Tapping Hardened Steel

AntCaps

AntCaps

Joined
May 6, 2009
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Hey guys! yet again i have a question about a process i have no idea about.
So iv been planning my grail blade for a very long time and recently I was thinking about handle attachment i know i want them to be removable just in case i decide to swap them out. So iv decided since the stock is going to be thick enough the most direct strong and simple way of doing it would be to tap the tang of the blade.

So my question is is tapping hardened steel possible?
Is it a matter of going very slow and using lots of lube?
Anyone out there with experience in this matter id greatly appreciate your help.

Thanks again!
 
If tapping a hole would work, might through bolting it work? Is there no way you can tap the hole before heat treating? Maybe you can differentially harden the knife so the tang is softer?
 
How is it the tang is hard instead of in the annealed state? I miss read your post. You don't want to tape holes in hardened steel. You will ruin a lot of taps in the process.

Fred
 
i thought about tapping prior to heat treat but i know iv read that after heat treat hole that were priviously drilled will have shrunk (unless im dreaming it up) and i cant do a differential HT because its A2 and iv read thats thats a hard thing to do.
Theres a great chance that im remembering that iv read wrong so if you can differentially heat treat let me know.
 
Fred sorry im not explaining myself enough Im desinging a full tang knife i want to tap holes through it so changing scales is as simple as removing 6 machine screws no barrel nuts no chainrig bolts. ill see if i can get a picture drawn up :)
 
AntCaps said:
i thought about tapping prior to heat treat but i know iv read that after heat treat hole that were priviously drilled will have shrunk (unless im dreaming it up) and i cant do a differential HT because its A2 and iv read thats thats a hard thing to do.
Theres a great chance that im remembering that iv read wrong so if you can differentially heat treat let me know.
Click to expand...
If you have the holes drilled and tapped you can chase the holes with a new tap and oil and clean them out. You should have no problem.
Fred
 
The dimensions shouldn't change enough to matter, your best bet with A2 is to do the threads before HT. You can do a spot anneal on the tang after heat treat and then thread with some steels, but A2 will not be very friendly to this method.

You could also press-fit some threaded standoffs into the tang if you can size the holes right, but I would probably go for a threaded hole in the tang in this case just for tidyness.
 
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Fred just so i know i understand what you are you saing i should tap the holes prior to heat treat than re tap them after? i think it could work because there would be a significant differance in the amount of material id be removing.
If thats not what you meant please let me know.
Thanks
 
AntCaps said:
Fred just so i know i understand what you are you saing i should tap the holes prior to heat treat than re tap them after? i think it could work because there would be a significant differance in the amount of material id be removing.
If thats not what you meant please let me know.
Thanks
Click to expand...

I perform this 50 times a month using 01 steel and its 5/16 thick. I drill and tap the holes while the steel is annealed and then chase them after they have been hardened and tempered. You just want to use tapping oil as you said while turning the tap in and out until it clears.

Fred
 
Awesome! Fred you are the man!
Thanks guys this place is the best so many people with so many skills.
I cant wait to get this monster started.
Thanks again.
 
I worked in a shop for many years before the job I am at now. We machined and heat treated tons of 52100 made into small parts with tapped holes from as small as 6-32 to 5/16-18. If you check a drill chart for the size drill you will need for the thread you are planning to use you can go up the next size (just a few thousands of an inch). These will most likely be letter drills NOT fraction drill because they are ground more precise. By going a few thousands larger you will be able to run a tap through the hole after heat treat to clean up the threads without it binding. USE LOTS OF BLACK TAPPING OIL. You can also do a test thread on a piece of scrap to see how much the heat treat will affect the hole size. In my experience if done right it will not change much. Remember the bolt tolerance is not near as precise as you tapped hole will be.
Also if you find that your hole has shrunk you can run an O.D. die over your bolt threads to make them smaller to fit.
 
I'm a little late to the party here...

To my knowledge, it is not possible to tap hard steel.

Hard steel can be threaded by thread milling and thread grinding, both of which require specialized equipment, and neither of which are cheap.

It is not unusual for threaded holes to distort or fill with scale after heat treat. As Fred pointed out, these threads can be cleaned up with a tap.
 
Thanks guys i think what im going to do is pre drill and tap the holes and clean them up post heat treat.
But im also going to take some of shaving sharps advive ill try it with another blank from the same material and batch and if it works on one of the smaller hobby knives ill do it to my monster.
Thanks again
 
When tapping before Heat treat, in the toolroom we would use a tap of a larger "H Limit"

This increases the pitch diameter of the thread.

Just drilling with a larger hole often won't do too much, because you aren't changing the diameter of the thread, just the percentage of thread.
You want to actually increase the pitch diameter, and only a larger H Limit tap will do that.

FWIW, carefully consider how much thread engagement you will have if you just tap the tang.
It's often not enough.

Threaded spacers are often a better choice, as you can make them just shorter than the thickness between screw heads, Maximizing thread engagement.

They have the added benefit of working as locating pins for the scales and adding tremendously to the shear strength of the assembly.
 
What about small sex bolts? Even stronger and lots easier. Fastenall would have them.

Those big corby or whatever bolts are too big, IMHO.

Wouldn't have to stagger your holes that way either.
 
Our shop has tapped some hardened material in the past. The correct (expensive) taps are required, and the set-up has to be perfect. This is not an operation that can be done manually..CNC equiptment is a must using a controlled tapping cycle for the perfect feed and speed.
 
melsdad said:
Our shop has tapped some hardened material in the past. The correct (expensive) taps are required, and the set-up has to be perfect. This is not an operation that can be done manually..CNC equiptment is a must using a controlled tapping cycle for the perfect feed and speed.
Click to expand...

There are taps sold for "hard" steel, but I think they're talking about prehardened P20 etc. I don't think they'll work on steel ~ HRC 60.
 
Great idea.

shaving sharp said:
I worked in a shop for many years before the job I am at now. We machined and heat treated tons of 52100 made into small parts with tapped holes from as small as 6-32 to 5/16-18. If you check a drill chart for the size drill you will need for the thread you are planning to use you can go up the next size (just a few thousands of an inch). These will most likely be letter drills NOT fraction drill because they are ground more precise. By going a few thousands larger you will be able to run a tap through the hole after heat treat to clean up the threads without it binding. USE LOTS OF BLACK TAPPING OIL. You can also do a test thread on a piece of scrap to see how much the heat treat will affect the hole size. In my experience if done right it will not change much. Remember the bolt tolerance is not near as precise as you tapped hole will be.
Also if you find that your hole has shrunk you can run an O.D. die over your bolt threads to make them smaller to fit.
Click to expand...
 
I agree with Fellhoelter... you're thread engagement for each screw is going to be half (or probably less) of what the thickness of the steel is, unless you stagger the fasteners. Not to mention, I think you're needlessly complicating things. Just get some sex bolts as mentioned, and you can just drill th scales and tang to match the diameter of the "stand off".
 
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