I am not very experienced with boring on the lathe. I have just acquired (from China) a carbide insert-holding boring bar for my mini-lathe (a Sieg C3, a 7 x 14 in American parlance).
The tool holder for this lathe is so sized that an 8mm high tool has its tip exactly on the centre line of the work.
The shaft of this new boring bar is an 8mm round rod with two flats milled opposite each other, presumably to give the tool-holder and its screws something flat to grip. These flats are around 7mm between faces.
The insert has pronounced negative rake with respect to those flats, so its tip is only about 4mm above the bottom flat rather than the 8mm which would put it on centre.
When I bought the lathe years ago it came with some dedicated brazed carbide tooling, and the boring bar with that lot has the tip pretty well on the centre line. It also has a quite pronounced positive rake—quite the opposite of the new bar.
I realise that if I put the new bar in the tool holder without shimming it up, the curve of the hole will effectively alter the rake of the insert to be somewhat less negative, a change that will vary with the diameter of the bore. Is this the manufacturer's intention?
It's entirely possible that something got lost in "translation", if we can politely so call the Chinglish description on the Ali Express-based vendor's website, and that I have thereby bought a tool intended for some specialist purpose that I cannot guess at. The vendor does hold himself out as a CNC specialist, if that makes any difference.
As it was only NZ$11 I'm not going to lose sleep over the purchase, but if anyone can explain what's going on here, I would be most grateful.
The tool holder for this lathe is so sized that an 8mm high tool has its tip exactly on the centre line of the work.
The shaft of this new boring bar is an 8mm round rod with two flats milled opposite each other, presumably to give the tool-holder and its screws something flat to grip. These flats are around 7mm between faces.
The insert has pronounced negative rake with respect to those flats, so its tip is only about 4mm above the bottom flat rather than the 8mm which would put it on centre.
When I bought the lathe years ago it came with some dedicated brazed carbide tooling, and the boring bar with that lot has the tip pretty well on the centre line. It also has a quite pronounced positive rake—quite the opposite of the new bar.
I realise that if I put the new bar in the tool holder without shimming it up, the curve of the hole will effectively alter the rake of the insert to be somewhat less negative, a change that will vary with the diameter of the bore. Is this the manufacturer's intention?
It's entirely possible that something got lost in "translation", if we can politely so call the Chinglish description on the Ali Express-based vendor's website, and that I have thereby bought a tool intended for some specialist purpose that I cannot guess at. The vendor does hold himself out as a CNC specialist, if that makes any difference.
As it was only NZ$11 I'm not going to lose sleep over the purchase, but if anyone can explain what's going on here, I would be most grateful.
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