Creating interlocking parts in a 3d file

In the 6th appointment of ask a 3d designer, Alvise is widely talking about the possiblity of 3d printing objects composed of several interlocked parts, explaining the constrictions related to their design. Our Lead Designer is applying those rules, optimizing two different models, first in 3DS MAX and then in Inventor.


Alex : I'm Alex Gryson User Experience Designer here at Sculpteo, and Alvise ?

Alvise : Hello everyone, I'm Alvise Rizzo, I'm a Product Designer at Sculpteo.

Alex : And so , just to explain very quickly, this is the second Webinar this week. We got two each week, and first is a guided tour where we go through picture by picture of the various tools and optimizations which are available on Sculpteo on site, which we develop in house. And this second Webinar which is on Tuesday and is : Ask a 3D Designer. This is where we get your 3D files which you want some help on, or that have been refused for some reason, or rejected by our printing center. We'll help you figure out what the problem is it and how to fix it.
So just again , Monday we had this guided tour Webinar at 7 o'clock Paris time in the evening, and at 6 o'clock in the evening Paris time on Tuesday is : Ask a 3D Designer. If you have other models that you'd like to show us for some other weeks, don't hesitate to send it to I'll just type the email. So don't hesitate to send us.. Ho we have « Enric », so « Enric » was with us yesterday, and so welcome again. We also have « Herve », still in the waiting room, I hope he will join us soon , and we have four participants for the first time, so welcome evrybody to the Webinar. Again if you'd like 3D model for this Webinar next week, send us your model or your request to
Just to quickly sum up the advance on what we have been to, and what we will be at, 10 days ago we were at the Maker Faire in Paris, « I don't know if you can see my arm right here, I got my gobelet » (4,05). It was a great event, I was there, a lot of Sculpteo was, they were trying to get down for a few hours. Great event, great family event with a lot of different people, so I was really happy to be there.
There's another event which is coming up, I just get my notes here, it's the 3D Print Show in London, It will be, If I'm not mistaken the 21st to 23rd of May, so it's coming up next week. Will you be able to come along and see us in London? It's a much more focused event, it's much more focused on 3D printing. As opposed to the Maker Faire which is more the general maker event. If 3D printing is your special interest, it's a great show, there's a lot of differents types of people there from 3D printers, 3D designers, and there's going to be Adobe, there's going to be us, and a lot of other great things going on. So if you're in London do come along to that show as well.
Just very quickly Alvise could you tell us what we will be looking at this week on : Ask a 3D Designer ?

Alvise : Sure, so this week we have a file that « kindly said unproductable » (5,17), precisely it's a acorn and it's made up of two differents parts the shell and the seed of the acorn and they present a couple of problems.
I'm strating to share my screen and show you the file immediatly.

Alex : And if anyone has any question, don't hesitate to ask them in the chat. I'll manage to read the chat, so I'll stop Alvise while he's sharing his screen, so he can answer your question. So don't hesitate to ask those. Sorry go ahead Alvise.

Alvise : Thanks, so now you should be able to see my screen. I'm in Sculpteo website, and I'm already in the review page and solidity is checking this file. So as I said it's an acorn, and this file has been refused last week and the reasons was multishells and depowdering problems. So let's take a look to the first shell, I'm in the review tab in our reviewer page and I'm accessing the cutaway view here on the model. So our tool sees inside the model, so what we can see is the seed inside....

Alex : I'm sorry Alvise, I can’t here you.

Alvise : … so this must be kind of a gadget, and If you want the seed to be printed together with the shell...

Alex : Sorry we didn't reboot on when you were telling us what the user requested. What did Cedric want from this model that you were mentioning ?

Alvise : Yeah, Cedric ask us how to make this printable, his file has been refuse and the featured reason provided by our printing center is : multishells and depowdering problemes, so two problemes at the same time in this file. I'm trying out to show you where and why those problemes are present on the model.
So the 1st one, I'm referring to is a multishell probleme that we have been talking about, and already say all time, on these troubles. You can clearly see it in this cutaway view those several shells. For sure one is the external shell of this acorn, we will keep it for sure, and the second shell the user told us to keep is the seed inside the model. This can be print together with the shell, in order to make it movable inside, so we're dealing with interlocked parts. We also have been talking about interlocked assembly in other Webinars.

