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Complete Lure Design Course – Building Lure Guts the Old School Way

Complete Lure Design Course - Building Lure Guts the Old School Way 1

Alright, we’re on to part three of our fishing lure design series. If you missed parts 1 and 2, you can find them HERE. What we have after parts 1 and 2 of this series is our half of our basic lure shape and now what we’re going to do is work on the internal weighting and the cavities where you might want to put rattles or weights. Then what we’ll work on is the aligning of the two halves to put them together once we print them. If you’ve seen any of my other videos, you know that I’ve printed complete lures in one piece and have put the weights inside the eyes but I’m not going to do that in this video. When it comes to putting weights in the eyes and in the cavity, there’s a lot of complications and I want to show you a more traditional way with some slight tweaks specifically for 3D printing that you may not have seen before. Let’s go!

This is the basic twitch bait shape we left off with, I made some basic changes to the curves but it’s close to where we left off in the last video. What we’re going to di is break it into pieces first. I do this to make it easier to visualize the lure as it comes together and to hollow out certain sections. If you want to hollow out certain sections, we can click on the shell tool on this face and then give it a number. This number represents the thickness of the shell. So for example let’s just say 1.5 millimeters and it’ll crunch for awhile and then I’ll have a 1.5 millimeter edge all the way around and it’ll be completely hollow. So that’s great if you’re doing something like a topwater bait or a popper and you just need it to float. Now the only thing is if you make it this hollow, it has a tendency to roll since it has the same buoyancy all the way around.

Creating Hollow Cavities

In general when you talk about a lure, the front and the back of the lure tend to be solid and this is where we’re going to take advantage of some of the processes in 3D printing to give us a leg up over more traditional lure making techniques. So, what I’m going to do is create a sketch on this plane, I could even create it on that face if I wanted to and I’m just going to draw a line. This basically divides up the lure with these lines. I’m also going to throw in an eye real quick (I’m just going to make it an 8 millimeter circle but you can make it whatever you’d like) and I do that for a couple of different reasons. One is it gives me an idea of where this eye will sit if I do decide I want to print this lure in one complete piece instead of two halves. Two, it gives me an idea of where, in relationship to the hollow part and the solid part, I’m going to be. I only want this eye to sit in the solid part of the lure so I’m going to cut the body into parts and leave some solid and hollow out the middle part for buoyancy.

There are a lot of different ways to get buoyancy in a lure, but I’m going to try and make it to where we don’t need to add any additional weight to have this lure act the way we want it to in the water float-wise. So I got these two bits in place and it’s about 20 millimeters, I’m now going to make one more line and I’m going to make this a spline. I’m going to make my line, move it up and then put a little bit of a bend on it. So now we’ve laid out, with these lines, the parts that are solid and the parts that are going to be hollow. So now what I do, I’m going to finish sketch and split this body up using the splitting tools. I can use two splitting tools here since they’re both going the same way. We now have 3 bodies here but I’m going to turn off the tail and the head sketch so that I’m just left with the body. Now we’re going to split the body again using the split body tool to get a top and a bottom. We’re going to turn off the bottom of our body because we want that one solid, and what we’re left with is just the top of our body.

hollow cavity on bait in Fusion 360

So now I have this little sliver of the lure and now I can actually use the shell command to hollow it out. Click on shell, click the face and for this lure let’s just say 1.5 millimeters. Fusion 360 is terrible at shelling things, it frequently messes up. What happens is in the corners, if it gets too thick, Fusion 360 does not like to wrap them and fill them in. So if you run into errors or problems, just know that you have to make your numbers smaller and sometimes it’s the smallest of increments that make the difference. I’ll make this one 2. Now you cannot select multiple faces and bodies, it’s only going to hollow out one on the inside and that’s fine. So, let’s click okay. If I bring back my head and my tail really quick just to give you a visualization, what I’ve done is basically make an air cavity up top. In this air cavity, you can put your rattles up there or whatever you want to and it’s going to also provide buoyancy on the lure. Now all of the rest of the lure will be solid resin and be significantly heavier. What I don’t know, is if it’s going to be heavy enough and that’s what you really need to know. I suggest testing them with whatever kind of weights you’re using as it’s very much a trial-and-error process to figure out how much of an air gap you need there.

