"Aussie" wrote in message
...
On 16-May-17 7:15 PM, Jim Wilkins wrote:
"Aussie" wrote in message
...
I'm trying to part off some 12mm (1/2") PVC rod and am hoping to
not
have to face the resultant parts.
The sides of the cut are terrible, not smooth at all.
I'm using a HSS parting off tool similar to this:
http://www.assetplant.com/WebRoot/Store/Shops/shop/5512/2DE6/890C/F386/E667/C0A8/C83B/12E3/1-2.jpg
Any pointers on how I should sharpen the tool?
How important is finishing the tool with an oil stone after
grinding?
Should I have a dip/notch on the top face behind the cutting edge
to
deflect the "chip"?
How critical is the speed?
Thanks.
Something is wrong but I can't tell what without examining all the
details of your setup, many things can cause problems.
When my 1/16" wide HSS cutoff blade stops behaving well, usually
when
parting stainless, I hollow-grind the end to the curve of the wheel
and stone the cutting edge to feel sharp to my finger. My Multifix
tool holder gives the blade a 4 degree back rake angle. I stopped
grinding a chip breaker in the top surface because I can't make it
as
smooth as the factory finish.
As for speed, if the blade chatters I reduce it until the cut
quiets
down, typically at 300 RPM.
It cuts PVC water pipe very smoothly, enough to use it for turning
to
final diameter.
-jsw
Thanks Jim.
As usual after posting asking for advice I tried again with more
success.
I ground the front face square with a little bit of rake.
The top face is flat & square
I dressed it with a flat diamond knife sharpener.
I increased the speed to 850RPM.
I had to grind the top face down about 4mm as the tool holder isn't
the correct one for my lathe.
It's not perfect but its much better than the 'rubbed & melted" cut
I was getting before.
http://imgur.com/a/eYmJo
I suspect that your cutoff bit may not be perfectly square to the
spindle axis.
When I reinstall the toolpost I turn the compound to 28 or 29 degrees
for threading, roughly align the toolpost and tighten its bolt, then
loosen the compound swivel screws and press the cutoff holder against
the spindle end to perfectly square it while retightening the swivel
screws.
If I tighten the toolpost bolt last instead I unavoidably shift things
a little from the wrench torque.
-jsw