Beginner's Guide to Fit and Tolerance in Fusion 360 - Get the Perfect Fit from Your 3D Printer / CNC

hey everybody welcome to practical alchemy today i'm going to be introducing you to the concepts of tolerance and fit in fusion 360. now this is a fundamental concept if you are going to be using fusion to create things that you're going to actually make whether that be via cnc or 3d printing because it's very important to make sure that your parts fit together the way that you want them to this tutorial is going to be broken up into two sections in the first section i'm going to be explaining the concepts of tolerance and fit in the second section i'm going to be showing you how to create a simple fit and tolerance guide so that you can understand the intricacies particular to your machine if you'd like to skip to section two i have posted the time code here so without further ado let's jump into explaining tolerance to do that i'm going to use this simple part demonstration here what i've done is created a simple block with a hole in it and a post that is intended to fit inside of that block if we go into the sketch view you can see that what i've done is create the sketch and i have made an extruded cut into the block and i have made an extruded post using the same size hole now theoretically you would say well this will be a perfect fit when i 3d print these two components i'm going to show you the cross section view here these parts should be also perfectly aligned and so i should have a perfect fit between them but when you go to 3d print these you will quickly find out that that is in fact not the case why well because your machine no matter what it is is going to have a certain amount of tolerance associated with it in this example i am going to assume that we are going to be 3d printing this part and when you think about 3d printing especially something like an fdm printer you are going to be printing in layers so while you're the cad model for your post is going to look like this the actual post is going to look something more like this where you have all these very very very tiny layers of filament that are being deposited and the actual surface that is being printed out is going to have some divergence from what you have actually specified and that divergent from the quote unquote true dimension that you specified is known as the part tolerance now i've created this artificially but these little ridges stick out from the true dimension by 0.35 millimeters that's really small if you pull out your ruler and look at how wide a millimeter is and then think about 0.35 of that it's very small it's almost imperceptible when you're looking at it but the effect that that produces when we jump back into our section view is that rather than having two parts that fit together perfectly we now have one part that is overlapping the edge the interior of that channel by point three five millimeters so we would define the tolerance of our shaft at point three five millimeters from the true dimension now going one step further let's imagine that not only are we 3d printing the shaft but we are also 3d printing the post so that post is going to have the same issue and we're going to have the same issue with tolerancing where we have a 0.35 millimeter offset from the true dimension that we have specified and when we combine these two together we will see that now we not only have a interference from the sides of the post we also have an interference from the interior side of the hole so in truth these parts are now overlapping by 0.7 millimeters this effect is known as tolerance stacking and is the exact reason why if i was to 3d print these parts as dimension they would not in fact fit together so in order to compensate for the inherent tolerances of our manufacturing process in this case it would be our 3d printer we need to introduce some fit into the dimensions that we are specify so that moves us to our next example which is a discussion of part fit when it comes to part fit there are three types interference transition and clearance fit the first type of fit that we are going to discuss is interference fit and as the name implies that is the fit where you are going to have some interference between the side walls of this park and the sidewalls of this part so switching to the section view what you can see here is similar to the first example that we discussed there is some overlap between the geometry here and the geometry here and you have intentionally specified what that geometry is why would we do this there are instances where we would want parts to be joined together without them being able to come apart easily so within the blanket term of interference fits there are a few types there is a press fit where you are simply pressing the fits together there is a driving fit which requires some type of hammering or pounding or maybe a clamp to push them together and a force fit where you are actually somehow destroying the part or altering the part in order to get these together so maybe you're heating it up to get it to melt a little bit or maybe you're freezing it to get the part to shrink a little bit but essentially all of those are captured under the umbrella of interference fit the next type of fit will go to the opposite side is called a clearance fit now in a clearance fit you have actually specified the geometry of one part to be offset from the second part by a certain amount so that it can move freely within that part so going back to our front view and going back into our section view we'll see that this body is offset by a certain distance here so that it is able to freely slide through this slot another advantage here is that you may want this part to not only slide but also be able to rotate so whether if you've got some type of rotational hinge or you've got some type of slider you are going to want to create a clearance fit and as you might imagine the larger this offset is the more clearance that you're going to have so you may have a you know a resisted sliding fit where you want something to be able to move but with some resist mechanical resistance or you may be able to want it to freely slide or freely move through the hole now in the third example which is right in the middle here is what is known as a transition fit transition fit is basically an offset that is just large enough so that the parts fit together without interfering with each other transitional fit is really designed for parts that are just going to be fit together that are maybe be further connected via screws or hinges or some type of latch system so in summary the three types of fit that you