Broke a cutter, not sure why (G code in here)

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ctwo
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Re: Broke a cutter, not sure why (G code in here)

Post by ctwo » Mon Jan 30, 2017 2:13 pm

I'm sure I need some new cutters, so I bought some from ebay. We can still blame the cutters because they were inexpensive and likely from Asia, but were shipped from somewhere local. 2 flute carbide and high helix.

I was using lazycam to create a spiral toolpath. The tool came down -0.150" DoC centered on the outer edge of 1" aluminum round bar vertical in the vise. Then the tool cuts a spiral path inwards, 0.020" per rev. It is looking good except for the large chip pushing off ahead of the cutter. I am conventional milling and getting small chips along with a single large one that I think is a thin part of the OD surface just not getting cut off. I do not know how to make this lazycam change the spiral direction. At about 3/4 way around, the end mill snapped off right at the collet.

At that moment, 1/8" cutter with 3/4" flute length, 1/8" shank, 0.150" DoC, not quite a full slot, but 0.0775" (I forget this term, but how much of the end mill diameter in the cut) when it broke. 6 ipm, 3k RPM, and I measured run out at the tip was 6 tenths. Doesn't seem like it should have broke, but that is about the hardest I'd push that end mill and expect it to survive.

I loaded a 2 flute, one flute chipped, 3/16" ball end mill and ran the code again and have a nice clean cut. I was getting small chips and it felt like this end mill could take a lot faster feed.
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GlennW
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Re: Broke a cutter, not sure why (G code in here)

Post by GlennW » Mon Jan 30, 2017 5:43 pm

Your feed rate was double what it should have been for a 1/8" 2 flute cutter at .150" DOC.
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Re: Broke a cutter, not sure why (G code in here)

Post by ctwo » Mon Jan 30, 2017 7:45 pm

My spreadsheet does not have a field for that other parameter (either one, actually), and there must be a difference between full slot at 0.150" DOC and a few thou axial DOC at 0.150" DOC (light side milling).

I just guessed at 6 ipm because that was around the numbers I've been getting before. So, I guess the terms I need to account for are Axial Depth of Cut and Radial Depth of Cut. I think I was supposed to assume max axial depth was no more than 1/2 diameter up to full slot. I also expected the cutter to come down and just touch the side of the stock, and slowly spiral inward only 20 thou.

Would these parameters be additive to the actual chip load and thusly accounted for? I do not see these parameters in other calculators. Perhaps a simple adjustment is to just multiply the feed rate by tool radius/DoC.
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RET
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Re: Broke a cutter, not sure why (G code in here)

Post by RET » Tue Jan 31, 2017 9:30 am

Hi ctwo,

Yes, I'm pretty sure the feeds are additive. As Glenn says, you are still trying to push too hard. If it were me, I would start out at 1" per min. or even less and see what kind of finish & performance I got before trying to increase the rate. I would also use climb milling. I use it almost all the time. Don't be hung up on trying to get anywhere near commercial speeds. If you can be successful at a slower rate, ultimately you will be farther ahead than if you try to push too hard and break something. The ball end cutter sinks much better because the ball end acts like a drill. With it, you should be able to sink straight down with no problems. In some applications, it might even be easier to run the program first with a ball end cutter, then change cutters and go back and rerun the program again to get what you want.

Climb milling gives a better finish and is easier on the cutter which also stays sharp longer. To use it however, you have to have no give at all in your machine. If there is any play, you WILL break the cutter.

Why don't you just write the code to do what you want instead of using spreadsheets etc? Break the circles/spirals or whatever into 90 degree sectors or less. That seems to be what the 3D cad programs do to get the shapes they want. They have little bits of code that all hang together to get the final result.

Hope this helps.

Richard Trounce.

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Re: Broke a cutter, not sure why (G code in here)

Post by ctwo » Tue Jan 31, 2017 9:54 am

GlennW wrote:Your feed rate was double what it should have been for a 1/8" 2 flute cutter at .150" DOC.
Darn, now 6 ipm does not have much meaning to me on paper, but when I see the cutter moving it looked too fast, so I reduced the feed to 40%, 2.4 ipm.
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Re: Broke a cutter, not sure why (G code in here)

Post by ctwo » Tue Jan 31, 2017 10:06 am

RET wrote:Hi ctwo,
Hi Richard, It's not that I'm trying to push to commercial speeds, but that's just a reference. I'm sure a commercial operation would have been running something like what I was trying to do at speeds over 100 ipm. I tried 6.

I am making a silly trinket, just embossed letters and shapes on aluminum. With the outline of the letter and arc in Z, that is a very complicated thing to program just via typing in notepad. The spreadsheet will generate much of tool paths with formulas that I create. The tool paths are usually correct, so there are other problems. This time I was using LazyCam, part of Mach3, and there is NO provision to make that program do this climb milling. I tried Image2Gcode but it would not run on my Win10 system. Even the F-engrave started running very slow now in Win10.

If I run this at 1 ipm, I will have a part that could be sold for maybe $5, but with a couple hours of machine time. OK, we are not making money here and that is not the point. It should not take hours to mill these kinds of things. I can reference amateurs using extruded aluminum framed router tables that making parts magnitudes faster than I.
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Re: Broke a cutter, not sure why (G code in here)

Post by GlennW » Tue Jan 31, 2017 10:44 am

It's all about spindle speed, and you are limited to way below what you need for that size cutter.

An 18K router could run about 19 ipm feed rate.

Here's what it looks like:
Cut Data.jpg
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Re: Broke a cutter, not sure why (G code in here)

Post by ctwo » Tue Jan 31, 2017 11:57 am

Well, looks like HSMA is 3 ipm. I believe I was running 2.4 ipm. I guess we go back to looking at the spindle taper? It is tight though.

I was looking at the cutter under mag. It lasted less than 3 inches. The flute corners show very slight signs of wear, one flute was a little darker. I was only pleased to see wear on both flutes since I did have some tool runout. I also noticed some aluminum welding about 1/3 up from the tip. Just a very slight amount on the lip and trailing relief. I had brushed on cutting oil at the beginning, watched about 1/2 way around, then walked away about 3 steps before I heard the snap. I bet it would have made it if the WOC was not more than 50% tool diameter. After this first run around, the rest of the cuts were only going to be 20 thou WOC and varying DOC less than 0.150.
Standards are so important that everyone must have their own...
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Re: Broke a cutter, not sure why (G code in here)

Post by ctwo » Tue Jan 31, 2017 3:30 pm

I bought a 20 pack of these 1/8" cutters. I have updated my program to not take as wide a cut on the initial trip around the stock (I moved the starting diameter out to 1.1" so should only see ~20 thou WOC). I'm tempted to run it at the same speed, but may program 1 ipm and see how it goes. I may be able to take video. My camera limits to 10 minutes of HD, but it's great because I can set frame exposure to 1/6000 sec so if you pause the video, you won't see blur but rather a crisp snapshot. I don't think youtube will play nice with that though...
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Re: Broke a cutter, not sure why (G code in here)

Post by GlennW » Tue Jan 31, 2017 3:49 pm

Make sure you are climb milling.
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Re: Broke a cutter, not sure why (G code in here)

Post by ctwo » Tue Jan 31, 2017 4:06 pm

It won't, that's the limitation of this software. I could not program this same thing manually, not very easily. I think it's how they calculate the steps, using +degree increments. I tried incrementing in -degree and it locked up when posting. I'm supposed to have something else that works better, but it would not run, might be a Win10 issue.
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Re: Broke a cutter, not sure why (G code in here)

Post by ctwo » Sun Feb 05, 2017 2:08 pm

Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

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