Texas 3D

My Feedback: (16)

Let's say I am changing engine mounts. What is the best way to tap the holes in the firewall, so they have enough strength if there is a need to drill right next to the old hole due to hole location ? Will a simple wooden dowel and epoxy do the work ?

MinnFlyer

My Feedback: (4)

Pluging the hole with a wooden dowel would work fine for filling the hole, But regardless of whether or not there was a hole there before, I wouldn't tap the firewall. Install blind nuts behind it.

Texas 3D

My Feedback: (16)

that's exactly my fear ! If the old hole is to close to the new hole, the blind nut might only grab on one half because on the other there is that hole. No if I tap it with a dowel, it should have something to grab, but will it hold ?

hattend

My Feedback: (20)

But if you plug the old hole with a dowel and can drill straight, the blind nut will go in the new hole with no problem. Drill the hole for the blind nut almost the same diameter as the outside of the blind nut, it'll seat very easily. Then dab some epoxy on the blind nut to help hold it.

If that's not what you wanted to hear, I guess I don't understand your problem. I definitely wouldn't tap the hole to hold the engine on. The load is not spread out enough that way IMHO.

banktoturn

Texas 3D,

I think you are using the word 'tap' to refer to plugging the old hole. Usually, to tap a hole means to cut threads in the hole, so that a screw can be driven into the hole. I assume you just want to know whether the spot where you plugged a hole with a dowel and epoxy would be strong enough to support a blind nut installed right next to the old hole. If you get a tight fit and a good glue joint all the way around, I would guess that it would be strong enough, but I would still prefer to add a layer of light ply to install the blind nut in, if you have room.

banktoturn

Texas 3D

My Feedback: (16)

of course I mean plug and not tap. Don't know what happened here :bananahea Could it be because I am German ?
Thanks for the input, and sorry for the confusion.

Giant Scale

If you can get access to the back of the firewall, I'd use a nylon insert lock nut instead of a blind nut. Use a washer or small piece of aluminum against the firewall under the nut to help spread the load.

Lee Belew

My Feedback: (2)

Ulf

when drilling the hole in the firewall that is to be plugged, drill it a litter smaller than the dowel to be inserter and then hammer the dowel into the hole. round the dowel a little on the end before forcing it in the hole. Make the dowel the thickness of the firewall. once the dowel is forced into place soak both the inside and outside of the firewall where the dowel was inserter with thin CA this will soak deepen into the wood than the epoxy.

I fly at Fort Bend R/C in Rosenberg, and Live in Sugar Land.
Lee

Woody_100

I'm rebuilding my Cub after a crash, and after reading the above I need to ask....
Should I glue all the wood nuts in place. At the moment, I've just pressed them into the wood, and they hold well at the moment, after a few flights with vibration/loads etc. I'm concerned they might a) come loose, b) fall out after future removal of the screws.
What do you experienced folk think I should be doing?

Lee Belew

My Feedback: (2)

Woody_100

If you made the holes for the blind nuts a little small so that were really tight to seat in place You are ok. They will stay. If you make the holes the same size as the part of the blind that goes through the firewall or if they are a little tight you may need to ca them in place. Fill the threads with vaseline before CA the nuts in place.

Lee

Woody_100

Cheers Lee, will do

Texas 3D

My Feedback: (16)

Thanks for the tip Lee ! I fly out at Scobee !