Thermwood C53 router - Jerky motion

[Gavin Armstrong]

Hi,

I have a C53 router (1997) and I am having trouble with the machine not slowing down for corners. The router will continue at full speed and make a 90 degree turn of direction, this causes the head to vibrate leave marks in the work piece.

Slowing down the overall feedrate solves the issue in part, but I would like the router to run at much faster feedrates so its not really a good solution.

I have had some success adding in a G804 or G806 into the start off each program. But this only really works on curves.

I was thinking this might have something to do with the look ahead feature but the square shapes causing the problem are only made from simple staight lines with only four coordinates to desicribe each shape and not a whole bunch or tiny splines.

Many thanks
Gavin

[Forrest Chapman]

Try adding a G090thruwhatever. I would suggest starting at G0905 and if that's too fast then go lower like G0902. It may be that someone set the default to high.


Forrest

[Gavin Armstrong]

Thanks Forest, what does the g905 do to the machine?

[Brad McIntosh]

Hard to tell without seeing the code but, if it is a software/nc code issue than there are two things that I would check - Forrest's G09 is one...

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Forrest is referring to the "TANGENCY FACTOR" and the format is G09F##, where ## represents 1 through 20. The default on the machines is usually 1.

The Tangency Factor on the older machines (Pre-Smoothing G07F##) set the threshold at which the machine would consider two entities tangential and thereby not coming to a stop, but instead combining the entities into the same motion/velocity curve.

Normally you do not need to increase the default as most software will create tangential line and arc segments when possible. You will see a Tangency Factor of 3-5 when you have 3d surface modeling where the toolpath is made up of small line segments with very small angle changes that are not tangent but that you would like the machine to "flow" through as it they were. Any angel change larger than the threshold set by the Tangency Factor will still cause the machine to come to a decelerated stop and then an accelerated start in the new direction.

You may want to check to see if someone has added a G09F## with some "stupidly large" value that would have increased the tangency threshold to the point that the 90 direction changes would be attempted without stop and start at the corner.

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Another thing to check is: IF the program generating the code has placed arc moves in the corners in order to "roll" the tool around each while still producing a square corner - then you should check for the presence of the ARC SPEED FACTOR parameter - G08F##. This commands numeric parameter increases or decreases the default "speed control" that is applied to tangential arcs. The control by default has a calculation built in the will automatically adjust the velocity of the machine as it goes through arcs. This adjustment is based on the size of the arc radius. IF the radius is large, then there may not be any decrease in speed. But as the arc gets smaller and smaller (the smaller the arc the more "instantaneous" the direction chance gets), the controller will automatically decrease the speed in the arc - decelerating as it approaches it and then accelerating back up to speed as it leaves it.

A numeric parameter is like a multiplier for the built in calculations. 1 is the default (calculate as usual) and should normally be fine and you do not have to explicitly define the G08F1. If you want to reduce the arc velocity you would use a multiplier less than one (<1). G08F0.5 will halve the natural velocity adjustment calculations of ALL arcs that follow. If the parameter is larger than 1 (>1), then this means that the velocity calculations would result in increased values. G0F2 would double the default calculations.

You may want to check for a G08F## with a number/parameter greater that 1.

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Both of the G09F## and G08F## parameters do not need to be explicitly defined in the NC code if the defaults are all that are required. (Which is in most applications is all that is required.)

You should also check directly with Thermwood's software support and/or technical services. program@thermwood.com - service@thermwood.com

[Gavin Armstrong]

Many thanks for your help Brad,

After looking again at my cam program I see it was in fact rolling the tool around the corners as you suggested. Just going to give it a test run with the option to keep corners sharp but I am confident this will solve the issue.

I may still have an issue with tight internal corners as my cam package will not output arcs, the machine will prob still hurry round these internal corners and casue the head to vibrate exiting the corner. But these corners are far less common and I feel confident I can find some sort of work around

Thanks again
Gavin

[Will Williamson]

Thanks for the explanation Brad. You are an real asset to the Thermwood team