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Dubro Swivel Ball Links

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Dubro Swivel Ball Links

Old 03-24-2017, 04:08 PM
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Square Nozzle
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Default Dubro Swivel Ball Links

Anyone have 2-56 Dubro swivel ball links in their stock (black nylon with a swivel ball in one end, self threading hole in the opposite end for a pushrod)? What is the outer diameter of the pushrod end. Being the weekend, Dubro is closed and I want to know if the 2-56 size has enough material in the pushrod end to accept a 4-40 threaded pushrod. I know they have what they call a 2-56/4-40 swivel ball link but the hole in the ball actually sized metric and is a sploppy loose fit for a 2-56 bolt.
Old 03-24-2017, 05:56 PM
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ByLoudDesign
 
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Found on ServoCity.com
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Old 03-24-2017, 06:46 PM
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blvdbuzzard
 
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If you are talking this style, they look like they have enough meat for a 4/40.

http://www3.towerhobbies.com/cgi-bin...&I=LXD912&P=ML

Buzz.
Old 03-25-2017, 04:21 AM
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The swivel links I'm thinking off I would not try to tap out to 4-40.
seems to me it would weaken the wall strength and cause the link to fail under load
Old 03-25-2017, 06:29 AM
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Square Nozzle
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Thanks for your input guys. ByLoudDesign led me to the Servo City site where I got most of the dimensions I was interested in for the swivel ball linkage except for the "shank" O.D. The other dimensions provided, indicate that the 2-56 and 4-40 appear to use the same body with a smaller bore diameter in the ball. If that's the case than what blvdbuzzard is saying is likely correct. There is sufficient material to drill and then thread in a 4-40 pushrod. I was in the same boat as jetmech05 with concern that drilling for a 4-40 rod would reduce the wall thickness to a point that would invite failure.
Old 03-25-2017, 06:34 AM
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Unless your push rod is extremely long, you will not flex a #2 rod. if you test tap one for 4-40 try and break it. You dould always use those very same tie wraps at the very end and lock it in place with epoxy!!
Old 03-25-2017, 09:04 AM
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This system is going onto my PC-21 with a Wren 44 Turbo prop engine. The airspeed will probably be near 100 MPH. With all of our jets we use very stiff pushrods. That's why the 4-40 rod. I will be using 2 1/2" Hangar 9 titanium turnbuckle rods with the swivel ball links. I want to use 2-56 bolts through the control horns primarily for looks. 4-40's are just to big and I think the 2-56 bolts have sufficient shear strength for the application. If someone can give me the OD of the shank on the 2-56 swivel ball link I'll know how to proceed. If the shank has a .187" OD, than as I suspect, it has the same body as the 4-40 link.

Last edited by Square Nozzle; 03-25-2017 at 09:08 AM.
Old 03-25-2017, 11:09 AM
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Sense I am using it in my 1:4 scale Beechcraft 350i King Air for the nose gear bay door, I drew it up to conform to the Servo City image. I imported the image into AutoCAD, scaled it so the dimension given were correct, traced it! The boss body seems to be shy of 3/16", as you can see from the attached image.
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Old 03-25-2017, 02:25 PM
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Wrong part BLD. The swivel ball connector is a black nylon fitting with a brass ball inserted in the end opposite the shank that receives the pushrod. The Dubro catalog P/N is 367 for the 2-56 part. I took a 30 minute drive to the only good hobby shop near the north east corner of Connecticut and bought a 2-56 swivel ball link. The shank OD is the same as the 4-40 part. I drilled out the shank hole to the 4-40 tap drill size and all is well. Now I have a 2-56 ball bore with a 4-40 threaded hole for a turnbuckle push rod.

Thanks to you all for your assistance. We all learned something.

Last edited by Square Nozzle; 03-25-2017 at 02:33 PM.
Old 03-29-2017, 01:21 PM
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I got a call back from Dubro today. It appears that the information on the Tower Hobbies site is either misleading or down right incorrect. Dubro makes a 2-56/4-40 and the ball bore is sized for a 2-56 machine screw. It is not .112" as noted in the tech notes on the Tower site for the 2-56/4-40 link. As I stated above, you can drill out the shank on a 2-56 link or buy the 2-56/4-40 link.
Old 03-30-2017, 07:21 AM
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I use the 2-56/4-40 ball links on almost everything and have had good luck with them. I have never noticed the screw loose in the ball.

Scott
Old 04-01-2017, 02:01 PM
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Art ARRO
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John,
Glad you got that linkage sorted out. BTW I'm headed out to Toledo next week for their RC Show. PM me if you need anything, as the show is the largest hobby shop on the planet with 150+ vendors. I usually pick up a bunch of stuff that is hard to find in local hobby shops. Look at www.toledoshow.com and the Exhibitors listing and open the respective websites.
Take care,
Art ARRO

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