Using threaded insert

In the past I have used blind nuts for my 4-40 engine mount bolts. I have had a some spin out from tighting them to tight. I was wondering if the Dubro 4-40 size threaded inserts would have better luck. Who has had any experience with them?

Quite a few hits when I did a search of the forum:

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=2139&forum=DCForumID1
http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=4473&forum=DCForumID1
http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=4831&forum=DCForumID1

What about drilling a 4-40 size hole for the blind nuts, then a larger hole for the threaded inserts and use them both? anyone try this?

I suppose it would work, but the threads on the inserts and on the blind nuts would have to be "in synch".

When I had British Motor-Cycles 30 or so years ago these inserts were very popular, used to repair the thread for the spark plug.
Heads were made of Aluminium ( actually.. Dural... Durable Aluminium ???? )
Ham-fisted Bikers would tighten the spark plug too much and strip the thread for the plug..... Of course, I, myself NEVER did this......
Easilly fixed.. buy a kit of a tap and a spring-like device, which formed the new thread... drill and tap for the spring and you have a bullet-proof thread which you will have to work really hard to break.........
These come in kits for various size threads... go to a good Hardware Store which speciallises in nuts and bolts.....

Just recently, at work, I made some 5/16 threads into aluminium using this method... Ham-fisted machine operators have been screwing bolts into this 2 or 3 times a day for the past 5 years.... NO failures.

Sometimes blind nuts fail just because they are kinda trashy to begin with. But most of the time it is simply because we apply more torque than is required to the fastener.

I have (somewhat) eased the problem with use of a "T-" shaped hex key. It has been formed from one piece of wire, such that excessive torque allows handle end to deflect. Poor man's torque wrench.

Having had indifferent results--others report much success--with threaded inserts, I cheated recently. ARF Flite Streak, drilled motor mount locations to .250, installed hardwood dowels. Drilled mount holes again. Counter-bored, from left side of fuselage, for threaded inserts. Drilled just deep enough they are flush with fuselage side. Pretty tight hole, although not as tight as specified, suitable amount of epoxy.

Seems to work just fine. And is maybe the technique I was missing along, as previously I had installed these things from the engine side of maple motor mounts. If so, consider me humiliated...

>Sometimes blind nuts fail just because they are kinda trashy
>to begin with. But most of the time it is simply because we
>apply more torque than is required to the fastener.
>
>I have (somewhat) eased the problem with use of a "T-"
>shaped hex key. It has been formed from one piece of wire,
>such that excessive torque allows handle end to deflect.
>Poor man's torque wrench.
>
>Having had indifferent results--others report much
>success--with threaded inserts, I cheated recently. ARF
>Flite Streak, drilled motor mount locations to .250,
>installed hardwood dowels. Drilled mount holes again.
>Counter-bored, from left side of fuselage, for threaded
>inserts. Drilled just deep enough they are flush with
>fuselage side. Pretty tight hole, although not as tight as
>specified, suitable amount of epoxy.
>
>Seems to work just fine. And is maybe the technique I was
>missing along, as previously I had installed these things
>from the engine side of maple motor mounts. If so, consider
>me humiliated...
>
>Dan
Dan alluded to trashy material but did not mention any source. I will not either except to say that it's a major supplier and not Dubro. This manufacturer uses a very soft alloy for a lot of it's accessories and you would do well to buy another brand if you need long term durability. I've seen the threads on some of these let go simply from normal vibration from running. I personally try and get the steel one if possible unfortunately these have a larger footprint but I can live with it. Dennis

Seems to me you guys are having a lot of your problems because you mount your engine directly on the maple beam. I always cover the top of my maple with a piece of 1/32 HARD aluminum epoxied on and held at each end with a very tiny screw for extra insunance. The size of the plate is about twice the area of the angine lug and ir prevents the maple from squeezing and being a springy foundation for you engine to sit on. Thats were you get a lot of loosening and bolt breakage.I never seem to have my engines come loose and I do sometimes use lock nuts just to be safe but just as often I dont bother and I have no problems . Keith Varley

>Easilly fixed.. buy a kit of a tap and a spring-like device,
>which formed the new thread... drill and tap for the spring
>and you have a bullet-proof thread which you will have to
>work really hard to break.........
>These come in kits for various size threads... go to a good
>Hardware Store which speciallises in nuts and bolts.....

