# Drilling and tapping hardened steel



## Naiveambition (Feb 23, 2017)

The project I'm working on requires two holes in hardened steel. May possibly be stainless but not sure.   I don't have the option to anneal and reharden for multiple reasons so, I am looking into alternatives.   When I first looked into this the drill bits were extremely exspensive ( 300$)for one     Like that's gonna happen 

The tapped hole is 6/32 if I can remember correctly and drilled hole is  .125

I've ran across some YouTube videos that mention a sharpened masonry bit which is fine for the drilled hole,  but for the tapped hole it will be important to have it sized for tapping, as most are standard sizes not related to tapping.  I have a small area of flexibility I suppose on tapping a little larger hole.

Any suggestions


----------



## abby (Feb 23, 2017)

Carbide drills are available but even if you drill the hole how will you tap it ?


----------



## Buchanan (Feb 23, 2017)

You could get somebody with an orbiting head on a EDM Machine to spark the thread. You just need a copper thread with the correct pitch but smaller diameter. They could also spark the hole to start with.


----------



## goldstar31 (Feb 23, 2017)

It seems perfectly possible to reduce an oversize masonry drill to be a correctly sized carbide drill. There are pages and pages here and elsewhere of how to grind and how to make the appropriate tooling as diamond and carbide is so freely available and cheap. I recall years before this internet thing that we sharpened masonry drills on a worn out diamond wheel that had done service for cutting spectacle lens blanks. 

As for tapping, there is seems to be no reason why the tap is cut with nothing more than a diamond nail file. 

After all, if one looks at the gearing that was cut for the Gutenberg printing machine, it was done with a wood chisel.

Some clever arse is going to decry my comments but dear old Professor Chaddock made hardened steel ball bearings -in his home. workshop. Where he made bits for the first atomic bomb is unclear!

Remember the brain is the largest mass in the World which has  to be fully explored

Norm


----------



## Wizard69 (Feb 23, 2017)

The first question you should ask yourself is how hard is hard?  You can buy carbide drills, usually single flute, that will drill through most materials.  These aren't that expensive but you may need more than one.  

At work i once had to pierce some hardened components and only had a small carbide drill.   I used that to drill the initial hole and then followed up with a carbide end mill.  The end mill of course couldn't handle the material and chip and eroded badly.   In the end the end mill ground its way through. 

Such an approach may disgust trained machinist but the overwhelming focus was getting a machine inline as fast as possible. 

This doesn't solve your threading problem though.   6-32 is pretty small which makes me wonder what the application is.  There may be alternatives to trying to tap threads that small in hard steel.  



Naiveambition said:


> The project I'm working on requires two holes in hardened steel. May possibly be stainless but not sure.   I don't have the option to anneal and reharden for multiple reasons so, I am looking into alternatives.   When I first looked into this the drill bits were extremely exspensive ( 300$)for one     Like that's gonna happen
> 
> 
> 
> ...


----------



## bb218 (Feb 23, 2017)

I agree that you need to know how hard the material is, if you are talking 40 RC or less then it is do able. Anything harder that that will be VERY difficult to tap. Most hard materials I have tried to tap the tap froze in the material and would not back out. Orbiting EDM is the best chance for threading the material if over 45 RC

Mike


----------



## kvom (Feb 23, 2017)

With a CNC mill you could thread mill the holes.


----------



## dnalot (Feb 23, 2017)

Hi

Drill hole a little oversize  and ream for a  tapered pin. loctite and drive pin into place. Drill and thread the pin. 

Mark T


----------



## Nick Hulme (Feb 23, 2017)

Thread milling may be the way to go, depending on your job size you can mount it on a face plate and thread mill it on the lathe with a high speed spindle on the cross slide, it's just like single pointing a thread but with a spinning tool, 

 -Nick


----------



## goldstar31 (Feb 23, 2017)

Not many of us with milling spindles these days. It's a bit like finding hen's teeth amongst the rocking horse manure.  We're a sort of dying breed( well, not yet)

Regards

Norm


----------



## Chiptosser (Feb 23, 2017)

You really need to determine the material, hardness.

Yes, a masonry bit will work,on hard materials.   But! and or if.

You really need to have a means to sharpen and size the carbide.

The geometry of the cutting edges of  carbide will determine how well the tool cuts, how long the edge will endure. There is a great deal of heat generated and a ridgid set-up ideally needed for good results.

The thread size that you are mentioning, 8-10 pitch is mighty small, to try thread mill.   
That is : to interpolate threads. 
 I don't know if there is a tool that small, in carbide to do thread interpolation for inside threads.  

But as mentioned by dnalot,  If it is permissible,   drill a hole larger than needed, allowing plenty of wall thickness, over tap size.    
You can tapper the hole or step it.   Then you can plug the hole with a mild steel, brass or what ever you want for the application.

Then you can:  peen,glue,weld,braze the plug in, then drill and tap.

