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Will a plug weld be strong enough?


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Pictured is a railing I'm finishing  up. I have plug welded the post to the base because it looks better to me. I'm a little worried that it might not be strong enough. The post is 1x1 with a 3/4" hole drilled in the mounting plate for the weld. This project has been all about the details and I don't want the look of a fillet weld. Am I asking for trouble?

 

Thanks for your thoughts-

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That looks good! Welding if done well is very strong, the contrary is true as well. A plug weld on that should be quite adequate, I would be more concerned at the thickness or lack thereof on the base plate, I'm presuming it's not corten or hardox.

 

Ian

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Greetings FE,

 

I can not see where the next vertical post is but by the looks of the rail that part is not under the same stress as the riser.  I don't think you will have any problems with your plug weld .   What I have done in the past is to create a short 3/4 tenon and taper the ends for the weld.   I just drilled a 3/4 hole and file it square.  Then filet weld the edges..  It is the same but with a little more surface area for the weld..  Good luck

 

Forge on and make beautiful things

Jim

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Ian,

Base plate is A36 and 1/4" thick with 3/8" mounting holes. Its going on a 3" thick slab walkway. 

Jim,

This rail is short with only the one post. It mounts to the wall on the other end. I like your suggestion on making a square hole. I think I will do that next time.

 

Thanks guys! 

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If you are looking for maximum strength from a hidden weld and bevel it out or employ a deep penetration welding technique so that the weld is through the whole profile, there is a risk of a blowout of molten metal on the front surface. The way around this would be to notch a piece of plate so that it can be placed against the topside of the rail and base plate while you weld on the other side, it will control molten metal by drawing heat away and setting it before it it comes right through.

first pass, weld half, reposition the plate weld the other half, crank the heat up for the second pass, stand back and look smug :)

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Keep in mind that standard welding rod is 60-70 kpsi, and the base metal is 36 kpsi. Even a gorilla on steroids could not pull a 1/4" plug weld apart if you make a halfway decent full fusion weld. Countersinking the hole so that you have a beveled edge bowl rather than a straight sided shaft to weld in helps guarantee fusion at the root.

 

Time honored tradition: make a sample in scrap metal. When the weld cools, put it in a sturdy vise and smack it repeatedly with a 3 pound hammer in the direction of greatest stress. If the base metal gives before the weld, you can sleep well at night.

 

Personally, I would worry more about sideways stress pulling the anchors up or distorting the thin base plate, I would want thicker plate, steps or buttresses at the base to distribute the load.

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You make a good point John. How thick of plate would you go? 3/8 or 1/2? Its going on a 3 to 4" thick concrete walkway. I'm planning on 3/8" ab's that go all the way through to wedge at the bottom of the slab. Really, I would like to use epoxy but its to cold out and I'm afriad it won't set properly.

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Really, I would like to use epoxy but its to cold out and I'm afriad it won't set properly.

 

 

 

I've used Hilti epoxies to set structural rebar and column anchors in temps well below freezing. ( I want to say when we were doing this the highs were in the mid to high teens in Feb. ) I can't remember which epoxy we used right now, but the data I have on my desk for the typical HIT-HY-70 we use to set bolts in block and so on is rated down to 23deg F ( gel time 10 min, full cure 6 hours according to the spec sheet.) The spec sheet for HIT-HY 150MAX-SD shows material temps to 14 deg F. ( gel time 180 min, full cure 12 hours according to the spec sheet.)They have a bunch of other adhesives as well. From what I recall, we simply told our Hilti rep what we needed to do and he pulled up the data and made the recommendation along with all the supporting data for us to send the the engineer for approval.

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When I do a plate to post connection hidden weld on an architectural piece this is what I do.   Forge a tennon onto the end of the newell post, upset the shoulder to get another visual detail with the swelling of the post bottom, drill the plate for the tennon size, countersink the heck out of the underside of the hole stick the tennon thru and weld, grind off flush. 

 

I agree with John McP, 1/2" thick would be wicked strong, 3/8 probably ok. 