Dave,

The most common brand name for theis is "Helicoil Thread Inserts". And I'm sure McMaster Carr would have them. Don't tap threads into aluminum without them... Seriously, they are vastly superior in strength and durability compared to tapping the bare metal. Really a wonderful product.

Hammer your blind nuts into good hard motor mount (Read: maple) material, and weep some hot (use a $cote gun) 2 hour epoxy over and around them. Do this with the 4-40 bolt in place.

Don't worry about getting the bolt out when everything dries. The torque you put on a screwdriver or Allyn wrench far, far exceeds whatever gripping power the 'poxy will have.

I like to put the blind nut in place, then put epoxy between nut & hardwood (Use a tooth pick). Then slowly tighten down the blind nut with a wrench. (I have had them fail by hammering them down). Spred a little epoxy over the edges of the blind nut & your done.

I have used inserts when blind nuts failed. Great fix.

Great replys! Now I would like to give a example of installing blind nuts from what I have learned here. Please be nice grading my report. Giving me an A+ would be nice but that would be to nice. I,m just a beginner.

This is not to detailed so here it goes. When you have your mounting holes drilled to size, say for a 4-40 bolt and blind nut. At the blind nut side use a somewhat smaller dowel rod, or drill bit and wrap and glue with Ca some sandpaper around it, say 250 grit. Now turn the sanding rod in the blind nut hole to ruffen it up and make it just a bit larger then the drilled hole,"Not to large." This I belive will give the epoxy room to grab onto. Also ruffen the outer part of the nut also, being carefull not bending up the barbs or marking them up. Is it likely to have this done this way, or is a tighter fit better? I just thought that if it's to tight that their would be no room for the epoxy to grab on to.

I use a 5/32 drill bit to relieve the back side of the mounts for the blind nuts. I cut a piece of brass tubing just the right length to use as a drill stop for a hole depth of about .120

After the holes are drilled use a C clamp and scrap ply on the engine side to seat the blind nuts.

I'm having a heck of a time getting answers to my queries lately.

As posted earlier, is counter-boring from side of motor mounts away from engine the way this is being done by those who have had success?

And it seems that for my personal needs, answers have veered somewhat. Look, standard hobby shop blind nuts are all trash. I don't care about all the dandy tricks for getting them installed; they are still going to fail and it doesn't have anything to do with how well or poorly they have been installed.

In fact, knowing in advance the things will lose grip on a fastener I make an extra effort toward installing them such that they are easier to remove and replace with a new blind nut.

Further, other than a motor mount application, I have devised terribly clever, totally ingenious ways to eliminate blind nuts in the rest of the model.

If one of you comes up with the Hot Deal for use of threaded brass inserts, I'm set...

Dan, could you give a better explanation on your technique of what you mean in detail on counter boring on your first post. Thanks!

Having had indifferent results--others report much success--with threaded inserts, I cheated recently. ARF Flite Streak, drilled motor mount locations to .250, installed hardwood dowels. Drilled mount holes again. Counter-bored, from left side of fuselage, for threaded inserts. Drilled just deep enough they are flush with fuselage side. Pretty tight hole, although not as tight as specified, suitable amount of epoxy.

Seems to work just fine. And is maybe the technique I was missing along, as previously I had installed these things from the engine side of maple motor mounts. If so, consider me humiliated...

Dan

Greg,

Hmmm, that was pretty clear to me, but then again I wrote it.

Ignoring the hardwood plugs, meant to reinforce whatever wood Top Flite used for motor mount sticks in the ARF Flite Streak, I drilled the four locations for motor mount bolts and I believe they were drilled to 1/8".

On the side opposite the motor--left side of the fuselage on a profile--I drilled these holes over-size to accomodate brass threaded inserts. The holes are just deep enough to allow full insertion of inserts, meaning that from the motor side all you can see are 1/8" holes.

