Torque Spec for M4 Screw (Sanity Check)...

[Observer]

A torque spec is not something that is really common in my experience on the schematics.  So, off to inquire with customer service of one of the large big game reel manufacturer and they came back with a response.

They provided a range, but the lower number was 168 in*lbs. 

This is the provided torque spec for each of the M4x9 screws used to secure the reel foot to the frame.  I am not a mechanical engineer, nor do I work in an industry that works with this type of hardware, but I do know how to use Google and used it quite extensively after having my eyebrow raising moment, doubletake, re-reading, and re-reading again that I wasn't missing a decimal point or a unit. 

So, for those that are more familiar in this field, mind commenting or sending a PM if desired about your thoughts about this torque spec for this particular use case and application?
   

[Tiddlerbasher]

168 in/lbs is way too high for a 4mm screw even if it was made of unobtainium
I think the quoted figure is missing a decimal point i.e. 16.8 in/lbs or pound inch (more correct).

The torque values will vary dependant upon the materials used.
E.g. 4mm steel into steel (dry) approx. 2 - 3nm (18 - 26 lb-inch).
If lubing the screws (and I hope you do ) reduce the torque by 25%.
Steel or plated brass into aluminium you can half those numbers - different materials (eg stainless, unkown - or stainless 18-8 or 316) is only a tiny difference -BUT screw it into aluminium, whatever you think it should be - halve it

When I demonstrate a torque screwdriver to anyone they are always surprised how far out they are out with their 'guesstimate'.
For reel work I would recommend a torque screwdriver of 0-3nm, a very large Everol may require a 0-5nm (max) maybe

[buzzawak]

I personally have found that when doing up a 4mm screw the elbo click torque wrench is the most accurate tool to use.

[Tiddlerbasher]

This is what I mean by torque screwdriver:



0.5-3 nm, standard 1/4" bit holder.
https://www.amazon.co.uk/LKK-KK-Adjustable-Screwdriver-Precision-Instrument/dp/B092DP9Q4M/ref=sr_1_259?dchild=1&keywords=torque+screwdriver&qid=1623412302&sr=8-259
Chinese maybe but they are good. I have checked their accuracy (% uncertainty) against a calibrated Wiha driver -they were all within + or -2%

When I puchased a range of these, some years ago, I payed way less than the current asking prices (almost half ). Perhaps a case of Covid price hiking


I have noticed that some scope manufacturers now specify torque settings for the scope clamps. In the UK many electrical fixings, like mains consumer units, now also specify torque settings.

[Wompus Cat]

This is what I mean by torque screwdriver:



0.5-3 nm, standard 1/4" bit holder.
https://www.amazon.co.uk/LKK-KK-Adjustable-Screwdriver-Precision-Instrument/dp/B092DP9Q4M/ref=sr_1_259?dchild=1&keywords=torque+screwdriver&qid=1623412302&sr=8-259
Chinese maybe but they are good. I have checked their accuracy (% uncertainty) against a calibrated Wiha driver -they were all within + or -2%

When I puchased a range of these, some years ago, I payed way less than the current asking prices (almost half ). Perhaps a case of Covid price hiking


I have noticed that some scope manufacturers now specify torque settings for the scope clamps. In the UK many electrical fixings, like mains consumer units, now also specify torque settings.

Alas .......the by gone days when ya could tighten a Plow Bolt down till it Squeaked then one Half Turn More.  after you took all the blame Guards off.

[Tiddlerbasher]

  Yup!

[Observer]

To close out the original topic, the OEM got back to me admitting to an error, and gave me a much more nominal spec of 26lb*in or 2.95 Nm torque spec for the M4 stainless steel screw.  Still a schmidge high IMO, but considering it is intended to be screwed into an aluminum frame of the reel, it still seems a bit high per Tiddlerbasher's comments about halving it. 

Thanks for the sanity check.

But on a related but slightly different note, this got me thinking about a couple of things...

1.  The torque driver referenced seems to be a nice tool to have for reel maintenance and maybe some other applications too.  Pricing a similar one in the US is about $55.00 USD sourced from an overseas manufacturer.  The same source offers a torque wrench, in 1/4" format with double the range (up to 6Nm) and same step size as the driver and "better" accuracy which seems to be more versatile and general purpose.  Seems like the advantage for the driver is the smaller/compact form factor and better control since it's inline with the screw being torqued, where as the wrench is acted upon at a 90 degree angle.  So, if versatility is high on my list, it looks like the wrench is "better"?  Am I missing something obvious here where the driver is better?  Ideally, I'd just get both, but I can't do that.  Welcome your thoughts.

2.  As I mostly fish saltwater, everything that this site advocates for managing corrosion with all exposed surfaces make perfect sense.  Hence, I grease just about everything.  So taking a step back and looking at screws/bolts/fasteners/etc in general, where they not in such a harsh environment, should they still be greased?  Thinking about this, I concluded the answer is yes.  In any environment where there is a reasonable chance of seizure or corrosion and regardless if it's load bearing or not, I think it might be best practice to grease.  A bit sad my father never taught me this...  unless I'm completely wrong here?  Welcome your thoughts. 


 

[Tiddlerbasher]

I grease or oil just about everything, lube is good

[boon]

Keep in mind if you're lubricating a thread the manufacturer's specified torque goes completely out the window, because you will get a way higher clamping force (and importantly, fastener stretch) from a lubricated thread torqued to x than a dry thread. Although it may seem counter-intuitive, you have a higher chance of stripping threads or popping the head off the fastener with a lubricated bolt than a dry one.

[Tiddlerbasher]

A further consideration should be the screw head - A torx/hex head screw can take more torque than a slot head, obvious really
There are plenty of charts on the interweb.
The only time I would use a torque 'wrench' would be for bolts or nuts (usually large ones, eg wheel nuts). I think a screwdriver is more appropriate (and usually more accurate) for lighter duties.
I will always advocate at least trying a torque screwdriver - even if it is only used to 'calibrate' your hand. I think most people will be surprised how 'tight' 3nm is (purely as an example)