Smoothing aluminum table saw top

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I have a ten year old table saw with an aluminum top. Overall it serves my needs at this time (and more importantly, my budget), but I've noticed the surface isn't very smooth. It's flat, but the surface itself feels rough (sort of like sandstone). I'm starting to get into a somewhat better quality of woodworking and I'm also seeing it leave some black marks on the wood (from the table, not the blade), which from the searching I've done seems to be from rough aluminum.
I know cast iron is the "standard" surface, but a new saw isn't an option at this time.
I've done some searching about smoothing the top, but mainly what I've found is to use paste wax (no silicone!) to protect it and make it slick. Before applying that, I was wondering about possibly a light touch with something like 0000 steel wool or 600+ wet/dry sand paper. Would something like this help (or hurt)?
Any suggestions would be appreciated.
Mike O.
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Mike O. wrote:

I've smoothed small aluminum parts by burnishing, filing, and sanding. I'd suggest burnishing any rough gouges and scratches first. This lets you work some of the metal back into the top - while simply removing spurs and edges ensures that there will be voids of the same volume.
After burnishing where it makes sense to do that, sanding with 600 grit (and finer) will help to smooth the surface. I'd look for a flat metal plate to use as a sanding block.
And for a final polishing, you might consider a small amount of WD-40 on typing paper wrapped around your block. Aluminum is soft enough that the typing paper is sufficiently abrasive to do a good final polishing and smoothing.
When the smoothing is done, I like to do a final cleaning step with acetone and either paper towels or an old T-shirt. Johnson's Paste Wax (a couple of /thin/ coats, renewed periodically) seems to do a good job of protecting the surface.
--
Morris Dovey
DeSoto, Iowa USA
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Mike O. writes:

<snip>
Why not make a sled and get on with it.
With a sled, who cares what the table looks like?
--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
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Lew Hodgett wrote:

Just last week I discovered that my sled was too short for ripping 144" boards and 96" panels. Seemed a lot easier to /not/ use a sled.
--
Morris Dovey
DeSoto, Iowa USA
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"Morris Dovey writes:

Doubt I'd try to do either with an aluminum top table saw, but if I did, would need a bigger sled than normal<G>.
Lew
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wrote:
I've had a shopsmith mark V for a lot of years... part of my "twice a year, if I remember" maintenance is to go over the alum. table tops with new 3M abrasive pad (one of those green thingies) glued to a piece of scrap 1x6... I go over it lightly, looking to remove any burrs or whatever and old wax buildup.. After washing with soap and water and rinsing well, I put 2 coats of old fashion paste wax on the table top and it feels like a new saw..
note.. you're polishing the table, NOT resurfacing it, so keep the pressure light and use something straight and flat to back up your abrasive pad...

Mac
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[... stuff snipped...]

There's no major gouges or scrapes in it, it just doesn't feel as smooth as I think it should, and it's leaving marks on wood.

Should I wet sand it w/600 grit? If so, with water or something else (mineral spirits, acetone, etc.)

I've actually got some 1 and 5 micron polishing sheets for fiber optic cable polishing that I thought I might use at the end, before waxing it.

The plan was to put some Johnson's wax on it, but I figured I'd like to get it as smooth as possible before putting the wax on.
Thanks for the response.
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On 16 Sep 2004 10:13:51 -0700, snipped-for-privacy@hotmail.com (Mike O.) wrote:

don't worry too much about polishing the aluminum. just get it flat and reasonably smooth.

use the minimum amount of abrasives. if the table has been anodised you want to preserve as much of that as you can for as long as you can

probably overkill, but it probably won't hurt. the wax is the main thing.

the wax will wear out fairly quickly. you'll be reapplying it regularly. try to get in the habit of doing it before the black marks become a problem. if you think you have to go through the whole rubbing out/ polishing sequence first it will probably be less likely to be done. most of the time it will just need a quick wipedown with the paste wax.

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Wax it first and see how that does. If you don't absolutely have to sand a machine table, don't. If you absolutely must, use a very fine grit and a flat steel sanding block.

