To pin, or not to pin

[Ron LadenParticipant @ronladen17547]

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 question……pin 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.

Ron

[Anonymous]

Posted by old mart on 14/11/2019 19:03:14:

…………….you 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.:

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:

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?

Andrew

[Michael GilliganParticipant @michaelgilligan61133]

Nice demonstration, Andrew … Results as expected.

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 ?

MichaelG.

[AlanWParticipant @alanw96569]

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.

Alan

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

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

[not done it yetParticipant @notdoneityet]

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.

[AlanWParticipant @alanw96569]

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

[Author]

Posts