Trouble Cutting Silver steel

Job done, thanks to all who helped.

Well done, Chris

MichaelG.

That should do the job once hardened and tempered and by going for the reduced 2.5mm end you have created a solid shoulder to take the loads.

Insert is CCGT 060202 so 0.2mm tip radius

Many thanks Jason

I knew how good the Sherline was for this type of work & thought i would try with the full 5/8" length stuck out of the chuck, i did not have any 1/8" silver steel so had to use 3/16" silver steel & used my ER25 collet chuck. I used DCGT070204 aluminium inserts ( very sharp inserts) & turned the first 8mm length down to 2.5mm, then turned down the second 8mm length to 2.5mm. Finish was excellent so i thought lets just put a .0001 clock on the piece & see how true it was running along its length, @ the chuck end it ran spot on true @ the outer end it showed .00005 run out. This also wasn't with a brand new insert it was one that i had used on a few jobs before but was still nice & sharp. The very final spring cut was done in one along the 5/8" length.

What speeds were you using? I would guess 1500 rpm to flat out, depending on the actual diameter being cutat the time, would be appropriate as a starting point.

Jason B - can you tell me what the grade/material the insert is please?

John 🙂

Hi John Silver Steel

Chris

My advise it to use a quality brazed carbide for precision micro work. I base this on no experience but equally when starting out if your advisor is top notch it would be foolish to ignore the advice. But yes I will try the other recommended inserts there normally are several methods to reach an objective. Equally trying to cut silver steel with my home ground HSS could add problems to my cutting. Anyway a lot learned and even more I am yet to discover.

Chris

Good job indeed Chris, but it's not finished yet!

The advantage of Silver-steel is that it can be cut to shape in the soft condition and then hardened by heat and quenching. As it is your punch is the right shape and finish (well done!), but if it's put to work the point will soon blunt and perhaps bend.

With a blow-lamp in dull daylight (so you can see the colour properly), heat the silver steel tip to 'cherry red'. This is the approximate colour of a glace cherry. The length of time the silver steel is held to temperature is proportional to the weight of the object being treated. Experts may disagree, I suggest about 15 seconds for your tip. Then, without dithering, plunge the tip as quickly as possible into a bowl of cold water and swirl. Use plenty of water to absorb heat quickly, and stir vigorously to prevent steam forming an insulating layer and delaying the quench.

Rapid cooling freezes silver-steel's internal structure in very hard form. This can be tested by running a file over the metal; the file should skate rather than cut. If the file cuts, repeat heating and quenching. This can't be repeated indefinitely, maybe 3 strikes and you're out. Advanced workers can adjust hardness by warming the water (softer), or by quenching in oil, or increase hardness by adding table salt to the water.

Unfortunately hardening makes silver-steel brittle, which isn't good in a punch. The cure is to relax the hardness slightly by tempering, that is holding the metal at medium heat, say 200°C, for a relatively long time. (Depends on the weight of metal being treated, I suggest 30 minutes in a domestic oven would be enough for your punch.) Tempering reduces brittleness and makes the steel tougher.

In a clock, a pivot made of silver-steel might not be tempered. There's advantage in leaving a bearing not whacked with a hammer glass-hard because it will take many years to wear out. (In practice Blue Pivot Steel seems to be preferred by clockmakers - it's sold pre-hardened but not so hard it can't be cut in a lathe.)

Whether a steel will harden or not depends mainly on how much Carbon is in the alloy. Mild-steel is low Carbon and isn't effected by heat-treatment. Silver-steel is a high-carbon steel and it's hardening properties are improved by adding a dash of Chromium and Manganese, perhaps also Vanadium.

HSS is also a high-carbon steel, but this family of alloys contain Tungsten, Molybdenum and Cobalt. These have the effect of lifting the temperature needed to alter the internal structure of the steel, and it remains hard at low-red heat. Hardening and tempering of HSS is best left to the professionals. The higher temperatures, longer soak times, and accurate temperature control needed can't be managed with a manually operated blow-lamp. In the workshop, HSS is bought hard and usually ground to shape, though it can be cut with Carbide if need be.

Dave

Edited By SillyOldDuffer on 26/08/2019 09:16:40

They are not silver steel as suggested above.

Don't know the exact make up of the carbide but they are from APT, I have linked to the hobby ones that come 2 in a box but I buy 10 in a box which is a little cheaper. Same inserts in both just different amount.

Just a couple of things to add to what Dave said, you will find it very difficult to heat just the tip of your part, so heat all of it, trying to heat just the end could overheat it as it is already pointed.

When you plunge it into the water do it vertically as you could cause the metal to bend if done at an angle as one side will shrink before the other, not such a problem on small parts but would affect longer ones more.

I for one will certainly not be using brazed carbide tools over the excellent **GT inserts for both surface finish & precision.

I've been using **GT inserts on my Sherline all weekend with 3mm silver steel. Unsupported, at least 15mm hanging out of the collet, half of that turned to a long, 6 degree taper. Great finish and so little deflection you can "rely on the dial"

I was originally planning to use a female centre but there was no need.

These inserts make turning SS like turning EN1A.

Chris, I urge you to try these. If you want to hone your turning skills, you can be up and running straight away. Just make sure they are centred well and run them at full speed below 4mm OD.

I understand the urge to follow your mentor but that can come later when you have more turning experience.

Also you talk about brazed tools for precision micro work. Most of the work you are going to have to do is not precision micro work, for example your centre punch and the other tools you are going to have to make.

Following the advice of the forum and getting a good, all purpose tool is going to get you moving forward towards your goal.

I don't mean to sound all evangalistic about these inserts but since I've started using them (on forum advice), there has been one major thing not to worry about (tool sharpening) so I've been able to concentrate on making stuff.

Just try it,

Steve

The 16mm length of silver steel coming out from the chuck & was turned down to 2.5mm diameter on my Sherline was done @ around 1200 rpm with DCGT insert. Out of interest i put my tacho on to check my speed that i turned @, i also checked the tacho for accuracy by running @ full speed & got 2804 rpm. Not bad as Sherline state 2800 rpm @ max speed.

A big thank you Silly chap you have saved me looking this up.

Regards

Chris

Chris/Dave.......just be a touch careful about leaving your clock pivots 'glass hard'...ie untempered. it's not just wear that is there to catch ignorance. In the glass-hard state a small pivot is incredibly delicate and snapped off in a moment by very low loads. Personally, I will not make that mistake again and always temper to 'straw' so that there is some lee-way.

Edited By Bob Stevenson on 27/08/2019 10:04:51

Chris, I think a few wires have got crossed! A microwave oven is unsuitable for tempering.

Microwave ovens generate a radio wave tuned to the excitation frequency of Hydrogen. As food is full of water they are an efficient way of cooking because heat is generated directly inside the food.

Though spectacular sparks may ensue, Microwaves aren't good at heating metal because the waves cannot penetrate the surface and zapping metal, close to a short circuit, is likely to damage the electronics. For tempering, Microwaves are pretty much useless. An ordinary oven, gas, electric or an Aga is fine.

Dave

Yes and no. I'd agree that a microwave oven isn't suitable for tempering steel. But when heating food they work by dielectric heating, not by being tuned to a specific molecular resonance.

Andrew