I have purchased a galvanized metal picnic table frame that i am going to attach treated planks to make an 8 ft. picnic table. The manufacture suggests using carriage bolts but i would rather use a fastener that I can countersink that would give me the same fastening strength as a carriage bolt. Suggestions??

 

Counter-bore the holes for the carriage bolts to allow them to be flush, or slightly recessed from the surface of the planks. If recessed, you could even use a wood filler to fill the counter-bores and make the bolt heads disappear.

You might want to re-think the idea of using treated" planks as the treatment is quite toxic. A good porch and deck enamel (paint) would likely be better.

 

While ACQ is far from a lollipop, it's toxicity is far less than it's predecessor (cupric arsenate). You would probably have to chew on a piece of lumber a while to ingest enough to cause much harm. And since chewing fried chicken is far better at a picnic than ACQ, I think you are safe to use it. Porch enamels are good if you coat all 6 sides of the untreated lumber, since this table will probably be outside all the time.

I agree with counter boring the holes for the carriage bolts. It is a more secure fitment and won't tend to pull out with age as lag bolts would.

 

And in case your not familiar with countersinking, you would use a 5/8" or 3/4" spade bit to make an 1/8" deep recess. Then drill a pilot hole, but not too big or the carriage bolt will spin.

 

Or use a flat head bolt and make an 1/8:" recess with a spade bit as suggested by Xsleeper. They have a square shoulder like a carriage bolt to hold them in place.




Or the more traditional flat head stove bolts.

 

All, appreciate the replies. The carriage bolts will be 3/8". After counter sinking for the bolt head should i drill a pilot hole one size smaller & tap the bolt through to ensure a tight fit

 

Ray, do most hardware stores have "Flat Head bolts"? From the picture that looks like that would be my fastener of choice

 

Some hardware stores may carry them. Here is one link. They are too short but the supplier mat have longer ones. https://www.amazon.com/Stanley-Natio.../dp/B002KFZUJE

Also look here: https://www.google.com/search?as_st=...-1ltRqbHtivGM:

 

Note, can't use regular zinc plated hardware on treated lumber. Has to be rated for ACQ or they will be eaten up in a relatively short time.

Stainless or hot dipped galvanized are the normal go to's, either that or coated screws like DeckMate brand, but I don't know of any coated bolts.

 

The "flat-headed bolts" that Ray mentions are more properly called elevator bolts. They are a bit on the expensive side but here is one company that sells them mail order. https://www.boltdepot.com/Elevator_b...-8_3_8-16.aspx

(I have no connection with Bolt Depot other than as a satisfied multi-time customer.)

 

Holy crapola Furd....$9+ for one bolt? Or a box of 25 for $175? That's kinda crazy, even for stainless. This could be the most expensive pic-a-nic table ever built...lol.

 

New wood is soft and the carriage bolts will pull down into the wood sufficiently that nothing offensive will be sticking up to cause any issues.

 

The new wood will crinkle at the pressure point making it ugly. Counterbore is a neater way to go. You can still pull them down tightly using locking washers below to keep them that way.

 

I would use 2x lumber and fasten with 1.5 inch lag screws installed from the bottom. No exposed bolt heads on top. The bracing incorporated into the metal frame will keep the table rigid.

 

Ken, I tried that once to make it "pretty" on top. Third time we moved the table they all pulled out, and it will get worse as the wood ages, I believe.

 

After an hour on line the best price I have found for a stainless 3/8 x 2 1/2 elevator bolt is $7.06 apiece, and since I need 20 that's going to add up being more then the frame. Can I get away with counter sinking stainless 3/8 x 2 1/2 flat head machine(stove) bolts. Will I get the same "clamping force" as I would with carriage/elevator bolt?

 

Yes, flat head stove bolts should work fine and you may be able to get them at the hardware store.

 

My god, get a bag of hot dipped galvanized carriage bolts for $5, countersink them and be done with it.

 

I have to agree, way too much thought here, every picnic table I have sat at in my life had carriage bolts lets get on to some real issues to solve!