[LeeWay]

Here is an old video I posted.
It is using my home made 80/20 mill in brass. Now for the most part, this was far too conservative even for this mill.
I managed to get the finish path right though. Pretty much a mirror finish with no ripples. That mill has an X2 spindle head on it, though it is driven by a large DC motor and timing belt.

If it can do it, yours can too.

https://www.youtube.com/watch?v=9eyA2kq7lDM

[TurboStep]

I'm just throwing things out there as I have no idea.

I just love posts like that!

So, according to my calculations using the value of 5.4 as explained in the other thread, this would give 5000RPM / 5.4 / 38ipm => 24.4 "ripples per inch" or about 0.040"...

Ripples are .040" apart according to my super accurate eyeballs with a caliper.

Doesn't anyone notice any similarities?

Nobody?

[cobrakai]

Climb mill for roughing (it pulls on your ball nut), leave .005-.008" on the wall, it depends on what type of endmill you rough with, size and material. If it's a small HSS endmill leave .008", if roughing with a big Carbide endmill then leave the wall at .005"

Conventional mill for finishing, it pushes back on your ball nut, and will provide a superior final finish, I usually run this at 50% ipm of what it was Roughed at

Get a GOOD Variable helix endmill - takes the harmonics out of it. If in Aluminum, get a ZrN coated endmill - I use Helical Brand for all my Aluminum

Simple advice and this assumes you have your Gibs tight and use a proper way oil

I'm using one of the high helix cutters from Maritool: Square End 3 Flute High Helix End Mill Finishers - MariTool

It's a high quality bit no doubt. I also have used a variable helix end mill from LakeShore with a ZrN coating which was noticeably quieter - until I chipped it and cried.

Why do you recommend conventional milling for the finish pass? I was under the impression that climb milling was basically always better. I have never done a finish pass conventional milling, but I have done regular passes that way and the surface finish is always rough and just bad in comparison.

Here is an old video I posted.
It is using my home made 80/20 mill in brass. Now for the most part, this was far too conservative even for this mill.
I managed to get the finish path right though. Pretty much a mirror finish with no ripples. That mill has an X2 spindle head on it, though it is driven by a large DC motor and timing belt.

If it can do it, yours can too.

https://www.youtube.com/watch?v=9eyA2kq7lDM

Based on your video, you are going much, much slower than I was. 1/4 of the speed. I might put some stock in the vise and just manually do some passes at different feed rates and directions and watch what happens I might even video it and show it here.

I just love posts like that!




Doesn't anyone notice any similarities?

Nobody?

I see Your calc worked! Now what does it mean? LOL

[G59]

I see Your calc worked! Now what does it mean? LOL

Exactly. I'm wondering that too.

[SCzEngrgGroup]

Here is an old video I posted.
It is using my home made 80/20 mill in brass. Now for the most part, this was far too conservative even for this mill.
I managed to get the finish path right though. Pretty much a mirror finish with no ripples. That mill has an X2 spindle head on it, though it is driven by a large DC motor and timing belt.

If it can do it, yours can too.

https://www.youtube.com/watch?v=9eyA2kq7lDM

A "mirror" finish is never the result of cutting - it's the result of going so slowly that the chipload is too light, and you're "rubbing, which burnishes the surface, and dulls the cutter rapidly in the process. An actual finish cut will always leave cutter marks, but a good finish cut will make those marks so small as to be insignificant. NOT a "mirror" finish, however.

The same applies to climb vs. conventional milling, most especially for finishing. Climb cutting is nearly always preferred, unless the machine has significant backlash, as it results in a significantly higher chipload, all else being equal. Conventional cutting with small WOC always leads to rubbing, and quickly dulls the tool. Again, if you're getting a "better finish by conventional milling, you're almost certainly rubbing, and basically abusing the tool.

Regards,
Ray L.

[cobrakai]

Interesting^! That's what I thought too. I learned in a class that you really shouldn't cut below a .001" chip thickness or else you get rubbing. So the struggle is maintaining proper speed&feed while getting the good finish as well.

[TurboStep]

I see Your calc worked! Now what does it mean? LOL

You see, but you still don't believe...
First of all you have only confirmed that the ripple frequency correlates with a frequency of about 16-17Hz, without FFT I would now suggest reading the thread I linked to earlier to decide for yourself whether a) you feel that imbalance is indeed your problem and b) whether balancing is an option for you.
Alternatively, slowing the spindle/motor down should reduce the amplitude. I found it to be just too slow for my needs, but it depends on your pain level.
Step

[cobrakai]

You see, but you still don't believe...
First of all you have only confirmed that the ripple frequency correlates with a frequency of about 16-17Hz, without FFT I would now suggest reading the thread I linked to earlier to decide for yourself whether a) you feel that imbalance is indeed your problem and b) whether balancing is an option for you.
Alternatively, slowing the spindle/motor down should reduce the amplitude. I found it to be just too slow for my needs, but it depends on your pain level.
Step

I read through your thread. Looks like a lot of chasing balancing issues - the motor, pulleys, belts, spindle, etc could all be out of balance. If I learned anything in mechanical vibrations, it's that balancing is an incredibly complex science! I am going to run some tests to try to find a spindle speed that reduces the harmonics (if that is the issue). If that's not the issue, and simply a function of my cutter or feed rate, the pattern should exist the same at 500 RPM as it does at 5000 RPM.

