Gunsmithing Question for machinists and such

[doc76251]

Which thread count is preferred for screwing in a machine screw to standard (soft) Home Depot Aluminum? Are finer threads preferred or are courser threads? I am attaching an aluminum bedding block to a steel .22 LR receiver. There will be no threads in the steel, the steel screw head will be inset into the steel.

I really just need to know which has better holding power in softer metals, coarse or fine?

Cheers,

Doc

 

[chpprguy]

Re: Question for machinists and such

Best IMHO would be to use a helicoil/keensert/etc....

 

[strikeone]

Re: Question for machinists and such

Put a little thread locker(Loc-Tite Blue)on it if you can't heli-coil it

 

[chpprguy]

Re: Question for machinists and such

...

 

[Jered Joplin]

Re: Question for machinists and such

Doc,
Go coarse. I know Doc........If you think he is going to install a helicoil you are mistaken. That would require setting his beer at ease way too long.

 

[border_reiver]

Re: Question for machinists and such

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JJoplin</div><div class="ubbcode-body">Doc,
Go coarse. I know Doc........If you think he is going to install a helicoil you are mistaken. That would require setting his beer at ease way too long. </div></div>

and coarser threads take less time to screw in..a win-win ha

 

[KTDLS7]

Re: Question for machinists and such

Doc,

Great suggestions above to use a heli-coil, especially if the screws are going to be frequently removed.

If no helicoil, then coarse-pitch screws are what you need to use. Coarse threads have a larger threadform relative to screw diameter which is critical in soft materials (i.e. compare a 10-24 to a 10-32). Caution when tapping the aluminum - galling can easily occur. Use a new (not dull) tap with lots of cutting fluid. Use compressed air and fluid to flush the cuttings out of the bore of the cut.

Kevin

 

[Victor N TN]

Re: Question for machinists and such

Doc,

All I can find at the moment is refering to mild steel. The book says to increase the max torque rating for a standard fine thread by 9% over standard course threads. When tapping aluminum remember to use some kind of lubricant like Tap Magic. Kerosene works really well in a pinch. Remember to use anti sieze compound on the bolt threads. (I still favor heli-coil in aluminum if at all possible. But I have a boat load of tools for doing it.)

 

[sirhrmechanic]

Re: Question for machinists and such

Doc: Softer the metal, coarser the thread. Less galling as you cut. Use Red LocTite. Use Kerosene as your tapping lubricant in Aluminum. Cheers, Sirhr

 

[doc76251]

Re: Question for machinists and such

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JJoplin</div><div class="ubbcode-body">Doc,
Go coarse. I know Doc........If you think he is going to install a helicoil you are mistaken. That would require setting his beer at ease way too long. </div></div>

Truer words have yet to be spoken

Thanks for all the input guys I just couldn't remember if it was coarser for softer metals or finer and figured I'd ask. This will be a fun little project I am doing if I can ever get time to get near a mill to pare down a 1" cube of aluminum I haven't gotten my hands on yet. Ahhh delays, delays, delays ......

Cheers,

Doc

 

[jasonixo]

Re: Question for machinists and such

Don't skimp on screw length- Use the longest screws possible- unless you install Heli-Coils... Then the best you can do is install screws that are the depth of the insert.