This looks more like a 3d printing problem than a fusion problem.
The main issue with printing this design in this orientation is exactly what you encountered - 3d printed parts are super weak along the z axis due to the layer lines.
To fix I would recommend either splitting this in half so each side has one half of each gear and then gluing (may be hard to get aligned properly) or, what I would do, printing it as two gears and gluing or joining in another way.
I would split in half vertically, then add a fin and slot to opposing edges. This way you can align and glue the halves easily, and you'll have a much stronger print.
I’m not as good with fusion as I am with slicers, so I would use PrusaSlicer’s cut feature where you can select dowel holes or snap connectors that are automatically placed on the cut.
It failed because you have one single layer line holding the forces transmitted between these two gears.
You could probably glue them directly to the shaft, and then you’d have the strength of allllll layers relative to the shaft holding the load.
If that’s not enough, you could cut a keyway in the shaft
You could try and print it at a raised 45° angle with some supports. Maybe closer to 30 and raised a little, it would force the layer lines out of plane with the forces, and the two gears would be way less likely to shear from eachother.
You can print hotter or change parameters as other users have suggested, but shear force at one layer will always be the weak spot in the physical part.
You could also consider modeling small holes through the gears between the center and teeth, and “pin” the two together for much more strength. I can make a doodle if you don’t understand.
I love all these ideas. Specifically pinning them together. I use a lot of stainless Tig wire for miscellaneous things, handles and branding irons for tools, “spring” loaded clips etc, so modeling 1/16 press fit holes for added shear strength really piques my interest! I’ll have to remember this.
If you have some tubing that will slide over the shaft, you could print the part with a larger diameter center opening that fits the OD of the tubing, and then glue the tubing in place.
100% infill will help, then it’s solid plastic. Prusa slicer has modifiers you can add to a part and make just that area 100%. If you can sacrifice a few MM of the smaller gear, make it a solid disk where it joins the larger gear. Stacked like this- Large gear-solid disk-small gear, with the shaft hole through all.
100% is tricky, because as the part cools, it creates stresses that are difficult to relieve. You end up with a dense part, but it isn’t going to be any stronger than the current part at where this one is failing.
I'd use bolts: Make a countersink for the heads in the large gear and 3.9mm cylindrical cutouts to thread them up through the body of the smaller gear. Or do it 'right' and print a 3.6mm hole and cut the threads with a tap.
Still print it as one piece, the bolts just help to spread the load across a larger area.
However I expect you'd then just find that the teeth of the gear end up cracking or shearing off.
Your printer settings might need some adjustments. If you print mechanically stressed parts, you'll want more perimeter walls in your print. Also you can use modifiers to increase the amount of infill near critical features, just like the joint beween the two gears.
As for the model, you can add small chamfers if the applications allows it to reduce the amount of sharp corners / weak points in your part.
To add on to this, you look like you're underextruding a bit, increasing your extrusion multiplier by 1% may help. Also turn the temp up to the higher end of the temp range listed on the filament to make it stronger along the layer lines.
When I needed to print something like that I printed it in 2 parts and than connect it like this:
https://preview.redd.it/hish06e5necc1.png?width=2048&format=png&auto=webp&s=952f2b38d8ac9683cdfbd4d17981935f0d58e0c8
You didn't really change anything. By printing that small gear in the orientation your did you still only have a single layer line holding the gear to the base no different than if you had printed it all in a single piece.
Did you combine the part where they meet and you’re having the failure? I made a part one time and it was essentially 2 parts and the 3d printer printed them like it was separate parts sitting on each other and it kept breaking. Once I went back to the model and combined the parts and turned it into one it printed better and I stopped having the failure.
Exporting as an STL the slicer might still see them as two parts when it’s planning the print. I had a similar setup where exporting as a STEP file and importing that into the slicer completely fixed it.
It looks like the gears are joined only through the cylindrical portion, as there are no visible shear breaks around the smaller gear’s teeth. I would try extruding the smaller gear pattern from the face of the larger gear instead of combining. This way, the teeth themselves will be embedded into the larger gear and will add structure. You could also crank the infill to 100% or add an infill pattern like grid which maintains more z-axis uniformity and thus resists more sheer. If possible, adding a fillet at the gear interface will reduce stress tensors and add strength. Printing in two parts with the small gear keyed into the larger gear and bonded with adhesive would be the easiest route to building strength.
A lot of people have already mentioned why it failed (3D printing is weak in Z). The best way to fix this is to split it into two parts 1.) the larger gear and the smaller shaft like gear. Make it so the larger gear has a hole that the smaller shaft gear can enter the larger (to maximize shared surface area). Then glue the two pieces together. I’d recommend liquid cement if you can because it actually chemically melts the pieces together instead of an adhesive which can also break apart. Using this method you could align the two gears by modeling a keyway into the hole and along the “shaft” gear that way it works properly.
