Can I cut these bolts down?

[Mr Punter]

I have some steelwork and most of it will be covered by the ceiling / resilient bar arrangement, apart from a top plate and some bolts.  The bolts project about 30mm and I wondered if I could trim them flush with the nuts to reduce the impact when it is boxed in, or is it a no-no?

 

[JohnMo]

You need to leave about two threads out the end of the nut, other than that fill your boots.

[G and J]

Would it be quicker and more effective to invert them so the spare thread sticks up into the void?   The bolt head may well be smaller than the nut. 
 

Might be an idea to do one at a time mind.  :-0

[JohnMo]

10 minutes ago, G and J said:

Would it be quicker and more effective to invert them so the spare thread sticks up into the void?   The bolt head may well be smaller than the nut. 
 

Might be an idea to do one at a time mind.  :-0

That's not good engineering practice, the thinking is if the nut came off the bolt falls out, bolt from top, nut falls off bolt stays in place. In this case would it matter?

[G and J]

4 minutes ago, JohnMo said:

That's not good engineering practice, the thinking is if the nut came off the bolt falls out, bolt from top, nut falls off bolt stays in place. In this case would it matter?

Good point.  And I guess if you angle grind through the bottom of the nut and the bolt the nut will never fall off.

 

We never rivet anything (apart from pop rivets) nowadays do we. 

[MikeSharp01]

1 hour ago, JohnMo said:

That's not good engineering practice,

You could make it so by double nutting or Castle nutting it. Alternatively, assuming the nuts are not under load would be to use half nuts and then leave the 2 thread clearance. You could probably get down to bolt head thickness that way.

[joe90]

2 hours ago, JohnMo said:

In this case would it matter?

No. 

 

2 hours ago, G and J said:

We never rivet anything (apart from pop rivets) nowadays do we. 

So, belt and braces, cut off leaving a couple of mm and rivet it over, never will it come apart.

[G and J]

10 minutes ago, joe90 said:

No. 

 

So, belt and braces, cut off leaving a couple of mm and rivet it over, never will it come apart.

So hit it hard with a big hammer.  Won’t help, mind, but sometimes it just feels good.   😉

[joe90]

2 hours ago, G and J said:

with a big hammer.

A ball pein hammer and hit the edges to “rivet “ it over (mushroom).

[Conor]

I had this issue on our balcony but our SE said no way to trimming. Had to double batten under the rafters to hide the offending bolts.

[joe90]

29 minutes ago, Conor said:

our SE said no way to trimming.

I would be very interested in why not, surely any stresses are within the bolt and nut but not the excess bolt 🤷‍♂️, any comment @Gus Potter ?

[JohnMo]

1 minute ago, joe90 said:

I would be very interested in why not, surely any stresses are within the bolt and nut but not the excess bolt 🤷‍♂️, any comment @Gus Potter ?

There are zero mechanical advantage to the threads beyond the 2nd thread overhanging the nut. In fact aeronautical engineering would only have 1.5 threads out of the nut.  The strength from bolted assemblies come from the bolt/stud being approx midway in the elastic range. This is why it's important to torque assemble. Bolted assemblies fail more from being under torqued rather than over torqued.

[SteamyTea]

9 hours ago, JohnMo said:

Bolted assemblies fail more from being under torqued rather than over torqued

Is that why the Rover K series engine was so reliable, the head bolts were torqued to yield.

 

"Tighten it till it goes loose, then back half a turn"

 

Why not a blob of weld?

[saveasteading]

10 hours ago, JohnMo said:

fail more from being under torqued rather than over torqued

So correctly torqued sounds like good idea. I was taught ' turn of the nut' on structures. This meant finger tight then half a turn with a normal spanner. Cutting the ends off is to be avoided.

Find a shorter bolt.

 

I was also taught to fit the bolt from below. It means you can easily  see when one is missing.

[joe90]

30 minutes ago, saveasteading said:

turn with a normal spanner.