will be dealing with are an interference fit this is for mechanically locking parts together a clearance fit which is used for hinges and other moving components and a transitional fit which is used for parts that simply need to fit together so now that you understand the basics of tolerance and fit the next question is how to determine the parameters of these three fits for your specific machine or machines to do that i use a fit block and they're very simple to create i'm not going to walk you through the entire cad process but i will show you the basic construction all you really need to create a tolerance block is a simple rectangular sketch that forms the base and then a rectangle where you have specified the true dimensions of your part i've offset that rectangle by a specific amount and then i've also created a linear pattern of that same rectangle across the block i then converted those rectangles to sketch geometry and offset them by a decreasing amount so the first one you can see is offset by one millimeter point eight point six point four and point two you can also see that i have created a text box that calls that out from there all you have to do is simply extrude each of those blocks up and i also like to deboss those call outs those dimensional callouts down into the block and as a separate part i have done an extrusion of a part with the true dimension on the interior so once you've got those both printed out you are going to take your tolerance block and you are going to essentially go down every single hole and test the fit this is going to be very loose clearance move to 0.8 and it's going to be a little bit tighter when i get to 0.6 it's going to be just tight enough that i feel like i'm getting a decent sliding fit or clearance fit and then i'm going to move over to 0.4 and i'm going to realize that this is in fact too tight and i can't put these together all right that means that my tolerance range is approximately 0.6 millimeters and then what i'm going to do is i'm going to create a second tolerance block that anchors around that dimension so if 0.6 millimeters is where i'm finding a good transitional fit what i'm going to do is i'm going to then bracket off of that 0.6 so you remember the last block had a 0.8 millimeter offset and a 0.4 millimeter offset i really want to zone in around that 0.6 millimeter so again i'm going to take that fit testing block and i'm going to go along my surface and make a note of how each of these dimensions fit we may determine that 0.6 millimeters is a really great transitional fit while 0.7 is the perfect clearance fit for us for a slight slider and 0.55 millimeters is as much as i can reasonably do for an interference fit without having to get out my hammer and you may have to go through this step one or two more times to really hone in on exactly what you want there may be situations where you want more of a press fit and there may be some situations where you want more of a driving fit where you actually have to hammer it down and if your 3d printer has tighter tolerances than mine you may actually find that you need to hone in and .55 is going to be a great transition fit but you need to go down to 0.535 in order to get a good press fit you may not have quite as wide of a fit bracket as i do just as a quick reference for me personally i most often run a makerbot 2 in draft mode so for me 0.5 millimeters is a perfect clearance fit for most sliding or rotationally fit parts 0.4 millimeters is a great transition fit and i can move it down to point three millimeters for an interference fit that i can tap together with a mallet but of course based off of the manufacturing that method that you're using and based off the tolerance of your machine your mileage may vary so before we break for today the last question is now that i know what the fit of my machine are how do i use them so let's go back to our original example of our simple block and our post let's say i want this post to have a clearance fit with this block maybe i'm making a simple enrichment toy for a baby so i know with my 3d printer that for a clearance fit i need to use an offset of 0.5 millimeters so what i can do is i'm going to go into the top view and i'm going to create a sketch here and i am going to project the edge geometry and then i'm just going to do a simple offset of 0.5 millimeters all right and then i am going to do convert this edge to construction geometry and then finish the sketch do an extruded cut i'm going to cut into the block and i actually want the direction to be oh and up to an object going to extend up to this also going to increase the offset by 0.5 millimeters because i need to not only make the hole wider by that dimension but also make it deeper by the same dimension hit okay and going back to that original example let's pretend that we have a little bit of tolerance on this part we can go to our section view and now you can see that i've got a enough clearance around the edge of my post in order to slide into this block without any unintentional interference and that is everything that you need to get started so quick recap anytime you have a manufactured part you have a certain amount of tolerance inherent to the manufacturing method beyond the true dimensions that you specified and in order to account for that you have to introduce some fit into your dimensions there are three types of fit interference fit clearance fit and a transition fit and the smaller offset between the specified dimensions that you have the tighter the fit between the two parts will be when you go to set up your machine and start modeling in a 3d environment you want to create a fit testing block that allows you to very simply try out different offsets to figure out where the parameters for your different fits should be set and once you go through that once you may have to go through a second round in order to really hone in the tolerances but it's very simple and once you have this file you can use it infinitely so when you get a new printer just run it again and you are good to go all right everyone i hope you enjoyed this content if you did leave me a like if you had any questions or topics that you'd like me to address in future videos throw those down in the comments and as always hit subscribe so that you can be updated with future content releases and continue learning with practical alchemy all right everyone thank you so much for watching and i will see you in the next one and don't forget to hit save

Channel: Practical Alchemy

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Length: 17min 3sec (1023 seconds)

Published: Sat Sep 03 2022