 

As for epoxy, you are in Cali, right?  How cold can it be?  They do work down in low temps, just expect a slower cure time to full strength.  There are also wedge anchor systems like what Red Head sells that would be sufficient for a railing.  Some hydraulic grout under the base plate wouldn't be amiss.  

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Greetings again FE,

 

What I have done many times in the past is to coat the plate underside with clear silicone to combat any rust transfer to the concrete ..  It will happen it always does..   Sounds like you have it going your way..

 

Forge on and make beautiful things

Jim

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  • 2 weeks later...

nice looking railings.
many good comments in here. another approach, altho it might be too late now, is to extend the vertical piece thru the base plate and thru the slab. you could mortar or epoxy it into a drilled hole in the concrete. that way the 1" bar and slab take any stress from a fatty leaning on the railing, and the baseplate is basically for looks. You can tack on fake bolt heads to throw them off the track.

i like the no fillet weld look, but does that gap hold water and rust faster? do you plan to fill it with paint or epoxy?

Mike

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First; It looks great! Very appealing. Secondly; using a plug weld in this fashion has been used time and time again. Long as your weld has complete fusion into both members of the base material, you'll have nothing to worry about. Plus, typical hand railing is not meant to be "structural" meaning it is not intended for consistent service at or above 200 PSI.

 

-Hillbilly 

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Depends on how you welded it.

Did you use a 110 mig or 1/8" 7018 on 125 amps?

 

1/4" baseplates are plenty strong enough especialy considering that;

A. It is not the only thing holding the rail.

B. Your plates are plenty wide making them harder to bend.

 

The reason the integrity of the plug weld is so important is the lever effect caused by the length of the post.

Therefore the proper test is recreate the piece with the post the same length, the aply 140 pounds of force at the end of the post, while restraining the plate in a vice.

 

As mentioned, always countersink for plugwelds when possible.

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Well, I went and cut the plate off and welded on a section that will imbed in the sidewalk. I thought that not only would it be stronger, it would look better... Before I cut the plate off I tested one of them. I put the plate in a vice and pushed on the rod. Actually, I did this as part of my decision to cut the plates off. Anyway after about a dozen back and forth flexes the plate started to work away from the post. Meaning, I was tearing the weld out of the plate. Figuring this is a railing for an elderly couple, to be placed on a set of steps that ice up in the winter it needed to very strong and able to hold a person with a slip and fall momentum. Post imbedded in concrete with epoxy should do the trick. I'll take pictures of the install as soon as it is warm enough to install it...

 

 

Thanks for all the suggestions! and reasons why....

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The weather FINALLY cooperated and I was able to install these railings!

As promised, a couple pictures of the final product. I used Hilti Epoxy. Pink Bubble gum I think they call it..... Set up solid with temps in the low 20's

Home owner is very happy!!!!

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post-6253-0-22021500-1387517240_thumb.jp

post-6253-0-27895200-1387517271_thumb.jp

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Railing looks really sharp. I see you even epoxied the wall mounts as well. Am I looking at false rivet on the plates on the wall, or screws? if they are false, that sort of explains the epoxy. If bolts, I'm guessing you used the extra to help seal out water and get a good fit to the wall. Nice little "extra" that many wouldn't have bothered with.  I also see you mounded it up a bit around the post. I see a lot of guys that core and use anchoring cement or epoxy leave the anchor area low for whatever reason. Then it tends to collect water and rot the posts.

 

I've never seen that pink Hilti stuff before. All the stuff I've used was sort of beige/grey, but then they do have quite a few different types available. In fact I was working outside in the mid 30's with epoxy this morning. Pushed the job back from yesterday to today because the temps are supposed to just go up from now until Sunday here.

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Thanks DSW!

I used all-thread to mount to the wall and bolts. Holes had epoxy as well as the fillet. I hate seeing when people leave a valley for water to sit in. Ya, I didn't even think to check the color of the epoxy. I assumed gray and that was all I could get locally. Pink of all colors Shheesh! I'll be painting it in the spring....

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Looks like the right decision, no trip hazard and much cleaner at ground level. some nice lines and proportions.

 

I have to admit, I like the look of the two rails superimposed in the first photo, could almost pass for 30's deco, might have to sketch something for the scrapbook as a reminder.

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