Aluminum finish techniques?

[QSPSB]

Hey guys!

How do you guys go about removing your tooling marks on aluminum.. I know how to wet sand them and polish to mirror finish... Is there a special technique you guys do to achieve such a smooth surface?

Perhaps i need to purchase better end mills or something.. I've just been using 2/4 flute center cutting end mills..

Thanks in advance!

 

[Bernd]

A good single cut mill file to remove tool marks, then sanding with different grades paper to get to your mirror finish.

Bernd

 

[Metal Butcher]

Q, Milling leaves tool marks, its a given. Theirs not much you can do to eliminate that completely. If you are using a damaged or poorly sharpened cutter that adds to the problem. On a mill, if its out of 'tram' that will cause each shifted cut to have a 'step', that will need a good amount of file work to remove. Cutting fluid sometimes helps a little, but it will not eliminate tool marks.

Aluminum is very easy to file and sand. You can finish it up with what ever look you prefer. I like to finish up with a dirrectional non glare sanded surface on most of my flat areas, and a fine cut turned finish on cylindrical parts. Some prefer to finish up with a high gloss polished surface.

There are no secret magic methods, just plain old elbow work, using a file and sand paper.

-MB

 

[shred]

Yeah, you pretty much have to cut out major tool marks-- grinding, filing, sanding, blasting, wire-brushing, ... . I'm by far from a bling-meister, but my favorite power tools for the job are my 1" belt/disc sander and my little micro blaster. Close behind them is the wire wheel for just blending in all the tool marks to a brushed finish, but in the end there's still a whole lot of hand work to get to the 'bling' level.

You can also try a vibratory tumbler like the pros do-- I use one occasionally, but it takes a very long time (days to weeks) unless you get into the commercial-sized wet tumblers and multiple grades of ceramic media.

 

[QSPSB]

Bummer!

I had hoped there was a special end mill you use or something... I trammed the mill and it's correct... I'm using 4 flute end mills @ about 2300 rpm and it don't look to bad... I just thought there was a special type of end mill to achieve such a smooth finish...

Once i get going on the engine this is the type of finish I'm hoping to achieve below...

 

[aheg1220]

Multi-flute high-helix end mills leave a very nice finish, but not completely perfect...

 

[Fingers]

I always spray my last cut with wd40 or paraffin on aluminum, I find it helps me get a nice finish and leaves the cutter nice and clean, also you could use a fly cutter bigger then the part you are making if itis the top surface you are milling, this would leave you with no join marks where your cutter moves across
Jamie

 

[Omnimill]

Have you tried a Fly Cutter with a radiused cutting tip, can give a very fine finish that you may not wish to remove!?

Vic.

 

[mu38&Bg#]

I think you're cutting with CNC. For side milling, do a climb cut finish pass with a new carbide endmill taking a few thousandths. For facing with a small endmill, corner radius endmills (bull nose in some parts of the world) give me the best finish. Play with speeds and feeds until you get the best finish. I think the rest is in machine quality, spindle/collet runout, spindle rigidity, vibration, ways, etc. When you see beautiful parts out of machine shops you have to remember they are using equipment that is much more rigid, accurate, and can hold incredible tolerances compared to home shop tools. Surface finish comes with that.

I also find that often the mirror shine on aluminum looks much worse than it is. A few passes with very fine sand paper really makes it look good.

 

[QSPSB]

WOW!

You guys are a great deal of help here... thank you!

I am in the process of converting the mill over to cnc as we speak... I'm just trying to think ahead and want to learn all the '' tricks of the trade '' so to speak well before i run into an issue... My mill is quite rigid... It's just a little X2 mill but I stiffened up the column with a brace and it's bolted down quite well as well...

I'm currently machining the Z-Axis thrush bearing retainer mount for it... On my el-cheapo home made rotary table... I suppose i could turn the spindle speed down a tad... It just seams to cut much cleaner at a higher rpm... However. I do need to purchase new end mills... I've been using these for about 3 years... As for the depth of my cuts go... I haven't a clue how much I'm cutting per pass... I just ease it in until i can hear it makes contact then i rotate the table a full pass... and so on.... I can't wait to get this thing converted to where i can then actually know what cut depth/feed rate/spindle rpm/etc I'm going...

