Bolt Size

[Capebuild]

I'll use carriage bolts to hold the cabin to the chassis frame. I'm planning on 1/2 inch... but wondering if that diameter bolt is large enough.
Can someone recommend if this is adequate or should the diameter bolt be larger. It's holding the cabin to the chassis ... want to make sure it's got enough holding power.

thank you.

John

[eLink]

You will probably hear a lot of different opinions on this, but I think most people use only 3/8" dia. carriage bolts (or elevator bolts). I used 12 of them along with torque washers.

[QueticoBill]

Nothing wrong with 1/2" but if its holding wood, its many times stronger than the wood. A lot of study and engineering in grad school showed for wood, a 5/16" grade 2 exceeded the strength of the wood it was holding.

[noseoil]

3/8" is more than enough. Carriage or elevator bolts are fine for this application. Here's a chart. I used 3/8" bolts, but a single 1/2" grade 5 bolt would be fine.

[QueticoBill]

The wood being the weak spot, more smaller bolts better than fewer larger bolts.

[Philip]

My rule is never carriage bolts to mount anything. They might be nice you don't need to hold the other side when you tighten. But the trade off is if you ever need to remove said carriage bolts. Once the nuts/bolts get rust on them. They only spin in what ever they bolted down.


I use bolts only. Working most of my life as a maintenance person. I can't tell you how many thousands of carriage bolts I have had to cut off. Laying under something with a torch, cutting off carriage bolts leads into learning new words to call the engineer that made the decision to use them.

[Pmullen503]

Agree on the use of carriage bolts, especially in wood. They are a one time fastener. I would recommend some grade 8 bolts for their superior rust resistance.

[Capebuild]

Thank you all for your comments and help. Grade 8 hex bolts it is. Makes sense about being able to tighten from both ends and they seem to have more tensile strength than carriage bolts.

Thanks again. You learn something every day.

[gudmund]

used to be grade "8"s $$cost$$ so much more than 2's 0r 5's, but now 'not' so much more = why not grade "8"s ...................

[QueticoBill]

The reason I would not use Grade 8 is because it is no better than Grade 2 if used to anchor wood. The wood will fail first. As a life long designer, over design just feels inelegant to me. I just like things strong enough, around a design factor of 5, and inbalance.

[PCO6]

Grade 2 or 5 x 3/8" bolts should be fine. I'd also use a fairly large OD flat washer on the wood side. I've used fender washers of about 1.5" OD on things like this.

[GuitarPhotog]

The all-aluminum body and angle iron frame of my 1948 teardrop are held to the 1-1/2" angle iron frame with eleven 10-24 machine screws and square nuts. One every 12 inches of the 10 foot length. It hasn't moved in 73 years. You are building an airplane not a house.

My $0.02 worth

<Chas>

[PCO6]

The all-aluminum body and angle iron frame of my 1948 teardrop are held to the 1-1/2" angle iron frame with eleven 10-24 machine screws and square nuts. One every 12 inches of the 10 foot length. It hasn't moved in 73 years. You are building an airplane not a house.

My $0.02 worth

<Chas>

LOL! Whatever works! I've built off road race cars and used Velcro to hold some of the aluminum body panels on. They never separated even in a roll over.

In the words of the late Colin Chapman regarding lock washers ... "why would I give them a free ride around the track?". Meaning it's better to keep the weight down in non-critical places.

[Capebuild]

after quite a bit of back and forth thinking about this I'm going to use elevator bolts. at the beginning of this conversation I did not know exactly what elevator bolts were. Since then I've give quite a bit of thought about this (being a big decision). I realized I didn't like the hex bolts sticking up so much the way they do. And I do like the elevator bolts lying somewhat flat against the floor surface. So there we have it.

John

[sagebrush]

I used twelve 1/4-20 self tapping flat head trailer deck screws. Left overs from my trucking days .

Will