More Drilling AEB-L Post HT

[robwil]

What is the impact of the heat generated drilling post heat treatment in respect to stress risers, stress cracking and such?

 

[Storm W]

For small holes I use a 1/8 carbide paddle bit from Amazon and after a post from JTknives inhale been using burrs. I find that AEB-L warps when drilled soft so I dont do it. I use high speed and light pressure. After the 1/8 hold it's easy enough to open up what a carbide masonry bit.

 

[AVigil]

I find that AEB-L warps when drilled soft so I dont do it.

It will warp with or without holes, it is a characteristic of AEB-L. But if you quench with heavy plates this solves the problem pretty much. You can temper with the blade clamped and that helps as well.

With AEB-L it will even move days after heat treating. I now have my slip joint parts in AEBL clamped in a vise and left there for several days until the steel stops moving.

 

[JTknives]

It I’m cutting your blades on the cnc I will pop start jokes for free. I will also drill the holes for you as well, we charge a buck a hole. I have not had any warping issues from holes. I use a carbide burr to drill hardened steel or opening the popped hole to 1/8”. After that I use a carbide straight flute or a dagger point carbide drill. The burrs work super good but only on hard steel. If you use them on something soft thy gum up and rip themselves apart. I found this out the hard way when opening up some popped holes. The holes where hard from cutting but soft bases steel. I have a video somewhere showing how I do it.

 

[Storm W]

It will warp with or without holes, it is a characteristic of AEB-L. But if you quench with heavy plates this solves the problem pretty much. You can temper with the blade clamped and that helps as well.

With AEB-L it will even move days after heat treating. I now have my slip joint parts in AEBL clamped in a vise and left there for several days until the steel stops moving.

I find its 50/50 if it warps. If it is going to warp it's going to happen on any drilled hole. It sounds like the way to prevent all of this is having a way to keep it straight for as long as possible but that doesn't help much if using LN.

 

[Rhinoknives1]

It I’m cutting your blades on the cnc I will pop start jokes for free. I will also drill the holes for you as well, we charge a buck a hole. I have not had any warping issues from holes. I use a carbide burr to drill hardened steel or opening the popped hole to 1/8”. After that I use a carbide straight flute or a dagger point carbide drill. The burrs work super good but only on hard steel. If you use them on something soft thy gum up and rip themselves apart. I found this out the hard way when opening up some popped holes. The holes where hard from cutting but soft bases steel. I have a video somewhere showing how I do it.

I do use Carbide Burrs to counter sink all of the holes in my blades, AEB-L & Nitro-V after they are waterjet cut, them to Paul Bos for HT. Then to me....No problems yet with stress risers... stressing!

 

[AVigil]

I find its 50/50 if it warps. If it is going to warp it's going to happen on any drilled hole. It sounds like the way to prevent all of this is having a way to keep it straight for as long as possible but that doesn't help much if using LN.

I have had it warp right in the middle of the blade where no holes are. All my aebl is LN cryo, and then surfaced ground flat.
Days later it will show a slight warp, other knifemakers have observed this also.

So now after LN cryo, my blades go in a vice for at least 3 days and clamped tight.

After 3 days when taken out they will stay straight usually. I did just have a slip joint blade develop a tiny convex warp but a few minutes on the disc sander took care of that.

 

[tkroenlein]

What is the impact of the heat generated drilling post heat treatment in respect to stress risers, stress cracking and such?

Drilling (Or any machine operation) should not generate enough heat to affect heat treat. MANY machining operations are done to hard tooling to maximize precision, without ill effect.

 

[Cushing H.]

