Polishing Flat Aluminum Surfaces

Hi guys;
I'm looking for some ideas from any of you with experience in metal polishing. I often make up aluminum parts which need to buffed out to a
level of perfection that will look good under show chrome plating. A typical part, like a couple I made up this afternoon, is made from 0.090 6061 plate, about 3" x 4" with a milled opening and a dozen various sized holes.
The problem is, what's an efficient way to get the scratches out of the flat surface and bring it up to a mirror shine? The last part is easy. Once the surface is up to about 1500 grit level, it's no problem to buff it out with a sewn cotton wheel and tripoli compound. How do you get from scratches to 1500 grit while keeping the surface flat and even, without excessively distorting the holes and openings?
Right now, I'm hand rubbing the surface with a hard rubber block and various grits of emory paper. I start with 320 and go through 500, 800, and 1500, using drops of WD-40 as a lubricant. This works pretty well, but it's very tiring and takes way too much time. I need a power method of doing this.
I've tried many types power wheels, such as hard felt buffing wheels, Norton "finishing" wheels, Scotchbrite flap wheels, etc., and haven't found anything that works for this. It seems that any wheel that's firm enough to cut will tend to leave waves and ripples. Softer wheels with coarser compound would distort all the edges of the openings and holes. I've tried using emory paper on an electric "detail" sander (with the recipricating triangular pad), but that just loaded up the paper instantly and added more scratches.
Any ideas? I'm thinking of a miniature version of a random -orbit sander, with a 1" dia rubber pad, turning about 60 rpm, using various grits of lapping paste. Maybe I could rig up a small random orbit head on a drill press?
Thanks! Bruce Johnson Johnson's Extremely Strange Musical Instrument Co. Burbank, CA
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some sort of lapidary equipment polisher? there's 2 types that i have that would do this. a flat lap with small sized grit followed up with a felt pad with cerium, or a vibrolap using the same materials. they polish slabs of rock/etc with these type of machines.
regards charlie http://glassartists.org/chaniarts
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Now you know why professional quality polishing is so expensive.
You need a fairly hard backed abrasive to avoid dishing holes and making ripples. Try a pneumatic orbital sander, hard rubber pad, waterproof abrasive paper, soapy water as a cutting fluid and lubricant. This should allow you to use up the paper without loading it up and making scratches.
Randy

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snipped-for-privacy@ix.netcom.com wrote:

I don't do this regularly, but it does come up on occasion. I use wet or dry sandpaper on a hard surface, like a surface plate. If you wet the back of the paper, it may stick all by itself, without gluing it. (But maybe that's the purpose of the hard rubber block.) I use water as the fluid, and lots of it, and wash the sandpaper frequently under the faucet to remove aluminum buildup. I could probably rub the part for only a couple of minutes per grade of paper.
I suppose a belt sander could be used with the appropriate abrasive. Don't look in the local hardware store, look at Norton or other commercial abrasive makers.
Jon
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Hello Jon;
Yes, I'm familiar with that technique; I use the paper on a glass plate to lap the surfaces of woodworking plane irons and chisels, etc.
In the case of these aluminum parts, I'm trying to find some way to power the process and speed it up significantly. These are custom hardware parts for guitars and basses, so it's not a high tolerance flatness issue, they just need to look good under plating. Right now, almost 2/3 of the labor of making the part is in polishing the flat surfaces. There's got to be a better way tucked away in pro polishing shops!
I'm wondering whether it's better to do the sanding in a linear form, as in a belt sander, or in a random-orbit disk form? Maybe either would work as long as the paper is kept cool and lubricated enough to keep from loading up. I've thought of, for example, building a small tabletop version of a woodworking stroke sander, using some standard 2" wide belts and a coolant flood system. Maybe the finer grits would be a leather belt and buffing compound?
Another alternative might be building some kind of rotating or recipricating head into a small drill press, using the quill to apply a gentle downward pressure.
I'm just surprised that I haven't seen any machine or components available for doing this operation. It's got to be a fairly common problem.
Thanks for your ideas!
Bruce Johnson Johnson's Extremely Strange Musical Instrument Co. Burbank, CA
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snipped-for-privacy@ix.netcom.com wrote:

First, using a lot of coolant (water) with a water-tolerant abrasive will help a lot. Second, you might want to see how lapping machines work. A lot like a miniature potter's wheel. I set up one from a piece of gear I had laying around. I stuck self-adhesive diamond lapping film to the wheel, because I was doing precision optical lapping, but the basic idea should work for your use. You'd attach a sheet of the appropriate sandpaper to the top of the wheel and turn it on. A water dripper could keep the paper wet. You would hold the part onto the sheet with the desired force, and turn it so it doesn't get all the lines in one direction. If you had one wheel for each grit size, you could just move each part from wheel to wheel as it progresses. Or, you could do all the pieces on one size before changing paper to the next grade.
I think you just aren't looking in the right place. These machines are generically called lapping machines.
Jon
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wrote:

