Door Problem!! Major Warping

[rob g]

We fired up the smoker for the first time today to season it. The door warped like a banana! The door is approximately 34" wide x 29" high x 1.5" deep. The main panel is 1/4" mild steel with the left and right edges broke up 90 degree. The top and bottom fill pieces are 1/4" x 1-1/2" with the bracing being 1/4" x 1-1/4". The door is insulated with a 16ga skin welded around the perimeter. Shortly after firing up the smoker the door started to warp about 2" (even with a large clamp on it). When the door cooled it came almost back to flat. The main panel wasn't 100% flat, but pretty close, when it was first welded. After cooling we welded some 2x2x1/4t angle on the inside of the door and it still warped when heated again. We are going to pull the skin off to see what the braces look like inside. Any ideas on what is going wrong? Is the interior bracing undersized or laid out wrong?

[rob g]

Another pic

[dacolson]

That’s an aggressive warp Rob. Given the inner bracing you added I’m really surprised. I probably would have done an X brace instead of the horizontal ones on the inside. All that bracing at 1/4” on the interior I would have thought should be more than adequate by themselves though. Not sure what the answer is here but I’m interested in hearing some ideas.

[rob g]

One issue might be the braces were only stitched into place. He's going to lay in some channel. In a few spots, add more weld to the existing braces and see what happens

[Kcd2016]

This seems like a stupid question before I ask it but how big was the fire? The rest of your fb is insulated, right? What about the door panel? It wouldn't think it would need much fire... either way that's a lot of warping, I'm surprised the added angle didn't fix it. That channel ought to do the trick! *Crosses fingers*

[rob g]

I'm not sure how big the fire was. They had the main chamber up to 200F in about 30 min. The initial fire was positioned closer to the door than the tank. The firebox and door are both insulated. The door seems to come back to straight (or as straight as it started) when it cools. I'm thinking not having full welds on the braces might be part of the issue. He is adding more weld to the existing braces then he is adding a couple pieces of C4 channel, notched over the braces, and everything welded solid. I'm thinking my initial bracing design is also part of the problem. It probably did more to prevent twisting than the bowing we are seeing.

I've got a request from another friend with a tank for a smoker design. I'll be able to make the changes to this one easily to suit the next one.

[Kcd2016]

If it's not too late I'd think I'd notch the braces rather than the C4 channel.

[rob g]

If it's not too late I'd think I'd notch the braces rather than the C4 channel.

You might be right but I think it is probably too late. If the C4 is welded around the braces it should maintain most of its integrity. If we cut the braces then the piece under the channel isn't going to do much as it can't be welded.

[Big T]

It's hard to tell from the pictures but it doesn't look like the original X-brace was fully welded where it crossed itself in the center. If it isn't, that would allow it to open up when it gets hot and cause the corner of the door to pull away from the FB. I don't think that the X-brace has to be fully welded down each side but the stitches need to be a little closer together.

[rob g]

It's hard to tell from the pictures but it doesn't look like the original X-brace was fully welded where it crossed itself in the center. If it isn't, that would allow it to open up when it gets hot and cause the corner of the door to pull away from the FB. I don't think that the X-brace has to be fully welded down each side but the stitches need to be a little closer together.

I'm sure that's probably part of the problem. By the time we get more weld added and more reinforcement pieces added we aren't going to have to worry about the door wanting to bounce off the hinges as it goes down the road lol

[Dirtytires]

My guess is you introduced some stress at some point in the fabrication....your door has a lot of pieces to it. Also, if the door is not insulated than the thinner outer skin would heat differently than the inner wall and could be pulling it.

My door is insulated and is made from 2 single pieces of 0.25 plate for the inner and outer wall. I put a simple 'X' out of 0.25x1 flat bar thru the middle and it has not moved a bit in the last 5 years since I build it.

[SheffSmoker]

Wow, the amount it moves when heated but then returns when cooled makes me think it's acting like a bimetallic strip!

It is all the same carbon content steel isn't it? That's the only thing I can come up with.

[rob g]

Update:
Cole added 3 pieces of C4 channel across the width of the door. He notched out the existing flat bar braces so the flange of the channel could get full welds against the main plate. A relatively small fire has got the cook chamber about 275F. When we put a straight edge across the door it is within 1/8" ( at temp). Not perfect but pretty good. The face of the firebox has a bit of bow in opposite to the door. The door can be pulled close with the center clamp even at temperature. It looks like he has to cut the hinges off and re-position them to help fix the situation where the firebox and door are fighting each other. Possibly a 1/4" gasket vs the 1/8" we have now. A few more tweaks should make us happy.

Future consideration for next time:
- Make sure the main door panel is 100% flat before welding. We don't think it was.
- More welds on the bracing. They were probably insufficient to start with this time.
- More bracing across the width. I think the initial bracing did more to minimize twist than bow.
- Add some small gussets to keep the front firebox panel from moving.
- I like the mentioned method of 1/4" inner and outer skin. With plug welds to the interior bracing this would be really solid. Our door was 1/4" material with 1-1/2" breaks on either side, 1/4 × 1-1/4" bracing and a 16ga outer skin.

So far we are happy with most of the build. The cook chamber door seems to seal fairly well after a few adjustments to the flanges.

[dacolson]

The nice thing about a door is that you can replace it later if it’s too troublesome. Doors are a pain in general. You’ve got a great build. Hope you put it to use soon.


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[towtruck]

Nice build.

My 2 cents on the door issue.....you have too many parts to it that all expand at different rates. I would start over and build a door like some of the others have suggested they built.