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daveo
10-29-2009, 08:40 PM
I have polished some gun parts, brass and stainless and got them to a mirror. But when you look at them in the right light or angle, you can see swirls in them. Kinda like a car that has been buffed. Is there an easy way to get them out? I tried rubbing them by hand but no luck.

aboard_epsilon
10-29-2009, 08:47 PM
you have to start with the roughest grade needed to get rid of any imperfections / scratches pock marks

if that grade is 100 wet and dry ...then use it........and stage by stage keep going up

EG
100 240 400 600 800 1000.........then onto the polishing mops

all you're going to do without these pre-stages is polish leaving nullified deep scratches behind...showing through in the final finish.


all the best.markj

daveo
10-29-2009, 08:53 PM
I finished most to 1000 grit, they do look the best but still swirly....

Evan
10-29-2009, 08:58 PM
You need at least two buffing wheels, three is better. The compounds you use must be specific to the metal in question. This is a large subject. I could write a small book on what I have learnt by trial and error to achieve polished surfaces with close to zero haze. One of the most important thing is that before embarking on the next finer grit size ALL of the scratches larger than the current grit size must be removed.

The rule of thumb with polishing is that 90% of the scratches take 10 percent of the time to remove and the remaining 10% require 90% of the time. That is for each step. Also, the grits work better cold than hot so the work must be allowed to cool often. This is especially so for the final polish.

Harder materials are easier to bring to a very high polish but take much longer than soft materials like aluminium.

This is an aluminium mirror CNC cut and then hand polished. It's a special parabolic mirror that produces much less fish eye distortion than a spherical mirror.

http://metalshopborealis.ca/pics5/mirro3.jpg

This is a steel mirror:

http://metalshopborealis.ca/pics5/mirrorsteel.jpg

For aluminium the best final polishing material I have found is Mother's Aluminium Polish applied with a buffing wheel made of baby diaper flannel.

For Steels I use various grades of rouge. If its hard steel then cerium oxide puts on a good final finish.

It is essential that all traces of the previous grit be removed from the work before starting with the next finer.

daveo
10-29-2009, 09:04 PM
Thanks guys.... Very neat Evan, Can that aluminum mirror be used in a telescope? Thats my next project....

Evan
10-29-2009, 09:12 PM
The quality isn't good enough for fine optical work but it makes a decent all sky reflector for a web cam to watch for aurora, which is what the project is about. Turning a solid metal mirror from stock that is good enough for a telescope is the province of a very few machines on the planet.

One is the LODTM at Lawrence Livermore National Lab. It's the Large Optical Diamond Turning Machine and is able to turn mirrors to better than 1/4 wavelength of light accuracy.

http://ixian.ca/pics6/lodtm.jpg

https://www.llnl.gov/str/April01/Klingmann.html

Black_Moons
10-29-2009, 09:59 PM
theres lots of tables online and indeed with most boxes of polishing compound on what compounds are for what materials for first/second/third polish, a quick google can find them for ya. ('how to polish metal' is a search query that comes to mind)

john hobdeclipe
10-29-2009, 11:15 PM
A couple of thoughts:

1. Evan, please do write that book on metal polishing. I'll buy a copy.

2. About 20 or so years ago, I read an article in some car magazine about mirror polishing wheels. I don't remember all the details, but one thing really stuck in my mind...they said they finished up with corn starch!

smiller6912
10-29-2009, 11:20 PM
I found this to be helpful when I have buffing questions:
http://www.caswellplating.com/buffs/buffman.htm

EVguru
10-30-2009, 06:31 AM
Something like this any help?

http://www.axminster.co.uk/product-Micro-Mesh-Abrasives-804806.htm

Peter.
10-30-2009, 06:50 AM
How do you polish that stuff Evan is it done by machine with a lapping slurry or do you do it by hand?

Evan
10-30-2009, 08:59 AM
I use a variety of methods both wet and dry. I polish using buffers, the mill and lathe, and most especially my horizontal low speed grinder for roughing and medium fine polishing before buffing. The low speed horizontal machine is most useful and I often use semi flood water poured on by hand to polish metals and plastics. The wheels are a combination of actual 10 to 12 inch grinding wheels and a selection of plywood wheels faced with peel and stick aluminum oxide disks. I also make polishing disks from emery paper and stick them to various supports using spray on contact cement.
http://metalshopborealis.ca/pics/hgrinder1.jpg
http://ixian.ca/pics6/nutinsert.jpg

I have a separate shop space for the grinding and polishing machines to keep the grit away from the lathes and mill as much as possible



For polishing very small items that are very hard such as carbide tooling or alloy steels I use diamond dust or Cubic Boron Nitride powder. In particular, diamond dust is absolutely unbeatable for putting on a glossy finish on carbide tooling. That finish is directly transfered to the work when cutting.

Polishing is a subset of the general group called abrasive machining. Abrasive machining is very widely used in industry but often ignored in the home shop other than a grinder and sander or two. I use my mill as a surface grinder sometimes. I am not too concerned about grit harming the ways since the ways can be replaced in a few minutes with no need for recalibration or alignment. That said I still take precautions to prevent damage.

Circlip
10-30-2009, 09:15 AM
Going back to the slavery days, used to have to embed cross sections of material in a Bakelite slug and grind and polish the surface to a mirror finish to be etched and looked at on a microscope for grain boundaries etc.