Alex : Yes, we actually just spoke about one yesterday as well.

Alvise : So beside the shell and the seed inside, there are other elements you can see on this cutaway view that the user don't want to keep, and those are the reasons why this model as been considered multishells. There are creating an error in the file, so for sure here that can be considered as noisy shells, and there is this kind of thing that is the result of modeling errors. I think there're must be kind of boolean operations and this is the intersection that brings these two shells, they just stay there inside the model and we have to find a way to get ride of it. Also here on the bottom, there is some geometry that is just strange, the user don't want to keep that. So that's the reason why it has been refused, it's a multishells file.
The second reason, as I mentioned before is a depowdering probleme. So of course you know about laser scintering technology, how it works and that powder needs to get taken off the model and this is why we provide a tool to hollow models that ask to put at least two holes in the model in order to depowder it after printing. In this case what we see is not a classical hollow model with the website tool, the geometry of the acorn itself present a cut in the shell that allow the model to remove the powder. But in this case it's just too tight, just too small in order to let all the powder get outside of the nut. So what we should do is just makes it larger.
The second depowdering probleme is here, inside the seed, that area has the same principe, it depends of the hollowing of the internal seed and it's just impossible to get the powder out because the seed is moving inside this acorn and there's no way to, for the technician, propel the sand and remove the powder with air and sandwasting. So we will do it in a while.
So maybe Alex can explain us what the depowdering needs and why we have to care about all of this.

