Free 186 More Best Homemade Tools eBook:  
Get tool plans

User Tag List

Results 1 to 4 of 4

Thread: Safely turning eccentrics with 3jaw chuck

  1. #1
    Supporting Member mklotz's Avatar
    Join Date
    Aug 2015
    Location
    LA, CA, USA
    Posts
    3,515
    Thanks
    362
    Thanked 6,546 Times in 2,156 Posts

    mklotz's Tools

    Safely turning eccentrics with 3jaw chuck

    If you want to turn an eccentric (common model engine job), the best tool to use is the 4jaw chuck; it provides a secure hold on the offset blank. However, many amateurs have only a 3jaw chuck.

    Thus arose the practice of inserting a shim between one of the jaws and the stock. I don't care for this approach for safety reasons. Since I have a 4jaw, I've never tried this shim idea but I would be leery about the shim coming loose and creating a disaster if it was thrown out.

    Despite my concerns I wrote a program to calculate the size of shim required. It's in the ECCENT archive on my page.

    There is a much safer way to do eccentrics with a 3jaw. It goes like this...

    Imagine a tube bored to be a sliding fit on the parent stock. A slot of sufficient width to pass one of the three-jaw chuck jaws is milled in this tube. The parent stock is inserted in the bore and the whole thing clamped in the three-jaw chuck such that one jaw passes through the slot to seat on the parent stock while the other two jaws seat on the circumference of the tube. Obviously the centerline of the parent stock is offset from the lathe spindle axis and turning will produce an eccentric. If we know the OD of the parent stock and the amount of the offset required, it's possible to calculate the OD of the tube needed to produce just that offset when clamped as described above.

    The program, ECCENTUB, to implement these calculations is available in aforementioned ECCENT archive.

    Safely turning eccentrics with 3jaw chuck-eccentub.jpg

    186 More Best Homemade Tools eBook
    ---
    Regards, Marv

    Experience is always far worse than pessimism

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

    baja (Apr 10, 2021), cogentia (Apr 10, 2021), DIYer (Apr 10, 2021), Jon (Apr 14, 2021), old_toolmaker (Apr 10, 2021), rayh__ (Apr 9, 2021)

  3. #2
    Supporting Member Frank S's Avatar
    Join Date
    Aug 2015
    Location
    Peacock TX
    Posts
    11,619
    Thanks
    2,176
    Thanked 9,112 Times in 4,361 Posts

    Frank S's Tools
    Marv there have been times when I was needing an eccentric like for making a cam over clamping tool Usually these are not mission critical so scrolling out the jaws then setting 1 of them out of time by 1 or 2 turns would suffice but my chucks were always plenty large enough to still have plenty of turns on the jaws in the scroll
    Your ides is much better as you can control the offset by the OD of the split sleeve

    2,000+ Tool Plans
    Never try to tell me it can't be done
    When I have to paint I use KBS products

  4. #3
    Content Editor
    Supporting Member
    DIYer's Avatar
    Join Date
    Aug 2013
    Posts
    3,055
    Thanks
    791
    Thanked 1,880 Times in 1,677 Posts


    Thanks mklotz! We've added your Eccentric Turning in a 3-Jaw Chuck to our Machining category,
    as well as to your builder page: mklotz's Homemade Tools. Your receipt:




  5. The Following User Says Thank You to DIYer For This Useful Post:

    old_toolmaker (Apr 10, 2021)

  6. #4
    Supporting Member old_toolmaker's Avatar
    Join Date
    Dec 2017
    Location
    Cape Coral, FL
    Posts
    579
    Thanks
    647
    Thanked 455 Times in 184 Posts

    old_toolmaker's Tools
    Marv,
    This is an interesting approach to offset turning with a 3 jaw universal chuck. Safety is an important consideration for sure. I have a nice 4 jaw independent chuck so I am set for offset turning, but I will keep this idea in my bag of tricks if the need ever pops up.



    2,000+ Tool Plans
    Dick


    Links to some of my plans:

    https://www.homemadetools.net/forum/...965#post105972 OFF-SET TAILSTOCK CENTER PLANS
    http://www.homemadetools.net/forum/s...995#post112113 SMALL TURRET TOOL POST PLANS
    http://www.homemadetools.net/forum/l...994#post112111 LARGE TURRET TOOL POST PLANS
    http://www.homemadetools.net/forum/m...383#post110340 MINI-LATHE CARRIAGE LOCK PLANS
    http://www.homemadetools.net/forum/s...191#post106483 SMALL QC TOOL POST PLANS
    http://www.homemadetools.net/forum/q...849#post119345 QUICK CHANGE LATHE TURRET
    http://www.homemadetools.net/forum/m...949#post119893 MINI LATHE COMPOUND PIVOT MODIFICATION

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
  •