Loctit 648 information and help

[Ye-Ole Steam Dude]

Hello everyone,

I have used Loctite thread compound in the past, but never any of the Loctite 648. I read all the specifications on the main spec sheet from Loctite ( I even saved a copy of the pdf ) and the initial cure time on all the graphs appear to start at 2-1/2 to 3 minutes.

Today I machined from brass a new crankshaft for my current project Steam Engine No.4. I had already built one and silver solder it together. I got all the parts laid out and prepared the bottle of Loctite and got extra shop towels and paper towels ready.

OK armed with that knowledge from the spec sheets, I applied a ring around the shaft at the first location and slid on the first lobe. Wiped off a bit of excess and applied a second ring and slid on the second lobe, again wiped off some excess and started to align the two lobes (this has only been 45 seconds to one minute tops) and I almost could not move the second lobe. Fortunately I was able to get it off. The first lobe was STUCK in place and no way of moving it, as it turned out it was in the correct location.

What is the secrete in using this stuff, other than act at the speed of light.???

Thanks in advance for any advice,

[crueby]

Other than moving fast, no other option I know of. Thats why I use the 603 retaining compound version for shafts, longer working time before it says 'enough, its staying THERE' on you. Either version can always be removed with heat from a small torch, cleaned (it will leave some goo behind that can be scraped off), and redone.

[Ye-Ole Steam Dude]

Other than moving fast, no other option I know of. Thats why I use the 603 retaining compound version for shafts, longer working time before it says 'enough, its staying THERE' on you. Either version can always be removed with heat from a small torch, cleaned (it will leave some goo behind that can be scraped off), and redone.

Thanks Chris,

I will order some of the 603.

I have a 50ml bottle of this 648 and the 680 so I will have to find a use for it somewhere. Haven't tried the 680 but the specs are the same except the 680 is for larger gaps, not a close fit.

Thanks again,
Thomas

[Alan Haisley]

Other than moving fast, no other option I know of. Thats why I use the 603 retaining compound version for shafts, longer working time before it says 'enough, its staying THERE' on you. Either version can always be removed with heat from a small torch, cleaned (it will leave some goo behind that can be scraped off), and redone.

Chris,
If some heat allows you to separate the parts, does some heat allow you to adjust the parts? Or does enough heat to get it to move damage the chemistry so it will no longer hold?
Alan

[Ye-Ole Steam Dude]

Hi Alan,

As you already know, I am new to using 648. The way I read the specification sheet is that heat is used only to remove the part. They then tell you how to clean up the residue. Hopefully Chris has some experience that he will share.

When I have time, I plan to experiment with wrapping the parts in paper towels and placing them in the freezer to chill them down. The "curing" time is based on temperature so maybe 10 or 15 degrees cooler will retard the "set" time.

Thomas

[b.lindsey]

Thomas, most if not all Loctite products cure in the absence of air. I suspect in your case, the closer the fit, the faster it will begin to cure, since there is less air between the parts. The 648 can fill up to .006". My thought is that closer fits, which I assume you had will cure faster...it could be the specs are based on maximum clearance.

Bill

[Ye-Ole Steam Dude]

Thomas, most if not all Loctite products cure in the absence of air. I suspect in your case, the closer the fit, the faster it will begin to cure, since there is less air between the parts. The 648 can fill up to .006". My thought is that closer fits, which I assume you had will cure faster...it could be the specs are based on maximum clearance.

Bill

Hey Bill,

Yes you are correct about the absence of air as per their specs, and yes on my fit. This was a 3/8" reamed hole with a piece of 3/8" brass rod...almost zero tolerance. And boy was it quick...he he. I surely was not expecting it to be that fast after looking at their chart/graph.

I just applied (20 minutes ago) some of the 680 on a loose fit brass to brass and it still has not set up. In this case there is plenty of air so it might take all night.

I did order some 603 and will give it a try.

Learn something new every day.

Later,
Thomas

[crueby]

After heating to remove it, its best to clean it up and start over, it doesn't reset again. At best it will be gritty enough to keep a screw from  loosening.

[Ye-Ole Steam Dude]

After heating to remove it, its best to clean it up and start over, it doesn't reset again. At best it will be gritty enough to keep a screw from  loosening.

Thanks Chris, I appreciate your help and this should help Alan also. Long day for me, going to close up the shop and fix a drink.

Later,
Thomas

[Mayhugh1]

You can increase the working time by chilling the Loctite. The data sheet for 680 shows the cure time as a function of temperature. - Terry

[steamer]

Wot Bill said.  Run a looser fit.

[crueby]

You can increase the working time by chilling the Loctite. The data sheet for 680 shows the cure time as a function of temperature. - Terry

Being in Texas, is your shop air conditioned? If quite warm, Terry is right,, it could speed up the curing, just like with epoxy, and chilling it and parts will help. I've had epoxy with an hour pot life go off in minutes in a hot workshop in summer.

