Troubles milling 4140 Normalized with BP mill

[keeena]

This is the project I'm working on: new dies for a DiAcro finger brake. Have to make 4 of these blanks then chop 'em up into various width fingers. This first blank I did solo to get a handle on working with the 4140 and order of ops, but now I should be able to gang the other 3 and go to town.

 

[Weldingrod1]

Band saw to remove the bulk? That's what I did with my Magnabend clamp bars

Sent from my SM-G892A using Tapatalk

 

[woodchucker]

I think this is probably the main reason I was having trouble. I also had much better results with indexable carbide which also made me realize my feed / chip load per tooth was probably too low for the solid EM. I think I was too conservative as I'm more used to using HSS and thought that charging in at high IPM would be bad. Nope!

No coolant; my mill isn't configured to handle it (no collection tray and whatnot). I would like to get a fogbuster setup at some point though.

Anyway, an update:

I switched to a 3/4" 3FL indexable carbide and woah: big difference. Chips a more normal blue color, zero sparking. I did have to use a small DOC (0.060") to avoid chatter. These inserts are designed for up to a ~0.375" DOC but I couldn't come anywhere near that in the 4140. I'm sure I could do better DOC with some tuning and if I shorten the EM. Here's a vid of the cutter in 1018 from the previous owner who I bought the mill from; looks to be about a 0.120"? DOC:

This feed rate is so much faster than the HSS than I'm used to...guess you just gotta send it.

I also tried out a 2", 4 insert indexable face mill using params from FS Wizard. Small DOC (0.040") but decent MRR due to the full 2" WOC. This one made perfect chips dark straw-to-blue and nice chip formation...really cut like a dream.
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I plan to buy a couple new solid carbide EMs since I would like to get a higher DOC for certain ops. I was getting pretty frustrated earlier thinking I might have to abandon this particular project; glad to be on-track.

if you don't need the square tip, get a radius on your end mill. it will prevent you from chipping the tip off as easily as they do. 0.030r, or 0.060r is a good starting point.

 

[rabler]

My general impression is that HSS is much more forgiving than carbide, even more so in a mill than a lathe. Carbide needs the right feeds as well as speed, and the range it'll work well is narrower than HSS, especially given that you quickly run into rigidity/chatter limits of the machine. But once you get it figured out, it is nice to use, especially as you move up from mild steel.

Ironically one of the best setup for my shop for milling with carbide is a 6" face mill with 10 SEHT inserts in a old 1944 K&T 3K vertical. Spin it at 500 RPM, so about 800 SFPM, and it'll chew through stock like crazy. That's what 9,000lbs and 10HP gets you.

 

[keeena]

Band saw to remove the bulk? That's what I did with my Magnabend clamp bars

Did you shove that bar thru a vertical bandsaw?!? How many hours did that take?! Its a nice cut - looks dead straight.

I was probably going to do the same thing though. Will need to get a new blade to replace the one that got smoked chopping the raw stock into blanks for milling.

if you don't need the square tip, get a radius on your end mill. it will prevent you from chipping the tip off as easily as they do. 0.030r, or 0.060r is a good starting point.

Yep, I've been collecting inserts from eBay as they come up. Most of my inserts have a 0.031 or 0.047" radius, but they come in radii up to 0.126". These projects are my own; radius is usually not too critical.

I know that round is one of the stronger shapes, but doesn't a larger radius result in larger cutting forces? The larger radii inserts are more readily available on eBay but I've been avoiding them.

My general impression is that HSS is much more forgiving than carbide, even more so in a mill than a lathe. Carbide needs the right feeds as well as speed, and the range it'll work well is narrower than HSS, especially given that you quickly run into rigidity/chatter limits of the machine.

You're right about manual machine limits. I've only been buying inserts on the tough side of the scale for what Walter-Valenite calls 'unfavorable milling conditions'...a.k.a. old knee-mill driven by an unskilled operator using questionable workholding

 

[woodchucker]

keena, I am talking about a radius on the end mill.. not inserts. And they cost more than a regular end mill, but will hopefully save you grief.

 

[Weldingrod1]

My cut took about 45 minutes for a 24" long. I set up a fence to do it. The cut off part spread away from the stock about 3/4" by the time I was done. Pretty weird. After bandsawing I narrowed the angle and smoothed it some with a grinder. I was really glad that I figured out this dodge; I really didn't want to try and mill that sucker!