Flat Head Screws

Cris_Bowers

I've been making my own flat head sheet metal screws because there is only a narrow range of lengths available within Standard Content. I noticed that Onshape's countersink holes were significantly larger than the screw heads causing a gap between my parts. As such I have also been modifying countersink holes to match my screws. Today I actually had an opportunity to use a flat head machine screw and attempted to use Standard Content for it. When I went to insert it into the now modified countersink hole I had made, the head was significantly larger than my hole. So I went searching to find out what the proper diameter for flat head screws is. I'm not sure I came up with an answer so I wanted to reach out to the community to see if anyone could verify the sizes within Onshape.

I found a table on some fastener website that lists screw sizes per ANSI B18.6.3-1998:

For #8 the head diameter was listed 0.285" min. and 0.312" max.; McMaster-Carr has it at 0.312"; Solidworks has it at 0.285"; Onshape has it at 0.338"

For #10 the head diameter is listed at 0.333" min. and 0.362" max; McMaster-Carr has it at 0.362"; Solidworks has it at 0.34"; Onshape has it at 0.392"

Jason_S

@Cris_Bowers , 

Can you share a document here to show what you are seeing? Yes, our hole tool autofills the countersinks to 82° (As for ISO, there is only one standard countersunk angle from what I could find with my research, 90°), but you can change this manually in the dialog.



What I think you are running into a mating problem. We cannot mate to the virtual sharp of the cone that defines the countersink yet.


Take a look at this document to see what I am talking about:
https://cad.onshape.com/documents/96e225622e275b1a6f07f5a0/w/57a42187c394f01fed000d3c/e/5f0fa98facf122577a73314d


In the real world, the countersunk face of the bolt would sit against the countersink of the hole, meaning the tips of the cone are coincident. Right now the Mate connectors are in a place that makes mating difficult. We are looking to change this very soon, but first need a Mate connector snap point to the tip of an implicit cone.

As for the difference in size, I will go do some research into ANSI, ASME, ISO, and DIN standards and come back with my findings.

billy2

I've noticed this issue using ISO flat heads. I haven't tried to figure out what's going on.

I do realize that flat head are hard to replicate in an assembly. Not sure if it's user error.

One problem that I encounter is with counter bore holes and I keep forgetting to change the type from tap to clearance. Therefore, I have to chase all my c'bore holes and open them up. The defaults seem to be killing me. C'bore holes that are set to tap? Why? Because I last used a tapped hole?

Other than that I like the hole feature and standard library. There are issues though, mostly my fault and having to remember to check the default settings.

Cris_Bowers

I don't have anything I can share publicly. What you are showing in your example is basically what I'm seeing. I don't use the mate connectors provided on the screws. I use a fasten mate on top center of the screw to the top center of the hole. In Solidworks I would coincident mate the edge of the screw head to the wall of the countersink. The Solidworks method is preferable.

brian_brady

This works for for mating flat head screws into a countersink. First use a fasten or slider to put the screw into the hole and be close. Then delete the mate that you just made and use a tangent mate with the countersink surface in the first box and the large diameter edge from the conical surface of the screw head in the second box.

I tried using a slider with a tangent. The screw seated just fine but then the tangent mate turned red. I don't like red.

Scratch that, it works if you use the top edge of the countersink and the large diameter edge of the conical surface on the screw.

Jason_S

That does work, but you shouldn't have to use a tangent mate. Changes coming soon!

Cris_Bowers

Jason_S said:

That does work, but you shouldn't have to use a tangent mate. Changes coming soon!

If these changes also come with the ability to specify custom lengths other than the single 1.25" length that is available for a #8 flat head tapping screw, I'll be happy. It really sucks not being able to use something that is supposed to make life easier.

AngleC

Jason_S said:

That does work, but you shouldn't have to use a tangent mate. Changes coming soon!

Has the following been implented yet? "We cannot mate to the virtual sharp of the cone that defines the countersink yet."

Inserting a 100 degree flathead from Standard Content into a 100 degree CS hole feature still does not correctly place the screw.  This is OK if one just has to correct a couple instance mates, but on some sheetmetal enclosures each panel can have dozens.

NeilCooke

@AngleC yes you will see a mate connector location at the tip of the cone of the countersink 

eric_pesty

  This is OK if one just has to correct a couple instance mates, but on some sheetmetal enclosures each panel can have dozens.

@AngleC
As a side note, if you have "dozens" of screws, you can hopefully leverage the replicate feature as long as you don't have dozens for different screw sizes! Unlike a "regular" pattern, the replicate feature works on multiple faces/parts at once.