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On Wed, 26 Dec 2007 02:05:42 GMT, "Harold and Susan Vordos"
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wrote in message
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I've just bought a diamond wheel-dresser which is a steel rod with a
block of steel at the end with a 1.5" x 1/2" face with coarse diamonds
stuck to it.
Anyone know how the diamonds are attached?

They are usually set in a copper alloy of sorts.

And how rugged are these
things to having the diamonds knocked off?

Unless yours is one of the plated variety (it would likely be nickel
colored
if so), you don't have to worry about knocking the diamond off, it's not
just glued on the surface. It is held captive by being poured in the
matrix.

Thanks, Harold, this thing is silver all over (looks plated).
Does this mean it is fragile? If so, how should I care for it over and
above what you recommend in general?

That be the case, yeah, the diamond isn't all the securely set. I highly
recommend you do not use it to knock off the aluminum you mentioned. Use a
dressing stick or a star dresser to remove the aluminum, then use the
diamond to smooth the wheel.

You may not like the surface the diamond cluster leaves. Diamond, being
very sharp and hard, will prepare the surface so smoothly that it won't
grind as well as a wheel that is dressed with a star dresser. The
advantage of the cluster diamond is that it's a lot easier to get the wheel
true. You may find that you can use a (sintered) dressing stick to
slightly rough the wheel once it's true, which will actually improve its
cutting characteristics. I use dressing sticks almost exclusively for my
pedestal grinder, although on rare occasion I'll use a mounted diamond to
move a lot of wheel when it's required. For grinding HSS off hand, a
diamond dressed wheel is not good at all.


Should the dresser be held against the tool rest, or can you
just hold it freehand?

While you may be able to use it freehand, a rest helps control the cutting
action. It's also a little safer, If you slip freehand, you can end up
tangled with the wheel. You can believe me when I tell you that hitting
a
running wheel with your hands can ruin a good day.

This I know, but don't ask me how

I happen to know a bit about that as well! I'm getting the distinct idea
that it's for the same reason.
:-(



Are light "cuts" advisable? I've been a naughty
boy and used the wheel for aluminium. I have stood to one side, just
in case, however.

Don't horse it----but insure that it makes contact well enough to actually
do something to the wheel. Introduce it to the wheel, then work it
sideways, slowly feeding inwards until you have the surface of the wheel
as
you like it. Keep it moving side to side to avoid creating grooves in the
wheel, which can actually ruin the dressing tool.

By horse it, I guess you mean push it in so hard it slows the wheel?

I'm not convinced you could put enough pressure on the wheel to do that.
In your case, if you push too hard, you could dislodge diamonds. The
aluminum that's present will do its best to do so anyway. I was struggling
with the notion that you had a matrix set cluster, not a plated one. Be
real careful with the plated one-----the only thing that holds the diamond
on is the plating that is applied to the entire thing. Diamonds, being
conductive, allow for full encapsulation with nickel, so once you uncover
half the diamond, it's free to fall out, and often does. I suggest a light
touch, allowing the diamond to do it's work without grooving the wheel.
Keep the cluster in constant sideward motion, so it can't establish grooves
in the wheel. They'll undercut the sides of the diamond, then they'll
release.


Also. I've just bought a new slower speed grinder (1425 rpm - 4-pole
on 50Hz) with a gray GP wheel and a white alumina wheel. Which would
be the best for touching up carbide-tipped lathe tools?

Neither one.

While I don't recommend them, aside from diamond or CBN, only a silicon
carbide wheel will perform with any degree of satisfaction on carbide.
Aluminum oxide (both of your wheels are aluminum oxide) is far too soft to
be effective.

Why is one white and one grey? The Al2O3 white one is meant for HSS
and apparently does a better job on that, so what is the grey one
meant to do? The white wheel has WA 12 L stencilled on it, and the
grey has A 60 M, I think (not too sure about the A as only half of it
got stencilled) Then there is the maker's brand, and 40 m/s.

How the aluminum oxide is made makes a difference in how it performs.
That's why Norton offers various types of aluminum oxide wheels. Some are
far better suited to grinding particular types of alloys---such as the 38A,
which cuts fast and cool when grinding HSS. They all work, just some work
better than others. The rank novice may not notice the differences at
first.

Regards the markings, they defy common markings, so it's hard to say what
they mean. I'd venture a guess that the L is the hardness, as is the M.
The 12 is a mystery, unless it stands for 120, which would be a fine wheel.
W I have no idea, but the A likely designates aluminum (oxide). The
other marking makes more sense, with the A obviously aluminum (oxide), and
the 60 the hardness. There's a lot more to wheel markings than yours
display. My guess is they're not American made.


If you want really good results, buy a diamond wheel, and run it wet.

Can you do this on a 1425rpm dry grinder? What would an 8" diamond
wheel likely cost? Would you just let water drip slowly from a bottle
on a shelf via a plastic tube?

For carbide lathe tools, the type 1 wheel isn't a good choice. Carbide is
best ground without hollow grinding, so a type 6 wheel is the wheel of
choice. One that would serve your purpose very well would be only 6"
diameter, and would have a 3/4" face (on the side of the wheel, which is the
working surface). It yields flat grinds, so you don't undercut the tool,
weakening the edge. That's important if you put tools to work. No big deal
for scratch cuts, however, but then you are likely not taking advantage of
the use of carbide if that's how you're using it. HSS would likely serve
better unless you're machining hard materials.


Otherwise, a green silicon carbide wheel will work. The dust is
hazardous------causes silicosis-----and the finish such a wheel leaves
leaves a great deal to be desired. Silicon carbide (green wheel) isn't
all
that much harder than carbide, so it tends to club it off instead of cut
it
cleanly the way a diamond wheel does.

Way back, I just used the grey wheel that was in the grinder without a
thought. jack

And it did a poor job of almost everything, didn't it?

Seemed OK to me, but then, I'm just an inexperienced amateur.
Maybe it had a SiC wheel in it, coz it seemed to put a nice edge on
out carbide tools. This was just a small lathe in a university
laboratory workshop.No critical work was ever done on it.

If it put an edge on the tool and actually moved the carbide, it most surely
was silicon carbide. Aluminum oxide is substantially softer than silicon
carbide. So much so that when you apply tungsten carbide to an aluminum
oxide wheel, it tends to glaze each of them without doing much more. You'd
have a dreadful time trying to put an edge on tungsten carbide tools with
aluminum oxide, and they'd likely cut very poorly because the cutting edge
wouldn't be keenly sharp, which is key to performance with light cuts using
carbide tools. Roughing cuts are far more forgiving, assuming you go to
negative rake. That's a whole different world, not to be confused with
machining with positive rake.

Harold

Thanks for your help, Harold, jack