Surfacing aluminum

I have a piece of 6061-T6 aluminum (4" by 12" by 1/2") that I want to
cut to a uniform arbitrary thickness but a close tolerance to flat (+
or - .001"). The surface finish should look "professional". I have a
small horizontal mill, a small vertical mill, a surface grinder and a
belt sander available. All are big enough to handle the piece without a
second setup.
Which machine would you use and why?
Gary
Reply to
grice
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Either the vertical mill with a big flycutter or the horizontal mill with slab cutter.
You say small on both mills, so making the wild assumption that implies maybe a bench mill, I would suggest the horizontal mill would be better. I say this is better because a fly cutter is an off balance load on your spindle. If you don't have enough rigidity in the total machine you may get some chatter. A 4"+ slab cutter is going to be much more expensive than an equivilent fly cutter.
JW
Reply to
jw
Flycut it on the V-mill then paint it.
Reply to
Tom Gardner
Reply to
David Anderson
As others have mentioned, a fly cutter makes a very nice finish on aluminum. If you can't swing a 4" cutter, make two passes with a 2" flycutter. You will need to be trammed in very well to assure that there will not be a step.
Whatever you do, you should take equal cuts on both sides to allow for slight warping of the slab.
Reply to
DT
The answer is obvious: Whichever is your best machine. Holding .001 over that large of an area demands a machine with essentially no wear in the ways. Most older mills are a few thou "swaybacked," which you don't notice on small stuff, but it really shows up over long pieces...
Jerry
Reply to
Jerry Foster
Use the local grinding house. That is, if you want to look professional, or, be flat, square and parallel before you have cut through to your table.
Reply to
J. Carroll
While it likely doesn't matter in your case, you are unlikely to achieve the tolerance you have specified with that piece of material by simply flycutting. Actually hitting +/-.001" flatness over 12" is not trivial, especially with what is probably extruded aluminum.
To answer your question (and to agree with everyone else) flycutting is the way to go. With a sharp cutter you should be able to take a very light finishing pass which will make the effect of the unbalanced nature of the flycutter negligible. As another aside, you should consider investing in a facemill if you're going to be doing a lot of that type of work. Much more productive.
Regards,
Robin
Reply to
Robin S.
Define "professional". Polished? Jeweled? Matte? Regular pattern of tooling marks?
Reply to
Richard J Kinch
Which one has a power feed (of the mills)?
Is one of the mills in better nick than the other?
Forget about the sander.
A flycutter, or a "sticky sharp" end mill, on the more accurate of your mills.
One direction will cut a little nicer than the other. Recognise and use this to advantage. A nice pattern of evenly spaced cuts, with a shiny rainbow refraction pattern, look good, feels nice under the hand, and makes the crows drool (crows, the guys that stop dead in their tracks when they walk by and see shiny stuff onthe bench).
Cheers Trevor Jones
Reply to
Trevor Jones
I chose the word to be "A nice pattern of evenly spaced cuts, with a shiny rainbow refraction pattern, look good, feels nice under the hand, and makes the crows drool (crows, the guys that stop dead in their tracks when they walk by and see shiny stuff onthe bench)."
THAT is as good a definition as I've run across.
In response to other questions: Both mills are benchtop models but heavy for their size. Each has a 5" by 20" table. Neither has a power feed. The vertical mill is in better shape than the other one.
Thanks for the information. I'm off to find a face mill.
Gary
Reply to
grice
If you're really serious about the +/- 0.001 inch tolerance, invest in a knife-edge straightedge and test the raw material first. Use in subdued light with a backlight to highlight the contact surfaces. Chucking the work to the table can easily warp the item much more than 0.001. On occasion, I have used a castiron sub-table with a fresh finish cut, then hold down the work with contact cement that will quickly release with moderate heat, say 200-deg F. The contact cement will be more than strong enough to withstand stress from the flycutter with a sharp bit and light cut, and will not likely warp the work piece.
Reply to
David Anderson
One of the "off-the-wall" thoughts I had about "lite cuts" was to mount the aluminum on my surface grinder and replace the grinding wheel with a 1/2" wide milling cutter. Since the grinder is controlled by a VFD, I can reduce the RPMs to just about any speed I want.
What do you think about that approach?
Gary
Reply to
grice
We do some things in aluminum sheet stock. I have looked for a "professional" finish also. Engine turning is out of the question for the size, patience, tooling, and time involved. Buffing to a mirror finish falls in the same category, though we have done it on a few small items. To date I have ended up using 180 sand paper disks on an orbital sander to provide a uniform matte finish.
Reply to
DanG
Has anyone mentioned just buying ground aluminum tooling plate? Randy
Reply to
Randy Replogle
There are reasons to keep a shaper :-)
Mark Rand RTFM
Reply to
Mark Rand
Some WAGs (as I've never heard of anything like this being done...)
A grinder spindle is a precision tool. Interrupted cuts (such as you're describing) are *not* what the spindle is made to deal with. Look up the price of new spindle bearings.
Manual/hydraulic grinders have no provision to controlling the table feed to the degree required to prevent grabbing and jamming in aluminum. You'd probably end up burning/breaking your cutter and/or tossing your workpiece.
Mag chucks don't have the same holding power has screw clamping devices (vices and hold down clamps) do. Again, potential for grabbing and tossing your part, no matter how you got it to actually stick in the first place.
Mills are made for this job. Grinders are not...
Regards,
Robin
Reply to
Robin S.
Ayup
Gunner
"Deep in her heart, every moslem woman yearns to show us her tits" John Griffin
Reply to
Gunner
Although not what you're wanting, a nice finish can be had by tumbling aluminum in a vibratory tumbler (burr box). We've finished an entire machine that way but things to watch for are the rock size. To small and they get in the tapped holes, to large and yo end up with a pitted surface. 15-30 minutes seems to work well. Sheet stock does NOT work well unless it's small enough to fit in the box
R. Wink
Reply to
R Wink
Sand blasting with walnut hulls works pretty well too. Nice matt finish.
Gunner
"Deep in her heart, every moslem woman yearns to show us her tits" John Griffin
Reply to
Gunner

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