Spindle speed for a carbide end mill

[Inferno]

For the most part, I work with aluminum or other soft metals but I have a project I need to do. I need to modify some bearing blocks that are a mild steel and prefer to use my carbide bits over my Chinese HSS.
Since I work with mostly soft metals and use fairly small bits, I have my spindle speed set pretty high. It does the trick and I never really bother with the math.

Switching spindle speeds isn't fun. It doesn't take that long, I know, but it's still not fun.

Anyhow, I am thinking of using a 1/2" carbide end mill.
I believe I've calculated that I need 400-500 rpm to get the best cutting and not damage the bit. Does this sound accurate? I don't have a water cooled system

 

[WobblyHand]

Mild steel with carbide 1/2" end mill = 2670 RPM according to https://littlemachineshop.com/mobile/speeds_feeds.php
Go half that if you feel uncomfortable. 500 RPM is more like what you would use for HSS.

 

[twhite]

Mild steel with carbide 1/2" end mill = 2670 RPM according to https://littlemachineshop.com/mobile/speeds_feeds.php
Go half that if you feel uncomfortable. 500 RPM is more like what you would use for HSS.

Agreed. You would be fine going 1200-1500 in mild steel. Keep the teeth loaded do not let the cutter dwell at all. Same for HHS the dwell part.


Cutting oil is my blood.

 

[Inferno]

Well, it turns out that a carbide bit will cut through a bearing housing. It wasn't happy. Sparks flew.
I probably cut the life of the bit in half unless I have it dressed. I have another one so I'll wait to have them dressed.

I wasn't trying to cut the bearing race. I was trying to get close without cutting. I should have used my better glasses.

The project will work, though. When I cut the other one I'm taking the bearing out of the housing.

 

[markba633csi]

I use fairly slow speeds with carbide cutters on steel quite often- with cutting oil of course
Speed charts are often for production shops where time is money and they want the fastest material removal possible
For work-hardening materials like stainless yes, you need to observe the charts, but for soft steels it's not so critical

 

[erikmannie]

For us hobbyists, I believe that there is no penalty for choosing a conservative spindle speed in tandem with a conservative feed speed for a reasonable (non-aggressive!) DOC, and seeing how it goes.

If you don’t like how it’s going, you can change one variable at a time, and hopefully things will improve.

I always keep a composition book in the shop, & I definitely write down what works (including if the pleasing surface finish is either climb or conventional milling (which is reflected in my notebook something like “table moving away from the street” or “table moving South”)).

 

[Illinoyance]

FS Wizard for your phone is real handy. Free.

 

[Inferno]

FS Wizard for your phone is real handy. Free.

Downloaded. Thanks!

 

[pontiac428]

I like FS Wizard, but I take what it gives me and divide it in half!

To be honest, I mill like a hack with carbide- in steel, I crank the RPM and feeds until the chips come off gold with a touch of blue and the finish looks good. I don't mind letting the mill work a bit, but I still end up at half the speed the wizard gives me and it feels like rock-n-roll. HSS is another story, you gotta treat it nice or it won't last.