Author Topic: newbie - end mill grooves, mill jams  (Read 2528 times)

Offline arma16

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newbie - end mill grooves, mill jams
« on: March 17, 2016, 04:07:41 AM »
Hello....I'm totally new to the world of CNC machining and wanted to get some opinions. I cranked out my first lower receiver fine, tested it, no problem. Trying to make my second one and the machine mills for a while, then jams (spindle stops). When I took the part out, I see the grooves in the attached picture. I'm figuring that my end mill is dull, but that doesn't really make sense since my first lower was shiny smooth the whole time. What else could be causing this? The end mill walking? I tightened down the collet nut as hard as I could. Please tell me it's not a bad spindle or something.

Thanks for your help...

Offline Ca_Longshot

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Re: newbie - end mill grooves, mill jams
« Reply #1 on: March 17, 2016, 08:25:40 AM »
The possible cause.....
Since Aluminum is a gummy and galls.
Check you endmill to see if you have any aluminum welded to it.
Are you using a good cutting fluid??
Check you are using a reasonable speed and feed rates

Also check your mill.
Make sure the Gibbs are tight but moves freely... and are well oiled
Check the spindle too....

Good Luck,
 Ca_Longshot
« Last Edit: March 17, 2016, 08:34:28 AM by Ca_Longshot »

Offline arma16

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Re: newbie - end mill grooves, mill jams
« Reply #2 on: March 18, 2016, 04:07:44 AM »
Thanks for these ideas. It does look like there is some aluminum welded to the sides of the end mill. I've got a new one coming in the mail, will let you know how it goes.

Not using any cutting fluid, and the speed and feed rates were pre-programmed in the file I'm using, so I don't think there's any problem there.

How would I check the spindle to see if it is good/bad?

Is there a good/bad way to mount the end mill in the collet? for example, do I loosely thread the collet + collet nut on the spindle, then insert end mill, or thread collet + collet not + end mill on the spindle all at once? does it make a difference?

sorry for the really basic questions. I'm going to take a machining class, just haven't got to it yet.

Offline Ca_Longshot

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Re: newbie - end mill grooves, mill jams
« Reply #3 on: March 18, 2016, 08:28:29 AM »
Not using any cutting fluid
You might want to use some... try WD-40..
Lube helps keep the heat generate down with cutting. It also help with the chip removal process.

How would I check the spindle to see if it is good/bad?
Just check to make sure everything is moving smoothly and no excessive movement(I.e. spindle bearing conditions..)

Is there a good/bad way to mount the end mill in the collet?
When I change my collets, I clean the nut, collet and spindle of any metal particles.
Before I insert an end mill, I will wipe it down to make sure the shank is dry (not oily) and clean.

I hope this helps...

Ca_Longshot

Offline Ca_Longshot

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Re: newbie - end mill grooves, mill jams
« Reply #4 on: March 18, 2016, 05:26:59 PM »
Here is an example when no lube is used... aluminum welded to the end mill.
Also resulting damage to the finish of the cut....


Ca_Longshot

Offline arma16

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Re: newbie - end mill grooves, mill jams
« Reply #5 on: March 18, 2016, 08:06:02 PM »
wow thanks a lot! great advice, I'm learning a lot. Thanks for taking the time.

The machine i'm using came with a pre-programmed g-code cut file that uses a small depth of cut in order to avoid needed lube. If I wanted to try it, how often/how much wd-40 would I spray while it's cutting?

New end mills arriving in the mail tomorrow, will let you know how it goes.

Offline Ca_Longshot

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Re: newbie - end mill grooves, mill jams
« Reply #6 on: March 19, 2016, 08:49:48 AM »
If you are going to use WD40.
 You need enough lube to keep the cutting clean.
Since the most of the lube exits wit the chips.
So give it a squirt every couple of passes...

Once you get more involved into CNC milling. You will be wanting to look into lube-chip removal setup.
This can a full flood system, fog-mist system, or what I use ,"Minimal lube aerosol " system.
My system mixes a  very small amount of a special vegetable base lube with compressed air.. The air helps blow the chips out of the cutting area. Also it helps cools the cutting area


Since my CNC is a small bench top unit. It does have the horsepower th jog out .25" at time...

Here is the results..


Good Luck
« Last Edit: March 19, 2016, 07:08:27 PM by Ca_Longshot »

Offline arma16

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Re: newbie - end mill grooves, mill jams
« Reply #7 on: March 19, 2016, 05:52:39 PM »
well, the new end mill is performing great. by comparison, the old one was pretty damaged. the corners were chipped and a couple spots of welded aluminum. that's a good lesson learned...

Using my infrared thermometer, the lower is reaching temps of about 105 deg F and the end mill around 120 deg F (a little hard to measure the end mill though). how hot is too hot?

i'm drooling over your setup...showed it to my wife and she about fell over. I guess I need to break her in a little slower. someday...


Offline Ca_Longshot

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Re: newbie - end mill grooves, mill jams
« Reply #8 on: March 19, 2016, 07:07:05 PM »
That is the temp range you want keep...

If you want to give you better half a real shock....
Have her look at this post...http://www.cncguns.com/forum/index.php?topic=3108.0
It will give you a good look at my setup..