I’m trying to print this box that has 4mm inset magnets. The holes are 4.15 so it should be a snug fit, but fit. In the full size print , they they don’t. No amount of force will get them in. When I cut it up to get a quick print to test various hole sizes ((small piece on the left), it fits in 4.15 with ease They fall out at 4.2.
I’m baffled. I’ve done inserts at a .1 tolerance before with no issues. H2C, .2 layers, 200 mm/s, 2 walls, 10% cubic
Maybe this can help as it is not only about the size. Shape can help too:
A drop of super glue is what I normally use in this case.
Measure the holes with a caliper at a few angles to see what it actually is, then adjust your holes to correct it. Maybe it is the X/Y hole compensation or something more complicated.
I know how to correct it if needed. My question is why it behaves differently in the test piece vs the whole box.
There is probably warping happening on the box around the holes, but the small part doesn’t have the same stress
At a guess, a given shrink during cool down is dependant on the total part size. At least to some extent.
2% of 10mm versus 2% of 100mm…
Have you tried measuring the holes that fit vs the holes that don’t? What is the difference?
At 4 mm, it’s a little too small to measure the ID with the calipers I have.
This should be pretty easily do able with basic and cheap calipers. I would suggest getting some that can do this if yours are different for some reason.
Getting a reliable sub millimeter measurement on small holes is actually pretty difficult with a set of linear calipers due to how the measuring points are offset and pointed. For reliable measuring a sent of gauge pins should really be used.
Gauge pins only tell half the story as it’s a go/no go. Using calipers at multiple locations can help determine if there is a skew to the part which is likely what is happening. His magnets are acting as a single size gauge pin. We are trying to diagnose now why the same modeled hole is different in two different models/parts.
Interesting discussion. But has anyone already considered that the magnet have a also a tolerance?
Everyone seems to assume that the magnet is D4.00mm in size. I think OP should also measure the magnet size to see if there are deviations. I have measured many different sizes and types of magnets over the last years and some are up to 0.10mm larger than nominal.
I thought that too, I did measure them and while they all ran a little large, none were more than .05 big. The confusing part is that depending on how I cut the magnet section out of the larger model for testing, sometimes they will fit in 4.1, and sometimes I have to go as big as 4.4. Just for giggles I did a test print with PETG-CF, and they fit like a glove in a 4.1 hole. It’s something in the model geometry causing greater than normal shrinking.
Salut !
Ah c’est bizarre ton truc Moi j’ai pas encore fait de trucs avec des aimants donc je peux pas trop aider…
Mais du coup la seule différence c’est la taille de la pièce entre celle qui marche et celle qui marche pas ? Peut-etre que sur la grosse pièce y’a un problème de retractation du plastique en refroidissant ? Genre ça se déforme un peu plus ?
Ou alors c’est un soucis de calibration de l’imprimante sur les grandes surfaces ?
Désolé je débute encore donc j’suis pas sur de mon coup Quelqu’un a une idée ?
First post here.
I assume some of the pros on here have methods for dealing with producing accurately sized parts, but I haven’t seen any. I have a fairly robust hobby machine shop and I’m accustomed to working with tolerances of .001 inches. But shrinkage isn’t a significant problem when machining metal. After a few frustrations on some holes, I printed what I call a scale block. It’s 35mm x 10mm x 5 mm with three holes in it, 3mm, 4mm and 6mm. Then I checked all dimensions with a mic. Definitely some shrinkage and enough to screw things up on fitted parts. The long dimension on the block had the least deviation percentage-wise, which makes sense. At least this gives me a method to allow for it, which mostly solves the problem. I think going forward if I need something to be a precision fit and it’s a size I haven’t checked I’ll print a small test piece to get me in the ballpark. I suspect other factors have an impact, such as type of filament, thickness of the part, etc. But at least it gives me something to work with. I’d love to hear any suggestions on other methods. Always looking to learn and improve.
Specifically regarding the magnets, I found that my H2D set at default settings using PLA Basic worked well with a .5mm increase on hole size and depth. Did a piece with 2 stacked 5mm x 2mm magnets in two places on the part. 5.5 mm diameter and 4.5 mm depth. They fit perfectly and the print job over them was flawless. I was going to upload a photo of the scale block but I keep getting a message that I can’t embed photos in a post. Obviously that’s not true. Maybe because I’m a new user?
Gauge pins will get you close but decent gauge pins are not cheap. Because I do machine work I have them but it may not be common for 3d printing, especially as a hobby. But variance with plastic is a lot so you can only do so much, even with gauge pins.
Good point. The ones I’ve measured are pretty close but certainly not precision ground.
The problem here is that Bambu Studio also seems to be doing some corrections on holes.
There are so many factors that influence the hole size, that it is almost impossible to get standard rules. But experience helps to come up with good starting parameters
Things that influence the size are:
But if I would require a large series of products (which I normally don’t) it’s worthwhile to design a prototype (even a test block is not a good reference in all cases), print it and then compensate the dimensions.
Usually 1 prototype is enough if you already start with offsets from experience.
And if I am making just one or two parts, I usually go to the lower end of the bandwidth and machine the holes to size. Heating the magnets slightly above Tg also helps to get them in a tight hole. Some magnets don’t like too much heat, but most can withstand 200C without losing strength.
You could consider providing a bore for the magnets as shown in the image. This would allow the magnets to be inserted with significantly less force. At the same time, only local stresses that are evenly distributed in all directions are generated within the component. This helps to prevent the component from cracking or splitting, either during insertion or later due to delayed stress.
In addition, this design would be less sensitive to diameter tolerances of the magnets.
