01 tool steel tapping

[Naiveambition]

First off can it be done. Have a boring head that needs threaded to 6/32 and I'm Wondering if I messed up and used wrong steel. The web is saying I may need a special tap? At this stage I'm really hoping to save the part since its the last step needed. Annealing is not an option so?...

 

[rklopp]

Is it hardened already or not? If it is typical of as-bought O-1, tapping should not be particularly difficult with a decent tap, some lube, a straight start, and a proper-size hole. If already hard up to perhaps HRC 45, you can go oversize by perhaps 0.005 to 0.010 on the tap drill and use a brand new high quality tap. For the drilling, go at, say 25 FPM max with tons of oil and don't hesitate on the feed. Quit as soon as there is any sign of burning the drill corners.

 

[Naiveambition]

As bought it is not hardened. I was able to turn the 3/4 inch shank on my 7x 10 lathe. So did not foresee tapping issues. Tap started out ok the would strip the hole, after this I increased hole size and was able to get bout 3 turns then would lock up. I knew better than to crank on it so I used a bolt to see if threads were taking. U can see in pic where it snapped. Better a bolt than the tap🤓.

Could the heat generated by hand tapping coupled with oily lube cause a hardened spot ahead for oncoming threads, just enough to stop the tap

 

[10K Pete]

Must it be 6-32? Can it be 6-40? 6-32 is the weakest of all taps which is why
we use 6-40 or 6-48 in harder tougher steels like gun parts.

Stop and examine/list the critical requirements for the tapping/screw and then
pick the best solution.

The drawing callout may not be the correct one!!!!

Pete

No nothing you could do would harden the part.

 

[Naiveambition]

6/32 is the print dimension. I will need to go to next size as hole is not fully threaded. If the taps you mention will work then I will buy them. I did not know there was a separate tap scale for harder steels
I think6 /40 would fit for my dimension so does tap need to be exotic, like colbalt, straight flute , spiral, etc...

 

[rklopp]

This should be easy-peasy. You don't need weird size or special taps, just a quality, sharp taper-point plug tap, such as OSG or Greenfield. Forget hand taps, forget no-name discount Asian, forget Sears Craftsman, forget Vermont American, forget Hanson. These will only cause grief. Taper-point taps are sometimes called gun taps because they shoot the chips out ahead. Even in a blind hole, you can dig out the chips with a small drill after you're done. Are you absolutely sure the tap drill size was correct (#36)? Is the hole deep enough? Was it a decent drill? How did you guide the tap? Do not even think about attempting free-hand tapping in this situation, especially entering a curved surface. The high sides will catch first and push the tap off-line. It would help to countersink the hole a little before tapping to cure the curved surface issue.

If it was up to me, I'd do it with a spiral flute tap, but those are more fragile, or even a thread forming tap in soft O-1. (What you have is almost certainly "normalized", which is about the most machinable condition possible for O-1.)

I suppose it is possible to make a hard spot by totally frying the hole with a dull drill, but you literally have to get the material orange-hot and have it cool fast by the remaining cold metal mass. You would know it!

 

[Swifty]

I agree that a good quality HSS tap needs to be used, then there should be no problem

Paul.

 

[Naiveambition]

I think you hit it on the head with the tap starting off center without having the neccasary beveled relief. Though the tap looked straight. I noticed the screw was wobbly at first then settled down torwards the bottom of the hole. I will try this tomorrow and hopefully report good news.

 

[10K Pete]

6-32 tap has the weakest structure of any of the smaller taps. It has less metal
in the center, compared to the amount of metal it's trying to remove, than other
sizes. It is UNC.

6-40 tap is much stronger as it has a larger core compared to the amount of
metal it's trying to remove. Considerably. It is UNF.

Now let's go beyond UNC/UNF. How many flutes has the tap you're using? Probably three or four. Give that up and get a two flute 6-40. Now there's
a lot of metal in the tool to resist breaking. Now put that together with a high
quality tap and proper technique.

NOW it's 'easy-peasy', because you've given yourself every advantage.

Pete

 

[goldstar31]

Might I comment, please?

Ignoring all this correspondence- so far- might I ask why one really needs to use tool steel- and coughs discreetly- has to harden it?

I have a small boring head was made of pretty ordinary mild steel- probably leaded stuff but it came from my scrap bin. If there had been a bit of cast iron of suitable size, I would have used it. If you look at the tailstock of your tail stock poppet it probably is soft and this, like it or not has to be there , working ALL the time--------------------------------drilling boring or whatever.

So my boring head- and a lot of my homemade tools are made of soft metal. The only concession is a tool part which has to cut. What holds the tool to be cut is 'soft'.

But returning to the adjusting screw, it is always - screwcut after drilling. Then tapped!

My guess- and is only a guess, is that you drilled your home and were over enthusiastic, got it hot and quenched it with cutting fluid. In other words, your fancy would be tool steel was already tempered before you put a tap in. And got a raft of problems!!!!!

There is no intention of trying to criticise you as you are simply following the advice of - someone who should know better.

Apart from the 'little bit' at the end of many of my tools, the rest is soft and will not temper- no matter what I do or don't do

Regards


Norman

 

[Parksy]

Drilled and tapped tool steel the other day and had zero issues. Will only ever tap straight after drilling, so everything is lined up and I can use the chuck to support the end of the tap. Haven't broken a tap using this method and if tapping hard material, will only use HSS taps.

 

[Swifty]

Tapping tool steels should be no problem at all, after more than 35 years working with all types of steel making press tools, problems were few. Use the right size drill, don't let it work harden the steel by using a blunt drill or running it too fast. When hand tapping, use a small square to check that the tap is not on a lean, and use a cutting oil.

Paul.

 

[Naiveambition]

Well plan c and d came together today. I was able to tap easily using10/24. Initially I thought 8/32 but didn't want to risk anymore chances.
So moving on I, drilled two more holes for gib holders, and using the countersink knowledge, tried 6/32 again. Well that went bad:wall:, then realized my holes are on the wrong side of workpiece. So now need to redo my mating dovetails again:wall::wall:. So after removing broken tap I finished in 10/24. Still need to find the tap holder. I remember hearing the telltale clanking of it going all the way down an behind the tool box after throwing it:hDe:

I had never planned on hardening, I was hoping for reduced long term wear using a tool steel vs softer steel. Would of liked the ways to be hardened but this is personal preference and as you say would be worth nill as far as machining is involved, but is nice to brag to the Buddys .

I think most issues were not countersinking coupled with being round , so thanks to who pointed that out. I will follow advise on small taps since all of mine are 3 flute. Thanks for all replys