Hole dialog discussion

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M4x
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Re: Hole dialog discussion

Post by M4x » Sat Nov 14, 2020 12:17 pm

rynn wrote:
Sat Nov 14, 2020 11:04 am
UR_ wrote:
Sat Nov 14, 2020 3:44 am
uwestoehr wrote:
Sat Nov 14, 2020 2:20 am
I had a look at the norms, and they only define screw heads, not how the holes for a countersink/bore must look.
Please have a look at "DIN 74 countersinks for countersunk head screws" and including DIN ISO 20273.
The problem is, these cost a fortune: DIN 74 (42,88 €) and DIN EN 20273 (30,23 €)
That’s why most developers here do not have access.
I've access to both. Ping me if I can be of any help.
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uwestoehr
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Re: Hole dialog discussion

Post by uwestoehr » Sat Nov 14, 2020 12:26 pm

chrisb wrote:
Sat Nov 14, 2020 12:14 pm
I asked Yorik if this can be payed from the FreeCAD account.
Please not, this is not necessary. All tables defined in the norms are available for free. I am strongly opposed to spend money for 10 ore more different screw norms.
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Re: Hole dialog discussion

Post by chrisb » Sat Nov 14, 2020 5:07 pm

uwestoehr wrote:
Sat Nov 14, 2020 12:26 pm
All tables defined in the norms are available for free.
Probably. But many websites are rather interpretations of the norm, and it is usually impossible to see where they deviate from the real document itself.
Hopefully M4x can shed some light on this. I am, of course, against spending money for something that can be found for free. But I am even more against investing time following the wrong path, albeit only a slight deviation.
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Re: Hole dialog discussion

Post by uwestoehr » Sun Nov 15, 2020 12:58 am

chrisb wrote:
Sat Nov 14, 2020 5:07 pm
many websites are rather interpretations of the norm
They want to sell their screws. The norms for sure follow the norms - no one will setup a product line which nobody will buy or send back. So when they write according to " ISO 4762" and then specify a table we can be sure these are the dimensions of screws defined in this norm. Moreover, I of course checked several screw seller pages.
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M4x
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Re: Hole dialog discussion

Post by M4x » Sun Nov 15, 2020 7:54 am

I'll have a look and compare the tables to the norms later today.
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M4x
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Re: Hole dialog discussion

Post by M4x » Sun Nov 15, 2020 2:19 pm

DIN EN 20 273 : 1991 Durchgangslöcher für Schrauben = german translation of the ISO 273 : 1979 Fasteners; Clearance holes for bolts and screws
The links uwestoehr provided earlier are correct but some values the norm defines are missing. I assume because those are uncommon in practice. I've asked duckduckgo.com and found this photo from a (I guess) Mechanical and Metal Trades Handbook or something like that: Link photo ISO 273 / DIN EN 20 273 values. I've checked all values, the table in the linked photo is complete and correct according to the norm mentioned above.

DIN 74 : 2020-01 Senkungen für Senkschrauben, ausgenommen Senkschrauben mit Köpfen nach DIN EN 27721 = Countersink for countersunk head screws, except countersunk head screws with heads according to DIN EN 27721
This norm defines four different countersunk types (A, E, F and G), gives information about what countersunk type should be used with which screw type (described by a norm of course) and includes tables with the relevant dimensions.

Further more, the norm tells us something about how, in special cases, other countersunk depth should be handled.
example
countersunk type A for an M4 screw should've a depth of 2,1 mm.
Screenshot from 2020-11-15 15-11-50.png
source:http://www.iim.maschinenbau.tu-darmstadt.de/cad_ptc/cad2002/DIN-Info/DIN74.html
Screenshot from 2020-11-15 15-11-50.png (36.93 KiB) Viewed 354 times
If you'd need a depth (t [the norm uses t_1]) of 3 mm, the diameter d_2 would change accordingly. And you'd write something like "countersink DIN 74 - A4 x 3" to make that clear.

Does this help already? I probably have access to all screw related norms and could read up on specific questions / check if found tables are correct and so on. I must confess that I didn't read the whole thread so I'm not entirely sure "where" the discussion is at the moment :oops: :roll:

edit: typo
Last edited by M4x on Sun Nov 15, 2020 6:41 pm, edited 1 time in total.
chrisb
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Re: Hole dialog discussion

Post by chrisb » Sun Nov 15, 2020 6:03 pm

And this saved FreeCAD another 73,11€. Thanks for looking it up.
You need at least FreeCAD 0.19.23300 to edit my current sketches.
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M4x
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Re: Hole dialog discussion

Post by M4x » Sun Nov 15, 2020 6:45 pm

You're welcome. I'm glad that I could help. I'd even do it again :P
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Re: Hole dialog discussion

Post by uwestoehr » Mon Nov 16, 2020 9:38 pm

M4x wrote:
Sun Nov 15, 2020 2:19 pm
Does this help already?
Yes. Thank you. Note however, the ISO screw definitions differ in the height if the screw heads from the ISO norms. Thanks to @rynn we have the new feature to select a screw definition norm to get a proper proposal for the cut depth.

uwestoehr wrote:
Sat Nov 14, 2020 12:08 pm
So we have 2 issues:
- some of our "close fit" diameters for metric holes are incorrect (we use e.g. values like 3.15 despite the norms define a precision of max 0.1 mm)
- we don't support the defined "coarse fit"
I'll correct/add this after the pending PR is merged.
Here is the PR: https://github.com/FreeCAD/FreeCAD/pull/4058

- It adds the coarse fit
- it takes whenever possible the hole diameters of the ISO norm
- While implementing this, I found out that we did not support the sizes M4.5, M7 and M39, They are normed and you can buy screws in that size, e.g. here M39: https://schraube-mutter.de/schrauben/m39/ I added these sizes with the PR.
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Re: Hole dialog discussion

Post by chennes » Tue Nov 17, 2020 3:40 am

In the PR on Github I commented on the name used for the largest of the clearance hole sizes: @uwestoehr went with "Wide," but that doesn't match either the ISO standard or the reference I normally use for these (Glover's Pocket Ref). uwestoehr suggested we discuss the name here.

I agree that the ISO's naming of "Fine," "Medium," and "Coarse" for the clearance hole fit is confusing, and that "Wide" is a better choice. However, I've never seen clearance holes described using that term before. I don't know if there is precedent for it, so I suggest that maybe using "Close Clearance," "Normal Clearance," and "Loose Clearance" is even more clear/descriptive, and has at least one other source (Glover). That said, there's no reason to treat Pocket Ref as an absolute authority on the manner: it might be a good idea to use someone else's terms instead of making up our own, though. Is there another reference for what terms to use in this menu?
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