There are a number of applications for this type of repair, just use your imagination.


----------



## Buchanan (Feb 23, 2017)

Drill an oversize hole with a sharpened masonry drill.Any old oversize. Press and locktite in a soft steel plug and drill and tap the plug. The same kind of idea as Danalot, What does the screw hold?  I have sparked threads with an adjustable eccentric rotating holder. It is a bit of a fiddle but it works.
Deryck


----------



## Blogwitch (Feb 23, 2017)

For drilling hard materials, search around where you live for hard plate drills. They are mainly used by locksmiths and don't cost much.

The ones I use can drill through spring steel with no problems and do really drill accurate sized holes.

http://www.leofixings.com/Hardplate-TCT-Tipped-p/9892.htm


John


----------



## Chiptosser (Feb 23, 2017)

As Blogwitch mentioned hardplate, drills , these would be called Die maker or toolmaker drills.

These are available in couple of configurations.  A die makers drills can be a solid carbide spade , there are spotting drills and carbide tipped.

These are a lot more expensive for doing a infrequent job.  The spade shape drills are very nice to use.

I'll have to check into the hardplate drills, that are common to the UK.


----------



## MachineTom (Mar 11, 2017)

I needed to drill a 4-40 hole in a 2" Ball Bearing x 6. First ground a small flat spot, then using a carbide twist drill 3/16" about 1/2" deep, into this I pressed a pre-drilled spud, then tapped the 4-40 hole. 

Pre drilling the spud gives the metal somewhere to expand when pressed into the ball.


----------



## tornitore45 (Mar 11, 2017)

Has anyone noted the OP is talking about a 6-32 thread = 0.108" = 2.6 mm?

So far Buchanan has offered the only practical solution.:thumbup:
If this is a DOE or a NASA project then there are more options.


----------



## Nick Hulme (Mar 12, 2017)

tornitore45 said:


> Has anyone noted the OP is talking about a 6-32 thread = 0.108" = 2.6 mm?



Yes, I have a Thread Mill or two in the drawer for that size range ;-)


----------



## tornitore45 (Mar 12, 2017)

> Yes, I have a Thread Mill or two in the drawer for that size range ;-)



And the 10,000 RPM lathe spindle to do it. In that magic drawer.


----------



## bazmak (Mar 12, 2017)

A little more info with photos and description would not go amiss
How hard is the material.You mention S/S that is not hard.Is it file hard
if so it can only be drilled and a softer plug fitted to drill and tap
If its S/S hard then it will be difficult to tap at that size but not impossible
I personally have never heard of spark eroding a thread that small
What is the item?,can it be remade in drill rod and then rehardened
Can it annealed to work and the hardened.Again I say not enough initial info
that is why you are getting some weird and wonderful ideas most of which 
can be ignored for our type of work


----------



## Buchanan (Mar 13, 2017)

If it is very important I will spark erode the thread in for you. But we need more information. What does it hold and what are the stresses  and in what direction. 
Buchanan


----------



## Naiveambition (Mar 13, 2017)

Thanks fellows for all the tips and tricks.  I located two straight flute carbide drills that supposedly drill thru files. So this is the next step.  If I can't make it thru with these I will probably try the masonry bit to make a plug.  The threading is still iffy at this size , so not sure what will happen.  If I can locally anneal then problem solved. I liked the idea of using a rod in drill press  to anneal, as I can't anneal the whole part then reharden,temper etc...

As for hardness no clues but, a file will not scratch it so I'm guessing around the hardness of a file.  I'll update sometime this week and let u all know what happened, and if I need a next step


----------



## Nick Hulme (Apr 23, 2017)

tornitore45 said:


> And the 10,000 RPM lathe spindle to do it. In that magic drawer.



A fast Lathe Spindle? that would be no good for thread milling, just really fast conventional threading, try that to a shoulder!  
For thread milling, and other things, I have a Tool Post Spindle and pfft to your 10000rpm, it does 15000rpm to 30000rpm with tools up to 6mm shank ;-)


----------



## Naiveambition (May 7, 2017)

Thought I should offer some closure for anyone interested in this thread.  Was finally able to summon enough courage to go for it. Lol.   

I had bought a special set of straight flut carbide drills ( forget their name but can be found using google search for file drilling)   They performed better than I anticipated.  Drilled without annealing and no oil  at 2000 rpm.  Went thru like I was drilling aluminum.  Well the drilling went fine but not the tapping.  Broke off 6/32 tap. Maybe I could of waited on a two flute tap and finished, but I got antsy and redrilled another hole next to it , then enlarged with a masonry bit to fit a plug.  This had the added benefit of also removing the broken tap.   Was tapped for 10/32 and will spot weld  into place. File flush and were in business.  

I may try drilling thru a file just for the heck of it so I can test what these drill bits are capable of. But on same note I don't want to bust a 15$ bit on testing if it goes bad.  Maybe in a couple weeks I can summon the courage again lol


----------

