Q: making aluminum angles

I have a few pairs of short rectangular strips of aluminum I wish to
make angle brackets out of.
I will fab as necessary to accomodate two (2) flat head screws for
each pair.
For better precision, is it wise to include dowel pins, or just leave
as is with the flat head screws which self-align the 2 parts ?
I used to follow another machinists idea, in that they used
counterbored socket heads along with dowel pins. It was a bunch of
holes, though! Would countersunk flat head screws suffice for best
precision?
It's a simple job, just want to hear thoughts on this.
thank you.
Marcel
Reply to
dragonbreed
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There are two usual reasons for using pins; one is two locate a part precisely, the other is to keep the part from shifting once it's been installed. The flat heads, by virtue of their conical heads, will do a fair job of preventing your bracket shifting. Pins will locate the bracket much more precisely. Using both pins and flatheads together should be avoided if possible.
Reply to
Ned Simmons
Won't the pins and flatheads fight with one another, unless the pins are installed first, and then the screwholes drilled et al?
Or, use pins with Filister headed screws in counterbored pockets, so the pins define the location and the screws hold things together.
Joe Gwinn
Reply to
Joseph Gwinn
I just made an angle ( 90deg) with 1/2" Aluminum 3" wide and use 3 10-32 FH screws worked fine. I did all the holes on a mill and used a very close fit for the clearance part of the csk. hole. Of course the accuracy of the angle is going to be determined by the accuracy of the machining of the edges.:-) ...lew...
Reply to
Lew Hartswick
[Assumption: the OP is not a well-equipped tool and die maker]
The pins will win, and you can use pan head screws. The real fight is between misaligned flatheads, where the first one tightened wins. Dowel pins may not work if you drill this on a misaligned drill press and the holes are slanted.
The quick & dirty way is to clamp the assembly in position and then drill and tap each hole sequentially. My own even dirtier method is to drill the outer piece slightly smaller than clearance and then tap both, so a pan head screw becomes an interference fit when tightened. That also helps start the tap straight. I only do this when the shop doesn't have good equipment.
How much "precision" do you really need? The heads and threads of commercial flathead screws aren't necessarily concentric. You could try "Shoulder screws" but still the threads may not be exactly centered so you might need to ream a through hole and fasten them with nuts and washers.
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Jim Wilkins
Reply to
Jim Wilkins
...
This is exactly the point. Any answer here is meaningless without knowing what your requirements are. Your answer need not be specific, as in so many thousandths - just knowing what you're doing with these brackets would suffice.
Bob
Reply to
Bob Engelhardt
I'm using a manual mill. The strips in question are 3/8" in thickness. Precision is the key here, since a set of these brackets will ultimately be used as sleeve bearing housings for a reciprocating shaft. I'm going to go forth and do what I've been doing all along, and use dowel pins. Thanks for all responses. Marcel
Reply to
MarcelG
That's what I was getting at when I said to avoid pins and flatheads together.
Yes, though I'm partial to socket heads.
Reply to
Ned Simmons
Hi Ned. Why partial to socket heads, and what alternatives would you suggest ? Thanks. Marcel
Reply to
MarcelG
Because that's the way we've always done it.
Socket head caps screws are made to well defined dimensional standards from high strength materials.
The heads are relatively small.
They can be set in counterbored holes only slightly larger than the heads, i.e., no wrench clearance required in the c'bore.
A full set of Bondhus wrenches for #2 to 1/2" SHCS costs about $15, and every industrial mechanic carries a set in the back pocket of their jeans.
They're relatively inexpensive, at least in small sizes, and available everywhere.
As far as alternatives go, if you need to make the mating parts separately, and you can get them positioned properly in this manner, your decision to use dowel pins is probably the way to go. If you can (or need to) tweak the orientation of your bearings at assembly, you might consider drilling and pinning at assembly with taper pins or roll pins. Taper pins will be more secure and repeatable, especially if you may need to disassemble and reassemble your device. Roll pins are cheaper and easier.
Reply to
Ned Simmons

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