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  1. #1
    Join Date
    Jun 2009
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    Cootamundra
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    73

    Default Marking out hollow bar

    I've got a 300 mm lenght of 80mm hollow bar that I want to make a jig out of. I need to drill and tap it to hold 4 bolts. They will be located at 0, 90, 180 and 270. What's the best way to accurately measure bolt locations around the circumference?

  2. #2
    Join Date
    Jun 2010
    Location
    Melbourne
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    40

    Default

    Do you have an indexing or dividing head to use?

  3. #3
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    Jun 2009
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    Cootamundra
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    Default

    Quote Originally Posted by aussiejoeblow View Post
    Do you have an indexing or dividing head to use?
    I wish. Got a lathe and small mill but no indexing or dividing head.

  4. #4
    Join Date
    Jun 2008
    Location
    Victoria, Australia
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    74
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    5,080

    Default

    Hi Bidgee,

    Depending on how accurate you need it, you could just make a temporary dividing plate out of cardboard or something else, make the diameter as large as possible.

    You can draw a right angle with compass and ruler. Measure the diagonals to cross-check it's square.

    Regards
    Ray

  5. #5
    Join Date
    Apr 2009
    Location
    Horsham
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    92

    Default

    Hi Bidgee,

    If you can hold the bar in the lathe, maybe between centers, you should be able to use the gear on the back of the spindle as an indexer. Mine is 40 tooth, so I have a pointer that slots into the teeth to loosely lock the spindle then I use a HSS tool to scribe a mark, remove the pointer, count the required number of teeth 10 in this case and lock then repeat the process. Sometimes I will scribe the circumference as well and center punch at the intersecting lines. Just remember not to run the spindle with the pointer in place, I usually unplug the lathe when doing this.

    I hope this makes sense

    Regards,

    Jayson

  6. #6
    Join Date
    Aug 2008
    Location
    Adelaide
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    68
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    1,373

    Default

    If you have a 4-jaw chuck and it will hold the bar then you can easily mark out your 90 degree marks. Place something on the ways closest to you such that you can back the outer end of one chuck jaw onto it. Mark out your first point using a HSS tool in the tool-post.

    Then rotate the chuck so the next jaw is sitting on the same object on the ways, mark out the 2nd point, repeat for all 4 jaws and you should be done.

  7. #7
    Join Date
    Nov 2007
    Location
    melbourne australia
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    3,228

    Default

    Dunno how accurate this is, but I've used it before. Cut a 50mm wide strip of paper from an A4 sheet. Wrap it around the pipe and mark where the paper overlaps. Lay paper strip on a flat surface and divide the distance between the mark and the end of the strip by the required number of divisions. Re-wrap the strip around the pipe and tape in place. Mark or centre punch the pipe at the marks on the paper strip.

  8. #8
    Join Date
    Jan 2011
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    Far West Wimmera
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    63
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    Default

    I'd go with Gavins idea first, ensuring the edge of the jaws are not damaged of course, then Jaysons if it wont work. I admit I thought of jaysons idea myself then decided the next one was easier. Good luck. I would suggest making a drilling guide from a piece of the pipe as well. his can be clamped on while drilling. Fit an end stop to get exact distance from the end of the work. Ideally use hardened silver steel insert in guide. I can say this because I just got a supply from US. I haven't used it yet.

    Dean

  9. #9
    Join Date
    Jun 2009
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    Cootamundra
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    Default

    Thanks for all the good ideas.

  10. #10
    Join Date
    Sep 2008
    Location
    texas, queensland
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    i think this would work lets see if i can explain it .
    all that is needed is a square or a bit of angle with the measurement of the radius marked on each leg of the square out from the corner ( 80mm pipe would be a mark on each of the 2 legs at 40mm ) sit the pipe in the square transfer both marks then rotate pipe quarter of a turn line up one of your marks on the pipe with the mark on the other leg of the square and you can mark one more and so on . hope that makes sense it sdoes to me anyway .

    johno
    'If the enemy is in range, so are you.'

  11. #11
    Join Date
    Oct 2008
    Location
    blackburn vic
    Posts
    297

    Default

    Someone posted a good idea a while ago.
    Get yourself a degree plate from an engineering supply (or a motorbike shop)
    Make an adaptor to fit the left hand end of your lathe spindle and mount the degree plate on it
    make a pointer for the degree plate
    Mount your pipe in the lathe chuck
    Scribe a line around the pipe in the appropriate spot
    Set the degree plate to 0 degrees
    Scribe a line along the pipe using a lathe tool
    Rotate pipe 90 deg
    scribe another line
    Rotate 90 deg etc
    etc

    Roger

  12. #12
    Join Date
    Oct 2010
    Location
    melbourne, laverton
    Posts
    1,910

    Default

    make a plug to fit in the hollow bar find centre. and use simple geometry to mark out the angles required. maybe with the help of a combination set.

  13. #13
    Join Date
    Aug 2007
    Location
    Saskatoon, Saskatchewan, Canada
    Posts
    292

    Default

    You can also through bolt a couple square plates or blocks to the ends of the hollow bar. Serve for layout and as work holders when drilling the holes.

    Pete

  14. #14
    Join Date
    Oct 2007
    Location
    muswellbrook
    Posts
    9

    Default

    This is assuming your cross slide top cover is parallel to your tool travel.

    set up in lathe. set center height for tool. scibe line on circumference at points needed along length. scribe line across face. Using a square on your cross slide rotate job 90 deg and set up using scribed line on face. scribe out points along length again and across face. rotate job and mark out the rest. should be spot on.

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