HS 908 headaches!!

[aarvig]

I am building my THIRD flappin set of these HS908 brackets. First set I screwed up cutting to close with the band saw. Second set I drilled the nine holes only to discover my edge distance was off by a bit too much. The third set everything is perfect except the center upper alignment hole I drilled has about 1/64th of an inch difference in height relative to the other center alignment hole on the other HS908. No matter how accurate I am with my measurements when I centerpunch the hole or when I drill I am off by a very small margin. My fear is that my horizontal stabilizer will not be sitting square on the fuselage.
My questions are as follows:
1.) Am I being to picky?
2.) Is there a way to drill the center upper alignment hole so that the two alignment holes end up in perfect alignment?

 

[Don Jones]

I am building my THIRD flappin set of these HS908 brackets. First set I screwed up cutting to close with the band saw. Second set I drilled the nine holes only to discover my edge distance was off by a bit too much. The third set everything is perfect except the center upper alignment hole I drilled has about 1/64th of an inch difference in height relative to the other center alignment hole on the other HS908. No matter how accurate I am with my measurements when I centerpunch the hole or when I drill I am off by a very small margin. My fear is that my horizontal stabilizer will not be sitting square on the fuselage.
My questions are as follows:
1.) Am I being to picky?
2.) Is there a way to drill the center upper alignment hole so that the two alignment holes end up in perfect alignment?

You might be to picky, though perfection is unattainable, you can get close

I drilled the alignment hole in one bracket, then placed the brackets back to back with the "foot" sitting on a flat surface, clamped them together, then match drilled the alignment hole in the other bracket. Comes out close to perfect as you can get. Cleco them to the spar and clamp a straight piece of angle between them so they are on the same plane and finish drilling the rest of the holes.
Hope this helps

 

[Rupester]

Yup ...me too ...

I did the same as Don to match drill the holes. Don't obcess too much about these brackets and the levelness of the HS. You can shim under either or both brackets to level like hundreds of other RVers.
Another hint if you haven't heard: Always drill first with a sharp new #40 bit. They start easily in the center punch hole and drill nice and true. Then enlarge the hole with whatever final-size bit you need. Once I learned that trick, drilling precise holes never vexed me again.

 

[mculver]

I was also unhappy after my third try. Spar is drilled now, though, so not able to change anything out.

I am still thinking that a group buy of some CAD versions of these make a lot of sense. Baffles me why Vans doesn't pre-fab these.

 

[aarvig]

You might be to picky, though perfection is unattainable, you can get close

I drilled the alignment hole in one bracket, then placed the brackets back to back with the "foot" sitting on a flat surface, clamped them together, then match drilled the alignment hole in the other bracket. Comes out close to perfect as you can get. Cleco them to the spar and clamp a straight piece of angle between them so they are on the same plane and finish drilling the rest of the holes.
Hope this helps

Don, this advice saved the day for me. I did exactly this and presto, no difference from side to side now. The measurements are EXACTLY the same on the upper center hole...since that is the only one that matters for positioning. Right down to a 64th of an inch. THANK YOU!!!!!

 

[aarvig]

I did the same as Don to match drill the holes. Don't obcess too much about these brackets and the levelness of the HS. You can shim under either or both brackets to level like hundreds of other RVers.
Another hint if you haven't heard: Always drill first with a sharp new #40 bit. They start easily in the center punch hole and drill nice and true. Then enlarge the hole with whatever final-size bit you need. Once I learned that trick, drilling precise holes never vexed me again.

Thanks for the advice. I will do this next time. Yes, the number 30 bit roams around a lot relative to the 40, so next time I drill number 30 I will start with the 40. Thanks!

 

[Camillo]

And if I may add, when drilling, go very slow. Rotating speed will have a gyro effect, thus making the bit "walk".

 

[aarvig]

I was also unhappy after my third try. Spar is drilled now, though, so not able to change anything out.

I am still thinking that a group buy of some CAD versions of these make a lot of sense. Baffles me why Vans doesn't pre-fab these.

Mike,
Do you think we could start a side business together? I agree with you on prefabing these with at least the primary alignment hole in them. Especially with the need to be accurate side to side. I spoke with Vans today and they said that it was very important to be "as close as you can feasibly get" side to side so the HS sits level. However, they also said that HS tip difference of 1/4 to 1/2 inch is when issues start in terms of straight flying. However, if you extrapolate 1/64th diff at the HS908's out to the tips I imagine you could end up with 1/4 inch height variation pretty easily. I am sure there is a math equation that could give us that answer but it is far to early in the AM for me to be doing algebra!

 

[mculver]

I am going to revisit my brackets -- am serious about coming up with a CAD version, and even got a quote on them. High water mark on cost is likely to be $25-$30 each (so times 2). How many people would be interested?

Mike,
Do you think we could start a side business together? I agree with you on prefabing these with at least the primary alignment hole in them. Especially with the need to be accurate side to side. I spoke with Vans today and they said that it was very important to be "as close as you can feasibly get" side to side so the HS sits level. However, they also said that HS tip difference of 1/4 to 1/2 inch is when issues start in terms of straight flying. However, if you extrapolate 1/64th diff at the HS908's out to the tips I imagine you could end up with 1/4 inch height variation pretty easily. I am sure there is a math equation that could give us that answer but it is far to early in the AM for me to be doing algebra!

 

[aarvig]

Mike,
I made my last set yesterday evening using the technique Don Jones described and they came out perfect. The only hole that matters for position is the upper center. Drill through one. Put them on a flat surface with the foot down on the flat surface, clamp them together and match drill the two that way you get accurate vertical position.
The other holes don;t have to be "perfect" as long as the edge distance is OK. I'd be interested in a CAD set but now that I have an acceptable set of 908's I am more than ready to move on to the next phase of building!

 

[Don Jones]

Glad I could help

Don, this advice saved the day for me. I did exactly this and presto, no difference from side to side now. The measurements are EXACTLY the same on the upper center hole...since that is the only one that matters for positioning. Right down to a 64th of an inch. THANK YOU!!!!!

Your Very Welcome! Glad I could help someone. I get a lot of help on these forums and it's nice to be able to reciprocate.
I just mounted my horizontal stab to the fuse a few days ago and with the fuse all leveled up, when I set the digital level across the stab it read 0.0