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  1. #1

    Need fabrication advice please

    I'm working on a project right now that I have a few questions on and hopefully someone with more fabrication skills than me(new to welding and fabrication!) can share some ideas.

    I need to build a part that can swivel but also take some weight. Attachment 677
    I know the picture is small but I'm not the best with computers! You can click on it to see full size.

    The round pipe is the connecting point. It will need to swivel on a piece of round stock. Right now my plan is to have the pipe about 4" long, Then on the frame(not shown, this piece is attaching to the frame) I will weld a 2" piece of pipe above and below the 4" piece and run a piece of 8" solid stock threw all the pipes to hold them together. Hopefully this makes sense!

    The pressure is going to be forcing the bracket up from the frame. I don't believe it's going to be alot of pressure but still need to have a strong connection at the swivel. Should I be using a plastic bushing of some kind in the pipe so the bracket swivels easier? Any kind of advice on the best way to fab this up would be greatly appreciated!

    Thanks, Scott

  2. #2
    Contributing Member MXtras's Avatar
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    Re: Need fabrication advice please

    I think your design is sound - based on what you describe anyway. Plastic bushings would help it swing easier but I guess there are a lot of questions to really determine the requirement.

    Some issues with what you are going to do: Keeping the pipe straight and true when welding can be a challenge. Here is exactly what I would do.

    Fit everything up - cut, de-burr, smooth and clean. I would position everything together with thin washers between the parts to allow a slight gap between the parts - possibly for either Nylon or bronze washer(s) later, so have a plan on the final wear/glide washers and make room for them and add a little clearance. Fit everything together and clamp it together (through the pivot) so it is a solid column for welding - less chance for things to move around this way. Tack it all around, then weld it into place. Pull it all apart, check for spatter or any internal deformation, clean everything up and do the final assembly with whatever lubrication you deem fit.

    Scott
    If it wasn't for the last minute I wouldn't get anything done

  3. #3

    Re: Need fabrication advice please

    Thanks for the help Mxtras. This is actually for a spring compressor. I saw one online that was really nice but came with a huge price tag so I'm going to try and come close to what they have on a much lower budget! I'm thinking of using a 3/4" pin to hold the parts together and swivel on. Can I just use round stock or should I get a nice smooth/polished rod to go in there? Is there a place to see what size pipe and rod combo to use to get a good fit and still swivel? Also you mention assembling with lube, I'm pretty new to the fabrication world so is there a lube you would recomend for this? Thanks again for the advice. I'm sure I'll have some more questions about fine tuning my ideas for this project.

    Here is a video of the compressor if your interested, video even has some eye candy using the machine! http://www.youtube.com/watch?v=0Mt1UBTp0zk
    Last edited by ponch37300; 08-21-2009 at 12:16 PM.

  4. #4
    Contributing Member MXtras's Avatar
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    Re: Need fabrication advice please

    Round stock would work but it's typically not all that round. Don't hesitate to look at using the unthreaded shank of a large bolt - just an option - maybe not for a 8" long pin but perhaps you could use 4" long pieces from each side rather than a continuous pin.

    Clearance - .002" is about the limit to what I would consider 'precise', but that tight in unfinished, unmachined bores (pipe) is not likey to work - especially since the round stock won't be round with .010"-.015". If you are dealing with pipe and round stock, you are likely going to have a kind of sloppy fit. Schedule 40, 3/4" pipe and a 3/4" pin makes around 0.074" of clearance - pretty sloppy.

    For a precise fit, I would machine the pivot parts. This not being an option for you, I assume, I suggest getting a 12" piece of 3/4", schedule 80 pipe from www.mcmaster.com (part #7972K115) for $12.68 which has an ID of 0.742". You could then use a small flapper wheel on a die grinder and open the hole up a little to fit your 3/4" round stock and you could end up with an acceptable fit. Might not be an option for you, though if you don't have a die grinder.

    Here's a chart of the ID of pipe - maybe you could find a different size that would fit together well with readily availble round stock:
    http://www.wiremasters.com/SubFolder...re%20chart.htm

    Also - dig around Mcmaster. You might run across something that strikes a different approach.

    With some digging and planning, you can likely get a fairly good fit. McMaster has precision shafting, dowel pins and all kinds of stuff like that and they sell in short lengths. Do some digging and let us know what you end up with.

    Scott
    If it wasn't for the last minute I wouldn't get anything done

  5. #5

    Re: Need fabrication advice please

    Thanks Scott. I have been on mcmaster alot lately trying to find some of the parts I need. Sometimes it's hard to find what your looking for when you don't exactly know what it is your looking for or what it's called! The pin doesn't have to be 3/4" either, that is just the size I picked without knowing the tolerences so it could be something else. I will search some more on mcmaster and see what I can come up with for pins. Thanks again for your help.

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