Bright steel

I have bought some bright steel to make tool makers clamps. Problem is I can't cut a thread in the stuff. Good quality taps used, correct size holes and even tried oversized holes but no joy. Years of cutting threads but not had this problem before. Steel is dulling new, unused taps.

Anyone had this problem? I have read another post where it was suggested that the holes were the wrong size r the taps were blunt. No so in my case.

Stephen are you using a tapping compound e.g. Rocol RTD? Especially helpful if it’s stainless steel or gauge plate etc. What size thread/pitch/thread form? What is the material grade?

Alain

Sounds like work-hardening.

A mistake maybe? Someone thought 'bright' meant a shiny stainless steel was wanted rather than Bright Mild Steel.

If it is a work hardening stainless steel the taps may be blunt now.

Dave

The steel is definitely not stainless. I was trying to tap 5/16" BSF, 24tpi.

HSS tool blanks are also bright and steel, without knowing what you bought its a bit hard to say. Did it saw and drill OK?

Try the spark test on your bench grinder

Doesn't have to be stainless steel to be tough on cutting tools. Steels with a fairly high manganese content can be as well. It's what they make prison-cell window bars from! ( No good smuggling in a hacksaw blade).

The above would imply not mild steel, it's a bit bendy, did you tell the supplier what it was for?

Not sure what would imply that the ones I made at school were bright mild steel and still going strong.

Hand cut ok with hacksaw. Milled ok but seemed to be a bit harder than usual to drill.

Stephen, the way it works is that if you want to know a material's machinability you need to know exactly what it is. "Bright steel" (sic) could be one of countless different steels. "Bright mild steel" would bring us closer, and EN1A, for example, would more or less nail it.

If your supplier didn't give you a code such as EN1A and, what's worse, described it merely as "bright steel", it's impossible to say exactly what it is you're trying to machine and why it's causing you problems.

It’s described as bright mild steel. No numbers.

I made some pliers at school, case hardened jaws and 1/8" handles with a twist near the jaws, they looked great , but boy did they bend .

I wouldn't buy any steel without a spec. If it's a ME supplier he bought it from a stockist, so should know what it is. If supplier won't tell you what it is go elsewhere. Good Commercial Quality means they've lost the cert.

Working on the assumption for now that it should be readily machinable with good quality drills and taps, what are your taps exactly, i.e. brand and type? Are the holes blind or through holes? How deep? Can we see an image of a now dulled tap and a hole it struggled with?

You say you're trying to thread 5/16" BSF x 24 TPI. But 5/16" BSF is 22 TPI.

What brand of taps are you using? Sometimes you get a duff shipment that are not correctly manufactured or heat-treated.

Try drilling and tapping a hole in a piece of known mild steel that you have machined before without problems. If it taps OK, then your problem is the bright steel stock you bought for the toolmakers clamps.

As a suggestion, try heating to a dull red heat and let the material cool as slowly as possible buried in something like vermiculite. That will certainly alter the crystal structure and it might be enough to let you get on with making your clamps

Regards Brian

Apologies, I was initially trying UNF which is 24 tpi. Drilled a new hole After tap ruined and tried BSF.

Easily done! If only there was a single standard system thread system that did away with BA, BSW, USS, UTS, BSF, BSC and others.

Oh there is - metric!

I shall be hiding in my bunker for the rest of the week...

Dave

You're right SillyOldDuffer. Unfortunately, before you know it someone will want to split metric into coarse and fine....