Alex : Yeah, just your sound has been bucking up a little bit, so for anyone who had missed some of those parts, I will also summarize what Alvise has been explaining.
Alvise recount here we have an acorn with two principal parts, the outer shell and the inner nut, and this inner nut should be floatting within the higher one. In order to do that, after we have printed the model wich is made of several states of layering down powder, we need to get rid of that powder. You can imagine that basically we build up this model by melting certain parts of the powder layers, and when it's finished, there's densely pact powder inside which we need to get rid of. Now what Alvise is going to do and while I'm speaking, Alvise can start doing this, so don't hesitate to look between his screen and my webcam, he is going to fix up the model by, first of all getting rid of this multishell issues. You can see that when Cedric was trying to make his model, he was obvously doing sometimes some boolean operations between left inner shells that we need to get rid of in order for the printer to get the sense of inside and outisde. The other probleme that we need to take care of on this : is making sure that the internal geometry of the nut, that we have inside allows for easier depowdering. I'll just explain why depowdering is important, the first reason is that no one want to receive there model with a little bit of powder that will be coming out of the model over time. If your model is difficult to depowder, this is an unavoidable reality of the technology used. You're going to have some powder left, which is going to hook on some crams and cracks which we are not able to get out with our air blaster. So basically what Alvise is going to do here is make the hole a little bit larger and uniform, make the form inside a little bit more unifrom. So we will get rid of all of that powder.
I'll just explain very quickly why it's important to have holes at a certain size, in our last Ask a 3D Designer Webinar, we had some questions about why it was important to have holes at a certain size, of a certain depth, why depowdering was important, things like this. I'm trying to explain using my hands but it's quite difficult. So I'm going to explain with some drawings and sketches here. Basically if you can see the webcam, and if you don't, just tell me on the chat box, what you deal with is when we have this kind of structure, this kind of wall like this, where we are trying to get powder out of a certain hole by blowing air, so we just blow air to this hole. The problem is that depending on the size of this hole, the depth of the hole and size of your particular powder print, you can end up building kind of, hum you can see, kind of arch with the powder particule. So the powder particules basically block inside this hole and create an arch which is extremely strong, especially in those scales and it completly blocks the powder from getting out. So what we need to do is fix this in several little wells, it eases to make the hole bigger. So what you can see here is by simply widending the hole, it will make the arch much wider, so the arch instead of being able to prevent the air flow, by being much wider is much weaker, and the air can throw and get those powder particules out. That's what we are trying to do. Now we have an automatic tool on the website called hollowing and it takes care of all of these differents things that I'll be showing with a little more detail here, and if you can't see what's I'm transmitting, please say it on the chat box. So basically what we have here are important factors when we are trying to get a hole. There is the size of the powder particules, wich for us in that case is sixty microns for our finest powder to between a hundred and a hundred fifty microns for our thickest powder. The other two factors really important are the depth of the hole and the diameter of the holes which is right here. So based on these three factors you can change the size of your hole to make sure the depowder is possible. When you're talking about the automatic hollowing tool that we have online, when you click hollowing, we can automatically hollowing the geometry being sure that the wall thickness the hole diameter are all the proper size, being sure that the materials you're using will be depowder easily. So in most cases, getting any kind of model that you're trying to print, and using the online tool for hollowing is your best option, it's the only way to garantee that your hole will be the right size for depowdering, mesures hole will be taken up to have a solid model. So we really do suggest that in every case possible, you use that tool.
The difficult that have here is that we're nor able to, the geometry of this files is such that hollowing is not going to have any effect, it's already hollow. This is a demonstration of what Alvise is trying to do, I don't know if you can see this but on the webcam you can see a kind of white plaque with lots of little black holes in it. Basically this is a test piece, we regular the caliber on machines, we regular the test on machines, pretty much everytime we've got to print, It's the only way to be sure that you can see some results. So we deisgned a little test plaque here which I'm trying to show you here, I'm just putting it on this black back frame so you can see it. So basically what we have here is: as you go up, you have holes of different parameters, so there are very large holes and very smalls one, as you go across there are thicker and thinner. So you can see this, that maybe it start relatively thin and it progressively get thicker and thicker and thicker. So this is a way for us to be sure that our machines have consistent results for a gaving powder. So you can see that over here you have thin holes that allow us to get the powder out of pretty much any holes size. So very thin walls are very easy to get the powder out of, so that's explaining our arch thing. The arch is not being able to build the strong one with those small holes because the wall is too thin, so the powder get kicked out. However when you get over here where the walls are very very thick even if the hole is very big, it's very difficult to get the powder out.
So that's the problem that we are dealing with in 3D printing, it's that depending on the geometry, and this is a simple case, this is just a flat wall, if you do that with a lounge surface it's going to be different and so this is lot of things to be taking in account.
Now what Alvise is trying to show you here is, first of all he is simplifying the internal nut, and this is what we're doing here, he's working with Mesh Mixer wich is made by Autodesk, this is free software, and on the outside, after the internal nut has been shape, on the external shell of the acorn we've both to make sure that that tiny little prick we saw just got to wider up a little bit, so we can be sure that the powder can get out. To check out, on our ressources pages and materials pages, we give you guidlines on all of these specific stuffs, on all over materials. So if you need to know about the hole size, the hole depth, thing like this we also allow you to do that yourself, you just have to check out on our ressources pages, where you'll be able to see what the specific sort of materials are going to do that in you're favourite software.
So as you can see here, Alvise is the just painting around the geometry here and that's why we see these orange shapes. While Alvise is finishing up with this model, does someone have any question? If you do please don't hesitate to ask in the chat, especially for talking about these kind of specific things, such as hollowing depowdering, the tools we have on Sculpteo, the way that you can fix things certain software, don't hesitate to ask in the chat. Okay so you can see Alvise working within. So Alvise could you tell us what you're doing here?

Alvise : Right, so I can start descripting what I'm doing. Hum, so the first part of the demonstration have been using, welI can show you, by going back to the first thing I've done. MeshMixer provide the tool to delete the...

