10mm (3/8") rougher screaming in 304SS

Madis Reivik · Jan 24, 2011

Hello !

I have a problem.
10mm rougher bit, depth 1/2D (5mm) running at 1900rpm, feed 200mm/min (8 ipm). Material 304 stainless steel, quite a small detail (about 3x2 inches).
Problem: when changing direction, endmill "screams". And after some work (maybe after 2 feet of cutting) it breaks.

I'm using manufacturer specified speed for slotting, so this should not be the problem. Also, I do not have vibration - I do not hear it and the endmill corners are good, i think that corners are first to go when there is vibration.

Is the problem in sharp corners ? I'm using GibbsCAM to generate the paths and it will generate 90 degree sharp corners.

I have Fanuc Robodrill T14.

Thanks for paying attention !

Dave K · Jan 24, 2011

When you call this a rougher, are we talking about a hog mill? Most endmills that are made for roughing, don't really have sharp corners, they are either radiused or angled.

Other than that, isn't the robo drill a 30 taper machine? If so, you may just be asking too much out of that machine.

Matt@RFR · Jan 24, 2011

How far is the endmill hanging out of the holder? Is it HSS or carbide (I'm guessing carbide from your SFM)? Sounds like it is deflecting quite a bit while cutting, then when it changes direction it is digging into the corner. If you can force at least small G2/G3 moves at each direction change, I think that would help.

This is where HSM excels.

Also, assuming this is a 4 flute endmill, your feed is pretty slow at .001" IPT, although it should work.

Madis Reivik · Jan 24, 2011

It is fixed in collet chuck and it is quite short. Yes, it is carbide. I think it is not bending much, since I have quite good vertical wall finish. Also, the rigidity of Robodrill (it has BT30 taper) should be enough for this endmill, since it does not have any vibration and it is running smooth and quiet when milling straight passes.

The rougher I'm using is a variable helix type and has slotted edge (not way edge). My supplier confirms that the same type of mill is used in lathe milling head, which has very low rigidity and gives good results.

So, are you suggesting that I should try to round path corners and the problem is when direction makes instant change from 0 to 90 degrees ? I too suspect that this is the case. Why is this ruining the tool ? Because of bending or too small chips ?

Actually, I have already two suggestions today to use HSS mills. I think I have to try. What is the physics behind this ? What kind of lifetime could I expect from HSS endmill in 304 SS ?

My wish is to find the cause of problem, not only to eliminate it by trial and error - I want to gain as much knowledge from problems as possible, it helps to forget the hundreds of Euros I spend to replace broken tools

Please excuse my bad terminology, the english we use in Estonia is probably quite different from english in United States

Dave Cross · Jan 24, 2011

Yeah this is why I hate Gibbs

You could look into getting the volumill plugin for Gibbs, so you have some HSM capability, its pretty much a must for stainless. Then you can crank it up to 6-8k rpm and 50-150ipm all day long, no joke.

Madis Reivik · Jan 24, 2011

I try to get rid of Gibbs. Since I use Solid Edge, CAM Express seems an obvious choice because it is integrated with Solid Edge. Hope this will help. But it takes a little time to get software licences.
Meanwhile, should I try to round the corners of paths that gibbs generates ?

Dave K · Jan 24, 2011

I think the suggestion of rounding the corners is a good one. The reason would be that, when one axis stops, and the other axis starts, your machine will have a fraction of a second pause between the moves. It may be so slight that you don't even see it happening, but it's there. And during that momentary pause, the tool gets a chance to "relax". It's at that point that you're probably getting the chatter.

Rounding the corners would eliminate this. As you reach the end of one move on one axis, the other axis has already begun moving to make the "arc" around the corner. This keeps constant tool pressure on the tool, and no time for that tool to have any "relax" moments.

Hope I explained that good enough. BTW, your English is fine.

John Welden · Jan 24, 2011

You're probably asking a bit much from your 30 taper. They're not called Robodrill because they're really good at milling.

A 5mm slotting cut with a 10mm end mill in 304ss, on a 30t machine is a big cut. Plus RoboDrills are relatively light machines. You could try taking 2.5mm depth of cut.

you said your tool holder is short, but not how short. It makes a big difference.

How are you plunging into the part? Helix? Ramp?

ipmmiller · Jan 24, 2011

Madis Reivik said:
It is fixed in collet chuck and it is quite short. Yes, it is carbide. I think it is not bending much, since I have quite good vertical wall finish. Also, the rigidity of Robodrill (it has BT30 taper) should be enough for this endmill, since it does not have any vibration and it is running smooth and quiet when milling straight passes.

The rougher I'm using is a variable helix type and has slotted edge (not way edge). My supplier confirms that the same type of mill is used in lathe milling head, which has very low rigidity and gives good results.

So, are you suggesting that I should try to round path corners and the problem is when direction makes instant change from 0 to 90 degrees ? I too suspect that this is the case. Why is this ruining the tool ? Because of bending or too small chips ?

Actually, I have already two suggestions today to use HSS mills. I think I have to try. What is the physics behind this ? What kind of lifetime could I expect from HSS endmill in 304 SS ?

My wish is to find the cause of problem, not only to eliminate it by trial and error - I want to gain as much knowledge from problems as possible, it helps to forget the hundreds of Euros I spend to replace broken tools

Please excuse my bad terminology, the english we use in Estonia is probably quite different from english in United States

Madis i've recently used the MariTool variable helix tialn coated (.250 em) in 304s at 1700rpm with a very conservative .064 depth and no flood coolant,just ran a vacumn behind it, and i ran the same em for about 8 hrs and cut a bunch of parts before it even moved the amp needle.They are made to run fast and dry in hard material,very quite also at higher rpm, but im still learning them so im conserative.This was on a little emco maier F1 mill,less than 1 hp, 30bt taper.I dont have alot of experience with 304 but i was very happy with the tool life and finish, im still using the end mill in crs.HSS on this machine at that rpm at any feedrate in 304 would have turned blue and died without flood in the first couple minutes.Try a Mari,you'll love it

Madis Reivik · Jan 25, 2011

Actually, I reduced depth and used another type (wavy edge) 4 flute rougher with higher rpm and feed. Quite good results, but after about 10meters of cut one tooth broke. Other tooths seem to have a small amount of sticky metal on them. No vibration. No plunging, side entry only.

Tool length from collet end is 35mm (1.36 inch)

Or maybe I should change to a 8mm rougher ?

Or maybe it is the case of thermal shock, since I use coolant (as recommended by tool supplier) ?

Also, the idea of using Volumill is good, I checked the website and it seems very logical approach.

I do not make much stainless on Robodrill, but I want to have a couple "proven" tools and feeds to use when there is demand.

I have one 10mm HSS + coating rougher bit too, I will check this out. The speed is not much lower compared to carbide, so it could be the solution.

Search

Largest Manufacturing Technology Community on the Web

Search

10mm (3/8") rougher screaming in 304SS

Madis Reivik

Hot Rolled

Dave K

Diamond

Matt@RFR

Titanium

Madis Reivik

Hot Rolled

Dave Cross

Titanium

Madis Reivik

Hot Rolled

Dave K

Diamond

John Welden

Diamond

ipmmiller

Cast Iron

Attachments

Madis Reivik

Hot Rolled

Similar threads