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Carriage Bolt OR Exterior Wood Screw

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Carriage Bolt OR Exterior Wood Screw

Post  ralitaco on 5/8/2015, 9:22 am

I have a question for all the experienced carpenters, contractors, woodworkers, DIY'ers, etc.



When attaching 2x4 legs to another 2x4 like I did in the picture above, is it better to use carriage bolts as I did or could I have just used screws OR a combination of the 2? Also, what are the benefits / drawbacks of each method.

Thanks
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Re: Carriage Bolt OR Exterior Wood Screw

Post  AtlantaMarie on 5/8/2015, 9:40 am

Personal opinion as a woodworker, you did much better by using the carriage bolts.  That's a LOT of weight once the box is filled.  Screws probly would have torn out eventually (and probly sooner rather than later).


Looks REALLY good, btw!
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Re: Carriage Bolt OR Exterior Wood Screw

Post  boffer on 5/8/2015, 9:58 am

Generally, in house construction:

  • screws and nails are used to keep materials in contact with each other.

  • carriage bolts and lag screws are used to carry weight.

  • the weight of horizontal members should be carried by vertical members when possible
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Re: Carriage Bolt OR Exterior Wood Screw

Post  FRED58 on 5/8/2015, 8:47 pm

@boffer wrote:Generally, in house construction:

  • screws and nails are used to keep materials in contact with each other.

  • carriage bolts and lag screws are used to carry weight.

  • the weight of horizontal members should be carried by vertical members when possible

FWIW, I agree.

Nice job!
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Re: Carriage Bolt OR Exterior Wood Screw

Post  ralitaco on 5/9/2015, 12:46 am

@AtlantaMarie wrote:Personal opinion as a woodworker, you did much better by using the carriage bolts.  That's a LOT of weight once the box is filled.  Screws probly would have torn out eventually (and probly sooner rather than later).
Hmmm...I may need to put some carriage bolts on my other TT because I just screwed in the 2x2's every 6"

@AtlantaMarie wrote:Looks REALLY good, btw!
@FRED58 wrote:Nice job!
Thank you very much.


@boffer wrote:Generally, in house construction:
screws and nails are used to keep materials in contact with each other.
That makes sense. Since the top 2 2x4's are not carrying weight, I guess screws would've sufficed there, right? Although, I think I like the look with the carriage bolts

@boffer wrote:...carriage bolts and lag screws are used to carry weight.
This makes sense too since they are much thicker than the screws AND they go all the way through both pieces of wood.

@boffer wrote:...the weight of horizontal members should be carried by vertical members when possible
I think I did that by adding the 20" pieces on the back of the legs under the horizontal sides



@FRED58 wrote:FWIW, I agree.
Its worth a lot to me, thank you.
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Re: Carriage Bolt OR Exterior Wood Screw

Post  AtlantaMarie on 5/9/2015, 8:37 am

I think it looks just fine, Ralitaco.

Are those wire shelving units you're using in there for the bottoms?
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Re: Carriage Bolt OR Exterior Wood Screw

Post  ralitaco on 5/9/2015, 9:36 am

@AtlantaMarie wrote:I think it looks just fine, Ralitaco.
Thank you. I think it looks fine too. I was working on another and was thinking about cheaping out on the hardware mainly because I didn't have enough carriage bolts on hand. But now that I understand that the carriage bolts are used to help carry the weight I will just get some more. 

@AtlantaMarie wrote:Are those wire shelving units you're using in there for the bottoms?
And yes those are wire shelves. I got a bunch of them for free so I decided to give them a go instead of the hardware cloth. they are not galvanized but I think they will last at least as long as plywood, if not longer, before they rust. And how could I pass up on FREE.

btw, I like your new avatar
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Re: Carriage Bolt OR Exterior Wood Screw

Post  boffer on 5/9/2015, 11:38 am

Ralitaco, you're putting a lot of thought into your design, so here's another perspective that may or may not be helpful.

Your design has good mechanical strength ie. the weight is being carried by the structure itself.  Imagine it this way: if the only  force on your TT was gravity pushing straight down at a 90° angle, your TT would support itself without any fasteners.  

But in the real world, there are forces on the TT from all directions,  such as wind, somebody leaning against it, not being perfectly level, etc.   The 20" legs transfer the weight of the box to the ground.  The tall legs aren't carrying any weight; they are strengthening the joint where the top of the 20" legs contact the box.  That joint is susceptible to any force that isn't perpendicular; that's where any wiggle (and failure) would occur.  

You could've strengthened the  joint with gussets or bracing, but your design is probably the cleanest looking.  I too would have used carriage bolts on the tall legs where you did, not because they are carrying weight, but because in the long term,  screws might loosen due to  seasonal changes causing the wood to expand and contract, and from continually resisting the back and forth wiggling.

You've built a very solid and good looking TT.  
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Re: Carriage Bolt OR Exterior Wood Screw

Post  sanderson on 5/9/2015, 11:50 am

+1

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Re: Carriage Bolt OR Exterior Wood Screw

Post  ralitaco on 5/9/2015, 12:21 pm

@boffer wrote:Ralitaco, you're putting a lot of thought into your design, so here's another perspective that may or may not be helpful.
Probably too much  Smile

@boffer wrote:Your design has good mechanical strength ie. the weight is being carried by the structure itself.  Imagine it this way: if the only  force on your TT was gravity pushing straight down at a 90° angle, your TT would support itself without any fasteners.
Got it...makes sense

@boffer wrote:But in the real world, there are forces on the TT from all directions,  such as wind, somebody leaning against it, not being perfectly level, etc.   The 20" legs transfer the weight of the box to the ground.  The tall legs aren't carrying any weight; they are strengthening the joint where the top of the 20" legs contact the box.  That joint is susceptible to any force that isn't perpendicular; that's where any wiggle (and failure) would occur.
I had to read this a couple of times to understand but now I got it. I was struggling to grasp that the 32" legs were not carrying the weight because in my head they were the legs and the 20" pieces were the supports, but in actuality it is the reverse. (insert AHA moment here)
Since the weight is on the 20" pieces and the 32" pieces are supporting the 20"piece, would I have been better off using 1 or 2 carriage bolts to join those 2 pieces instead of just screws?

