# What causes his "Pock Marked" finish ??



## GreggC (Mar 5, 2018)

Hey guys,
Please look at this finish,
What causes this "Pock Marking"
Im turning 1.20" aluminum,
400 rpm,
Im using carbide bits See link

https://www.ebay.com/itm/5pc-3-8-Sh...773612&hash=item1ec7d16d86:g:qpUAAOSw4P1ZxLf6

My feed speed is .0047,
Cuts are .003 / .004


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## T Bredehoft (Mar 5, 2018)

just a guess, chips impacting on the cut surface, either just friction or being crowded by following chips.


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## Ray C (Mar 5, 2018)

Low RPMs and it looks like you're not using any coolant or lube.

Turn at 800-1000 RPM.  Feed rate is OK.   Cuts are very light so you'll see the tracking of any/all imperfections in the cutting edge.

Also, tell us how the piece is supported and how the tool is positioned.

Ray


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## GreggC (Mar 5, 2018)

Ahh, more RPM's, interesting.
I need lube cutting aluminum ??
The piece is supported in the chuck and with a live center.
The tool is at 90*, I was getting cut lines so I rounded the bit to get a better finish,
Rounding the bit helped, now the cut lines are very light.


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## GreggC (Mar 5, 2018)

T Bredehoft said:


> just a guess, chips impacting on the cut surface, either just friction or being crowded by following chips.



Chips impacting the piece will cause this ??


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## Bob Korves (Mar 5, 2018)

Using inserts, make sure they are sharp inserts.  Speed up as suggested.  Use kerosene or WD40 as lubricant.  Use a deeper cut.

For that job I would prefer a very sharp HSS cutter with plenty of rake and clearance, still higher speeds, but not as much as for the carbide.  The cut should be about as deep as the nose radius.

It appears to me that the metal is tearing instead of cutting.

Think sharp, plenty of relief, and lubricant.


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## markba633csi (Mar 5, 2018)

Gregg what brand and model of lathe? Also, what flavor of aluminum
I second Bob K above- try HSS tool
Mark
I've never had that issue and I just have a cheezy little Atlas


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## Ray C (Mar 5, 2018)

GreggC said:


> Ahh, more RPM's, interesting.
> I need lube cutting aluminum ??
> The piece is supported in the chuck and with a live center.
> The tool is at 90*, I was getting cut lines so I rounded the bit to get a better finish,
> Rounding the bit helped, now the cut lines are very light.



Yes, coolant or lube for AL.  Without coolant or lube, it can/will weld to the tip of the insert.
SFM for aluminum is anywhere between 100 and 150 so, with 1.2" dia and carbide inserts, you need 800-1000 RPM.  RPM for carbide = 8 x SFM/dia.

If you have OK ventilation, one quick light spray of WD-40 will work.  You will get some fumes though.  Be mindful of how much smoke you generate in the shop.   Long term, it catches-up with you.


Ray


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## GreggC (Mar 5, 2018)

markba633csi said:


> Gregg what brand and model of lathe? Also, what flavor of aluminum
> I second Bob K above- try HSS tool
> Mark
> I've never had that issue and I just have a cheezy little Atlas



Shop Fox M1049


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## GreggC (Mar 5, 2018)

I have zero experience with HSS cutting tools,
Can anyone make a suggestion what to buy ??
Maybe hand hold me and post a link ??


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## GreggC (Mar 5, 2018)

This started when I was trying to remove the cutting lines,
I rounded the bit, the cutting line mostly went away, now I have pock marks.


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## markba633csi (Mar 5, 2018)

You were having some issues with gears wearing out on that machine- where do you stand on that situation? Did you ever resolve it?
Mark


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## Ray C (Mar 5, 2018)

The pock marks are likely from either (or both) tearing due to low RPMs or, weld build-up on the tip of the insert. Also, do you know what specific kind of aluminum that is?  60xx and 70xx series machines fine.  20xx, 30xx and 40xx series machine a little bit worse than warm bubble gum.


Ray

EDIT:  I can tell by looking at it, it is not 70xx series.  It could be 40 or 60 just based on color/sheen.


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## GreggC (Mar 5, 2018)

markba633csi said:


> You were having some issues with gears wearing out on that machine- where do you stand on that situation? Did you ever resolve it?
> Mark



Hey Mark,
I posted on the Gear Thread that I discovered a gear shaft gouged,
I groomed it and reinstalled, then I oiled all the apron fittings until
oil was dripping on the chip pan.
Oil, oil, oil !!
It appears to be working well.


