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02-27-2009, 05:32 PM #1
How should you remove Helicoil thread inserts?
My beautiful fixture is ruined if I can't dig these f'n helicoils out and replace them with the free-running kind.
I bought "locking" helicoil inserts because I need them to stay put and didn't want to put a ton of torque on the bolts. Helicoil advertises these as retaining locking torque over many assembly cycles. Well, my experience has been quite a bit different. The inserts shredded my stainless steel bolts and on the third assembly cycle they locked the bolt right up, regardless of gobs of anti-seize grease. I drilled the head off two bolts and the first one came out and pulled the helicoil insert halfway out so I could unwind it. The second one seized so hard that when I put vice grips on the threads, I twisted the bolt right off.
What's the best way to extract helicoils? I'm hoping I won't destroy the STI threads in the fixture.
Why in the hell did these locking helicoils fail so miserably do to what they were advertised to do? Was it the stainless bolt on stainless thread insert that caused galling or something? Has anyone else used these successfully?
02-27-2009, 05:55 PM #2
02-27-2009, 06:05 PM #3
I'd drill out the mess, aiming for a hole just a little smaller than the helicoil tap drill, then pick out the remains. Hopefully you can reach the hole and get lined up on it using the mill. Start the drilling with an endmill to ensure the drill doesn't walk.
Do you have to use a stainless bolt?
02-27-2009, 06:20 PM #4
I've had good luck removing free runing coils with regular ez-out's. Never tried to remove any locking coils yet, but might work.
02-27-2009, 06:23 PM #5
use dry lube inserts for stainless screws
Heliciol makes inserts with dry-lube coating for stainless screws.
The inserts are black not red like the normal locking inserts.
Stainless screws are prone to galling, not a good choice for reuse.
Ultra Coat screws from Mc Master are good steel screws for fixture use.
To remove a helicoil drill out any broken screw at minor dia.
Use a extra fine center punch to force end of the top coil
to the center of the hole. Grab with needle nose and pull straight out.
It will unwind out of the hole.
02-27-2009, 06:26 PM #6
rklopp, I got the bolt drilled out. Now I'm going to try to extract everything peacefully and move on to the free-running helicoils.
I guess the thing I didn't have to use was the stainless steel helicoils. I didn't think about it when I ordered them, and got stainless so they wouldn't go to rust.
I'll post pics of how this job has to work. It's a fun story.
The whole problem is that I need to use the part's bolt pattern to hold it down for 3 machining operations. The bolt head can only have a length of .062 or thereabouts.
SO, I chose to use stainless steel "sidewalk" bolts that are common within hurricane's reach for boarding up windows. It's a stainless steel 1/4-20 bolt with a .750 diameter x .125 head, and a phillips drive.
I turn the sidewalk bolts down to .495 diameter and .06 head length and I've still got enough phillips to drive them. Well, that doesn't really work out either. :>
The fixture was nice though...
Then it gets assembled to a top plate and sits in the mill just like this, with some O-rings in the grooves:
The fixture is for two different parts, derby covers for H-D motorcycle engines. 5 hole pattern is for the twin cam motor, 3 hole pattern is for the evo motor.
Most of the reason this is difficult is because they want the derby covers made out of 3/8" thick aluminum plate. I'll post a pic of one when I get back from the hardware store :/
02-27-2009, 06:29 PM #7
You're supposed to use an anti-size compound.
I would only ever fit these (locking) as 2nd choice in a once only assemble (for shake resistant anti-vibration applications).
For 1st choice I'd go with normal threads and use loctite 222.
We use a lot of aluminium fixtures (for the cnc mills) and use M6 and M8 threads for retaining billets/clamps etc.
These are plain threads and quite often only get tired after a thousand or so in and outs.
When the thread goes, we helicoil (with FREE RUNNING!!!).
If that goes, we wind it out with a triangular scraper pushed into the top of the thread, and replace the insert.
If things are bad and we have to go bigger, we would tap say M12, and loctite a piece of M12 studding flush into the fixture and tap in the centre of it M6 (or whatever size) again. Thus making an oversize 'solid' insert.
Oh, and for fixtures, don't use stainless bolts. They are soft. Use heat treated alloy steel. Much better.
02-27-2009, 06:34 PM #8
If they are stuck solid, see how they feel about a little circular pocket milling with a nice solid carbide endmill
02-27-2009, 06:40 PM #9
Helicoils are actually very easy to remove.. No drilling and fussing needed.
There is pointy tool, like a triangle on the end of a screwdriver, you poke it into the hole, and turn it out backwards. it will unwind the top coil, and holding pressure down on it, the coil winds up tighter, and comes out of the hole.
Of course, once you get the first coil loose, you can grab it with a pair of pliers, and pull the coil out of the center of the hole, maybe a little "unwinding" motion to peel it right out..
Don't know how to describe the tool, made by Helicoil, strangley enough. Just a sharp pointy spade bit you jam into the coil, and unwind it..
Real easy, and am I ever glad I found out how to do it!
02-27-2009, 06:44 PM #10
i use heli coils alot and i generally use the heli coil removal tool sold by heli coil. if you use heli coils often i would recommend buying one of there tools. i believe they cost less than 30 dollars, from msc. it is a very basic tool look it up and try making your own.
