Silver steel works fine for me when making cold chisels. So I suspect your hardening and/or tempering is off. Are you using an electric furnace or the heat 'n' hope method?

An 8mm diameter 250mm long rod is very slender. So irrespective of what steel you use it will be prone to buckling under load; basically a design flaw.

Andrew

You don't really need to heat treat the whole length, just the business end will do. Good chisels will be some form of alloyed steel probably with vandium, chromium, etc in it but chances of being able to buy a short length will be slim.

Also the angle of your cutting edge should be right for what you are intending to cut so least likely to be damaged Also do your shaping of the end before heat treat to reduce risk of grinding overheating things. An 8mm chisel will only suit light cutting so trying to take of a big chip will more likely result in a bent shank which is on a looser anyway due to dia/length ratio.

If you're going to be stuck with 8mm which REALLY sucks then I would say you need one of those pile driver type hammers to give you accurate maximum force blows every time

The hammer weight has a hole in the middle and it travels up and down the chisel shaft until it hits the dead stop, you can make one with a cheap welding kit

Dont kno what they call them

aha! A sliding hammer!

crowbars are made of very tough steel but I can't say I've ever seen one in 8mm

Edited By Ady1 on 23/07/2022 09:36:46

Hi Nick, you could probably pound that all day with a 14lb sledgehammer without a problem, the chisel I had in mind was about 2ft long and 1/2 diameter, it was my grandfather’s who was a plumber by trade. Faced with some concrete chiselling for some new fence posts I bought a Screwfix cheapy SDS drill/ breaker, it did the job in style and if it never comes out of it’s box again it was worth every penny. Cast steel used to be the material of choice for cold chisels and was what my apprentice made chisel was made from, CrV seems to have become popular nowadays.

Mike

If I wanted something stiff at that length, I would be re-engineering a 3/8’ socket drive extension bar. Not sure how good a chisel tip they might make, but likely better than the OP has managed.

There are better grades of steel for making cold-chisels, but they're harder to heat treat than silver-steel, and I suspect Chris' problem is caused by faulty heat treatment. The metal needs to be heated quickly and evenly to the right temperature and then smartly quenched. Like telling jokes, timing is critical!

• Important to prevent heat loss, I always build a nest around the item out of soft white insulating firebrick.
• My small 1kW torch is unable to heat a long length of steel evenly. I have to use two, which are cheap but hard to manage. Big torches deliver a lot of heat quickly over a broad area and are much easier to get right. Sadly, a big torch and gas cylinder are expensive for odd jobs.
• The nature of the requirement makes the heat treatment more critical than anything I've done. I usually only need a hard tip at one end and leave the rest softish. Chris seems to want a chisel hard at the tip, which only gradually softens towards the hammer end to resist bending. Unfortunately, the ratio between length and diameter of his chisel is over 30:1 making that difficult! Less than 20:1 is more normal and cold chisels are usually even stubbier; my slenderest is 15:1. To get close I think the heat-treatment needs to be near perfect, which is difficult with ordinary equipment.

What might help short of making a perfect chisel is arranging for the blow to the hammer end to accurately directed. When hit with an ordinary hammer swung in an arc, the force applied to the shaft will be slightly off-axis causing it to flex. Once a bend develops, lever action multiplies the bending force and the shaft kinks and probably fails catastrophically. A tool that delivers a hammer blow exactly inline with the axis allows much more force to be applied without bending the shaft. Perhaps a slide hammer?

Commerical cold-chisels are made of drop-forged hardened and tempered steel, usually one of the extra tough alloys. Much better than anything that can made in a home workshop or even by a well-equipped blacksmith. Buying one and grinding it down to shape would be the best answer, but it's a lot of work.

Dave

Given that good screw drives and socket extensions will be chrome vandium steel then little need to add a tip, just grind the end to the desired shape.

Rebar is quite good for chisels

If you are goung down the welding route, why don't you buy some hard facing electrodes?

regards Martin

I liks Jason's suggestion of a screwdriver blade being cut, ground and made into your tool. As long as you keep it cool when grinding the ends.