SeamusG

Hi all,

My planes are mostly 40 / 60 size units. For the most part they use 2-56 size rod at the ends. Some call for 4-40 size rod for the ailerons. I use standard sized servos with torque ranging from 45 - 90 from Hitec & JR. Servo horns are standard nylon stuff provided with by the mfg. Control surface horns are nylon pieces from Du-bro, Great Planes or SIG.

It appears that the horn holes are 1/16" - at least my pin vise with a 1/16" bit is snug but doesn't remove any material. When I snap a standard 2-56 clevis on the fit is very snug. If I chose to open the horn hole up with a 5/64" bit the fit is sloppy - there is noticeable slop at the control surface - especially when both the servo horn hole and the control horn hole is opened up to 5/64".

What is the proper technique for correctly sizing the holes in the horn (servo or control surface) and a clevis (threaded or soldered)?

What size bit should be used to open up the horns when using 4-40?

TIA,

EloyM

My Feedback: (194)

You can adjust the hole size perfectly with number (size) drill bits. 1/16 is .0625 - 3/64 is .0781, a BIG difference! A No. 52 bit is .0635, just .001 larger than the 1/16 bit and is often the perfect choice, depending on the material and the technique in drilling.
No. 51 is .0689, for a bit more clearance. With some of the foreign made clevises, you may have to resort to metric size bits which fall in between.
As for technique, just turning the bit in the hole does not make a perfectly sized hole, as the plastic gives. After getting the bit halfway into the hole, pull it, without turning it, back out. So doing will ream out the plastic to a perfect size.
And you are going at this the right way, and NOT using Z bends which generally result in too snug or too sloppy fits, and further distort the plastic they are inserted into. I have never seen a piece of mil-spec, medical or professional equipment using anything as crude as a Z bend.
Keep the quality and precision.

SeamusG

Thx EloyM - looks like "it's all about the tools" . How many standards sizes are there? Geez. [sm=lol.gif]

I'm thinking that once I get a combination "right" then stick with it. For instance, if I get the right fit for Sullivan clevis's, JR servo horns and SIG control horns then stick with that combination and avoid mixing and matching mfg. Yea, easier said than done 'cause I'm sure that the soft nylon pieces will vary even within a brand.

Well, it's off the my LHS ...

jaka

Hi!
Go metric instead! the holes are drilled using either 1,6mm or 1,7mm drill bits.

Hatzman

The purchase of a complete set of numbered and lettered drill bits is perhaps the best tool investment I ever made. The numbered go from #1 - 0.2280 to #60 - 0.0400 and A - 0.234 to Z - .0413. I bought the set along with a standard 1/16" to 1/2" bits in a case for under $20 at Harbor Freight. It was a special sale, and you might have to wait for another.

TedMo

there are 3 standard drill sizes sets, number 1-60, fractional 1/16-1/2, letter. not counting metrics. Having number and fractional sets will likely give you all you will ever need. You can get these sets quite cheaply for the hobby use however if they will be used for high speed steel they won't last very long.

AviationNut

n/m - misread original post.

42etus

My Feedback: (2)

I use a caliper to measure the pin on the clevis and then select the same size drill bit. It is usually 0.0625 or 1/16th inches. Drill out the arm and I'm good to go. The fit comes out nice and snug and slop free. The other guys are right about the drill bit sets that include number sizes. They are invaluable and the Harbor Freight sets are very affordable.

SimonCraig1

I use a rats tail needle file and slowly open the hole out from both sides until its a snug fit i.e. the clevis pin doesn't pop straight out the hole on opening. You can get a very good slop free fit this way although there is a slight risk of over doing it and having to start again with a new horn....

SeamusG

Well thanks much guys - there's a Harbor Freight within a mile from the house. I'm developing 3 sets of tools - auto / home / RC - and I keep promising myself that I won't borrow from one to feed another (yea, right!).

Bottom line - create a snug (not tight / not loose) fit between the clevis' pin and the horn. Best tool set would include digital calipers, drill bit sets and a sense of humor.

Now if the shipment of bearings would just show up! Time to fly.

91zulu

My Feedback: (2)

# 11 X-Acto blade. works perfect every time.