Grizzly mini-mill & resonance?

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DianneB
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Grizzly mini-mill & resonance?

Postby DianneB » Tue Nov 14, 2017 6:52 am

I have a Grizzly mini-mill that I bought a few years ago but hadn't used much until recently. I am an absolute novice with vertical mills and could use some advice.

When using an end milling cutter, particularly when taking less than a full cut, I sometimes get a vibration (resonance?) that gets kind of scary and, in worst case, the vibration causes something to slip/move. It seems to be a resonance with the "natural frequency of the mill".

Other than changing the RPM of the cutter, is there anything I can do to help reduce the resonance of the mill?

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NP317
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Re: Grizzly mini-mill & resonance?

Postby NP317 » Tue Nov 14, 2017 10:43 am

Change cut-depth, RPM, or feed speed. All effect vibration.
And make sure you lock all mill axis that you are not moving.
~RN

John Hasler
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Re: Grizzly mini-mill & resonance?

Postby John Hasler » Tue Nov 14, 2017 11:13 am

In addition to what RN said if anything ever slips you aren't clamping well enough.

John Evans
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Re: Grizzly mini-mill & resonance?

Postby John Evans » Tue Nov 14, 2017 11:59 am

Make sure all gibs are correctly adjusted. Lock axis not in use and put a light drag on the axis in use.Use conventional milling only not climb.

Inspector
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Re: Grizzly mini-mill & resonance?

Postby Inspector » Tue Nov 14, 2017 12:56 pm

Sometimes packing plasticine on areas not being cut will absorb the vibrations.

Pete

jcfx
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Re: Grizzly mini-mill & resonance?

Postby jcfx » Tue Nov 14, 2017 3:17 pm

Adding to the above, a dull end mill will introduce vibrations.

I was guilty on some of the above, too fast, too deep
and as the end mill dulled vibrations crept in.
:oops:

tornitore45
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Re: Grizzly mini-mill & resonance?

Postby tornitore45 » Tue Nov 14, 2017 3:34 pm

What do you mean with full cut? I hope you are not expecting to take the full length of the flutes. A mini mill can only take passes on the order of 0.05 in steel and 0.15 in Al.
Mauro Gaetano
in Austin TX

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DianneB
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Re: Grizzly mini-mill & resonance?

Postby DianneB » Tue Nov 14, 2017 3:42 pm

tornitore45 wrote:What do you mean with full cut? I hope you are not expecting to take the full length of the flutes. A mini mill can only take passes on the order of 0.05 in steel and 0.15 in Al.


I meant when cutting with only a small portion of the diameter of the mill. For example, if taking a piece down flat, the end mill may be cutting around 1/2 of its diameter until the last pass when the remaining material is only a fraction of the mill's diameter. (Don't think I am explaining this very well LOL!)

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GlennW
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Re: Grizzly mini-mill & resonance?

Postby GlennW » Tue Nov 14, 2017 4:02 pm

Width of cut or "step over" is only part of the equation.

Depth of cut needs to be addressed as well.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

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WesHowe
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Re: Grizzly mini-mill & resonance?

Postby WesHowe » Tue Nov 14, 2017 4:55 pm

Since you mentioned only cutting 1/2 the mill diameter per pass, I would ask if you know the difference between "climb" and conventional milling? In case you don't, climb milling is when you set the direction of cut such that the teeth of the cutter pull the cutter toward the work. This is less problematic with more rigid mills, but in effect as each tooth starts to bite the metal, any play or flex will cause the cutter to take a larger cut than normal. This has the same effect as using a higher feed rate. As each chip would release, the cutter would move back to an unstressed position, only to then be pulled again when the next cutting tooth bites in. This repeating pattern might be your grinding noise.

Cutting a slot where teeth on both sides make contact does not have this problem, because the pulling forces balance each other out. To do a facing job on a rectangular object, try cutting right-to-left on the rear side, move to the front and return from left-to-right. This means your final pass will at or near the center of the part as measured along the Y axis (front to back).

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DianneB
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Re: Grizzly mini-mill & resonance?

Postby DianneB » Tue Nov 14, 2017 5:18 pm

WesHowe wrote:I would ask if you know the difference between "climb" and conventional milling? In case you don't, climb milling is when you set the direction of cut such that the teeth of the cutter pull the cutter toward the work.


Okay, now I know what you mean. (I am a novice at milling.) I try to avoid situations like "climb".

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WesHowe
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Re: Grizzly mini-mill & resonance?

Postby WesHowe » Tue Nov 14, 2017 10:02 pm

Well, then if you avoid climb milling, it must not be the cause of the grinding noise. That means the other posters are probably right, depth of cut and feed rate are the likely culprits. On a larger mill I get that when I get too aggressive with my cuts. For me that is often just too high a feed rate. I have a power X feed, and I usually use it, however Y is manual and I sometimes get too pushy with that handle.


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