Orange Peel on Nickel Silver? (knife making)

[shineonyou]

Hello all!

I'm a knife maker and I'm having problems with (kind of) 'orange peel'
when polishing nickel silver (and brass too, though rarely used).

The surface (mirror shine) is speckled with tiny pits, as if the material
has been torn away.

I don't seem to have this problem when polishing e.g. stainless steel blades
or sterling silver.

For the most part, my knives are sanded (after rough grinding P40 - P120
& filing with smooth cut files) from P240 through each grit down to P2500.

I've tried both felt and sewed muslin wheels - 3" to 6" diameter.

The compounds I'm using are a white cut & color compound called
Ultrapol 76, and a high lustre compound called G 300 A. (both from
Schmidt's Polermedel - from my research they seem to be quite appraised
and are also common among the Swedish knife making suppliers)

I'm using a lathe for the polishing, at 1500 RPM - I know this is quite slow,
especially for the smaller wheels (but smaller wheels give me more precision
and better viewing angle).

The lathe is capable of 3000 RPM, but that's not a comfortable speed
(heavy vibrations) - and with a 12" wheel I can't see what I'm doing (the
angle is quite flat, and I'd like to refrain from polishing my forehead )

Could the low RPM/SFM be the problem, or what am I doing wrong?

I'd be very grateful for any thoughts on this problem,

Magnus Ekblad (Sweden)

[mpierich]

At what stage in the process does the "orangepeel" first show up?

[woodjames]

I've had this happen before. It's due to the ''grain'' size of the base metal. Obviously you aren't working with plate, but I'll give you an example of what caused it for me, and then how to overcome it.
The example is when I plate copper if I do it at a fast rate it does so with larger less dense grains, and a slow rate is much finer and denser. Great story, what does that have to do with you? It sounds like the nickel silver/brass has larger grains to it, maybe due to the forging process or what-have-you.
What would happen to me is when polishing, when trying to buff out all the pits that were created, it lost it's ''flatness'', and resembled fresh paint - lots of hills and valleys. It was readily apparent when I sanded with a fine grit with a rigid sanding block afterwards, as it caught all the high spots at first.
What I did to fix the problem was to apply compound more often, working white on a loose wheel (check Caswell's site for an example), and using less pressure on the wheel. At first I thought that it was metal buildup on the wheel causing it, like it was cutting into it, but after more trials and experimentation I don't think that was the cause.
After sanding to 2500 grit it really shouldn't take too much buffing to bring out the mirror shine, it sounds like you are taking a couple steps backwards.

Hello all!

I'm a knife maker and I'm having problems with (kind of) 'orange peel'
when polishing nickel silver (and brass too, though rarely used).

The surface (mirror shine) is speckled with tiny pits, as if the material
has been torn away.

I don't seem to have this problem when polishing e.g. stainless steel blades
or sterling silver.

For the most part, my knives are sanded (after rough grinding P40 - P120
& filing with smooth cut files) from P240 through each grit down to P2500.

I've tried both felt and sewed muslin wheels - 3" to 6" diameter.

The compounds I'm using are a white cut & color compound called
Ultrapol 76, and a high lustre compound called G 300 A. (both from
Schmidt's Polermedel - from my research they seem to be quite appraised
and are also common among the Swedish knife making suppliers)

I'm using a lathe for the polishing, at 1500 RPM - I know this is quite slow,
especially for the smaller wheels (but smaller wheels give me more precision
and better viewing angle).

The lathe is capable of 3000 RPM, but that's not a comfortable speed
(heavy vibrations) - and with a 12" wheel I can't see what I'm doing (the
angle is quite flat, and I'd like to refrain from polishing my forehead )

Could the low RPM/SFM be the problem, or what am I doing wrong?

I'd be very grateful for any thoughts on this problem,

Magnus Ekblad (Sweden)

[shineonyou]

Thanks for your input, James!

(thanks mpierich too for entering the discussion)

Your explanation sounds very reasonable since I don't notice
the pits until I polish the handle. I hope I'll have luck with your
solution as well (usually I'm not comfortable with the lack of
control/precision when using a loose wheel).

