Reaching out for machine screw info

[Dan in MI]

I've been scouring the web to no avail.


I have 1/4" thick aluminum. I want to drill and tap the 1/4" edge. What I am looking for is the accepted maximum screw size for that thickness. I can probably get a #10-24 to work, but I think that will leave the walls too thin. 8-32 would be fine for the aluminum but I'd rather the #10. is there a chart or spec for this? What is it called?

 

[Fox Mike]

Google 'drill and tap sizes'. All kinds of charts appear

 

[contender]

One thing to consider is the load requirement of the 2 pieces once they are screwed together. I know there are drill & tap machinist charts,, but none that I'm aware of that show the load limits etc.
If the load you intend to put on it is very light,,, and the 10x24 will work dimension wise,, then use the 10x24. But if you need a bit more load bearing then use the 8x32.
I don't have my machinist handbook handy,, but I always use it to determine what sizes I can use,, AND I always look at the load requirements. The booklet has all the drill & tap sizes for both coarse & fine threads, with the drill sizes & dimensions of what's needed to D&T anything.

 

[Feel the 'Pane]

Are you building a box or ?

 

[WanderLust]

Rule of thumb info from my frequent visits to machine shops when developing machines or parts:
Fine threads hold better than coarse threads, from the sheer contact points.
Longer screws are better than short, for the same reason, BUT... that maxes out with each thread size. Call it 1-1/2" max length,
and then its hard to keep them straight on narrow widths. As Contender noted, a good chart is your friend. Remember that Loc-tite
will give you strength beyond mere thread counts, and NEVER use stainless screws with Alooneyum! :)

 

[Daryl Licht]

Sad part about getting old, I used to know this off the top of my head but had to look it up. #8 screws are .164" diameter, #10 is .190". In the edge of a piece of 1/4" material the wall would be pretty thin.

 

[NikA]

Fine threads are not recommended in aluminum due to the low shear strength allowing the shallow threads to pull out.

Given that concern I think I'd want the wall thickness to be at least equal to the thread height. For 24 TPI that'd be 0.036", so #10-24 would not follow this rule.

 

[roylt]

Like said above you really don't give us the complete picture. Why do you need a bolt in the side of the aluminum?

 

[Dan in MI]

Shortly after I posted I finally found two places with the answer. There is no load in my application but was wondering about durability which prompted the question.

Here is the answer I found. Thanks for the input.

1

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The distance will be a function of the load applied by whatever is secured by that thread.
If the load is effectively negligible, then the positioning can be as close as possible without the cut threads breaking through the wall.
If the load is larger, then sufficient material around the hole must be allowed for, and if the load exceeds the strength of the threads in one hole then multiple holes or a different thread form may be considered.

 

[gunzo]

Two rules of thumb to begin with are:

Coarse threads for aluminum & at least a screw depth of 1x the diameter of the screw. Deeper can add pull strength but there are diminishing returns.
Next, the walls on the tapped part are only a factor & a smaller percentage of the tapped hole.

Then,,, the accuracy of drilling & tapping on centerline. If I could hit "dead nuts" center I might go with a #12 fastener.

Otherwise, without further info, it all seems a bit over thought. OTOH, from an engineering standpoint, when in doubt, add more fasteners with the inclusion of dowel pins.

 

[Dan in MI]

No **** Sherlock!
Looks like something out of a eighth graders science fair project
They should have just said "it depends...."

I agree but it was one of only two answers I could find. The other was primarily for inserts (helicoil, etc...)

Thread pitch, depth, D&T charts are in my bailiwick. I just wondered if there was a genuine spec for wall thickness.

This application is just an adjustable stop for a moving part.

 

[NikA]

If yours is truly a no load application, I would tap it #6-32. Not knowing your setup but suspecting a drill press at best, smaller screw will accommodate more potential misalignment between the hole and the rest of the workpiece.