Methods to securely attach a 3/16 cast aluminum band to a 6061 brace?

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dansawyer

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Below is a photo of a 'splint' to repair an aluminum casting, the black ring. The ring id is 14.3 inches. The casting is broken just about where the vertical tile line crosses the part. The splint is currently attached on the sides with a 1/4 tapered flat head screw and on top. This is to stablize the part for completing the attachment process.
I would like to add at least more bolts / screws on each side. I am concerned about weakening the casting. In order to make the current screws to fit they will have to be countersunk and a portion of the head ground off.
What alternative methods of attarhment are there?
My thought is more smaller bolts / screws will weaken it less then fewer larger ones would.
(this was the final outcome of an previous project. the 'ears' where desinged with hand coded g-code and machined on a linuxcnc Bridgeport.)
Thanks in advance,
Dan





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What’s the application?

I work on airplanes, so I’m partial to rivets for all things aluminum, but they also make some pretty spiffy structural adhesives today.
 
dansawyer said:
Below is a photo of a 'splint' to repair an aluminum casting, the black ring. The ring id is 14.3 inches. The casting is broken just about where the vertical tile line crosses the part. The splint is currently attached on the sides with a 1/4 tapered flat head screw and on top. This is to stablize the part for completing the attachment process.
I would like to add at least more bolts / screws on each side. I am concerned about weakening the casting. In order to make the current screws to fit they will have to be countersunk and a portion of the head ground off.
What alternative methods of attarhment are there?
My thought is more smaller bolts / screws will weaken it less then fewer larger ones would.
(this was the final outcome of an previous project. the 'ears' where desinged with hand coded g-code and machined on a linuxcnc Bridgeport.)
Thanks in advance,
Dan
Click to expand...

Did you mean 1/4" diameter flat head screw? I don't know what a "1/4 tapered" screw is. Please clarify.

You seem to be asking about two different "attachment" requirements. One seems to be attaching the ring to the splint. Another seems to be attaching the ring to something else.

IMHO, if you provide more information you'll get the best answers.

Is the splint intended to be attached to the ring permanently or temporarily?

You didn't show the entire ring in the photo so I need to ask, is there any reason you can't roll a new ring from rectangular aluminum extrusion?

A higher quantity of small fasteners is not necessarily weaker than a lesser quantity of larger fasteners. Think of rivets used in aircraft construction.

I don't understand what you're needing, so I can't provide better advice yet.
 
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i think he's using flat head machine screws and calling them 1/4" tapered screws

he seems to be wondering if he puts more holes if it will weaken the overall structure

i would concur that riveting would be the way to go
adhesives have come a long way, some are stronger than the metals they can bond
 
Not sure if there is any limitations on the placement of reinforcements but I would try sandwiching the part around the crack with metal sheets or carbon fiber.
 
extropic said:
Did you mean 1/4" diameter flat head screw? I don't know what a "1/4 tapered" screw is. Please clarify.

You seem to be asking about two different "attachment" requirements. One seems to be attaching the ring to the splint. Another seems to be attaching the ring to something else.

IMHO, if you provide more information you'll get the best answers.

Is the splint intended to be attached to the ring permanently or temporarily?

You didn't show the entire ring in the photo so I need to ask, is there any reason you can't roll a new ring from rectangular aluminum extrusion?

A higher quantity of small fasteners is not necessarily weaker than a lesser quantity of larger fasteners. Think of rivets used in aircraft construction.

I don't understand what you're needing, so I can't provide better advice yet.
Click to expand...
Yes, good question. There are two rings, this one and a second that is not damaged, The inside of the rings attach to a telescope. An aluminum bar connects the rings, the bar attaches to each ring. The bar is perpendicular to the rings. The bar itself is attached to the telescope mount. The bar was not damaged when the ring was broken. My plan is the bar will attach to the crosspiece in the picture.
Yes, the splint is designed to be perminent.
I could replace the entire ring with a rolled ring made of steel.
One question is would rivets be appropriate solution?
 
Ulma Doctor said:
i think he's using flat head machine screws and calling them 1/4" tapered screws

he seems to be wondering if he puts more holes if it will weaken the overall structure

i would concur that riveting would be the way to go
adhesives have come a long way, some are stronger than the metals they can bond
Click to expand...
Yes, they are tapered head screws. I have not countersunk the one the picture.
I believe drilling into the ring will weaken it. I am asking if more smaller screws #8, will be more effective than fewer larger ones, 1/4 as an example.
The original ring broke due to torque from mounting. The original moment arm was about 4 inches on the top of the ring. The splint extends that arm to about 9 inches, the end of the ears. The objective to to spread the force across the length of the ears. I am thinking at least 4 connection points per ear would be about right.
 
I still don't have a completely clear picture of the application or what caused the break.

Since it's your intention to attach the splint permanently I recommend using both aluminum rivets and a quality epoxy.

Because you already have a clearance hole for 1/4" fastener, use 1/4" aluminum rivets. I suspect two rivets (widely spaced) on each "ear" with be fine. The rivets are primarily to resist peeling forces and secure the joint while the epoxy cures. Wet the faying surfaces completely and instal the rivets while the epoxy is still wet.

Prepare the faying surfaces and cure according to the epoxy manufacturers recommendations. I would use 3M 2216 (because it does not cure glass hard) but there are other good epoxies.

In the future, to make the circumstances more clear, provide a picture of the WHOLE broken part.
Also show a picture of the part in situ, as it is intended to be used, to provide a context. Close-ups are great for detail, but it's hard to understand "elephant" from a photo showing a square foot of hide.

The common name for the fasteners you pictured is "flat head screw" or "flat head machine screw". The presence of a "taper" (CONE) is assumed.
 
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