Hello
I am trying to cut a piece of 13cm high and ± 30 cm long. However it seems to skip steps on the first loop around the text. The issue starts where the bit enters the MDF piece.
I have milled it 3 times now and it looks like the issue becomes bigger. Now I do have to say that I cut the part further and further away from my starting point. So this might have something to do with it.
Am I correct that it is skipping steps here? And does anyone have some suggestions on how to fix it?
thanks
I think it is unlikely that you are skipping steps, because it is usually not so consistent and it doesn’t tend to happen at the beginning of the job (or not only at the beginning of the job).
I think this could be something more like backlash or stiffness in one axis.
Check the grub screws. Also it looks like you are doing ‘conventional’ milling instead of climb milling. That will cause the tool deflection to cut into your part, whereas climb milling deflects away from your part, which can get cleaned up in later passes.
Thanks for the suggestion Jamiek, I will check them and tighten them all.
Will also check ESTLCAM how the milling is set like you suggested as I have no idea how it is been set. I only know it does do a finishing pass.
This also looks suspiciously like an issue I had with my Low Rider (mine was more exaggerated though). It turned out it was the wheels traveling to one side. The cut that convinced me it was that problem was a cut in purple HD foam.
Here is the post where I was figuring it out, and a picture of the tracks I added to force it to travel straight:
So, I checked the screws and they are all very tight without any play.
I changed the milling method but that ran into an issue where I had to kill the job (damn that was scary). It got jammed on the inner circle of the letter O, probably because I did not use any holding tabs. But that wasn’t an issue before using the conventional way of milling, so will need to experiment there.
I still need to finish my machine, as I did not make any more progression to where I left in my build log. So I will definitely look for a temporary solution to guide the wheels like Jeffe suggests, and try once more.
Yes it seems that way.
I know you´ve already mentioned it elsewhere to try some tracks, so it is on my list as an upgrade. But haven´t had the time just yet to actually do it. Not sure if I should move this up in my priority list. I still need to make a flat workarea too 
I have been experimenting with the conventional vs climb milling.
It seems to have some impact too…
This is conventional milling; see how it travels layer by layer.
That´s a big difference as you can see. It is exactly the same job, just different way of milling.
However… the climb milling is causing multiple issues on my machine making it unusable.
It jams on area´s where the mill is cutting close to a previous part, or when breaking through my piece of wood onto the spoil board. And I also noticed it breaks layers of MDF easily causing a jam once again.
Did you have this issue on all your jobs?
Because, what I do notice is that a simple square or triangle cuts just fine (using conventional milling). But when using more curves or a longer piece (30cm or so), the issue starts as soon as it cuts the second layer into the wood.
The nail in the coffin for me was cutting the purple High Density foam from Home Depot (HD foam). I had the stairs appear there, where there was zero load from the material. If that couldn’t cut straight, then the machine was doing it to itself.
Conventional vs. climb makes it go clockwise vs anticlockwise (I can never remember which is which). So that further supports the idea that the machine has a bias in the X. Because the direction it travels would change which way the X slop would go.
I didn’t spend any time trying the machine before attaching some strips of wood. My Brad nailer was already loaded and nearby. One quick trip to the table saw to make some strips and a few minutes to tack them down (I didn’t use glue, they don’t have to be strong, just in the right place so it won’t jam). The next cuts in HD were perfect, and I haven’t looked back.
YMMV. This is all just my opinion. Many people have no issues with it.
yeah, I am sure your totaly right.
Think I´ll go find myself some HD foam to test it out.
Will report back when that happened.
Thanks a lot for you insights!
a follow-up;
it has been hard to find “HD foam” in my area so I settled for XPS polystyrene panel.
Using the exact same gcode, it becomes clear that the used material doesn´t make a difference. The moment LR2 started a second pass the line was no longer aligned.
When the job was done, a view on the side showed indeed the same issue as when using MDF.
It´s becoming clear to me that the L2 moves sideways on the table.
Some dust remained from a previous job. It made it easy to track the direction the wheels roll. As you will see, the line gets wider where the part is been milled.
Will see if I can add a wheel guide for now, and if that fixes my issue, I will upgrade it completely, to use something else then skate wheels. I am just a bit worried that maybe the XZ_Main isn´t square. If that´s the case a wheel guide will not make a difference.
