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View Full Version : what aluminum has the smoothest cutting properties



replicapro
06-25-2004, 08:43 PM
I don't know what type of aluminum Im working with, as it is scraps to practice with. It seems that no matter how fast the machine is going or how slow I go, the cuts are rough.

I switch over to 360 brass or even cast blocks of resin, and I get nice smooth cuts. Steel cuts the smoothest of all.

So is all aluminum the same?

DAB_Design
06-25-2004, 09:09 PM
In my experience, for the most part, most common alluminum alloys machine very similar. I have seen some that are more "gummy".

Out of curiousity, what type of cutter are you using? If it is a facemill, does it have a positive or negative rake?

replicapro
06-25-2004, 09:12 PM
Im using some of those micro sized ones I picked up on ebay. You know the ones where you get a mixed bag of 70 end mills for $20

However I also tried it with some regular 4 flute and got the same results. Rough on aluminum and smooth on brass and steel. So I guess I just have to find out what type of aluminum is most dense or something.

DAB_Design
06-25-2004, 09:32 PM
What speeds and feed have you tried?

replicapro
06-25-2004, 10:07 PM
up to 2000 rpm

Ken_Shea
06-25-2004, 10:40 PM
replicapro you need to increase the speed, do not know what size cutter you are using, type of mill, feed or type of cut but you may need to slow the feed down and be sure and keep the chips out of the way which may well be most of the problem, best to flood them out or blow them out with air, however you do it keep them out of the way. I have got the best cuts using a aluminum cutting carbide cutter.

Ken

HuFlungDung
06-26-2004, 12:49 AM
T6061 aluminum alloy is nice to machine. There are other grades such as "utility" which are gummy as hell.

You should definitely find a way to apply lubricant when milling aluminum, as this will help greatly. Although you can cut it at high speeds, it still gets quite hot, and since its melting point is not all that high, the chips tend to weld together, and to the cutter. Lubricant will help keep the chips flowing.

sendkeys
06-26-2004, 08:17 AM
im told fortal is one of the best.

like stuff at http://www.mousebar.com/fhome.html or on ebay . just do a deja.com search get some reviews.

DAB_Design
06-26-2004, 08:28 AM
Originally posted by sendkeys
im told fortal is one of the best.

like stuff at http://www.mousebar.com/fhome.html or on ebay . just do a deja.com search get some reviews.


For those prices, does it cut itself? :D

Not sure if it's just the area I live in, but 6061 last time I checked was around $1.35/lb (delivered if you ordered enough).

metlmunchr
06-26-2004, 12:26 PM
If you dig around a bit, you'll find Fortal is just a name for a French manufactured 7075 alloy. Internet hucksters have attempted to create some mystique around it in an attempt to sell scraps and cutoffs at extremely high prices. If you can find it, 6262-T9 will make you think you're in heaven as far as machining goes. It has the corrosion resistance properties of 6061, slightly higher strength than 6061, and the machining properties of 2011 screw stock.

duluthboat
06-26-2004, 04:08 PM
It often is not the alloy in the aluminum that makes it hard to machine but the hardness. If the stock is marked it might be something like 7075 T-6 351. The hardness is the number after the T which tells you the hardness. It runs from 0-9, soft to hard. T-0 is so soft it’s like trying to machine gum. Very sharp tools and special cutting fluid is a must with soft aluminum. T-7 is common and is very nice to machine.

Gary :D

sendkeys
06-26-2004, 06:12 PM
dab_design.. ya its a little pricey :) but i seen it on ebay for cheaper :)


Metlmunchr ya for what i seen you're right about it being basicly 7075 . but here what one person said ona nother board. If there right or not im not sure.Also your right about them trying to get top dollar but you can find cheaper stuff :)


Posted by person another another forum The statement about the nature of Fortal vs. 7075 (i.e. chemistry) is
essentially correct. Like the QC-7, Fortal is basically off-spec 7075, but
if I recall correctly, Pechiney has a process to manufacture a product with
high properties that are essentially the same throughout the plate. In
thicknesses over 4", this is very important, as 7075 tends to get "gummy"
towards the center of the plate.""