[TurboStep]

It will still be there at 500rpm but it will almost certainly be too small to see. Start at higher spindle speeds and reduce in steps of say 500rpm and observe the difference. You really don't want to have to finish at 500rpm unless you really have to.
As an afterthought: You might also try varying the speed manually with the potentiometer to try to find a "sweet spot". Your ripples appear to be particularly prominent, judging from your photo, so you may also be exiting a resonance at this frequency. A relatively small change may bring a significant improvement.
Step

[BAMCNC.COM]

I say conventional because of how the endmill will pull your table around when climb milling. Conventional keeps it "held back" and will produce a smoother finish on a Finishing pass with the parameters I gave you.

You guys can fight a harmonic ghost all day, don't think the effort is worth it.

Also if you are chipping corners then my guess is you are plunging, or ramping more than 4* into the stock. If you *MUST* do either then get a radius endmill please. .010 is enough.

[tmarks11]

If that's not the issue, and simply a function of my cutter or feed rate, the pattern should exist the same at 500 RPM as it does at 5000 RPM.

Not necessarily, as the vibration imparted by the imbalance in the spindle and motor may be of a slight enough amplitude such that it won't be detectable on your finished part...which was what Turbostep said, but I just wanted to say it again

[tmarks11]

The same applies to climb vs. conventional milling, most especially for finishing. Climb cutting is nearly always preferred

Conventional keeps it "held back" and will produce a smoother finish on a Finishing pass with the parameters I gave you.

I have found that if you put 3 machinists in a room, one will claim conventional milling is the way to go, another will argue for climb milling... until the third one hits them over the head with a chair to get them to shut up because they are interrupting the broadcast during his break time...

Of course those arguments are only valid when you are talking about manual machining. Once you get into cnc, climb milling is the way to go.

[waltpermenter]

I have found that if you put 3 machinists in a room, one will claim conventional milling is the way to go, another will argue for climb milling... until the third one hits them over the head with a chair to get them to shut up because they are interrupting the broadcast during his break time...

putting a group of hobby machinists that have never worked in the industry in a room is even worse.

[LRF]

My 2 cents...I have the same finish issue as being discussed. Looks exactly the same. My finish indicates a frequency of about 16Hz. It doesn't change with either feedrate or RPM or chipload. As I cut climb on all the finish cuts I can't say its the same if conventional. The appearance is a little different in appearance when cutting along the Y or X axis but basically the same Hz.

If someone figures out the cause I would love to know.

[BAMCNC.COM]

lol, You can make fun of me all you want, but here is the article I read when it was new (couple years old maybe), I then thought about, and tested a few different ways to see if the theory was correct.

Climb Milling vs Conventional Milling


You want to prove me wrong, then do it with actions not just words. To many armchair quarterbacks here - get out and do something. Oh and Tell Bob that you think he is wrong too.

Just because it's a CNC Machine means nothing, there are still Mechanical backlashes present along with tool deflection.

[LeeWay]

The video I posted is showing conventional milling, correct? Moving clockwise with a clockwise spindle. That machine, though based on 80/20 has nice parts. THK HSR 25's and NSK preloaded precision ground ball screws. No backlash to speak of. I could not measure any. I'm sure there is some, but it can't be much if I can't measure it. Great finish with conventional milling on a cnc machine.

[waltpermenter]

50 years experience in the machining industry here, climb milling gives a better finish, take that to the bank!

[LeeWay]

If those parts were any shinier that come from my video, I'd have had to wear shades to prevent eye damage from the glare.

[SCzEngrgGroup]

The video I posted is showing conventional milling, correct? Moving clockwise with a clockwise spindle. That machine, though based on 80/20 has nice parts. THK HSR 25's and NSK preloaded precision ground ball screws. No backlash to speak of. I could not measure any. I'm sure there is some, but it can't be much if I can't measure it. Great finish with conventional milling on a cnc machine.

Lee,

No, that is all climb milling. In climb milling, the cut begins ahead of the spindle centerline, and the chip is ejected behind the tool. The chip starts out thick, gets thinner as the spindle rotates, and is thinnest as the chip is ejected. In conventional milling, the cut begins behind the spindle centerline, and the chip is ejected in front of the tool. The chip starts out thin, gets thicker as the spindle rotates, and is at maximum thickness just as the chips is ejected.

So, to climb cut when cutting an outside profile, with a RH tool, the toolpath will run clockwise around the part, when viewed from above. An inside profile will run counter-clockwise. Conventional cuts will be exactly the opposite in both cases.

Regards,
Ray L.

[LeeWay]

Thanks, For clarifying Ray. All of my parts are programmed this way, but I just never really thought about it. I just assumed it was conventional. The machines sound good doing it this way and the finishes are nicer.

That is an X2 head with two deep groove bearings in the spindle. It cuts nicely on the side of the tool, but top finishes even with a face mill leave a lot to be desired.