What is your favorite end mill and usage

[Susquatch]

I just broke a pricey 1/2" carbide end mill making a vise stop. I didn't think I was doing anything wrong, and the mill was not complaining, but I'd rather not do that again anytime soon.

Thankfully, the part is not ruined. I can remove the damaged section by milling the jaw clearance step at that location.

So this begs my question:

Say you are squaring up and sizing some common cold rolled steel (bar, plate, etc), what is your goto end mill size and type for general milling?

How fast do you turn it?

What feed rate do you use? Since I don't have a power feed, just a general comment here would do. Eg, very slowly or just below complaint, slowly enough so it purrs, fast enough so it buzzes, etc.

How deep are your standard cuts?
(20 thou at a crack, 30 thou, 50 thou, as deep as I need but temper my feed rate to match the depth, etc

How much of the diameter of the mill bit do you use per pass? (3/4, 1/2, 1/3, 1/4, etc).

Any and all advice and other info will be appreciated and absorbed like a hungry sponge.

 

[RobinHood]

Here are the recommended speeds & feeds out of the SOWA tool catalogue for plain and coated carbide end mills.



For 1/2” end mills, I usually use 1200 rpm and up to 15”/min feed rate.

When side milling, the engaged length is 1.5 D max and 0.1 D depth of cut. (This info is also out of an old SOWA catalogue, for a HSCO end mill).

 

[PeterT]

There is lots of speed & feed & DOC info on the internet like RobinHoods guidance. But stepping back a bit, if you determine you were generally in the range, breakage can happen for other overriding reasons:
- part is not secure or allowed to flex, too much part stick out and/or tool stickout, to much tooth load which flexes the part or EM, insufficient tool grip
- mill table: if traversing X, best practice is to lock Y & of course Z
- feed direction: I think already discussed but safer to conventional mill at least until finishing. Climb milling requires both rigidity & low float movement
- older mill play: leadscrew/nut float. Some of this can be minimized with table lock but movement is movement & if the tool is free to dig in can dig it feeds on itself until something give

I'm kind of fond of these roughing EMs. They are more tolerant of higher removal rates & actually easier on your older/looser/lower HP machine. Nothing wrong with carbide at all but they are more brittle so more sensitive to all the other factors.

 

[Susquatch]

Here are the recommended speeds & feeds out of the SOWA tool catalogue for plain and coated carbide end mills.

For 1/2” end mills, I usually use 1200 rpm and up to 15”/min feed rate.

When side milling, the engaged length is 1.5 D max and 0.1 D depth of cut. (This info is also out of an old SOWA catalogue, for a HSCO end mill).

The charts are solid gold. Thank you!

The half inch data you gave me previously fits nicely with this. All except the feed rate. "up to 15" per minute" is 1/4" per second. The upper end of that seems crazy fast to me. But maybe for surface skimming it's ok. After all, you did say "up to". Nonetheless, I think I'll stay well shy of that till I get my sailor's legs.

How much of a cut (depth and width) would you normally take per pass when squaring up stock with a 1/2" end mill?

 

[YotaBota]

He's an interactive "feed and speed" chart from Little Machine Shop
https://littlemachineshop.com/mobile/speeds_feeds.php

 

[Susquatch]

....... older mill play: leadscrew/nut float. Some of this can be minimized with table lock but movement is movement & if the tool is free to dig in can dig it feeds on itself until something give

I'm kind of fond of these roughing EMs. They are more tolerant of higher removal rates & actually easier on your older/looser/lower HP machine. Nothing wrong with carbide at all but they are more brittle so more sensitive to all the other factors.

I suspect the worn feed screw/nut is what bit me. It doesn't seem to matter which way I feed the work, the bit wanders around more than I think is reasonable. I was unlocking the Y lock to take a corner and mill in the Y direction when it happened. My guess is that the end mill took a bigger gulp of material than it could handle when I did that. Not only did the bit break, but there was a pretty darn big bite (about a 16th or so) that didn't finish getting removed. My table has just over a tenth of an inch free play on both axis. I have tried to figure out how the table could have accumulated that much freeplay to "let loose" when changing directions, but am left empty handed. In my mind, it should not have grabbed, it should have walked away. That's why I'm wondering about the depth and width of a normal cut. I am suspicious that I was cutting too wide and that generated some endplay movement that wouldn't happen with a cut less than 1/2 the width of the bit.

