# LocTite 680 Strength?



## brasssmanget (Feb 5, 2017)

Anyone have experience with Loctite 680? I'm considering anchoring the pintle bolts in the sidewalls of a cannon barrel with this. The fit is very tight, but slip-fit size. I cut slits do let the excess escape when pressing in the bolts. Do you think this is strong enough, or is welding required?? Holes are 5/8"D X 3/4" deep.


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## 4GSR (Feb 5, 2017)

The heat and sudden impact from firing the cannon may destroy the Loctite in short time.  Suggest brazing or silver solder them in place.  Leave about .002-.003" clearance around the pins, place a silver solder disk in bottom of flat bottom hole with flux, heat and watch the solder flow up around the pin to the surface.  Let cool.  Same process as for brazing carbide to a metal shank.  Ken


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## brasssmanget (Feb 6, 2017)

Once again - thanks for the tips and suggestions. I'll probably go with silver solder or weld.....my heat source is limited to Mapp gas and propane - not sure if that's enough for these trunnions and barrrel....


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## Terrywerm (Feb 7, 2017)

MAPP gas might be a bit of a push for that cannon barrel, as it will be a huge heat sink and I don't think your torch will be able to direct enough heat at one spot fast enough for silver soldering to work. You can certainly try it, but don't be surprised if it doesn't get hot enough.


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## brasssmanget (Feb 8, 2017)

Agreed. Just not enough for the size, based on what I've used it for in the past. 

I'm not even going to try silver soldering. Welding should work - albeit a  bit messy and will require some post weld cleanup I'm sure......


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## Glenn Brooks (Feb 8, 2017)

How about turning threads to a tight fit and screwing the pintle bolts in? 

Glenn


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## brasssmanget (Feb 9, 2017)

I considered doing that, but threading the barrel holes would have required setting up again on the mill for squareness of tap, and I already turned the trunnions, so that would mean making two more for threading. I don't want to restart a project - at least not yet. Welding will be faster and pretty solid too.......


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## Glenn Brooks (Feb 9, 2017)

Sure, 
Understand and agree.  One way to get more heat for welding would be to make a table top forge out of some fire brick - a three sided heat reflective shield to contain and redirect radiating heat from your  barrel back into the joint.  Then put one or two additional map gas burners on the part to maintain temperature while using another to do the actual soldering.   

This is the set up a local cast iron repair shop uses to weld and braze large broken cast iron parts back together.


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## brasssmanget (Feb 9, 2017)

Someday maybe I'll have a makeshift forge/oven.....someday.......


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## Tozguy (Feb 9, 2017)

See below


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## Tozguy (Feb 9, 2017)

If the barrel is a big heat sink, how is it going to get too hot for Loctite?
Your original idea should work with something like this, maybe.
http://na.henkel-adhesives.com/adhesives/product-search-1554.htm?nodeid=8797948444673


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## Glenn Brooks (Feb 9, 2017)

Loctite starts loosing strength at 200 degrees, progressively gets weaker until failure at around 
450...


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## brasssmanget (Feb 10, 2017)

Well here is the scoop. I did use 680 and pressing in the trunnions a couple of days ago. Tried heating with Mapp gas until they (one) turned blue and still could not budge it loose or turn it in the socket. I'm still going to tack-weld them in, but I'm thinking this is going to be strong enough for now. If there is ever a failure I can get to them easy enough......

Quite a project - and very enlightening for a novice hobby machinist.


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## Tozguy (Feb 10, 2017)

Loctite provides a lot of technical info. This one pertains to a category apart from thread lockers, i.e. retaining compounds, in case anyone is interested. 

http://na.henkel-adhesives.com/industrial/retaining-compound-14963.htm


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## Groundhog (Feb 10, 2017)

Loctite High Temp Retaining compound;
Loctite 234772 Green 620 High Temperature Retaining Compound, 10 mL Bottle


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## Groundhog (Feb 10, 2017)

brasssmanget said:


> Well here is the scoop. I did use 680 and pressing in the trunnions a couple of days ago. Tried heating with Mapp gas until they (one) turned blue and still could not budge it loose or turn it in the socket. I'm still going to tack-weld them in, but I'm thinking this is going to be strong enough for now. .



When you tack weld you will likely dissolve the thread locker won't you? If not I think thread locker re-hardens after it has been heated (but I'm not sure).
If I were you I would use a high temp retaining compound (post above) instead of a thread locker. They are designed for different applications.


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## brasssmanget (Feb 10, 2017)

680 is more of a retaining compound is it not??


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## Tozguy (Feb 10, 2017)

Its a bit confusing sometimes when the charts and tables from Loctite don't correspond with each other.
This decision tree lists 620 as the best hi temp retaining compound. 
http://catalogs.na.henkel-adhesives...okCode=asb15flx&PageLabel=126&Sgt=11&lang=enu

Elsewhere (link above), 680 is shown as a candidate also.


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## Groundhog (Feb 10, 2017)

brasssmanget said:


> 680 is more of a retaining compound is it not??


Yes it is. Sorry, I was wrong in thinking that it is a thread locker. However, I did not see it listed as a "high temp" retaining product - for what that is worth.


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## DAT510 (Feb 10, 2017)

In the end, I think it comes down to how much heat you think the pintle bolts will see?  Loctite 680 loses 50% of it's strength at 125C.  ~90% at 200C.

Here's the TDS for Loctite 680.  The "Hot Strength" graph is on the lower right of the 2nd page.       http://www.loctite.tw/twc/content_data/327273_UPGRADE680EN.pdf

Hope this helps,

Chris


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## brasssmanget (Feb 10, 2017)

Yeah Chris - I find myself over thinking this thing. Any firing will be spaced by at least 5-10 minutes, and projectiles are not a sure thing right now. I don't think heat is a factor, but stress and shock from firing might be - possible jarring them loose. Moot point since I already welded them in this morning. 

Might just spend it's life as a signal cannon tho....


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## KBeitz (Nov 20, 2018)

Make sure you use an activator in a blind hole/


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