Lathe HSS Toolbits for 12L14

[gmac]

While I'm waiting for my first order of 12L14 steel to arrive I've been reading anything I had on how HSS toolbits should be ground for this material. The references I have contend that side and end reliefs should be about 10 degrees, but side rake is in the range of 10 to 22 degrees for free machining steel and top rakes of 15 degrees are noted.

I don't know if all this refers to a roughing/knifing tool or a facing/finishing tool. What kind of nose radius is recommended, if any? What toolbit shape and lubricant will provide the best final finish?

All this applies to a lightweight lathe (Taig). I've ground up some toolbits specifically for aluminum and parting off but other than that only have the original Taig "starter set" of toolbits. Lots of blank 1/4" bits ready for grinding...what should I prep for the 12L14?

Thanks guys
Garry

 

[steamer]

Hi

Running a lathe by Southbend

Running and Engine lathe by Colvin.

My Logan Manual

The Hercus lathe manual, which I attached.

There are some pretty good descriptions. 12L14 turns very easily, I think you will find what your looking for.

Hope it helps

Dave

View attachment Hercus TextBook of Turning.pdf

 

[BillH]

Don't be too overly concerned about the angles. Practically speaking, you only want the cutting edge to be touching the work, nothing else rubbing the workpiece. If the angles are too great, the cutting tip has less support and does not last as long. As long as just the cutting tip is making contact with the work, it'll work. Of course you'll want to experiment, maybe use chip breakers, trying more rake, etc. Just jump right in and experiment!

 

[shred]

I found 12L14 to cut pretty well on the Taig using the factory HSS toolbits. BillH is correct.. btw, the Taig is small enough that you might want to start with what some of the books call 'finishing' tools.

 

[Tin Falcon]

Gmac:
Take a look here this may help you understand pages 7-5 to 7-7
http://www.metalworking.com/tutorials/ARMY-TC-9-524/ch7.pdf

Like I have said before these angles are the best for this material. These angle will put the least strain on the machine give good tool life and decent cutting rates. A general purpose bit will work but likely not as well.
Sulpherized oil for steel
Tin

 

[shred]

Since the Taig does not fit an Armstrong tool holder, you can't just copy what's on Figure 7-4 there, but the angles will work if applied to a horizontally-held bit.

Since we're talking about a lathe with a bed shorter than my forearm that can be carried in one hand, the only part of the toolbit that does any work is the area close to the tip, so that's where to focus your attention when shaping.

 

[gmac]

Thanks for the input everyone. Shred has hit on my stumbling point - the angles induced by the use of an Armstrong holder and how that applies to all the tool angles recommended in various literature. Is it with or without the Armstrong holder?

I have fingers crossed that my material shows up before the weekend so I can experiment. I've ground up a few bits in preparation - suck it and see what happens!!!

Thanks to Tin and Steamer for pointing me to the Army and Hercus reference material.

Cheers
Garry

 

[rake60]

Garry tool geometry isn't really all that complicated.
The tool cuts where it contacts the material.
Any contact added to that cutting point is drag.

Let's make it simple.
Imagine a spinning log of soft soap that you press your foot into.
It's going to get smaller but your foot is going to get hot and controlling
the amount of soap removed is a game of chance.
Now just use your large toe.
We see a little control coming into effect but it's still unpredictable.

My point is, the geometry of a tool isn't as critical as the book makes it out to be.

It cuts at the point of contact.
Anything beyond that point needs to clear.
Too much clearance comprises the strength of the tool.

In other words, there is NO perfect answer.
It's a learn as you go process.
The metal will teach you what it wants.

Rick

 

[shred]

Here's a link on grinding tools-- the Sherline is similar to the Taig, so if you follow these, you'll end up with a good bit. The nomenclature they use is a little different than the rest of the world but the end result is the same.

http://www.sherline.com/grinding.htm