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Turning Sterling Silver on a Manual Lathe

dgfoster

Diamond
Joined
Jun 14, 2008
Location
Bellingham, WA
I have been asked to make a sterling silver "nose cone" for a trophy. The dimensions will be .500 by 1.6 with the typical slightly bulging cone shape for 2/3 of its length and the final 1/3 being a simple vertical cylinder. This will be a one-off deal.

I have not been able to find much on machining silver porbably because most of the time it is cast using lost wax.

Before I aree to this, can anyone give me a clue as to how it turns and what optimal shape a HSS cutter should be ground? I anticipate using a manual lathe and files and crocus cloth. A mirror finish will be the goal.

Denis
 
Sterling is 92.5% silver. Coin is 90% silver. I have machined coin, but not sterling. I have sawed and filed and engraved sterling. Coin is rather like unleaded brass to machine. It makes long stringy chips and works better with a cutting fluid. One of my old books actually said oil of wintergreen is a good cutting fluid, specifically when hand engraving. I got some from an old-style druggist (50 years ago). It may have helped, and it certainly smelled good. Today's prices dictate taking measures to capture your chips and recycle them.

I would use HSS wood-working tools and a T-rest to turn the curved shape you describe.

Once the turning is done, either grade of silver is easy to polish with silicon carbide paper and a buffing wheel with white rouge compound.

Larry
 
Silver is treacherous to machine. It can grab and get ruined if you are turning it freehand. I have turned silver many,many times working on PGA trophies,retirement gifts,etc. in Williamsburg. So,be careful. It is snarly,snaggly,and not the most fun to turn!! Copper is worse.
 
I have not turned a lot of silver but I have fly cut and milled thousands of silver contacts. It is much like machining soft aluminum. It cuts easily, so that is not a problem, but getting the chips clear is. Use a HSS cutter with a lot of rake and clearance and it must be very sharp. The clearance must extend all the way to the cutting edge, no rounding. It has a strong tendency to gall if there is any drag at all. I usually hold the front of the cutter against tthe wheel on a bench grinder in one position so the clearance is concave, then carefully lap it with a fine stone against the cutting edge and the bottom of the concave surface, stroking from side to side without allowing any vertical rock. A cutting oil is necessary. I use Mobil Gear 632, which doesn't seem to be listed any more. The lubricant is mainly to prevent chip bonding to the cutter and to allow the chip to slide away smoothly. A high film strength is desirable, but a heavily sulphurized oil will tarnish the silver. Surface speed doesn't seem to make a lot of difference if the cutter is right.

Sterling is a lot easier than pure silver.

Bill
 
Thx G,L, and 9100

Thanks for the three great replies, already. They are very helpful.

I think I will go for it.

Any more thoughts form others would be very welcome. There is not a lot of room for messing up when working with silver.

Denis
 
Turning silver is not that difficult. Carbide or HSS need to be razor sharp as 9100 said.
However, polishing should be accomplished with polishing compounds called grease and red rouge, using kerosene. I'm not familiar with white rouge. We also use some Norton / St. Gobain Polybond wheels.

All the best,
Payson
 
Polishing - bon ami (household cleaner) might work well.


Can't say I've use it on sterling, but it works very well on most metals. Little water, a rag (careful) and some rpms is all you need.


as a bonus, you might have some under the kitchen sink. Seal with a paste wax, it'll slows the tarnishing.
 
For polishing I use 1 micron synthetic sapphire from Microabrasives with a soft cloth or Viva towel and oil or water. If you use water, distilled is necessary because the chlorine in tap water instantly forms silver chloride, the same sort of compound used in photographic film. Artist Bonnie Rasmussen and I once made a presentation piece of silver and no matter how carefully I polished it, the surface had a brown scum. I finally realized that the silver chloride was darkening from exposure to light. I switched to distilled and even the engraver asked how we got such a bright polish. Microabrasives sent me 1 Kg samples of .3 1, and 10 micron abrasive, more than I will use in my lifetime, so if you want some, I will send you a few grams.

Bill
 
You bet!

9100,

I really appreciate the chlorine and brown scum tip. Who'da thunk!

And the kind offer of the micro abrasive is also appreciated. I will PM you my address and happily pay postage.

Many thanks also to Monomer and Payson. Each person seems to have important pieces of this puzzle.

Denis
 
I was thinking along the lines of, why is wastage a problem as you can just remelt, cast, and try again, when it dawned on me you don't need to turn the silver at all. Just turn the wax.

Turn a wax model of the piece leaving a sprew. Cast plaster around it. Melt out the wax, drying the plaster. Fill with melted Silver. Break mold, file, and polish.

There are a lot of tweeks to this method. Search 'lost wax casting.'
 
Starbolin,

Thanks for the idea but you might notice in the first post mention of lost wax casting of silver. The problem for me is I do not have the knowledge or equipment to cast the silver. I do have a lathe and limited (Now better) knowledge of turning. I do think it could be interesting to do the casting, but that is a whole new field to learn. Not practical for one-off.

Denis
 
There's no need to cast the silver yourself, there are plenty of outfits that do nothing but that for the jewelry industry. Just send them the wax, and they send you the casting, very straight forward. Rhode island used to be full of them, but I'm sure there are many in your area, just ask any jewelry maker.