This topic has some similar issues.
I know @jeffeb3 had similar issues. I did, too.
Some of these LR2 builds just like to walk sideways, it’s one of the issues the LR3 is addressing.
I have a bit of work in on adapting the LR3 fix to the LR2, but it’s not complete.
I think that some constraining strips inside the wheel tracks are likely to resolve your problem. The X axis travel will bind if the rails arent good, and if it’s a little out of square, the constraining strips will at least make your tool path repeat reliably until you figure out the squaring issues.
You can also to a really quick test to make sure you assembled it square. Measure the distance between the back wheels and the front wheels. The distance should be the same. if not, it will want to make a giant circle.
A second possibility is you are not starting square and you are hitting the side of your table, basically driving crooked.
A third is you are just trying to move way to fast, rapids and cutting speeds.
If the distances are very accurate, and the rest check out, you can add a rail like Dan suggested.
The other thing you have not mentioned is if you are wired individually, series or parallel. What board, what drivers and what current are they at.
There are a ton of things that can cause this sort of thing.
Another thing to try is air cut the entore parimeter of your piece to make sure there is noe wires or cords snagging, and offset will happen on the first lap after that it should cut fine.
Your climb vs conventional is making this all seem very odd, like you might actually just be moving to fast.
That is the part that makes me think it isn’t tracking straight. The results are different in clockwise and anticlockwise directions. The drift is in a different direction.
I guess it could be, such a weird one. The machine still has to make the same moves, just ends up being on the other side of the table. Clockwise vs counterclockwise on a circle still gets a circle, but you do have experience with this. I could never get mine to do it.
Thanks for thinking with me guys, I appreciate it!
Yes, I know for sure that it isn´t square, nor is the bed level. I still have to make time for this. It´s like you say, if repeatability is ok, then that´s ok for now 
I have some 5 meter long Alu L profile from the house renovation laying around. So will cut this in the coming days and mount it to the table.
I have installed the upgraded belt holder, for the GT2 belt. So I know it starts parallel on both sides, but when running from one end to the other, it slowly goes to one side of the table. As it needs to re-align when going back home to the initial belt holder. Will measure the distance between those wheels and report back.
Well I still need to experiment with those settings, for now I use the suggested speeds in the Wiki. So I hope this will not be the reason of the issue.
Regarding the setup; I use the recommended SKR Pro, with steppers in series. So “pretty stock”. I do however still need to find some time to properly work away the wires. So maybe this is part of the cause.
Thing is, if I just mill simple and small items all goes well, longer items, or like a name and it is giving issues.
But you guys gave me things to try, I´ll report back soon.
Update:
I´ve installed two alu L profiles sitting against the skatewheels.
It does indeed help with making a clean cut. However, I also seem to notice that if I run too fast, the wheels might jam. Maybe I installed them a tiny wee bit close. But that will wear out.
This is a before and after, using the exact same settings and tool.
Wonder if I would be able to get rid of the last lines caused by the finishing pass. They are barely visible, but in my quest for perfection … 
As the brackets make the table unusable, I´ll probably will be looking for an alternative. But maybe I´ll try to hold on few days, as I´ve read LR3 might solve this issue too.
Is your finishing pass full depth? There should be no load on a finishing pass and you can use the whole bit to get one smooth cut.
You can’t have binding. It is a bummer you got it so close they are binding. Can you offset the screws in the other direction to let you adjust the fit? You only have to move one rail out. Alternatively, you could try to make the gantry a small amount wider.
no, I also do this in multiple passes. Tbh never tried to do this in 1x only
I often chose to do first pass in for example 2mm, finishing in 3mm.
Yes, this is what I did. During install I added 3 pieces of tape between the wheels and rail, to have some small amount of room. However there seems to be some flex after the first run, but also overnight. As the first run was ok, second one not. The same as parking it at night, and the day after.
So rolled the wheels from one side to the other, and it seems to be wearn out already, it no longer jams. So me happy 
Game changer. Your machine can handle it. Give it a try. For soft stuff try leaving 0.5mm for the full depth finishing pass.
That is indeed a game changer, that I´ll need to try.
how different is your “finishing pass” setting vs the regular then?
