Tips/Techniques Cutting High Strength Steel Forging

[Tom Kitta]

Sorry guys, this is one time when things got messed up by thread hijacking. I can not find where I posted about the carbide INSERT DRILL I bought.

I did end up using a brazed carbide boring bar to open the hole in the drawbar after drilling with a regular Carbide drill AT HIGH PRESSURE LOW SPEED. Even the boring bar was used with high pressure and low speed. It might not be recommended practice but it worked! Now I want to know why. That's the engineer in me, not the farm equipment repair guy.

The drawbar is done.

After completing the bar, this thread became about exploring the high pressure low speed aspects of Coles method - not about Coles method. From here on you can call it the Susquatch Method cuz it isn't Coles anymore. @mbonds comments earlier about how dissimilar metals relate to forgings were my inspiration.

There is no doubt that an unconventional method worked. The bar is done and in service performing as hoped.

So I bought one of these carbide insert drills.

View attachment 47653

This is NOT a boring bar. It is a DRILL! Note that one ENTIRE EDGE of both inserts cut!

I'm going to try it on the left over stub of the drawbar using high pressure low speed. Might shatter it, might work. Gunna find out!

I have like 50 of these. Have not really figured out how to use them - need to see some videos. part of the problem is that shank is not MT and sometimes huge.

 

[Susquatch]

I have like 50 of these. Have not really figured out how to use them - need to see some videos. part of the problem is that shank is not MT and sometimes huge.

Wow! If it works I might be interested in lightening your load a bit.

The one I have is a 1" drill with a 1" Weldon shank. I just got the Weldon holder for it so I'll be trying it shortly.

I should prolly try it in regular steel first at conventional speeds. But I got it specifically to experiment with forgings at high pressure and very low speeds. So that's the objective. Swim slow or sink.

 

[Tom Kitta]

I tried few times but I only managed to damage the drill bit - so I need to watch some videos. Some of the drills I have are like 50cm long 2" with 2" shank.

 

[Susquatch]

I had some time off today and tried that big drill. At higher speeds and normal pressure, it wouldn't touch that forged bar. So I turned the speed right down and cranked up the pressure. And guess what? It worked! I didn't want to drill all the way through the whole bar but here is a photo of a good start.



Note that there is a little nub forming. I don't know why. Unless that nub causes a problem as the cut progressed, I have no doubt that I could have drilled all the way through the bar if I had wanted to.

A good knowledge tip for my eulogy. To machine forged steel, use carbide, go slow, and apply lots of pressure.

@mbond - you were right about the way it cuts. The two offset inserts created a scalloped hole bottom. But it isn't as noticeable as I expected.

 

[mbond]

re high pressure and low speed. Metals are composed of interlocking sets of crystals. When you 'cut' them, you are tearing some at the edge out of the main body. Work hardened material does not have clean edges between the edges of these crystals - they have been smashed together and are entangled.

Think of a snowball you make of fresh powder and how easily it falls apart versus one that you have pressed and squeezed over and over.

This is a mechanism parallel to, and not mutually exclusive with, the actual hardness of the metal, which generally makes it 'tough'.

If you have ever tried to push your fingers through a well consolidated snowball, you know that once you finally press hard enough, the material fails along a slip surface that is close to circular. That also pushes the 'cutter' your finger up and out of the work. If you don't reposition your finger lower down, then you won't be able to break any more off of the snow ball. In the same way, enough pressure has to be applied so that after a slip, the cutter continues to bite into the work

The slow speed part is a matter of practicality I think. High pressure takes a lot more power and generates a lot more heat. If you don't have it, you have to go slower so that you can apply the same force (over a longer time, that consumes less power) and avoid thermal issues with the cutter and the work

it should also be noted that low pressures can also cause the cutter to 'burnish' the work instead of cutting into in.

 

[mbond]

I had some time off today and tried that big drill. At higher speeds and normal pressure, it wouldn't touch that forged bar. So I turned the speed right down and cranked up the pressure. And guess what? It worked! I didn't want to drill all the way through the whole bar but here is a photo of a good start.

View attachment 47700

Note that there is a little nub forming. I don't know why. Unless that nub causes a problem as the cut progressed, I have no doubt that I could have drilled all the way through the bar if I had wanted to.

A good knowledge tip for my eulogy. To machine forged steel, use carbide, go slow, and apply lots of pressure.

@mbond - you were right about the way it cuts. The two offset inserts created a scalloped hole bottom. But it isn't as noticeable as I expected.

Our messages crossed mid flight, but that picture makes a lot of sense

 

[Susquatch]

Agree with your thoughts.

The slow speed part is a matter of practicality I think.

My mill has LOTS of oomph. Way more than I used. I don't think low speed is a matter of practicality.

I'm thinking it's more a matter of allowing the forged metal the time it needs to let go under all that pressure. Since the metal granules are all mooshed together, I am thinking they are like a strong adhesive that can't be released quickly. It has to be stretched slowly before it will separate.

But who knows, might be something else. One thing it's not is lack of torque.

 

[mbond]

if you have enough power, then I think you could do high speed and high load, but i think you might break something.

there is certainly a time factor when discussing material 'failure'. Microseconds matter. At a certain point you are looking at something like the 'viscosity' of the metal

 

[Susquatch]

if you have enough power, then I think you could do high speed and high load, but i think you might break something.

Yes, I wanted to try it but chickened out for exactly that reason. What I can say is that higher speeds without pressure would not touch it

there is certainly a time factor when discussing material 'failure'. Microseconds matter. At a certain point you are looking at something like the 'viscosity' of the metal

YES!

I'm thinking Toffee. Pull it slowly and it stretches, pull it fast and it breaks. Not exactly that of course but similar.

 

[mbond]

There are a lot of analogies I think

 

[jorogi]

What do the chips look like ?

 

[Susquatch]

What do the chips look like ?

They are in the photo in post 124 above. One side makes a big huge curl. The other side makes little flake curls.