I had a 300 plus pound guy break my step off when boarding the copilot side of my RV 10. I've been meaning to open up the floor board and fix the slight wiggle in the step. It didn't break because of the wiggle, the weld was insufficent. Anyway, I've been thinking a long time about how to fix the wiggle in the step and here is my solution. The solution is how to retrofit a tapered pin to hold the step in place. Machined taper pins are a good way to connect parts that you don't want to rotate/slip. The standard hole left when we drill the AN 3 bolt to hold the step leaves anything but a round hole. This leads to the slop which just gets worse over time.
I understand some have used a straight reamer and a AN 4 bolt to fix the loose step. Too easy.
So, I purchased a couple of new steps and had them powder coated. My original ones are chromed. I decided to go with the powdercoat secondary to cost. I don't believe the chroming process had anything to do with the failed weld. There just wasn't enough material to hold the step in place.
First, I had to cut acess holes in the baggage floor. I did not put them in in the first place. I'd recommend installing some for those who are still building. Next, take the nut off and then I had to use a air grinder to cut the bolt to get it out. There isn't enough room to remove the bolt from the top.
Now, it was easy to pull out the tube and then slide in the new step. I used a story stick and referenced it off the flap on the other side to get the rotation correct for the new step. I then used an angled scriber to mark the top hole and came in from the bottom with a number 12 drill to mark the bottom hole.
Now, this hole is not at a 90 deg angle to the cylinder of the step. So, take a number 40 drill and drill thru from both sides. I then made up a drilling jig to hold the step.
I used a 6 inch number 40 drill to find the correct angle. It took wedges on the back of the jig to set the angle correctly. Then lock everything down so that it doesn't move. I have seen elsewhere where an alumninum block was inserted to help hold the bolt in place. Off to order a 12 inch bar of 1 1/2 inch aluminium rod to make a 2 inch long plug. Once I had that turned so that it would slide into the step, I drilled and tapped a 3/8 x 1 hole in the end of the plug so that I could slip it into the end of the step and set the depth. I thought that I might have to put the plug into the step to drill it, but found out that since I hadn't moved the drill fixture, all I had to do was to lay the plug in place and drilled thru it with the number 40 drill. I slipped it in the step and now I had a number 40 hole thru both the new step and the plug. I epoxied the plug in place with JB weld.
I then stepwise enlarged the hole in the step. I did this out of the jig and would not recommend doing it that way for the next step. Enlarge the hole stepwise to 0.210 inches. The pin that I used is a number 4 taper pin, two inches long, Fastenall part number 1169064. The small end is 0.210 and the large end is 0.247 inches. It takes a number 4 HSS hand reamer part number 0328880, also from Fastenall. Then pins cost about $2.50 and the reamer was about $30.00. Ream out the hole in the step From The Bottom so that the small end of the pin just gets to the top of the step. You want to end up with about a 1/4 inch on each side of the weldment/fixture in the fuselage. ( sorry, I don't have the plans here to put in the part number)
Take a 2 inch block of wood and drill it out to 0.210 inches and then use the taper reamer on the block. You now have a squared up block to slip the pin in and then drill and tap the narrow end about 1/2 an inch deep for a 4-40 screw.
After you have bondoed up the fuselage and repainted where the broken step has bent the corner of the fuse (another 3-4 hrs), insert the new step into the plane and set the clocking with the story stick.
Now, enlarge the hole in the bottom of the fuse so the taper reamer will fit and not be skewed by the fuse skin. Ream the weldment, step, plug all together until the reamer just comes up thru the top hole.
Insert the taper pin from the bottom up thru the fuse. I taped it to the end of a small piece of 1/4 20 threaded rod that I happended to have at the hanger. Then, use the rod as a punch to set the pin in place. I then had about a 1/4 inch of the top of the pin showing through the hole.
I then made up a 4-40 allen head screw, #4 lock washer, number 6 washer, and a small aluminum sleeve 5/16 inch diameter by about 3/8 inch long. The pic shows 1/2 long, but I ended up shortening it to make it easier to put the screw in the pin.
I then used some blue locktite and put the screw in place. The step was now rock solid. I'm going to wait a couple weeks before I redo the other side. I want to make sure nothing changes and it stays solid. I think it will. If it ever does loosen up, I can always re ream from below and remake the pin/screw fixture. Getting the hole thru the step without having to change the hole in the weldment of the fuse is the trick. One of my engineer friends recommended putting loctite on the pin before insertion. I didn't want to do that because you have no way of pounding out the pin from the top. There is just no good way to get at it. If I was building the plane again, and not retro fixing, I'd find a way to get more "mass" on the weldment. I'd have someone tig weld a 1/4-3/8 inch scrap above and below, then plug the step as above, then use a AN 4 bolt and use a reamer to finish the hole. I just don't think there is enough mass in the weldment with the inability to get a round hole with a regular drill.
