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Thread: How much seam root will I find inside Sch 40 pipe?

  1. #1
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    How much seam root will I find inside Sch 40 pipe?

    I have a project that asks for two lengths of pipe to telescope for length adjustment. I am looking for smaller pipe to slide inside larger pipe without excessive sloppiness. Total adjustments needs to be 2 feet from minimum to maximum, no less than 12" length of small pipe inside the larger pipe.

    Choices are
    A: 2-1/2" inside 3" or
    B: 3" inside 3-1/2".

    Specs for sch 40 pipe of those sizes (from Engineeringtoolbox.com)

    Nominal OD ID
    2-1/2" 2.875 2.47
    3" 3.5 3.07
    3-1/2 4.0 3.55


    A: If I try to slide the 2-1/2" pipe inside 3" pipe the spec shows 0.195 clearance (0.0975 all the way around) which looks like plenty of room, almost a sloppy fit.

    B: If I try to slide the 3" inside 3-1/2" pipe the spec shows 0.050 clearance (0.025 all the way around) which looks almost snug. But what of the root bead from the welded seam during manufacture? Regrettably I do not have much opportunity to view or test fit before making a purchase.


    Any suggestions?

    - Mondo
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  2. #2
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    Re: How much seam root will I find inside Sch 40 pipe?

    I believe you will be unhappy with scd 40 pipe.

    Seamless tubing is what you want. The fit will be predictable and consistent.

    Drawn over mandrel (DOM) tubing is what it will likely be listed as.
    Last edited by MinnesotaDave; 05-21-2021 at 08:08 AM.
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  4. #3
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    Re: How much seam root will I find inside Sch 40 pipe?

    Thank you for the response.
    Yes, I am familiar with DOM tubing. The problem is DOM is not available at my local steel supplier. I would need to get is shipped in from I don't know where and that adds expense. The project does not require that much accuracy, a sloppy fit will work, I am just trying to limit the sloppiness.

    - Mondo
    Member, AWS
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    Craftsman Lathe 12 x 24 c1935
    Atlas MFC Horizontal Mill
    Craftsman Commercial Lathe 12 x 36 c1970
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  5. #4
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    Re: How much seam root will I find inside Sch 40 pipe?

    You can get seamless sched40 pipe. Also most erw sched 40 pipe is skimmed on the inside to remove the seam. It's usually down grade pipe that has the seam remaining. Can't speak for pipe from you know where though, that can be anything.

  6. #5
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    Re: How much seam root will I find inside Sch 40 pipe?

    Thank you! This is good info. I will ask for seamless sch 40 pipe when I call my supplier.

    - Mondo
    Member, AWS
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    Atlas MFC Horizontal Mill
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  7. #6
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    Re: How much seam root will I find inside Sch 40 pipe?

    I would simply build up 3 or 4 areas with weld and grind to fit . If you do that in 2 spots along the length you can get whatever fit you desire. Depending what it's for duct tape wrapped around may also work.

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  9. #7
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    Re: How much seam root will I find inside Sch 40 pipe?

    You can go with oilfiled tubing also. 2 3/8 tubing will fit inside 2 7/8 tubing just fine. Finding any larger than 2 7/8 will be difficult.

    Another trick - grind a groove in the inner pipe to clear the seam on the outer pipe. Has an added benefit of preventing twist in the slip joint.

    I also saw a video where a guy built a seam shear out of a disk & an allthread that would skim the seam out of the pipe (or sq tubing in the video - looked like a pretty simple tool to build.

  10. #8
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    Re: How much seam root will I find inside Sch 40 pipe?

    Quote Originally Posted by Mondo View Post
    Thank you! This is good info. I will ask for seamless sch 40 pipe when I call my supplier.

    - Mondo
    Ask for A106B seamless shed40 pipe.

  11. #9
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    Re: How much seam root will I find inside Sch 40 pipe?

    Quote Originally Posted by M J D View Post
    I would simply build up 3 or 4 areas with weld and grind to fit . If you do that in 2 spots along the length you can get whatever fit you desire. Depending what it's for duct tape wrapped around may also work.
    I like the weld beads idea!

    I am building an adjustable length log hauler to carry logs out of the woodlot. The concept is to build a frame similar to what is used for farm hay wagons. Straight axle at the back, steering axle at the front with a long tongue, connected by telescopic tubing drilled in multiple places for a cross pin to allow setting two or three length adjustments. Never intended for public road use. Not really big loads, maybe six or eight 12" TO 24" diameter logs at a time, 10' to 17 ft. at the longest.

    - Mondo
    Member, AWS
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  12. #10
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    Re: How much seam root will I find inside Sch 40 pipe?

    Depends on the amount of slop you can live with. I doubt you will have seam interference with your selection. But that is a large gap. I, couple weeks ago, used 4inch over 3.5 inch schedule 40 at .029 clearance and had to file seam, not flush. There is a considerable amount of play at that clearance after seam removal.

    Also, check other schedule pipe dimensions. And pipe/tube combo.

    Farmersamm and a couple other have posted on telescoping tube technique

  13. #11
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    Re: How much seam root will I find inside Sch 40 pipe?

    Ridged conduit might work?
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  14. #12
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    Re: How much seam root will I find inside Sch 40 pipe?

    Quote Originally Posted by Fast Leroy View Post
    Ridged conduit might work?
    Yes, anything made for electrical will be smooth on the inside. I never tried fitting one inside the other though so not sure how tight/sloppy fitup would be. There is rigid and there is intermediate, possibly by mixing and matching 2 sizes could be found that would fit together nicely. Alternately if it does not need to be round, 2.5" hitch stock could be used with 2" inside it.
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  15. #13
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    Re: How much seam root will I find inside Sch 40 pipe?

    Now I'm in the right forum I posted this crap in the wrong place.

    If you need a very concise, and fairly close tolerance fit..............................

    Name:  diaphragm1.JPG
Views: 72
Size:  225.8 KB Make a diaphragm that fits your tubing. You can make it as precise as you want. Insert the two pieces in the tubing.......round, or square.

    Name:  diaphragm2.JPG
Views: 72
Size:  222.4 KB I needed a wobble free jackstand to support the trailer in the background. You can do anything if you get creative.

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