How to get the best machined finish on aluminum casting? With my face mill,
I get a near mirror finish, but with internal boring bar, I get a terrible
finish, despite variations in tool geometry. A cutting fluid?
TIA, Dave

David Anderson wrote:

How to get the best machined finish on aluminum casting? With my face mill,
I get a near mirror finish, but with internal boring bar, I get a terrible
finish, despite variations in tool geometry. A cutting fluid?
TIA, Dave

use a hi speed steel tool that is honed and polished on the cutting
edge.


John

On Sat, 31 Dec 2005 01:11:59 GMT, "David Anderson"
wrote:

How to get the best machined finish on aluminum casting? With my face mill,
I get a near mirror finish, but with internal boring bar, I get a terrible
finish, despite variations in tool geometry. A cutting fluid?
TIA, Dave

Yes, use a cutting fluid by all means. If the cutter gets gummed it
will produce a really awful finish.

Check for chatter. You may need a stiffer boring bar.

David Anderson wrote:
How to get the best machined finish on aluminum casting? With my face mill,
I get a near mirror finish, but with internal boring bar, I get a terrible
finish, despite variations in tool geometry. A cutting fluid?
TIA, Dave


Maybe you need to tell us about the machine, how the boring bar is
mounted, etc.

I got a 3" boring head and set of carbide boring bars a long time ago.
I got horrendous chatter and finish that looked like the scales on a
Carp! I had the boring head mounted on a 1/2" straight shank arbor
into a 1/2" collet on a Bridgeport M head. The speed was probably too
high, and the spindle/arbor wasn't stiff enough. I eventually upgraded
my machine to a Bridgeport J head, and got a boring head arbor that was
a straight mount into the R-8 taper. Suddenly, I could do no wrong!
I've never had chatter with the boring head since. I sometimes bore
aluminum dry, but usually brush on a film of dark cutting oil with
a toothbrush.

Jon

David Anderson wrote:

but with internal boring bar, I get a terrible
finish, despite variations in tool geometry. A cutting fluid?

I always use cooling fluid. That helps.
But I have to admit that it took quite some time to get the right tool
geometry. Now, I use very aggressive angles and a lot of honing the bits
surfaces to a mirror finish. Use very low rpm.

Also check that the lower end of the bit doesn't touch the bore.


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

Jon Elson asked the right questions. The face mill worked fine on my
vertical milling machine. The trouble began when I moved the same workpiece
to my lathe and used a 1/2 inch dia Williams boring bar in a toolpost holder
to bore 1.500 inch dia x 3-inch deep, using a 3/16 HS steel bit (not
carbide). Both operations dry. I will try again with a freshly honed
cutting edge plus cutting fluid and maybe reduced SFM . Dave

"Jon Elson" wrote in message
...
David Anderson wrote:
How to get the best machined finish on aluminum casting? With my face
mill,
I get a near mirror finish, but with internal boring bar, I get a
terrible
finish, despite variations in tool geometry. A cutting fluid?
TIA, Dave


Maybe you need to tell us about the machine, how the boring bar is
mounted, etc.

I got a 3" boring head and set of carbide boring bars a long time ago.
I got horrendous chatter and finish that looked like the scales on a
Carp! I had the boring head mounted on a 1/2" straight shank arbor
into a 1/2" collet on a Bridgeport M head. The speed was probably too
high, and the spindle/arbor wasn't stiff enough. I eventually upgraded
my machine to a Bridgeport J head, and got a boring head arbor that was
a straight mount into the R-8 taper. Suddenly, I could do no wrong!
I've never had chatter with the boring head since. I sometimes bore
aluminum dry, but usually brush on a film of dark cutting oil with
a toothbrush.

Jon

According to David Anderson :
Jon Elson asked the right questions. The face mill worked fine on my
vertical milling machine. The trouble began when I moved the same workpiece
to my lathe and used a 1/2 inch dia Williams boring bar in a toolpost holder
to bore 1.500 inch dia x 3-inch deep, using a 3/16 HS steel bit (not
carbide). Both operations dry. I will try again with a freshly honed
cutting edge plus cutting fluid and maybe reduced SFM . Dave

That is also a lot of extension for a plain steel boring bar --
six times the diameter. You could possibly get away with that much
extension with a solid carbide bar (with HSS or carbide insert tooling),
but for a plain steel boring bar, I would suggest that you use a 1"
diameter boring bar for everything that you can use it for. (Perhaps
start the hole with a tailstock-mounted drill bit, then take it up to a
1" bit (if your tailstock will handle a 3 MT shanked drill bit), use the
smaller boring bar to get enough diameter to clear the chips on the 1"
diameter boring bar, and then switch to it for the remaining work,
including the finish cuts.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

David Anderson wrote:
Jon Elson asked the right questions. The face mill worked fine on my
vertical milling machine. The trouble began when I moved the same workpiece
to my lathe and used a 1/2 inch dia Williams boring bar in a toolpost holder
to bore 1.500 inch dia x 3-inch deep, using a 3/16 HS steel bit (not
carbide). Both operations dry. I will try again with a freshly honed
cutting edge plus cutting fluid and maybe reduced SFM . Dave
There's your problem. Sometimes, I use an end mill as a boring bar.
A 3/4" or 1" dia end mill would make a much better boring tool than
your 1/2" bar. Since you need a 1.5" hole, there's no need to use
a small bar. And, since you need over 3" extension, you need something
stiff. Since you are using HSS, you can't go crazy on the SFPM, but
usually faster gives better finish. You should be able to run it at
1000 - 1500 RPM to get 400 - 600 SFPM.

One other trick. If you have a long boring bar, with a "tail" sticking
out the back of the tool holder, it can vibrate, and make a sort of
tuning fork. I have rubber-banded tool blanks and other stuff to the
back end of the bar to damp out these vibrations. If you can feel the
back end of the bar vibrating at ALL, then you need to make up some kind
of damper for it.

Jon

On Sat, 31 Dec 2005 17:30:22 -0600, Jon Elson
wrote:

David Anderson wrote:
Jon Elson asked the right questions. The face mill worked fine on my
vertical milling machine. The trouble began when I moved the same workpiece
to my lathe and used a 1/2 inch dia Williams boring bar in a toolpost holder
to bore 1.500 inch dia x 3-inch deep, using a 3/16 HS steel bit (not
carbide). Both operations dry. I will try again with a freshly honed
cutting edge plus cutting fluid and maybe reduced SFM . Dave
There's your problem. Sometimes, I use an end mill as a boring bar.
A 3/4" or 1" dia end mill would make a much better boring tool than
your 1/2" bar. Since you need a 1.5" hole, there's no need to use
a small bar. And, since you need over 3" extension, you need something
stiff. Since you are using HSS, you can't go crazy on the SFPM, but
usually faster gives better finish. You should be able to run it at
1000 - 1500 RPM to get 400 - 600 SFPM.

One other trick. If you have a long boring bar, with a "tail" sticking
out the back of the tool holder, it can vibrate, and make a sort of
tuning fork. I have rubber-banded tool blanks and other stuff to the
back end of the bar to damp out these vibrations. If you can feel the
back end of the bar vibrating at ALL, then you need to make up some kind
of damper for it.

Jon

A long 2 flute (or even 4 flute) endmill makes a GREAT boring bar,
and is simply ****ing amazing when used with plastic. Just be sure to
set tool angle a bit so there is no drag.

Gunner

"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.

Think of it as having your older brother knock the **** out of you
for torturing the cat." Gunner