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

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

Postby GlennW » Sun Jan 01, 2017 11:47 am

I was referring to high spot blue, not layout blue.
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ctwo
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Re: Broke a cutter, not sure why (G code in here)

Postby ctwo » Sun Jan 01, 2017 12:39 pm

Yes, I'm sure. Dykem and grease? I think I should blue up the spindle and see what sticks to the holder. I'll try some red grease.
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ctwo
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Re: Broke a cutter, not sure why (G code in here)

Postby ctwo » Sun Jan 01, 2017 1:03 pm

Small spot of a thick clay-based red grease. I ran my finger up and down the spindle bore to apply the thinnest coat I could. I removed the tool two more times and wiped off all the grease and ran my clean finger up and down the spindle bore each time to remove even more grease and spread it around even. The photos are 2nd and 3rd insertions.
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blue-01-IMG_0631.jpg
blue-02-IMG_0632.jpg
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GlennW
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Re: Broke a cutter, not sure why (G code in here)

Postby GlennW » Sun Jan 01, 2017 1:50 pm

This:
download.jpg
download.jpg (3.97 KiB) Viewed 1150 times


Does the spindle have any end play?

Put an indicator on the end of a tool holder and try to pry up and down on it.
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ctwo
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Re: Broke a cutter, not sure why (G code in here)

Postby ctwo » Sun Jan 01, 2017 7:29 pm

That would be a two week item, the grease no good? No end play.

I did discover one programming error that runs the cutter full depth while I was watching it cut some wood.
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Re: Broke a cutter, not sure why (G code in here)

Postby Harold_V » Mon Jan 02, 2017 2:48 am

ctwo wrote:the grease no good?

Not in my opinion. If grease was acceptable, it would be used for scraping. To my knowledge, it isn't. Get a tube of proper blue. It will last a lifetime.

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

Postby GlennW » Mon Jan 02, 2017 10:44 am

ctwo wrote:BTW, I think that stepping and other slop you see in the part (1st pic) is from the longer end mill flexing. I could easily see it bending and flick out of the cut. The shorter end mill did not do that and the cuts look good, but it still broke.

The shorter end mill had to have flexed if it broke.
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ctwo
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Re: Broke a cutter, not sure why (G code in here)

Postby ctwo » Mon Jan 02, 2017 8:39 pm

GlennW wrote:
ctwo wrote:BTW, I think that stepping and other slop you see in the part (1st pic) is from the longer end mill flexing. I could easily see it bending and flick out of the cut. The shorter end mill did not do that and the cuts look good, but it still broke.

The shorter end mill had to have flexed if it broke.


Yes, there is one part of the code that side mills full depth (0.5") that needs to be corrected. Otherwise, this reminded me of trying to mill with a drill bit.
Standards are so important that everyone must have their own...
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RET
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Re: Broke a cutter, not sure why (G code in here)

Postby RET » Tue Jan 03, 2017 8:52 pm

Hi ctwo,

After looking through this thread, it seems you are just trying to push everything too hard. Don't begin to try to run anywhere near commercial speeds; for most of us it isn't possible or necessary. I run at something like 1/10th of those speeds and I am almost always successful in what I want to do. Lets put it this way. If you can do what you want successfully (a good part with good finish) with no broken cutters, aren't you further ahead even if it takes a little longer?

In your first instance, I think you are pushing way too hard for the cutter RPM. and that's why it breaks. In addition, in your code you have G1 then f7 with no coordinates telling where G1 is supposed to go. Does Mach have something like Sherline's Backplot that allows you to test out your program before you actually run it? Backplot gives error messages for any code errors, it also gives a 3D, 3 axis picture of what the code is doing.

In your picture with the aluminum block it is easy to see that the end mill is deflecting a lot with the passes; no wonder it breaks!

Finally, end mills don't like to sink at all and you have to do it slowly at very low feed rates if you want them to work. Often its easier to drill a hole for the cutter instead. They cut quite well horizontally as long as you stay within their capabilities. High length of cut to diameter ratios means the cutter will deflect easily. To work under those conditions, you have to use climb milling with shallow depth of cut and slow feeds. On one part I've made from aluminum I'm using a 1/4" dia. 4 flute cutter with 1 3/4" length of cut. It works, but it is tricky setting up the conditions for success. In that same part, I'm using a 3/8" dia. end mill which sinks in a small part of its travel and I have to slow things down a lot for that bit and even then the end mill still doesn't like it at all.

Finally, carbide end mills stay sharp longer and I think they deflect less, but they will chip very easily. Even a little bit of cutter deflection or play in the ways or other parts of the machine will cause chipping because of the sudden tooth loading shock.

This seems a bit long, but its what I see from what you have posted. I'm not always right but I hope this helps. Usually If you break a cutter, something isn't right.

Richard Trounce.

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

Postby Magicniner » Sat Jan 07, 2017 7:02 am

ctwo wrote: so it was flexing in the cut.


Is it the tool flexing or is the machine flexing or is it a bit of both?
Get the trial version of HSM Advisor, it tells you how much your tool will flex in the cut you're calculating, if you program a cut with minimal tool deflection but still get the flick on break-out at the end of a slot it's not tool flexing.

- Nick

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

Postby ctwo » Sun Jan 08, 2017 9:46 am

Nick, the tool was wandering around so much you'd think I had a regular drill bit in there. I need to buy cutters so at least I will have some new ones.
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...

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

Postby RET » Tue Jan 10, 2017 10:40 am

Hi ctwo,

If the cutter behaves the same as a drill bit, it probably isn't sharp. Also, if you short chuck a drill, its pretty stiff & won't wander. If you grind the flutes of a drill to give some relief, you can make it cut sideways like an end mill as long as it doesn't stick out very far. That can be done as a temporary fix if you don't have the proper size end mill.

Look at the end mill you have been using under a microscope to see if it is sharp. A jeweller's loupe will also do, but it isn't as good as the microscope. The cutting edges should still appear sharp even when magnified. If the cutter is dull, the forces required to make it cut will be a lot higher and the cutter will deflect. I can hand sharpen two flute cutters (even down to 1/8"). The small ones I do under the microscope with a Dremel. Its surprising how well that works. With any of this, the key is to be able to see what you are doing.

Short answer: if you can see the cutter deflect, something isn't right. Yes, any cutter will deflect a bit under load, but it shouldn't be so much that it jumps out at you.

Hope this helps a bit.

Richard Trounce.


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