End Mill Snapping

[btu44]

I'm thinking your breaking end mills because the chip load is pretty heavy at .0015 per tooth. Thats typical for for a 1/4 EM. The chip load per tooth I see suggested for 1/8" EM in aluminum is .0005 - .001"

It's also good to check the tool run out for such a small tool. The slotting parameters I listed has a chip load of .0006". If theres something like .002" of run out, that can break EMs.

Here's 2 videos I did on runout if interested.
http://www.youtube.com/watch?v=2rur6oFaYhY]TTS Runout - R8 Collet.wmv - YouTube

[kevinro]

Hmmmm..... I think I would reconsider my position on GWizard! Your speed and feed values are quite a ways off. You should be going much higher RPM and much slower feed.

GWizard came up with 5100 RPM @ 12.24 for the .011 depth and .125 width.

GWizard has been going a pretty great job for me.

[Magnum164]

I think you guys are more interested in selling me on Gwizard than you are helping me to understand how to determine the proper RPM's and settings to select.. Did you notice where I stated I cut back to 12F and had no problems?


So for the Gwizard impaired let me ask the question again...

The parts are taking about 20 minutes each and I need to cut that down some. With the 770 is there an advantage to using a higher speed to increase the feed rate?

Any thoughts? I realize I can play with the settings all day long and run analysis in Gwizard. The stress engineers do that at work all day long. But at some point you either have to put the numbers to metal - which can be costly, or you can ask others who have been there and get a starting point and suggestions. Carbide was a good suggestion and perhaps using the higher speed rates. I'll start there and perhaps email the mfg to get some info while I wait for the bits to get here.

[TXFred]

The parts are taking about 20 minutes each and I need to cut that down some. With the 770 is there an advantage to using a higher speed to increase the feed rate?

Absolutely. Not only will you decrease your cycle time, you may get better looking parts. Carbide tools make prettier cuts at the right surface speed.

Every cutting tool has an ideal surface speed. This speed is determined by finish quality and cutter life. The smaller the tool, the faster you must run the spindle to get the right surface speed.

If you switch from HSS to carbide, the ideal surface speed increases.

So, look up your work and cutter materials, and find the ideal surface speed. Use that to calculate the ideal spindle speed. Then take that and your ideal chip load, and you can calculate the feed rate.

Frederic

[bobeson]

I think you guys are more interested in selling me on Gwizard than you are helping me to understand how to determine the proper RPM's and settings to select...

I'm not trying to sell GWizard; that's how *I* fiigure out my feeds and speeds, and I think you're hearing a chorus of voices saying "use GWizard!" not because we get kick-backs from Bob, but because GWizard works better than any almost other method for determining initial feeds and speeds. Machinists with years of cutting time have learned how to estimate their feeds and speeds pretty quickly, but unless you have that body of knowledge yourself I don't think you're going to get any better starting points than what GWizard has to offer, and that includes polling cnczone members. For myself, looking up feeds and speeds for a given cut takes only a few seconds; if I want to explore the parameter space I can fool around with optimizers and various "what-if" scenarios, but that all happens in a few minutes tops, certainly not "all day".

[dbrija]

As to the question of endmills, the 3 flute coated carbide from Maritool are nicely priced and make nice finishes.

[Magnum164]

As to the question of endmills, the 3 flute coated carbide from Maritool are nicely priced and make nice finishes.

I might try some, looks like I need to do some experimenting. I ordered some 2 and 4 flute from Monstertool. I could only find a 30DEG Helix so we see how they will do. I also ordered one coated to see how it does.

However, I realized why not do to my profiling what I am doing to the slots inside. I am hogging them out with a 1/4 coated EM then following up with the 1/8 EM just to get the smooth finish and smaller corner radii. It's also a heck of a lot quicker.... So why not profile my parts (actually its slotting) with the 1/4 EM then just follow up with the 1/8 EM for the radii as well. Would mean wasting more material but would cut faster.


Now on to the RPM issue. I can increase my RPM, but the runout issue has me concerned. I am not 100% sure my ER20 holders are balanced. I will have to go back and see what Tormach states about the higher RPMs and how to make sure everything is still in balance. I know they sell balanced ER20 collets for that reason.

And I still have a optical tach on the way.. I have never checked the RPM on my machine... Should get a baseline I guess.

[kevinro]

I think you guys are more interested in selling me on Gwizard than you are helping me to understand how to determine the proper RPM's and settings to select.. Did you notice where I stated I cut back to 12F and had no problems?

You asked a very legitimate question: How to determine the speeds and feeds for the tools. You got a very legitimate answer: With very few exceptions, we all use GWizard.

If you wish to do it without such a software tool, then you will have to spend time doing all of the calculations by hand. There are many variables to take into account that you will need to account for. It is tedious, requires digging through charts and graphs from manufacturers, evaluting the materials you are cutting, calculating tool deflection based on the amount of stickout from the tool, evaluating how much horsepower is available on your spindle, and much more.

You did state that you cut back to 12F and had no problems. If you had started with GWizard, you would have started at 12F and had, well, no problems.

Not trying to sell you anything. You can drive a nail into wood with your thumb, a rock, or a bowling ball. We are suggesting you use a hammer like the rest of us!

Kevin

[Magnum164]

Geez... And I thought being married was rough...

You asked a very legitimate question: How to determine the speeds and feeds for the tools. You got a very legitimate answer: With very few exceptions, we all use GWizard.

If you wish to do it without such a software tool, then you will have to spend time doing all of the calculations by hand. There are many variables to take into account that you will need to account for. It is tedious, requires digging through charts and graphs from manufacturers, evaluting the materials you are cutting, calculating tool deflection based on the amount of stickout from the tool, evaluating how much horsepower is available on your spindle, and much more.

You did state that you cut back to 12F and had no problems. If you had started with GWizard, you would have started at 12F and had, well, no problems.

Not trying to sell you anything. You can drive a nail into wood with your thumb, a rock, or a bowling ball. We are suggesting you use a hammer like the rest of us!

Kevin

[kevinro]

Geez... And I thought being married was rough...

I don't get it.

You ask a great question, and then are pretty rude to us when we answer honestly. Sorry I was unable to help you.

Kevin

[300sniper]

maybe i missed it. magnum, how did you come up with your initial rpm/ipm?

[Magnum164]

maybe i missed it. magnum, how did you come up with your initial rpm/ipm?

I think you and TXfred may very well have hit on my frustration. While you can enter any RPM and chipload and get numbers to enter into a program. How should I select them.

The 4K RPM was a starting point just to get the parts I had done... I generally try and use between 525 and the 10K (I think) RPM to keep from having to change my belt since I generally use smaller than 1/4EM's.

So based on what TXfred had suggested, perhaps I should have found a good surface speed to start with? BTW, I checked and the end mills were Interstate, so probably can work backwards from there and determine how I should have started.