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On Wed, 15 Sep 2004 22:34:11 -0400, "Mike O."
I wouldn't take abrasives to an aluminium top unless I was prepared to re-anodise it afterwards, or if it had already lost any anodised surface. Unless you live in a desert, aluminium can quite easily re-develop a poor surface just from ongoing surface oxidation - don't leave it unprotected.
--
Smert' spamionam

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What you describe is the result of corrosion, not oxidation. In the absence of any corrosive agent (e.g. salt or acids), unprotected aluminum oxidizes rapidly -- and the thin surface layer of aluminum oxide _protects_ the underlying metal from further oxidation. There just isn't a problem with "ongoing surface oxidation" in aluminum, unless the oxide layer is repeatedly abraded away. Aluminum unprotected by any surface finish such as paint, lacquer, etc will survive continued outdoor exposure for _years_ because it forms its own protecting layer.
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
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On Thu, 16 Sep 2004 12:58:52 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

What's the (practical) difference ? For aluminium in workshop conditions, the form of corrosion most likely to occur _is_ an oxidation. Steel bolts through aluminium in damp conditions might show galvanic corrosion, stressed forgings in machine tools can break owing to intergranular corrosion. Tabletops though are going to do it by surface oxidation.

The trouble is that randomly formed aluminium oxide doesn't protect very well. It's thin, it's porous and it's permeable. Surface oxidation is ongoing. If you want an impermeable oxide film, you have to make it yourself. The same applies (to a lesser extent) to stainless steel in kitchens - if you don't passivate it deliberately, there can be all manner of staining problems as it slowly does it itself.
If you have a damp workshop (I certainly do), then white powdery surfaces on aluminium are the natural state of things, unless you take precautions (But then, I have as much stock in my workshop that's scrap aircraft parts and old engines as I do for raw timber).
Much depends on the alloy. Alloys used for extrusion or casting (and thus most sawbench tops) are admittedly less likely to show powdery surface corrosion than alloys for barstock and machined components. Lots of cast tabletops (those gridiron ones) still do it though - goodness knows what's in the alloy.
The problem with sawbenches particularly isn't that the top is likely to disintegrate, but that the corrosion that is there isn't compatible with being a sawbench. It can leave discolouration on timber. It's also so soft that just sliding timber over it is enough to be abrasive, removing one layer and introducing another.

This depends on the alloy. Most castings will disappear entirely if left outside. Look at an old aircrash site sometime - there's a big oval patch of bare earth, because the aluminium that's still there as hydroxides is a powerful weedkiller. Aircraft (and Landrovers) are mainly aluminium / magnesium alloy and the stuff practically vanishes while you watch.
--
Smert' spamionam

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The practical difference is that aluminum oxide, once formed, is not subject to further oxidation. It doesn't behave like iron in the presence of oxygen and water.

But once the layer of oxide is formed, the oxidation process _stops_.

Iron tabletops, sure. Not aluminum.

Hogwash. It protects perfectly fine. I have an aluminum-frame greenhouse in my back yard that's _at_least_ thirty years old, with no protection from the elements other than the protective film of aluminum oxide that naturally forms on any aluminum surface in an oxygen-rich atmosphere. If what you say is correct, it should have disintegrated long ago. It hasn't, and probably will outlive either of us.

If that's happening to aluminum in your workshop, then you have some source of corrosive fumes. Water alone will not cause aluminum to acquire a white powdery surface.

I had a Sears tablesaw with an aluminum top that, over the years, as I changed residences, lived in two different garages (both unheated) and two different basements -- and it never exhibited a white powdery surface. If this is happening to you, it means that you have some source of corrosion present _other_than_ water and oxygen.
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
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On Thu, 16 Sep 2004 19:32:35 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

No, the oxidation continues. A randomly formed oxide layer just isn't adequately impermeable.

If not anodised at the factory, then it was at least passivated.
--
Smert' spamionam

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Andy Dingley wrote: > Aircraft (and Landrovers) are

Birmabright old chap, birmabright (land-rovers)
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wrote:

Indeed so.
Have you ever looked at L-R's officially recommended flux for gas welding it ? "Hari-Kiri No 2", from some place in Birmingham. I'd love to get a tin, just for the name.
Mind you, it's probably full of fluorides, so the name isn't unreasonable.
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wrote:

This is probably a dumb question, but how can I tell if has any anodized surface? It just has a grey "brushed" aluminum look (the same as it's always had); there's never been any color to it.
Mike O.
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Anodizing is extremely thin. If it has any wear on it, you've already gone through the anodizing.
John Martin
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On 16 Sep 2004 18:25:47 GMT, snipped-for-privacy@aol.com (JMartin957) wrote:

not all anodizing is colored. it comes clear too. once you wear through it you'll be able to see the difference.
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snipped-for-privacy@thanks.com wrote:

Since the Mike O. said his top was leaving black marks on wood being cut, I assumed that the anodizing has been at least partly worn away.
It didn't occur to me to suggest checking for dirt/grease/oil/etc before doing anything else.
In my experience (IMX?) the smoother the surface, the less effort required to maintain and keep clean.
--
Morris Dovey
DeSoto, Iowa USA
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