What causes his "Pock Marked" finish ??

[francist]

On the "Pock Marked", I can't tell from the photo but is it physical deformed or just looks that way? I can see the radial cut marks but can't see what the speckles are.

I have run across some extruded aluminum recently that looks like it has been galvanized when turned. Only seems to occur in the outer skin and goes away further in. Odd stuff, possibly a defect from the foundry.

Me too. Your description of looking like galvanized is a good one -- the appearance of very small flakes or crystals but (in my experience anyway) the surface is not actually deformed. It just looks like it is, almost like a metal-flake paint.

-frank

 

[Buffalobull]

Give the part squirt of WD40 like Bob Korvas recommended you will be amazed with the results. It keeps the tip of the carbide from galling up and ruining the finish. I use it for most operations on aluminum except tapping

 

[GreggC]

I have a similar tool set and if the inserts are TCMT21.51, then the radius is 1 or 1/64" ,I am learning about inserts myself but for what it's worth I think this 1/64 is the ideal radius for a small lathe.,another bit of info is ,read the back of your insert package, if says P), M, K, it means it is designed to cut P=Mild steel, M=stainless steel and K=non ferrous/aluminum .

Here is the best explanation posted by our very own [B]swatson144[/B],,
https://www.hobby-machinist.com/threads/inserts-and-cheap-chinese-holders.6302/.


TCMT21.51 1st position is the shape. This cannot change round peg triangular hole.
TCMT2.51 Insert clearance angle C=7° This can be changed depending on what your material needs**** add more later.
TCMT21.51 3rd position is tolerance class. M is pretty low. If you see anything else in this position (unlikely) except U or N it would be an improvement with no real effect.
TCMT21.51 Insert features.T, with hole, one countersink, and chip groove on one rake face. Pretty much can't change this and still get the larger screw to fit.
TCMT21.51 Size in qty of 1/8" 2 in this case because the inscribed circle of the 3/8" holders in our example is 1/4" can't change or the insert will be too big/small for the holders.
TCMT21.51 Thickness in qty of 1/16" x 1.5 or 3/32" changing by .5 +- probably would not make much difference except adjusting the height at the tool post.may be no decimal
TCMT21.51 Corner Radius in qty of 1/64" can (should) be changed. 1 = 1/64" which is pointy. changing to something rounder can offer an improvement in surface finish.

Ken,
These are the bits Im using,
TCMT2151
Last number is a 1, very pointy.
Can I assume I should look for a 2 or 3 ??

 

[GreggC]

Well guys,
Here's my latest attempt,
It came out pretty nice,
I use the tool holder Mike suggested because Im turning from right to left,

I increased speed to 1000 RPM as many have suggested,
I used WD-40 as a lube,
The cut was .008
I can still see ever so slight the cut lines, maybe because the slowest feed on my lathe is .0047
and my bit has a distinct point.
Still, looks pretty good.
Thoughts, comments ??

 

[GreggC]

I gotta tell you,
This is a messy business !!
1000 RPM spraying W-40 is messy !!

 

[GreggC]

Also, at 1000 RPM that apron moves FAST !!

 

[mikey]

Try it at 2000 rpm and the slowest feed, or feed manually. You do not need to spray it with WD-40. Just spray a bit on the work and use a brush to spread it around. Take a deeper roughing cut, maybe 0.050", and it should cut much better. Try a 0.008 - 0.010" deep finishing pass and see what the finish is like.

As it is, the finish looks much better but try it at max speed - the finish will make you smile. It gets even better with a HSS tool ground for aluminum.

 

[Ray C]

I gotta tell you,
This is a messy business !!
1000 RPM spraying W-40 is messy !!

Just one quick spray of WD along the length of the shaft is all it takes. Once again, keep an eye on how much fumes you're inhaling.
Don't worry too much about the finish of 6061. Just wipe it with a paper towel and you'll have a million little scratches on it instantly. Fresh 6061 has a very, very fragile finish. Most of the time, 6061 comes with a "hardened/tempered" outer surface that's often done with precipitation hardening or other processes that accomplish the same thing. It does not make the metal stronger, it just puts a tougher skin on the surface. If you set the piece alone for a few weeks, the skin will self harden. I believe you can leave it at an air-exposed elevated temp of about 800F for 24-48 hours and it will accomplish the same thing.

FWIW, I've probably cut several tons of 6061 in my shop every year I usually have about 200lbs of misc stock at any given moment.

You can cut AL with HSS if you want. Either way works. For carbide, just use anything that has a point on it. Don't over-think when cutting AL anymore than you would over-think how to tear a piece of cotton candy off the cone.

Ray

 

[GreggC]

Try it at 2000 rpm and the slowest feed, or feed manually. You do not need to spray it with WD-40. Just spray a bit on the work and use a brush to spread it around. Take a deeper roughing cut, maybe 0.050", and it should cut much better. Try a 0.008 - 0.010" deep finishing pass and see what the finish is like.

As it is, the finish looks much better but try it at max speed - the finish will make you smile. It gets even better with a HSS tool ground for aluminum.

Hey Mike,
The top cut is 2000 RPM slooow manual feed,
The bottom portion is 1000 RPM slowest auto feed.
Top portion looks pretty good.

My slowest feed rate on my lathe is .0047, pretty fast at 1000 or 2000 rpm,
Is there a mod to slow it down, custom gears ??

 

[GreggC]

Just one quick spray of WD along the length of the shaft is all it takes. Once again, keep an eye on how much fumes you're inhaling.
Don't worry too much about the finish of 6061. Just wipe it with a paper towel and you'll have a million little scratches on it instantly. Fresh 6061 has a very, very fragile finish. Most of the time, 6061 comes with a "hardened/tempered" outer surface that's often done with precipitation hardening or other processes that accomplish the same thing. It does not make the metal stronger, it just puts a tougher skin on the surface. If you set the piece alone for a few weeks, the skin will self harden. I believe you can leave it at an air-exposed elevated temp of about 800F for 24-48 hours and it will accomplish the same thing.

FWIW, I've probably cut several tons of 6061 in my shop every year I usually have about 200lbs of misc stock at any given moment.

You can cut AL with HSS if you want. Either way works. For carbide, just use anything that has a point on it. Don't over-think when cutting AL anymore than you would over-think how to tear a piece of cotton candy off the cone.

Ray

Ray,
Thanks for the advise,
Im in my garage with the door open,
I think Ill add a fan to move the fumes away even quicker.
Not so messy with just spraying the piece, not constant spray.
Im such a beginner !!