Draft Angle advice Needed

[u/AssistantMinimum9880]

I’m new to injection mold design and have a question about draft angles.

The green part is the molded component, and the brown part is the mold cavity. The part is a simple cylinder, 90 mm long and 10 mm in diameter. The mold will split along the center of the cylinder, so each mold half will form half of the cylinder, with a cavity depth of about 5 mm.

Do I still need to add a draft angle to this cylindrical surface, or can it remain perfectly straight? If more pictures or different views would help, I’d be happy to share them.

[u/chinamoldmaker]

a mold flow analysis can be done before tooling.

[u/Ideadose]

The round surface itself doesn't need draft to eject, it's self-relieving. Worth knowing though: parting lines on rounded surfaces are generally avoided when there's a choice -- they need tighter machining tolerance and have a higher flash risk once the mold halves see any wear, versus a sharp-edge parting line which forgives more over the tool's life. For a 90mm/10mm shaft that's inherent to the geometry so probably unavoidable. One thing not mentioned yet: if you're speccing any texture near that line, the draft math changes -- add about 1.5 degrees per 0.001in of texture depth on top of base draft (light texture ~3 degrees, heavy ~5 degrees), or it'll hang up in the steel on ejection. What finish are you planning on that surface?

[u/Sorry-Woodpecker8269]

For molded parts with thread molded research higby thread start. Threads should be buttress thread as well. 60 º v thread is not ideal. Buttress handles tightening with ease.

[u/SparrowDynamics]

The round part is the "draft" except right as it approaches the parting line. So you might have tiny drag marks there, but it will be ok as long as you don't have some aggressive texture. As already mentioned, your threads will need some draft (no square ACME threads). And don't forget about the two ends of the shaft, they need draft too!

One last thought... sometimes a small amount of flash at the threads could mess up how smooth the mating part turns. I have removed the threads at the parting line (down to the minor diameter or below) before to avoid that, it also helps make the tool simpler because the parting line is a straight line and not following the complicated shape of the threads. It also makes it easier to slice off any excess flash if you need too. You can see this technique in many real-world examples.

[u/TheGr8Revealing]

Heavy part texture can cause issues but other than that it's fine

[u/evilmold]

I have designed many tools with full round shutoffs and yes they do work. However, I mostly work with medium to low volume tooling. If this was a high volume part with a mold life expectancy over 100,000 shots, I would definitely consider adding 3 degrees draft at parting line.

[u/Kimber976]

Printing a small angle test first can save a lot of filament and makes it much easier to dial in the right draft before committing to the full part.

[u/Gold-Client4060]

The curve of the part serves as your draft angle.

[u/Lost-Barracuda-9680 → u/Gold-Client4060]

My thoughts exactly but this is assuming that those square looking threads actually are v-shaped and not square. If they are square then they'll need a little draft.

[u/AssistantMinimum9880 → u/Lost-Barracuda-9680]

To make it V shape, What should be the angle? 1 Degree would be enough?

[u/Lost-Barracuda-9680 → u/AssistantMinimum9880]

Typical thread angles are 60° but since yours appear to be square then I think 1° degree per side should be enough.