No matter how careful I am, I *always* have some scratches
left when I get to polishing - despite close inspection during
sanding. Thus, I have to be more persistent with the polishing
- and as you suggest, this might be the problem.

I guess that I just have to be even more careful during sanding...
and I'm not rushing things as it is, I spend hours sanding...


Cheers,
Magnus

[mpierich]

I've never had it happen with stainless, but I can produce it very easily in aluminum by using greaseless compound with no white rouge for lubrication. I theorize that the greaseless being fairly aggressive but carried on a flexible substrate (a cotton wheel) allows grains of abrasive to individually dig into the metal - probably without regard for any grain pattern. The white rouge fills in the spaces between individual grains and prevents them from digging in. You need a similar solution.

I can take the same piece and go over it with a cartridge roll of the same grit as the greaseless, and the orangepeel is gone - because the cart roll is rigid and acts more like a straight-line sander, and thus the individual grains won't dig in on a micro scale.

[shineonyou]

I now have two conflicting suggestions:

1 - Soft wheel minimizes the tearing of material
2 - Flexible wheel may cause pits

Actually, both your suggestions seem plausible - either
pulling out a metal grain or abrasive grains digging in.

Perhaps you experienced folks (no offence, I mean *all* of you)
could provide some "dos" and "don'ts" (for nickel silver) in regard of:

- Wheel material and hardness
- Compo courseness and abrasive substance (i.e. Silicon Carbide, Aluminum Oxide, Tripoli, etc.)
- Speed/SFM (if this is mainly a *time* factor, it's OK - if I need to upgrade my hardware I have a $ problem)
- Applied pressure

I neither have the economy (primarily) nor the time to buy and
try all possible combinations on the market - I'd like some hints
on which end to start testing.

I'm currently using a white *cut & color* compo (Schmidt's Ultrapol 76).
From the description of it, it seems fairly aggresive (and medium greasy)
- comparable to their second *cutting* compo (Wabo 600) in cutting
action, but with brighter finish.

Quote:

"76, white
Top grade cut and colour compound. Cut similar to Wabo 600, but leaves
bright finish. Finishes produced by 54H, Blue and Green are even brighter.
One of the best cut and colour compos for stainless steel and a benchmark
for over 10 years. Relatively greasy, but the grease is important for the
excellent cutting and cooling properties of 76. Greasier than 70 grey, Green
and Blue, but not as greasy as 54 H."

Unquote

For this compo I currently have a 6" Glued Muslin, 6" Loose Muslin,
6" Soft (SG45) Felt, 3" Medium (SG55) Felt, and a 12" Sewn Muslin.
(keeping in mind that the preferred/practical speed is 1500 RPM)

I lack a frame of reference and thus have no real idea of just how agressive
this compo is in terms of e.g. grit size. (wouldn't it be great if all compos could
be graded just like sanding grits, or in microns or mesh?)

My final coloring is done on a 6" Loose Muslin or 6" Soft (SG45) Felt with
high lustre G 300 A compo, which neither cause nor conceal any pits or
scratches.

I haven't done any methodical testing of combinations of wheels and
compo since this knife model (full tang with nickel silver bolsters) is
quite new to me, I've just made a few as of yet. It's been several
months since I made the last one, and I just recently remembered
this forum.

When reading your replies I realize that I probably should perform further
testing (and keep a detailed record of it) in order to provide better
background information. I haven't kept a record of the exact combinations
I've tried this far, and my memory fails. My previous knife models have
been "stick tang", and using sterling silver or stainless steel I've never
encountered this problem before.

I have read a lot on polishing over the years, but sometimes it's just too
much information, or it's impossible to relate different products/brands
to each other, or the information sources are simply contradictory.

I greatly appreciate all your effort to help me, and I'm sorry for my lack
of background information. If you can't help me based on my scarce
information, then I'll be back at a later time (when I've done more testing)
with more specific info.

(But still hoping for some hints on where to start my testing)

Yours,
Magnus

[mpierich]

I doubt you'll find many (if any) in here who have polished nickle silver. You're getting information where the effect was seen on other materials.

If nickle silver is commonly used in knifemaking, I suggest you try knifemaking sources for more specific information.