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How to press fit bushing into W925A Flap Hinge Bracket?

KazooRV-9A

Well Known Member
Patron
I'm working to fit the .375" dia bushing into the W925A flap hinge bracket on my RV-9 wings. The drawing calls for a press fit.

The bushing does measure .375" dia and the hole in the bracket is measured at .311" dia. I bought a 3/8" reamer as shown.

The question is how to finish the holes in the bracket, to achieve a press fit of the bushing? The .375" dia reamer I bought won't fit into the .311" dia hole without some further increase in hole size. AND the alignment of these 3 bracket holes was critical in the assembly of the wing, specifying that you run a string through the three holes to ensure alignment.

How have builders installed these bushing?

Andy C.

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Back in my day as a machinist, we would chuck up a new reamer and lightly hit it with a fine stone VERY LIGHTLY to remove any burrs and that would ensure a tight dowel or bushing fit. Easy enough to press those bushings in if the bracket is not installed using a bench vice and a couple blocks of hardwood. If those brackets are installed, be very careful when you ream to keep it straight and you don't move the reamer around as you run it through. You can press that bushing in using a C clamp and protect the bushing with a block of hardwood.
 
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I used a socket over one side (to give the bushing somewhere to go) and then an adjustable clamp to squeeze the bushing into place, seemed to work pretty good.
 
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Well,,, Yes the brackets are installed. You can't put the bushings in before installing the bracket, because the wing skin wouldn't go over the bushing.

The initial issue is, that the bushing is .064" dia larger than the hole in the bracket, how do you get the bracket hole to a size, that the bushing will press into?
 
Well,,, Yes the brackets are installed. You can't put the bushings in before installing the bracket, because the wing skin wouldn't go over the bushing.

The initial issue is, that the bushing is .064" dia larger than the hole in the bracket, how do you get the bracket hole to a size, that the bushing will press into?

Drill it .010 under size then ream.
 
The rule of thumb for interference fits is .001" interference per 1" diameter. So for a 0.375" bushing, the interference would be .0004" (rounded).

There are tables in Machinery's Handbook showing classes of fit, the appropriate one being force and shrink fits, class FN1 (light drive fit). However, these tables show the shaft tolerance (the bushing) being +oversize/+oversize and the hole being + oversize/size. In your case the bush is 0.375 or size. So the tables aren't much help. However, the tolerance limits in the amount of interference is also specified. So for the 0.375" bushing, the FN1 interference would be 0.0001" to 0.00075", our rule of thumb is right in the middle of this range.

A 3/8" reamer will produce a hole 0.375" diameter, the same size as the bushing. So you should either get a slightly smaller reamer or stone the one you have as a previous poster mentioned.

I'd suggest you make some practice parts before you do the ones on the wing. The construction manual has you align the three flap brackets with a string prior to final riveting. Once this is done, with a little care, the three holes can be enlarged concentrically, maintaining the alignment.

I haven't installed my bushings yet, so thanks for bringing this up.
 
This is the main part of my question:

"with a little care, the three holes can be enlarged concentrically, maintaining the alignment."

How to do this and maintain alignment? At assembly the 3 flap brackets were in good alignment as punched by Van's. This was good because changing any of them would have been a pain. So there's a need to get the 3 holes within .XXX" dia of the reamer, and the question is how to do this. I could progressively drill them, using numbered/lettered drills, but am wondering if this would maintain alignment. Or is there some tapered reamer that I should use to get to the final sizing? Remembering that as I noted, there's .06X" to be
enlarged before reaming to a press fit size for the bushing.
 
Haven't done mine yet, but here's the method I'm considering. Machine a stepped shaft (really helps to have a lathe), one end of which is a snug fit in the hole in the flap bracket, the other end is the diameter you intend to drill through the flap bracket. Drill size to be smaller than the final ream size. Make a small plate that you can clamp onto the flap bracket and thick enough that it will act as a drill guide to keep the drill perpendicular to the existing hole with a hole in it a snug fit over the stepped shaft which is in the flap bracket hole. Clamp the plate in place on the flap bracket. Drill through all six flap bracket holes using this method. Then run the reamer through the plate and use this to keep the reamer perpendicular to the flap bracket. No need to clamp the plate at this stage.
 
I am building a 10 and the wings were QB (similar flap style as the 9). The brackets were installed on the wing and presumably the guys did all of the drilling / reaming on the bench, where it would be much easier to do what you are discussing here. I had no problems working the slot in the skin over the bushings when I installed it. The slot is long, so it's easy to fit the bushing through in the center of the slot.

9 and 10 may be different, but thought I would throw this out there to help.

Larry
 
Those brackets should have been reamed to size on a drill press to maintain a 90* alignment BEFORE the brackets were installed. It would have then been very easy to position the brackets in alignment using a .375" (3/8") steel rod to rivet the brackets in place, and afterwards press in the bushings. It would be easy enough to still ream those holes to fit the bushings and maintain hole alighnment. Use a couple more reamers to sneak up on the .375" before you final ream for the bushings. Unlike a two flute drill bit that WILL wonder, a multi flute reamer will maintain the hole location,,,,,at least good enough for this purpose.
 
Well that's all water under the bridge,, I didn't see any notes in the 8-1/2X11 instructions that said to fit these bushings before installing the brackets. Unless I missed it... not impossible. And I just thought they'd interfere with sliding the skins on. I suppose I could have drilled and reamed the holes in line on a drill press beforehand, but just didn't think that far ahead. (Why did Van's drill the holes 1/16" smaller than the final intended bushing dia),,
Apparently I'm not alone.

