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Building Tips and technical articles. => Building techniques => Topic started by: bob whitney on January 31, 2023, 02:10:53 AM
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i have had trouble with the newest 4-40 blind mounting nuts spinning . ACE HARDWARE sells 3 mm allens .they are almst the same size as 4-40's .the 3 mm blind mounting nuts are almost twice the size of the standard 4-40 .infact u might need to trim back the side closest to the motor for a four bolt back plate
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i use the dubro 4/40 they are small in diameter and dont come loose,i bought a pack of 20 from the hobby shop here....Doug
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I've used a lot of the 3 mm ones and liked them well enough. My entire life I've had occassionall problems with the 4-40 blind nuts, usually in the motor mounts when they get fuel soaked over time. Not sure if the 3 mm are any better because I haven't removed a lot of stuff I've used them on. As some point, I started epoxying a 1/8 piece of wood over the back of the blind nuts in an effort to stop them from being pushed out. I can't really say if that helped or not, because I probably haven't removed an engine more than a couple of times since I started doing that. I'm not a fan of the blind nut, but still use them because I haven't had a better substitute for tight areas.
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The only time I have had any issues with blind nuts from DuBro is when I failed to run a tap through them first to remove any flashing and taper the entrance with a Dremel before inserting them. I have used the old, really old, method of soldering "visually capable" nuts to a brass plate and using small screws to keep it in place, and putting on a plywood cover as has been mentioned. Now that I am 100% electric, I doubt that I will have any more oil soaking to deal with. One thing I have seen on a profile, but not tried myself was drilling a very small hole in the flats of both nuts and inserting a wire between them to keep them from ever rotating.
Ken
ps - another thing I did "back in the day" to reduce oil soaking was to bush the mounts with brass (today I would use aluminum or CF) tubing.
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I have also had to run a tap thru them to clean up the threads. I seat blind nuts with epoxy, and get a bead of epoxy around the barbed flange. I never had one come loose. For oil soaking protection, I coat the hole with epoxy, using a pipe cleaner to get a thin layer of epoxy in there.
Another problem that sometimes shows up with blind nuts--the threaded barrel section is not always perpendicular to the barbed flange. If you install it so that the flange is in contact with the wood, all the way around, you might find that the screw has to go in a bit slanted to get it in at all. So, before you get everything in place, run a long screw thru the blind nut from the back side and see if it starts binding up before it gets all the way thru the hole.
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Another problem that sometimes shows up with blind nuts--the threaded barrel section is not always perpendicular to the barbed flange. If you install it so that the flange is in contact with the wood, all the way around, you might find that the screw has to go in a bit slanted to get it in at all. So, before you get everything in place, run a long screw thru the blind nut from the back side and see if it starts binding up before it gets all the way thru the hole.
y1 y1
Jim - I have had this happen more times that I would like. I don't press the nut into the hole, I pull it with a long bolt with a large washer on top. Leave the bolt in till the epoxy sets but not hardend then gently remove it. You have to use some tapping to get the tabs into the wood but having the bolt do the final pull really works. I also found that putting the bolts back in after the epoxy is cured with a couple of washers to simulate the motor and leaving them there to keep crud out of the holes really helps.
Ken
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Hey Bob! Jim Carter here from Titusville. Just a thought ... you might want to take a few minutes and try the blind nuts, #602-50, from RTL Fasteners. I've been pleased with them although the barrel/shank is a bit shorter than the Dubro but they're not as big, overall, as some that I've received from Brodak, the BH-265.
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I've been very pleased with the blind nuts I get from RTL.