Alex : Well, Alvise I'm sorry but I can't here you, we are having self probleme on your own and video's probleme as well. So just to figurate with what we've seen, in MeshMixer you use to, well Mesh Mixer have several simple tools which are very very powerful.
So in this case Alvise had selected the internal nut, the internal shell that we have and he has made it solids, which has a fact where he filled in the little hole. So the little hole we had, which was causing detention problemes with futur powder coming out, he has made it solids, he changed the accuracy of the making solid tool, to make sure that he is filling in any gaps to a certain degree, while still maintaining the design intent that Cedric had in mind, when he created this model. Then what Alvise has been doing is removing some of the noise, the internal noise from the scan. Now I believe he is moving on widening that crack. So we have this crack in the acorn that we need to get the powder out of, depending of the scale of the model, which might be very very small. So imagine that Alvise is going to use very precize tools…, here is a sculpting tools to mold this crack and widen this crack out.
And again if anyone as a specific question, even a non specific one, don't hesitate to ask in the chat.
We can see here that Alvise is smoothing out and widening this crack here. Basically for white powder we need this crack to being about at least, I would say 2 or 3 millimeters but for a long crack like this, it doesn't matter. Rememeber we were talking with the arch, if you do a loads of small holes, it's not going to change anything, you just ends up with a lots of small arches which is juste awful. In fact a small arch is stronger than a large arch, that wy we're trying to widening out this hole. With a very large hole the arch is bigger. So lots of little holes is not the same as one big hole of the same diameter. So we re trying to make this the biggest as possible here while still maintening the design intent that Cedric had in mind.
So again if you need any specific information about the parameters here, about the walls of that holes, in order to get the powder out, we have excellent guidlines available on our website basically on the topical materials and ressources. Hum either those mean you can grab informations on our materials and on the various design guidelines that you need to expect in order to make sure that your model is printable.
So before adding your project don’t hesitate to look at the materials there’s a lot of informations even to the exportation stuff. There is a lot of explanation in there.
So If I’m not mistaking, we have fixed the intrnal nut and widened that crack and now If I’m not mistaking we’re doing some operations to be sure that we have a single shell on the outside. So now we have only two shells, the internal nut and the outer shell of the acorn. While we’re saving and uploading this I’ll just rexplain someting that we had yesterday. Hum, yesterday when we went for the « Take a tour Webinar », we look at difference between a multi piece model and a single object. For the people who were not a tour webinar yesterday, I’ll just quickly explain. A single object but between many parts is a lot like our acorn there, the nut can’t come out of the acorn or it could be like a chain, here on my Sculpteo tooling and If you see, we have this chain here which is an unsecable object that it has to be printed as a single piece. The ball which is inside the Sculpteo logo as to be printed as a single piece. So here, after the upload has been successful, we will need to chose « single object ». What is important is that we know that all of this objects have to go as one file into the same machine. Instead we will genuinly have something on like those sharped pens. I can print them all separatly and instead I printed the acorn separatly frome the last. Because everything can be set writting physicly, which mine that you can optimize our processes, It mean that we know how much cost production is going to be needed how many pieces are going to be depowdering ? How many pieces are going to be painted or dyed ? Hiw many pieces on work are going to be shiping and things like this. So all of that are very important informations and If you don’t have a definition, it supposed to be much more difficult. So do make sure that you give the right answer that we automatically chose multi piece. So here you chose a single piece beacause it’s the probleme we re working on know. We have a fix note here and if we go to the cutuaway view again
Sorry, so Alvise is just uploading the cutaway here and we see a white hole here. So we see this acorn is of 20mm wide, so that hole know is about 10%, so it should present no problemes know for depowdering. It should be wide enough. Again here a 3D software sould be able to mesure that or here with finalprouf by using the blueprints you should be able to see that.
In fact you can see the bottom here, just that the bottom, the 3D printers ask me If final prouf have some white size blueprints and those blueprints can be use to mesure everything precisely on what your final prouf will be. So please don’t hesitate to use this tool as well, it’s free, you don’t need to buy anything you just click Final proof and you generate that blueprint.
So we have a question here from Henry. He is planning to make a bearing assembly, « The best way to envision it is to imagine a door hinge that as been sliced, so there are two parts : an upper and a lower, both movable, and a single fixed part in the middle. I would like to make this as an interlocking part. I can tolerate some slop in the fit . Is this feasible ? »
Yes this is absolutly feasible and it’s actually really common use cases, to have an inner articulated object. One thing that is important is that, you should definitly check out our guidlines. And again for some of you, this is what we’re looking at here. It’s the hole which is very very very long on a very large surface. We won’t need a slice enormous gap between the pieces to be sure they can move. So you can see here, If its a very thick wall with a very small gap, it’s going to block, so check out the guidlines for our web classique, generally it provok a few more milimeters . I think the distance s 0.5 milimeters. So it’s going to keep about half a milimeters between the internal stable part and the two movable queels. It should be ok.
Again it depends on the man, If you ‘re very very thick part or the very very long part. I tried to get a bit more space, so the powder can be worked out of the nut visible and in order to make sure that the nuts fuse together.
Hum I have other, well this is just one type of pieces, and we have other parts that just play movement. So If you can, I mean send us an e-mail It’s a little dimension in order to give you guidlines on-line. And What guidlines is it, well it’s difficult to know for every single piece it will depends on the geometry. But it’s definitly feasible, it’s something we do all the time.
So Alvise our nut has been fixed right ?