And if reamers only open up the last thousandth's or so, it would seem like it would take more than a few reamers to get from .064" dia smaller than the final size. I don't see this as a feasible plan. Correct?

terrye, does your approach take 6 stepped shafts, because you'd drill out the smaller snug fit end in the bracket each time?

Will progressively drilling them by hand in small size steps, up to where they can be final reamed, really wander too far from a centerline alignment that will work with the flaps? The flaps are pretty long.
 
terrye, does your approach take 6 stepped shafts, because you'd drill out the smaller snug fit end in the bracket each time?

No. One stepped shaft to align the plate, then push the stepped shaft out thru the plate to reuse on the next hole, leaving the plate clamped to the flap bracket.

I just measured my flap brackets and they are just undersize from 0.375" (I primered them). Maybe Vans missed a step on yours?
 
After reaming the hole to final size, I used a C-clamp to press the bushings in place.
Note the duct tape to protect the aluminum and brass.


(Click to enlarge)
 
Inserting the flap hinge bushings...

Sounds like the holes in the hinges are not consistent in size. I used a couple big washers and adjusted some vice grips to get the right fit.
danny
 
Ok terrye I finally understand your approach. I have a lathe also, will look into making such a guide.
I?ll gage pin all my brackets, see exactly what Van?s sent me. Seems to be some discrepancy in reported factory hole size...
 
I built my wing 14 years ago, so I likely forgot exactly what I did, but I think you're overthinking this.

When you rivet on the brackets, the idea is you use string to make sure the existing holes line up as best you can. Then, just ream the holes so you can press fit the bushings.

The alignment of the 3 holes isn't THAT critical, I don't think. You'd have to really have them out of alignment to cause any kind of binding or issue with the flap movement.

A quick phone call to Vans will confirm. Comment here if I'm wrong.
 
I just measured all 6 of my flap pivot bushings and they are all 0.376" OD. This should provide an interference fit on a 0.375" reamed hole.
 
I think Clay is on to something. Surely these three bushings will have a different alignment when the wing is generating lift vs mounted on a rig in the shop vs parked on the ramp. The design must have some slop to account for the wing's natural flexing. I was looking forward to riveting on my brackets today before i saw this thread...:)
 
This was my Question to Van's Support:

Gentlemen,
I have a question on installing the .375" O.D. dia bushings in the W-925A flap brackets. This is an older kit (90072), and the as-supplied holes in the brackets I have, measure .311" dia. (The brackets have been installed and the skins are in place).
How do I get the bracket hole size to a press fit for the bushing? I posted this on the Van's website, and some (not all) other builders have posted that the holes in their brackets are at/near press fit sizing, while the ones I have are approx. 1/16" undersize, or much too small for a single reamer.
Given that the plans have required checking that there's close alignment of the 3 flap brackets, how do I best enlarge the holes to a size that will allow press fit? I did not attempt to install the bushings before installation of the skins, as they would have interfered, and when I went to do the bushing installs later, I found this issue.
Thank you,
Andy Cotyk

This was their Answer:

"They've always been undersize, but should be reamed here.
Hard to know, but probably years ago some escaped without reaming – that 's the perils of picking up used kits: 97002 doesn't have a wing allocated so someone must have picked up a used kit somewhere to go with the other kits.
All that said, at this point you're going to have to find a way to ream them to .374 – replacing the brackets isn't feasible now.
Good luck,
vans"

1. This was a wing kit that came with my build (is #90072, not #97002..)
2. I don't see what it matters, that I took over a kit from another builder that passed away. I mean, the real "Peril" here, was that the brackets were manufactured at a diameter much too small to final ream to fit the supplied bushing. I don't appear to be the only builder asking how to do this.
3. "I'M going to have to find a way to ream them". No guidance from the Manufacturer...?
4. I usually get far better assistance from Van's support, I am surprised at this response.

In the end, I plan to make a drill guide as terrye described in this thread. I'll drill accurately/aligned to a size that can be final reamed. I'll post pictures of it when I get it made. This would seem to be kinda important, don't want to foul this up considering how hard it would be to replace a bracket!

A.
 
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Here is the drill guide I made, The thick part of the guide is hard nylon and the stepped shaft is Delrin. The "arm" is aluminum. Just materials I had around.

I traced the shape of the end of the flap bracket onto the hard nylon, and cut it out. I drilled and tapped the hard nylon piece for 8-32 flush head screws, and counterdrilled the aluminum arm for them, and attached the arm. Then turned the stepped guide shaft on a lathe. Small end fits the .311" dia flap bracket hole as supplied from Van's, and the stepped part fits loosely into the "U" drilled hole.

The guide hole is .368 dia. (Drill "U"), which was the closest I had to .375" dia. I did a test piece with this drill size, with the .375" dia reamer I bought, and it worked OK. I was able to press the .375/.376" dia Van's supplied bushing into it acceptably.

So you line up the guide to the flap bracket with the stepped shaft, and clamp the guide arm to the flap bracket. Remove the stepped shaft and drill "U" through the existing flap bracket hole. Then remove the clamp and guide and hand ream the hole with the .375" dia reamer. Debur the hole lightly, then press the bushing into place.

Thank you terrye for the suggestion.

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