Comments welcomed.
Dr Fred
N515FW
330 hrs
I understand some have used a straight reamer and a AN 4 bolt to fix the loose step. Too easy.
So, I purchased a couple of new steps and had them powder coated. My original ones are chromed. I decided to go with the powdercoat secondary to cost. I don't believe the chroming process had anything to do with the failed weld. There just wasn't enough material to hold the step in place.
First, I had to cut acess holes in the baggage floor. I did not put them in in the first place. I'd recommend installing some for those who are still building. Next, take the nut off and then I had to use a air grinder to cut the bolt to get it out. There isn't enough room to remove the bolt from the top.
Now, it was easy to pull out the tube and then slide in the new step. I used a story stick and referenced it off the flap on the other side to get the rotation correct for the new step. I then used an angled scriber to mark the top hole and came in from the bottom with a number 12 drill to mark the bottom hole.
Now, this hole is not at a 90 deg angle to the cylinder of the step. So, take a number 40 drill and drill thru from both sides. I then made up a drilling jig to hold the step.
I used a 6 inch number 40 drill to find the correct angle. It took wedges on the back of the jig to set the angle correctly. Then lock everything down so that it doesn't move. I have seen elsewhere where an alumninum block was inserted to help hold the bolt in place. Off to order a 12 inch bar of 1 1/2 inch aluminium rod to make a 2 inch long plug. Once I had that turned so that it would slide into the step, I drilled and tapped a 3/8 x 1 hole in the end of the plug so that I could slip it into the end of the step and set the depth. I thought that I might have to put the plug into the step to drill it, but found out that since I hadn't moved the drill fixture, all I had to do was to lay the plug in place and drilled thru it with the number 40 drill. I slipped it in the step and now I had a number 40 hole thru both the new step and the plug. I epoxied the plug in place with JB weld.
I then stepwise enlarged the hole in the step. I did this out of the jig and would not recommend doing it that way for the next step. Enlarge the hole stepwise to 0.210 inches. The pin that I used is a number 4 taper pin, two inches long, Fastenall part number 1169064. The small end is 0.210 and the large end is 0.247 inches. It takes a number 4 HSS hand reamer part number 0328880, also from Fastenall. Then pins cost about $2.50 and the reamer was about $30.00. Ream out the hole in the step From The Bottom so that the small end of the pin just gets to the top of the step. You want to end up with about a 1/4 inch on each side of the weldment/fixture in the fuselage. ( sorry, I don't have the plans here to put in the part number)
Take a 2 inch block of wood and drill it out to 0.210 inches and then use the taper reamer on the block. You now have a squared up block to slip the pin in and then drill and tap the narrow end about 1/2 an inch deep for a 4-40 screw.
After you have bondoed up the fuselage and repainted where the broken step has bent the corner of the fuse (another 3-4 hrs), insert the new step into the plane and set the clocking with the story stick.
Now, enlarge the hole in the bottom of the fuse so the taper reamer will fit and not be skewed by the fuse skin. Ream the weldment, step, plug all together until the reamer just comes up thru the top hole.
Insert the taper pin from the bottom up thru the fuse. I taped it to the end of a small piece of 1/4 20 threaded rod that I happended to have at the hanger. Then, use the rod as a punch to set the pin in place. I then had about a 1/4 inch of the top of the pin showing through the hole.
I then made up a 4-40 allen head screw, #4 lock washer, number 6 washer, and a small aluminum sleeve 5/16 inch diameter by about 3/8 inch long. The pic shows 1/2 long, but I ended up shortening it to make it easier to put the screw in the pin.
I then used some blue locktite and put the screw in place. The step was now rock solid. I'm going to wait a couple weeks before I redo the other side. I want to make sure nothing changes and it stays solid. I think it will. If it ever does loosen up, I can always re ream from below and remake the pin/screw fixture. Getting the hole thru the step without having to change the hole in the weldment of the fuse is the trick. One of my engineer friends recommended putting loctite on the pin before insertion. I didn't want to do that because you have no way of pounding out the pin from the top. There is just no good way to get at it. If I was building the plane again, and not retro fixing, I'd find a way to get more "mass" on the weldment. I'd have someone tig weld a 1/4-3/8 inch scrap above and below, then plug the step as above, then use a AN 4 bolt and use a reamer to finish the hole. I just don't think there is enough mass in the weldment with the inability to get a round hole with a regular drill.
Comments welcomed.
Dr Fred
N515FW
330 hrs
