Buildup on Cutting Edge of Boring Bar

In the last few days I've had to make a number of small parts out of 6061 Aluminum. Some needed to be bored so I picked a standard HSS boring tool. The first couple parts went fine. I was using WD40 as a cutting fluid as I have done in the past when the all of a sudden I started getting a build up of the aluminum on the cutting edge. At first I thought it might need to be sharpened so I did a close inspection. It looked fine so I took it to another lathe and chucked up a piece of 316 stainless. It cut the stainless just fine. I took it back to the first lathe and tried boring again with the same results.

Rather than fool around with it I just grabbed another bar. This one had a brazed carbide tip. It cut just cut fine. Not only did I finish the part that was in the lathe, I made 3 more without any problems. Any ideas why the first HSS bar wouldn't cut the aluminum without a buildup, but did just fine on the 316?

Probably crap aluminium, some of which can be very speed sensitive.

Limy Sami said:

Probably crap aluminium, some of which can be very speed sensitive.

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Bingo, crappy Chinese 6061. Why anyone buys that crap is beyond me. The influx of Chinese 6061 in the English speaking world is directly related to all the "I am having trouble cutting aluminum" threads we have had lately.

Polish the top surface of the tool.

And give it LOTS of rake. No fear of breaking a sharp positive rake tool in aluminum, so make a hook tool that's sharp as a razor.

I would assume the cutter that failed was an insert tool. Check the coating. If it has Al in the mix such as TiAlN or AltiN which are excellent for steel, the cutter will do that. The aluminum workpiece will weld to the aluminum in the coating.

Tom

hss boring bar hand sharpened on bench grinder not very precise and has no coating to help with sticking.
.
some use a fine hand reamer stone to make cutting edge smoother but it will still be a uncoated tool

I missed the HSS.

Tom