material filling in small holes in the design

I’m trying to print a plastic holder with holes in the bottom because I want to run thread through the holes. I’ve printed multiple times (4 different times) with my lulzbot mini 2, but I keep running into this problem where the plastic (I’m using Polymaker PLA) ends up filling in the small holes. Is there a way that I can configure the printer to protect the holes from being filled in with plastic?

I’ve attached the STL file that I designed for printing.
LM2SE05MM_holderv2.gcode (352 KB)
I also have the gcode generated by the Cura software (using version 3.6.18).
holderv2.stl (75.9 KB)
I was unable to figure out how to get the INI configuration file, because there was no “File > Save profile” menu option as documented here:

I’ve also attached pictures of what my print looked like:

And I have pictures of what I wanted it to look like. I’d printed it with a different 3D printer. I don’t remember the model or which company made it.

I thought maybe changing the profile from “Standard” to “High Detail” might have an impact, but it didn’t. My nozzle is “0.5 mm”, which is the default. Is it possible that I might need to get a smaller nozzle?

For small holes, I generally have found it best to let the printer fill them in a bit – especially if I’m going to attempt to thread them. I simply use a drill bit to remove the excess material.

My concern with changing the geometry of the part, or with using a smaller nozzle, is strength. The thicker the flow, the stronger (the boundary between each “stream” from the nozzle and the adjacent solidified “stream” is weaker than if one used a larger stream – so using the largest diameter nozzle practical makes a stronger part, and that usually matters for holes one is going to use for mechanical fasteners). The other issue is simply that the edge of a “stream” is not perfectly vertical - so if one adjusts things so that the hole’s minimum diameter is “x”, then that really means that there’s a lot of that hole’s edge that’s actually inset from that dimension - in other words, the average diameter is something greater than “x”, which results in the part being weaker around the hole – and far less material for threads to grab onto if you thread the plastic.

If you prefer to create the parts without any material intruding into the hole, then it would be helpful if you can provide some dimensions – how large is the hole (in mm)? That would help determine if you could improve that by under-extrusion, or by changing some of the slicer parameters, or if you really would need to switch to the 0.25 dia tool-head. (It does look like you’re over-extruding a bit from the photos)

Thank you for the reply.

I agree that drilling is effective at clearing out the holes, and I might do that, but it doesn’t solve the problem of them getting filled in. I would like to print the without material intruding in the holes if possible.

The holes in the part (all 4 of them) are 1mm in diameter.

Can under-extrusion be achieved by adjusting the idler? What slicer parameters would I be looking at adjusting?

It looks like you’re over-extruding right now - which may very well be contributing to the problem. For example, if you’re actually extruding 110%, that means you have an excess of 10% of the plastic that needs to go somewhere, and filling in your holes is a great place for that extra plastic to go!

There are two factors that go into the extrusion - diameter of the filament, and the length of filament that’s pushed through for each step of the extruder motor. The first is easy – use your calipers to measure the diameter of the filament you’re using (every reel is different, and sometimes for lesser-quality reels, it’s different at different points in the spool!). Measure it in several places in the first meter or two of the spool, and average those readings. That gets entered into your slicer. In my experience, the 3.0mm filament is supposed to be 2.85mm, but most of mine tend to be in the range from 2.88 up to 2.95 mm. Check that often, and make sure you update that figure in the slicer whenever it changes (and whenever you change the spool of filament, of course).

The other factor is how much filament gets pushed through for each step of the motor on the extruder – that’s the e-steps value, and is unique for each tool-head (at least for the classic tool heads, I think the aerostruders are less variable, but don’t have any of those heads). The value may be on a sticker on the back of your tool head, but I prefer to measure using my filament and set it myself. Here’s a guide to doing this:

I’ve update my e-steps often; going through the process is easy, and it forces one to pay close attention to the mechanics of the tool-head, which has been helpful in spotting early signs of trouble twice now for me (cracks in the idler assembly, for instance).

The e-steps doesn’t change very often, so you set that in your printer firmware (per the link above), not usually in the slicer. The filament diameter is very often changing, so that gets set in the slicer. When correct, you should find that a 1mm hole may not be 1mm in diameter, but it will certainly be open rather than filled up with plastic.

One final thought – you might be printing slightly too hot – if the plastic is too hot when extruding, it can flow too much and fill in the detail. On the other hand, when its hot like that, it tends to adhere to the adjacent layers better, so the part is stronger. It’s a tradeoff.

The other thing you can do is if you want a 1mm hole, model it to be 1.5mm (or some other “larger than 1mm” value).

I do agree, however, that you are over extruding. The simplest adjustment is to reduce the flow. Try 98%, 96%, 94%, etc. You don’t have to print the whole part, just enough layers to determine if the adjustments you make are having the effect you want.

Thank you again for the replies!

Unfortunately, my calipers don’t give me good sub millimeter accuracy, so all I can tell about the diameter of my plastic right now is that it’s between 2.5 and 3.0 millimeters.

I’ll try checking/adjusting the e-steps value and the changing the flow value and then post my results. I won’t have access to my printer again for about a week though, so I’ll post the results then.

I tried checking/adjusting the e-steps value, and it looks like my printer is extruding the correct distance.

I also tried printing at 90% flow, and, while it resulted in a little less plastic, the holes were still filled in.

I saw there was a setting to print the bottom “concentric” and thought maybe that would protect the holes better from being filled in, but it also didn’t work too well.

I’ll try printing at a lower temperature. I’ve been printing at 205 deg starting temp (which is the default for this material).

You made me curious – so I downloaded the STL, sliced it with Cura 21.08, and printed it on my Mini 1.04 (Polymaker Polymax PLA, at 205C, layer height .15mm, nozzle is the original 0.50 mm nozzle).

Not sure what it is, but it printed pretty nicely. So I have to think it’s not that your printer can’t do it, it’s got to be something in the slicer, or perhaps temperature (although 205 worked ok for me…)…

I tried reducing the printing temperature to 175, but I still didn’t get my holes printed anywhere nearly as nice as yours were.

I didn’t know there was a Cura version 21.08. The current version offered on the lolzbot site is 3.6.18…

It’s nice to know that my printer should be able to print the holes nicely. :slight_smile:

The holes present in the bottom of the design are printable, if you’d like detailed help dialing in your settings reach out to the support team with these pictures and a picture of the print when using PolyLite PLA and the standard setting. Also include information on your Z-axis offset. FWIW, this design could be improved with either thicker outer walls to prevent those two gaps, or by using the SE tool head. Either way, the support team can help those small holes in the base print more cleanly:

Thank you Orias. I’ll try reaching out to the support team. I’ll update this thread with what I learn.

I reached out to support. They were able to reproduce the problem that I experienced. They indicated that the holes were small and may not have enough space to print correctly. The SL tool head was recommended because of the smaller nozzle diameter (0.25 mm vs 0.5 mm).

Settings to change that were recommended to me for printing with the 0.5 mm nozzle were “Outer before inner walls” and “Outer wall inset”. I tried modifying these settings without much improvement in printing the holes.

The support team printed my part with the SL 0.25 mm tool head using the high detail profile and sent me a picture.

From the picture, it looks like the smaller tool head is doing a much better job of printing the small holes. I expect to print a lot of small items where I might have small holes, so I expect to pick up the smaller nozzle diameter.