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Thanks for filling in the gaps in my response. On the other hand,I've extr=
acted a grade 8 bolt that had snapped on a rockershaft pedestal, not exactl=
y a high stress application. I attributed it to the differences in thermal=
expansion between the steel bolt and the aluminum pedestal. But, perhaps i=
t was a faulty bolt. There was a rash of counterfeit grade 8 hardware in d=
istribution a couple decades ago and perhaps those have found their way in=
to your local hardware stores where inventory tends to move slowly.
=20
Dave Massey
=20
=20
-----Original Message-----
From: Michael Porter <mdporter@dfn.com>
To: Dave <dave1massey@cs.com>; levilevi <levilevi@comcast.net>; triumphs <t=
riumphs@autox.team.net>
Sent: Thu, Nov 24, 2016 6:13 pm
Subject: Re: [TR] Threads and Bolts
=20
On 11/24/2016 11:51 AM, Dave wrote:
=20
=20
Bolts with no slashes are grade two. The grade of the bolt is ind=
icated by the number of slashes plus two. I do not recommend grad=
e two for suspension duty. =20
=20
I've heard said that the trade-off with Grade 8 bolts is that =
they are stronger but more brittle. Since I am not a mechan=
ical engineer I cannot make a recommendation on substituting a gra=
de 8 for a grade 5 but I would be concerned that the increased bri=
ttle nature may be a detriment. Considering the seriousness of the=
consequences of a suspension failure I would think again about ma=
king substitutions. And just about anything you need is available=
next business day from McMaster Carr (and other sources, =
certainly). But you may have to buy more than you need and pay s=
hipping.
=20
I don't think fine thread vs coarse thread makes much diff=
erence.
=20
=20
Brittleness is relative. The optimum condition for a strong bolt is =
toughness, the combination of tensile strength with resistance to both =
deformation and crack propagation. It's just a function of metal crysta=
lline behavior that higher tensile strengths are inversely proportional =
to rate of deformation. The general perception is that bolts with very =
high tensile strength offer no protection from sudden breakage once the =
yield point is reached, but that's not exactly true. A lot depends upon=
the loads imposed. If a grade 5 bolt works reliably in an application,=
breakage is very unlikely with a grade 8, because the grade 8 yield poi=
nt is higher. This also allows for somewhat more clamping force, thus r=
educing the tendency of the fastened parts to move around under load. =
=20
=20
The latter is important, because any bolt loaded in shear will fail =
at about 65% of UTS (ultimate tensile strength). Even so, I've seen gra=
de 8 bolts that have deformed badly without shearing. For example, on t=
he buses we built, the rear axle was attached to a pair of spring beams =
(the item carrying the air springs that supported the weight of the bus =
and transmitted those loads to the axle). Each one was attached with fo=
ur 3/4" grade 8 bolts in a box pattern, with a precision center pin to p=
ositively locate the axle. Due to an engineering error (through holes t=
oo large), under big side loads (like the driver whacking a curb while i=
n motion--much more common than one would think, especially in NYC), the=
spring beam would laterally rotate around the center pin, putting the b=
olts in direct shear. Those dynamic loads, due to excessive movement, w=
ere much larger than the clamping load because movement adds kinetic ene=
rgy. I saw one of those grade 8 bolts after such mistreatment, and it h=
ad an "S" curve in it, so that the centerline at the head of the bolt =
was offset from the centerline at the bottom of the bolt by nearly 1/2"=
, and yet, the bolt had not cracked or broken. That's where the toughne=
ss of the bolt comes in--which depends upon a number of factors, such as=
the alloy, the kind of heat treatment, precipitation hardening, temperi=
ng and anti-corrosion coatings (to prevent corrosion cracking).
=20
To my mind, a properly-made grade 8 bolt will be superior in perform=
ance to any grade 5 bolt, especially in suspension work. It's important=
to know the loads imposed, though. In racing, a grade 5 will be fine i=
n areas where the maximum load imposed will be sufficiently below the UT=
S of the bolt, and the clamped pieces are inspected regularly for stretc=
hed or deformed bolts, but the extra insurance of higher yield strength =
and higher clamping force make a grade 8 preferable. I'd much rather ha=
ve a bolt that never reaches its yield point under maximum load than one=
that yields and deforms before failure.
=20
=20
Cheers.
=20
=20
--=20
Michael Porter
Roswell, NM
Never let anyone drive you crazy when you know it's within walking distance=
....
