there must be a secret trick for this ?

[fairchild1934]

I'm building my horizonal stabs. Making the trailing edge tubes that have the bushings for the elevator hinged to bolt to. I made the first one. Not 100% happy with it. drilled the 3/8 holes and made the bushings to be welded into them. where I am having trouble is figuring out a way to get my punch marks for the holes to be in the EXACT same clock position --- one to the other. The first one I'm off by about 2 or 3 degrees. Just enough that I can see a slight difference when I put 4 inch bolts through the bushings.

Here is how I did it but there must be a more precise way.
i have the tube in the holding blocks and fastened down to the table. I took steel blue and inked the tubes. Then I took a long stainless steel ruler and bridged between the LE and TE tubes-- and scraped the surface of the TE through the ink making a mark at 12-Oclock through where each hole goes.
Then I center punched each hole that was facing up where I scraped through the ink. Then I flipped the tube over and made a paper measuring tape to wrap around the tube to find the exact opposite side and made a sharpie line lengthways down the tube representing the 180 degree clock position. Then I moved the tube into the lathe. I put a spring wire with a needle point in the tool post. i aligned the point with the punch mark. Then I scratched a ring around the inked tube and made a circle around the tube that passed through the punch mark. Then --- that circle and the longitudinal sharpie mark intersected where I needed to make my 2-nd punch mark.

That kind of worked but I am off just a little on the first one. Apparently my first two punch marks were not perfectly lined up with one another.

So how- do I punch two marks in the tube and keep them EXACTLY at the same clock position with each other ?????? does anyone have a good idea for this ?

( I think I can move my holes in the first one if I have to--- but I wanted a perfect interference fit between the bushings and the tube. )


Anyone see a solution here ?

Tim

[alaskabearhawk]

You are working pretty hard when there is a simple solution, at least from my point of view. I used a V-block drill jig clamped in place with a C-clamp. The ends of the v-block have scribed lines that help align to the centerline. I verified the fore-aft alignment with a square and you can fine tune the hole with a chain saw file, if necessary. YMMV

http://www.mykitlog.com/users/display_log.php?user=yeeeha&project=527&category=7248&log=162021&row=120

https://www.aircraftspruce.com/catalog/topages/vdrillguide.php

https://www.amazon.com/Gator-Tools-V-drill-V-drillguides-Standard/dp/B00J3ZYEJQ

[fairchild1934]

Thanks ABH-----
getting the hole in the center of the tube is not the problem-
the problem is getting a hole in each end of the 4 foot long tube and getting the two holes in EXACTLY the same rotational position. So later when I bolt the hinges on the through bolts are BOTH exactly perpendicular to the stab. I dont see how a V-Block accomplishes that mission---- can you elaborate ?

Tim

[alaskabearhawk]

If you look at my kitlog entry you can see that I used a square to align the long bushing material at a right angle to the table and fine-tuned as necessary.. Making sure the tube (aft spar) is secure to the table and doesn't rotate, do that on both ends and you are golden. If you want, you can slip the bushing material or any long, straight rod into the v-block to check that the block is clocked correctly fore and aft. Another option is to use a small digital level on the v-block to verify it is parallel to the table surface. If it's off a hair and you have to file it a bit, the gap won't be (or shouldn't be) so wide that the welding rod won't fill whatever gap there is.

I hope this clarifies it a bit...you can do it!

[geraldmorrissey]

My plan is to drill those holes after the assembly is final welded to account for any warpage. I'm lucky to have a neighbor with a mill so I will chuck the whole assembly level and drill the aft spar inboard holes and the leading edge strut holes. Even if you had to farm out this process I can't think it would be prohibitively expensive. I will not drill the aft spar outboard holes until I install the assembly on the fuselage. This is because I already have my brace wires and I want to locate the attach bushings inboard/outboard on the aft spar tube so that my wire terminals are located at the center of their adjustment range. Just my way, I'm a big fab on assembly guy.
Cheers
Gerry
Patrol #30