M2 grub screw durable enough? Material?

[TJW1991UK]

Hi, I am new here.
I am a beginner musical instrument designer with an interest in innovative hardware for the guitar. I look forward to using this forum to learn about many topics.
Today I am here for very simple stuff really. I hope this is in the right place, I couldn't seem to find a subtopic for such a simple question!

I am drafting a part to have prototyped and am unsure of something. One person has warned me away from using something as small as M2 here, but I am limited on real estate and will have to redesign a significant amount of the product to go bigger, and am quite trapped in the design.

This is the part:

The small grub screws either side of the string that are used to raise the height of the block the string sits on.
M3, occasionally M2.5 is the industry standard.

Is M2 durable enough to be serviceable? What should I use for the grub screw and the block it goes into? Stainless steel?
Both threads and heads need to be durable. They don't have to last for ever, but they are used to adjust the height of a string pushing down with around 20lbs of tension.

Any advice is hugely welcome!
Thank you

 

[drawoh]

TJW1991UK,

I hate set (grub) screws for most applications. This one may be okay. Try to find oval point screws, so that they don't dig a hole in your guitar. Beware of stainless steel. For screws, this material usually is soft. You want hardened alloy steel, and you want some sort of hardened panel for them to push on.

I don't know anything about people who tune guitars. Is there any chance they use torque drivers?


--
JHG

 

[TJW1991UK]

Thanks!
I should specify, these are adjusted often regularly by the end user. It is the norm for them to be adjusting m2.5 or m3 hex screws with supplied allen keys. It is not incredibly unusual for somebody to maybe strip one on an old guitar being clumsy. I just want to make sure m2 aren't terribly worse.
I'll definitely note that down about hardened alloy steel. They do indeed push against a metal baseplate as pictured in the similar example photo (which isn't mine by the way).

 

[Tmoose]

" somebody to maybe strip one"

Does the internal hex get rounded out, or do the threads of the screw or block "strip ?

 

[TJW1991UK]

Typically it would be the hex getting rounded, but I'm also concerned about threads being smaller on the m2 if they happen to be fragile. I haven't heard of actual threads being stripped before in this situation

 

[racookpe1978]

If the internal hex "holes" are being regularly stripped out when used by a "mechanically qualified musician" (or a musical mechanic as the case may be) I'd would be even more leery of trying a smaller hex screw. Smaller = less wall material to be hit by the improper sized hex head driver = more likely to fail faster.

So go larger. 3 mm or even 4. Advertise "Tougher, more resilient hardware!" "Guitar hardware so tough even a trombone player can adjust it." And provide TWO hex head wrenches when you sell it.

 

[Tmoose]

Most any time I damaged a set screw's internal hex it was due to a worn or wrong size hex head (Allen) wrench.

The ASTM F912 mechnical specs for internal hex socket head set screws are ALL about the socket wall strength.
6. Mechanical Properties

​

6.1 Socket set screws when subjected to a torque test in accordance with 11.2 shall withstand application of the test

​

tightening torque specified in Table 2 without evidence of the socket reaming or the screw bursting.

​

6.2 Socket set screws shall have a hardness of 45 to 53 HRC. The hardness limits shall apply throughout the screw from core to surface.

 

[BrianE22]

I'd supply a tee handle wrench to use instead of the standard L shaped. The T handle keeps bending to a minimum.

 

[drawoh]

BrianE22,

How about a hex key with a straight, knurled handle, to reduce torque? You don't need and you don't want the leverage of a T-handle.

--
JHG