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## GreggC (Mar 5, 2018)

Ray C said:


> The pock marks are likely from either (or both) tearing due to low RPMs or, weld build-up on the tip of the insert. Also, do you know what specific kind of aluminum that is?  60xx and 70xx series machines fine.  20xx, 30xx and 40xx series machine a little bit worse than warm bubble gum.
> 
> 
> Ray
> ...



Hey Ray,
Its 6061.


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## GreggC (Mar 5, 2018)

Here's the million dollar question, 
How much should I be taking off on a finish cut ??


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## Ray C (Mar 5, 2018)

GreggC said:


> Here's the million dollar question,
> How much should I be taking off on a finish cut ??



With carbide, minimum of 10 thou DoC.   With 6061, you can go pretty deep.

Ray


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## GreggC (Mar 5, 2018)

Ray C said:


> With carbide, minimum of 10 thou DoC.   With 6061, you can go pretty deep.
> 
> Ray



My Lathe can handle taking .010 ??
Shop Fox M1049


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## Ray C (Mar 5, 2018)

GreggC said:


> My Lathe can handle taking .010 ??
> Shop Fox M1049



I should think so...  3/4 HP is more than enough.   I used to cut 20-30 thou with a clapped-out Atlas 618 with a 3/4 HP motor.


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## GreggC (Mar 5, 2018)

Thanks guys,
Ill try it tomorrow and report back.


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## tq60 (Mar 5, 2018)

If you are observing "cut lines" the feed rate is too much for the radius of the tool.

Plus the tool may not be correct.

Meaning if you are cutting from right to left the left side of the tool is doing the cutting.

Many may have a pointed tool like a 60 degree thread cutting tool that due to the point they can cut grooves or threads instead of removing material.

Aluminum can be nasty stuff and dawn works wonders but can cause rust.

ATF works very good on lots of things and with it giving a high detergent level cleanup is easy and the machine will be cleaner with ease use and wipe down.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk


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## mikey (Mar 6, 2018)

Greg, which of these tools are you using?




For turning toward the headstock, you should be using the second tool in from the right. The last one on the right is for facing.

I think those inserts are TCMT inserts. If so, they are a triangular positive rake insert with a 7 degree clearance angle. Typically, these inserts are used in steel, not aluminum, although they will work. Do you know what your nose radius is? 

I agree that your speed is way too low. Cutting speed for aluminum varies with the source but for carbide inserts, the typical speed is somewhere over 2500 SFM. For a 1.2" OD piece of 6061, you're looking at a spindle rpm of over 10K, which you don't have, so just run at the max speed your lathe will run at. Adjust your feed to the mid-range of what you have available and adjust up or down as needed for a decent finish. 

Roughing depths of cut with this insert varies with the insert maker. I have tools that use that insert and know that you can easily take a 0.100" deep roughing cut. Finish depth of cut depends on the nose radius; typically, you can use about 1/2 the nose radius and the insert will cut. For example, if you have a nose radius of 0.008", a finishing depth of cut would be around 0.004" and the insert should cut without deflecting too much.

Looking at your work piece, I am going to guess that your speed is way to slow and your feed is too fast. Your depth of cut is probably okay for a finish cut. I would use WD-40, too. 

You might want to look at the SCLCR tool holders that take the more modern CCMT and CCGT inserts. They will work well for you on that 9" lathe but as others have suggested, HSS is also a very good option.


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## Z2V (Mar 6, 2018)

GreggC said:


> I have zero experience with HSS cutting tools,
> Can anyone make a suggestion what to buy ??
> Maybe hand hold me and post a link ??


Not a suggestion on where to buy but a good suggestion on what to read to grind your own HSS cutting tools. Many of us  here have taken a lot out of this thread, great reading and the grinding process is explained in such a way that you can’t help but not make a tool that cuts good.
Give it a look!


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## GreggC (Mar 6, 2018)

mikey said:


> Greg, which of these tools are you using?
> 
> View attachment 260919
> 
> ...



Hey Mke,
I am turning from right to left,
I am using the center tool at 90* to the piece, which is straight on, clearly a mistake
after reading Tq60's post and reading what you said about using the second from the right
It clicked, I now understand whats happening, this afternoon I will change the tool.
I don't know the nose radius on my bits, the tool set I bought did not say,
Is there a recommended nose radius for aluminum ??
I need to learn about these CCMT / CCGT inserts, can anyone point me in a good direction for that info ??


