Tempering requires a long soak, hours, at relatively low temperature, so a quick blast with a hot blowtorch isn’t right.

I’ve an article where LBSC mentions leaving parts overnight on top of a dying coke brazier.   Likewise, forum members who work with chilled cast-iron sometimes recommend leaving hard castings overnight on the remains of a coal fire.   I don’t have a brazier or fireplace!

Anyone tried a barbecue kit?  The simple type consisting of a bed of charcoal in a small tin tray.   In principle, set fire to one in the garden and wait for the charcoal to glow.  Then put the items on top of the charcoal and cover to smother the fire. Leave until cool, overnight.  The cover should be an insulator to slow down the cooling.  Maybe a metal dustbin lid with an old towel on top.  Dredging my unreliable memory, I think LBSC also suggested whitewashing delicate parts to protect them from oxidisation and dirt.   The modern equivalent would be a stationery correcting fluid like Tippex.

The best way is an oven! Clean, with accurate temperature control.   Making an electric oven from Nichrome wire, glass-wool, and insulating fire brick isn’t rocket science, but surely too much bother and expense for a one-off job.

Silver-steel can be tempered in a domestic oven, but that’s a special virtue.  Most steels need higher temperatures.  May be the warning is just in case the laser cutter unluckily causes severe hardening, when mostly it’s not a problem. Dunno, I’ve no experience of laser cut metal.  Be interesting to see what others suggest.

Dave

Why would a domestic oven not be sufficient to lower the hardness of any edges to a reasonable value?  Doesn’t need to fully soften those edges, only make them less brittle, if that is important.

 flatness is a concern but so is good even machinability

NDIY Reason enough for me to normalise, particularly if any of that machining may be on only one side of the parts

A domestic oven at a pinch or a home made oven using a couple of oven elements and a stat wound up to 400c is the thing you need. A K type thermocouple and a kiln controller would be the ideal or even a secondhand pottery kiln. There’s a few ideas as to how to do it WHY is up to the OP ! Noel

On 3 October 2025 at 09:51 JasonB Said:

Richard the hole for those bushes may not be a good enough fit if laser cut and need finishing, laser cut holes may need tapping,edges may be too rough and need machining or draw-filing, cross holes may need drilling for pins or oil points, etc all reasons why you may not want to work a hard surface.

OK, thanks Jason.

Amazing how the laser hardens low and ultra low carbon steels when we in the workshop have to add something to it to do that!!

Not sure I follow you regarding the CO2 lasers Jason. That’s just the lasing medium surely which just dictates the wavelength of the photons in the beam. No CO2 at the target.

Correct. Oxygen is more effective (carbon steel) but at the cost of more slag. Nitrogen will give a cleaner cut.

The reason why even mild steel can take a harden has to do with cooling rate. Even low carbon steel can be hardened (to a degree) with very rapid cooling. The rapid heating of the laser allows the heat to flow very quickly to the cold surrounding material, similar to welding. But it shouldn’t be too bad on mild steel, it won’t be anywhere as hard as high carbon steel.

Annealing can’t hurt, heating to a dull grey should do the trick if you want to cover your bases. Dull red (in darkness) is probably around 500C and would be overkill. Anything above 250C will help.

Looking at their website they don’t deliver anything beyond S355 in the mild steel category.

I have bought items from Model Engineers Laser and have yet to find any hardened edges. I think this is a notice just to cover themselves.

The first thing to do is to try to find any hard edges with a file as Dave S posted 11 days ago.

JA