02-27-2009, 06:54 PM #11
To remove the helicoil, take a small triangular jeweler's file and file a small notch in the top ring of the helicoil about 15° back from the end of the coil. Then stick a 3 cornered scraper(or a sharpend screwdriver, or the tool helicoil sells, etc) down into the coil and engage the notch you just filed. Turn the tool counterclockwise and is will contract the springy coils and allow you to uncrew it out of the hole far enough to get pliers on it and finish the job. Don't file the notch so deep that you break the coil off at that spot, just deep enough and sharp so the scraper can grab it.
Stainless on stainless is really hard to lubricate. SS gun people have some magic potions for it.
02-27-2009, 07:48 PM #12
Just a word of caution. Be careful jerking the coils out with pliers. In aluminum you may find your threads came out with the coil.
02-27-2009, 07:49 PM #13
I have removed thousands of heil-coils from aluminum. Our aircraft products use them in every threaded hole that gets a screw.
Take a .062 drill blank ground to a sharp point and take a small light tap hammer and get under the very end of the heil-coil, tap it enough to bend the end out a little bit.
Next take a triangular burring knife (or the heil-coil removal tool, if you don't have anything better to spend your money on) and back the heil-coil out.
Do not grab the heil-coil and pull in aluminum threads. You most likely will pull the threads out with it.
Heil-coils self locking parts are meant to retain a screw so it won't vibrate out. It does'nt effect the torque put on the fastener or it's holding power, it just replaces a lock washer.
Like they said above, don't use SS screws in this aplication.
Try this and they will come right out.
02-27-2009, 08:25 PM #14
Thank you all for your advice. At first it didn't look like the inserts wanted to move, but I used a punch to bend out the start of the thread coil and used another install tool to back them out, just like you guys said.
Only one had to be unwound out, the one with the snapped off bolt. The rest screwed out nicely.
I knew something like this was going to happen with the helicoils. I've never used them before.
I had a bone to pick with HeliCoil for this little comment of theirs "HELI -COIL SCREW-LOCK INSERTS permit repeated assembly and disassembly" but then I thought nah, forget it... yo holmes, to Bel Aire!
This is the lathe profile of the part I'm making. 6.3800" is the OD, .350 is the length, and .062" is the head clearance I got. Gray is the aluminum plate that I've machined the pink hole and counterbore into, then I rip the OD on the mill by screwing the plate down to my fixture through the bolt circle.
Because of the .062 head clearance, I cut down "sidewalk bolts" to .495" OD and .06 head thickness.
Those are my fixturing bolts.
It doesn't work though. Even though the phillips drive matches a #3 perfectly, it still wears out right away. The .495" diameter of the bolts I made worked out nice, because it would locate the bolt circle concentric to the fixture when I put the fixture in the lathe, and then back on the mill. That concentricity is kind of important to the part.
Basically I take the plate and put it in the mill and drill and c'bore the bolt pattern. Then I bolt the plates to the fixture and rip the OD. Then, I put the fixture in the lathe and bolt the plates onto it and turn the face profile. Then, I put the fixture back on the mill and machine a fancy symbol into the spherical profile of the face.
Here's your buffed aluminum result. The part is buffed so it can be chromed.
it could have been done with 1/2" plate so that I can use button-head screws. That would have cost an extra $60, of course.
I guess by the time they try to get buffer wheels down into the grooves, they erode enough material that it shouldn't matter how concentric the symbol is. I know I stopped caring about 6 hours ago :>
02-27-2009, 08:44 PM #15
It's not a problem with the locking helicoils - the standard ones will give you the same problem, it's a galling problem with stainless torqued against stainless, which is not usually a good idea without some sort of coating or anti-sieze at a minimum.
02-27-2009, 08:59 PM #16
psh I had gobs of anti-seize in those holes. that didn't help.
well, good. I got the fixture repearied and I'll have something to read about this weekend.
02-27-2009, 09:43 PM #17
02-28-2009, 12:59 AM #18
I have a solution for your problem. You already have o-ring grooves in the fixture, now drill galleys and make it into a vacuum fixture. Replace the helicoils with dowel pins in jig bushings so they will locate and be easy to remove. As a vacuum source, go to the autoparts store and get a Robin AC evacuator venturi vacuum pump and connect this to a small air tank (like the 5 gal tanks they have for inflating tires) and add a ball valve. You drill a 1/8 galley through the plate, put a couple of 1/8 holes in the face of the plate, then connect the galley to the ball valve with some push-connect air brake lines.
For less than $100 you will have your own vacuum fixture and avoid all this hassle.
02-28-2009, 09:45 AM #19
I think your real problem was the SS hardware. use regular bolts and it will be fine. I get many undreds of cycles out of helicoiled fixtures
02-28-2009, 10:21 AM #20
Perry, excellent suggestion! Thanks for the details, that's something I've wanted to make for a long time.
What I really need is non-stainless helicoil inserts. The sidewalk bolts I'm using only seem to come in stainless, and with Phillips or slotted drive.
The reason I'm using sidewalk bolts instead of shaved down button heads is because the sidewalk bolts can be turned down to .495 to fit into the .500 c'bores of the plate, this way I can keep concentricity from mill to lathe to mill again.
Basically I take the top half of the fixture and grab it with the chuck jaws in the lathe and mount the parts the same way, with those turned down sidewalk bolts. That way I can turn the lathe op with no vibration in the lathe. Pie jaws might work, but the fixture absolutely works. I can rip the parts as hard as I want with those three bolts holding it down.
If anybody has any other ideas on how to run this job, I'd love to hear them.