Hello,
I am looking for the American Standard for Countersunks. I found the standards for the screws (like ASME 18.6.3-1998). But I want to know how big/deep the thru hole for this screws should be. The German standard for this is DIN74 but it's only for metric screws. Does somebody know such a standard for non-metric screws?
Thank you Kai
Try searching the various supplier sites, many list Standards to which they supply. This site does that
John
Dear Kai Schaeffer:
...
An internet search for: "#4" and "clearance hole" provides 2762 hits. The first on AltaVista Advanced is:
David A. Smith
If you can't find spec's or design guides for CS holes look at standard drill sizes.
- CJF.
Thank you for this tip. I am sorry, but could you explain what "gilding the lilly" means? I didn't understood this. But I have a good excuse: I am not a native speaker. :-)
The problem I see is that I no have the clearance hole, what is not so bad because it is half of the information I need. But I still need the depth or the upper diameter of the cone.
Kai
Dear Kai Schaeffer:
Guilding is a process of applying gold leaf to a surface, presumably to beautify it. Apply such a treatment to a lilly to improve its beauty and it is, well, pointless. The beauty of a flower is both its "instantaneous value" and that it is so soon gone.
You need to establish the cone then, and not the clearance around the threaded portion. Set the head of the screw to be flush or a few tenths of a mm below the surface to be mounted against. Presumably you have a good specification on the screw, so that if you manage the "sheet" properly, the screw won't surprise you.
How good is the screw specification?
David A. Smith
Now for my pennance:
Gilding is applying gold leaf. Guilding, the best I can figure is forming a guild or union of sorts. Gelding is a male horse that isn't quite so male.
I spelled it wrong. Sorry.
David A. Smith
" guiding the Lilly " English saying, the Lilly ( flower ) is beautiful as is, gilding it ( covering with gold ) would not improve it... thus doing work which adds to cost, but makes the product no better ( or worse ) is known as guiding the Lilly
Standard countersink cutters are available, their outer diameter is a little larger than the screw head, and they should be run in to give a small lip to the countersink for the screw to be flush or bellow the surface level.
The size of the hole depends on depth of materials and accuracy of parts. It's not uncommon to find the countersink goes through the bottom of a sheet component, leaving an oversize hole and the underlying threaded hole must then be countersunk a little to allow the screw to pull down on the sheet.
As a "rule of thumb" ( rule derived from practical experience ), with high accuracy parts the hole can be to the thread nominal size, but add 5% and go up to the next standard drill size for most jobs.... if the parts have a large tolerance then increase the hole size until you are sure you will not get the screw chewing into the side of the holes in a worst case fit.
Hope this helps
Jonathan
Barnes's theorem; for every foolproof device there is a fool greater than the proof.
To reply remove AT
----- Original Message ----- From: "Kai Schaeffer" Newsgroups: sci.engr.mech Sent: Tuesday, August 12, 2003 7:54 PM Subject: Re: Standard for Countersunk
I would have thought that the hole size is the same as the head unless there is a need to design it otherwise. I have seen situations where the countersink is very deep in order to recess the head. This is especially so when the screw is holding a consumable material such as a wearing strip. Otherwise, the heads are normally flush with the surrounding material. I suspect that the depth of the hole is the designers decision. Obviously, the countersunk angle must be the same as the screw. Can't really help anymore. Cheers
John
Clearance hole should be large enough so the head of the countersunk fastener locates your parts. Holes and fasteners are not perfect and ideally you don't want the fastener head and its body fighting each other over part alignment. In some situations its not that critial but as a general rule the clearance hole should be a least a "free fit" and preferably a little larger. Also using quality fasteners can help avoid joints that are cosmetically and/or functionally substandard.
Dave Miller
A long time defacto standard is the chart in _Machinery's Handbook_ which gives close and free fit drill sizes for screws. I tired of using the copy from the 1950s I inherited early in my career and bought my own shiny new copy in 1976. I assume the chart is still in the current edition. Close fit clearance holes are for assemblies made to relatively tight tolerances. Free fit clearances are for assemblies layed out and drilled by hand. As an example, for a 3/8" bolt the close fit is .3860 (W drill) and the free fit is .3970 (X drill). (People often wonder what those funny lettered drill sets are for.)
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