End mill won’t cut, just dulls

gbyoung · Aug 28, 2018

Kind of confused as to why this is happening. Using a 9/16” dia., HSS TiN coated 2-flute end mill, I had just cut a 9/16” section out of a steel, rear, motorcycle suspension link. Basically did this with three plunge cuts, then a pass back and forth to eliminate the resulting radii. Piece is just under ¾” in width and the cut wasn’t made all the way through. I left ~1/16” of material per the customer’s request. No problems that I could detect and it cut as I was expecting.

I clamped up the second link to make a similar cut, and it wouldn’t cut. The bit just started to chatter and dulled. Thinking I had damaged the bit on the first link, I replaced the bit with a ½” wide coated one and the same thing happened.

Even tho’ it’s an odd shaped piece, I am 99% sure I had everything clamped up tight. Mill is a Bridgeport Series 1.

I should add that my experience level is minimal. Strictly a hobbyist.

Aggravated, and confused.

???????????

plastikdreams · Aug 28, 2018

Are you running the mill in reverse by chance?

Gobo · Aug 28, 2018

How hard is your workpiece? If a file bounces off, you are going to need carbide.

BobRenz · Aug 28, 2018

plastikdreams said:
Are you running the mill in reverse by chance?

Sounds silly, but it happens easily -

That happened to a friend of mine who used an old motor on a drill press - the drill bits didn't cut; they just burned. He tried new bits, then suddenly saw that the press was running backwards.

FredC · Aug 28, 2018

A lot of things can ruin a tool. Unknown hard material has already been mentioned, too many RPMs for the material for the material probably kills more tools too soon than anything else, unknown material makes it tough to choose the right speed what is appropriate for one is too much for another. Abrasive material, sand cast material can be full of sand sometimes, I did a couple of jobs in copper, boy was that abrasive. The copper material was not cast but cold drawn, just its nature to wear out high speed tools.
Expensive carbide tools are very easily chipped on a manual mill, if that option is chosen, have your ducks in a row as broken $70 cutter will just ruin your day.

Joe Pie · Aug 28, 2018

I have never been a fan of 2 flute end mills on steel. 4 flute minimum. What RPM are you running the cutter at?

DMF_TomB · Aug 28, 2018

gbyoung said:
Kind of confused as to why this is happening. Using a 9/16” dia., HSS TiN coated 2-flute end mill, I had just cut a 9/16” section out of a steel, rear, motorcycle suspension link. Basically did this with three plunge cuts, then a pass back and forth to eliminate the resulting radii. Piece is just under ¾” in width and the cut wasn’t made all the way through. I left ~1/16” of material per the customer’s request. No problems that I could detect and it cut as I was expecting.

I clamped up the second link to make a similar cut, and it wouldn’t cut. The bit just started to chatter and dulled. Thinking I had damaged the bit on the first link, I replaced the bit with a ½” wide coated one and the same thing happened.

Even tho’ it’s an odd shaped piece, I am 99% sure I had everything clamped up tight. Mill is a Bridgeport Series 1.

I should add that my experience level is minimal. Strictly a hobbyist.

Aggravated, and confused.

???????????

.
obviously you need to state rpm and feed rate and length mill sticking out of tool holder as well as many other things. most can look at a dull end mill and figure out why its dull

thermite · Aug 28, 2018

gbyoung said:
Kind of confused as to why this is happening. Using a 9/16” dia., HSS TiN coated 2-flute end mill, I had just cut a 9/16” section out of a steel, rear, motorcycle suspension link. Basically did this with three plunge cuts, then a pass back and forth to eliminate the resulting radii. Piece is just under ¾” in width and the cut wasn’t made all the way through. I left ~1/16” of material per the customer’s request. No problems that I could detect and it cut as I was expecting.

I clamped up the second link to make a similar cut, and it wouldn’t cut. The bit just started to chatter and dulled. Thinking I had damaged the bit on the first link, I replaced the bit with a ½” wide coated one and the same thing happened.

Even tho’ it’s an odd shaped piece, I am 99% sure I had everything clamped up tight. Mill is a Bridgeport Series 1.

