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- July 23, 2016 at 9:41 am #15133
I recently wanted to do a larger cutout (~19.5″ x 29″) but could not get it square. I have checked the x and y lengths and they are equal. As a test I used the LCD and drilled 4 1/8″ holes at the extreme corners and measured the diagonals. I was off about about 1/4″. I then unfastened the legs on the x axis (my longer axis) moved the frame a little bit and tested again; same result. I tried several more times and it would not change. I finally moved the x axis by almost 1/2″ noticeably moving the frame and ran the test. Once again the same distance off on the diagonals. I am confused as to what might be causing this.
With the origin on the lower left it is the diagonal from lower left to upper right that is always the long distance. I have been moving the far x rail to the left.July 23, 2016 at 3:45 pm #15150
Make sure your frame diagonals are spot on, as close as you can get them. Then before you start your cut make sure your rollers are equal distance from the corners on each axis. when you move the gantry around you can kind of twist it. I have been cutting the MP3DP frames that are 15.5″ squares and now they are coming out as perfect as I can measure with a tape, and a large square. The first time you do it it will make sense and only takes 30 seconds or so.September 23, 2016 at 5:15 pm #18230
This was similar to the exact issue I was about to post about. I just finished installing an aluminum rigid coupler to replace the second one I broke and when I went to move the x axis back to home I noticed it skewed to the side slightly as I moved it. I’m trying to think how I could reduce some of the slop off of the x and y but short of tightening down the bearings (which I dont want to do being that I cracked the first roller block I installed when building the machine from overtightening) I am not sure how to accomplish that. My first test drawings and cuts didnt look to bad but I havent started testing for accuracy yet… just working on getting it actually cutting the design I throw at it.September 30, 2016 at 12:50 pm #18769
So I have been battling this problem from day 1. I disassembled all of the rails and started over. It appears that the issue may reside with my middle assembly (I purchased the kit prior to the new middle assembly so I have the old one).
I have the outer rails equal in distance end to end and diagonally. I checked several times and had a friend check as well. I tried to do the roller equal distance from the corners but am not able to achieve this.
It is when I assembled the inner rails and middle assembly (without Z axis rails installed) that I encounter issues. I can get my X axis (long axis in my case) inner rail parallel to the outer rail, but the Y axis inner to outer is not parallel. If I hold the X axis in place and try to get the Y axis parallel I can see the middle assembly physically flex. I am off about 3/8″ (axis is 32″ in length). If I get this parallel the X axis is not parallel. I have loosened up the bolts on the “Gray” pieces (same pieces as shown in assembly pictures) but it did not help.
I am not sure where I go from here.
Attachments:September 30, 2016 at 2:32 pm #18774
How far off is it, 3/8″ across the diagonal? they should be bolted down as perfect as you can get them, withing a 1/16″ should be easy enough? If the gantry bars are off when you put them into the rollers they should get closer as they force them more square.
You should be making any adjustments with the z axis in place, or at least the rails, they open it up. You can follow the new instructions it is pretty similar to the old one. So I suggest making the outer frame as square as possible, with nothing on it. Then make the center assembly as square as possible with all 4 rails in place but not on the frame, then when you connect the 2 it should actually get a little better because of the rollers trying to align things.
If it is really far off check the calibration of your printer, all three axis test a 100mm movement with calipers it should easily be within about .2-.5mm over 100mm.October 1, 2016 at 12:21 pm #18833
Did some more trials and testing today, but first I will answer the questions.
The 3/8″ is the difference in the y axis gantry rail to outer rail end to end (see attached picture in previous post). (i.e. one end has the gantry and outer rail 4″ apart, the other end is 4-3/8″ apart) The Diagonal measurement to the corner blocks is within 1/16″.
Trials today. I was able to get the starting distance between the gantry rails and the frame rails parallel to each other. Power on the controller and re-checked the distance and it was still good. I jogged the gantry almost the full length of the x axis and back again. On the extend motion The y gantry y rails ended off about 1/8″. On the return motion they ended up being 1/4″ to 3/8″ off. It was always the same, the gap got greater on the end away from home position. I then drew a rectangle and noticed that x side away from home measured shorter. It looks like the return move was shorter than the outgoing move. I have tried to capture this pictorially with the attachments.
I also noticed that when I power of the controller the steppers are not energized to hold position. After a move they are energized for a time and then seem to “relax”. Does this sound correct.
Any thoughts would be welcome.
Attachments:October 1, 2016 at 12:25 pm #18836
I position my rollers with a measuring tape before I start every single job. Dragging the gantry around by hand no matter the size will always leave the rollers not evenly spaced.October 4, 2016 at 7:00 am #18940
I have been following this thread because I am also experiencing this a little bit also. Ryan you mention that before every job you reset yours to square. I have built a couple spacer blocks to use to set the rails accurately every time. I am thinking what I would like my machine to do is as soon as the controller and everything gets power I would like for all of the steppers to be energized and hold their position. Thoughts?October 4, 2016 at 7:58 am #18941
Ok I think I found my own answer. What I was noticing is after I would set the space with my spacers the steppers would de-energize after a bit and when they would do that they would relax and I would lose the parallelism by a little bit. I did some research and found a line of code in Configuration_adv.h. The line is: #define Default_Stepper_Deactive_Time. It looks like the default setting is 60 seconds and changing that will allow me more time to make sure the steppers dont relax and I can set my z height and get the X0, Y0 set and start the job.October 4, 2016 at 10:26 am #18951
My zero is always in a different position, blocks/spacers are not an option. I set the tool to my zero/home, then move all 4 rollers by hand to where there are equal with their mate using a tape measure. They stay there and then of course when powered up they are locked in. It sounds to me like this is more accurate, if you have to power your steppers to hold them, something seems off.
I will make a video next time I make some parts but it is not complicated, pretty sure I have some pictures of it on here somewhere.October 4, 2016 at 10:55 am #18955
Sorry I mislead you. I use the blocks to set the tubes equal and square then once that is done i move the gantry to my Zero position using the LCD screen. I believe I have seen those pictures somewhere.
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