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Dynamic Milling VS Machine Accuracy....over time


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I kind of need eveyone's serious thoughts on this.....

We all know Dynamic Milling makes a series of these funny  spline looking  toolpaths. So while our machines are dancing away at these crazy toolpaths , apparently our ball screws are really going through some rough times. 

Someone told me that Dynamic milling is very nice....but like with all things....at a price. The price seems to be a thought that the ball screws wear out quicker due to the constant high speed motions and that if you value machine accuracy dynamic motion should be avoided.

It was said that it's good for automotive because machines run all the time due to high volumes and after a few years the machines pay for itself so you can get rid of them but if your a small to medium sized machine shop and you want your machines to last that you should avoid Dynamic milling.

The person is dead set against Dynamic Milling and hates it. He is completely convinced that Dynamic Milling reduces machine accuracy quickly as opposed to conventional contouring.

Based on the physics of the machine....is he really wrong?

How right is this person?

 

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You can filter it and use arcs, or some machines like matsuura have the ipc for corner rounding and smoothing. The dynamic air moves have also gotten better over the years also

You could also get linear motors and eliminate the ball screw all together.

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In a huge amount of cases, if you are not using it, you are losing money. A LOT of money. You are not competitive. Simple as that.

I blew an X & Y ballscrew doing one particular job peel milling. There was not enough movement and back/forth oscillation caused (I think) false brinelling.

But I got them rebuilt using next size up balls and all was good. A cheap repair and a lesson learned.

My machines had been using the paths since the X5 era, and they are still working now with just that one issue.

What you will have to do, is use look ahead on your toolpaths (Fanuc G05/G05.1 etc) filter for arcs as Leon has said, and if you're running low end machines (read cheap), you'll probably have to servo tune the parameters to stop the machines from beating themselves to death with mechanical shock.

But the upside is all well worth any small downside.

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11 hours ago, M4573RMZD said:

I kind of need eveyone's serious thoughts on this.....

We all know Dynamic Milling makes a series of these funny  spline looking  toolpaths. So while our machines are dancing away at these crazy toolpaths , apparently our ball screws are really going through some rough times. 

Someone told me that Dynamic milling is very nice....but like with all things....at a price. The price seems to be a thought that the ball screws wear out quicker due to the constant high speed motions and that if you value machine accuracy dynamic motion should be avoided.

It was said that it's good for automotive because machines run all the time due to high volumes and after a few years the machines pay for itself so you can get rid of them but if your a small to medium sized machine shop and you want your machines to last that you should avoid Dynamic milling.

The person is dead set against Dynamic Milling and hates it. He is completely convinced that Dynamic Milling reduces machine accuracy quickly as opposed to conventional contouring.

Based on the physics of the machine....is he really wrong?

How right is this person?

 

I think a lot of it depends on the quality of machine. If you are talking a high end Japanese machine with high quality mechanical components and top notch servos for smooth motion, then you should be fine. If you are talking a cheap machine, those are not built to last regardless of how you use them. 

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It depends on 2 things.

Do you have a low end machine that can't take advantage of these toolpaths?

How you program it is another big factor.

 

Dynamic milling is a huge timesaver in most scenarios. And if your parts could benefit from it but you're not using it, then you're losing money because your competitor IS using dynamic paths.

I've been using Dynamic on my Okuma mills for years. I think 7+ years. And have yet to replace a ball screw because of my toolpaths.

In fact, I've only replaced 1 ball screw because of a crash.

 

 

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Using dynamic paths in Ti and 17-4 for three and a half years on a 2015 Haas.  I false brinelled the y axis thrust bearing by peeling a .020" wide slot with a .010" endmill about 3/4" long, 12 slots indexed around a part, 12 parts.  Got that replaced and learned my lesson.  Since then I've made dozens of those parts with no damage by peeling about 1/4" and making a 3" diagonal move and back, then continuing.  Machine still holds a tenth all day if I hold up my end.

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I turn micro lift to zero and only double my back feed. Having the z axis come up .005 or whatever small micro lift distance you are using on large tool paths ain't good on the ballscrew. False Brinelling and lack of lube es el Diablo. I think if you have adequate distance in your moves and not peel milling a .280 slot with a 1/4 endmill it is not detrimental to the machine. Probably even better for it, compared to the violent chattering of 50 percent step overs and trapping the cutter. 

 

Dynamic, Vortex, Volumill, and Adaptive  tool paths have been on long production runs for quite some time. I have not seen any increase in ball screw replacements. 

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On 6/13/2019 at 6:46 PM, Leon82 said:

You could also get linear motors and eliminate the ball screw all together.

from what i understand linear motors have not caught up to ball screw's speed in fine small motions.

100 m/min rapids are still pretty 'exciting':blink:

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Sometimes it helps to do the math. If a part costs 3 hours of conventional milling time at 50-80% spindle load, versus 1 hour with Dynamic at 25% spindle load, the clear winner is dynamic. The tools on that first part are going to have a much shorter life, in fact probably not even close, depending on material.

Maybe it is rougher on the ball screws, but my tool life in aluminum has basically increased to infinity with Dynamic toolpaths (unless of course i break the tool due to error). With steels and Ti, I am easily seeing 25-50% higher tool life. My spindle loads are much lower, and my parts come off the machine way faster, with better surface finish.

All of those factors combined justify pushing my feeds to the max with Dynamic toolpaths as much as humanly possible. I never even use 2D pocket anymore because its a waste of time to me. Keep in mind that in this game, time is money and if you save 60% of your money on tooling and faster parts, but you have to replace ball screws once every 3 years, you probably made way more money to justify the business expense of replacing those ball screws. Its probably also way cheaper to replace or recalibrate your lead/ball screws that it is to replace a blown out spindle cartridge, which I recently had to do.

 

In my experience it is also way easier and more consistent to program using the Dynamic approach, especially in complex 3D applications or even just complex pockets

 

Edit: Agree with above, you need some serious lookahead capabilities, a modern controller, and the servos to be able to harness the power of these paths. Most new-ish machines have these capabilities.

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31 minutes ago, Tim Johnson said:

Linear motors only do 100m/min? Our 2005 and later enshu machines do 90m/min with ball screws.

Looks like rapids on a Matsuura linear motor machine are 90m/min:

https://primemach.com/wp-content/uploads/2019/05/MATSUURA-LX160LowRes.pdf

They claim up to 1.5G acceleration:

http://www.metalmecanica.com/documenta/contenido/7083493/6.pdf

 

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9 hours ago, M4573RMZD said:

Just for everyone's input the Machine I'm using is a Mazak VC-500A /5X  

We have a VC300A-5X....runs fine with the dynamic paths, I do send out programs with G61.1....I have found the new Smooth controls seem s to prefer it that way.

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23 hours ago, Old_Bear said:

We have a VC300A-5X....runs fine with the dynamic paths, I do send out programs with G61.1....I have found the new Smooth controls seem s to prefer it that way.

I flip back and forth with G64 and G61.1 via misc int.  The dynamic paths really love G64 but leave enough stock!

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19 minutes ago, jlw™ said:

I flip back and forth with G64 and G61.1 via misc int.  The dynamic paths really love G64 but leave enough stock!

On the latest Smooth controls, holding size, machining corners ever, recently noticed an issue at the overlap of a start/stop in G64.....feeds were only in the 45IPM range

Turned on G61.1....issues all went away....seems these very latest controls are very picky

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