I should add that my experience level is minimal. Strictly a hobbyist.

Aggravated, and confused.

???????????

Sounds like the "perfect storm", multiple challenges all coming together at once, here.

- HSS, not Carbide cutter, and you've said NADA about what cutting oil or coolant was used. HSS into steel, you can furnish flood cutting oil, flood coolant, or more frequent cutter funerals. Your choice, pick any one.

- "two flute endmill" doesn't sound like a "plunge" endmill, and you are starting out with a "plunge" operation. Three of them, per-each part.

- Second piece so dramatically different from first piece that was milled unremarked? Fresh endmill dasn't touch it EITHER? Hardness of at least the surface is BOUND to be different. It might not even be the same mystery metal alloy.

- Until you SPECIFY an alloy, and are certain that was what was supplied? They are ALL "mystery metal" to we chikn's out here in radioland. If, for example, you've gotten hands onto a Mangalloy? God may have mercy on your soul. There is no mercy, anywhere, for the cutters.

4CW

gbyoung · Aug 28, 2018

thermite said:
Sounds like the "perfect storm", multiple challenges all coming together at once, here.

- HSS, not Carbide cutter, and you've said NADA about what cutting oil or coolant was used. HSS into steel, you can furnish flood cutting oil, flood coolant, or more frequent cutter funerals. Your choice, pick any one.

- "two flute endmill" doesn't sound like a "plunge" endmill, and you are starting out with a "plunge" operation. Three of them, per-each part.

- Second piece so dramatically different from first piece that was milled unremarked? Fresh endmill dasn't touch it EITHER? Hardness of at least the surface is BOUND to be different. It might not even be the same mystery metal alloy.

- Until you SPECIFY an alloy, and are certain that was what was supplied? They are ALL "mystery metal" to we chikn's out here in radioland. If, for example, you've gotten hands onto a Mangalloy? God may have mercy on your soul. There is no mercy, anywhere, for the cutters.

4CW

Oh, I'm sure it was the perfect storm + throw in the inexperience level and it was waay perfect.

RPM = ~230 (per digital tach)
Yes, correct direction.
Bit advertised as being good for center cuts and plunging
2-flute HSS and HSS TiN coated is all the have at present
No coolant
Steel type unknown, but pretty damned tough; it's a suspension part
First link cut just fine, so was expecting the same for the second. That'll learn ya, huh?

DMF_TomB · Aug 28, 2018

gbyoung said:
Oh, I'm sure it was the perfect storm + throw in the inexperience level and it was waay perfect.

RPM = ~230 (per digital tach)
Yes, correct direction.
Bit advertised as being good for center cuts and plunging
2-flute HSS and HSS TiN coated is all the have at present
No coolant
Steel type unknown, but pretty damned tough; it's a suspension part
First link cut just fine, so was expecting the same for the second. That'll learn ya, huh?

.
some steel is a heat treated high strength alloy and very difficult to machine with hss end mills. usually have to use carbide. many steel parts are case hardened also difficult to machine
.
and some are in high gear and going fast when they thought they were in low gear going slow rpm

gbyoung · Aug 28, 2018

It’s really frustrating and debilitating when you float along after having a number of successes under your belt with aluminum and steel, then get thrown under the bus with a situation like this one. I wasn’t feeling cocky when I took this project on, but felt it was something I could do a quick turn on and get along with life.

Poop!

I was probably just lucky.

Another learning experience, eh?

I think…………..

gbyoung · Aug 28, 2018

Someone had responded earlier and commented that he sharpened mill bits as a side business. No longer see his post.

Was wondering if it would be worthwhile to get the ones that I have dulled sharpened? These are not high end bits, but ones I picked up through McMaster-Carr a couple of years ago. One is a Niagara, not sure of the second one.

If the fella reads this, please PM me and we'll go from there.

TIA

thermite · Aug 28, 2018

gbyoung said:
It’s really frustrating and debilitating when you float along after having a number of successes under your belt with aluminum and steel, then get thrown under the bus with a situation like this one. I wasn’t feeling cocky when I took this project on, but felt it was something I could do a quick turn on and get along with life.