So guess it would only really metter on cut off bigger then 4inch. :)

metlmunchr
06-26-2004, 07:47 PM
"Posted by person another another forum The statement about the nature of Fortal vs. 7075 (i.e. chemistry) is essentially correct. Like the QC-7, Fortal is basically off-spec 7075, but if I recall correctly, Pechiney has a process to manufacture a product with high properties that are essentially the same throughout the plate. In thicknesses over 4", this is very important, as 7075 tends to get "gummy"
towards the center of the plate.""
------------------------------------------------------------------------

That could very well be the case. The sole US importer of Fortal stresses its dimensional stability and consistent machining characteristics for use in short run molds as a cost saving effort compared to mold steels. Mold use would obviously imply heavy sections. Mold steels are far from cheap, and an aluminum material fine tuned for mold use would command a premium price and still be cheap based on time savings. I suspect it performs as stated. However, I seriously doubt all the hundreds of "Fortal" cutoffs of rounds, flats, plate, and every other imaginable shape peddled over the internet have ever spent even a moment of their lives in France. I just can't envision metal warehouses across the US filled with a premium priced 7075 variant, whose specialized properties aren't even applicable at common thicknesses, shipped in from 6000 to 9000 miles away, in the hopes some shop owner with money to burn will happen along and buy the stuff. I'd guess most of these drops are run of the mill 7075 being peddled by the typical less than honest internet clown. The company who imports Fortal will sell it to anyone who wants to buy it, in cut to size sections, so there's no reason other metal distributors would be selling or processing it to generate these drops.

sendkeys
06-26-2004, 11:03 PM
Originally posted by metlmunchr
" seriously doubt all the hundreds of "Fortal" cutoffs of rounds, flats, plate, and every other imaginable shape peddled over the internet have ever spent even a moment of their lives in France.

rofl didnt think about that :) very true :)

mineralman
07-06-2004, 01:58 PM
I have been turning and milling 6061 hobby stuff for about two years. It machines okay. For some experimentation, I ordered some 2011 aluminum. Machining the same parts I've been making for two years, the 2011 is head and shoulders above the 6061! The chips from holes peel off so easily and machine so smoothly. It machines so nicely that it's worth the little extra 2011 costs to machine some of the more difficult parts.

BTW, I machine everything dry except when threading (Tap Magic for that). Lubricants just don't seem to help aluminum.

Larry
New Orleans

metlmunchr
07-06-2004, 05:49 PM
Yep Larry, 2011 screw stock is nice stuff to work. You just have to pay attention to the final application of the part, since 2011 doesn't have nearly the corrosion resistance of 6061. Most of the metal suppliers' catalogs will have a table listing how each of the common alloys rates in various categories such as strength, corrosion resistance, and machinability. I mentioned 6262-T9 in an earlier post. It's got the corrosion resistance of 6061 and the machining properties of 2011. Why it's so damn hard to find is beyond me. Using aluminum specific inserts can be a big aid to getting good results regardless of the alloy being worked. Like is often the case with tooling, some of them look real expensive until you actually try them and realize the results you're getting make the tooling cost per part seem cheap in comparison to tooling that may initially cost less.

svenakela
07-07-2004, 05:00 AM
I was making a pretty uge mould once and couldn't get the cuts nice at all, until my working friend poored his soda on it, the surface went from terrible to mirror polished in a second. All I had to do was to add some water and then it was the best cut ever. Since then I've been using water with a little bit of soap when I've been cutting aluminium with very good result.

Cheers,
Sven

mineralman
07-07-2004, 07:40 AM
[QUOTE]Originally posted by metlmunchr
>I mentioned 6262-T9 in an earlier post.
I've not heard of 6262. Is it a new alloy? Actually, I'm looking for something that machines like 2011 and costs like 6061--- in other words, cheap! The application is nothing that requires strength or corrosion resistanct.

>Using aluminum specific inserts can be a big aid to getting good results regardless of the alloy being worked.
I'm looking into getting some insert tooling for my lathe. What's a good insert shape/style for turning aluminum?

LarryO
New Orleans

metlmunchr
07-07-2004, 11:20 AM
Larry, 6262-T9 isn't a new alloy. When I've managed to find it now and then, it's typically priced about the same as 2011, or a little higher than 6061. Like everything else, the price is directly tied to the volume produced.