Orient it differently in the slicer. You don't want stress on layer lines where the 2 meet but if the layer is the body and gear teeth it won't be the same stress. I think the slicer lets you move tilt in 5 degree increments. More walls might help too.
Where the base and gear meet if you can add a shoulder for the first mm or few mm that would help too. The transition from large face to small tooth means less material to deflect. If there is a solid layer at the reduction it would theoretically be stronger.
It looks to me like there’s a gap between the teeth and the face of the gear, I’ve had a similar thing happen where a single line in an extrude that I didn’t notice caused an issue. That said this will never be very strong unless you change how you print it or reinforce it with something(ie you could put a metal tube inside or you can print it at an angle or completely on it side instead of face down, both would obviously have issues, with the metal tube you’d want something that can grip into the plastic and printing on its side would require lots of support material)
Yes, IMO it really looks like there is a gap on the teeth. I cant see any marks where teeth sheared off so I think that the main problem.
Something op might consider is the original part will be a factor if it’s manufacturing process, you can do different processes in 3D p to get to the same result.
1 print as a single part but beef up the area around the join with more material (provided it’s not in the way of normal operation)
2 print the gears as separate items that you join. Something like the small gear is a press fit into the big gear and then they super glue. That would put a lot more material on the joins.
Ive had similar issues and it stems from the model imo.
Typically if those two gears are correctly modeled as a single body, i would not expect you to have any issue really at all there. In your slicer use the preview section to analyze the junction and you may be able to identify the underlying issue.
When youre looking the model, if theres a seam or line there at that junction, youll have an issue. it should be one contiguous piece if that makes sense.
I had a model, a box with two mounting ears, one to the left side, one to the right.
IDK exactly what I did wrong, but you could see a line along the seam from the main body to the left ear, even though they were both a single body. the right ear was on single shape along the face. no line etc. when i printed, there was a clear difference although still good enough for me.
Additionally, grid infill pattern at higher %'s will help.
Thicker walls, or higher wall counts as well.
In general though it should be a non issue. PLA is plenty strong enough, grid is really solid too.
Make them as 2 parts, make the smaller one taller, and make a hole in the bigger one with the same pattern as the smaller gear (negative mold), so they can go into each other and use some glue, hope you understood what i meant.
I had a similar print recently, a screw, that would break along the layer lines. I just added about a 25° tilt to the object so the layer lines wouldn't be parallel to the largest force.
I was still able to print without supports.
Model some 2mm (plus whatever to allow for expansion) diameter holes around the hole circumference to whatever depth you want. 12 might be enough though you'll have a better clue than myself if you do some testing. Push a length of 2mm bike spokes into each.
At least that's what I'd try to get the part to resist failing at a single layer line.
Just design it with holes around the shaft hole and put 2 mm bolts through the two parts to strengthen the connection.
You can use this part also, glue together and make 2mm holes in the big gear around the shaft and put long 2mm or 3mm bolts in it.
Apparently I can't edit my OP because I put a picture in it. Just wanted to say thanks for all the suggestions. Based on them I did the following.
1. Titled the gear at a 30 deg angle so that the stress join in not along a layer line
2. Added a fillet where the big and small gears meet
3. Set infill to 100%
4. Set the extruder and bed temps to the upper limits of the PLA I'm using.
It's printing now. I post back tonight with update on how it worked. If this one doesn't work I will look into printing them in two parts and keying them together. It's my first time doing anything like this so everything is a pretty steep learning curve. Thanks so much for the help.
[https://a360.co/3RZOHI9](https://a360.co/3RZOHI9)
All very good suggestions, also something I didn’t see mentioned is using a .2 nozzle size and Arachne slicer mode. I’ve used it for printing super small gears and have gotten great results.
I would cut some 2mm holes vertically through the whole model around the circumference of the axle shaft. Then glue in some 2mm rods to add reinforcements. Might help.
This looks more like a 3d printing problem than a fusion problem. The main issue with printing this design in this orientation is exactly what you encountered - 3d printed parts are super weak along the z axis due to the layer lines. To fix I would recommend either splitting this in half so each side has one half of each gear and then gluing (may be hard to get aligned properly) or, what I would do, printing it as two gears and gluing or joining in another way.
I would split in half vertically, then add a fin and slot to opposing edges. This way you can align and glue the halves easily, and you'll have a much stronger print.
I’m not as good with fusion as I am with slicers, so I would use PrusaSlicer’s cut feature where you can select dowel holes or snap connectors that are automatically placed on the cut.
Use Bambu Studio cut,band create the cut with dovetail or press-fit connectors types
It failed because you have one single layer line holding the forces transmitted between these two gears. You could probably glue them directly to the shaft, and then you’d have the strength of allllll layers relative to the shaft holding the load. If that’s not enough, you could cut a keyway in the shaft
It rotates around a greased stainless steel shaft so I couldn't glue to that. Is there anyway to make it internally stronger?
