Cross Over Tube for Pizza Oven

[Don52]

My friend John’s brother Dave owns a bar in Northern Michigan, which is an economically depressed area. He has an industrial pizza oven that was purchased in 1984. Over time the cross over tube has rusted out and the welds holding one of the two brackets have rusted off. The oven manufacturer is still in business, but doesn’t sell the cross over tube as a replacement part. A new double oven similar to this one would cost $26K. Pizza ovens are very hot. The pilot light ignites flames in a cross over tube, which lights four burners.

1. Burner assembly


Before John retired, he owned a Fluid System Engineering company, so he asked one of his former technicians Harry bend up a replacement tube.

2. Old and new tube assemblies


3. Rusted tube


The first step was to make the brackets. I like to scribe shape of the bracket as well as the hole and slot locations. I find that this gives me a second check on locations and dimensions.

4. Scribing bracket


5. Cutting out bracket

[Don52]

6. Sanding edges of bracket


7. Center drilling bracket


For non-critical slots I like to drill a hole in each end of the slot and then plunge the cutter into one hole, make a pass then increase the depth of cut on the other end before returning to the starting hole.

8. Drilling bracket


9. Milling slot


I typically use the power of the mill using the back gear to reduce speed, to tap the holes, because I don’t own a tapping head. For thru holes I use spiral point taps, which push the chips ahead of the tap and through the back side of the hole. For blind holes I use spiral fluted taps which pull the chips out of the hole.

10. Tapping holes

[Don52]

11. Brackets done


I really like to use hog mills to square up stock, because they cut fast and leave a decent finish.

12. Squaring up crimp tool


13. Drilling crimp tool


I chose to bore the hole in the tool for the tube and for the crimp area in the same setup to assure that they would be concentric. I had a 3/8” reamer which I used for the tube bore in the tool. I didn’t have a .340” reamer, so I bored the hole for the crimp portion of the tool.

14. Boring crimp tool


15. Reaming crimp tool

[Don52]

16. Crimp tool 1st op reamed


17. Installing dowel


18. Using center finder


19. Reaming crimping tool


20. Crimp tool done

[Don52]

The swivel fitting on the end of the cross over tube is actually just a standard barb fitting. The tube was crimped loosely to hold the barb fitting in place, but still allowing it to rotate for installation. The barbed fitting has an .040” orifice in the end, which acts as a jet which accelerates the air as it leaves the fitting. This creates a low-pressure area, which in turn creates a vacuum. The cross hole through the tube near the end of the barbed fitting allows air to suck into the tube. This means that gas doesn’t leak out of the small space around the barbs, but instead sucks in air past the barbs.

21. Crimped barb fitting


22. Crimp Mark on old tube


I drilled a larger hole most of the way thru the orifice and just drilled the .040” hole through the last 1/16”.

23. Orifice pieces


I used my arbor press to install the orifice.

24. Orifice press fit


25. Orifice installed

[Don52]

26. Arbor Press with crimping die in place


27. Crimping swivel fitting


28. Fitting crimped


I had to rotate the waist of the Bridgeport to allow the tube to pass the left end of the table.

29. Setup for drilling holes


I installed tight fitting blocks in the Tee slot and then bumped the 1-2-3 blocks against them. (a red arrow points to one of the blocks.)

30. End view of setup

[Don52]

I used a parallel against the back side of the 1-2-3 block to set the position of the tube.

31. Parallel to set tube position


First I center drilled a drill point and then I drilled the 112 holes with a #76 (.020”) drill.

32. Drilling hole


33. Close up of hole


34. Crimping end of tube


35. Tube crimped

[Don52]

I used my Fireball Tool magnets to hold everything in place for welding.

36. Setup for welding


Here is a picture of me welding the brackets.

37. Welding brackets to tube


38. Brackets welded


39. All done


40. John holding the completed cross over tube


John plans on going to the Upper peninsula in two weeks to visit his brother and to install the new cross over tube.

-Don

[Larry4406]

Excellent job!

Great write up and pictures showing the process.

Hard to believe the oven manufacturer does not sell that part.

Free pizza for life?

[Fast Leroy]

Man that is some nice clean work!

Your friends brother will be very happy.

[Munkul]

There's some hours gone into that! Nice work.

Out of interest, how do you know that the crimp around the hose barb is gas tight? I think I would have soldered it personally, although the crimping was more satisfying to see.

[Don52]

Excellent job!
Great write up and pictures showing the process.
Hard to believe the oven manufacturer does not sell that part.
Free pizza for life?

Thanks, I'm sure that John's brother would treat me to a pizza next time I make it up there.

Man that is some nice clean work!
Your friends brother will be very happy.

I like to help out hard working people, who are just trying to support themselves and their family.

There's some hours gone into that! Nice work.

Thanks, it was a stump the chump job. I thought that some of the techniques that we came up with might help someone else.

Out of interest, how do you know that the crimp around the hose barb is gas tight? I think I would have soldered it personally, although the crimping was more satisfying to see.

The swivel fitting is necessary for assembly and disassembly of the cross over tube. John and I wondered about the leakage between the barb fitting and the tube. It turns out that the orifice creates high velocity of the gas, which creates a vacuum, so air is sucked in through the cross hole and from the tiny space between the barbs and the ID of the tube. In other words gas doesn't leak out but air leaks in. (We did test it with compressed air and the orifice does indeed create a vacuum.)

By the way I enjoyed the study that you did back in 2018 comparing short-arc, pulse and spray. I have been playing with spray and dual shield recently. I did take a welding class on spray pulse, but I currently don't own a spray pulse welder.

-Don

[Munkul]

The swivel fitting is necessary for assembly and disassembly of the cross over tube. John and I wondered about the leakage between the barb fitting and the tube. It turns out that the orifice creates high velocity of the gas, which creates a vacuum, so air is sucked in through the cross hole and from the tiny space between the barbs and the ID of the tube. In other words gas doesn't leak out but air leaks in. (We did test it with compressed air and the orifice does indeed create a vacuum.)

By the way I enjoyed the study that you did back in 2018 comparing short-arc, pulse and spray. I have been playing with spray and dual shield recently. I did take a welding class on spray pulse, but I currently don't own a spray pulse welder.

-Don

Nice, that makes perfect sense.

No worries, glad it was helpful Oscar has done some studies on pulse spray as well which is quite interesting as he got slightly different results to me. Since then I've bought a different machine and the penetration and usability of pulse spray is much better, so I use it a lot. It still doesn't replace dip transfer for thin metal or vertical/overhead though.

[walker]

Nice work!

[El Greco]

Great thread, but the best picture is John because he appears to be thinking “holy crap how did Don52 replicate this thing so perfectly”.

[Don52]

Great thread, but the best picture is John because he appears to be thinking “holy crap how did Don52 replicate this thing so perfectly”.

We will find out if it works as soon as John gets up there. I believe that it will work.

-Don