Poop!

I was probably just lucky.

Another learning experience, eh?

I think…………..

LOL!

You been running steels without knowing their provenance and without cutting oil, you didn't get THROWN under no bus, Pilgrim!

You low-crawled under it yerself over sharp gravels on yer own bruised belly-fat!

Lessons learnt, first two year on former line-shaft horizontals, stinky old brown sulfurized oils fore I was even ALLOWED to mess with a vertical.

Back in the day, I thought an "end mill" was something Proctologists used for prepping for hemorrhoid transplants so the new tissue didn't reject the host.

Way some of the poor devils are abused to death - the endmills, not the hemorrhoids nor their aircraft carrier battle groups - I may not even have been wrong..

PeteM · Aug 28, 2018

You might take a small file (triangle, knife, etc. pattern) and lightly attempt to file the intended cut area. Hopefully there is a place in the already-cut link where you can try the lightest bit of a cut to compare. Could be one was through or case hardened, the other not so much? If the file cuts a small groove easily, the steel is soft. If it wants to skip over the surface, it's pretty hard. In between, you'll have to compare yourself.

Did you plunge into the material? Center-cutting is hard on a cutter, even when designed for that purpose. As you (actually the material) approach the center of the cutter, the speeds and feeds and chip clearance become all wrong. So, generally speaking, you want to cut normally from the side of the cutter, in -- avoid plunging straight down in -- when that is an option.

thermite · Aug 28, 2018

PeteM said:
generally speaking, you want to cut normally from the side of the cutter, in -- avoid plunging straight down in -- when that is an option.

+1 "CNC Guys" get the option of "programming" a ramped-in toolpath. They get damned good "mileage" out of their cutters, too! So much so, they even have the option of "wasting" some of it where more revenue for higher throughput easily justifies more spend on tooling.

Manually, you may have to do a bit of dancing on the con-trols.

Pays-off, similar manner, even if never quite as well.

The other thing that "pays off" is having lots of endmills. Not all the same, but SEVERAL each in the sizes you expect to use the most, and in more than one style.

ALL of them are "consumables", not heirlooms meant to be onpassed to the Grandchildren, still sharp.

JohnEvans · Aug 28, 2018

Unless you a large quantity or a local source ,resharping 1/2 and smaller mills is not cost effective time you add shipping etc. Plug for me here! Watch the tooling/parts for sale forum as I pick up mill lots when and where I can then offer here before Ebay .

Paolo_MD · Aug 29, 2018

If you really need to plunge-cut a piece, you're much better off by drilling a hole ~70-80% of the diameter of the endmill you intend to use and plunge-cut just a corona with your endmill. Much more effective and drill bits are significantly cheaper than endmills, especially if you buy industrial leftovers of odd sizes on eBay (for this purpose you need just to be in the ballpark, not a precise diameter.

Paolo

thermite · Aug 29, 2018

Paolo_MD said:
If you really need to plunge-cut a piece, you're much better off by drilling a hole ~70-80% of the diameter of the endmill you intend to use and plunge-cut just a corona with your endmill. Much more effective and drill bits are significantly cheaper than endmills, especially if you buy industrial leftovers of odd sizes on eBay (for this purpose you need just to be in the ballpark, not a precise diameter.

Paolo

Dang! Never ONCE crossed my mind, as the company toolroom clerk just ticked whatever we drew to the job slip code.

But I'm going to shamelessly emulate that, NOW .. as they come off MY dime, and drills? Have I EVER got DRILLS!

Thanks for that!

DMF_TomB · Aug 29, 2018

i have worked at places where 95% of parts are heat treated steel and or case hardened. even with carbide end mills you have to take extra care in milling. usually have to take very very light depth and or width of cuts

gbyoung · Aug 29, 2018

Appreciate all the comments.

I will try coming in (manually) from the side with the end mill cutting in the Y-plane to whack a notch in this mysterious piece of hard steel. 9/16" dia. carbide bit, dry (don't have coolant capability), can spritz with cutting oil - what would be the recommended spindle speed? I can set this with a digital IR tach.

????????

End mill won’t cut, just dulls

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