New Build Steel Frame Router

[Gary Campbell]

I have not been able to find any documentation on the acceleration setting. Usually acceleration has units of m/s^2 or ft/s^2. In Acorn the unit is in Seconds, so I am guessing that's the time to accelerate to full speed? (Intuitive) Internally there must be a conversion to acceleration m/s^2. If we increase max feed-rate without changing the accel time, the acceleration m/s^2 will increase? What happens when we use feed-rate override?

Sorry if I am asking something that already been covered. I have not been able to find it.

In my (imperial) world accel is Inches per minute per second. Like you correctly stated, Centroids accel setting is time to full speed, therefore if your max (rapid) rate is 1000 ips and accel setting is .5 your acceleration would be 2000 in/min/sec. If your feedrate for a given file is 300 ipm, then accel would be 600 ipm/sec for feedrate moves.

As you can see, using time is a plus that allows more reasonable accel rates for both rapids and feeds. Make sure that you are aware of both as you lock in a setting.

[kfedd]

Thanks Gary for the explanation.

Slower moves will also accelerate slower. I have to think about why that's a benefit.

I guess that is different to most other hobby CNC controllers which use units/s^2.

[Gary Campbell]

Slower moves will also accelerate slower. I have to think about why that's a benefit.

Of course they do. Feedrate motion is accompanied with cutting, cutting action can seldom tolerate the acceleration that rapids can.

Acorn 4 may be a hobby priced package, but make no mistake the Centroid controller behind it is a full blown, top of the line industrial controller.

[cnckeith]

i updated TB1 "out of round circles/arcs"
https://www.centroidcnc.com/dealersuppo ... oads/1.pdf

[suntravel]

i updated TB1 "out of round circles/arcs"
https://www.centroidcnc.com/dealersuppo ... oads/1.pdf

From my experience, you can have nearly perfect round cutting with 0.04mm backlash, if corrected and setup ok,
but anything over 0.01 mechanically would show up on the surface quality every 90 degree.

Uwe

[kfedd]

Thanks guys for all the great input. I am hoping to find some time this weekend to make some adjustments as suggested, notably 4,000 steps/rev, and overall turns ratio. I will report back.

[kfedd]

I changed my steps/rev to 4000, and noticed a strange resonance in my Y axis when jogging at certain speeds with the MPG. Seems to be worst at a speed of 175IPM I can feel and hear loud vibrations in the Y axis fixed and floating ends, and at the ball nut connection to the Gantry. Quite jarring. If I run an MDI move at 150 IPM in the Y axis the vibration is gone, and at 200 IPM the vibration is also gone. I tried different steps/rev 2000 and 8000, and it does not change the resonance. I decoupled the ball screw from the stepper in the Y axis, and turning the stepper alone at 175IPM does not cause any resonance. The resonance seems to be caused by the ballscrew rotation at around 440 RPM. The X axis uses the same ballscrew but shorter, and does not cause any resonance. Sorry for the bad video.

175 IPM


150 IPM


200 IPM


I found this thread where a shapeoko had a similar issue with a diagonal movement.
https://community.carbide3d.com/t/shape ... t/57630/77

In hind sight the brackets supporting the Y Axis motor and fixed end, floating end, and gantry connection are 3/8" alloy angle, so a little like a tuning fork. Tried clamping some weight to see if it would change the resonance frequency, but not enough to make a noticeable difference. Might try again with more mass.

Anyone have any clever ideas to eliminate or at least shift this resonance to higher RPM / speed?

[Nigelo]

You could try temporarily sticking some sound deadening rubber to the brackets to see if that reduces the harmonics. If it does, you know it's the brackets which seems highly likely from their appearance. Then redesign the brackets with substantially stiffer profile perhaps even triangulated.

[cnckeith]

yes triangulation is the answer.