How do I tell if a cable is good for Damascus or not?

Galvinized, throw it away.  Small strands decarborize, for a good knife don't use it.  I wouln't go below 9/16 diameter for a knife.  You can go as small as you want for ornimental stuff.  In the end forge it up, make a test blade and see how it works out.  I'm sure there are a million and one threads on ifi that cover that topic.

After first making sure it's not plated, contain lead lays or plastic you would test it the same way you would test any piece of steel to see if it was "blade-worthy":  Spark test and heat, quench and break test

I met a guy in May that told me he got a bunch of the metal tines used by the street sweeping truck and they act like high carbon steel. In their normal state from the street sweeper they are like springs. The soften to wire and harden to snap like a twig.

I did a grind test on the cable, at it had a ton of sparks so it must have a fairly high carbon content. 

Well were they "bursty sparks" or just sparks?  Compare to grinding on a scrap file.

 "bursty sparks" that sounds like a golden age or silver age funny book name.

Maby a side kick or cub reporter.

An excitable shipboard radio operator, perhaps?

Maybe a Radar from MASH type!

Makes  guy want to write a Bursty Sparks story eh? Something along the Tom Swift line?

 

Frosty The Lucky.

Well were they "bursty sparks" or just sparks?  Compare to grinding on a scrap file.

always like peoples attempt at trying to explain something that really is a visual thing with suck minor differences that it is very difficult to get across.

I would say the main people that would get the description are people who already know the spark test. Really a trial and error adventure with a smith a stack of steel (known steels help) and a grinder.

they were "bursty", however, the trail of sparks was only about a foot long, and usualy you get a 3'+ tail of sparks. relevant?

varies by type and wear on the wheel, and how hard you are pressing.  IE rougher condition wheel throws larger sparks which can travel farther, harder pressure similarly throws larger (and more) sparks, see above :)

What do you mean "usually"?  Who?  Using what equipment? What speed? How hard?

 

Best way to do it is to build your own sample library and compare the sparks to known samples by trading off.  This helps deal with a ton of variables in the making of them.

 

For me I can generally get a long trial of sparks with my 9" industrial angle grinder and a short trial of sparks with my bench grinder---for the same piece of steel!

I think we need a new sticky some place on the site. Everyone get a bar or 2 of known steels and with the same wheel do some spark tests and post photos of them. If someone needs a question like this answered then have them find a leaf spring or something and do a test posting mystery steel and leaf spring. Now I know that you will never KNOW 100% what the leaf spring is made from but it will be a walk like a duck type test to some degree.

I bought a few scraps from a rigging supply store the other day. Varied sizes and lengths. I asked about the paperwork they had on them and it turned out they used cable with steel that had .7 carbon

I bought a few scraps from a rigging supply store the other day. Varied sizes and lengths. I asked about the paperwork they had on them and it turned out they used cable with steel that had .7 carbon

 

70 points carbon will make a nice functional blade. I'm looking forward to seeing how it works for you.

 

Frosty The Lucky.

Another misconception with the spark test is the hardness of the steel. Don't ever go by how far the sparks fly go by the shape of the sparks. A hardened piece of hight carbon steel will creat a nice shower of sparks off of a high power grinder while that same piece of steel in an annealed state will throw significantly less sparks but they will both have a similar pattern.

I'm not claiming to be a pro in any of this metallurgy, this is just my experience with grinding different steels.

"For me I can generally get a long trial of sparks with my 9" industrial angle grinder and a short trial of sparks with my bench grinder---for the same piece of steel!"

 

 

To get a similar spark trail I think you need to  change the way you "hold" your bench grinder! :P