Poor finish, aluminium

[emtor]

Yes, I've looked into those. Seems like a good idea.
If my four bolt improvement acts up I'll add two set screws.
If I get any more problems I'll go for the solid tool post solution.
If anything, these problems with cheap lathes makes me learn a lot about lathes, so when the day comes to buy a large second hand monster I know what to look out for.

 

[petertha]

You waited until post #11 to tell us you melted the aluminum yourself?
Before you go any further, chuck up a piece of regular 6061 & see if it makes a difference. If it turns out nice & shiny, I think you have your answer. Mystery metal is going to be difficult to make a recommendation.

I use the un-coated CCMT & DCMT inserts like what was suggested. But in all honesty if I am too lazy to change out an insert for a quick part to one favored for steel, the finish isn't appreciably different with the same nose radius. But they are more prone to gumming & make different chips. WD40 or cutting fluid specifically for aluminum helps with the sticky stuff clogging the tool tip. Try not to breathe the fumes. Example pic - these parts were knocked off from 6061. Pictures of machined metal tend to exaggerate tool marks but you should be able to achieve this with no effort.

 

[rwm]

I have done a lot of casting and I have NEVER been happy with the machined finish of aluminum. It is gummy and typically gives the random smooth and rough finishes you describe. Degassing is not enough. I have even tried heat treating with some improvement. Forget about casting your own aluminum stock. You will not be happy with it compared to extrusions.
As others have said, perfect your lathe setup using factory made aluminum extrusion then apply that to the castings if you must. Also it will be hard to get a true T6 temper even if you have a heat treating oven. The temp for solutional heat treatment of aluminum is very near the hot-short temp. You will likely melt or damage the stock. In industry this is often done with a salt bath to avoid this.
If you want to cast stock, I have had much better success with brass and bronze some of which has been posted here.
Robert

 

[emtor]

Haven't melted any aluminium lately.-been too busy at work and with fiddling with the lathe on my spare time.
My lathe started it's career by chattering a lot. Regular turning and facing was OK if I took very shallow cuts, but chamfering and parting off . . . forget it.
The lathe would howl like a stuck pig. So . . . I've drilled extra holes in the compound rest to secure it with four bolts instead of two, made new T-slot bolts and tightened up the cross slide gib screws. It offers a bit more resistance now and the tendency towards chattering is gone.
-Bought a HSS parting tool and a box of inserts,-made in Austria, and now I can part off steel like it is butter. No chatter.
Chamfering is a breeze. I am able to push the whole side of the insert into round stock and turn a nice 60 deg. taper.
I almost couldn't believe my own eyes when the insert produced chips the width of the entire side of the insert.
Despite being a mini lathe this thing appears to be pretty sturdy after all. I've been experimenting with taking deeper and deeper cuts for each pass and the lathe seems to refuse to complain no matter how much I push it.
This thing finally begins to act like a lathe now . . . and I've even managed to make it run reasonably silent.

 

[MrWhoopee]

Well, being a knife maker I'm building a programmable heat treating oven. Knowing the temps and time durations to heat treat aluminium would make it possible to do just that. I found the methode for 6061-T6: After smelting, let the aluminium cool to room temp. Then re-heat to 980 deg. F.
Hold for one hour and quench in water. Heat to 400 deg. one hour or 350 deg. five hours or 325 deg. eight hours.
The only problem is that the aluminium will deform quite a lot, but this is no problem in my case since I will be casting round stock, not parts.

In order to harden aluminum, you have to know what alloy you have. From your description, the pieces you are working are an indeterminate blend of several grades. Since a lot of your feed stock was castings, my bet is no hardening process will work. Casting alloys are different from the age-hardening alloys. You can't expect a lot from what you have.