=20
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<font color='black' size='4' face='Arial, Helvetica, sans-serif'><font
size="4">Thanks for filling in the gaps in my response. On the other
hand,I've extracted a grade 8 bolt that had snapped on</font><font size="4"> a
rockershaft pedestal, not exactly a high stress application. I attributed
it to the differences in thermal expansion between the steel bolt and the
aluminum pedestal. But, perhaps it was a faulty bolt. There was a rash of
counterfeit grade 8 hardware in distribution a couple decades ago and
perhaps those have found their way into your local hardware stores where
inventory tends to move slowly.</font>
<div> <br>
</div>
<div style="clear:both"><font size="4">Dave Massey</font><br>
<br>
</div>
<div> <br>
</div>
<div> <br>
</div>
<div
style="font-family:arial,helvetica;font-size:10pt;color:black">-----Original
Message-----<br>
From: Michael Porter <mdporter@dfn.com><br>
To: Dave <dave1massey@cs.com>; levilevi <levilevi@comcast.net>;
triumphs <triumphs@autox.team.net><br>
Sent: Thu, Nov 24, 2016 6:13 pm<br>
Subject: Re: [TR] Threads and Bolts<br>
<br>
<div id="AOLMsgPart_2_19ae3d4a-4309-4f78-aa31-2d3a79fa5aaf">
<div bgcolor="#FFFFFF" text="#000000" class="aolReplacedBody">
<div class="moz-cite-prefix">On 11/24/2016 11:51 AM, Dave wrote:<br>
</div>
<blockquote cite="about:blank"><font color="black" size="4" face="Arial,
Helvetica, sans-serif"><font size="4">Bolts with no slashes are
grade two. The grade of the bolt is indicated by the number
of slashes plus two. I do not recommend grade two for
suspension duty. <br>
<br>
I've heard said that the trade-off with Grade 8 bolts is that
they are stronger but more brittle. Since I am not a
mechanical engineer I cannot make a recommendation on
substituting a grade 8 for a grade 5 but I would be concerned
that the increased brittle nature may be a detriment.
Considering the seriousness of the consequences of a
suspension failure I would think again about making
substitutions. And just about anything you need is available
next business day from McMaster Carr (and other sources,
certainly). But you may have to buy more than you need and
pay shipping.</font><br>
<br>
<font size="4">I don't think fine thread vs coarse thread makes
much difference.<br>
</font></font></blockquote>
<br>
Brittleness is relative. The optimum condition for a strong bolt is
toughness, the combination of tensile strength with resistance to
both deformation and crack propagation. It's just a function of
metal crystalline behavior that higher tensile strengths are
inversely proportional to rate of deformation. The general
perception is that bolts with very high tensile strength offer no
protection from sudden breakage once the yield point is reached, but
that's not exactly true. A lot depends upon the loads imposed.
If
a grade 5 bolt works reliably in an application, breakage is very
unlikely with a grade 8, because the grade 8 yield point is higher.
This also allows for somewhat more clamping force, thus reducing the
tendency of the fastened parts to move around under load. <br>
<br>
The latter is important, because any bolt loaded in shear will fail
at about 65% of UTS (ultimate tensile strength). Even so, I've seen
grade 8 bolts that have deformed badly without shearing. For
example, on the buses we built, the rear axle was attached to a pair
of spring beams (the item carrying the air springs that supported
the weight of the bus and transmitted those loads to the axle).
Each one was attached with four 3/4" grade 8 bolts in a box pattern,
with a precision center pin to positively locate the axle. Due to
an engineering error (through holes too large), under big side loads
(like the driver whacking a curb while in motion--much more common
than one would think, especially in NYC), the spring beam would
laterally rotate around the center pin, putting the bolts in direct
shear. Those dynamic loads, due to excessive movement, were much
larger than the clamping load because movement adds kinetic energy.
I saw one of those grade 8 bolts after such mistreatment, and it had
an "S" curve in it, so that the centerline at the head of the bolt
was offset from the centerline at the bottom of the bolt by nearly
1/2", and yet, the bolt had not cracked or broken. That's where the
toughness of the bolt comes in--which depends upon a number of
factors, such as the alloy, the kind of heat treatment,
precipitation hardening, tempering and anti-corrosion coatings (to
prevent corrosion cracking).<br>
<br>
To my mind, a properly-made grade 8 bolt will be superior in
performance to any grade 5 bolt, especially in suspension work.
It's important to know the loads imposed, though. In racing, a
grade 5 will be fine in areas where the maximum load imposed will be
sufficiently below the UTS of the bolt, and the clamped pieces are
inspected regularly for stretched or deformed bolts, but the extra
insurance of higher yield strength and higher clamping force make a
grade 8 preferable. I'd much rather have a bolt that never reaches
its yield point under maximum load than one that yields and deforms
before failure.<br>
<br>
<br>
Cheers.<br>
<font size="4"><font face="Arial, Helvetica, sans-serif"></font></font><br>
<pre class="moz-signature">--
Michael Porter
Roswell, NM
Never let anyone drive you crazy when you know it's within walking
distance....</pre>
</div>
</div>
</div>
</font>
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