First day with new carbide end mill

[DPittman]

I was milling out a slot in some stainless steel with a .250 carbide end mill. It was going smoothly I thought...but I backed out to make the slot a bit wider and it snapped the end mill. I was milling dry and although I was going slow it was getting hot and it appears some swarf is welded to the sides see picture.
I dont want to remove the piece from the setup and am hoping to be able to use the broken end mill to continue to widen the slot by .062" on both sides. I have the length needed I just need to make the slot wider now. ⁰

Looking for suggestions on how to proceed.

 

[Chipper5783]

How much did you have sticking out? Do you have a rigid set up? At the time the end mill broke were you climb milling or conventional milling? Swarf and re-cut can give you major problems (the #1 reason for flood coolant is to move the chips away) - I assume you can't use flood coolant so an air blast is a reasonable alternative. Cut the end mill off and carry on.

 

[DPittman]

How much did you have sticking out? Do you have a rigid set up? At the time the end mill broke were you climb milling or conventional milling? Swarf and re-cut can give you major problems (the #1 reason for flood coolant is to move the chips away) - I assume you can't use flood coolant so an air blast is a reasonable alternative. Cut the end mill off and carry on.

I had quite a bit sticking out and think I could have done better there. Yes fairly rigid setup and taking pretty light cut. I call what I was doing a conventional cut not climb milling but I'm not sure that is quite the right term as the cutter was cutting on 3 sides of the mill. I plunged the cutter in and then moved y axis the length of the slot.
I've got more milling on the other side to do....the brown piece is the original plastic piece and im making the replacement out of stainless steel. Picture shows top and bottom of the pieces.

 

[DPittman]

I dont have a v groove block thingy to clamp this piece in....this is the only way I can think of holding the piece to mill the remaining flat spots. ....I dont think this clamping method is legit?

I need to use the milled flat spot on the bottom of the piece as the reference to get things straight.

I suppose I could turn the piece on it side in the vice and mill the end flat spot successfully but the middle channel has got me baffled.

 

[DPittman]

Would this be okay for the middle channel milling?

 

[YYCHM]

Would this be okay for the middle channel milling?

I'm thinking NOT. How about clamping it directly onto the table?

 

[Chip Maker]

What was the cutter rpm. You should be using coolant especially with stainless. Try plunging the slot at .020" at a time full depth (with a new cutter). Should be running at a minimum of 500 rpm. Then come back and run the cutter at the same x,y settings followed by widening the slot in .010" increments. When you widen the slot, both at the beginning and end plunge the slot. When you do the spring cut, you won't need to plunge.

 

[DPittman]

I'm thinking NOT. How about clamping it directly onto the table?

I didn't think of that! Thats why I ask here....folks always have ideas.

 

[DPittman]

What was the cutter rpm. You should be using coolant especially with stainless. Try plunging the slot at .020" at a time full depth (with a new cutter). Should be running at a minimum of 500 rpm. Then come back and run the cutter at the same x,y settings followed by widening the slot in .010" increments. When you widen the slot, both at the beginning and end plunge the slot. When you do the spring cut, you won't need to plunge.

Rmp was 1200. No coolant. I'll try to figure something out.

 

[Tom Kitta]

for 1/4 carbide RPM was low. I usually run 1/2 at around 1200 rpm in stainless. For 1/4 try at least 2000. This is actually considered slow even for dry.

Your endmill looks like its a 2 flute for aluminum - it is definitely not for SS. Uncoated carbide 2 flute == AFAIK aluminum. Can use on steel in "emergency" but from experience I can tell they do not last long at all.

Breaking endmill like this usually is due to some sudden high load - as in your endmill caught something or something moved. Most people are not running their endmills hard. Running "hard" is possible with tiny endmills even when careful - like 1/8.

Fortunately you can get replacement 6mm carbide endmills for steel for around... 6 CAD max.

 

[DPittman]

for 1/4 carbide RPM was low. I usually run 1/2 at around 1200 rpm in stainless. For 1/4 try at least 2000. This is actually considered slow even for dry.

Your endmill looks like its a 2 flute for aluminum - it is definitely not for SS. Uncoated carbide 2 flute == AFAIK aluminum. Can use on steel in "emergency" but from experience I can tell they do not last long at all.

Breaking endmill like this usually is due to some sudden high load - as in your endmill caught something or something moved. Most people are not running their endmills hard. Running "hard" is possible with tiny endmills even when careful - like 1/8.

Fortunately you can get replacement 6mm carbide endmills for steel for around... 6 CAD max.

Thanks for the info....I've got a 4 flute 12mm coated carbide that I will be trying next.

 

[PeterT]

Some ideas
This might be a good application of a finer tooth roughing end mill to first make the center slot in consecutive passes & save your carbide EM for edge finishing the slot sides once the material is hogged out. I've always found roughers cut efficiently, make less vibration & better chips, especially tougher materials. They just seem easier on everything especially when you don't have many great clamping setup options, which you don't. The milled flats should be fine with the carbide.

