108 Degree Chain - V'Block (re-discovered)

Many many moons ago one of the Old Masters that I was overcome with
had made a large set of "Chain-V's". All I really ever retained was when
I asked him why the 120 degrees looked a little tight, he said
"It aint 120", and said what it was, and why.

My whole intrigue at the time was the size of the Bar (HBM) and I barely
payed attention to his answer. This week in my exploration forced by
the necessity of doing 4 Large bearings (Bores are 22" nominal),
without haveing any V-Blocks anywhere near large ehough, I used a
lever-hoist and my Devlieg modulars to git-R-done.

Man IT all came back to me, out of the foggy past!
108 Degree Chain - V'Block (re-discovered)

His premice was / is a Pentagonal "squeeze" by the chain.
He even showed me that if a tube-wall was thin and tended to distort
you could adjust by inserting a block to pull the top "in".
I assume this is what he meant, his part didn't need it
and mine don't either..... as wall thickness is addequit.
{ schetch is conceptual only }.......... BUT I'm onto a few Ideas.
Open to the "Best Idea" (challenge) as I rarely find mine till I'm done.
Gimmy some metal BOSS !!

Oh Oh OHHh,,,, He said a 90 doesn't give the right squeeze or a good size-range,
and more blocks would need to be made. And he didn't like 120's as
too much downward distortion was the tendency causing oval bores.

That is excellent, and your drawing shows the concept very clearly. Thanks for sharing that. I now have a copy in my file.

And being an odd number of lobes, no one will find the out of round with either a bore gage or T gage.

gbent said:

And being an odd number of lobes...

Click to expand...

Seems to me when I was a kid and my Mom would comb my hair, she would mutter something to that effect, and "can't quite put my finger on it.".

That's an interesting thing, M1M. Thanks.

The machinist (Jim) would not have used the odd-lobe effect
to dissguise lack of roundness, although I'm certain he would have been
aware of that,
as he was Aware of EVERTHING, ts'why he was a Master.

The weird thing is; I've come close to remembering this but not quite
there on several occaitions. The chains yes, and even the unusual angle,
but in the back of my mind was this {72 degees} thing ???
A puzzle peice out of place, once I pondered a set of 105 degree V's
simply as a compromise, better range than 90's and better centering than 120's.
BUT it finally dawned on me, 72 degrees is the angle of contact.
SO Jim's V's would have been 108's........then I could hear him say it again.

I had also been distracted by the 108 degrees being cross-cut, with the
beautifull look of a very fine and accurate planer cut. Back then the angle
may have been better (more easilly done accurately) on a planer.
There may have been several sets made, at one time, that I was unaware of.
The ballance was done on mills.

USMCPOP;
Enuff hair and beard can offset that lobe thing.

Just a wee bit off depending on block size

Belding said:

Just a wee bit off depending on block size

Click to expand...

Not sure why you've arbitrarily led the chains to the block outboard edge.

What's to stop a body slotting the block or put eyebolts on top so the chains can be rigged further inboard (admittedly the OP conceptual drawing is a little misleading in showing the chain curving in midair, but it's a concept drawing, and it does show inboard chains, (arbitrarily) vertical in their drop)

Incidentally, I don't see why further two pads could not be taped at the desired pentagonal points ...

Troup said:

Incidentally, I don't see why further two pads could not be taped at the desired pentagonal points ...

Click to expand...

Good point.

M1M asked me to post this as he's having some 'puter issues:

The first is simply what I asked for steel for.... 2" HRS to make one BIG 108 degree V.


The second is my fall-back.... enough steel for a mount to bolt my 2 larger DeVlieg Modular uppers to.

Here is link to a modular chain fixture that has a wide range of adjustment - http://www.royalworkholding.com/wp-content/uploads/2009/03/modularfixturesspecs2.jpg

Less contact with the part is often better. Especially if the cylindrical piece is a casting.