Inserts were then installed with epoxy.

This made the installation more like one sees with the dreaded blind nuts, the only real difference being depth of the fastener and a higher quality, longer lasting piece installed.

The way I had done it previously was simply to work from the motor side of maple bearers, drilling for and installing threaded inserts flush with top of the bearers. Just such an installation failed when I crashed my first Impact, although it may have been a good thing the inserts pulled free of the mounts instead of breaking the engine in half.

Same type of installation failed during run-in of my 72, although this time vibration first loosened the inserts and then proceeded to pull 'em right out of the maple. The test stand was a temporary piece, I am quite willing to admit it was slapped together as it would not be needed after an hour or so of running the new motor. But it was a surprise to see epoxied inserts get pulled from what originally were pretty tight holes.

Thus it was that most recently I installed threaded inserts from the far side of the mounts, figuring they would be a lot more secure.

Again, if I come off as whack job when it comes to the first two tries with threaded inserts, please be gentle. Everybody knows I am a SNAG (Sensitive New Age Guy).

>>Everybody knows I am a SNAG (Sensitive New Age Guy).<<

Uh, huh. Yea, Right...

Hi Dan; I have used the brass inserts in several installations where I was changing from one engine to another where the mounting holes were different. This was in full fuse jobs where I could not get access to install blind nuts. I just drilled from the motor side and installed with epoxy. Never had a problem. But I wasn't using a 4 stroke shaker either.

I have a .12 motor going on a TomCat profile. I went ahead and finished the paint job before I drilled out the engine mounting holes, because I was waiting for my asp engine from overseas. I do however just got in today. I drilled some smaller holes and it looks like the 4-40 threaded insert will be a little to wide. I don't want to take a chance on it splitting the edge of the hardwood mount, so I was wondering if the next size down insert would be to small. I,m waiting for my order from Dubro for some extra inserts. Would the 6-32 be ok, or the 8-32 ones. I,m getting them both. Thanks!

I would *consider* drilling the holes and tapping them for a 10-24, then add epoxy and screw in some thoroughly cleaned brass machine screws. Flush off both sides, then drill and tap for the 4-40's. The problem with the typical brass inserts is that by the time you drill and install the insert, there's very little maple left. Maybe not a big deal for the front ones, but not good at all for the rear ones.
The alternative, and what I will probably do on an ARF Flite Streak that I just got, is to put the bolt heads on the far side from the engine, and elastic lock nuts on the engine side (washers on both sides). An aluminum or even steel plate under the bolt heads and under the engine lugs would be an improvement. (for Dan's eyes only) Steve

Well changing my ideas is always happening. I think on this plane, even with a .12 motor I will drill all the way through the fus. Use blind nuts, then over that tighten agaist the blind nut a nylon lock nut. Might not look like I first wanted. But do you think this will hold up for the .12? Has anyone used this method?

>The problem with the typical brass
>inserts is that by the time you drill and install the
>insert, there's very little maple left.

The method I saw posted by Phil gets around this problem. What you do is mount the inserts in the middle of the motor mount wood. This means, of course, that the engine won't fit between the bearers until you carve away some of the wood on the top inside part of the bearers. Then the engine will drop in, with some of the wood projecting under the crankcase, and plenty of wood around the inserts.

I think part of the problem with this discussion is there are at least two sizes of these threaded inserts floating around, and it wasn't too long ago that I saw both sizes in a hobby shop.

Whoa! Preceding sentence sucks! I have seen 4-40 and 6-32 threaded brass inserts in two different outside diameters but same internal thread size. The 6-32 pieces in particular were huge and I can see where installation of them in a typical maple stick would be problematic.

However, the smaller sizes are fine. And Steve, the good 'uns are available at McLendon's! By the each.