Sequence was, 200, 400, 800, 1200 wet and dry paper grinding on a turntable with a water flood system to flush the particles away and keep the sample cool.

At each stage the scratches were checked to ensure no gouges on the surface or back to 200.

After this, two stages of Diamond polishing, again on turntables, using Parrafin as a coolant/lubricant, and god elp yer if the Chief Metalurgist caught yer putting too much Diamond paste on the wheel to do the job quicker.

All this to QC the incoming material to make millions of the little buggers on my name title.

Oh happy daze.

Regards Ian.

spope14
10-30-2009, 10:44 PM
I have spent years polishing metal to fine grades without swirls, and there is one very common flaw that few get. The need for absolute cleanliness between sandpaper / buffing/ clover compound/diamond polish grades, and the absolute need to keep polishing implements specific to a material.

By this I mean that when you switch from a 240 grit to a 320 grit sand paper, or even finer to the 1500's and then to the compounds, you need to keep the sandpapers seperate and away from the "dust areas" of the work you are doing with the coarser items. You then need to clean the piece completely and even machine areas to keep any "tramp particles" from the last abrasive grade out of the work being done by the next grade. Even a few or one grit from a 220 grit abrasive while doing 320 work will result in some errant scratches that are too deep for the next stage (say 400, there will be scratches of 220 grit in your 320 work). On and on, you MUST keep clean work and abrasives when polishing, being sure not to drag in larger grits by accident. This causes many a swirl or strange scratch.

The idea of keeping implements specific to a material comes to this. For the best polishing on a buffer, switch wheels between different buffing compound grades, clean the buffing area as best as you can, then use a wheel for the next finest grade (brown, red, then white for what I do, and I even use blackboard chalk as a compound). I also mark wheels used for steel, aluminum and brass and keep them for that material only. Steel wheels will put major marks on brass or aluminum parts as steel is harder.

Expensive at first, but in time, saves tons of money. Also, the quality is top notch. Sounds extremely "nutso", but this has worked for my candlestick and stainless steel work for nearly 20 years now. Once I got this, I never have problems.

boslab
10-30-2009, 11:32 PM
Going back to the slavery days, used to have to embed cross sections of material in a Bakelite slug and grind and polish the surface to a mirror finish to be etched and looked at on a microscope for grain boundaries etc.

Sequence was, 200, 400, 800, 1200 wet and dry paper grinding on a turntable with a water flood system to flush the particles away and keep the sample cool.

At each stage the scratches were checked to ensure no gouges on the surface or back to 200.

After this, two stages of Diamond polishing, again on turntables, using Parrafin as a coolant/lubricant, and god elp yer if the Chief Metalurgist caught yer putting too much Diamond paste on the wheel to do the job quicker.

All this to QC the incoming material to make millions of the little buggers on my name title.

Oh happy daze.

Regards Ian.
i have to admit to making more than a few myself, what was interesting was when you would xray a peice of steel with a microfocus xray, find an inclusion in the steel, mount it start polishing to get it exposed for the microscope then polish right through the little bugger, are we there yet?, no polish some more, are we there yet? no etc.
mounted micros wernet too bad, polishing a mirror, no thanks i think i'll leave it to Evan, i still have blue diamond paste [5 micron] uner my nails from yesterdays platinum polishing exercise
mark

Evan
10-31-2009, 12:15 AM
Speaking of diamond paste I did some looking on line since I am running a bit low on one grade. I found a dealer that drops ships from Thailand at extremely good prices. They have every grit from 50-60 to .5 micron and the price is around 11 to 15 dollars for two grams. Two grams is a lot of diamond dust and will last me for years even if I am wasteful. A little goes a very long way. If you have any requirement to polish hard metals then diamond dust is the way to go. It can also be used to trepan glass or tile using a brass or aluminum tube as the lap.

http://www.diamondtech.com/products/categories/diamond_powder_price_list.html

Peter.
10-31-2009, 06:59 AM
Evan how would diamond dust be used for polishing/sharpening an insert, as you alluded to earlier in this thread?

boslab
10-31-2009, 07:06 AM
stick it on a felt wheel, or on the polishing disk of a horizontal polisher i think would be good
mark

Black_Moons
10-31-2009, 08:43 AM
Evan: Ways can be replaced? Woah what kinda mill do you have with replaceable ways?
Nifty url, I allways wondered where I could buy bulk industral diamonds and how much it would be. I wonder if its possable to easily home plate your own tool shapes (like small die grinder burrs or cut off disks). then again I guess you can just embed it in like copper for short term usage right?

Evan
10-31-2009, 08:50 AM
To put a sharp edge on an insert with diamond dust you would use a small cast iron lap mounted preferably horizontal and rotating at low rpm. This would be an easy machine to build and in fact is on my list. It would be essentially the same as a diamond faceting machine.

Here is an example but there would be no need to get this fancy. You sure could save some money on inserts.

http://ixian.ca/pics6/faceter.jpg

You could also use a diamond grinding disk available on that site at very reasonable prices. They are diamond grit electroplated to a spring steel disk which is intended to be held to a platter via magnets so they can be changed instantly without tools.

Black Moons,

Check my project gallery at the link below to see my mill.