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Thread: Dims Tolerances and the 3 bears, looking for rules of thumb with my project Gin Pole

  1. #1
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    Dims Tolerances and the 3 bears, looking for rules of thumb with my project Gin Pole

    Just like the story of Goldilocks and the 3 bears, I while I am not so shapely skinny (more roundish) and with very hairy legs. I am looking for what is just right. I plan to have my parts cut by a water jetter and know they hold tolerances quite well, but what about for fabricated assemblies? Everything was going quite well when 3 things caught my attention. But first here is the project at hand: https://weldingweb.com/vbb/showthread.ph...ns-appreciated

    Ok, back to our fairy tale:
    First was the fact that i specified 7/8" hole in the shackle brackets I got from an eBay seller, he sent what he had on the shelf which had a .900 hole. This caused me to purchase a bridge reamer.
    Second the specs from Warn winch specified .44 to .46 bore for the 7/16" mounting bolts .
    Thirdly I was also going to have the water jetter cut out some plate for the compressor bracket and for the rear motor mount for a Cummins 5.9 with a Bendix 550 air compressor and SAE 2 Flywheel housing adapter. I had a compressor bracket for a single cylinder compressor and the holes are 14.5-14.75 bore for a 12 mm bolt. The flywheel housing takes 12 mm bolt also but have no mount to compare hole size. I did find a blue print from Cummins Marine so I have the dims of the housing for the rear mount, but how big do I spec the bore. Of note here Cummins do break the gearcase housing that the compressor bolts to more than rarely and the flywheel housings regularly have to be helicoiled so I think the facotry specs might be a little on the large side to compensate for the myriad manufacturers casting the blocks and making the accessory parts.

    This also lead me to wonder about three thing that I should address before I finish the dims to send to the water jetter:
    how close to tolerances should I spread the horizontal pieces of the gin pole where the mast head bolts on to the 2" rectangular tube for easy assembly and reassembly while not compromising strength 1/16" clearance or more

    Should I spec larger bore holes for the the bolts in the horizontal same masthead to boom pole attachment.

    On the mounting bracket for the compressor should i stay with the 14.5-14.75 bore holes are make it a little tighter? What oversize do you recommend for the rear engine mounts.

    I'm just looking for a comfy bed without the scary surprise awakening! LOL!

    Thanks in Advance!
    Last edited by gentrysgarage; 05-22-2019 at 03:01 PM.

  2. #2
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    Re: Dims Tolerances and the 3 bears, looking for rules of thumb with my project Gin P

    So why did you need a reamer for the shackle brackets if they are already bigger than the shackle pins?
    Lincolin Power Wave 450, Lincoln Powermig 255, Lincoln Pro Mig 140, Lincoln Squarewave Tig 275, Miller Big 40 G(with Hobart Hefty suitcase), Thermal Arc 95S and Esab PCM875 in an already full machine shop.

  3. #3
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    Re: Dims Tolerances and the 3 bears, looking for rules of thumb with my project Gin P

    Quote Originally Posted by propanehotrod View Post
    So why did you need a reamer for the shackle brackets if they are already bigger than the shackle pins?
    I did not know what I should hold my tolerances to, but I like to jig things up. I no longer work at a machine shop, but if I did I would have cut a piece of round stock down to .900 to register the 2 shackles that are the on each side of the lower boom pivot. I choose the lesser cost and got a deal on a reamer off of eBay. But I don't know how much "sloop" I could get away with. I used to follow the blueprint given and really don't know how much to put or how tight I need. Thanks for any insight you can give me!

  4. #4
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    Re: Dims Tolerances and the 3 bears, looking for rules of thumb with my project Gin P

    Tolerance is one of those things that can make all the difference. Too tight or too loose will both cause problems and make your build more difficult. In the machine shop general practice is 1-2 fractional drill sizes over for all bolt holes. That translates to 1/64-1/32" In the Fab shop its generally 1/16" over and structural steel erection is often 1/8" over. It helps to keep in mind what it is you are working on. Bolting a winch to a flat plate requires no real precision. I would say Warn's specs are fine. When you are dealing with pins and shackles and such a little extra slop is your friend. Its much easier to assemble and work with. Machine components like your compressor bracket often have tighter tolerances but keep in mind its the clamping force of the bolt that does the work not the not the snugness of the bolt in the hole. 1.75mm seems pretty sloppy though. Id think 1mm over would be fine.
    One last thing. Around here many oilfield winch trucks were built with a torch and a welder. A really nice build might have involved a drill press. Super precision is not necessary for the majority of a winch truck and will make the build harder.
    Lincolin Power Wave 450, Lincoln Powermig 255, Lincoln Pro Mig 140, Lincoln Squarewave Tig 275, Miller Big 40 G(with Hobart Hefty suitcase), Thermal Arc 95S and Esab PCM875 in an already full machine shop.

  5. #5
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    Re: Dims Tolerances and the 3 bears, looking for rules of thumb with my project Gin P

    Quote Originally Posted by propanehotrod View Post
    Tolerance is one of those things that can make all the difference. Too tight or too loose will both cause problems and make your build more difficult. In the machine shop general practice is 1-2 fractional drill sizes over for all bolt holes. That translates to 1/64-1/32" In the Fab shop its generally 1/16" over and structural steel erection is often 1/8" over. It helps to keep in mind what it is you are working on. Bolting a winch to a flat plate requires no real precision. I would say Warn's specs are fine. When you are dealing with pins and shackles and such a little extra slop is your friend. Its much easier to assemble and work with. Machine components like your compressor bracket often have tighter tolerances but keep in mind its the clamping force of the bolt that does the work not the not the snugness of the bolt in the hole. 1.75mm seems pretty sloppy though. Id think 1mm over would be fine.
    One last thing. Around here many oilfield winch trucks were built with a torch and a welder. A really nice build might have involved a drill press. Super precision is not necessary for the majority of a winch truck and will make the build harder.
    EXACTLY what I was looking for Thanks PropaneHotRod!

  6. #6
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    Re: Dims Tolerances and the 3 bears, looking for rules of thumb with my project Gin P

    Im an inspector for a military defense contractor. Our MIL prints are generally .03 for any measurments out two decimal places and .010 for any out too 3.
    --Gol'

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