Yes i was taught this, not a 1/2” socket  and bar on a 7/16th nut!

32 minutes ago, saveasteading said:

Cutting the ends off is to be avoided.

 

32 minutes ago, saveasteading said:

Find a shorter bolt.

What’s the difference 🤷‍♂️

[G and J]

5 minutes ago, joe90 said:

What’s the difference 🤷‍♂️

The cut surface invites corrosion more?

[JohnMo]

30 minutes ago, saveasteading said:

So correctly torqued sounds like good idea. I was taught ' turn of the nut' on structures. This meant finger tight then half a turn with a normal spanner. Cutting the ends off is to be avoided.

Find a shorter bolt.

 

I was also taught to fit the bolt from below. It means you can easily  see when one is missing

I came from a different direction RAF, so aeroplane engineering, where a loose bolt is very bad, a missing bolt could be catastrophic. So was always working with gravity to ensure things stayed where intended. Then oil and gas, where a dropped object could easily injure or worse. So again always inserted from the top, never the bottom. When I started in the oil and gas industry and we experienced multiple bolt failures on reciprocating compressors, analysis of the failure mechanism was bolts fatigue failing. What was happening the bolts were not tightened enough, (difficulty getting bolt tensioning equipment in to the tight location), so the bolt wasn't in the elastic range, where the bolt can stretch and contract indefinitely without fatigue failure. 

[ProDave]

All this talk of what if the nut comes off.  But no mention of nyloc nuts or even loctite?

[joe90]

16 minutes ago, G and J said:

The cut surface invites corrosion more?

https://www.toolstation.com/cold-galvanising-spray-paint-400ml/p60070?store

14 minutes ago, JohnMo said:

aeroplane engineering,

Where lots of wired castellated nuts are used (or were!).

[G and J]

19 minutes ago, JohnMo said:

where a loose bolt is very bad, a missing bolt could be catastrophic

Boeing don’t seem to mind too much nowadays….    😕

 

In reality I wonder how vital the bolt becomes over time.   I wonder if after construction it’s actually just a peg that’s needed.  Hence bolt from the top would be sensible. 

[saveasteading]

34 minutes ago, joe90 said:

What’s the difference

It gets hot.

There should be 3 turns beyond the nut,

Irs probably a tough cut

Corrosion, as above.

It possibly can't be turned off again.

38 minutes ago, joe90 said:

What’s the difference

They come in multiple choices of length for choice and to not waste steel, and to not stick out too far. Buy the right length.

31 minutes ago, JohnMo said:

I came from a different direction RAF,

And planes are pegged together?

Certainly that seems to be how a glider wing is fixed.

 

Here is something i was surveying last week. A steel portal frame. At this joint, if the wind lifts the roof, then the bottom bolts go into tension, and lots of it. With normal downward loading the rafter tries to rotate around the bottom of the haunch and the top bolts go into tension. With no nut it simply doesn't work

Oops. I am on the wrong device....photo to follow..

[joe90]

So @saveasteading do steel frames come with torque settings fir the fixings?

[SteamyTea]

39 minutes ago, joe90 said:

torque settings fir the fixings

There are standard torque settings for bolts, does depend on what grade they are.

A skilled fitter will know the Nm off by heart.

[saveasteading]

39 minutes ago, joe90 said:

torque settings fir the fixings?

In my experience  we were forbidden, by our supplier,  to use a torque wrench. But erectors would turn up with huge tools so that was their norm. 

[Mr Punter]

1 hour ago, G and J said:

Would it be quicker and more effective to invert them so the spare thread sticks up into the void?

 

I thought that but they were fitted with an impact wrench, which I don't have.  I think I would struggle to undo them.  I only have an adjustable spanner that would fit.  It is an M20 bolt.

 

There are some good ideas here but I don't know what will be best.

 

Double nutting, castle nutting, half nut, loctite, do not trim, spray with Galvafroid...

 

I may try using my adjustable to see if I can loosen one of these, then look at my options.