Sunken Bolt Alternatives 1

[Helepolis]

Hi all,

I'm designing a product that is build out of CREUSABRO 4800: Hardness HB 370, Elasticity Modulus 205 GPa, UTS 1200 Mpa, YS 900 Mpa.

On some of the parts i want some of the heads of the bolts to be sunken below the surface, like a sunken bolt, but without actually using one as the manufacturing of the countersink is quite expensive and i want to keep the costs to a minimum

Was wondering what other solutions are there for using regular Hex Bolts or Cap-Head Bolts so that their head will be sunken bellow the surface (inserts or specialized bolts), so all i'll have to do is to drill a straight hole.

Thanks.

 

[JNieman]

Counterbore.

Also, you don't have to use two different drilling operations to make a hole, whether counterbored or countersunk. You can get a drill made that will do it all in one operation. Think of it like a center drill but with the drilling length suitable to whatever you're drilling, and the taper at 82 or 90 degrees to suit the hardware.

This keeps it to a single operation.

 

[Helepolis]

It's a good suggestion but the company that manufactures the CREUSABRO parts for me charges extra for the counter-sink, the holes for the bolts are made during the plasma cutting of the parts.

 

[Jboggs]

Can you picture a fastener that attaches thru a plain cylindrical hole without protruding above the surface? I can't. If you can, please post an image. Seems to me your only other option is to weld it. You could send the bolts thru from the other side but then your holes would have to be tapped.

 

[IFRs]

Dimple the hole and use a pan-head bolt?
Thread the hole and use a stud?
Weld a stud on?

 

[Helepolis]

@Jboggs unfortunately i cant right now, i asked because the more i work on different projects i discover more and more ingenious ways for solving problems like this one, so i was hoping this time wont be an exception and i'll find something with your help .

 

[JNieman]

Unless you want to use some kind of wedge-anchor or split pin, you're SOL. A headed fastener needs a surface to bear upon. You must consider non-headed fasteners if you can only use plasma-cut holes. However, depending on the thickness of the material, the plasma cut surface may be disappointing if considering expanding shank fasteners. Maybe studs with a chemical adhesive or something. The alternative solutions would depend upon the requirements, which I know nothing of, right now.

I'd be curious what else might pop up from others, though.

Personally, I'd accept the countersink/counterboring of holes because it's simple necessary for fastening. Common alternatives can be even more expensive.

 

[Helepolis]

I'll try to explain as much as i can of what im trying to do.

Basically the product is for the military, should protect electronics from shrapnel and explosion blast so the material is 8mm thick, that means i have enough surface area for some kind of insert that will act as a nut for the bolt.

I have two moving surfaces that are in a very close proximity to each other, if i use a bolt and a nut on one of those surfaces either the head of the bolt or the nut will interfere with the movement of the other surface, so im looking for a possible solution on how to eliminate this problem by hiding the bolt head (sunken bolt) or the nut (insert of some kind).

I've worked previously with brass inserts with knurled surface but for polymer applications, and not sure what type of inserts to use when it comes to steel alloys.

In the worst case scenario i'll go for the countersunk bolts, but this is a chance to find another elegant/simple solution for this problem.

 

[BUGGAR]

First, what military?

 

[Helepolis]

I don't see how it matters , but it's not for active duty it'll be used in training, that's why it's CREUSABRO steel and not ballistic steel.

 

[BrianE22]

If there is enough taper in the plasma cut holes maybe you can hammer in a split tapered piece so that is below the surface. The top of that is the seat for your bolt. Probably not possible especially for just 8 mm.

 

[KENAT]

So you really want threaded inserts?

Penn Engineering 'Pem Nuts' and the like may be a solution depending on various factors including material hardness, hole tolerances...

http://www.pemnet.com/fastening-products/pem-self-clinching-fasteners-new/

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[JNieman]

I decided against suggesting threaded inserts because if countersinking is too expensive, tapping that type of steel certainly will be! I figured that they also wouldn't want to pay for the hole preparation / precision required of Pemserts either. But I could see /some/ situations where it might be better. Rare and exceptional ones, imo, but some.

 

[3DDave]

Countersink is the cheapest method. If it weren't no one would use it. They would do something else.

Military use means no through-hole fasteners, which is probably the reason for the question. A projectile hitting a through fastener will turn the rest of the fastener into shrapnel on the other side of the armor.

Seems like a design change is required to eliminate the need.

 

[Helepolis]

@3DDave, I'm aware of that but there are strict guidelines on how to operate this devise. The blast will be from a kinetic impact only (no explosives), and never from a direct impact with the device itself otherwise it's outside of the device's operating parameters, so the main concern are shrapnel.
Furthermore, all of the faces facing directly at the impact are without any openings.

But maybe you are right and there are no apparent less costly solutions, and a design change is the way to solve it.

Non the less, I've learned something new from KENAT.

Thank you guys for your help, but if anyone has more idias i will appreciate it.

 

[berkshire]

From the parameters you have given , it looks like you choices are down to what kind of stud welded pin shall I use.
B.E.

You are judged not by what you know, but by what you can do.

 

[hendersdc]

This kind of thing is an option but would require the hole be tapped. I would think the cost of tapping and the high cost of the insert itself would add up to more than just countersinking the hole though.
[URL unfurl="true"]http://www.invert-a-bolt.com/1-2-fastener.php[/url]

 

[BUGGAR]

And why they welded APC's instead of riveting. Forget this if RPG's are in your product future.