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## agfrvf (Mar 6, 2018)

I have the cheap brazed carbide from Horror fraught and found I get a nice surface with a heavy cut. .01"


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## mikey (Mar 6, 2018)

GreggC said:


> Hey Mke,
> I am turning from right to left,
> I am using the center tool at 90* to the piece, which is straight on, clearly a mistake
> after reading Tq60's post and reading what you said about using the second from the right
> ...



I would suggest you get this tool set from Precision Matthews: http://www.precisionmatthews.com/shop/38-turning-38-boring-tool-set/

This set includes both RH and LH turning tools and a steel boring bar. All tool holders take the same inserts, CCGT for aluminum and CCMT for steels. 5 of each type of insert is included to get you started. The silver colored CCGT inserts are uncoated positive rake inserts that will perform really well in aluminum. I do not know the nose radius of these inserts but PM will probably know. These inserts are common and cheap on ebay and will work well on your Shop Fox 9" lathe. 

To use them, use the RH tool to cut toward the chuck and the LH to cut towards the tail stock. The shank of the tool is oriented perpendicular to the work piece and it can both face and turn in this position. You will really like these tools, Gregg.


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## projectnut (Mar 6, 2018)

I'm not sure what kind of machine you're using, but .010 sounds more like a finish cut than a heavy cut.  To me a heavy cut in aluminum could be as much as .250 per pass.  A light pass would be in the .030 to .040 range, and a finish pass would be .010 to .005.  Unless you have a rigid machine,  sufficient speed, and a sharp tool a pass of .005 or less would more likely be rubbing off material than cutting it off.

As for HSS tools I'm not sure anyone sells them pre profiled, and if they do you can bet they're considerably more expensive than creating your own from a blank..  Generally they're sold as blanks and the person buying them profiles them to the shape they need.  You can buy tool blanks individually or by the box from places like Shars, McMaster, Travers, or any number of other tool suppliers.  The nice thing about HSS is that you can make them any shape you want with just a bench grinder, belt sander, disk sander, or any other inexpensive grinder using an aluminum oxide wheel.  If you need a new profile for a different job you can easily regrind an existing tool rather than  have to go buy a new one.

Personally I use HSS more than 80% of the time.  I like the fact that I can make a tool and keep it in the drawer for the next job without having to worry about how much it cost.  Victor Machinery sells tool blanks for $.81 to $8.55 depending on size.  I doubt many hobbyists will be buying 5/8" and 3/4" blanks, so the prices more realistically are between $.90 and $3.60 per blank unless you're buying in volume.

A simple way to remember the difference between RH and LH tooling is that a RH (Right Hand) tool is used when cutting right to left.  A LH (Left Hand) tool is used when cutting left to right.  The L or the R  is the position the cut starts from.


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## Ken from ontario (Mar 6, 2018)

GreggC said:


> I don't know the nose radius on my bits, the tool set I bought did not say,
> Is there a recommended nose radius for aluminum ??


I have a similar tool set and if the inserts are TCMT21.5*1*, 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 . 


GreggC said:


> I need to learn about these CCMT / CCGT inserts, can anyone point me in a good direction for that info ??


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.


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## jbolt (Mar 6, 2018)

A good source for CCMT holders and CCGT inserts. https://latheinserts.com/TOOLS-FOR-HOBBY-LATHES_c82.htm


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## jbolt (Mar 6, 2018)

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.


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## francist (Mar 6, 2018)

jbolt said:


> 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


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## Buffalobull (Mar 6, 2018)

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


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## GreggC (Mar 6, 2018)

Ken from ontario said:


> I have a similar tool set and if the inserts are TCMT21.5*1*, 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/.*
> ...



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 ??


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## GreggC (Mar 6, 2018)

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 ??


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## GreggC (Mar 6, 2018)

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


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## GreggC (Mar 6, 2018)

Also, at 1000 RPM that apron moves FAST !!


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## mikey (Mar 6, 2018)

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.


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## Ray C (Mar 6, 2018)

GreggC said:


> 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


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## GreggC (Mar 6, 2018)

mikey said:


> 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 ??


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## GreggC (Mar 6, 2018)

Ray C said:


> 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.
> ...



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 !!


