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Mast screws. How tight?

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Turbaani
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Mast screws. How tight?

Postby Turbaani » Tue Jul 14, 2020 11:55 pm

How tight can one screw the 4 bolts that hold a mast?

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Re: Mast screws. How tight?

Postby Trent hink » Wed Jul 15, 2020 12:22 am

In my experience just snug is plenty. No need to crank them down.

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Re: Mast screws. How tight?

Postby Peter_Frank » Wed Jul 15, 2020 7:28 am

4?

I have never seen that, usually it is 1 or 2 or 3 max, in each end.

Assume you are talking about 2 in each end.
An alu or carbon foil?

If carbon, where there is brass inserts, you should not over tighten, a risk of destroying the thread.

You don't gain tightening screws hard in alu masts either, so as said, snug/firm is just fine :thumb:

Most importantly, wiggle the mast in place, don't tighten it in place.

8) Peter

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Re: Mast screws. How tight?

Postby Onda » Wed Jul 15, 2020 9:05 am

Best way is to look up the recommended torque for your thread diameter and material.
E.g. an M6 stainless steel screw should be fastened with ca. 8 Nm of torque.
Best way is to use a torque wrench as it is very easy to over-tighten such a small thread.
Otherwise, you should only use your thumb and three fingers close to the vertical part of a standard hex key and tighten the screw with the force of these three fingers. That will be enough.

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Re: Mast screws. How tight?

Postby Turbaani » Wed Jul 15, 2020 9:13 am

Peter_Frank wrote:
Wed Jul 15, 2020 7:28 am
4?

I have never seen that, usually it is 1 or 2 or 3 max, in each end.

Assume you are talking about 2 in each end.
An alu or carbon foil?

If carbon, where there is brass inserts, you should not over tighten, a risk of destroying the thread.

You don't gain tightening screws hard in alu masts either, so as said, snug/firm is just fine :thumb:

Most importantly, wiggle the mast in place, don't tighten it in place.

8) Peter
Alu foil, the attachment between mast plate and board. Bolt on other side and T-nut on other. Thanks for your opinion!

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Re: Mast screws. How tight?

Postby Turbaani » Wed Jul 15, 2020 9:15 am

Onda wrote:
Wed Jul 15, 2020 9:05 am
Best way is to look up the recommended torque for your thread diameter and material.
E.g. an M6 stainless steel screw should be fastened with ca. 8 Nm of torque.
Best way is to use a torque wrench as it is very easy to over-tighten such a small thread.
Otherwise, you should only use your thumb and three fingers close to the vertical part of a standard hex key and tighten the screw with the force of these three fingers. That will be enough.
8nm sounds reaaaallly low! Good to know. Need to be way more careful. I will try to get a torque wrench, thanks

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Re: Mast screws. How tight?

Postby Turbaani » Wed Jul 15, 2020 9:16 am

Trent hink wrote:
Wed Jul 15, 2020 12:22 am
In my experience just snug is plenty. No need to crank them down.
:thumb:

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Re: Mast screws. How tight?

Postby Peter_Frank » Wed Jul 15, 2020 9:38 am

Oh, you meant the baseplate to board connections, that is a complete different story.

These T nuts can easily be damaged if too tight, but you also want a firm connection.

No need for TefGel here.

Good thing is, if you ruin the thread, the 3 remaining will hold just fine, and you can go riding.
And get a new T nut maybe screw, later.
Not nearly as critical as the mast connection threads.

8) Peter

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Re: Mast screws. How tight?

Postby TheJoe » Wed Jul 15, 2020 11:01 am

Turbaani wrote:
Wed Jul 15, 2020 9:16 am
Trent hink wrote:
Wed Jul 15, 2020 12:22 am
In my experience just snug is plenty. No need to crank them down.
:thumb:
FML ! My snug has all ways been too tight. I'm fight a broke off bolt in my Moses Fuselage with a broke off easy out in it as well. I actually might have to go to a torque wrench.

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Re: Mast screws. How tight?

Postby Peter_Frank » Wed Jul 15, 2020 1:54 pm

I am not in doubt at all, how much to tighten my bolts, as I work with these issues for a living also, different material combinations.

But to share in numbers, just checked, I tighten 6 mm screws in brass around 2 to 3, max 4 Nm.
And the baseplate T nuts never more than 3 Nm, just checked now.

8 Nm is way too much, even for an 8 mm screw in brass T-nuts.
You could do it this hard, if long screws in an aluminium mast yes, but I see no reason to do this, except if they come loose too fast.
Some T-nuts are stainless steel, stronger, but in my experience it is better to tighten for the often used brass ones, as it is more than sufficient, and then you dont have to remember if you got one or another in your board, safer in the long run.


Back to our often used brass T nuts in the board slots, or carbon foils with brass inserts like in my case.

The brass is the soft thing here, that goes bobcus (horrible wrong soon) if tightened too hard, thread is ruined and screw just goes around without force now.
Especially the short flat T nuts for the baseplate, they can not take much.

Getting a torque wrench is overkill, way too expensive and you dont need it, once you got an idea of how much we are talking about here.

I use torque wrenches in my work yes, but there is a lot better way to find out "how much do you tighten" your screws.

Took a picture right now, use an angled Unbrako/Hex/Allen key, and a fishing scale.
Put your hand on the side of the tool to support, and pull the fishing scale till the screw either tightens further, or loosens again - even better, do it both ways so you get an idea.

Image


Now, having the force and the distance, you can calculate the torque:

Torque in Nm = Force in newton * Distance in meter.

In my example it could be I measure 2.1 kg on the fishing scale, and my Distance is 135 mm.

10 Newton is roughly 1 Kg or 2.25 pounds (so you can use your own fishing scale or luggage weight and convert).

Meaning I measure 2.1 * 10 = 21 Newton, and the distance is 0.135 meter.

This gives me a torque of 21 * 0.135 = 2.8 Nm.

You dont need to have a foil with Allenkey screws, you can just go and find ANY other screw in your house or shed, where you can use an Allenkey, as everyone got these.
Because you just have to measure a few times, and then feel with your hand, how tight it is, to know what range we are talking about


Hope this can help those who dont work with bolts or materials and numbers, to know how much they really tighten a screw/bolt :rollgrin:

We can discusss how much we find it good to tighten, we might not agree, but important for many to get a number of how much do THEY tighten, way too much or okay?
Most often not too little is my experience...

8) Peter
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