Free 186 More Best Homemade Tools eBook:  
Get 2,000+ tool plans, full site access, and more.

User Tag List

Results 1 to 5 of 5

Thread: Rattle your calipers

  1. #1
    Supporting Member mklotz's Avatar
    Join Date
    Aug 2015
    Location
    LA, CA, USA
    Posts
    3,434
    Thanks
    357
    Thanked 6,380 Times in 2,117 Posts

    mklotz's Tools

    Rattle your calipers

    This post is more about how to use a tool than it is a description of a new tool. Knowledge is arguably our most important tool so I think posts like this belong in the tools section of the forum.

    In his book, Home Machinist's Bedside Reader #1 (pg. 11), Guy Lautard describes a technique for measuring a large bore when you don't have a set of calipers large enough to span the diameter.

    Basically, you cut a "stick" to a length slightly less than the diameter of the bore and provide it with rounded or pointed ends. Inserted in the bore, this stick will "rattle" back and forth a (hopefully) small amount. You measure the peak-to-peak rattle and then use a formula to calculate the actual diameter. Lautard gives a formula but it looks like an approximation to me, although I haven't examined it closely.

    If the rattle distance is small compared to the diameter of the bore, the stick length itself is a very good approximation of the bore diameter.

    I wrote RATTLE.EXE to compute the diameter given the stick and rattle lengths in order to evaluate this procedure. You can use it to calculate the diameter if you need to use this procedure. You can download the program from my webpage.

    This is the way I was taught to use internal, spring type calipers. If you try to set the calipers to the actual diameter, you're very likely to spring them slightly. When withdrawn from the bore to be measured, they will unspring slightly thus affecting the reading. Better to set them so they "rattle" slightly in the hole and then measure them. RATTLE will prove to you that, if you make the rattle very small, the difference between the measured caliper distance and the actual diameter will be very small indeed.

    For an example, I used the values Lautard used in his book...

    S = 3.998
    R = 13/32 = 0.40625

    and the program yielded a calculated diameter of 4.003197. Lautard's approximation yields a value of 4.0033; thus, agreement to one ten thousandth.

    For a rattle distance of 0.40625/4.003197 = 10% of the bore diameter, the stick yielded the bore diameter with an error of only 100*(3.998-4.0032)/4.0032 = 1.3%. Decreasing the rattle distance will decrease that error still further.

    186 More Best Homemade Tools eBook
    Last edited by mklotz; May 4, 2018 at 10:11 AM.
    ---
    Regards, Marv

    Home Shop Freeware
    https://www.myvirtualnetwork.com/mklotz

  2. The Following 6 Users Say Thank You to mklotz For This Useful Post:

    JD62 (May 4, 2018), jjr2001 (May 5, 2018), Jon (May 3, 2018), Moby Duck (May 4, 2018), Seedtick (May 4, 2018), Toolmaker51 (May 5, 2018)

  3. #2
    Supporting Member Moby Duck's Avatar
    Join Date
    Jan 2016
    Posts
    387
    Thanks
    1,215
    Thanked 196 Times in 124 Posts

    Moby Duck's Tools
    Perhaps I am thinking a bit slow this morning. How do you measure the Rattle inside the bore?

    2000 Tool Plans

  4. #3
    Supporting Member
    Join Date
    Dec 2016
    Posts
    332
    Thanks
    3
    Thanked 122 Times in 98 Posts
    Sounds to me like that method is about as precise as throwing a hand grenade. I think I'll stick with my inside mics, or a bore gauge. The book you refer to, however is very interesting and informative.

  5. #4
    Supporting Member mklotz's Avatar
    Join Date
    Aug 2015
    Location
    LA, CA, USA
    Posts
    3,434
    Thanks
    357
    Thanked 6,380 Times in 2,117 Posts

    mklotz's Tools
    Quote Originally Posted by Moby Duck View Post
    Perhaps I am thinking a bit slow this morning. How do you measure the Rattle inside the bore?
    Lautard doesn't mention how that was done.

    If the "rattling" was done near the mouth of the bore simply holding a scale in place and reading the swing would work. Another way I can imagine would be to use a pair of dividers and keep opening them until their span matched the swing of the stick, then hold them against a scale. Remember, even a poor estimate of the swing will improve the estimate of the bore. A detailed error analysis would be a waste of time; if you really need to know the bore with high accuracy you'll use more sophisticated techniques.
    ---
    Regards, Marv

    Home Shop Freeware
    https://www.myvirtualnetwork.com/mklotz

  6. The Following User Says Thank You to mklotz For This Useful Post:

    Moby Duck (May 25, 2018)

  7. #5
    Supporting Member Philip Davies's Avatar
    Join Date
    Dec 2015
    Location
    Reading, Berks, UK
    Posts
    868
    Thanks
    1,184
    Thanked 1,019 Times in 342 Posts

    Philip Davies's Tools
    Very good indeed! I work often with learning-disabled fellows, who cannot read even a tape measure, but obviously this is a technique (leaving aside the arithmetic) they can master. You have prompted me to post a homemade tool, which a quick search has revealed that has not been previously posted.



    186 More Best Homemade Tools eBook

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •