Is loctite alone strong enough for a crankshaft?

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David Powell
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Re: Is loctite alone strong enough for a crankshaft?

Post by David Powell »

Thankyou all for your interesting and thought provoking comments and suggestions, This crankshaft is now loctited and pinned( 1/8 th in dowel pins in reamed 0.125 holes fitted with a smear of 680) I contemplated forcing the pins into 0.124 holes but did not do thatin case it made any problems.
Some years ago I built another using loctite only in an identical crankshaft made up of dowel pins for shaft and webs (throws?). It is fitted in a complete steam waggon and will be in steam this spring.
I have never been entirely happy about it. I will give it a jolly good taste of hard use and see if it stands up and let you all know
Regards David Powell
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milwiron
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Re: Is loctite alone strong enough for a crankshaft?

Post by milwiron »

I worked as a machinist in a shipyard for a number of years. Replacing large, water lubed, sleeve bearings was a common part of the job. Bronze bearings were a interference fit and were frozen, usually in hundreds of pounds of dry ice and "slipped" in place. Bronze bearings going in to an OK but rust pitted bore were epoxied in.

Thordon/urethane/elastomer plastic bearings were always glued in with Marine Tex or Red Hand epoxy.
If a Thordon bearing was going in to a fresh clean bore the o.d. of the bearing would be turned with narrow, close fitting, alignment bands on the ends with clearance between the bands for a proper layer of epoxy. In the simplest terms the bearing o.d. had a slight spool shape. A 36 inch long bearing would have end bands about an inch wide, a band or two would be added in the middle to avoid the potential of sagging.

Since those shipyard days I've done the same with Loctite on a much smaller scale. Many of the stronger Loctites need a few thou. clearance, or more, for curing and full strength. Filling the space between small alignment bands has worked well for me. Strong and no guessing on alignment.
Denny
"Measure twice, curse once."
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Greg_Lewis
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Re: Is loctite alone strong enough for a crankshaft?

Post by Greg_Lewis »

Great idea, Denny. Thanks for sharing that!
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SteveR
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Re: Is loctite alone strong enough for a crankshaft?

Post by SteveR »

Just out of curiosity, what is the steam pressure, piston area and crank throw? I'm trying to calculate the shear stress on the joint and I need those numbers to compare with the Loctite TDS. Also, if I understand correctly, the overlapping surface area is the pin circumference times the web thickness?

Thanks
SteveR
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David Powell
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Re: Is loctite alone strong enough for a crankshaft?

Post by David Powell »

Hi, the crank is for a two cylinder engine 1 1/16 bore by 1 1/2 stroke. The crankshaft and crankpins are 1/2 inch diameter, The webs are nominally 3/8 inch wide, but actually a little less as they were cut from some rusty plate which was cleaned up on a belt sander. The working pressure is 100 lbs. I am a determined driver and the waggon will be worked hard. Regards David Powell
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bushav
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Re: Is loctite alone strong enough for a crankshaft?

Post by bushav »

Fender wrote: Fri Feb 17, 2023 9:28 am Why not make the parts to a larger clearance, followed by a light knurling and finishing of the cylindrical components? This will give more space in the joint for the loctite, while preserving the alignment/squareness of the assembly.
My experience with knurling is you lose all semblance of tolerances and shape once the dies start pushing metal around as if it’s a liquid.
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David Powell
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Re: Is loctite alone strong enough for a crankshaft?

Post by David Powell »

A very able friend of mine used to lightly knurl and then turn back to size a bit over half the width of the jointed parts of his crankshafts before silver soldering the parts together. That scheme worked well, he got really good strong joints and accurate alignments.
Regards David Powell.
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Bill Shields
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Re: Is loctite alone strong enough for a crankshaft?

Post by Bill Shields »

Yes, works well with silver soldering. Provides even gap around.

Glue is slightly different, and while it can be made to work, takes a lot of care.
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Harold_V
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Re: Is loctite alone strong enough for a crankshaft?

Post by Harold_V »

bushav wrote: Sun Feb 19, 2023 8:21 pm
Fender wrote: Fri Feb 17, 2023 9:28 am Why not make the parts to a larger clearance, followed by a light knurling and finishing of the cylindrical components? This will give more space in the joint for the loctite, while preserving the alignment/squareness of the assembly.
My experience with knurling is you lose all semblance of tolerances and shape once the dies start pushing metal around as if it’s a liquid.
While I tend to agree with you in regards to the distortion one achieves when knurling, the terminology used (tolerance) is very misleading. Tolerance isn't established by a function performed on a machine--it's determined by the engineer of a given design. Nothing the machinist does can change that, although what the machinist does may cause a part to no longer conform to the tolerance that is allowed. Does that make sense to you?

When one reads and understands what Fender said, his comment makes sense. Key to his remarks is that the parts are fitted for proper alignment AFTER being knurled. That eliminates any potential error, and provides for correct alignment. The only questionable consideration then would be if the light knurling has any negative affect on the intended use of LocTite.

H
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SteveR
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Re: Is loctite alone strong enough for a crankshaft?

Post by SteveR »

The folks at Loctite do a great job of supporting their products. I'm not an ME, so I had to search for how to convert the compressive shear data to rotational shear and found this really great guidebook:

https://5.imimg.com/data5/AE/AX/JM/SELL ... nd-638.pdf.

The calculation input details shown here:
cylindrical bonding1.png
cylindrical bonding1.png (103.79 KiB) Viewed 1152 times

and the details of the joint design factors start on page 10.

I calculated that the engine will deliver 5.5ft-lb (7.5N-m) of torque and that the glue will provide 51N-m of strength for a 1-2mil bondline (I assumed f6 was 0.6 and f8 was 1.5 and the rest 1.0). My math might be off, but I did it 2x and my units came out ok.

Thanks for helping clear out the cobwebs.
SteveR
12x36 Enco Lathe, 9x42 Bridgeport, SMAW, O/A, Miller MIG w/gas, plasma
Not enough measuring tools...
1.5" Allen Models Consolidation on air.
1" FEF in progress
1" & 3/4" LE Projects
Measure twice, cut once, wait - it was supposed to be brass! :)
David Powell
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Joined: Thu Mar 13, 2003 10:38 pm
Location: Pickering Ontario Canada.

Re: Is loctite alone strong enough for a crankshaft?

Post by David Powell »

This math is above my pay scale! However, your posting suggests that the strength would be the strength of a shrink fitted joint PLUS the strength of the adhesive bond.
I have made shrink fitted cranks for other engines using the kitchen stove and fridge freezer ( With wife's full approval and co operation) They have been fully satsifactory, even my very demanding driving style has not undone or twisted one
However I chose to try loctite and slip fits with this crank to make final assembly, getting the cranks at 90 degrees rather easier than juggling hot and cold pieces to fit together at 90 degrees.
I regret I am still at a loss as to a conclusion, what safety margin would a loctited only crank have when simply flinging the reverser fully over to avoid a collision? My shink fit jobs will take it,
Regards David Powell.
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