Now if you’re print it solid, obviously you’re golden since you just print it and away you go. If you look at most commercial lures, you’ll see that they have a lot of different chambers in there and you can do the same thing here using the same technique we just did. Now I have a little hollow body in there and I can just join these all back together by combining all the target bodies using the join tool. You can play around with those numbers like 1 vs. 1.5 vs. 2 millimeters and come back and do the same thing with the top.

The Internal Extrusion Trick

We’re going to fuse all of these together, but before we do I want to show you one little hack that comes in handy if you want to use it. So when we’re hollowing this stuff out, we’re primarily concerned about the thickness of this top ridge here. If you get down to a point where you know you want to remove some material, the easiest way I’ve found is to extrude these internal faces. It’s an ugly hack but it works pretty well. This only works on a straight face and I can’t extrude this face, for example, and I have to run some more hack’s but it’ll work on these flat faces here. So I click this face, run it through, cut and then I click extrude. Once I do that, I run it through the back and click okay which removes a little more material if you need to open up a section to another section. Once you do that, you can put everything back together.

Rattles in Internal Cavities

I like to start with whatever body it ended up keeping the name for and then click combine. I select all of these other parts just by holding down the shift key, hit join and then you can see that extrusion gets a little weird. It doesn’t follow the path but quick side note, these belly cavities support rattles that will just go from side-to-side very quickly as the lure is wiggling. Whereas the long cavities up top really support when you jerk the bait and will make a lot of noise with whatever you have in there. That’s the reason for those two different cavities.

Designing Alignment Pins

Now, since we’re going to do two halves, we’re going to want to glue them together and we’re going to want some alignment pins. What I’ve seen a lot of people do is they’ll come in and they make a pin that’s round, they stuck it to one side and then put the hole in the other side. I find that that doesn’t really work well so I’m going to show you the process that I use that I think works best. To start off, we’re going to decide where we want our alignment points to be. Now, I know this lure is going to have a screw eye here in the front and in the back as well as in the bottom, so I want to avoid those areas. I’m thinking maybe here in the belly area would be a good spot for an alignment pin since it won’t impact the alignment. Also, this is a twitch bait so I’m going to have a lip so I want to avoid that area as well. You don’t necessarily have to do these alignment pins, you could wait until you did a lip. I’m going to have a whole video on making crankbait lips and incorporating them into your lower bodies coming up soon. I’ve made some really cool discoveries in that area for 3D printing. But today, we’re keeping it simple with the twitch bait so I’m going to put a pin here.

So, what we want to do now is let’s turn that sketch off, create a new sketch and I’m going to do that right here on this face. What I’m going to use is circumscribed polygons and we’re going to end up 3D printing these so the bigger the better. We want to keep them all the same size so I’m going with 2.5 millimeters and what that does is it just makes it easier to assemble the lure. This would be a good use for a parameter once you decide how big you want your polygon to be in all your lure builds. It’s a great thing to put into a parameter so you don’t have to keep remembering all those numbers going forward. You can print out a bunch of these pins in one shot and not have to print them each time you want to print a lure.

pin alignments on bait in Fusion 360

In case you haven’t figured it out yet, we’re going to extrude these out and we’re going to cut holes in the lure body itself for the alignment pins which in this case are hexagonal shaped. I need to avoid areas where I have my voids. So, we can finish this sketch and I want to extrude. I’m going to select all of these guys and I’m going to say symmetric and we can eyeball the distance here. Now the key here is I want to do a new body, I don’t want to cut these just yet and I’ll show you why. We click okay and now the cool thing about hexagons instead of circles is that when you have circles, you can still turn them when you put the lure together. With a hexagon, they’re going to slide in and then lock into place so you’re not going to have any potential for twisting. Now the downside to that, is if you have any kind of variations in your printing or anything like that, it can make alignment and fitting them together difficult.

Compensating for Elephant Foot

We’re going to compensate for that, and I’ll show you how. So, what we’re going to do is we’re going to combine these together, my target body and my tool bodies, and we’re going to cut so that I have little holes and it’s going to keep my pins. So now let’s hide out body and rename these pins which are all the same so I’m not going to need to export and print all of these, I'm just naming them so I know what I’m dealing with. Now we’re going to come in and we’re going to click these back faces and these front faces and we’re going to hit the F key for fill. We’re going to put a slight fillet on each of these edges because when I go to print, I’m going to print these faces flat to the build plate and that’s going to give me my best result. By putting a fillet on it when the edge is flat to the build plate, I get what’s called an elephant foot and it gets a bit bigger because it’s overexposed. We can compensate for that by putting a fillet here and still get a good fit.

