Thread repair

Bentwings said:

Is it possible to install a3mm heli coil in a 4 mm threaded hole . Will the new 3 mm screw hold reasonably well?

The hard part I see is that the 4mm threads will not be completely drilled or so the heli Coil insert may be hard to insert . This is through hole-I could possibly drill one side just enough oversized so the insert may go in easier
Byron

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SmithDoor said:

heli coil can fail.
I drill & tap for a threaded plug install plug with locktie . Then after the locktie has setup then drill and tap a new hole. thought of that too I even though I could

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Bentwings said:

I thoughtnofvthstvtoo I even thought it would be possible to put a spot of TIG weld on the end of the new lug to make sure it stays in.

The issue that complicates it is that I have such limited shop here at home I have a drill press and vice so I can drill holes I thought about using an aluminum screw and drill and tap . Loc tite of course .

There is a possibility that JB weld might work as there is not much force on the screw., the guy on project farm YouTube did a test on larger screws 5/16 I think that worked for him . There are many different solutions for this mess I got some heli coils and an installation tool coming so I’ll give it a try I YHINK . These are shaft collars . I cut off the clamp part now I’m trying to hold it so I can drill for 3mm on the other side it would have been so easy if I could get out to the shop. I even got around not using a counter bore by just milling a spot facing a flat on the blank side ofvthe collar it was quite a trick to locate and spot this with an end mill in my dumb drill press but it did work Cutting the cap off with a Dremel saw was another challenge I have fine aluminum dust all over I used tap magic and the dustgot in what little hair I still have . I had to use dawn and the back brush to remove it y’all probably think I’m nuts but I’ll do about anything if it’s safe. I even used a little duct tape around my safety glasses to keep the dust out of my eyes

By the way the dremel saw kit does work but the arbor is junk if a stiffer arbor and left hand screw mount were used and you are real gentle the things will cut soft stuff pretty nice I surely don’t recommend doing this operation by hand. Don’t run the saw at high speed and use cutting oil .

Thanks for the the tip I’m goingvto keep trying my sample had 3mm screws but the reorder has 4mm . No spec was given so that’s why the mismatch I got som 3mm stainless studs so I may use these instead of screws since there is only a flat I don’t need to worry about that . I have 3mm nuts too
Byron

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ChazzC said:

I've never used them, but they will give the best holding for soft materials and best reserved for those applications that need this additional strength due to their cost:

View attachment 137416
Also, while you may be able to use a hammer & punch to lock the larger sizes, for best results with the small ones (particularly as small as M3) you will probably need the installation tools ($55, but again if they job requires the extra strength and there's no other way . . .).

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Bentwings said:

ive used the larger sizes of hers and they do work very well I have some nut sett that I used on my fiberglass willys interior . These worked ok too . The 3mm heli coils will be the smallest I’ve ever used. The collars are anodized aluminum so vein small makes them very difficult to precision weld. If I screws a r mm aluminum
Screw in and just spot TIG welded the end I think they would be ok the give away is the collar is counterbored such that it would cut into the screw. I initially ground some screws Dow to clear the c bore also considered cutting a groove in the hub of the part to clear the screw . The screw is obviously weakened but there realy is not much clamping force on them . The one sample part hat had the 3mm screws worksvok so I think the heli coils will be ok I’ll have to install them deep in the collar but at least the screw will now clear the hub. Overall the idea was good if the purchased parts would have been consistent . My fault for not noticing the difference in screw size untill after the fact . The collars have very deep c bores so even the lower part of the cap screw head interferes. Had I had cad models I would have seen he problem right away . Well the heli coils should be here today so I’ll try them out. One ofvthe revues noted the install tool was not included so rather than add another issue I got the tool also breaking the tang off should not be a problem . This all started as a result of set screws or grub screws do not grip the shaft properly I had to provide for adjustable positioning ofvthe flywheels had I known there might be an issue I could have cut a small grove in the shafts and saved a huge problem. I’ve never liked set screw retention for pulleys and flywheels. The shafts are only 6 mm so pretty small to begin with . I see lots of other steamers with set screws but little is said about issues. I had a tough time getting the flywheel off the shaft after the screw cut a scratch in the shaft . The fit is very tight so it took a lot of careful refitting I’m just glad or fortunate that things were not spinning very fast or with a lot of power I wish I could have used the wedge clamping often used in in industry. Even a small shaft like this would have worked well . I don’t know how small a releasing taper can get but if our lathe gets back together I’m going to try and scale down something like Morse taper I may have to come up with a mini puller too slotting a 6mm shaft would be pretty tough . Even a micro jetway would be a challenge I think. Then a micro broach would be the cap . LOL

