Model Forum / General / Models / May 2008

They're also handy for sharpening drills and centre punches and taking
the burrs off cold chisels and generally removing relatively small
quantities of hard-ish material. Many of the typical small trade books
like Zeus and the Dormer Drill book that turn up a boot sales etc for
a quid or two have diagrams of what you're aiming for in terms of tool
shape. Hand sharpening drills can be a bit tricky, especially in small
sizes, but again it's a skill well worth learning even if only to
recover broken ones to start with.

Richard

That's all very well, but I personally agree with AC.
If you're a newbie who has just bought their first lathe, then the last
thing you probably want to worry about is learning to grind tools from
scratch. You want to stick some metal in the lathe, and make chips. A set of
preground tools will let you do that.
Once those pre-ground tools aren't cutting how they should, then they can
start to learn how to sharpen them, and how cutting angles work.

And your way is like telling somebody that if they want (fill in the blank)
cuisine, to cook it before they've even tasted it. Most people will of tried
what they want to cook before they try cooking it, or at least have a rough
idea of how it will taste.

True, but there's more than one route to acheive most things.

<big snip>

My first set of cutting tools were pre-ground.
They let me try out the lathe, and then once they started to get blunt, I
started to re-sharpen them.
After that I started to learn about cutting angles, before moving onto
grinding from blanks.
However, I now mostly use indexable tooling for easiness, but still use the
odd HSS tool mainly for profiles and flycutters.

I would personally recommend that any person new to the hobby, who hasn't
got anybody to guide/help them nearby, that they buy some pre-ground tools.
It might not be the ideal way, but it allows them to make some chips, and
provides them with a rough idea of how tools should be ground. From there,
they can go on to learning to grind them.

moray

 That pretty much covers it, really!

 Cheers
  Trevor Jones

I agree with the sherline pages, I learnt to grind tools following
this:
http://www.sherline.com/grinding.htm One thing I disagree with however
is the recommendation to have a cup of water to dip the blank in if it
gets to
hot (pretty sure it was this article). Dipping hot HSS into water can
cause micro
cracking of the steel. The water cooling is a throwback to Carbon
steel tools
HSS should be ground hard and quickly, faffing about taking light
passes wastes
time, and heats the blank excessively.
My top tip: clamp the tool blank in a pair of mole grips and have at
it, you wont
burn your hands, and its virtually impossible to draw the temper on a
good HSS
blank. grind it hard and fast to approximatly the correct shape and
then tune it up
on the other wheel, and finally (if you need a good finish) a diamond
'stone'
Dont worry to much about the angles, they are to aim for, not gospel.
The correct shape is one where the first and only bit that contacts is
the cutting edge.

Dave

Peter Hi, a friend of mine by way of a gift of a couple, introduced me
to the CCGT (aluminium) inserts a while ago when I still had time to
go into the workshop. In planning a return to work :-), I haven't yet
found an economic source (ie less than £5 each), have you - or is it
one of those instances that the bullet just has to be bitten?

Regards

Keith (short of both time and money)

 In the shop I work in, and as often as not, have to train apprentices
in, we do a lot of work that does not need the production rates as much
as we need the precision.

 We often have jobs where there are no practical carbide inserts
available (or they are silly money!) where HSS tools are quite capable
of being used.

 As a result, we still teach a lot of grinding, as a basic skil, so
that they will be able to, if they get to a job that can be done no
other way.

 I'm going to see about ordering in a package or two of those CCGT
inserts for or boring bars, though, and perhaps a few lathe tool holders
to suit.

 As someone else said, horses for courses!

 I beleive that a beginner is better served to learn to turn with a
tool that does not readily chip, and is relatively inexpensive, anf
forgiving to use.
 HSS suits what I need it to do at home on my S-7, for most things,
though I have a few carbide tools around that I can use.

 As to being at the grinder every few minutes. Not so much. I am
finding that tools will last sometimes for several hours use, now that I
do not do as many beginners mistakes. Regrinding a tool, is a good time
to contemplate what happened, and how to not have it happen again. :-)

 Now, learning to TIG weld! There is a way to teach yourself tolerance!
And electrode grinding!

 Thanks!

 Cheers
  Trevor Jones

That second insert looks the very thing. Very similar cutting edge to my own
silver inserts. My toolholder is a big FO 20mm shank jobbie that takes huge
15mm x 06mm DNMG inserts and was donated to me by above mentioned mate along
with 15 or so of the razor sharp silver inserts many years ago because he
didn't use that shape tool much. I just wish I knew who had made those
inserts because I've only got a couple with decent edges left now. Mind you
it shows how long they last given the amount of machining they've done over
those 15 years.

They don't just do my turning either. I made an adaptor for them for my big
flycutter and they do all the skimming of blocks and heads on my mill. By
volume of material that's many times the metal removal of the turning I do.
It's not uncommon for me to have to shave 2mm or 3mm off a cast iron block
or head and I'd hate to have to try that with an HSS tool. My carbide
inserts will do it all day long on 1mm cuts without showing any wear.

