Jump to content


Photo

Dovetail Attachment

  • Please log in to reply
4 replies to this topic

#1 langejcarl

langejcarl

    Mariner 2

  • *****
  • Posts: 202
  • Joined: 05 Jan 2005
  • Loc: Michigan USA

Posted 30 January 2010 - 08:26 AM

I have an 8 inch solid aluminum dovetail bar attached by cap screws to tube rings. I have a couple of questions. Do most people simply attach metal to metal? Do any of you put cork or rubber gasket material between the bar and the rings? Do any of you use washers between the bar and the rings? If so, regular cut washers or lock washers? Finally, do any of you place regular or lock washers between the cap screw head and the bar?

Thanks.

#2 mclewis1

mclewis1

    Thread Killer

  • ****-
  • Posts: 10891
  • Joined: 25 Feb 2006
  • Loc: New Brunswick, Canada

Posted 30 January 2010 - 09:41 AM

Metal to metal, with nothing in between. You want as much surface area between the bar and rings as possible. Washers or cork would diminish this.

Washers under the head of the bolt or nuts are fine, they prevent any gouging of the aluminum used in the bars.

#3 Doug D.

Doug D.

    Mercury-Atlas

  • *****
  • Posts: 2736
  • Joined: 23 Aug 2005
  • Loc: Virginia

Posted 30 January 2010 - 09:51 AM

I sometimes use washers for a couple reasons - e.g., because bolts are a tad too long to seat tightly or if I need clearance of dewshield with the bar. In these cases I'm using washers for spacers only and I haven't ever felt I needed to use lock washers.

If using cork or other soft materials you can introduce some flexure - if imaging that is of course bad...

#4 langejcarl

langejcarl

    Mariner 2

  • *****
  • Posts: 202
  • Joined: 05 Jan 2005
  • Loc: Michigan USA

Posted 31 January 2010 - 07:48 AM

I have a follow up question. If I mount the dovetail bar to the center holes on the tube rings the screws are a little long and I could damage the OTA. of course I could get shorter screws, but does it matter if I mount the bar to the top or bottom holes in the tube rings so that the scope rides a little higher or a little lower? The metal of the rings is thicker at those points such that the screws won't go through to the OTA.

#5 BlueGrass

BlueGrass

    Surveyor 1

  • *****
  • Posts: 1978
  • Joined: 25 Jul 2009
  • Loc: Wasatch Front, UT

Posted 31 January 2010 - 10:59 AM

If at all possible, use the correct length screw. I get all my 1/4 20 screws at Lowes. They have a good selection. Using the right screw means you don't have to worry about running them through the rings, damaging the felt or the OTA.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics