.060" Carbide End Mill = broken after second pass =HELP

[pontiac428]

60,000 rpm!!!!
Holy schnikies. I can run at 5% of that speed

Why are you spending money on carbide?! Annealed A2, D2, M2, O2, W2, whatever, is easy to cut with HSS, as you demonstrated to yourself with your slitting saw! One thing CNC machines do well is control feed rates. Smooooth, baby. No matter how much we want to try, herky-jerking the handwheels just can't be eliminated. I'd even suggest that carbide tools under 1/4" diameter have no business on a manual machine, for that precise reason. What do people have against HSS? I really want to know!

 

[Jeff.64]

Question for you smart-experienced guys

I ordered a .060" carbide end mill from McMaster. It has a 1/8" shank with a 1/2" length of cut.

I immediately realized I was running way too slow at 2,500 rpm. I'm hand feeding very slowly.

What RPM would you run? I can go as high as 4,800 but it's in the red zone on the mill. 3,000 is safe. Too slow?

The material is annealed A2. I already eased the cut by using a .032" slitting saw thinking this would help to not break the end mill
$35 down the drain. Grr$%^&*(!!

I know, why not use a slitting saw?? I just ordered a .062" from McMaster.
I want to learn from my mistake.

If you could enlighten me with any tips that come to mind you would make my day.
Thank you,

Jeff

I can't claim to be smart-experienced, but I did successfully cut an approximate 0.400" long by 0.0625" slot in a 1/8" thick O-1 using a 0.0625 end mill for an acquaintance twenty couple years ago. I was using a manual X2 minimill running around 4000 rpm. I took around 0.010" depth of cut at a time. I also predrilled each end of the slot first. I got lucky and did not break the end mill. I remember it to be an experience that I would not want to repeat. Very stressful.

If I had the wonderful machines in your list, I would make an trapezoidal shaped aluminum plate that would clamp onto the mill quill and on the small end, make clamping hole to accept a Proxxon IBS/E.

https://tinyurl.com/mu6v5xub

It has an aluminum nose perfect for clamping. It is very smooth running, unlike the Dremel hand vibrators I've used. Max speed is 20k rpm. On your part, I would cut away all but around 0.010" from the bottom and jam a shim in the cut slot, flip the part around and cut the remaining material starting in the through hole. The shim could prevent the slot springing shut and grabbing the end mill. And if it did, it would be easier to clean up the damage in the slot from the outside vs from in the clearance hole.

Or you can, depending on your max rpm of your lathe, mount the part on an angle plate attached to your cross slide. Put alignment blocks on the angle plate to aid in repositioning to cut the last 0.010" out of the bottom of the slot as in the above procedure.

Or if you can lock your lathe spindle, make a toolpost holder to mount the Proxxon IBS/E and cut the part on a face plate.

Or instead of the Proxxon IBS/E, use a toolpost grinder set up for ID grinding to hold the end mill.

I think the lathe cross slide would be easier to control than a mill table hand wheel / crank.

I would also don an Optivisor under a face shield to keep an eye on the chips in the slot.

Well those are my amateur suggestions for using an end mill.

In my modest shop, I would like you, use a 0.0625" slitting saw and cut almost through, re-orientate, pack a shim and carefully cut the small remaining material away.

It might be the lighting of the end mill.jpg shot of your part, but it looks like your mill could be slightly out of tram.

Happy New Year,
Jeff

 

[projectnut]

Another vote for the slitting saw. Over the years I've cut a number of slots as narrow as .014" as deep as .750" with a slitting saw. It took several passes, but with patience it worked out. I'm sure the arbor on my 1940's era US Machine Tools horizontal arbor isn't perfectly straight, but it's close enough that I can come within the desired spec when using an undersized saw and making a few passes.

 

[Janderso]

Why are you spending money on carbide?! Annealed A2, D2, M2, O2, W2, whatever, is easy to cut with HSS, as you demonstrated to yourself with your slitting saw! One thing CNC machines do well is control feed rates. Smooooth, baby. No matter how much we want to try, herky-jerking the handwheels just can't be eliminated. I'd even suggest that carbide tools under 1/4" diameter have no business on a manual machine, for that precise reason. What do people have against HSS? I really want to know!

I’m beginning to see your point.
I figured carbide would be the way to go because of it’s supposed to be more rigid?
It is also brittle as heck.

Making mistakes is my game man.

 

[pontiac428]

It's hard and holds an edge, but it doesn't deal with vibes and side loads so well and isn't at its best unless it's screaming fast. I've had small carbide mills pop instantly upon contact with the edge of a part from tiny amounts of runout that HSS would just shrug through. I'm not anti-carbide, but I only invoke the super material occasionally. I certainly don't need carbide for its wear resistance, just not enough machine cycles to see savings from tool life in my hobby shop. Tiny mills can't be sharpened easily either, so they are throwaways. If they're disposable, I'd rather lose them to wear than lose them to breakage. HSS is much more forgiving for breakage, so the cost of carbide in this case is tough to justify.

Jeff, goofs get their own line item in my shop plans. It's a part of the budget for me.

 

[talvare]

Hell Jeff, I have trouble not breaking carbide end mills twice that size. I agree with using a slitting saw for that type of operation. I have come to the conclusion that I don't have the skill or the appropriate machinery to reliably use those small carbide bits and I do have better success with HSS.

Ted

 

[homebrewed]

I've successfully used .0625" diameter carbide end mills in my X2 bench mill but it was slow going in every sense of the word. Shallow DOC's (as in, .005"/pass) and very slow feed at maximum RPMs. I avoid using small carbide EM's whenever possible. Power feed would take some (but not all) of the stress out of the job.

Sometimes the work configuration isn't compatible with a slitting saw so you're stuck with doing it some other way.

 

[Janderso]

Got it done.
I found a dull .064” slitting saw. Fed it .015” at a time. It followed the line for the most part but there is a slight deflection that I can live with.

 

[GunsOfNavarone]

I see Harvey Tool on Instagram and how TINY their endmills/drills get, they seem to specialize in these tools. From what I'm readiing sounds like your machine just doesn't have the RPM's available. Hats off for trying, I'd rather just throw $40 out the window than even try.
Just poke around on their site if interested...
Harvey tool

 

[projectnut]

When I built my lathe tool sharpening fixture, I used an .0315" end mill to make the 5* and 10* lines and an .015" end mill 1* lines. The 10* lines are .010" deep and took 2 passes. The 5* lines are .005" deep and took a single pass. the 1* lines are .005* deep and took 2 passes. I purchased 10 of each size thinking with my luck I would break several of them. As it turned out all the lines were made with a single end mill of each size.