Carriage bolt hole sizing

[blitz97]

Hello all

Anybody famlilar with standard practices for sizing of a square clearance hole in steel plate for a carriage bolt?

for example, a 3/8 carriage bolt has a .388 SQR neck. Should the the punch for this be .030" oversized, similar to a standard bolt clearance hole?

 

[racookpe1978]

Actually, it primarily depends on "why" you're using the carriage bolt. What material you're clamping, and how much force you're needing/using, and other details also matter, but to a lesser degree.

Let's say, for example, I'm clamping pressure-treated 2x4's outdoors with a 3/8" carriage bolt: I can actually put the 3/8 carriage bolt into a 1/2 dia galvanized washer to spread the carriage bolt's head pressure out and avoid pulling the carriage bolt too far into the wood. The square of the carriage bolt grips hard enough into the hole of the oversized galv washer so the bolt doesn't turn, and the oversized washer prevents the bolt from pulling through.

But, if you don't have "soft" wood or are going into metal where the square needs to "bite" firmly into the material, then you need to broach a square hole. Gaps between the square head and the square hole need to be as small as practical to avoid rotation.

 

[dinjin]

Your suggestion makes sense. Even 1/16 oversize should be ok.
I assume you are talking about an oversize square hole.

 

[blitz97]

Yes. In 1/4" steel plate. I have found that the inherent radius found between the square neck and the head of the carriage bolt will allow the bolt to not sit flush when installed in the steel with a tight fitting square hole. So a larger square clearnace hole is needed to account for this.

 

[berkshire]

You also need to take a look at die clearance on the punch. A punch with an oversized die will give you a rolled edge on the punch entry side which may be enough to get your carriage bolt to sit flush.
B.E.

 

[MikeHalloran]

I don't think there's a standard for seating carriage bolts in steel plate, because carriage bolts are made for building carriages. ... of wood.




Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

I think as Mike says, you have to make you own standards, the only advantage you get from using a carriage bolt in a plate like that, is tha you do not have to hold a wrench on the head of the bolt when you tighten it.
B.E.