Polishing/buffing questions

Well, based on lapidary experience. . .

It sounds like you're not getting all the scratches out at the earlier stages. At each stage of abrasive the goal is to produce a nice, even, haze of scratches -- finer and finer for each layer. Trying to polish out random scratches left over from an earlier stage is a losing game. And buffing compound (as distinct from a coloring compound like tripoli) won't take out anything at all.

I'd take it back several stages and work through the abrasives again, taking care each time to get that even haze of scratches before moving on to the next stage. And be sure to clean the surface and your tools thoroughly with a flood of water before you move on. Make sure there isn't any abrasive left in the 'grain' to mess up the later stages.

--RC

Sleep? Isn't that a totally inadequate substitute for caffine?

Excellent info, thanks, RC. Huge mistake I've been making I guess, is not cleaning the surface thoroughly enough.

I've surmised the diminishing scratch size thing, but I suspect I'm not educated enough in the stages of that process. In terms of just the paper sanding for instance, what would an advisable grit jump be? I start out with a really rough cone wheel to make the initial "flat" surface, then move to a strip of course abrasive paper. From there I go to 100 grit sand paper, then to 120, 150, 220, 320, 400, 800, 1000,

1200, 1500, then to the buffer. Shoot, looking at what I just typed, I guess some of those jumps are kind of huge. Probably should get some more in-between grit grades?

What about direction of sanding? On metal like this old iron, should one keep the sanding/grinding direction always the same, or should it be alternated at 90 degrees, say? I've been thinking that since it's such a grained metal, I should keep sanding in one direction all the time.

Bert

Perhaps 600. Otherwise that's fine, and it's far more likely that your problem is indeed stray grit (or moving up too fast) than the sizes you are using. Use a magnifying glass or loupe to examine the suface as you work. When you change grits, you need to work until there are no scratches made by the previous grit visible. There's no point in working one grit longer than that takes - there's also no point in moving up grits until that has been accomplished. If you don't carefully clean all traces of the previous grits off/out, you'll never get there, because old coarse grit will make new coarse scratches that the fine grits cannot eliminate.

A good trick is to use a Sharpie marker to check your "scratches" If you have a nice even scratch pattern the sharpie will be gone on the next pass or so. If you still have some deep scratches they will show up.

Eide

I'll definitely add the 600 and will absolutely pay more attention to cleaning in between grits. Thanks, Ecnerwal.

Bert

Now that sounds like a great suggestion for this old codger's deteriorating eyes!! I'll give it a try. Thanks, Eide.

Bert

At gunsmithing school we learned to always "cross our grits".

You work the surface up in prgressively finer and finer grit abrasives, but each grit is used twice, with the direction of abrasion being at right angles to eachother.

This makes it very easy to see if you have eliminated all the scratches from the previous pass.

As a rough guide, try about doubling the grade at each step. Start with 100 (or 80 if the surface is real rough), go to 220, then 400 or

600 and then 800 or 1000-1200.

The real trick isn't the number of grades it's the time you spend in each one. While it's hard to over-work a surface you'll usually find you spend less and less time in each grade. The important thing is to work at each grade until you've got that nice even haze of scratches.

Alternating directions 90 degrees is a good way to keep track of the developing scratch pattern, but it doesn't really matter, especially at the early grades. Remember all those scratches are going to be taken out in the next step down.

--RC

Sleep? Isn't that a totally inadequate substitute for caffine?

I was taught to double the grit number and work at 90 degrees to the last grit until all the previous marks are gone, and clean well between.

I like the Sharpie trick, will try that next time.

-- Carl West snipped-for-privacy@comcast.net

>>>>>>>> change the 'DOT' to '.' to email me

Makes sense to me...thanks, Ernie.

Bert

-with a lot of clippage-

Many thanks, RC. Just picked up some of the extra grits I need and will be applying all the advice so kindly offered here. I see I'm going to have to get a jeweler's loupe and a few more buffing wheels.

I'll let you know how it goes, but in the mean time, I just want to say thank you to everyone for so willingly offering up so much information.

Best regards to all,

Bert

p.s...RC - great sig line on caffeine!

To hark back to an early Usenet tradition, I will attempt to close this thread in the interests of saving web space.

You've all been extraordinarily kind in offering advice on the question I posed and I will be applying all of your input to my amateur efforts. I will post news of how it all works out but in the mean time, I hope that my subject doesn't further clutter up the archives of this group.

Again, thank you one and all.

Bert

You beat me to that one. :)

Haven't seen this tho--> wrought-iron has "grit" in it ;) As you remove the surface you expose more grit. Ok, so I've never worked with wrought iron. ;)

...but somehow can't help but believe that the slag in it will be slowly released to scratch whatever polished surface you try to put on it. :/

Sound right? ...or should I go away quietly? ;)

Alvin in AZ

Wrought iron does have silica slag in it which can act as an abrasive. Most polishing I have seen of wrought iron was done with a buffing wheel and progressive buffing compounds.

When I was a kid, my dad insisted on having cheese melted into his grits. (he was a southern boy)

to be back on topic, I do a quick etch (less than a minute) between grits, but we all know how dangerous that is :)

Sorry for being late on the scene, as it were, but I expect the lines are from the buffing wheel being charged with oxide grit supllied by the workpiece, which is coarser than the grit in the polishing compound. You are using different wheels as you progress to finer compounds, yes? If you can afford the time, and want a mirror finish on the face of your parts, track down a Micro-Mesh Abrasive Kit. Micro-Mesh makes abrasive paper (plastic) sheets to around 12 thousand grit. Use the various grits wet, and work your way through them, and the part comes out scary shiny. :-)

The Micro-Mesh abrasives are usually used for taking scratches out of such things as aircraft canopies and the like. Available from plastics suppliers. Works well on knife blades and the like, though labour intensive.

The Kit will set you back around $30 or so, and contains about 8 or 10 different grits, some polishing cloth and a sanding pad, as well as instructions. Worth a look, if you want to polish something small. to a very high level.

Cheers Trevor Jones

Alvin, you're right, and not right - at least about the pieces I'm working with. Some of the grain openings in the metal do include slag, but some of them also seem to be simple voids. It's different with every piece, so there's always a surprise that screws things up.

I'm definitely working out a technique for doing this, but generally speaking, polishing wrought iron is not a smart thing to do. You're all being incredibly helpful. Many thanks.

Bert

Ernie - yup, that's what it's boiling down to. After I do extensive progressive sanding (now up to 2000 grit before heading to the buffing wheel...) I've gotten four separate wheels to use four separate compounds on and things are looking pretty good.

Bert