Required Dimensional Accuracy for Printed Components

Mostly Printed CNC - MPCNC Troubleshooting
1

Greetings all, I’ve recently begun embarking on my journey to the MPCNC promised land, but as I’ve started printing out parts over the last two weeks I have become concerned that my printer may not be up to the task. I have a 1515 Kossel Mini that I got as a kit just over a year ago. It’s a good machine for all its breakdowns along the way, but I’ve coaxed some degree of predictable quality out of it.

The issue is the “some degree.” As mentioned, I’ve been printing parts for about two weeks now non-stop, using my own .25mm nozzle on an E3DV6 hot end. By and large the parts have come out beautifully and I was quite pleased, but after reading a post from another user (in the center upgrade thread) about how a dimensional inaccuracy of .2 - .3 could be a killer and lead to a nonfunctional machine, I got concerned and printed out a number of 25mm calibration cubes. After dialing in a few aspects, this is what I’ve got:

Nozzle Diameter: .25
First Layer Height: .18 (Max for nozzle)
Cont. Layer Height: .09
Infill: I do infill every 2 layers. The infill ends up being as solid as every two layers it does infill layer height at .18. I’ve found it lets parts print out much nicer with the same amount of time needed as printing at entirely .18 layer height with infill at every single layer.
Filament: Very high quality PLA with dimensional accuracy of +/- .05

My best settings so far having it at approx 25.04 x 25.12 but in every attempt one side has been consistently larger than the other. Now my issue is that delta printers aren’t square, and use an entirely different variety of math than Cartesian printers, and as you can see… the dimensions are not entirely uniform. The good news is that with the updated parts, both presently and soon to be released, there’s a lot that I need to re-print. As well, I’m probably going to use PET for my second attempt (assuming bridging works with that), but I need to figure out if it’s even possible for me to print the parts with my machine’s rather unique inaccuracies.

Any suggestions or advice? Can I get away with variable amounts of sanding? I can’t seem to find much about rectifying this sort of issues with delta printers.

2

That’s really not too bad. Easiest was to be sure is print one of the parts that have three bearings and see how well they grab the conduit. My problem was I was printing too big. I was .2 to .3 over. There was enough of an error that it couldn’t be fixed by tightening the bolts. I’m now printing a tad small, but that seems to be okay. Pet-g doesn’t bridge well, but none of the new parts require any large bridges. Just small ones above bolt holes.

3

Even if you order the printed parts, you may have a little sanding to do. A lot of that will have to do with the conduit you get as they all seem to vary in diameter slightly. I had to reprint a couple pieces at home and used my XYZ DaVinci Jr, and everything was cool. I think the parts are fairly forgiving in regards to your printer.

4

I agree, the biggest variable will be the conduit that you get. The .08mm variation between sides shouldn’t cause any issues at all.
I printed the 25mm version. I can’t remember exactly what my calibration cubes were but they were very slightly undersized. In turn all my parts would have been slightly small but I still found the overall fit to be a little loose. I had to tension the bolts a bit to get a good fit. From what I’ve read, most people seem to find the 23.5mm to be a tighter fit though.
That may have been down to the conduit here (it seems to be very slightly oval, bringing down the effective diameter where the bearings grip), but I would try and get the calibration cube values a little lower if you can just to be safe. If it was me I would try and have that .08mm variation in the 24.96-25.04mm range.

5

Thanks for the advice everyone! As it happens, I already had the variable at around the 24.96-25.04 when I set the filament width to 1.75 from 1.74. I have it at 1.74 now but I’'ll just change it on back. As far as the PLA vs PETG, I’ve still got another spool waiting of the former, so I’m gonna continue on with that. Any advice on what components to save the PETG for?