I would just add one thing having looked at your links and the
recommendation on the first one about using small corner radii on the
inserts. That's also how people grind HSS tools - down to a point basically.
I'd say that's flat wrong for inserts. If you have the wrong grade insert,
like those yellow/gold ones they show in the tool, you need a small corner
rad to get a sharp enough edge to cut anything. However the insert is then
weak and prone to chipping and won't last long. My silver inserts are 0.8mm
rad which is huge by conventional wisdom but they'll shave half a thou off
tough grades of steel to a mirror finish without blinking an eyelid. They
also never chip. The only thing that blunts them is when I have to machine
pressed steel valve spring caps to take double springs and the hard surface
skin takes a bit of getting under. Sometimes a really hard one comes along
and is so damn hard is screeches on the insert and I know I've just kissed
another cutting edge goodbye. It'll still be sharp enough for roughing work
but not worth a damn for fine finishing cuts or flycutting on the mill.
Under a glass you can see it's just been rounded a tad and that's enough to
kill the razor edge which is the critical thing in how they work

So I'd say stick to a larger corner rad but with the uncoated silver non
ferrous tips.

In fact the wisdom about HSS and carbide tooling isn't so different even if
it seems to split people's opinions so radically. On small lathes they both
need sharp edges to work well, which is little more than common sense
really. It's just that everyone tries to sell you the wrong carbide inserts
which don't have razor sharp edges and so it isn't really surprising they
don't work. Getting a sharp edge isn't all about grinding a tool down to a
very pointed tip. You can radius that tip off and the edge will still be as
sharp - it'll just be wider. They key things are the relief angle under the
tip so you're only cutting on the very top edge and also the top rake which
you can see from the pics the silver carbide inserts have a lot of. That's
what gets the cutting edge into the workpiece efficiently.

You wouldn't try to shave wood by holding the chisel at 90 degrees to the
wood and hitting the backside of it with the hammer. You point the tool in
at an angle to make it cut. However so many HSS tools get ground with bugger
all top rake so they can only cut well if the tip is very pointed and then
they burn out quickly. Carbide isn't a worse material than HSS in any
situation IMO. It can be ground just as sharp and will last many times
longer.

Think about parting off tools. It's a good place to start to understand how
cutting edges work. HSS or carbide it's still a 3mm wide blade or whatever
and you're cutting on the whole width of that on every job. If that width of
tool cuts ok why do you need any other turning or facing tool ground to a
point? Well no sh.t Sherlock, of course you don't. Compared to a parting off
tool even a 0.8mm rad on a carbide insert is bugger all. What matters is the
sharpness and rake of the cutting edge rather than how small a point it's
ground to.

I think people who are used to HSS just don't always understand carbide
properly or simply refuse to based on old prejudices. At the risk of
repeating myself the carbide inserts meant for roughing steel have rounded
edges and rely on machine hp to remove metal. They aren't cutting so much as
ploughing through the steel and relying on the fact they can reach
astonishing temperatures without breaking down or burning out. If you have
the hp and the speed you can force anything into anything. A lead bullet
will go through steel if it's travelling fast enough but if you tried to
scratch steel with lead by hand you wouldn't get far.

If you don't have hp and speed you want sharp and hard not round and soft.
HSS or carbide doesn't affect that it's just that carbide will always be
tougher and last longer.

I think the HSS versus carbide brigade need to kiss and make up and realise
that regardless of the tool material it's the cutting geometry that makes
them work properly and that will be similar for both types of tool. You
don't see carbide drills and milling cutters made with appreciably different
geometry to HSS ones but they'll cut into much harder materials and last
much longer on normal ones. Same with lathe tools if only people would
appreciate it and use the right tool for the job. That means rounded edges
if you have the hp to force them into the work and razor sharp edges if you
don't. It really isn't that complex.

I doubt if there's a single professional machinist in the world who relies
on output to make money that still prefers HSS to carbide for any job he
does. There are carbide inserts designed for just about anything you could
ever envisage machining. Saying HSS is the better or 'proper' way to cut
metal and you have to learn how to sharpen it or you're not a 'proper'
machinist is like insisting crossplies are still better than radial tyres or
telephones are all bollocks and the two tins cans on a string were good
enough for my grandad so they're good enough for me.

Carbide has superceded HSS like Homo Sapiens has superceded Neanderthal Man.
It's called progress and evolution. Learn to accept it and get over your old
preconceptions.

 They sell for less, when they are wholsaled out to the sellers of said
sets.

 Probably cuts way down on the number of phone calls the sellers of
kits get from the new guys, asking why they were given inserts for
aluminum, rather than for the steel they want to cut, too.

 Cheers
  Trevor Jones

Because the people who sell them aren't machinists and the people who buy
them don't know what they're doing?