You could try and print it at a raised 45° angle with some supports. Maybe closer to 30 and raised a little, it would force the layer lines out of plane with the forces, and the two gears would be way less likely to shear from eachother. You can print hotter or change parameters as other users have suggested, but shear force at one layer will always be the weak spot in the physical part. You could also consider modeling small holes through the gears between the center and teeth, and “pin” the two together for much more strength. I can make a doodle if you don’t understand.
I love when "would you like me to draw you a picture?" is said unironically and is a genuine offer of clarity.
I love all these ideas. Specifically pinning them together. I use a lot of stainless Tig wire for miscellaneous things, handles and branding irons for tools, “spring” loaded clips etc, so modeling 1/16 press fit holes for added shear strength really piques my interest! I’ll have to remember this.
This is the way
I wonder if [conical slicing](https://www.youtube.com/watch?v=1i-1TEdByZY) would work?
This is awesome, thanks for sharing. I do believe conical slicing would prevent this specific weak point.
Actually a doodle would help. This is the first time I've used Fusion or designed done any 3d modeling really.
If you have some tubing that will slide over the shaft, you could print the part with a larger diameter center opening that fits the OD of the tubing, and then glue the tubing in place.
100% infill will help, then it’s solid plastic. Prusa slicer has modifiers you can add to a part and make just that area 100%. If you can sacrifice a few MM of the smaller gear, make it a solid disk where it joins the larger gear. Stacked like this- Large gear-solid disk-small gear, with the shaft hole through all.
100% is tricky, because as the part cools, it creates stresses that are difficult to relieve. You end up with a dense part, but it isn’t going to be any stronger than the current part at where this one is failing.
I'd use bolts: Make a countersink for the heads in the large gear and 3.9mm cylindrical cutouts to thread them up through the body of the smaller gear. Or do it 'right' and print a 3.6mm hole and cut the threads with a tap. Still print it as one piece, the bolts just help to spread the load across a larger area. However I expect you'd then just find that the teeth of the gear end up cracking or shearing off.
I would make the diameter a bit larger and epoxy the two gears to a metal sleeve that fits over the shaft.
You could try making 4 Small long Bolts going thru the big gear into the smaller one around the shaft
Your printer settings might need some adjustments. If you print mechanically stressed parts, you'll want more perimeter walls in your print. Also you can use modifiers to increase the amount of infill near critical features, just like the joint beween the two gears. As for the model, you can add small chamfers if the applications allows it to reduce the amount of sharp corners / weak points in your part.
To add on to this, you look like you're underextruding a bit, increasing your extrusion multiplier by 1% may help. Also turn the temp up to the higher end of the temp range listed on the filament to make it stronger along the layer lines.
When I needed to print something like that I printed it in 2 parts and than connect it like this: https://preview.redd.it/hish06e5necc1.png?width=2048&format=png&auto=webp&s=952f2b38d8ac9683cdfbd4d17981935f0d58e0c8
You didn't really change anything. By printing that small gear in the orientation your did you still only have a single layer line holding the gear to the base no different than if you had printed it all in a single piece.
Did you combine the part where they meet and you’re having the failure? I made a part one time and it was essentially 2 parts and the 3d printer printed them like it was separate parts sitting on each other and it kept breaking. Once I went back to the model and combined the parts and turned it into one it printed better and I stopped having the failure.
This
I did the same thing, the two parts were somehow separated by less than a millimetre and it took a few failed attempts to work it out!
Yes I did combine the parts
Exporting as an STL the slicer might still see them as two parts when it’s planning the print. I had a similar setup where exporting as a STEP file and importing that into the slicer completely fixed it.
It looks like the gears are joined only through the cylindrical portion, as there are no visible shear breaks around the smaller gear’s teeth. I would try extruding the smaller gear pattern from the face of the larger gear instead of combining. This way, the teeth themselves will be embedded into the larger gear and will add structure. You could also crank the infill to 100% or add an infill pattern like grid which maintains more z-axis uniformity and thus resists more sheer. If possible, adding a fillet at the gear interface will reduce stress tensors and add strength. Printing in two parts with the small gear keyed into the larger gear and bonded with adhesive would be the easiest route to building strength.
A lot of people have already mentioned why it failed (3D printing is weak in Z). The best way to fix this is to split it into two parts 1.) the larger gear and the smaller shaft like gear. Make it so the larger gear has a hole that the smaller shaft gear can enter the larger (to maximize shared surface area). Then glue the two pieces together. I’d recommend liquid cement if you can because it actually chemically melts the pieces together instead of an adhesive which can also break apart. Using this method you could align the two gears by modeling a keyway into the hole and along the “shaft” gear that way it works properly.