The reason I did this in that specific order is if we go to look at a cross section of the lure, when we go to the back of the lure you see this little gap here. We see this because when we joined it, we didn’t have the fillet on so it cut out the non-fillet hole then we added the fillet. When we added the fillet it cut this material out from our pin, so this makes it slightly easier to deal with any variations in the printing, especially on this edge that’s going to be against the build plate. When we go to print this pin, you could put them off the build plate and use all kinds of supports but really I find that to be just a real pain. It’s much easier to smash them on the build plate, you compensate for it what a filler.

elephant foot in Fusion 360

Now we have our pins and we can hide them and we have our holes that the pins are going to go into. Now you can add another fillet around this edge if you want to. I’m going to select all these edges here and add a fillet and the reason I’m going to do that is we’re trying to give ourselves the best chance of having these two things slide together relatively easily, but tightly when we’re 3D printing. A good thing to do once you get your printer set up and printing and your resin really dialed in is you can do a test print of a very simple hole and a pin. I use a 10-millimeter hole printed out flat on the build plate and it should slide right in. Now the tricky part comes when you’re printing one piece in a different resin and the piece that’s going to slide into another resin. We’ll talk about that in more detail when we cover crankbait lips because I do print those in a different resin than my bodies. But for now, print these parts and slide them together. You should see that on the bottom you have an elephant’s foot, and it should stop it from sliding all the way through. Then you can start adding a fillet on there and see how much of a fillet you need to compensate for the elephant’s foot on that part.

Pilot Holes for Screw Eyes

So now we’ve selected all those edges and we’re going to hit fillet. We have a relatively small area of these flat surfaces here, but I think that’s good. So now, we’re going to add the pilot holes for my screw eyes and if you’re going to do a through wire or some sort of wire harness, the process is the same from a Fusion 360 standpoint. You would just draw the lines that I’m about to draw in whatever kind of path you needed them for your wire harness. So we’re going to do a new sketch and I’m going to click this back face again. I’m going to use a line tool and I’m just going from the back and I’m going to put this on a slight angle. Now what we’re going to do here is basically lay out where our screw eye holes are going to be, so I’ll just run with one right through the center and one through the belly. Obviously, you can put these wherever you need to but that’s what I’m sticking to.


Now we finished the sketch and I’m going to use the pipe command to cut out these holes. I click pipe and I’m going to click that and I know I need 1.45 so this is another number that you’re going to have to figure out on your own depending on what screw eyes you’re using, the wire you’re using, etc. You’re going to want to print out a simple block, make several holes in it of various sizes and see which one fits your hardware. I know this one works for my resin and the screw eyes I’m using fit to where they don’t blow apart the lure and I get a nice bite. Your number will be different. Right click okay. Let’s bring back the sketch again, create pope, same thing so it should have my number saved.

Fillets on Front and Back Edges and Mirror Command

One last thing we’re going to do here is collect that edge. I hit the F key for fillet and I’m going to put a slight fillet on the tail. I’d like it to be a little more but the angles aren’t working out. So I’m going to do a .3 there and I’m going to come up front now and let me show you a trick. I hit enter to get out of that fillet command but you can just come over here and click plus and add this edge. See if you can add a bigger fillet on there. That’s a downside to using more angular sketches, the fillets become more difficult. So now that I’ve gotten those edges done, now comes the exciting part. We go to create mirror and we want to make sure this is on bodies since it’ll default to faces. Our body mirror plane is going to be this plane right here and you could also click on this face if you wanted to. You’ll see it pop into place and there is our lure body. We want to make sure we are using a new body, we don’t want to join them together because we’re actually going to print this in two parts. If you were going to create a lure that you printed completely in one piece, you could join them and we’ll discuss that in a future video. Let me click okay and there we go, we have a very basic lure body.

Before Moving on to Exterior Detail

If we take a look at the section analysis, we scroll this back, we’ve created everything that’s needed to be created. We’re at a great point to print out this lure and see what it looks like and what it feels like in your hand and make adjustments. You’ll want to get all of that out of the way before you spend a lot of time working on details like eyes, gills and fins because that detail is very delicate and will break if you start to make major changes.

We’re going to discuss exactly how I set this up in the 3D printer in a future video and we add all the details but for now just throw it in there and try to print it however you think makes sense and see how it all fits together, especially if this is your first time making this lure.


If you want to see the other videos in this series, the playlist is right HERE.


Take care-Tight lines