Alvise : Yes and I’ve been uploading again and again on our website and I just change the hollow a little bit. Yeah, as you can see the seed is full, so normally for the powder, no problem here and the cut in the shell of the acorn is definitly large enough, I was mesuring before maybe you notice it ? I was mesuring in meshmixer with the mesuring tool and it’s 10mm now so that’s definitly enough for the size of this model. So yeah, this is ready to send to the printer.

Alex : Yeah, there should be no probleme. Well I’m afraid Cedric may not have been able to join yesterday, but we will contact him and let him see this video on youtube.
Just to explain to everyone really quickly how to use this video after on youtube. So If you were late or If you missed anything or go away to do something during the webinar, don’t worry. Everythig is online again afterwards.
So by tomorrow or the day after tomorrow, we should have that on youtube. So don’t hesitate to cheque that add or share with your friends if you find someting interesting
Hum I think that’s it for us for this week. So I think I start closing unless you got anything to add.

Alvise : Nop thank you.

Alex : Ok I just start closing up. So what we did is that we have Cedric onion here which had a couple technical problemes : a gap which was far too small but on top of that there were lot of residus, mesh noise inside that were linking multishells. So we needed to solve those two problemes. So we have this couple of problemes with the gap and the multishell of the acorn, so Alvise took those out by working with Meshmixer he got to wipe off noise and make sure i twas a single shell model ; But at list with two main shells which is what we wanted and then what we did was to make sure that gap that we have, in order for powder to come out was large enough, was over 2mm. So we can make that powder out, it’s just the general recommandation, again it depends of the degrees of your wall… but 3mm should be enough for most of cases to get powder out.
We have question from Henry on interlocking part and moving part. Generaly a gap between 0.5 to 0.7mm should be enough to make powder out depending on how much play you need in the object, and agi nit depends on the lenght. On much larger surfaces it’s going to be harder. So you have to take that in count, when you design you’re piece.
Finally just about events that are coming up : 21 to 23 of May we have the 3D Print show in London, Sculpteo would be presents, we will be giving presentation there will be Adobe with I believe a presentation of photohop.
Ok so there I think we’re done, so I’ll ask every one who as been on the presentation : do you have any questions, before we close, on multishell, coloring, depowdering…
Ok so I don’t see anyone typing so I believe we have an other successful 3D Design Webinar, so I’d like to thank you Alvise and of course Id’ like to thank everybody else.

Alvise : Thank you guys !

Alex : yeah thanks, and especially thank you for the questions, the webinar is already on the ressources page. Thank you for asking questions it really makes the webinar, so please continue to come to webinar and to ask questions. I think I wish you a wonderful evening or morning If you ‘re in the USA and have a godd day.
Bye bye until next time, and see you on Monday.