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To pin, or not to pin

Should I back up high strength loctite joint by pinning?

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AlanW16/11/2019 14:41:48
72 forum posts
10 photos

The machine has been finished and in use for getting on for seven years now and this is just a development (I never gave up chasing rainbows). The original adaptation was the subject of an article in MEW five or six years ago. I would quote the issue number but can't find the on-line index any more. I can put some photos up, though, when it is back in use. I promised Neil an article on further development but that is so long ago now that I doubt if it would still be of interest.


Michael Gilligan16/11/2019 16:59:38
15763 forum posts
688 photos


Personally ... I would have no hesitation in using 638 without pinning

I have fitted a new nose to a lathe spindle with 638 and then machined the Myford thread onto it without any problem.


AlanW16/11/2019 17:19:48
72 forum posts
10 photos

At last, some experience to back up the theory. I take it, then, that it is withstanding turning jobs where a lot of torque is present. In view of that, Michael, I may just reassemble and give it a try.


Andrew Entwistle16/11/2019 17:41:49
77 forum posts
147 photos

Hi Alan,

Another data point; seven years ago I secured the 1/2" throw crank on my power hacksaw to the 5/8" diameter crankshaft (both MS) using 638 only, with no issues.


Ron Laden17/11/2019 04:24:45
1938 forum posts
383 photos
Posted by Ron Laden on 13/11/2019 14:25:47:
Posted by AlanW on 12/11/2019 16:29:23:

failure in this instance would risk irretrievably damaging the shaft that would be difficult for me to replicate

Alan, I would have thought that answers your it to be certain.

Alan I use 638 all the time and swear by it but going back to what you said in your original post (highlighted above) and based purely on that I can't see how "not to pin" is even a consideration just do it and remove any doubt.


Andrew Johnston18/11/2019 20:32:00
5517 forum posts
648 photos
Posted by old mart on 14/11/2019 19:03:14: should try it some time....................

Well I did try it.

I don't have any 638 so I used 648, a similar high temperature Loctite. The pin was a short length of 5/8" low carbon steel and the block a scrap piece with a 16mm hole drilled in it.:

Loctite test before.jpg

The hole measured 15.96mm and the shaft 15.86mm, so a gap of 0.05mm. Before assembly the parts were abraded with emery cloth and cleaned with acetone. Assembly was as per the datasheet with a twisting action to ensure complete coverage. After assembly the parts were left in the airing cupboard for 72 hours to cure.

After curing, with the body in the vice and a Mole wrench on the pin, nothing moved no matter how hard I pulled on the wrench. I then put the parts in the electric furnace set at 300°C. After an hour or so I extracted the parts and put the body back in the vice and the Mole wrench on the pin. The pin moved under the weight of the wrench and came straight out . The Loctite had been converted to a light brown powder which brushed off easily leaving the original surface:

Loctite test after.jpg

Pretty much what one would expect from reading the datasheet with a bit of engineering interpretation. Datasheets are a marketing tool to help sell the product, so they're hardly likely to downplay the product while not telling actual lies.

Any questions? smile


Michael Gilligan18/11/2019 22:08:48
15763 forum posts
688 photos

Nice demonstration, Andrew ... Results as expected. yes

The only ‘question’ is: How likely is it that, in any foreseeable circumstances on a machine tool, the whole joint would get temperature-soaked to 300°C ?


AlanW19/11/2019 14:53:59
72 forum posts
10 photos

Hi Andrew,

It is very good of you to go to so much trouble. At  least now we all know that a) The joint would probably be OK without mechanical back-up, and b) Claims for temperature resistance need treating with caution.

I am with Michael where temperature is concerned; if the spindle (and bearing + lubricant ) reaches even half that sort of temperature, I would be already looking for a reason why. Would anyone ignore smoke coming from their car wheels?

I have decided to go belt and braces anyway. If the spindle were to come to a sudden stop through some unforeseen circumstance (finger trouble) there just may be a remote chance of the joint failing or weakening to let go on some future occasion. To avoid weakening the spindle by drilling through and pinning, I am going with radial grub screws into dimples in the shaft.

As an aside, I am also wary of the claim to be "resistant to lubricants". I machined a tight-fitting nylon cover to fit over the top of the joint as can be seen in the accompanying photos.



Edited By AlanW on 19/11/2019 14:57:31

Edited By AlanW on 19/11/2019 14:58:49

not done it yet19/11/2019 17:00:09
4662 forum posts
16 photos

Now, looking back on this thread, I think my plan might have been to shrink fit the small shaft into the larger section and then turn the larger diameter to size, with concentricity, before loctiting that in as a sleeve. But maybe my idea does not fit your scenario?

That is how (in reverse) I made a 22mm arbor for my mill - I shrink-fitted an oversized shaft into a MT blank arbor and then machined the shaft to 22mm. Not pinned and I very much doubt it will ever fail.

Andrew would not have parted his two pieces once properly shrink-fitted! Once fitted, only a differential coefficient of expansion might cause loosening on heating or cooling!

Probably of no concern, but I would have chosen something other than nylon due to possible size changes as it might dry out, depending on the situation.

AlanW19/11/2019 17:10:41
72 forum posts
10 photos

No matter how a job is done, someone, somewhere, is bound to use their preferred method and materials.

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