I might have (accidentally) discovered something important about this issue today. What I had run in to earlier was:

• It was "challenging" to start the hole (using carbide tipped bits) because no center punch could make a divot in the hardened steel.
• I could start the hole ... but I needed to do so by **lightly** applying the bit to the surface of the steel (too much pressure and it badly wandered). By doing this, the carbide tip would create a small divot that I could then apply pressure to.
• Once I had that divot, I could find the "sweet spot" in pressure (too little pressure, no cutting, too much pressure, things get hot or break really fast).
• I would drill a little, then stop and let things cool off. rinse and repeat.
• Towards the end of the cut, weird things would happen. The bit (still intact) would just stop cutting, OR, when it broke through the bottom of the hole (I do have an aluminum backer), the bit would bind and break. Replacing the bit with a new one, the bottom of the hole was completed and cleaned out nicely.

===> here is what I observed today: in putting in a new bit and applying to my **very** firmly clamped blade, my brand new bit also did not bite and cut in the hole. Oh Sh** I say. Looking more closely, I observed some pretty significant deflection of the drill bit ... so apparently the hole had been started and mostly completed fairly off-center from the chuck, I un-clamped the blade, re-centered so that the drill bit entered the existing hole cleanly (no deflection), and !!!! no problem at all completing the hole. the bit cut steel immediately, and when breaking through, did not break. My guess is that something about the geometry of the deflected bit did not allow the business end of the carbide to really engage and cut the steel at the bottom of the hole.

So... here is my thought (conjecture for now): when drilling hardened material like this with a carbide tipped bit, get the hole well started, BUT then un-clamp and re-center the bit so that is is drilling at a clean 90 degree angle to the steel, then complete the cut. If this thought is right, hopefully this will eliminate/reduce the loss of cut at the bottom of the hole, and also bit breakage upon breakthrough at the bottom of the cut.

This wandering / off-center cut by the bit is a problem with drill presses - undoubtedly with a mill - with shorter and stronger bits, this issue is reduced and contributes to their better success at drilling holes in hardened material.....

 

[tkroenlein]

Masonry blades do not have a properly shaped tip to cut steel. They are made to spin and hammer at the same time in a material that is much more brittle than carbide.

There is no inherent problem with drills or mills deflecting when you push straight down on them. Them problem is your pushing (down feed) exceeds the rate at which the bit is cutting.

A plain old solid carbide twist drill would make short work of this. High speed, coolant flood, and glacially slow feed. Solid carbide tools have little strength. You simply cannot feed those small diameters fast enough to get a chip or it will catch and explode. You want dust sized chips and coolant slurry produced when you drill.

 

[Cushing H.]

So you are suggesting slow speed, slow feed,and nearly continuous supply of coolant?

 

[Cushing H.]

There is no inherent problem with drills or mills deflecting when you push straight down on them. Them problem is your pushing (down feed) exceeds the rate at which the bit is cutting.

Im not sure if you understand my observation. The bit simply stopped cutting at all. After re centering and getting rid of the deflection, it cut easily

 

[tkroenlein]

So you are suggesting slow speed, slow feed,and nearly continuous supply of coolant?

Carbide generally works best with high tool speed (I go for the 3600RPM setting on my own drill press), slow down feed and lots coolant (flooding.)

When you run carbide slow, it causes "cold welding" of the material to the bit. That looks like galling, and may difficult to see on a real small edge.

A carbide tool doesn't cut like a HSS/cobalt tool. Most milling/drilling operations with the HSS tool use feed/speed that puts the cutting edge of the tool under the work hardened material that was just cut, so you may want a chip over .005" thick. Carbide tools rely on their hardness to cut relatively hard materials, but often lack enough strength to take such a big "bite."

 

[Storm W]

For what it's worth I like cutting wax. We used to use it in aluminum welding shops all the time. I find it less messy and it works well. Someone step in and tell me if there is a down side to it.

 

[Horsewright]

For what it's worth I like cutting wax. We used to use it in aluminum welding shops all the time. I find it less messy and it works well. Someone step in and tell me if there is a down side to it.

I use it often drilling holes in copper and nickel silver bolster material.

