• Welcome to engineeringclicks.com
  • How to make fasteners captive on machine guards

    Discussion in 'The main mechanical design forum' started by neilkernot, Mar 2, 2010.

    1. neilkernot

      neilkernot New Member

      Joined:
      Feb 2010
      Posts:
      3
      Likes Received:
      0
      The new machinery directive says that fasteners on guards have to be retained when the guard is removed. We have been looking for a cheap and easy solution to this euro-nonsense, and we think we may have solved it! Little 5p gadgets called "bolt retainers" from Components Direct fitted to a socket button head screw. Does anyone else have any other thoughts or ideas?

      There are various special fasteners you can buy, mostly they need to be pressed in which means they are expensive and less tolerant of misalignment. For simple guards, we always just had some holes or slots laser cut into sheet metal, and used a button head screw. The gadgets above work with this arrangement, and even work with slots. It's the most cost effective solution we can come up with, but we are interested to hear how others have tackled the problem.

      Neil
       
    2.  
    3. PeterB

      PeterB Member

      Joined:
      Feb 2010
      Posts:
      16
      Likes Received:
      0
      The most cost effective method that I have come across and used during my career, has been with either a captive 'O' Ring, or a captive fibre washer placed over the threads, on the underside of the top part. To make this work well, it can be good to have a recess/countersink in the upper surface of the lower part, if a flush closing is required.

      There are some fibre washer manufacturers who actually market parts for this, with a correct interference fit onto designated screw diameters. I may have one or two long-standing UK contacts for this if needed, but they might not be current any more
       
    4. PilotWorks

      PilotWorks New Member

      Joined:
      Mar 2010
      Posts:
      2
      Likes Received:
      0
      Maybe you can make a tapped hole on the guard instead of a thru hole and had the inner threaded part of the securing screw removed. This way, the screw will not drop off the guard and you are still able to tighten it to the frame.
       
    5. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

      Joined:
      Feb 2010
      Posts:
      233
      Likes Received:
      1
      I guess it depends on how large or small the fasteners are. If the guards are sheet metal, you could press PEM or Southco fasteners. They come in various sizes.
       
    6. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

      Joined:
      Feb 2010
      Posts:
      233
      Likes Received:
      1
      I think your answer there is a rotatable captivated nuts that could be mounted on the guarding permanently or semi-permanently. then on the frames of the machines there would have to be small studs matching the pattern of the nuts.
      It appears someone is working on a patent on the"rotatable captivated nut"
       
    7. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

      Joined:
      Feb 2010
      Posts:
      233
      Likes Received:
      1
      Thanks for your comments, but PEM and other pressed-in fasteners are expensive and have less flexibility than a simple screw in a hole or slot. The bolt retainers we found are a cheap and easy way to continue using this simple method.
       
    8. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

      Joined:
      Feb 2010
      Posts:
      233
      Likes Received:
      1
      The most cost effective method that I have come across and used during my career, has been with either a captive 'O' Ring, or a captive fibre washer placed over the threads, on the underside of the top part. To make this work well, it can be good to have a recess/countersink in the upper surface of the lower part, if a flush closing is required.

      There are some fibre washer manufacturers who actually market parts for this, with a correct interference fit onto designated screw diameters. I may have one or two long-standing UK contacts for this if needed, but they might not be current any more
       
    9. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

      Joined:
      Feb 2010
      Posts:
      233
      Likes Received:
      1
      I have used the o-rings for years in press guarding. You can also change materials to suit your application. i.e. a plating bath guard.
       
    10. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

      Joined:
      Feb 2010
      Posts:
      233
      Likes Received:
      1
      Hope this solution that I am sending will be useful as this is a totally practical solution.

      1) Cut a groove around the shank, immediately after the bolt head.
      Groove size should be 1 to 1.5 mm deep and 1 to 1.5 mm more wider than the guard sheet metal thickness.

      2) On the guard where the fastener is to be fitted, drill a hole of 2 mm diameter lesser than the shank diameter of the bolt.

      3) Take a tapered piercing tool (round ended) and hammer or press it on the drilled hole, till the hole edge will flare away from the sheet metal surface.

      4) Through the same pierced hole, drill a hole of 0.5 mm larger diameter than the shank diameter.

      5) Insert the bolt shank till sheet metal will fit into the groove.

      6) Flatten the flared surface by hammering or pressing the tool.

      7) The flared, but now flattened diameter will enter into the groove and the bolt will be loosely held into the groove by sheet metal for tightening / loosening.

      Kindly try this out on a separate sheet metal sheet to understand the sequence and procedure.
       
    11. LinkedIn Gopher

      LinkedIn Gopher Little furry chap

      Joined:
      Feb 2010
      Posts:
      233
      Likes Received:
      1
      These bold retainer will do the job, I have use these before and also captive fibre washers for a simple effective solution, one just need to allow in the design for not being able to fully unscrew the bolt and in the process loosing the washers inside the machinery. I have also a supplier for machine screws that had the shank relieved below the head as Sunil describes.
       

    Share This Page