Several years ago I was the rep for Heli Coil. I was fortunate to get a lot of "sales samples" 4/40 and 6/32 kits. Not only are they superior to any other thread insert they come in different lengths, 1/8", 3/16", 1/4" etc. I use them today on many applications. If you are trying to fix a motor mount, drill and tap for heli coil insert and then use JB Weld to strengthne the bond. I just smear some JB Weld into the hole , screw in the insert and let it cure. If need be just chase the 4/40 or 6/32 thread with a tap and you are done. The strengh is beyond belief.

>Several years ago I was the rep for Heli Coil.

Okay, so you would be the guy able to tell us where to buy them, correct? We have several retail/wholesale fastener operations, Tacoma Screw Products having the most interesting name, along with quite an array of neat stuff.

Would they be a logical source, or do we have to narrow our search somewhat?

From your description, and at least having a pretty good idea of what a Heli Coil (caps?) is, sounds like the hot tip.

>>Several years ago I was the rep for Heli Coil.
>
>
>Okay, so you would be the guy able to tell us where to buy
>them, correct? We have several retail/wholesale fastener
>operations, Tacoma Screw Products having the most
>interesting name, along with quite an array of neat stuff.
>
>Would they be a logical source, or do we have to narrow our
>search somewhat?
>
>From your description, and at least having a pretty good
>idea of what a Heli Coil (caps?) is, sounds like the hot
>tip.
>
>Dan
dan I said rep. that is a manufactures sales rep. I will research it and get back
dick

>>>Several years ago I was the rep for Heli Coil.
>>
>>
>>Okay, so you would be the guy able to tell us where to buy
>>them, correct? We have several retail/wholesale fastener
>>operations, Tacoma Screw Products having the most
>>interesting name, along with quite an array of neat stuff.
>>
>>Would they be a logical source, or do we have to narrow our
>>search somewhat?
>>
>>From your description, and at least having a pretty good
>>idea of what a Heli Coil (caps?) is, sounds like the hot
>>tip.
>>
>>Dan
>dan I said rep. that is a manufactures sales rep. I will
>research it and get back

A google search "helicoil" will send you to thousands of industrial suppliers. just ask for 4/40 or 6/32 in different lengths.
>dick

>>>>Several years ago I was the rep for Heli Coil.
>>>
>>>
>>>Okay, so you would be the guy able to tell us where to buy
>>>them, correct? We have several retail/wholesale fastener
>>>operations, Tacoma Screw Products having the most
>>>interesting name, along with quite an array of neat stuff.
>>>
>>>Would they be a logical source, or do we have to narrow our
>>>search somewhat?
>>>
>>>From your description, and at least having a pretty good
>>>idea of what a Heli Coil (caps?) is, sounds like the hot
>>>tip.
>>>
>>>Dan
>>dan I said rep. that is a manufactures sales rep. I will
>>research it and get back

DAN WHAT SIZE HANDLE DO YOU USE? LET ME KNOW.
>
>A google search "helicoil" will send you to thousands of
>industrial suppliers. just ask for 4/40 or 6/32 in different
>lengths.
>>dick

Dan, I would expect McLendon's or any decent ACE or TruValue Hardware would have Heli-Coils in limited sizes. Motorcycle and automotive shops have them for sparkplug hole repairs. I wouldn't be surprised if you have 14mm ones in the parts department where you work. Tacoma Screw or Hi-Strength Bolt should have a better supply than the hardware store. Boeing Surplus probably has a bucket of them someplace, for about $.50/pound. I would describe them as a tension coil spring made from diamond shaped (<>) stainless wire, with a 90 leg on one end. There are self-locking types, that will keep your bolts from coming loose, and they are frequently installed with LocTite. I never thought about using these in wood, but they should work ok, especially if you harden the tapped hole in maple with thin CA. Hmmmmm. I might try that in the Junkers Gobbleswantz engine swap. :> Steve

I'm not a fan of blind nuts...but do you guys use a lock washer with them?

>>>>Several years ago I was the rep for Heli Coil.
>>>
>>>
>>>Okay, so you would be the guy able to tell us where to buy
>>>them, correct? We have several retail/wholesale fastener
>>>operations, Tacoma Screw Products having the most
>>>interesting name, along with quite an array of neat stuff.
>>>
>>>Would they be a logical source, or do we have to narrow our
>>>search somewhat?
>>>
>>>From your description, and at least having a pretty good
>>>idea of what a Heli Coil (caps?) is, sounds like the hot
>>>tip.
>>>
>>>Dan
>>dan I said rep. that is a manufactures sales rep. I will
>>research it and get back
DAN WHAT SIZE HANDLE DO YOU USE? LET ME KNOW.
>
>A google search "helicoil" will send you to thousands of
>industrial suppliers. just ask for 4/40 or 6/32 in different
>lengths.
>>dick

dick byron

Dick,

My, oh my! It is the time of giving, sharing and caring, is it not?

Hmmm, there is no handle with me at the moment. The standard "Hot Rock" is slightly too tight for comfort. Ted's "Plus" handle was too loose, his standard size, adapted to my hand, needs be relieved nearly 1/8" top and bottom of grip.

I can get exact measurements by Monday morning.

And "Merry Christmas" to you too!

>>>>>Several years ago I was the rep for Heli Coil.
>>>>
>>>>
>>>>Okay, so you would be the guy able to tell us where to buy
>>>>them, correct? We have several retail/wholesale fastener
>>>>operations, Tacoma Screw Products having the most
>>>>interesting name, along with quite an array of neat stuff.
>>>>
>>>>Would they be a logical source, or do we have to narrow our
>>>>search somewhat?
>>>>
>>>>From your description, and at least having a pretty good
>>>>idea of what a Heli Coil (caps?) is, sounds like the hot
>>>>tip.
>>>>
>>>>Dan
>>>dan I said rep. that is a manufactures sales rep. I will
>>>research it and get back
I WILL BE WAITING.
>DAN WHAT SIZE HANDLE DO YOU USE? LET ME KNOW.
>>
>>A google search "helicoil" will send you to thousands of
>>industrial suppliers. just ask for 4/40 or 6/32 in different
>>lengths.
>>>dick
>
>
>dick byron
>
>
>Dick,
>
>My, oh my! It is the time of giving, sharing and caring, is
>it not?
>
>Hmmm, there is no handle with me at the moment. The standard
>"Hot Rock" is slightly too tight for comfort. Ted's "Plus"
>handle was too loose, his standard size, adapted to my hand,
>needs be relieved nearly 1/8" top and bottom of grip.
>
>I can get exact measurements by Monday morning.
>
>And "Merry Christmas" to you too!
>
>
>Dan
>

Ron B.
F4Fguy

Dan,

If you absolutely,positively want to use the brass inserts,the way you describe(counterboring the back side)is the way to do it.I still don't like it because of the loss of cross section in the mount.A better way would be to use short Helicoils installed from the back side.The Helicoil thickness is only one thread depth greater than the the bolt,leaving a lot more "meat".This works well even without using the"Helicoil"tap.Just counterbore the hole to the o.d. and depth of the Helicoil,grease up the bolt,fill the hole with epoxy,stick the bolt through the hole and the Helicoil,and pull the insert in place with the bolt,in much the same way I presume you did with the brass insert.I don't know about your area,but our local "ACE"hardware store has a good selection of Helicoils.One other thing,in another life I ran a lot of tests on thread inserts (do the term aluminum engine ring a bell?).There are lots of them out there,but only two were satisfactory.Helicoil was one,the other was actually better,but wouldn't work too well in wood,as it is installed with a thread forming tap swaging it in place.

>DAN WHAT SIZE HANDLE DO YOU USE? LET ME KNOW.
>>
>>A google search "helicoil" will send you to thousands of
>>industrial suppliers. just ask for 4/40 or 6/32 in different
>>lengths.
>>>dick
>
>
>dick byron
>

Dick,

While this simply must be more accurate than required, a favorite CL handle measures 3.164 inches between upper and lower protuberances.

(Once one gets in the habit of measuring with a dial caliper...)

Sorry for the delay.

Use a piece of 2mm thick ms plate x say 30mm x 7mm and tap it 4-40 or 5-40 and your problem is solved.