I think it will cost much less than buying a solid piece of silver that size.
 
you might want to consider grinding a chipbreaker profile into your cutting tool if you have a problem with stringy chips. Here's a profile I use when cutting copper...

img0624x.jpg
 
I have gotten to a point in my career where casting is a viable option for a whole lot of repairs and manufacturing. I do have a centrifugal casting machine but there are much easier ways to accomplish what you are trying to do. I cast a lot of broken emblems for antique tractors the following way using aluminum. Get some cuttlefish and take the broken part and squeeze it between two pieces. Hollow out a sprue with your pocket knife, wire the two pieces together and melt your aluminum. Pour it in your mold let it cool and then take it out and clean it up. I have done this countless times and it is easier then you can imagine. In your case you could turn you piece out of aluminum and use it to crush the cuttlefish. I guarantee it will work and quick.
 
I am personally not a fan of the cuttlefish method.

Depending on what you are charging, it might actually be cheaper to have the part cast. If I was set up with my casting bench, I'd offer to help. I'm sure kpotter on this board has one set up, you might contact him, or he can at least offer a good casting house.

So in that case, you cut the master out of cutting wax, then send it out. You can also have your through hole. The more time you spend polishing the wax, the less time you'll spend polishing the final.

Polishing is as follows, start with 220 grit emory and remove all scratches and tool marks, then 320, then 400, then 600. Once you make it up to 600, it's pretty shiney. Now you use a buffing compound called white diamond with a standard flap or felt wheel. Load the wheel, buff the part, repeat....don't spend too long on any one area or you'll leave a mark. Once you are happy with the polish, you switch wheels and clean your part with distilled water. Now load the wheel with red rouge polish compound. Repeat the process. The red rouge is mostly a wax that somewhat seals the piece. When done, wrap in clean cotton and send it off.

The price of silver dropped dramatically today. It can rebound just as quickly, make sure your estimate includes market variations in the silver. As was said, save all of your chips. If you don't ever use em again, you can send them to me :-) (put em on ebay at turning swarf)

In all honesty though, you are going to have a hard time getting a supplier for 1/2" diameter solid round stock. You will probably be better off starting with a wax.

Also, if you have the option, use argentinium sterling, no concerns about tarnish then.
 
Thx Richard, John, Snowman, and Crossthread

Yet more useful information. Very helpful to see a pic of the chipbreaker that would likely make this job easier.

The casting idea sounds quite interesting. I will have to check in on having some local jeweler do it and see what they would charge. The cuttlefish method sounds easy and is attractive as it is done all in-house. My guess is that it provides a rougher finish and less precise results than lost wax. And there would undoubtedly be a seam. Seems like all that might be pretty easy to deal with by finishing it on the lathe....

You guys are educating me and I appreciate it. I have to admit that I was biased toward turning just 'cause I wanted to try it. Looks like it might not be so practical.

Denis
 
+1 on the argentinium, but... Have you asked the client if it HAS to be solid silver?
Seems like a lot of work and expense for something you could easily turn in brass and have plated.
A nice thick plating of fine silver would look great and tarnish very slowly.

Just a thought.

Josh
 
Washing silver periodically with ammonia water helps it to not tarnish.

I recommend SHARP HSS rather than carbide,which doesn't get as sharp,unless you have special ways to lap it. Just be careful of grabbing if you hold the tools freehand. Tools held in the toolpost will be no problem.
 
Washing silver periodically with ammonia water helps it to not tarnish.
QUOTE]

Thanks! DIdn't know that

Here's a link for you in re: to casting. It will cost you A LOT less than having a local jeweler do it.

.: Best-Cast Homepage :.

Just a note, I have not done business with them, but they were recommended to me by kpotter who is a goldsmith when I asked about stainless casting.
 
+1 on the argentinium, but... Have you asked the client if it HAS to be solid silver?
Seems like a lot of work and expense for something you could easily turn in brass and have plated.
A nice thick plating of fine silver would look great and tarnish very slowly.

Just a thought.

Josh

It has to be solid sterling silver---part of the "specialness"

Washing silver periodically with ammonia water helps it to not tarnish.


I recommend SHARP HSS rather than carbide,which doesn't get as sharp,unless you have special ways to lap it. Just be careful of grabbing if you hold the tools freehand. Tools held in the toolpost will be no problem.

Nice tip, George. I like to use very sharp cutters all the time. I routinely use the method suggested by 9100 above: " I usually hold the front of the cutter against tthe wheel on a bench grinder in one position so the clearance is concave, then carefully lap it with a fine stone [I like to use a fine diamond lap dgf] against the cutting edge and the bottom of the concave surface, stroking from side to side without allowing any vertical rock. A cutting oil is necessary. " This method reliably produces a very sharp cutting edge that is easily touched up for the finishing cut.

Washing silver periodically with ammonia water helps it to not tarnish.
QUOTE]

Thanks! DIdn't know that

Here's a link for you in re: to casting. It will cost you A LOT less than having a local jeweler do it.

.: Best-Cast Homepage :.

Just a note, I have not done business with them, but they were recommended to me by kpotter who is a goldsmith when I asked about stainless casting.

Looks like a go to place for precious metal casting whether one off or in quantity. Impressive.

Thanks, all.
Denis
 








 
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