Wrong head diameter for M3 Cap Screw

[roger.froud]

I've just started using Fusion 360, and tried to use an M3 Cap Screw with a clearance and pocket for the head. The head diameter is miles too big. How is this possible? Surely this is a component that has been used thousands of times, so why is it wrong? What's the point in having a library if you then have to go back and do things the old way to get the result you need?

Doesn't anyone take the time to fix these issues? Surely I'm not the first to find this and try to feed it back.

I tried to feed this back, but Autodesk doesn't let you feed back anything unless you are using a version with a subscription.

[HughesTooling]

When I create a M3 counterbore I get a Ø6.5 counterbore. All the documents and tools I can find are also Ø6.5 so what size are you getting?

Mark

[TheCADWhisperer]

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@roger.froud wrote:

…tried to use an M3 Cap Screw with a clearance and pocket for the head. The head diameter is miles too big. How is this possible? 

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I have never seen a fastener in miles units.

I can only assume this is a units issue.

Can you File>Export your *.f3d file that exhibits this behavior to your local drive and then Attach it here to a Reply?

[roger.froud]

I'm surprised that you find this so funny. It's not appreciated.
Roger

[alan.jonesXHXUF]

Where are you getting the screw model from? 

[roger.froud]

I'm just using the Hole tool that's provided. I selected M3 and a counterbore. The sizes come from the Fusion360 install.

[HughesTooling]

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@roger.froud wrote:

I'm just using the Hole tool that's provided. I selected M3 and a counterbore. The sizes come from the Fusion360 install.

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And what size does the counterbore measure? For me it is Ø6.5mm and that is the correct size.

Mark

[TrippyLighting]

According to the engineers bible, 6.5 mm for the diameter is correct for a M3 SHCS (Socket Head Cap Screw).

That hole is dimensioned to accept a washer (6mm OD)  along with the screw, which is common practice!

[roger.froud]

Sorry, but it is certainly not standard practice to fit a washer then using a Cap Screw in a pocket.

The maximum size of an M3 cap screw head is 5.5mm according to this standard table...

https://roymech.org/Useful_Tables/Screws/cap_screws.html

The close clearance size should be about 0.1mm over that size.

[TrippyLighting]

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@roger.froud wrote:

Sorry, but it is certainly not standard practice to fit a washer then using a Cap Screw in a pocket.

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You can argue that with the folks that created the ISO standard.

Barring any bugs, Fusion 360 follows that standard.

I checked again and I was wrong. The standard washer OD for an M3 screw is 7mm. So the hole is not dimensioned to fit a washer.
But 6.5mm for the countersunk hole is still the current ISO standard. 

[TheCADWhisperer]

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@roger.froud wrote:

The maximum size of an M3 cap screw head is 5.5mm according to this standard table...

https://roymech.org/Useful_Tables/Screws/cap_screws.html

The close clearance size should be about 0.1mm over that size.

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The chart you linked does not show the standard for the clearance?

Do you have a reference for the clearance hole?

Exactly what standard does your company use?  ISO? ANSI/ASME?

Is that on the diameter or on the radius?

On the diameter that would be about half the thickness of a sheet of paper on each side.

Yikes!  That is a close fit.

I guess that SolidWorks has it wrong too?

Let's check Inventor...

Hmmm, where is my Machinery's Handbook...

[TheCADWhisperer]

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@TrippyLighting wrote:

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But 6.5mm for the countersunk hole is still the current ISO standard. 

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I think you meant Counterbored hole for SHCS.

[TrippyLighting]

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@TheCADWhisperer wrote:

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@TrippyLighting wrote:

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But 6.5mm for the countersunk hole is still the current ISO standard. 

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I think you meant Counterbored hole for SHCS.

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Yep

[roger.froud]

Fusion offers three types of clearance for the feature, but that doesn't seem to affect the head dimension. I would expect the smallest of these to be a close fit on the head of the bolt as well as the bolt clearance.  Something like 0.2mm over the largest head diameter tolerance would be acceptable.

Why can't you just override these values?

[TheCADWhisperer]

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@roger.froud wrote:

Fusion offers three types of clearance for the feature, but that doesn't seem to affect the head dimension. 

Why can't you just override these values?

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I noticed the same thing in SolidWorks - I didn't check deeper, but I would wager it is simply because this is such a small fastener.  Before even digging deeper I would make significant wager that on larger size fasteners there is a difference between the Close, Normal and Loose settings.

You can just override these values.

Simply use your own Counterbored Hole settings rather than the Clearance Hole.