I've become pretty darn good at doing precision work with my lathe. But I am finding that a lot of it doesn't translate well to the mill.

I do like your idea of using a roughing bit for the rough work. I'm not sure how that plays out on multiple parts though. Wouldn't it also double the number of setups because it adds a finish pass to everything?

 

[Janger]

I would use HSS a lot to get your sea legs. HSS is more forgiving and slower. Mainly though if you break one it isnt a calamity like breaking a expensive carbide one. Dull cutters also are much more susceptible to breaking.

 

[Janger]

Oh if your table moves that much the lead screws and nuts need to be checked. Make sure you are not climb milling conventional mill only.

 

[YYCHM]

I've had the best luck with 2 flute HSS and they are the easiest to re-sharpen.

 

[Janger]

My two goto EMs are a 1/4 4 flute carbide and a 12mm 4 flute carbide. I use them constantly. Also frequently use two different 2” facing mills with inserts. One with 5 inserts of 20 edges 10 per side donut shaped for steel. And another with aluminum inserts.

 

[Janger]

Check out this table from toms techniques:

http://tomstechniques.com/reference/

http://tomstechniques.com/wp-content/uploads/2014/12/CuttingSpeeds.pdf

I found his videos helpful too to get started.

 

[YYCHM]

My two goto EMs are a 1/4 4 flute carbide and a 12mm 4 flute carbide. I use them constantly. Also frequently use a two different 2” facing mills with inserts. One with 5 inserts of 20 edges 10 per side donut shaped for steel. And another with aluminum inserts.

You're talking about your CNC mill correct? Do you even have a manual mill now, I know you had maybe three over time?

 

[PeterT]

My table has just over a tenth of an inch free play on both axis. I have tried to figure out how the table could have accumulated that much freeplay to "let loose" when changing directions, but am left empty handed.

IMO that is a lot & needs to be dealt with. Pulling side to side like that is a good way to get a feel for slack especially if you have an indicator mounted to quantify what you are suggesting is 0.100" on both X & Y axis. Having float on both axis is double the fun because it is free to roam in an area as opposed to just a line as if only one axis had wear & the other locked. However its those temporary unlock transition moments when you set up for another traverse (just like you described) where the surprise can bite you.

Most people phrase this effect it in terms of dial backlash, its really the same thing. Its nice if you have DRO for following test but can do as easily with DTI in spindle against a reference block edge.
- dial in-feed direction only, say 3 turns so leadscrew backlash is fully taken up, don't reverse dial direction during process
- stop dial on handy dial reference like zero
- zero the DRO/DTI at this exact same spot
- slowly reverse handwheel until DRO/DTI moves off its null position, make note of how much handwheel dial movement has occurred (yours might be close to 0.100")

Video shows the ballpark shortcut without a DTI/DRO but I like the reference method more because its more repeatable & precise for what I also recommend: Repeat this at different spots on your leadscrew like 1/3, 1/2, 2/3 table displacement positions. You may find the wear is in concentrated in the middle most used area. Good to know but doesn't usually change the strategy or remedy if excessive wear is the issue. Next you need to know if you can dial this out acceptable with leadscrew nut anti-backlash adjustment as per video, so try that first.

If the available anti-backlash has been bottomed out by years of increased adjustment, then you need to pull LS assembly to examine. If you are lucky the majority wear will be confined to the brass/bronze nut (=sacrificial wear material). But if its also the LS threads, not at all unheard of, its new leadscrew time & usually do the nut as well so they are a happy low tolerance couple. I should have mentioned the dovetail gib adjustment also factors in this, but not really. Its more a tightness of fit to dovetails & angular table float. Some people crank up the dovetail tightness so it feels stiffer & floats less, but you are not fooling the leadscrew wear if that's the issue. Worse yet table can get sticky when too tight & the cutting action can easily kick the table through its float range & nasty surprise time. Wrecked part, broke tool etc. But you If you have that adjusted the gibs OK, suspect the focus is on lead screw / nut.

