Nut and Bolt Peoples - Question

[eldirector]

Looking for advice! Need to know what type of bit for my drill press to get for these fasteners. I'm drilling through a piece of 3/16 plate steel. Want the head to sit flush. I figure I need to drill the through-hole to size (5/16, in this case), and then another bit for the "flare"?

https://www.fastenal.com/products/details/1124256

 

[MilliJac]

You are looking for a countersink bit. Make sure you take note of the angle of that flat socket cap screw so it matches up.

 

[GLOCKMAN23C]

You are looking for a countersink bit. Make sure you take note of the angle of that flat socket cap screw so it matches up.

Utterback Supply should he able to help you out.

 

[MilliJac]

Also, I'm just a 3D CAD designer so no first hand knowledge or engineering degree, but I'm not sure that 3/16 mat. thickness is quite thick enough for that size of FSCS.

 

[MilliJac]

Utterback Supply should he able to help you out.

We use McMaster-Carr for this sort of thing at work, for what little in house fabricating we actually do. Crazy fast delivery, but I never see the shipping costs so it might not be feasible for him.

 

[Woobie]

You are looking for a countersink bit. Make sure you take note of the angle of that flat socket cap screw so it matches up.

Here's your answer. Drill bits won't give you the right angle, you'll need the appropriate countersink. I can't remember which one though.

 

[eldirector]

Also, I'm just a 3D CAD designer so no first hand knowledge or engineering degree, but I'm not sure that 3/16 mat. thickness is quite thick enough for that size of FSCS.

View attachment 50134

Yeah. I'm still digging around. I may need to step down to 1/4" thread to make this work. I definitely want the largest fastener size I can use. I suppose I can add a couple more closer together to make up for it.

Thanks for the quick replies! Getting me on the right path, at least.

 

[MilliJac]

Yeah. I'm still digging around. I may need to step down to 1/4" thread to make this work. I definitely want the largest fastener size I can use. I suppose I can add a couple more closer together to make up for it.

Thanks for the quick replies! Getting me on the right path, at least.

Do you mind if I ask what you are using these for? There could be an easier solution that just needs a fresh pair of eyes.

 

[Vamptepes]

If it was me drilling it I would use a centering bit so the bit doesn't walk. Then a drill bit for the main threaded portion. Followed up by a countersink bit to get it flush.

 

[olhorseman]

The through hole diameter will depend on how close the location of the hole must be. If you are simply holding two pieces together with a nut the following should work.
90 degree spot drill to .330/.360 diameter
Drill thru with 21/64 drill (.328 diameter) - can go to 11/32 drill (.343 diameter but spot drill to higher diameter)
Countersink with 82 degree tool to .656 diameter - tool @ https://www.fastenal.com/products/details/3355082?term=82+degree+countersink

 

[olhorseman]

Also, I'm just a 3D CAD designer so no first hand knowledge or engineering degree, but I'm not sure that 3/16 mat. thickness is quite thick enough for that size of FSCS.

View attachment 50134

The countersink to a .656 diameter will be the full depth of the material (.189 deep). When it comes to size, type, and number of fasteners it depends on the application, components, and what forces are going to be acting on the assembly.

 

[bigelowe]

Probably 82° counter sink is what you are looking for. More than likely you will make the original hole size bigger trying to go deep enough with the countersink to make the head flush with your metal plate. We use MSC supply for some tooling lkke this.

 

[eldirector]

Do you mind if I ask what you are using these for? There could be an easier solution that just needs a fresh pair of eyes.

Building a set of "rock sliders" for my Jeep CJ-7. Had a piece of 3/16 sheet 50" long and 6.5" tall bent with a 1.25" lip at the bottom. I'm fabing a set of rails that will be welded to the lower portion as a step and "rock guard". Rails are 2x2 3/16 square tube. The whole assembly will be bolted to the side of the body using the above bolts. I want something that will sit flush. Neat and clean.

Pic of the mock-up for reference:

 

[olhorseman]

1/4-20 flat socket cap screws to ASTM F835 should be plenty strong enough for your application. (each cap screw could suspend about 2 tons before breaking). I would use 4 or 5 on each side for safety factors.

 

[Rookie]

I used 1/4 inch steel rivets on mine. They took plenty of abuse and sat almost completely flush. Can't help with your original question, but I figured I'd offer an alternative.

 

[MilliJac]

1/4-20 flat socket cap screws to ASTM F835 should be plenty strong enough for your application. (each cap screw could suspend about 2 tons before breaking). I would use 4 or 5 on each side for safety factors.

Maybe I misunderstood his intentions, but if the fasteners were going horizontally into the frame and he is stepping on the tube, that would be a shear or bending load rather than a tensile load.

Again, not an engineer. I just do most of their work so they can put their stamp on it. They do the maths.

 

[Rookie]

They'll be going horizontally into the body which will be the weak point. The body will give before the bolts.

 

[MilliJac]

They'll be going horizontally into the body which will be the weak point. The body will give before the bolts.

Going into the body panels, not the frame itself?

 

[Rookie]

Correct.

 

[MilliJac]

Correct.

Oh, yeah, fasteners won't be the weak point then. I personally wouldn't step on the tube, but I suppose if you are using your Jeep as God intended you wouldn't be too worried about it.