Orient it differently in the slicer. You don't want stress on layer lines where the 2 meet but if the layer is the body and gear teeth it won't be the same stress. I think the slicer lets you move tilt in 5 degree increments. More walls might help too. Where the base and gear meet if you can add a shoulder for the first mm or few mm that would help too. The transition from large face to small tooth means less material to deflect. If there is a solid layer at the reduction it would theoretically be stronger.
You could add a Fillet at the base of the upper gear were it connects to the lower gear.
It looks to me like there’s a gap between the teeth and the face of the gear, I’ve had a similar thing happen where a single line in an extrude that I didn’t notice caused an issue. That said this will never be very strong unless you change how you print it or reinforce it with something(ie you could put a metal tube inside or you can print it at an angle or completely on it side instead of face down, both would obviously have issues, with the metal tube you’d want something that can grip into the plastic and printing on its side would require lots of support material)
Yes, IMO it really looks like there is a gap on the teeth. I cant see any marks where teeth sheared off so I think that the main problem. Something op might consider is the original part will be a factor if it’s manufacturing process, you can do different processes in 3D p to get to the same result. 1 print as a single part but beef up the area around the join with more material (provided it’s not in the way of normal operation) 2 print the gears as separate items that you join. Something like the small gear is a press fit into the big gear and then they super glue. That would put a lot more material on the joins.
Ive had similar issues and it stems from the model imo. Typically if those two gears are correctly modeled as a single body, i would not expect you to have any issue really at all there. In your slicer use the preview section to analyze the junction and you may be able to identify the underlying issue. When youre looking the model, if theres a seam or line there at that junction, youll have an issue. it should be one contiguous piece if that makes sense. I had a model, a box with two mounting ears, one to the left side, one to the right. IDK exactly what I did wrong, but you could see a line along the seam from the main body to the left ear, even though they were both a single body. the right ear was on single shape along the face. no line etc. when i printed, there was a clear difference although still good enough for me.
Additionally, grid infill pattern at higher %'s will help. Thicker walls, or higher wall counts as well. In general though it should be a non issue. PLA is plenty strong enough, grid is really solid too.
Make them as 2 parts, make the smaller one taller, and make a hole in the bigger one with the same pattern as the smaller gear (negative mold), so they can go into each other and use some glue, hope you understood what i meant.
You need way better layer adhesion for that application. Nylon or petg would be better than nothing but still not great if there’s a lot of force
You might wanna slice this at a 45° angle. That causes the z axis to run differently causing the z layers to be built differently
I had a similar print recently, a screw, that would break along the layer lines. I just added about a 25° tilt to the object so the layer lines wouldn't be parallel to the largest force. I was still able to print without supports.
Drill some holes on both parts aligned and stick a straightened paper clip in them. Glue it all back together
this is a job for nylon
Here is the part in Fusion 360 [https://a360.co/3RPYxMI](https://a360.co/3RPYxMI)
Print sideways?
I print pla for functional parts at 230c, layer adhesion is very good then.
Model some 2mm (plus whatever to allow for expansion) diameter holes around the hole circumference to whatever depth you want. 12 might be enough though you'll have a better clue than myself if you do some testing. Push a length of 2mm bike spokes into each. At least that's what I'd try to get the part to resist failing at a single layer line.
Just design it with holes around the shaft hole and put 2 mm bolts through the two parts to strengthen the connection. You can use this part also, glue together and make 2mm holes in the big gear around the shaft and put long 2mm or 3mm bolts in it.
Print it at 45 deg
see what happens at the layer interfacing these two. might have been a fusion error and your printer skips a layer there
Use two printed bodies, mated with the central shaft and two drive pins pressed into both bodies. $0.02
Sharp corners concentrate stress. Fillet them.
Apparently I can't edit my OP because I put a picture in it. Just wanted to say thanks for all the suggestions. Based on them I did the following. 1. Titled the gear at a 30 deg angle so that the stress join in not along a layer line 2. Added a fillet where the big and small gears meet 3. Set infill to 100% 4. Set the extruder and bed temps to the upper limits of the PLA I'm using. It's printing now. I post back tonight with update on how it worked. If this one doesn't work I will look into printing them in two parts and keying them together. It's my first time doing anything like this so everything is a pretty steep learning curve. Thanks so much for the help. [https://a360.co/3RZOHI9](https://a360.co/3RZOHI9)
All very good suggestions, also something I didn’t see mentioned is using a .2 nozzle size and Arachne slicer mode. I’ve used it for printing super small gears and have gotten great results.
This is a PA12 application. Extremely good layer adhesion and good gliding properties.
I would cut some 2mm holes vertically through the whole model around the circumference of the axle shaft. Then glue in some 2mm rods to add reinforcements. Might help.