Possibly did the EM get grabby when the slot broke through to the center bore? Sometimes machining has to go bass-akwards counter-intuitive. For example make the slot blind & do the flats while you have a solid rod chunk & do the through bore second op where you have a chuck or collet to grip lots of OD surface area. I'm not saying would have solved this problem or been easier, but always think that way: what is the toughest operation where you can utilize the mass to your advantage but still have reliable setup options a few steps ahead.

Generally I like to use Vee blocks on round things with biggish removal features if possible. Again your part may not lend itself to vee blocks because you are flipping to different orientations that have to be square or perpendicular to one another. But the principle is Vee blocks provide 4 lines of contact, vise jaws only 2, mill table & clamp kind of 1.5 depending on the strap. Arguably the vee block contact lines are shorter than vise jaw span but typically vise jaws provide a bit of top squeeze which means lateral plus a bit of downward clamping goes through the vee face to the round part. And this may save resting the round part on a parallel or partial parallel.

You probably are but just in case - always lock the non-moving mill table axis so it cant float or be drawn into the cutter. All it takes is a couple thou of grab & the EM usually loses.

Sometimes a slip of heavy paper between vise jaws & part can make a beneficial difference between gripping a part for duration of machinining. It provides some friction factor.

Good luck, looks like you were almost there

 

[DPittman]

Some ideas
This might be a good application of a finer tooth roughing end mill to first make the center slot in consecutive passes & save your carbide EM for edge finishing the slot sides once the material is hogged out. I've always found roughers cut efficiently, make less vibration & better chips, especially tougher materials. They just seem easier on everything especially when you don't have many great clamping setup options, which you don't. The milled flats should be fine with the carbide.

Possibly did the EM get grabby when the slot broke through to the center bore? Sometimes machining has to go bass-akwards counter-intuitive. For example make the slot blind & do the flats while you have a solid rod chunk & do the through bore second op where you have a chuck or collet to grip lots of OD surface area. I'm not saying would have solved this problem or been easier, but always think that way: what is the toughest operation where you can utilize the mass to your advantage but still have reliable setup options a few steps ahead.

Generally I like to use Vee blocks on round things with biggish removal features if possible. Again your part may not lend itself to vee blocks because you are flipping to different orientations that have to be square or perpendicular to one another. But the principle is Vee blocks provide 4 lines of contact, vise jaws only 2, mill table & clamp kind of 1.5 depending on the strap. Arguably the vee block contact lines are shorter than vise jaw span but typically vise jaws provide a bit of top squeeze which means lateral plus a bit of downward clamping goes through the vee face to the round part. And this may save resting the round part on a parallel or partial parallel.

You probably are but just in case - always lock the non-moving mill table axis so it cant float or be drawn into the cutter. All it takes is a couple thou of grab & the EM usually loses.

Sometimes a slip of heavy paper between vise jaws & part can make a beneficial difference between gripping a part for duration of machinining. It provides some friction factor.

Good luck, looks like you were almost there

I do have a roughing mill but wasn't sure about using it or not.....my inexperience.
I plunge cut a hole to the center bore and then traversed up the length of the cut and all was good. It was when backed out just a wee bit then the EM snapped. I suspect that it was as suggested,the backlash of the table and the fact there was welded swarf on the side that the now climb milling operation was too much for the long end mill.
Yes I had the y and z axis locked. No coolant and apparently running too slow rpm and more stick out of EM then was necessary. I'm learning....always the hard way.

It probably wouldn't hurt to use the roughing EM to get the bulk of the material off first and then clean up with the carbide even for the flat milling then huh?

 

[kevin.decelles]

Save the carbide . Watched enough goetswinter YouTube to know you can make more tools out of that. He’d probably take 15 minutes and make a metric dovetail cutter accurate ti 0.0002


Sent from my iPhone using Tapatalk

 

[YotaBota]

What are you using for a speed/feed chart?
Here is a link to a user friendly chart at LMS;
https://littlemachineshop.com/mobile/speeds_feeds.php

 

[DPittman]

Well I got er done..well a couple of small things to do but the machining is done. I'm happy with how it turned out. . As with most of my projects, I learned as I went, it took far longer than what the project is worth but it was time enjoyed!

It is a breech/receiver for a cheap pellet pistol that isn't worth the work it took to make this but that was beside the point.

 

[RobinHood]

Hey, if it is functional, and you had fun and learned something - I would call that a good job any day.

 

[Tom O]

Yep a good learning experience is the best time waster.

 

[PeterT]

Looks good. Ya now that I see the proportions better, there is no way you could bore the hole as a second operation without creating a different flavor of grief.
Maybe I missed it but what alloy of stainless is it?

 

[DPittman]

Looks good. Ya now that I see the proportions better, there is no way you could bore the hole as a second operation without creating a different flavor of grief.
Maybe I missed it but what alloy of stainless is it?

I haven't a clue what alloy of ss it is. It was a small chunk I had on hand that was given to me. Its totally non magnetic ( not all ss is non magnetic) . I was going to make it out of brass because it is so nice to work with but I think the stainless steel looks great and doesn't dull like brass ( either material is overkill for this particular project but it was a fun thing)