Need help with Chatter

[JohnM34]

Hey guys I really need help. I have been at this for 6 days now with no luck. I have a brand new 4 X 4 cnc router. I am getting chatter on my cuts and I can't seem to solve the problem. I am not sure if it is settings in mach 3 or if it is something with the machine. I am cutting 1/2 inch HDPE. I am using the manufacturers recommended bit, and I have used the g wizard feed and speed calculator to determine bit deflection with still no luck. I am losing so much money and need to get this machine up and running. The manufacturer hasn't been much help. They have had me do a bunch of stuff over the phone which hasn't fixed th problem and they are saying the machine might have to be sent back which isn't an option. Any help would be appreciated.

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[Cantabrigian]

can you post a video of what you're encountering? or photos of the setup and some machined parts?

[tony978]

I would say if you're using g wizard and still getting chater you need to hold the part better,look for have something loose on your cnc frame or the tool is ground wrong . just my two cents

[JohnM34]

The part is held down fine. I actually went to the extent of double face taping and screwing it down just to eliminate part vibration. The y axis is pretty clean but the x axis is chattering. not to mention I cant cut nowhere near the speed of the material manufacturers recommendations. They recommend 18k spindle speed and 120 - 200 ipm. I am cutting at 18 k and about 35 ipm just to achieve mediocre results,

[tony978]

What is your depth of cut ?

[tony978]

Ps and dia of tool ?

[JohnM34]

Here is a photo of the most recent piece i cut

[tony978]

I think your rpm is too fast . I say 35 ipm and 6000 rpm

[JohnM34]

I am using an Onsrud 63-781 which is a single flute spiral upcut O flute. 3/8 cut dia, 3/8 shank, 3/4 flute length, 3 OAL

[JohnM34]

I have tried increasing and decreasing feed rates and spindle speeds and get worse results on both axis. Right now this is only happening on the x axis. Everyone I have talked to so far cuts the exact same material at around 18 k and 180 - 200 ipm. I can't figure out why I can't get anywhere close to that

[tony978]

What are your depths of cut ? Sounds like your cuts are too big , leave .01 " for a finish pass

[JohnM34]

I am cutting .5 material and I have tried doing a single of .495 a double of .2475 and a triple of .165 all yielding the same results

[wayneb]

G'day

I had a similar problem with Aluminium. I found my machine had too much flex.

Cheers
Wayne

[tony978]

Try .05-.1"

[JohnM34]

I don't have a video at the moment but there is a pic as well as bit info spindle speed and feed rate toward the beginning of this thread. As far as the machine set up I am not entirely sure of the specs as far as motors etc. I am new to the cnc thing but it is made by a company called Industrial CNC and it is the apprentice 404 model Industrial CNC Routers | Our CNC Router Models - Shortcut 203 - Apprentice 404 - Artisan 408 - Craftsman 510 - Craftsmaster 612 - Toolchanger 510

[tony978]

Ya take a light depth of cut and fast feed !

[JohnM34]

Thats what I am afraid of Wayne. It wasn't the cheapest machine but not too expensive either. I am worried I got what I paid for

[Jon.N.CNC]

Been getting same problems.. im getting a sort of finish! Now your going to think this is crazy as did before whilst i was coming to this conclusion. but i tried g wizard tried everything read tons of forum posts and what's more annoying about it is why when i can get a mirror finish in aluminium?

But here is the setup i used that produced the best result for 15mm thick hdpe

5mm single flute up cut spiral all conventional do not climb cut at 18 ,000 800mm/min rpm ramp to 15mm doc.. with 3 0.1mm finishing passes @ 450mm/min now this bits very important! 1st pass use 19,000rpm 2nd 20,000 rpm 3rd 21,000rpm . now getting a glossy cut with a acceptable amount of chatter, more like just machine marks, over what previously looked like a saw blade, only£200 quids worth of hdpe later.

I know what your thinking "it will melt" it doesn't its not far of its limit.. it seems you need to making light fur not chips.

Its important that if you starting hearing chatter you speed up the spindle quickly.. the most important cut is the first any chatter in the first can exaggerate chatter if its bad in the finishing passes. even at 18 - 19 and 20000 rpm you are still getting small amounts of chatter and its only going up the range in each pass upto 21,000 that seems to reduce the larger chatter with a finer one, i suppose this is because at the same speed the bit resonates and the plastic absorbs the same frequency so the bit simply follows the previous passes chatter instead of cutting through it.

Hense why you cant just skip to 21,000.

This has been a bit of a pointless exercise for me now i know you cant get a completely smooth finish with hdpe having tried multiple bits in different material and doc from 1-15mm and rpms from 5500 @ 5m/min ( gwizard result .wasnt not good, was the worst of all the cuts) - 21,000 @ 0.5m/min ( only for finish, melts if you cut at this speed) climb, conventional, conventional and climb, multiple finishing passes various amounts. You name it i tried it, Any one that says you can i will call them a liar, I will probably never actually use this setup again and tell anyone that asks me to cut hdpe in future that i hope they aren't looking for a finish and are they going to trim the parts, in which case i may agree to cut it for them and it would be a 5-6 mm single flute upcut spiral conventional full depth of cut at 18,000rpm 600mm/min no finishing passes.