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# Accuracy

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This topic contains 4 replies, has 3 voices, and was last updated by  mdgli 1 year, 11 months ago.

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• #4189

mdgli
Participant

Hi,

I mainly do wooden things on it. Cutting and engraving.
Lately I started to do bigger things and then I realized that I have a few accuracy problems with my machine.

1. Squareness – There is a bit of flex in the middle bit so the tubes of X and Y can be easily go out of square. I was hoping that IE_Middle_Z_rigid_v2 will help. It improves the situation but not completely resolving .

2. Travel distance – I try to engrave 440mm square. I get X perfectly 440 and Y 442.3. Both have the same driver, same stepper motor and same DEFAULT_AXIS_STEPS_PER_UNIT.

Any advice will be well appreciated

#4199

Ryan
Keymaster

1)How big? How out of square? Are you sure it is flex and not you machine set off square? If you measure across the center is it exactly the same? How long is your z axis? Have you tighten things up lately I start loose and snug it up once and a while, or you can rotate your tubes to get a new surface if you are starting to get grooves.
If your z axis is hanging 8″ down it could be that moving, Either mover your piece to be cut up as close to the gantry as possible or cut down the height of the machine. I do all my cut as high as possible.
You can slow down and you should not get any flex in wood at all. If you are going to fast you might be able to flex it but I really doubt that unless you are running a very large build. They should not easily go out of square.
2)I have no idea what could cause that, unless you are making parallelograms from a non square build. Try taking off the cutting load and run a pen or marker and see if you are dragging too much. Problem 1 will probably solve problem 2.

#4207

mdgli
Participant

1)How big? 80×80 cm
How out of square? up to 3 degrees
Are you sure it is flex and not you machine set off square? outside frame is perfectly square
If you measure across the center is it exactly the same? on the outside frame yes
How long is your z axis? 30cm
Have you tighten things up lately I start loose and snug it up once and a while, or you can rotate your tubes to get a new surface if you are starting to get grooves. Yes
If your z axis is hanging 8″ down it could be that moving, Either mover your piece to be cut up as close to the gantry as possible or cut down the height of the machine. I do all my cut as high as possible. NA
You can slow down and you should not get any flex in wood at all. If you are going to fast you might be able to flex it but I really doubt that unless you are running a very large build. They should not easily go out of square. NA
2)I have no idea what could cause that, unless you are making parallelograms from a non square build. Try taking off the cutting load and run a pen or marker and see if you are dragging too much. Problem 1 will probably solve problem 2. I know, This one is a real puzzle 🙁

The squareness problem is more about the movement of the middle tubes. To demonstrate that I’d say hold the two side sliders of X axis and slightly push one forward and one back. It can move on my machine. Not much but a move that take the whole thing out of square.
So before I start my build I always check and fix the squareness but if I drag the axis by hand to bring it to starting point I risk ruin it.

#4208

SteveC
Participant

@mdgli,
Try moving the two X axis sliders oppositely but with the steppers locked/driven. You will see that they stay at the squareness that they “locked into”. If you start with the axes perpendicular then then will stay that way until the steppers are disabled. This remix is an attempt to make it easier to start out in square http://www.thingiverse.com/thing:918871. I have never tried it but let us know if it helps.

I did need to do some light sanding to remove some excess plastic extrusion on the X and Y slider/clamps which caused a bias in one direction/angle of both sides of both X and Y. I wrapped some very fine sandpaper around a dowel and it helped to tweak the X and Y to be square with the side rails.
Steve C

#4212

mdgli
Participant

Thanks @stevec,
Absolutely agree that when the steppers are locks machine will not go out of square as you can’t move either side of the tube.

The problem of squareness is probably a result of my working method.
I clamp a blank somewhere on the working area reset the axis position to 0 and position the “head” dragging it by hand. When the router bit is in position execute a “print from SD”.

When I drag the “head” to position I need the motors to be unlocked and probably not always I drag it evenly from both sides.

So now after I square the axis i never drag it by hand just move it using the controller and when it is in place reset origin (set all axis to 0).

If in any way I could “stiffen up” the axis cross it would make things eaisier.
This is maybe what this fella wanted to achieve
http://www.thingiverse.com/thing:1079878
http://www.thingiverse.com/thing:1096540

Thanks for the link you sent. Yes this make the squaring process easier and I think this guy faced similar problems to mine 😛

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