Re: tool bit angles for aluminum
>> Now that you've given up fast bikes and fast girls (or have you?) I'm
>> sure there's hope for you!...
>> OK, I jest!.... :P
> I hope you still have a Norton Commander or a GTS. :-)
> (Paul Pennycook).
Still got Granddad Norton and Babe Bristol.
Are you still rota-biking?
Drop me a line off list.
That's an effective honing jig but you still have to grind the tools
fairly frequently 'cos the honing angle is slightly different to the
By far the best way if you are honing a ground tool 'cos its far faster
but if you just hone to re-sharpen the honed face gets longer and
longer and the job slower and slower. Prolly regrind every 3 or 4
hones with this system but the tool positioning does not have to be
Its pretty much the normal way of doing things.
My mentors approach was to have a block that presented the tool to the
wheel so repeatably that full face honing could be used and simply
flipping the block got the different angles.
Your turned surface finish is basically a replica of the tool edge
surface finish so you only really need a super finish where the tool
contacts metal and where the chip flows across the tool. Hence only a
small part of the edge actually needs honing.
With full face honing you have to re-sharpen more often so you need a
really effective and accurate jig lest it become a complete PIA,
however you always have a really sharp tool.
I suspect half the reason for his set -up may have been to avoid
needing both a grinding wheel and a honing wheel, thinking about it I'm
pretty sure I caught him rough grinding a tool at work once. Good
grinders and wheels used to be very expensive and I guess he finalised
his set-up in the late '50s / early '60s period.
- --- In email@example.com, Clive Foster <clive_foster@t...>
>Your turned surface finish is basically a replica of the tool edge----------
>surface finish so you only really need a super finish where the tool
>contacts metal and where the chip flows across the tool. Hence only a
>small part of the edge actually needs honing.
So let me get this right....I should be honing the top of the tool
(side rake) AND the front tip of the tool?
Also, how big of a radius on the tool tip are we talking about?...Is
Theoretically the tip radius should be greater than the feed per rev
and the cut depth greater than the tip radius.
Seems to be generally accepted that taking greater = about twice is
good enuf for government work.
However this seems to be biased towards knife tools on hard materials
and bigger lathes. I tend not to worry about the cutting depth one and
just wind in 'till it all looks about right!
I've not got a Taig lathe but my Heavy 10 South-Bend is quite happy at
0.2" tip radius, well honed, on 50 thou roughing and 10 thou finishing
cuts on pretty much anything for feeds and speeds worked out using the
The big thing, especially on a sticky material like aluminium, is to
get the chips flowing off smoothly and continuously whether as a
succession of short curls or long ribbon. Honing all the faces ensures
that you are cutting with a smooth continuous edge. A little
discontinuity in the cutting edge is an open invitation for the
material to build up on it especially as the bottom of the
discontinuity cannot be as sharp as the rest of the cutting edge.
Honing the top also provides a smooth surface for the chip to flow
across as it comes off the work considerably reducing friction which
has got to help matters. That chip presses down Hard onto the tool as
it comes off.
Within reason the larger the radius the better the finish but the
greater the forces on the lathe. 1/32" sounds a good starting point for
a Taig but I wouldn't be adverse to trying something larger with a
small depth of cut, 5 thou or less and slow feed but relatively high
speed. With a larger radius its easier to get a smooth continuous
cutting edge but you will be using the tool more scraping or burnishing
than truly cutting.
Bottom line is that the books give a starting point but you have to
learn to watch the chips to judge how well the cutting is going.
Biggest problem is that too fast or too slow, too shallow or too deep,
too small or too large radius all give problems and frequently there is
more than one wrong combination which will give the same effect. Its a
great help having "one who knows" to show you the effects of the
various wrong combinations on your size of lathe. Amateurs tend to be
too ready to drop down to a tiny cut, tortoise feed and low speed at
the first hint of trouble. Sometimes you just have to lean on things
to get a result but the little Taig hasn't the physique to lean very
> So let me get this right....I should be honing the top of the tool
> (side rake) AND the front tip of the tool?
> Also, how big of a radius on the tool tip are we talking about?...Is
> 1/32" enough?
> To Post a message, send it to: taigtools@...
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> Let the chips fly!
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- --- In firstname.lastname@example.org, Clive Foster <clive_foster@t...>
>Bottom line is that the books give a starting point but you have toAmen to that! Let me reiterate that I have a Craftsman 6" x 18"
>learn to watch the chips to judge how well the cutting is going.
>Biggest problem is that too fast or too slow, too shallow or too
>deep, too small or too large radius all give problems and frequently
>there is more than one wrong combination which will give the same
>effect. Its a great help having "one who knows" to show you the
>effects of the various wrong combinations on your size of lathe.
>Amateurs tend to be too ready to drop down to a tiny cut, tortoise
>feed and low speed at the first hint of trouble. Sometimes you just
>have to lean on things to get a result but the little Taig hasn't
>the physique to lean very hard.
lathe, and not a Taig, if it makes any difference. In theory I should
be able to lean on it a little more than one would on a Taig.
According to my Atlas Manual of Lathe Operation, I should be able to
take a 20 thou depth of cut while facing, though I'm still having
trouble with taking even a 10 thou depth of cut.
Specifically, I'm still having difficulty getting the chips to flow
off the tool bit smoothly, and have been trying to tune in to why
this is happening. While I can normally visualize mechanically what
takes place in a given situation, there are so many variables taking
place here that I can't keep track of them all. As you mention, there
are combinations of several factors that need to be compiled.
Currently, I keep having to stop the lathe to remove work hardened
aluminum from the tool tip. From what you're saying, I think it must
be because I haven't been honing the top of the tool bit, so I'll be
trying this next.
I successfully turned one 3-1/2" diameter piece then began another
(of the same dimension.) At that time the tool began performing
poorly, and I honed the face again, but it didn't improve
performance. I didn't know that I only had to hone the tip of the
radius and not the whole face, as well as the top of the tool, so
this is another error that will need correcting.
Thanks again for your mentoring....I'll be regrinding and honing my
tool bits this afternoon, then will give it another try.