Author Topic: High feed speed on router results in rounded edges  (Read 7669 times)

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Offline derek

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Re: High feed speed on router results in rounded edges
« Reply #10 on: July 19, 2015, 06:21:35 PM »
I have the same problems as you. It will make a difference in the quality of the cut. It's really a problem if you are going into a corner that has the same radius  as the cutter. It can be quite violent. Any backlash at all will just exacerbate the problem. When I'm working on it I put a shot glass of water on the z head and watch the water vibrate and shake.

Derek

Offline ger21

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Re: High feed speed on router results in rounded edges
« Reply #11 on: July 19, 2015, 08:18:53 PM »
Quote
So I just figured something, it doesn't seem to exclusively be an issue of acceleration but one of velocity as well.

I bet if you lower your accel by half, it'll shake less.
It's really not so much the velocity, but how Mach3 accelerates and decelerates. Imagine driving in your car at a fairly quick rate, and then stopping very quickly, keeping even pressure on the brakes until you come to a complete stop. When you stop, the car will jerk backwards, as the suspension allows the inertia to carry it further than the tires.
Mach3 stops in a similar fashion, only instead of the suspension, it's the flex in the machine that allows it to jerk backwards as it comes to a complete stop. The bigger and heavier the machine, The more it's going to flex when you change direction. If you decelerate slower, then the machine may flex back to it's original state before it stops. If you decelerate faster, then it may not stabilize until it comes to a complete stop.

A lot of high end routers use proprietary controls, with S-Curve acceleration. At work, we have a Morbidelli router. It has a gantry that's supported at only one end, and is about 80" long. We regularly cut at 22,000 mm/min, and it cut's perfect, square corners at all times, and can take very deep cuts at high speeds with no noticeable flex. I don't know what the acceleration rate is, but I can assure you that it's far greater than yours. it reaches 22m/min in about 12" of travel.
However, if I try to cut something with lots of very short, straight segments, the quick direction changes can cause the gantry to vibrate enough to visibly affect the cut quality.
But in normal use, the S-Curve acceleration allows it to run perfectly smooth, with zero vibration.

On my homebuilt wooden machine, I've often used the Tempest test version of Mach3 for it's smoothness and accuracy, on a machine with a lot of flex.
Gerry

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Offline RICH

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Re: High feed speed on router results in rounded edges
« Reply #12 on: July 19, 2015, 10:27:17 PM »
xxtoni,

Quote
My question now is...does this really matter ? I mean does it affect the cut or wil it in the long term do
 mechanical damage to the machine itself (rails, bearings, ballscrews, servos even) ?


How are machines made more rigid so that things like this don't happen?

--------------------------------------------------------------------------

Good ones are enginieered and include historical experience that works.

For every reaction there is an equal and opposite reaction. F=MA

In good design the components are selected and properly mounted to absorb
or transmit the forces based on what can be generated by the other components of the machine during
 operation or even an upset condition. Life expectancy can be estimated for both accuracy and longevity.
There are different approaches to how the design is done depending on vibration, deflection, loading,
 static and dynamic evaluation,etc , etc.based on the machine specs.

RICH

Offline garyhlucas

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Re: High feed speed on router results in rounded edges
« Reply #13 on: July 20, 2015, 08:00:03 PM »
I think you should start cutting and see what happens. No one runs a machine empty and the force needed to move the tool through the material also has a damping effect of its own. I suspect you will run in to limits on how fast the tool can cut most of the time.  However your machine may not be very stiff. For instance what are the legs like under the machine?  Are they vertical legs with horizontal cross members only or are they braced with diagonals to make them stiff? If the table moves it will accentuate the motion of the gantry.  What does the table weigh? If is light weight it won't properly absorb the acceleration forces.  Lots of stuff to think about here.

Offline BR549

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Re: High feed speed on router results in rounded edges
« Reply #14 on: July 21, 2015, 10:10:49 PM »
What were the original settings and WHAT is the normal max cutting speeds required. 20 x the Acell rate change is a bit extreme .  Start at the original values and Set teh Vel to a reasonable value based on max cutting speeds. THEN start ramping up the accel say 10% at a time until it cuts smooths and very little corner rounding or starts shaking like a dog scratching fleas WHILE cutting. When you get to flea scratching start backing it back DOWN until it works ok.

ALSO remember you are working with SERVOs that require tuning as well. There is AXIS tuning and there is Servo tuning to deal with. IT can be a dance sometimes.  

BUT it does show you have PLENTY of power to work with Just needs tuning to run smooth.

(;-) TP

(;-) TP

Offline xxtoni

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Re: High feed speed on router results in rounded edges
« Reply #15 on: July 22, 2015, 05:13:21 PM »
Alright guys thanks again. Tomorrow I'll try to catch some time and experiment with some of the things you suggested and deliver some feedback.

Thanks for the suggestions! Much appreciated.

Offline Brian K

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Re: High feed speed on router results in rounded edges
« Reply #16 on: December 17, 2016, 01:14:47 PM »
The manufacture of the machine did not do their job.  You are experienceing issues with acc/dec, acceleration and deacceleration.  The manufacture should have delivered the machine with these already set. I don't know how far ahead Mach reads the code but on a Faunc 0 controller that I use it is 20 lines.  We have an Anderson Exxact in the shop that is very fast. Indexes at 3100 ipm and will cut 1.125" particlle board at 1200 ipm the controller handles the acc/dec to keep the tool where it should be.  A CNC router should never shake, ever.  when I visit a shop and their router is running I like to touch the machine and see if I can feel it change direction, you should not be able to feel any change when the machine changes direction.  I just reread and you mentioned the gantry shakes, wow!  If the gantry shakes any at all for what ever reason that machine will not give any dependable accuracy.