[Jasonb]

648 is the loctite I use most of the time and time does vary depending on the fit of the parts but have not had problems using it on small cranks. When assembling cranks I bond the pin to the two throws first using the main shaft to keep things lined up and let that cure. Then you have a "U" shape that can be slid along the shaft as one so both joints can be bonded at the same time and you only need to set it for position along the shaft

One other thing to consider is what did you clean the parts with, some cleaners can actually accelerate the cure time.

[Ye-Ole Steam Dude]

You can increase the working time by chilling the Loctite. The data sheet for 680 shows the cure time as a function of temperature. - Terry

Hey Terry,

Much better and easier to chill the Loctite than the parts. I will give that a test.

Thanks,
Thomas

[Ye-Ole Steam Dude]

You can increase the working time by chilling the Loctite. The data sheet for 680 shows the cure time as a function of temperature. - Terry

Being in Texas, is your shop air conditioned? If quite warm, Terry is right,, it could speed up the curing, just like with epoxy, and chilling it and parts will help. I've had epoxy with an hour pot life go off in minutes in a hot workshop in summer.

My shop is air conditioned but I keep it at 77 degrees. This would be easy to lower the temp about an hour before I use the Loctite.

Thanks Chris

[Ye-Ole Steam Dude]

648 is the loctite I use most of the time and time does vary depending on the fit of the parts but have not had problems using it on small cranks. When assembling cranks I bond the pin to the two throws first using the main shaft to keep things lined up and let that cure. Then you have a "U" shape that can be slid along the shaft as one so both joints can be bonded at the same time and you only need to set it for position along the shaft

One other thing to consider is what did you clean the parts with, some cleaners can actually accelerate the cure time.

Excellent idea on the procedure. I might take the crankshaft apart with heat, clean it real good again and try this method.

As far as cleaning, I had cleaned all the parts with alcohol several hours earlier. Just before assembly I ran over each "area" with some 1000 grit sand paper and wiped it clean with a paper towel.

Jason, thank you for this info.

Thomas

[Ye-Ole Steam Dude]

Hey again,

I know this example is not very scientific but so far I have found 648 to set up much quicker than the 680. I milled the face on a 1/4" brass round rod by .040 on both sides which is one of 2 roller valves. I cut a shape of .040 brass for a bracket that will hold the wheel. Laid the bracket flat, applied a drop of Loctite and then set one side of the 1/4" rod on the bracket. No pressure or real tight fit here.

First time I used the 680 and 20 minutes later it had not “set”. About 20 minutes later I checked and it had set.

Second valve rod, same as above but used the 648 and it set well enough in less than 2 minutes that I could lift the whole assembly as one part.

Only time will tell if after they have completely cured if there is a true bond of the two pieces and enough strength to hold all the pieces together.

I sure appreciate all the help and information from everyone.

Later,
Thomas

[Ye-Ole Steam Dude]

OK everyone,

I took apart the crankshaft using a Bernzomatic torch and to my surprise, the pieces came apart fairly easy. However, to get one lobe or one set I do not think is possible because the heat transfer along the main shaft loosened the second set.

My photos are not the best but you can see there is quite the mess left on the main shaft. I took some MEK to clean most of the crud and then used a course sanding sponge on the lobes to get back to bright brass. I put the shaft in the lathe and used a fine sanding sponge on the bottom while holding a course sponge on the top and turned the shaft at 600 rpm’s. The second photo shows how nice it turned out.

I then ran a reamer through all the holes and removed a bunch of crud from them. As you can see, it all looks as new and all the parts go back together OK.

I will try again to Loctite everything back together using Jasonb’s method. Not sure which of the two I will use, but I do plan to set the chosen one in the icebox to chill it down a bit and I will have the A/C in the shop turned down. Might wait til tonight.....

Thomas

[Ye-Ole Steam Dude]

Everything has gone so smooth that I was able to reassemble the complete crankshaft. I used Jasonb’s method and it was so quick and easy. I decided to try the 648 again but this time I placed the bottle in the refrigerator on the middle shelf for about 20 minutes. The chilled Loctite gave me an additional 10 to 20 seconds before it set up.

 I did the procedure in three steps:
First I made the “U’s” putting together two of the lobes and one 1/4" journal and clamping them flat for about 10 minutes.
Second I made a temporary jig to clamp and hold in place the first “U” (journal number one) and a backstop to stop the main shaft at the correct distance from the clamped journal. I slid the main shaft in the journal until it hit the stop and then withdrew just enough to apply the Loctite to the required area. Then I pushed and rotated the shaft until it hit the stop.
Step three, I made a second temporary fixture/backstop for journal number two and repeated the above procedure.

It all went as smooth as a river rock and I am a happy camper  and I feel like I have moved up one notch on the learning curve for using Loctite.

Hope this will help others and thanks to everyone for all your input and knowledge.

Thomas

[crueby]

Very nice, another one to file away (and hopefully remember it is in the file).