whats your strategy for tuning demensions

Say your part comes out a tenth or so of a mm big or small in x or y. What adjustments do you make.

Steps per/mm in the firmware

interesting. I thought it would be more or less flow assuming the error was a result of the extrusion width but actual travel adjustment would have the same effect without altering the extrusion proccess. see, I'm learning. thanks

Edited 1 time(s). Last edit at 04/07/2014 07:13PM by Bill Clark.

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Bill Clark
interesting. I thought it would be more or less flow assuming the error was a result of the extrusion width but actual travel adjustment would have the same effect without altering the extrusion proccess. see, I'm learning. thanks

Never change your X or Y steps per mm based on a print. Test how far the axis moves using a dial gauge or digital callipers to set the X and Y steps per mm if you can not use the belt and pulley sizes to get the X and Y steps per mm correct. If the print is coming out too large after getting the steps per mm correct then it will be an E steps per mm issue (or flow modifier in the slicer).

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A tenth of a millimeter? What the hell?

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Assuming parts are printing small, an alternate method assuming steps per mm are correct and your E steps are dialed in giving you good print results is to scale the part in your slicing software. PLA shrinks a tiny amount and ABS a bit more.

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Sublime

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Bill Clark
interesting. I thought it would be more or less flow assuming the error was a result of the extrusion width but actual travel adjustment would have the same effect without altering the extrusion proccess. see, I'm learning. thanks

Never change your X or Y steps per mm based on a print. Test how far the axis moves using a dial gauge or digital callipers to set the X and Y steps per mm if you can not use the belt and pulley sizes to get the X and Y steps per mm correct. If the print is coming out too large after getting the steps per mm correct then it will be an E steps per mm issue (or flow modifier in the slicer).

I've tried it both ways and have gotten good results from both. Any reason why you should base off none-printing movement?

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gmh39

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Sublime

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Bill Clark
interesting. I thought it would be more or less flow assuming the error was a result of the extrusion width but actual travel adjustment would have the same effect without altering the extrusion proccess. see, I'm learning. thanks

Never change your X or Y steps per mm based on a print. Test how far the axis moves using a dial gauge or digital callipers to set the X and Y steps per mm if you can not use the belt and pulley sizes to get the X and Y steps per mm correct. If the print is coming out too large after getting the steps per mm correct then it will be an E steps per mm issue (or flow modifier in the slicer).

I've tried it both ways and have gotten good results from both. Any reason why you should base off none-printing movement?

Simply put it is because we use math to make things and using the wrong numbers is wrong.

An example is like this. If you print a 20mm cube and it turns out 20.2mm's and you adjust your X and Y steps per mm to make it 20mm you will now be moving the axis 0.2mm's less for every 20mm's you move. So if you then print a 200mm object the machine will move 2mm's too little and you will end up with a large waste of plastic 198mm across, not the 200 you wanted.

The slicing software takes the object (say a 20mm cube) and then creates paths for the perimeter that are inset half of the extrusion width. If the extrusion width is 0.5mm's it will create a path in a square shape 19.5mm across allowing for 0.25mm's of extrusion on each side of the path it calculates. If your machine moves exactly 19.5mm's as it should then the only reason the part does not turn out the correct size is because the extrusion is greater than 0.5mm wide.

Hope that all makes sense.

EDIT: there is also a chance that the slicing software is to blame and testing with another slicer may reveal this.

Edited 2 time(s). Last edit at 04/08/2014 02:02PM by Sublime.

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Personally I do a combination of the 3 (calculate steps, adjust flow, & measure)

Step 1 is to set the X & Y based on calculated steps/mm.

Step 2 I will verify my e-steps and perform a single wall extrusion test to verify flow. Like someone mentioned each material has a different shrink rate. If you plan to print with different materials make sure to do this test for each one.

Step 3 I will print a 25mm cube, as well as a right angle "L" that is 150mm in the X and Y. In my experience I have gone round-n-round with dialing in dimensions using flow, only to have dimensions vary. Now everything has a tolerance to it, and where math is perfect manufacturing processes are not so much. I found that verifying dimensions over a range of distances can help show if there is % error. A 25mm cube is a small percentage of actual print volume. If your machine is producing a % error over distance you may not notice this on small calibration cube but larger objects you will.

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ikilledkenny
Personally I do a combination of the 3 (calculate steps, adjust flow, & measure)

Step 1 is to set the X & Y based on calculated steps/mm.

Step 2 I will verify my e-steps and perform a single wall extrusion test to verify flow. Like someone mentioned each material has a different shrink rate. If you plan to print with different materials make sure to do this test for each one.

Step 3 I will print a 25mm cube, as well as a right angle "L" that is 150mm in the X and Y. In my experience I have gone round-n-round with dialing in dimensions using flow, only to have dimensions vary. Now everything has a tolerance to it, and where math is perfect manufacturing processes are not so much. I found that verifying dimensions over a range of distances can help show if there is % error. A 25mm cube is a small percentage of actual print volume. If your machine is producing a % error over distance you may not notice this on small calibration cube but larger objects you will.

