Rule of Thumb

It will depend upon the material in question, the diameter of the particular screw and the loads involved but are their 'rules of thumb' for deciding how close to the edge of a particular material one can drill and tap to leave sufficient material for a secure fixing?

Ian,

I think it's fairly safe to assume that if there is room for the head of the screw [or whatever] to lie within the outline of the job there will be no problem with "breaking out".

"Aerospace and Defence" assemblies are commonly built-up from panels, using a row of cap-head screws tapped into an edge.

MichaelG.

Hi Michael

Thanks for clarifying this and apologies for my delaying in replying.

Ian

As a general guideline, when designing machine parts, I leave at least one material thickness, preferably two material thicknesses, between tapdrill hole edge and plate edge. Of course this isn't always possible, and if not, a quick stress analysis calculation is a good idea if forces or loads involved are high.

I'm sure others will say I'm dead wrong, but the approach has worked for me in industry for 30 years.

JD

Edited By Jeff Dayman on 13/08/2014 10:38:44

My only reference is for riveting aircraft skins, 2 diameters from the edge, and 5 diameters apart. This is basically for repair work. It is similar for bolts, just remember to make sure there is room for the head against anything on the opposite side from the edge, an example would be a cylinder base flange, you must have room to seat the nuts, and get at them with a spanner, even better a socket, or ring spanner. Ian S C

The question related to the feasability of bolting 65mm x 1200mm x 5mm plate to the ends of 125 x 65 x 9.5 parallel flange channel to create a rectangular frame. Working to 2 diameters would mean the bolts could be only 2mm to the flanges [9.5mm thk] and 1mm to the web [5.5mm thk ] which intuitively would seem too small. I think I may have to use corner angles instead.

I will do a stress analysis calculation as Jeff suggests [if google comes up with an explanation as to how to do so].

Ian

Hi Ian,

If you are thinking of bolting plate directly to the ends of channel I would not recommend it, there are stronger ways of doing it. Far better would be to make the frame out of channel pieces bolted through common faces and webs, then bolt your plate to the tops of the webs or the faces of two of the channels. If you post a sketch of your frame idea/plan in an album we would be able to make better suggestions.

JD

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Ian,

I had not realised you were working on such a large scale

... You might find some useful design ideas here

MichaelG.

Edited By Michael Gilligan on 14/08/2014 08:31:32