the normal way or am I being too cautious? I did find that unless the tool is perfectly square at the end it will flex and try to go in at a slight angle if too much is protruding from the holder.

John

Hi John

If you are able to part off 8mm DOC (16mm Diam) with a 1.4mm wide blade I wouldn't change your existing method, if it ain't broke why fix it.

Emgee