# Candy Questions in Tech 9



## ship (Feb 12, 2004)

Very tough question. Difficult to know off the top of your head, but something that would be good to have an idea about at least if not a way to figure it out even if the engineering part of it all is not your job.

Extra credit, how do you figure it out for the normal zinc bolts much less ones of other materials? 
In bolting a stair case to a platform, what makes you choose one bolt over another and what determines how many you need? 
What would be the tensile strength much less sheer strength of the above bolts?

Note: This is a very hard type of question even for me but something that does come up frequently if only in the most simple form of it. For instance, if you have a 3/8-16x4" Alloy socket head cap screw holding a 95# light, but need to extend it’s length to 6" how do you do so given 6" above bolts are not sold and it has to stay that type of screw head? Do you go with a 18-8 Stainless Steel socket head cap screw in the desired length, coupler on a threaded rod of appropriate grade, and if so what grade of coupler would you use? Do you have to spend $24.00 each for a grade 8 coupler or would say a grade 5 coupler work given it’s going to be stronger than the stainless one for the weight carried. 

What’s the sheer strength of a 5/16" zinc plated lag bolt, how do you figure it out so you know if it’s sufficient in strength, or if going up a size or adding more would be more appropriate.


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## ship (Feb 12, 2004)

By the way, this is not any kind of I’m cool type of thing, or that Ship’s attempting to stump or amaze anyone. Such questions do come up and school plus experience only help answer them, at some point when you need to know, learning how to figure it out is useful.

The idea is that as a stage hand or even electrician we make choices in engineering without thinking about them. How many bolts and of what size does it take to bolt a 3' tall by four feet wide stair case - without legs, to a platform? Lighting C-Clamps come with a ½-13 bolt of grade 2 strength, why not grade 3, 4 or 5? Fly system rigging equipment normally uses grade 5 bolts, verses truss uses grade 8 or stronger. Why and when you are into the unknown - such as thru bolting one pipe to another, what makes you choose the above grade/size of bolt? That’s the basis of the question. There is also a cost effective part to the question but it’s not mentioned nor is the option of adding more bolts.

Here is some help out of McMaster Carr: (http://www.mcmaster.com/ ) Do the find products part of the website and click on catalog page for engineering data on the bolts. Also getting used to McMaster Carr is a very important technical skill to learn. If they only sold food now because they do sell everything else - it’s the Sears Catalog of the turn of the century, only for tech people.

1/4-20x3" Alloy Steel Socket Head Cap Screw #91251a554

1/4-28x3" Gr.8 Hex Head Screw of Ultra-coating #91286a151

5/16-24x2" Gr.8 Hex Head Screw of Zinc plating #91257a611

5/16-18x2" Titanium Hex Head Screw #94081a591

3/8-16x2" Gr.5 Hex Head Screw of Black Oxide Coating #92965a632

3/8-16x3" Hex Head Screw of type #316 Stainless Steel #93190a636

1/2-13x2" Gr.3 Military Spec Hex Head Screw of type 18-8 Stainless Steel #92245a722

5/8-11x3" Gr.2 Hex Head Screw of Zinc Plating. #91309a806


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## wolf825 (Feb 14, 2004)

Hi Ship, 

I wouldn't begin to know the differences in the rating specs--like DIN933, DIN 912 and so forth and how they apply to use...or where to read up on that. But FWIW, I'm torn between the titanium and the Gr8 Zinc...and thats only a guess on my percieved strength of the metals and thickness of the bolts...

thats my guess...anyone else? 


-wolf


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## cruiser (Feb 14, 2004)

wanna convert the measurements lol


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## avkid (Mar 8, 2004)

weld it 8O


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## ship (Mar 9, 2004)

Something is wrong with my figuring but it would seem that the 5/8-11 Gr.2 screw wins on strength overall. If possible someone check my math so I also know the formula and how it works.

wanna convert the measurements lol - Cruiser
a 1/4" Bolt is about a M6
a 5/16" Bolt is about a M8
a 3/8" Bolt is about a M9.5 or M10
a ½" Bolt is about a M12 or M13
As for threads per inch, consider them to be course grade with the exception of the 5/16-24 and 1/4-28 which would be National Fine grade.

“A note from McMaster is that metric sizes are 4.8 carbon steel, comparable to Grade 2.” This would mean that the normal metric bolt is not going to be very strong.

I wouldn't begin to know the differences in the rating specs--like DIN933, DIN 912 and so forth and how they apply to use...or where to read up on that. But FWIW, I'm torn between the titanium and the Gr8 Zinc...and thats only a guess on my percieved strength of the metals and thickness of the bolts... - Wolf

Wolf you get the point, there is no ready or easy table for this and it is very unfortunate. This is my point in posting the survey. We assume we know what the heck we are doing, might even specify a Titanium bolt and think it’s strength is extreme, but it’s not with study. We also have to balance bulk in general verses bolt grade by instinct.

