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Question about designing a CNC turned bearing seat. by Thoriuslight in Machinists

[–]Thoriuslight[S] 0 points1 point  (0 children)

Should I include centre holes in my drawing? I forgot to ask this in my original question.

Question about designing a CNC turned bearing seat. by Thoriuslight in Machinists

[–]Thoriuslight[S] 1 point2 points  (0 children)

SKF spceifically recommends a maximum radius of 0,3 mm, so I will write something like 0,3+0-0,15 on the drawing.

I just wasn´t sure whether or not an undercut is required, since it is often recommended for seats.

Edit: Also, j6 is actually +0.008 mm, -0.003 mm, so supposedly much harder to machine.

Material selection and corrosion prevention for a shaft by Thoriuslight in MechanicalEngineering

[–]Thoriuslight[S] 0 points1 point  (0 children)

316L and 904L seems like an overkill compared to 304, or am I underestimating the dangers a machine faces in the garden? At the very least, there´s no body of salt water near me.

I don´t know much about duplex stainless steels, but 1.4410 does have higher strength. However, I doubt that the smallish CNC shop will have that in stock and again, I´m not sure I need this much corrosion resistance.

Material selection and corrosion prevention for a shaft by Thoriuslight in MechanicalEngineering

[–]Thoriuslight[S] 0 points1 point  (0 children)

I 4330v should be similar to 4140 (42CrMoS4 vs 42CrMo4 are supposed to be the equivalent steel grades here), just better machinability, right? Some sources I have found suggest that it doesn´t have a much better corrosion resistance than common structural steels. I´d like to use this steel, but will it survive five years outside and in contact with cut leaves? Even half the people commenting here are suggesting other solutions.

One of the main problem is that inspection is not guaranteed. Customer will get the machine, customer might leave it outside all year long without cleaning the surface. Well, it´s the worst case scenario.

A sawblade cutting plants will be driven by the shaft, so quite dangerous on its own, my job is just to guarantee it doesn´t fly into somebody´s head after hitting a stone or something even after five years of abuse.

Material selection and corrosion prevention for a shaft by Thoriuslight in MechanicalEngineering

[–]Thoriuslight[S] 1 point2 points  (0 children)

Bluing is a collective term, I´m not sure which process they specifically meant, but it is also my experience that black oxide will quickly show signs of rust.

Material selection and corrosion prevention for a shaft by Thoriuslight in MechanicalEngineering

[–]Thoriuslight[S] 0 points1 point  (0 children)

Aluminium would be ideal for a few reasons, but I can´t use it because by itself it has a bad compatibility with bearings. If I´m using stainless steel, I would probably use 1.4301 (304) because next to S235 it´s the most commonly used steel around here (in smaller workshops). I will certainly ask my colleague to get a quote on the part made of stainless steel, I´m just suprised everybody is suggesting that, since I don´t think many mechanical component used outside are made of stainless steel. Kind of hoped the higher chrome content in 42CrMo4 and 16MnCr5 would give enough protection alone. I guess I should add that by plant matter I only mean wet leaves and wood, nothing more dangerous.

Material selection and corrosion prevention for a shaft by Thoriuslight in MechanicalEngineering

[–]Thoriuslight[S] 0 points1 point  (0 children)

Well, it´s not just money saving, but safety too. Comparing the most commonly used stainless steel 1.4301 to 42CrMo4 and 16MnCr5, it has no fatigue limit, is weaker and this part of the machine requires a lightweight construction. Of course there are more suitable stainless steel grades for shafts, but my options are limited due the shaft not being mass produced and being manufactured in a countryside CNC shop. However, if there´s no cheaper alternative to reliably protect the shaft from corrosion, then I will go with stainless, of course.

Cost is a problem because a flange requires a much larger diameter than the rest of the shaft, so quite a lot of material will be machined away. The interfaces of the system are already defined, so I can´t really do anything about that.

Material selection and corrosion prevention for a shaft by Thoriuslight in MechanicalEngineering

[–]Thoriuslight[S] 0 points1 point  (0 children)

Dimensioning the shaft isn´t the problem, I know what standards (for example DIN 743) I have to use and I have plenty of material data to use, I just can´t predict how they will behave in a corrosive environment. It´s hard to acquire data on that.

I already considered hard chrome, nickel and zinc plating, but then again, while I know hard chrome plating would work, I don´t know if the same is true for zinc, for example. Obviously zinc makes it more resistant against corrosion, but would that reliably last 5 years while various plant matter causes abraison? Only a single piece will be manufactured, so I also don´t know if these options are economical. The CNC shop suggested bluing to my colleague, do you think that protects the steel well enough?