Trying to mill 316 stainless steel tube

[Luke]

Afternoon everyone,

Today, I've tried to mill a flat along a bit of 316 tube, so that it can be screwed to a flat surface.

I don't know much about machining, I'm learning at every step.

I think I had a reasonable cutting speed, and I was using plenty of oil to try and keep things cool.

- 16mm four flute HSS cutter
- Approx. 800 RPM
- Feed rate probably something like 200 mm/min
- 10 thou depth of cut on each pass

The actual finish of the cut wasn't too bad - shiny, with swirls from the cutter visible, but not pronounced. If I didn't keep spraying enough oil, the swarf would get drawn under the cutter and 'smudge' until it was cleared.

I had two issues;
1) material was getting burred over, rather than being cut,either side of the work piece, and it wasn't just a whisker, I had to grind it off.
2) The corners of the cutter are looking pretty worn, I would say it's now blunt.

I think the two are related, but I don't know what to do about it. I tried a deeper cut, 20 thou was making the spindle bearings grumble, but then it is an old machine. Is HSS ok for cutting 316? and how?

Any help would be much appreciated.

thanks,

Luke

 

[Pete.]

Your speed is miles too high. You should be about 300RPM for a 16mm HSS cutter in Stainless IMO.

http://machiningtool.blogspot.com/2014/10/milling-metric-cutting-speed-calculation.html

This chart claims 18meters/min for 316. Your 16mm cutter has 50mm circumference so 18000/50=360rpm

 

[Luke]

A few photos of the cutter.

 

[Pete.]

Yeah that's gone straight past dead and waiting to be re-incarnated.

 

[Luke]

I've done a quick google and it looks like re-sharpening them isn't an easy task either.

 

[Pete.]

Post it to me and I'll re-sharpen it for you. It won't be quite as good as new but it'll at least cut metal properly.

 

[Luke]

That's very kind of you, I'll send you a PM.

Any ideas on what caused the heavy burring? Is that due to the cutter having lost its edge, or is it an issue with 316? Or something else I was doing wrong?

Luke

 

[Pete.]

Simply too much RPM. The tips of the cutter can't conduct away the heat generated so they melt.

What machine is it?

 

[Luke]

Sorry, I meant on the workpiece.

I'm coming to learn how HSS must be kept cool. I previously tried to machine down a part that must have been incredibly hard, because the last HSS cutter I destroyed just went orange, then black, as I went to take the first cut. That makes me sound like a complete rough-ar$e.

It's a Bridgeport that I rescued from going to the scrap heap. the motor had a short to earth, so I replaced it with an IEC frame size motor, with an adapter made from 4 or 5 bits of 8mm laser cut to make an inverted top hat, bringing the shaft down to the same position as the original, running off a 1ph to 3ph 1.1kW inverter, and an arduino controller that (should) calculate the correct cutting speed for the material and the cutter size. I now need to check what values I used, because I've toasted a few cutters.....

 

[Luke]

The last mis-hap;

https://www.mig-welding.co.uk/forum/threads/struggling-with-using-an-end-mill-for-facing

The early stages of the Arduino controller. It's in a box now.

 

[Pete.]

The last mis-hap;

https://www.mig-welding.co.uk/forum/threads/struggling-with-using-an-end-mill-for-facing

The early stages of the Arduino controller. It's in a box now.

Wherever you posted that thread on the forum, I don't have access to it.

 

[Luke]

Me either....

https://www.mig-welding.co.uk/forum/threads/struggling-with-using-an-end-mill-for-facing.53103/

Hopefully that's better.

 

[Pete.]

I had an emergency machining job to do for someone this weekend my mate needed a part modifying for his bike before he goes off the the IOM to watch the classic TT. After that I had a go at recovering these end mills for Luke.

He sent me two endmills, the one in the above pic and another. Both were very blunt and the tips were over heated. I ground the cutting edges back until I ground back past the rounded edges to provide a sharp cutting point at the tip. This was done very roughly to allow me to cut the tooth-forming gashes.

I'd never had to cut the gashes before because I've been binning cutters that had gone that far so this was a bit of a learning curve for me. I consulted the Clarkson manual for the setup and helpfully it says something like "the depth isn't important and experience will let you learn the setting for the wheel height". So after a bit of trial and error I have managed to re-cut the tooth forming gashes.

After that I re-cut the primary and secondary relief angles and as you can see in the photo below It's now a usable cutter, but it also shows that I needed to take more care with the setup of the gashing because it's left a little pip near the middle of the cutter. Pic shows the one cutter I've recovered and the second one which needs the same treatment.

 

[Luke]

Thanks for your help Pete, what's the coating for?

 

[Morrisman]

Thanks for your help Pete, what's the coating for?

To protect the cutter while being stored, handled, posted etc.

It simply peels off with a thumbnail when you need to use the cutter.

 

[Pete.]

Actually, it's a trick of the light but yeah, they will have a crocell coating when they are done.

 

[Luke]

Well two cutters that were very blunt now have nice edges on again.

Thanks Pete, really appreciated.



Luke

 

[Pete.]

My pleasure. It's not exactly a professional-looking result as I had to take a couple of passes at getting the tooth forming gash right but at least they live to cut metal again.