Ok so here is the problem with that. Lets start from the end of my last example assuming we are calibrated to print the 20mm cube. Now when we print the 200mm cube we need to readjust the X and Y steps per mm so it prints correctly. Great we can now print a 200mm cube the correct size but when we print a 200mm cube 2mm thick with a 20mm cube on top of it in the middle we have the 200mm part correct but the 20mm part is wrong. How do you change the X and Y steps to account for both. You can't so all you can do is have the axis calibrated to move the correct distances and rely on the coordinates as calculated by the slicer based on the model and then use the features of the slicer make any changes. I for one use Kisslicer and Cura and all of my prints are within 50micron of the correct size (even the small holes) as long as I use a layer height below 0.25mm as large layer heights cause all kinds of issues with accuracy.

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Sublime

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ikilledkenny
Personally I do a combination of the 3 (calculate steps, adjust flow, & measure)

Step 1 is to set the X & Y based on calculated steps/mm.

Step 2 I will verify my e-steps and perform a single wall extrusion test to verify flow. Like someone mentioned each material has a different shrink rate. If you plan to print with different materials make sure to do this test for each one.

Step 3 I will print a 25mm cube, as well as a right angle "L" that is 150mm in the X and Y. In my experience I have gone round-n-round with dialing in dimensions using flow, only to have dimensions vary. Now everything has a tolerance to it, and where math is perfect manufacturing processes are not so much. I found that verifying dimensions over a range of distances can help show if there is % error. A 25mm cube is a small percentage of actual print volume. If your machine is producing a % error over distance you may not notice this on small calibration cube but larger objects you will.

Ok so here is the problem with that. Lets start from the end of my last example assuming we are calibrated to print the 20mm cube. Now when we print the 200mm cube we need to readjust the X and Y steps per mm so it prints correctly. Great we can now print a 200mm cube the correct size but when we print a 200mm cube 2mm thick with a 20mm cube on top of it in the middle we have the 200mm part correct but the 20mm part is wrong. How do you change the X and Y steps to account for both. You can't so all you can do is have the axis calibrated to move the correct distances and rely on the coordinates as calculated by the slicer based on the model and then use the features of the slicer make any changes. I for one use Kisslicer and Cura and all of my prints are within 50micron of the correct size (even the small holes) as long as I use a layer height below 0.25mm as large layer heights cause all kinds of issues with accuracy.

I might have not explained it the best before, so here is an example to what I am referring to. These are all just hypothetical values used to illustrate the example not actual values.

Calculated theoretical axis steps are 100 steps/mm, but actual movements steps are 101 steps/mm. Using the calculated values to create a 10mm cube your movement would be short 10 steps per axis resulting in a part that is .1mm undersized. Hey not bad being .1mm off is not bad at all, and with in most standard printed tolerances, but now if you printed a 100mm cube this would result in an axis being 1.0mm undersized. Now going back and increasing the steps/mm by 1 would change both the dimensions of the 10mm and 100m, but it would change it proportionally with the 10mm cube only seeing a .1mm change, and the 100mm cube seeing a 1mm change.

I think one thing that is overlooked with using belts is the actual pitch. A T2.5 belt should have a pitch of 2.5mm, but because of manufacturing tolerances and even belt stretch the pitch could be different. Something as small as a .02mm difference in pitch could change your steps per/mm by 1 if not more (example 1.8 deg motor, 1/16 step, 8 tooth pully, and T2.5 has a calculated value of 160 s/mm. If the pitch changed to 2.48, new steps would be 161.29 s/mm).

I do agree that if possible measuring the actual axis movement would be the best to verify travel, but setting up a caliper or dial indicator to be 100% parallel with your measurement axis can be the pain. Measuring right from the print is not the best solution, but is a good alternative IMO.

I also agree that getting the correct flow rate is one of the most important aspects of tuning a printer, and should always be done first before adjusting the axis. But adjusting the flow/e-steps can only get you to a point. To really tune in your axis's you need to take actual measurements. To me it is no different than adjusting your e-steps on your extruder. A person can calculate out what the theoretical e-steps should be, but you always want to verify this by running 100mm thru and verifying the actual movement.

A belt may have small errors in pitch from tooth to tooth, but it will have an exact number of teeth per meter. Therefore the pitch error over distance does not sum up, the pitch error is an absolute error.

It's a bit like using two poorly made 20 tooth gears - although there will be position error as you rotate the gears, every turn of the gears they will be back in the same state as originally. The error does not increase every turn!

There might be a slight adjustment needes if the tension in your belts is so high they are measurably stretching, but good belts should have negligible stretch.

Edited 1 time(s). Last edit at 04/11/2014 08:18AM by konwiddak.

A little late but thanks for the feedback guys. I have been scaling, adjusting extrusion width or changing the extrusion multiplier to dial it in. I am currently using a .2mm nozzle and will soon be going to a .1 or less to produce very small, well defined parts. I have actually been quite surprised how well the whole extruder is doing at regulating flow. Usually its difficult to even tell if the big gear is moving