Are we overthinking this AEB-L drilling thing? The two to the left are not, everything else is AEB-L. I just drill em pre heat treat with a #30 screw length bit. These guys are stubby and don't flex as much and don't wander as much. Then they are enlarged and counter sunk using a step drill, except the front hole on a blade that doesn't have a bolster or the bolster holes. I get em back from HT and they are all straight as an arrow, regardless of who I have do it. All are done at 63 RC.

I've never had an AEB-L blade break except a tip where the customer used it to pry (and actually admitted it).

 

[Seedy Lot]

I have drilled plenty of holes in hardened M2 in the 64-65rc range, I have had best results using Black and Decker glass/tile bits.

 

[AVigil]

To not confuse new makers who may stumble upon this post.

Drill your holes before heat treatment. This is a standard procedure in knife making and done by the best knifemakers.

Only drill a hole in harden steel if you forgot to drill a hole.

Some may choose to drill holes post heat treatment, that is their choice but it is not what most knife makers are doing.

 

[Cushing H.]

To not confuse new makers who may stumble upon this post.

Drill your holes before heat treatment. This is a standard procedure in knife making and done by the best knifemakers.

Only drill a hole in harden steel if you forgot to drill a hole.

Some may choose to drill holes post heat treatment, that is their choice but it is not what most knife makers are doing.

Agreed in general. In this particular case, I had planned to solder on a bolster and had only holes for pins for the scales done pre HT. We changed out minds, and decided to pin/glue the bolster - hence the need to now drill bolster holes in the hard material.
(aside - when I originally posted this thread, I had no intention to open a discussion on **whether** to drill in hardened material (that has been covered in other threads) - I only meant to comment that the AEBL is different (more difficult) to drill than my previous experience (15n20) - surprisingly so - which bodes well for its performance in the final knife. By the way - drilling non-hardened AEBL is not really a piece of cake either: in drilling the handle pin holes for these same blades, I apparently did not keep up the drill rate sufficiently, and the last few fractions of an inch of the hole got work hardened around the outer circumference of the bottom of the hole. The steel then laughed at every ordinary bit I could throw at it. Had to resort to drilling out the center of the hole with a smaller bit, then going at the remaining material with a small dremmel grinder attachment. Nasty.)

 

[JTknives]

I actually really prefer drilling after heat treat. I pop a small start hole and then heat treat. I really love the finish you get when drilling hardened steel with a carbide straight flute drill. Also chamfers superbly when hard and using my carbide tool. But I make all my pin fits tight as I finish The handle material off the blade and then epoxy in place.

 

[Natlek]

Looking more closely, I observed some pretty significant deflection of the drill bit ... so apparently the hole had been started and mostly completed fairly off-center from the chuck, I un-clamped the blade, re-centered so that the drill bit entered the existing hole cleanly (no deflection), and !!!! no problem at all completing the hole. the bit cut steel immediately, and when breaking through, did not break. My guess is that something about the geometry of the deflected bit did not allow the business end of the carbide to really engage and cut the steel at the bottom of the hole.

So... here is my thought (conjecture for now): when drilling hardened material like this with a carbide tipped bit, get the hole well started, BUT then un-clamp and re-center the bit so that is is drilling at a clean 90 degree angle to the steel, then complete the cut.

In this part of the World when someone figure something we say...You just discovered America THAT happens because masonry drill are not well sharpened , especially the top of carbide insert , so tip is walking around till it catch in steel . And IF it is not quality drill bits will bend because of off-center, pressure+heat .You don t need to clamp knife to drill hole with this kind of drill bits ,they can not do what ordinary drill bits can do when you drill steel ..... they are not dangerous . Again , buy quality drill bits for ceramic and glass and your problem is solved for good
Australian talks too much so skip this video clip to 3:25 , the same thing happened as you describe

Cheap one masonry drill bits from from USA .....I can bend them with pliers , to soft for any seriously work , soft brick maybe . But if I sharpen them they will drill in hardest steel........