Posted by Christopher judd on 02/08/2019 13:30:52:
…
mild steel for brackets brackets
Silver steel (stubbs) or 01 or w1 tool steel most other things such as pivots, arbors etc
Do not use modern blue pivot steel as is inconsistent.
For fine, intricate work use silver steel hardened and tempered by bluing to get the right hardness first.
Anyone know why chromium is added?
…
I have also just found out w1 steel is more like case hardened steel and that the hardness is more on the surface than all through the metal. Therefore the safer option is using 01 steel.
…
Mild steel for brackets etc, yes. Silver Steel, O-1 and W-1 are sold soft. They are easy to work and can be hardened before use. They are all better than mild steel for working parts likely to wear over time.
Blue pivot steel is sold hard and I guess is mostly shaped by grinding. There are times when pre-hardened steel is exactly right and times when it's a bad choice. The most likely explanation for inconsistency in Pivot Steel is buying cheapo from unreliable sources – what you get may not be pivot steel at all. Pay full price from a reputable supplier.
A disadvantage of O-2 is that quenching incorrectly can crack the metal or leave it dangerously weak and brittle. W-1 is easier to harden than O-2 and staying soft inside leaves it tougher than O-2 which is useful for many applications. As hardening is skilled work it pays to practice on odd bits of metal before trying it on a carefully made part that took hours to make. You have to judge temperature and soak time. With O-2 choice of quenching oil makes a difference too. I've not looked it up, but memory suggests Canola or similar, not old engine oil. Metal is moved from heat to quench as fast as possible, and agitate in the liquid briskly. Too low a temperature and the steel won't harden. Over high temperatures can damage the steel internally and make cracking and warping more likely during the quench, or burn the steel. Hardening is a bit 'three strikes and you're out' : every time the metal is heated it loses some of it's structure.
A good test of hardness is to run a file over the metal. In soft condition the file should bite; after hardening the file should skate over the surface.
Chromium is one of several metals alloyed with steel to improve it. Small quantities make steel stronger, higher quantities add corrosion resistance – 'Stainless Steel'. There are thousands of different steels out there, some are good to work with, others yuk. Nigel mentioned following the plans on choice of materials – always good advice.
Based on my learning disasters, I think O-1 vs W-1 vs Silver Steel won't make much difference until more experience is gained. Cocking up the heat treatment is more likely to cause bother in the early stages of a clock making career I think than choice of steel.
John Harrison made a lot of clocks in wood, now there's a challenge!
Dave
Edited By SillyOldDuffer on 02/08/2019 17:36:18