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## mikey (Mar 6, 2018)

Looks good, Gregg. Glad you got it sorted. 

If you have change gears for your lathe, you can alter the feed rate. Not sure its worth it, though.



GreggC said:


> Im such a beginner !!



This is where we all start, Gregg, every single one of us.


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## GreggC (Mar 6, 2018)

mikey said:


> Looks good, Gregg. Glad you got it sorted.
> 
> If you have change gears for your lathe, you can alter the feed rate. Not sure its worth it, though.
> 
> ...



According to my chart I am at the slowest feed rate,
Guess I stuck with it.


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## Ken from ontario (Mar 6, 2018)

GreggC said:


> Ken,
> These are the bits Im using,
> TCMT2151
> Last number is a 1, very pointy.
> ...


Greggc, I'm not an experienced hobbyist so my only advice is to listen to those who have been doing this for years.
 Mikey and Ray  have given you great advice so far:


Ray C said:


> 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.


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## GreggC (Mar 6, 2018)

I've got a pretty good handle on it,
The piece looks really good and I learned a ton !!
Thank you all very much !!


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## Ray C (Mar 6, 2018)

GreggC said:


> 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.
> ...



Oil burn-off from lathe/mill work is not outright poisonous but, repeated exposure will likely have ramifications in the long-term.  Also, watch-out for the cummulative/combined effects of exposure to many different things such as solvents, welding fumes etc.  And be mindful of your hearing and use ear plugs when things get noisy.   Screeching cuts on a saw or the loud gears of a lathe or mill will damage your hearing if you stick with this long term.

Your cuts looked good and hope it was fun for you.  Now get a micrometer or calipers and measure each end to see if diameter is constant along the length.  That's the next thing to think about.

Ray


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## crazypj (Mar 6, 2018)

I do a lot of 6061 and some 7075 plus a few castings. Due to the limitations of the cheap 3in1 I bought (pretty much paid full price as friend was getting divorced) At low speeds carbide isn't a good idea, I only use HSS as it's much easier to sharpen. 'Dry' cutting is a bad idea, you will get localised heat build up on surface and a lot of tearing. Depending on which size machine your using you may be better off just using a 'polished ' round nose roughing tool. It will probably chatter real bad when you get 1/4" deep but cuts around 0.100" should give a' mirror finish' using cutting oil or any light hydraulic oil. Majority of people use WD40 because it's easily available but I've always found it a pretty bad cutting fluid, even used engine oil works better and prevents build up on HSS tools. The only advantage I've ever seen with carbide tooling is alumunium doesn't 'stick' to it so easy but to be honest, I don't have ant machines capable of really utilising carbide tooling


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## GreggC (Mar 6, 2018)

Ray C said:


> Oil burn-off from lathe/mill work is not outright poisonous but, repeated exposure will likely have ramifications in the long-term.  Also, watch-out for the cummulative/combined effects of exposure to many different things such as solvents, welding fumes etc.  And be mindful of your hearing and use ear plugs when things get noisy.   Screeching cuts on a saw or the loud gears of a lathe or mill will damage your hearing if you stick with this long term.
> 
> Your cuts looked good and hope it was fun for you.  Now get a micrometer or calipers and measure each end to see if diameter is constant along the length.  That's the next thing to think about.
> 
> Ray



Hey Ray,
Thank you for the advice / concern in reference to health and safety,
I've spent the past 30 years as a heavy Jet Aircraft Mechanic working for UPS,
I am very well versed on this subject.
UPS pounds this stuff into our brains !!
Before today I was not using lube and had my garage door closed,
This afternoon I opened the garage door when using lube,
Plenty of fresh air.
I always use safety glasses or a shield and of course I have my Bose blaring some good Country / Western music !!
I took your suggestion and measured each end of a piece I just worked on,
I used a digital Vernier Caliper and measured both ends at exactly 1.095.
A least that part of my cheapo lathe is correct.


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## crazypj (Mar 7, 2018)

1/64" is roughly 0.015", a lighter than 0.008" finishing cut will give better finish as the radius of tip is the only thing cuting but with almost 0.005" feed rateyou will have the 'shrp' edge between radii. A 0.004" finishing cut with 0.005" feed puts more of the rounded edge in contact with 'extra overlap' I know that's not a good explanation  A 'whiteboard and dry erase marker would make it simple to explain, 0.015" circles 'overlapping' by 0.0047" per revolution


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