I haven't tried the WD-40 trick... I use 5 W 30 motor oil... I hit it with a does about every 5 minutes or so... It works quite well on the ways as well... Hoss from http://www.hossmachine.info/ let me in on this

And i thought the guys @ CNC Zone knew it all... wait a minute... I bet the majority of you guys are there as well... Disregard this last comment... :big:

Here are a few shots of what I'm currently machining... It doesn't look to bad... It's only a bearing retainer though... I still need to remove a few thousands from it

 

[Niels Abildgaard]

I use alcohol (C2 H5 OH) to finish aluminium.
It is safer than parafin as it evaporates all the time

 

[picclock]

I found that using a large diameter mill (20mm in my case) with WD40 and around 4-600 rpm will give a mirror finish. If you have a larger area a flycutter is the best tool. Bogs did a post on how to grind a finishing tool for it, but I found it blunted fairly easily (some of my HSS tooling seems a lot softer than others, probably down to the cobalt %). Since then I have changed it for an indexable carbide lathe tool which seems to give identical results on steel and aluminium. I always use loads of lubricant and a fine cut on the final pass for best results.

I still haven't worked out why the indexable tool gives a rough finish on steel in the lathe but a good finish in the mill. ??? I can only surmise that the stiffness of the machines may be a factor, but I'm not convinced.

Best Regards

picclock

 

[aheg1220]

picclock, have you tried bumping up the RPM on the lathe? Carbide likes high speeds. I was wondering the same thing as you were until I found out that my indexable carbide tool bits really like high speeds on the lathe. With carbide I turn most things at my lathe's highest RPM, which is about 2200 rpm.

 

[stevehuckss396]

That valve cover looks familiar!!

The marks were removed from the top of the cover with a 8 inch wheel on my grinder. It is like a 8 inch diameter scotchbrite pad about 3/4 inch wide. 2 strokes is all it took but that can be all it takes to remove an edge or corner so care must be taken.

The wheels were purchased from a club member for about 15 bucks a pop. New they are close to 75-100 bucks a piece. I bought 2 for myself.

 

[shred]

The long longitudinal scratches are kind of a giveaway of sanding, grinding or similar post-mill finishing. I think on one forum I read of somebody sandwiching a whole lot of 'scotch-brite' pads together to create a finishing wheel if you don't feel like dropping the coin on the real ones.

Mirror finishes are possible right off the tool, but it's not easy and takes just the right tools, materials and cut.

 

[mu38&Bg#]

When turning AL on the lathe I've also noticed that some bar turns and finishes very nice while another piece will be awful. I recently got some aluminum inserts and while they always cut nice and leave a bright finish, the surface roughness is still dependent on the previously mentioned factors. The cut is so nice that you can actually see the grain structure in the aluminum. If your inserts come with specific feeds and speeds, try them, you'll be surprised. Running the recommended F&S for aluminum inserts on a manual lathe can be downright scary. I turn and mill dry.

 

[Metal Butcher]

When turning AL on the lathe I've also noticed that some bar turns and finishes very nice while another piece will be awful. I recently got some aluminum inserts and while they always cut nice and leave a bright finish, the surface roughness is still dependent on the previously mentioned factors. The cut is so nice that you can actually see the grain structure in the aluminum. If your inserts come with specific feeds and speeds, try them, you'll be surprised. Running the recommended F&S for aluminum inserts on a manual lathe can be downright scary. I turn and mill dry.

Hi Greg, I too have noticed that some aluminum bars finish up nicer than others. I believe the reason is that I'm a big consumer of scrap yard mystery metals.

Could you elaborate on what "aluminum inserts" are? I don't recall seeing any in the catalogs that plague my library. And they might also be of interest to the O.P. of this thread

-MB

 

[mu38&Bg#]

There is not much selection for inserts made specifically for cutting AL. If you search ebay for CCGX you'll find several listings for them. These are the aluminum specific equal to CCMT inserts. Likewise DCGX, VCGX, etc. I know "GX" is the AL designation for Sandvik and they even offer more than one grade in some sizes. I'm using some I brightly polished inserts purchased from Shars, make unknown. I also have some Sandvik that are a dull gray, but haven't tried them yet.

Greg

 

[picclock]

@aheg1220
Yes, I've tried high speed blue chips burn holes in your shirt (and get trapped up the sleeves ) and lower speeds on the same metal bar that I've milled using the same type of carbide inserts. It's always comes out better on the mill. In fact, I'd go as far as to say that with steel a carbide bit on the mill produces an equally good finish to an HSS bit on the lathe.

I'd take pictures but they don't show up the surface differences and grain very well. With the light at the various angles a bad finish can be made to look really good and a good one bad. I've just come to accept it as one of those things - and either way the finish is good enough for my bits and bobs so far.

Best Regards

picclock

 

[Omnimill]

Nice, smooth and evenly spaced machining marks - normally Lathe cut, look good IMO. In fact there was a guy I met quite a few times during the 1990's who made Butt Hooks (for Target Crossbows) from Aluminium Alloy and these were a sight to behold. Even after Anodising the "wood grain" effect, probably due to vibrations in his milling setup looked fantastic. I've managed to get the same effect a few times in machined alloy parts but It's not something I could repeat!

Vic.