No Amazon delivery yet the stuff is out for delivery sometimes they stuff it in the mail box down the street. It’s 97 degrees and very humid so I may wait untill later to walk down there
Byron

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• easy to install and if fails you are basically were you started and can still use other options.
• requires odd size tap and you need to make (or get) the studs.
• Trick is to match outer diameter of stripped thread with tap drill size of replacement.
• It requires less space than a helicoil.

timo_gross said:

I saw some studs once for the scooter manifold. The threaded holes fail often on older engines. So they use a tap that fits just into the stripped hole. e.g. M7x1 for an M6 hole.
The M6 has the same outer diameter as the M7x1 tap drill size.
So the guy just threaded the sripped hole. Inserted a stepped stud. M7x1 on the one end and M6x1 for the other end.

• easy to install and if fails you are basically were you started and can still use other options.
• requires odd size tap and you need to make (or get) the studs.
• Trick is to match outer diameter of stripped thread with tap drill size of replacement.
• It requires less space than a helicoil.

View attachment 137431
p.s. if it is replacing a set screw, can you not just go one size up and grind the tip of the srew down to the "original size?

Greetings Timo

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timo_gross said:

I saw some studs once for the scooter manifold. The threaded holes fail often on older engines. So they use a tap that fits just into the stripped hole. e.g. M7x1 for an M6 hole.
The M6 has the same outer diameter as the M7x1 tap drill size.
So the guy just threaded the sripped hole. Inserted a stepped stud. M7x1 on the one end and M6x1 for the other end.

• easy to install and if fails you are basically were you started and can still use other options.
• requires odd size tap and you need to make (or get) the studs.
• Trick is to match outer diameter of stripped thread with tap drill size of replacement.
• It requires less space than a helicoil.

View attachment 137431
p.s. if it is replacing a set screw, can you not just go one size up and grind the tip of the srew down to the "original size?

Greetings Timonice picture! You can clearly see the reduction in diameter between threaded areas just enough to clear the hubs so I YHINK the heli coil will be the best option the trade off is that I won’t have a hex to tighten with. Over all just a simple thread mistake has caused a nightmare continuing backwards ifvyhe hubs would have had caps as connecting rods did , all would have been good and sun Mpls . I suppose a shallow grove in the crank shafts would have allowed screws to grip without marring the shaft

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Bentwings said:

had I for seen this I could have done that myself and avoided this mess . As usual hind sight repairs the mistake LOL I DID CONSIDER THIS as there are ARE LOTS F STEAMERS THAT SECURE ECCENTRICS with set SCREWS. IE GRUB DCREWS and things seem to work forever . I suspect that many examples don’t get run often or very for long. I like to run my models long and often my old Lionel electric steam loco probably would have been a candidate for complete o’ haul just as real steam loco s get by the time began learning about the iron ore trains near our house
It’s a good thing electricity was a good deal cheaper than today I had real iron ore and copper ore in my ore cars even rusty nuts and bolts in my scrap load cars we didn’t have aluminum beverage cans bak then they were real”tin” cans so they didn’t squash easily
Byron

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Lloyd-ss said:

Timo, I like the picture of the double-ended stud in your post. When the threads look good under magnification, with no tearing or irregular crests, it is a satisfying sight.

One thing I forgot to mention about helicoils is that it is very important to tap the hole deep enough with the special helicoil tap. If not, the helicoil will taper in at the bottom and the bolt will lock up in it and then you have a mess on top of a mess.

Edit: And I also forgot to mention that the special spring loaded tool (like a spring center punch) for breaking off the helicoil insertion tang after it is installed, is called a tang-banger.
Yup, that's the proper technical name.

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timo_gross said:

..................................

I just remember when I accidently made the holes in a casting too big. I turned down the head of an M4 screw to 5 mm on the lathe and threaded an M5x0.8 on the remains of the bolt head. I ended up with a short length M5 incl. 3mm hex.

Greetings Timo

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