minimum plate thickness for tapped hole 1

[RacingAZ]

I think I read this here before but I can't find it anymore.

What is the absolute minimum steel plate thickness I can use for a tapped hole to put a 1/2" dia. A307 bolt? I mean minimum from a fabrication stand point only.

I'm not looking to develop the bolt capacity. Very lightly loaded, if there is a load at all (100-200 lbs. tension).

 

[ishvaaag]

Since commercial steel sheet accepts such values for selfdrilled screws it must be in the sheet thickness range. Say 1 mm thick or less as long as the sheet is between the head and a hard place.

 

[desertfox]

Hi RacingAZ

Usually the depth is at least one diameter of male screw.
For tapping into steel with less strength than the bolt I would say at least 1.5 tmes screw dia.

deserfox

 

[ishvaaag]

Again the language translation ... tapped. Surely one wouldn't see as reliable if the tapped perimeter was as thin as by my former recommendation. Must be in some catalog or Mark's or whatever, will try later to find. Anyway the sound recommendations of desertfox sound hefty for 200 pounds.

 

[ishvaaag]

I attach 2 scans from the Residential Steel Framing Handbook.

 

[ishvaaag]

In the former, screw joints, in this power driven joints. If your application is neither, please describe the situation more exactly and we may find an appropriate capacity to post.

 

[GregLocock]

The problem is that a tapping operation is destructive, whereas a self tapping screw is a rolled threadform. A such a tapped thread is likely to need a greater depth than a self tapping screw would new.

I'd a thunk the answer would be in pitches, not diameters.

It also depends on how the thread is tapped - a hole that is tapped using a handheld wrench will have significantly greater widening than one that is machine tapped.






Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[GregLocock]

-new +need

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[ishvaaag]

My second post referred to say one blind bolt in which a troncoconical surface has to support the 200 lbs pull; by that design I wouldn't rely in 1 mm thick plate concomitant with the troncoconical surface. However for the scope of the book for which the tables are conceived, I would accept the tabulated values, or maybe a bit more conservative.

 

[Ron]

My thoughts are along the same line as Greg's. If you are using a 1/2"x13 (coarse thread) then in a 1/4" thick plate you'd get about 3 threads. If it has no tensile load on it, probably not a big deal unless it wobbles.

The minimums for this type of thing are based on loaded bolts and achieving something similar to what you'd get with a corresponding nut. As a rule of thumb, I suppose you could say that the plate thickness needs to equal the nut thickness for that bolt, if load capacity is an issue.

 

[bridgebuster]

I've also come across the rule of thumb that the tapped hole be at least the thickness of a nut. Take a look at the attached calculation - once again Ron is on the money - a more precise method based on number of threads.

 

[desertfox]

This as the same formula as bridgebuster's link however if you read the notes on this link:-

http://www.roymech.co.uk/Useful_Tables/Screws/Thread_Calcs.html

notes as on the site below:-

Various studies on thread loading have established that the shear stress is not evenly distributed across the threads. The first thread withstanding the load is the highest stressed and the next one is much less stressed and so on... . If the thread materials were very hard and did not yield the first thread could be withstanding nearly all the load. However because of material yielding there is some distribution of the load. A study (see link 2 below) has established that for a typical grade 8 nut the percentage of the load taken by consecutive threads are about 34%, 23%, 16%,11%,9%, 7% .... This effect can be alleviated by using very accurate threads and by using ductile materials for the components. It has been established that,for carbon steel, there is no increase in thread shear strength by having a thread engagement length in excess of the screw diameter. It is normal practice to use a tapped hole depth of about 1,5 x nominal diameter - this allows at least 1 diameter of good thread engagement.

A very simple rule that can be applied for that vast majority of applications is that a thread length of 80% of the screw diameter (standard nut height) is sufficient for ensuring that the screw will fail in tension before the female thread (nut) fails in thread stripping (assuming the screw and nut are similar materials). Equations below indicate how to make adjustments if the tapped metal (nut) strength is lower than the screw/bolt.


desertfox

 

[RacingAZ]

Thanks for the responses. Load capacity is not an issue per my OP. As long as it can hold 100-200 lbs. of tension. So the main thing probably would be as Ron mentioned, just to avoid wobbling when the bolt is in the hole.

Follow up question: What would be more efficient to fabricate? A plate with a tapped hole or a plate with a nut welded to a regular hole?

 

[Ron]

RacingAZ...if you have light loads, why not look into using Nutserts or similar. These are just inserted into a drilled hole and work like a pop rivet. Capacities of several hundred lbs. in the size you need are not a problem. Easy fabrication, quick.

 

[RacingAZ]

Not familiar with nutserts but when I googled it, very similar concept to a threaded insert. Good idea Ron, I'll look into it.

 

[rb1957]

does it Have to be a screw ? (ie removablity required ??) could a rivet do ??

whats on the far side ? free space ?? maybe an anchor nut ? (if you have pace for a nutsert, you've probably got space for an anchor nut.

 

[ewh]

Try PEM for the nutserts.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[port125]

We have specified blind bolts for a situation where we needed to bolt with no access to the nut.

One place to find them is from the Mcmaster catalog.
I beleave the brand name is "hollo-bolt"

http://www.mcmaster.com/#specialty-bolts/=ccyy45

however there are many differnt manufactures and suppliers available.

These are allowed by the AISC for structural applications (13th ed pp. 7-13)including in slip critical and tension applications.

The minimum plate thickness may not be an issue because you would not be relying on a thread for anything.

 

[RacingAZ]

There is free space at the far side. The bolt would actually go into a bent plate (desired instead of welded plates). So I have to balance the plate thickness between the max. plate that can be bent at the same time the min. that can receive a tapped hole.

3/16" to 1/4" are easy to be bent but if it gets to 3/8" thk., not a lot of fabricators can do it, I think.

If I go with inserts then I can simply use 1/4" bent plate. Then the question becomes which option is easier and cheaper to fabricate. A thin plate with threaded insert or a thicker plate with a tapped hole.

 

[Ron]

RacingAZ...the holes for the insert could be punched, so that would save a lot of time and fab effort. Not so for tapping...would need to be drilled and tapped. More expensive in my opinion.