If you switch to aluminum specific inserts, chances are you'll be able to do your parts from 6061 and most likely get far better finishes than you're getting now with 2011. Travers Tool handles a Korloy brand of insert that I've found to work great. It's a micrograin, uncoated, super high positive rake with surfaces polished such that they look like they're chromed. I'm using a CCGT 32.52 for normal turning and boring. The C shape(80 degree diamond) has excellent strength. For profiling which requires more clearance I use their DCGT 32.52 (55 degree diamond). Either of these inserts retail for about $5 each, but Travers has been running them on sale for about 3 months now at less than $3.75 each. For some reason, similar inserts from most any of the other carbide makers run in the $12 to $14 range each. I've been using the Korloys for about 6 months now and their life is very good. I've found JTS machine supply (on Ebay) an excellent source for boring bars for these types of inserts. For example I bought a couple of 1" bars for CCGT's from them for $33 each, brand new, and they're great. Similar bars from the major manufacturers are in the $160 range. JTS usually has these listed in various diameters from 1" down to about 3/8 or 5/16. The smaller ones are under 20 bucks. For turning toolholders, U S Shop Tools is a good source at decent prices. They list them under Swiss type toolholders. They sell direct, but generally not on Ebay. Most all this tooling will be listed as using CCMT inserts (or DCMT or whatever) which is a steel cutting variety with a molded chipbreaker. The CCGT's also fit the same tooling. The main characteristic of the tooling is a neutral rake seat made to use screwdown inserts with 7 degree clearance. Try some of these and you'll throw rocks at anyone who suggests you go back to the old methods of turning aluminum:D One caution: run these or any insert turning tooling either flooded or dry, but don't attempt squirting a little coolant on them now and then. They can stand heat, but thermal shock will fracture the edges in a heartbeat.

BT1
07-08-2004, 06:14 AM
We were talking about this recently and an interesting point was made about alluminium purchased that was virtually sitting there for twenty to thirty years, full large size plates varied thicknesses grades etc.

Machining this is absolutely beautiful, zero warpage. Guess time cures all.

metlmunchr
07-08-2004, 09:35 AM
Originally posted by BT1
We were talking about this recently and an interesting point was made about alluminium purchased that was virtually sitting there for twenty to thirty years, full large size plates varied thicknesses grades etc.

Machining this is absolutely beautiful, zero warpage. Guess time cures all.

That would certainly make sense. Certain heat treatable alloys of aluminum such as 6061 are "solution heat treated and artificially aged". The artiificial aging means the metal is brought to some elevated temperature after the solution heat treatment to achieve the same state that the material would achieve over some long period of time at room temperature. It seems reasonable that a chunk of plate sitting for 20 to 30 years would undergo some further aging past its as-produced condition. Sometimes aluminum is "over-aged" intentionally to produce a more stable form, although this additional stability comes at the expense of some loss of strength. Certain alloys will age fully at room temp in 4 or 5 days. In some instances it's desirable to fabricate them into some structure and let the aging take place after the structure is complete. Fabricating 2024 sheet is a good example of this. In the aged condition 2024-T3 sheet will break like glass if you attempt to bend it in a brake. To facilitate this, the aluminum is stored at -50 to -100 degrees F until ready for use. The age hardening then takes place after all necessary bending etc is complete.

The two tempers we most often encounter as machinists are -T3 and -T6. T3 is solution heat treated, cold worked and naturally aged. If a material carries a T3 treatment, such as 2024, then you know its one of the alloys that ages quickly at room temperature. T6 is solution heat treated and artificially aged at room temp. A material with a T6, such as 6061, would indicate its one of the alloys that does not age quickly at room temp. Further number designations, such as T6511 which is commonly seen on extruded 6061 shapes, are just further refinements of the process indicated by the first number in the string (the 6 in this case) and are generally not of significance to us as machinists.

BT1
07-09-2004, 10:10 PM
metlmunchr,

Interesting man.

I was told the Japanese leave machine housings - castings outdoors, painted throughout, for periods of time as a curing, aging type process thus making them more durable etc. Before they finish building the machine etc.

Then came the topic about Chinese machines!!!

metlmunchr
07-10-2004, 12:11 PM
Cast iron will definitely walk around if its not aged prior to machining. Heat cycling in an engine where the block wasn't fully aged before manufacture will cause significant movement. I've re-bored some large diesel engine blocks for oversize sleeves in a horizontal boring mill in the past. In a dry sleeve block where the sleeve bore looks much like the cylinder bore (long and straight), you can take a light initial cut and see all the places where the bore has changed shape over time. This is not from wear, as there is no movement between the sleeve and block. If you go back to a service manual and check the bore spacing spec, you'll generally find its off as well, indicating movement of the entire casting. I've seen variations in excess of .010" in where the bore is as compared to where it should be. In doing this work, the goal is to use the minimum oversize sleeve, but if the goal is to correct the bore spacing as well as correct deviations within individual bores, it becomes a tedious process where all bores have to be indicated true and their positions recorded, and then the amount to be machined out of each cylinder is calculated based on the cylinder whose position is furthest from its specified centerline. The real fun part of work like this is when you go thru all the process of determining where everything is and how much to bore, and then, on the last cylinder, the boring process shows up a crack the magnaflux failed to detect. You now have a large chunk of scrap iron that just happens to look like an engine block :D