Blue chips

[wawoodman]

I understand that blue chips are not a good thing; something is getting too hot.

Rockwell vertical mill.

Cutting 1018 cold roll steel. 1/2 inch, 2- flute, HSS end mill, end cut ~.015 deep, .250 - .375 wide. Hand feed, tried both fast and slow. ~800 rpm

Do I need to slow down the mill, slow down the feed, speed up either or both? I also tried a 4-flute mill with no discernable improvement.

Where am I going wrong?

[dallen]

check out toms videos he has one on the very thing your asking feed and speed

http://tomstechniques.com/

[Sunset Machine]

I like your numbers, but suspecting it isn't 1018. Slow down to 400 rpm and make sure the cutter is still sharp. Feed as slow as you can but still be making chips, not dust. It's easy to manually overfeed such a shallow DOC. .030-.050 deep might be more manageable while you're experimenting. Listen to it, feel the pressure.

There's a factor called "chip load". It runs about .002 per tooth, per revolution. A 4 flute cuts twice as fast as a 2 flute because you can feed the table twice as fast
(roughly speaking). RPM stays the same. You can calculate your feed into inches per minute (or seconds) and time yourself, just cutting air if you want.

Remember the first time you broke a tap or stripped a bolt? There's more to come.

[DaveH]

Normally blue chips mean the spindle speed is a little too fast - try 600 rpm. Of course the feed may have to be reduced.

For the same dia end mill, the faster the spindle speed - the faster the feed can be, the two are linked. However one cannot just increase the spindle speed and the feed and hope all will be well - it won't. Expressive spindle speed will blunt the HSS end mill very quickly and blue chips are an indication of this.
We are only talking HSS end mills.

Also have a look at this it may help.  http://www.metalworkingfun.com/thread-776.html
 
DaveH

PS I posted this a fraction of a second after Sunset posted

[wrustle]

I am also of the opinion it is not 1018 as your numbers are right in the ballpark.  

With a medium carbon steel you should be around 450-500 RPM.

Maybe try that and see how it works, that may be more an indication of what you're working with.

[wawoodman]

How would I tell the species? Online Metals sold it to me as 1018.

I'm thinking it's my fault, as well. I tried another new, sharp cutter (Niagara brand.) It was a thing of beauty, and I thought my problems were solved. However, within about a half an hour, it was noticeably deteriorating. The chips were tending towards blue, and I had chipped the ends of the flutes.

I did finish what I was doing, though, so now I can experiment.

[wawoodman]

DaveH,
I have read over your presentation in the past, and I really appreciate it.

I'm making a cut as shown in your End Mill picture. I'm doing it by coming down from the top, and then moving sideways. Go back to the start, lower depth of cut, repeat. Is that correct, or should I be moving in from the side, and then moving along my cut?

I think the rigidity issue isn't the problem, The Rockwell is a pretty beefy unit, although not a Bridgeport! I have suspicions about the vise, though. It's a 5" Kurt, purchased used. I don't think the jaws are toeing in at the top, and I'm having trouble getting work to seat firmly on the parallels. I've ordered a rebuild kit, and I'll see if that helps. If not, I'll have to consider a new vise.

[wawoodman]

Ed, it's a Rockwell 21-100.

[EdK]

(10-27-2015, 04:05 PM)wawoodman Wrote: Ed, it's a Rockwell 21-100.

Yup, I reread your first post and found where you said what mill you have so I deleted my stupid post.

Ed

[DaveH]

Wawoodman,
The way you are making the cut is fine and I don't think your vice is the problem.
I still have the feeling the spindle speed is too fast for the material.
Have you tried 400 rpm as suggested by Sunset.
Just remember milling with HSS has always been regarded as a slow process. Although better and quicker than a hacksaw and filing, tends to come out a lot squarer as well    
 
DaveH