Re: Those Cheap Diamond Inserts

On 7/30/2024 2:44 PM, Richard Smith wrote:

Bob La Londe <none@none.com99> writes:
 

On 7/29/2024 11:38 PM, Richard Smith wrote:

I heard diamond
* works for Ali because it has no solubility for Carbon
* does not work for irons/steels because the hard tool "disappears" by
    solution into the iron
?

>
My apologies.  I didn't at all mean something like a PVD diamond
coating.  DCMT is a diamond shaped insert.  Typically your find them
coated with TiN, uncoated, and occasionally with TiAlN or AlTiN
coatings.  My point was these small geometry inserts that work so well
in under power under-rigid machines like the typical import 7-8 by
10-16 mini lathe also work on a heavier machine.  If the big boy
inserts don't work these still do.  In this case I was cutting 304
stainless steel. It improved the finish, didn't require sharpening,
had less heat input, and did the job much faster net elapsed time.
>
FYI:  I do a fair amount of aluminum cutting, and generally I've found
bright sharp uncoated tools do the best job and have the best material
removal rate for me and leave a good finish.  Diamond was popular when
I first started cutting aluminum on machine tools, and more recently
ZrN has become the popular coating.  I've tried them and the simple
fact is a coated tool isn't as sharp.  They might work better for
larger tools on larger machines, but on middle weight machines with
limited horsepower (5 or less) a bright sharp uncoated tool works best
for me. For high speed flood coolant makes the tool last without chip
welding, but coatings do not.  On smaller tools horsepower isn't even
a factor as the tool can't take it anyway.
>
>
-- Bob La Londe
CNC Molds N Stuff

 Thx for this detail.
Interesting yes certainly.
Sorry "got the wrong end of the stick".
 I used cutting insert tooling - aagh - 30 years ago.
Vertical milling shell-cutter on steel.
Did well - they'd never seen steel chip ejection like a chain-saw
cutting timber.  Took a visit from the rep. who explained this is how
the tooling is supposed to be used :-)
Coated carbide inserts - coating the gold coloured one - a Ti nitride(?)
coating - for this steel.

Pushing it harder and harder.  As I once offended Jim a little (sorry Jim) over... time is money.  Even if you are doing something for fun, favor, self... time is still your most valuable nonrenewable resource.
I needed to make another batch of stainless mold cores today.  (Stock design that uses upto nine (9) 1.5in diameter cores to varY the size of the casting.  That's 18 cuts to true them up after they come off the saw.
My new inserts arrived a few days ago ago, but I wantedif I could bump up the speed a bit with that little hobby lathe size insert.  I had been using at at 300 RPM in low gear.  That's a starting SFM of 117 if I have done the math right.  I am sure there are folks pushing big turning centers orders of magnitude faster, but this is after all only a bigger import lathe.  Its still an import lathe, and while its relatively heavy, its light for its size.
Of course the SFM drops as the diameter is reduced.  Maybe I could go faster if I cranked up the speed as I reduced the diameter, but this is a single phase gear head lathe.  The motor just turns one speed.  The time to stop it and change gears would eat up any time savings.
Just for the heck of it I decided to see how much faster I could start. At 460 RPM the insert was still doing fine.  Still using the same insert I used when I started this thread.  I don't mean the same type.  I mean the same insert.  That means the insert was hitting the outside of the stock at 180 SFM.  The number doesn't sound much bigger, but the part time was definitely faster.
A couple ends with an intact insert at that speed and I decided to try the last couple parts at 755 RPM.  296 SFM.  That was significantly faster.  Part time was a lot shorter, and the insert still looks like when I started.  (I'll look at under magnification later)  It wasn't so fast that I had any issue keeping up, but it was fast enough I couldn't do anything else, like move the stock in the saw to cut the next rough blank.
Now that I have spares I think next time I cut a batch of these cores I am going to push it until I chip an insert to see just what they will do.
Please bare in mind that these are relatively light cuts.  The blanks come off the saw at about 1.4" to 1.41" and get trued to 1.375".
--
Bob La Londe
CNC Molds N Stuff
--
Bob La Londe
CNC Molds N Stuff
--
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