 

[PeterT]

I've become pretty darn good at doing precision work with my lathe. But I am finding that a lot of it doesn't translate well to the mill.
I do like your idea of using a roughing bit for the rough work. I'm not sure how that plays out on multiple parts though. Wouldn't it also double the number of setups because it adds a finish pass to everything?

A worn leadscrew / nut on a lathe manifests itself into problems similar to a mill actually. Float on a lathe means the cross slide / compound / travel can be drawn in & out of the work if allowed to roam. At minimum usually results in variable finish, variable dimensions, tool chatter.... In more tolerance specific operations like threading or especially parting off, same potential for similar WTF surprise moments.

The roughing EM is something I'd encourage to try but not a magic solution to a more fundamental machine issue. Roughers make more efficient chips for the same feed / power so generally less stress on everything. The core is thicker so more rigid, less deflection. They are reasonably priced (I only have clones). If I don't care about a parts aesthetics or fit I leave it with the little stripes resultant from side milling. Or actually liftthe table a smidge & finish pass removes a good portion of stripes. Otherwise yes, you rough with this & pop in a regular EM for finishing. So an economical strategy is if say 1/2" is your go-to EM size, nice to have the same in rougher so all the setup should be the same. just a 30 sec tool change & back in business. Finishing means measuring the part directly & adjusting the settings anyways. All EMs have tolerance +/- nominal spec. If the whole job will only take 10 minutes just use your your go to 'good' tool. But of course you will wear it faster. Its kind of an axe > saw > plane type principle to use woodworking analogy.

 

[Susquatch]

I would use HSS a lot to get your sea legs. HSS is more forgiving and slower. Mainly though if you break one it isnt a calamity like breaking a expensive carbide one. Dull cutters also are much more susceptible to breaking.

I prefer hss on my lathe. So it's easy to convince me of that. I think the only meaningful negative is that I can sharpen my hss lathe bits. I have no idea how to do that with mill tools......

 

[Susquatch]

Oh if your table moves that much the lead screws and nuts need to be checked. Make sure you are not climb milling conventional mill only.

Counterclockwise around the part from outside to inside. Right?

Preferably less than half the bit diameter at a crack. Right?

 

[YYCHM]

I prefer hss on my lathe. So it's easy to convince me of that. I think the only meaningful negative is that I can sharpen my hss lathe bits. I have no idea how to do that with mill tools......

https://canadianhobbymetalworkers.com/threads/end-mill-sharpening-jig-project.2444/

 

[Susquatch]

I've had the best luck with 2 flute HSS and they are the easiest to re-sharpen.

This I would never have guessed. I think every bit I have is four flute.

I will take your advice and get some 2 flute HSS bits.

Sharpen? You can sharpen them? Holy cow! It would be a miracle if I were able to do that right!!!

 

[Susquatch]

My two goto EMs are a 1/4 4 flute carbide and a 12mm 4 flute carbide. I use them constantly. Also frequently use two different 2” facing mills with inserts. One with 5 inserts of 20 edges 10 per side donut shaped for steel. And another with aluminum inserts.

I would have been afraid of a 1/4" end mill. But I'm willing to try it. 12mm is pretty close to 1/2.

I dunno if I'm ready for a big facing bit of any kind. But I do have a two inch fly cutter with a hss bit in it that I got in an auction lot a long time ago. I've never used it.

 

[YYCHM]

I would have been afraid of a 1/4" end mill. But I'm willing to try it. 12mm is pretty close to 1/2.

I dunno if I'm ready for a big facing bit of any kind. But I do have a two inch fly cutter with a hss bit in it that I got in an auction lot a long time ago. I've never used it.

Fly cutters work really well for sweeping large areas give it a go. I can get a better finish with my fly cutter than my 1" and 2" carbide insert facing endmills.