Stainless bolt torque strength?

[Tim Good]

I was fitting a chainplate the other day using M10 stainless bolts. I was going to tighten them down like buggery but thought I might check online for maximum bolt torques.

What I found is that for a A4 70 M10 bolt I don't want to be going more that about 45nm and about 50nm for the same A4 80 version. That working to about 70% breaking load of the bolt.

That doesn't seem very tight to me. I could quite happily crank up 80nm with one hand on my torque wrench.

Anyway should i really be able to only go to 45/50nm in an M10?

 

[vyv_cox]

The yield strength of annealed stainless steel is only about 50% of its UTS. Cold worked grades such as 70 and 80 will certainly improve this but only to around the figures you state. I would have thought that 50 Nm was plenty for a 10 mm bolt.

 

[jonjo]

What are you torqing against?

If there is any GRP sandwiched beware of turning it into GRP crumble.

 

[Graham_Wright]

………and beware of galling! I had to grind off my M20 chain plate bolts because of that. Copperslip is a must!

 

[Neil_Y]

50Nm is fine for an M10, over do it with SS and you risk galling. We suggest less (hand tight with short allen key) but generally bolt into bronze and use an epoxy as thread lock that also lubricates the thread as it's tightened. The quoted figure for a max torque should be around 70% of the elastic limit beyond which the bolt stretches permanently.

 

[Tim Good]

Ok so this was for attaching a hydrovane on the stern. It went onto solid 10-12mm GRP so I'd have thought I was no where near damaging the GRP i was sandwiching against.

Next week I attached a chainplate for a drogue with 6 x 10mm bolts so I'll be sure to find some A4 80's and go to 50nm but no further.

Out of interest is there any major strength difference between bolts and machine screw with the thread the whole way up?

 

[PotatoNavigator]

Never used a torque wrench on the boat, I go til it starts to tighten and then give it a quarter turn, always worked for me.

 

[sailorman]

I was fitting a chainplate the other day using M10 stainless bolts. I was going to tighten them down like buggery but thought I might check online for maximum bolt torques.

What I found is that for a A4 70 M10 bolt I don't want to be going more that about 45nm and about 50nm for the same A4 80 version. That working to about 70% breaking load of the bolt.

That doesn't seem very tight to me. I could quite happily crank up 80nm with one hand on my torque wrench.

Anyway should i really be able to only go to 45/50nm in an M10?

Just use an ring spanner, nip them up allow the sealant to cure then tighten with said spanner. its the backing plate doing the work & no amount of tightening will make the chain plate take more load

 

[AntarcticPilot]

I found out by experience that stainless bolts aren't a good choice for some applications. In common with most, my alternator swivels on a bolt into the casting at one side, and the belt tension is adjusted on a stay at the other side. I inadvertently replaced the swivel bolt with a stainless one (it was all the chandlers had), and a while later was alerted by various alarms going off that the alternator wasn't working - the swivel bolt had sheared. I replaced the bolt - and a little while later, the same happened. A light lit up when I realized that stainless might not be a good choice where there was a strong sideways strain and a rapidly changing load! So I've replaced it with a standard steel bolt, and hopefully all will be well.