Fly cutting question

[John TV]

Still consider myself a complete nuub and have so much to learn.

Can mild steel have hard spots?

Using a fly cutter for the first time on my mill. Using high speed steel and my first attempt at grinding a fly cutter bit. Squaring up mild steel stock purchased from steel supplier cut off bins. So I started cutting and all seemed to go well on first few passes. I was experimenting with depth of cuts and mill seemed to handle up to about .040 ok but backed off to .020 cuts. Chip color seemed ok not colored. Then midway through a cutting pass, saw a spark or two and cutter stopped throwing chips. Thought cutter must be getting dull so reground edges, the tip did look a bit hammered. Put it back in the mill and first run through, cutting fine then hit something hard and killed the bit. Long explanation to asking, should mild steel from a supplier have hard spots? It seems like mystery metal. I had a small braised carbide lathe tool that was approximately the right shape that cut through the hard spots ok but wow I wasn't expecting that. Is this typical?

John from MN


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[mikey]

Long explanation to asking, should mild steel from a supplier have hard spots? It seems like mystery metal.

In a word, yes. This is less of a problem with steels of known composition but for "mild steels", who knows what's in there. Stuff like A36 can have hard and soft spots and bar stock of Unknownium can, too.

 

[savarin]

I am turning a piece of unknownium steel and I believe the answer is yes.
This definitely has some harder areas in it.
Irrespective of how far out of the chuck it is the hard section causes a very fine chatter so its not at any particular section of the lathe.
As you have found I wound up the speed and used a carbide cutter and the chatter disappeared.

 

[Downunder Bob]

Depends a lot on where the said mild steel comes from, A particular grade widely known as Chinesium can often be found at low cost suppliers and big box type suppliers. Chinesium is generally made by recycling an assortment of scrap metal and can have inclusions of broken tool bits drills even small, pieces of carbide. Most shops do not sort out what goes into their scrap bins.

The shop that I get most of my scrap stock throw everything into the bins various grades of Mild steel, structural steel, cast steel, and cast iron including the aforementioned broken bits of HSS, I even rescued a near new 7/8" drill bit #2 MT the shank was bent so they threw it. I simply turned the shank down to clean up straight and now I have a good drill bit. They also throw worn out grinding wheels in there, so imagine what ends up in recycled steel.

The specialised metals suppliers will generally know where the stock they sell comes from, and how reliable it is, but you pay for the privilege.

As most of my stock is second hand from scrap bins etc. I have little to no knowledge of its origin or grade, So whenever I strike a hard spot I just slow it down and increase the cutting fluid

 

[Karl_T]

My son's company brings in steel by the rail car.

When they find a defect like this, the entire rail car is rejected. The steel lot then goes to the discount steel suppliers.

 

[Chewy]

Absolutely!! I beat a fycutter to death on a piece of unknown steel when I first got my Mill. Had a bunch of 1-1/2" square chunks of steel left over from about 25 years ago from my truck shop. Collected a lot of tooling for the mill with the sole purpose of making chips not things. First couple of cuts went fine, then saw sparks and no matter what I did to the bit it dug, ripped, gouged and broke tips. Thought it was me grinding. Got a Shars insert face mill and it cut the steel. A while later I used the fly cutter on aluminum and then steel and figured out that it wasn't me.

Regrind the bit with a big radius and then try on some known aluminum and then regrind a second bit (smaller radius) and get some 1018 and try it. 1018 is cheap and universal. Perfectly usable for most items and can be case hardened with Cherry Red. What you learn with 1018 will carry over to oither steels.

Charles

 

[John TV]

Thanks for the tips and thoughts. Another good lesson learned. Hearing from you all helps my self taught/you tube taught knowledge get valuable feedback I'm not sure would be available anywhere else.


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