if you're into making machines, i made one of these http://mrcol.freeyellow.com/grinder/flat_lap_grinder.htm in a 24" size, but it can be scaled up or down pretty easily. i got a piece of magnetic sign material, glued a piece of 1/4" thick felt (both from mcmaster-carr) to it, then use it as a polisher for glass objects using cerium as the polish.
regards, charlie http://glassartists.org/chaniarts
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You might want to redesign the parts. A little arc in the suface makes them much easier to polish. They also look better to many eyes and feel better to the touch. A dead flat surface is hell to make, usually not really necessary design-wise and appreciated by only those who won't buy your product because they would try to build their own!
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You might check into a jeweler's flat lap -- it's a machine designed specifically to polish and buff flat surfaces. The only issue might be finding a lap big enough to take your pieces -- the typical bench-top lap has a 6 or 8 inch diameter disk, so the size that you can work on is limited.
A lap's polishing wheel is a hard felt tapered edge disk, cut with several slots. You hold the work underneath so you can see what you are doing -- the rotation causes the slots to make the disk "transparent", so you can see through it.
Generally, they are used for polishing and buffing after the work is already sanded to about 600 grit. You could maybe use one for sanding by using a coarser grit compound on the disk, but I've never tried it that way. You can certainly polish and buff flats without compromising the surface, though.
Here's a picture of one: http://www.gesswein.com/catalog/catalog.cfm?cat=8&sub=8&subsub=2&catalog=1&CFIDD0321&CFTOKEN2490561
Regards,
Bob
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Bob;
Thanks for the info! That may be the "magic" technique I've been looking for. I wasn't familiar with the flat lap-style of buffing wheel. The Gesswein company also has a lot of other interesting buffing and polishing tools. I should have looked into the whole jewelry-making area.
The 8" flat lap wheels may be fine for the size of my parts, which are generally under 3" on a side. I can see setting up 3 or 4 of these wheels with different grits and moving the parts up through the sequence.
Thanks again, this opens up a whole new approach!
Bruce Johnson Johnson's Extremely Strange Musical Instrument Co. Burbank, CA
Bob wrote:

http://www.gesswein.com/catalog/catalog.cfm?cat=8&sub=8&subsub=2&catalog=1&CFIDD0321&CFTOKEN2490561
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You can, of course, use just a single machine by changing the laps, using a different lap for each grit. Unless you are doing continuous production, that is the way the machine is generally used. The machine has a tapered spindle and the lap just threads itself onto the arbor.
If I were you, I'd call a few of the makers, tell them what you want to do, and see what they have to say. Elaine Corwin (? sp.) at Gesswein is a frequent contributor to the online jewelry forums, and was able to answer a number of questions for me when I was looking to buy a magnetic finisher last year.
Regards,
Bob
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check out eastwood company in pottstown ,PA they have alot of polishing equipment and materials the best thing to do is get as clean mechanically as you can then do the final polishing by hand ,for something that small it will only take a few minutes to do it and it will look like a mirror ,and also check out to see what your local fire department uses on their firetrucks to polish the different aluminum and brass components and also try a polish I use called MAAS it works wonders it makes everything from chrome aluminum brass and copper look better than new ,you can usually find it in walmart back by the household cleaners ,and as soon as you use it you will see the results
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For those who would like to have a machine turned on certain pieces I found out about this technique years ago ,what you use is an old leather work boot ,valve lapping material and something with the diameter you need (I like using old engine valves they come in different diameters from small engines all the way up to big power units ,but you can use anything as long as it will fit in a drill press chuck) what you do is make sure the piece your applying the turning on is clean then take the old valve(or whatever your using) and attache a piece of leather from the boot using a high grade adhesive applied to the smooth side of the leather (the spray glue for sanding discs works real good) and trim the leather so it matches circular surface as close as you can get and take your time ,then put it in your drill press chuck now take the work piece and hold in place on the table and apply a dab of the lapping material on the work piece or directly on the leather and then proceed to place a full circle on the upper left most corner then proceed to apply another circle directly beside the first circle but don't overlap and keep doing this to the end using full circles then go back to the left and right below the first circle place your next row same technique and keep repeating until you get a bunch of circles in neat little rows ranks then go back to the start again and where you have four circles in sort of a square shape and place a circle right in the middle of the four at this point you will see the machine turned design start to form and when these full circles are done proceed to finish the out side edge and when you are done you will have a nice piece of machine turned metal Now a few tips keep applying the lapping material as you go along a lil bit goes a long way and it is relatively cheap for a tube (avaible at any auto parts store),do not muscle the drill press all you need is just enough pressure to hear the lapping material start to cut into the metal and you will hear when it is done cutting , once you get the hang of it start to experiment where you apply the circles and what I described above is basically just a simple technique to learn with then you can try doing spirals and other patterns ,and as long as you have a sturdy shaft for the drill and a flat surface for the leather it will work (like old one piece grinding stones ,old engine valves that are flat and you can even make one from a couple pieces of wood and a bolt or just get a solid piece of metal machined to the diameter you need) I had read this in a hot rod magazine a years ago ,tried it and it works pretty well and you can apply it to any piece you can get in the drill press and is relatively flat ,as you go along you will see what you can and can't do good luck and above all have fun
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Hey Baz,
Good tips!! Thank You. I've only tried a bit of this previously, and it didn't run out "patterned" very well, so I'll keep a "hard-copy" of this for future.
Take care.
Brian Lawson, Bothwell, Ontario. XXXXXXXXXXXXXXXXXXXX On Fri, 18 Nov 2005 03:04:16 -0500, snipped-for-privacy@webtv.net (badaztek) wrote:

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On Fri, 18 Nov 2005 07:54:12 -0500, with neither quill nor qualm,

I'll bet the pattern works out better when done on an XY table where you can count turns of the lead screws to apply it.
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