@boffer wrote:You could've strengthened the  joint with gussets or bracing,
where would you have put the bracing...just on the short side or also on the long side too? I had considered running a band around the inside of the legs to make it sturdier but after I attached the legs, I was pleasantly surprised at how sturdy it was. I may go back and add that band later

@boffer wrote:but your design is probably the cleanest looking.
That was one of my main objectives

@boffer wrote:I too would have used carriage bolts on the tall legs where you did, not because they are carrying weight, but because in the long term,  screws might loosen due to  seasonal changes causing the wood to expand and contract, and from continually resisting the back and forth wiggling.
Really I did it because that was what I saw done on many other boxes in particular Sanderson's

@boffer wrote:You've built a very solid and good looking TT.  
Thank you very much
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Re: Carriage Bolt OR Exterior Wood Screw

Post  boffer on 5/9/2015, 2:49 pm

@ralitaco wrote:Since the weight is on the 20" pieces and the 32" pieces are supporting the 20"piece, would I have been better off using 1 or 2 carriage bolts to join those 2 pieces instead of just screws?
 6 o' one, half dozen o' the other.  Basically, the long leg is holding the short leg in place.  Another option is to glue the legs together, along with the screws.

@ralitaco wrote:where would you have put the bracing...just on the short side or also on the long side too? I had considered running a band around the inside of the legs to make it sturdier but after I attached the legs, I was pleasantly surprised at how sturdy it was. I may go back and add that band later
That type of joint needs bracing in both directions.  

I have no doubt that your box would support a car.  But if you want to add a band, use it to make shelf.

I'll mention this because it's come up in other threads: When making TTs for seniors, make doubly sure that it won't slide or tip over if they were to fall against it.  

I can't imagine your TT's tipping over, but might be worth double checking once it's in place and filled with MM.
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Re: Carriage Bolt OR Exterior Wood Screw

Post  ralitaco on 5/10/2015, 11:32 am

@boffer wrote:Another option is to glue the legs together, along with the screws.
I was going to do that but did not for 2 reasons...1. I didn't have any glue at the moment and 2. I thought I might want to change out the 32" piece for a taller one for a trellis. In the end, I think I will go back and put in 2 bolts to make sure the pieces stay together.

@boffer wrote:That type of joint needs bracing in both directions...
But if you want to add a band, use it to make shelf.
good to know. The band would suffice for the bracing correct?

@boffer wrote:I'll mention this because it's come up in other threads: When making TTs for seniors, make doubly sure that it won't slide or tip over if they were to fall against it.  

I can't imagine your TT's tipping over, but might be worth double checking once it's in place and filled with MM.
Did that last night when I set them up but thank you very much for mentioning that.
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Re: Carriage Bolt OR Exterior Wood Screw

Post  AtlantaMarie on 5/11/2015, 7:00 pm

@ralitaco wrote:
@AtlantaMarie wrote:I think it looks just fine, Ralitaco.
Thank you. I think it looks fine too. I was working on another and was thinking about cheaping out on the hardware mainly because I didn't have enough carriage bolts on hand. But now that I understand that the carriage bolts are used to help carry the weight I will just get some more. 

@AtlantaMarie wrote:Are those wire shelving units you're using in there for the bottoms?
And yes those are wire shelves. I got a bunch of them for free so I decided to give them a go instead of the hardware cloth. they are not galvanized but I think they will last at least as long as plywood, if not longer, before they rust. And how could I pass up on FREE.

btw, I like your new avatar

Free....  NICE!  That's awesome!

You're right in not to go cheap on hardware.  That leads to uh-oh moments pretty quickly.  Build for the long-haul.

And thank you.  I like to change it out every month or so to keep people amused.  Razz
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Re: Carriage Bolt OR Exterior Wood Screw

Post  plantoid on 5/12/2015, 2:42 pm

I myself would take out the screws and replace them with coach bolts , once the thread has been well coated in silicone grease  .
When the bolt head pokes through add a big galvanized penny washer and fit a Nylock type nylon insert nut .

The washer is to spread the load evenly over the softer wood . the Nylocl nut is to replace a spring washer that will be the first thing to rust through and also cause the bolt thread to rust .
 
That way you know the bolts wont pull through easily , if the legs get lose there is a fair chance of tighten up the greased threaded nylock nut 
 
Use as big a coach bolt diameter as you can get away with , don't do a thin skinny cheapie for  they often snap in half or strip threads  under a bit of load /stress.
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Re: Carriage Bolt OR Exterior Wood Screw

Post  ralitaco on 5/12/2015, 10:28 pm

Thanks Plantoid,
I have carriage bolts in place currently. I think they are the skinny cheapies, but they are better than screws.

I just finished setting up my first 2x8 and if adding carriage bolts to the bed sides doesn't sturdy up the legs, I will need to add some bracing or most likely a band around the bottom.

I will keep you updated.
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Re: Carriage Bolt OR Exterior Wood Screw

Post  petee_c on 6/7/2016, 2:39 pm

carriage bolts or regular through bolts with washers on both ends to attach the table to the legs due to weight of the table when full.  Screws do not have a lot of shear strength.

As an aside,  endgrain doesn't have a lot of holding power....  the screws that attach the short sides of the table to the long sides are going through end grain.  There is a risk of the ends popping off over time.....

Peter  (pretend woodworker)
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