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By MetalShavings

August 28, 2017, 9:49 pm

Tool Chatter On Inside Corners

I've finally gotten to where I can trust the feeds and speeds I'm generating with HSMA. After editing my machine's overall settings I can now use the numbers I come up with and not have to stress out to much about whether I'm going to break another end mill. When I first got this software it seemed that the feeds and speeds it was churning out were overly aggressive for my under powered CNC mill. I should mention that my CNC mill is the Tormach 770 hobby mill. It doesn't have nearly as much power or rigidity as those used by professional machinist so it's taken me a while to figure out what will work on my machine and what will not work.

Anyway, I've come up against a problem that I don't think that the HSMA software can fix but, it may be able to help in figuring it out.

The small parts I'm cutting from 1018 bar stock require my 1/2" end mill to cut five inside corners that are only slightly larger in diameter than my end mill diameter. Every other tool path or cutting operation on these same parts runs quite well using the numbers that HSMA has calculated. It's when my end mill gets to those five particular inside corners that I get a lot of chatter. When I say "Chatter," I mean it sounds like finger-nails being dragged across a chalk board.

I know about the generally solutions for how to go about mitigating or stopping chatter but, I was wondering; can the HSMA software be tweaked so as to calculate a possible recipe to counteract this type of chatter? For example;[/i] if a speed of 4000 and a feed of 75 are calculated for my metal stock of choice, when my end mill gets to those inside corners, is it possible for an auxiliary set of numbers to be calculated to compensate for any potential chatter created by the end mill cutting in the tighter spaces such as inside corners?

I'm still figuring out my CAM software but I'm pretty sure there are settings that I can tweak that will either raise or lower either the DOC or the WOC if need be but, the questions for me would be, which direction would those setting be tweaked. This is where those additional Chatter-Compensation numbers would really help mitigate that pucker-factor I feel each time my end mill reaches those inside corners.

Just as a side note; I recently re-ran all my tool paths in order to utilize a slightly smaller diameter stub end mill to help counteract the chatter. I think it might still be helpful if the HSMA software could help figure out the correct "Chatter-Compensating" feeds and speeds to go along with the main feeds and speeds numbers for those who don't have years of experience to fall back on in order to combat the problem of chatter.

What do you think Eldar? Does this even make any sense?

MetalShavings

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By Eldar Gerfanov

August 28, 2017, 11:57 pm

Hello,

I am glad you got a hold of things. Please send me any recommendations you might have so I can make things work for other people right out of the box.

I know exactly what you mean.
But there is nothing that can be done about chatter in the corners. Especially on less than rigid machines. If you researched the topic you know everything about WOC AND thus LOAD spiking in the corner.

This is just something you need to be aware of at all times. So was I.

IE: I have a .25" radius and I know I can not mill it with the 0.5" endmill because it will look like crap. So I will use a 12mm or a 3/8" cutter to do it.

You can mitigate the problem by taking shallower depth of cut. In fact you should he fine switching to "slotting" mode and using speeds, feeds and DOC generated for that.

But in my practice I would either use a smaller cutter to finish the wall, or use the same dia cutter to plunge the corners before the final pass. Because generating special toolapths for shallower DOC just in the corner was a waste of time for my job.

Hope I could be helpful.

Regards.

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By MetalShavings

August 29, 2017, 12:55 pm

Thanks Elar:

I was hoping for an easy way out of this problem but it appears there is no easy way out. I thought about drilling out those inside corners before I did the roughing but it goes so much faster by just letting the roughing end mill do the work. It's just that the chatter drives me nuts.

I'm hoping that the smaller diameter end mill will at least mitigate some of that chatter.

MetalShavings

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By frank

September 24, 2017, 1:21 am

Hello, if i may...

For inside corners I use bigger mill(Add some offset from dim that you milling) to remove as much material as i can as quick as i can. I add min. radios to that toolpath with this tool can go (never allow that toolpath would go sharp 90 deg, it on x to y way there should be some R). Than pick some tool that R is approx. 1mm smaller than Pocket R. Also, use best toolholder that you can afford.

If you can, you could dodge a bullet on inside R with design change (https://www.youtube.com/watch?v=w5Xa7oTPcYM&t=234s).

Best regards, Franc

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By Eldar Gerfanov

September 24, 2017, 2:32 am

Hi Frank,

Thanks for pitching in!

ernaehrung004

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