Din numbers along with Rockwell Hardness are hardness of steel which roughly equates to grades of bolts except it only accounts for the surface hardness and not the flex. Glass has decent surface hardness for instance. The rough equation would be the minimum tensile strength in combination with surface hardness. That is if you can find a chart for the tensile strength and hardness of the various grades of bolt. 

Than it’s also size and mass verses sheer and tensile strength. Is a 5/8" Grade 2 bolt really going to be stronger than a alloy 1/4-20 bolt of alloy steel, and what effect will fine threading of a bolt have on the strength?

There are some things that you can cross off the list as un-important information for the moment where strength is involved and that’s coating of the metal - or at least normally with those excepting the black oxide coating which normally dictates a alloy steel if not otherwise mentioned. Surface coatings will be a detail for engineer stress in being able to hold the nut but not the overall strength of the bolt itself. Alloy steel or Aircraft Grade as it’s trade name might be is about a grade 9 or 10 in strength and while black oxide coatings can be applied to normal steel bolts of grade 2 which is normal when the bolt is not listed for grading or in this case the grade 5 bolt, it’s usually only applied to alloy steel. Ultra Coated bolts while resistant to corrosion does not otherwise add to strength. The coating might have a slight difference in overall sheer due to the surface hardness but after that it’s not much difference between a Ultra Coated bolt and a Zinc bolt.

Titanium is seemingly a extreme strength material but it’s going to be more a alloy of it mixed with steel as otherwise it would be probably too high in carbon content for tensile strength in general, plus expensive due to the difficulty in working. It’s primary use is in resistance to corrosion, salt water and chemicals. Rockwell hardness is B75 and Minimum Tensile Strength is 62,000psi. From the hardness and psi, it would appear that Titanium is not very strong, only slightly stronger than Grade 2 steel.

Stainless Steel in general is not graded the same. It’s certainly harder than standard steel but overall it’s not normally stronger than say a Grade 5 bolt. Grade 18-8 is standard, type 316 is slightly stronger in tensile strength. Type 316 is B85-95, and has a tensile strength of 85,000psi. Grade 18-8 is B85-B95 with 80,000psi.

Military Specification bolts means the bolt has tighter tolerances than normal grades of bolt. In the case of a grade 3 bolt of ½", is it going to be stronger than a grade 5 bolt of 3/8". Good question in mass verses strength.

Grade 8 is a “medium-carbon alloy steel that has been quenched and tempered for greater strength”. “Rockwell hardness is C33-39. Min. Tensile strength is 150,000 psi.” Grade 5 is C25-34 with a tensile strength of 120,000psi. for these sizes. Grade 2 is B70 and 60,000psi.

Alloy steel has a better thread to nut fitting which adds to strength, are traceable in materials meaning that out of liability the materials are up to specification even Military Spec. “These screws are heat treated, have a black oxide finish, and exceed the tensile strength of grade 8.” - McMaster Carr Hardness is C39-45 and minimum Tensile Strength is 180,000psi.



In general we can probably cross out the 5/16-18x2" Titanium Hex Head Screw #94081a591 having checked the description since it would be much less strong than a Grade 8 bolt of the same size. We can also cross out the 1/4-28x3" Gr.8 Hex Head Screw of Ultra-coating #91286a151 since a alloy steel 1/4" bolt will be stronger.

After that, it’s a question of what is the formula for bulk verses tensile strength than also bulk verses sheer strength which would be Rockwell Hardness. I don’t know but will present the formula for each, but it’s probably going to be safe to assume that any 1/4" bolt is not going to have a better strength in either dimension than a 5/8" bolt. We can safely cross off a 1/4" bolt from the list.

This leaves us with a choice of:
5/16-24x2" Gr.8 Hex Head Screw of Zinc plating #91257a611 
3/8-16x2" Gr.5 Hex Head Screw of Black Oxide Coating #92965a632 
1/2-13x2" Gr.3 Military Spec Hex Head Screw of type 18-8 Stainless Steel #92245a722 
5/8-11x3" Gr.2 Hex Head Screw of Zinc Plating. #91309a806


If you are not up to speed at this point than going back and studying before you specify would be useful.

Before we get into the formula, is it safe or not to assume that something 5/16" is going to have half the tensile strength as something double the size at 5/8"? Thus unless the 5/16" Gr.8 bolt has a tensile strength of at least 120,000 psi it’s out. In this bolt it would thus it is not crossed out yet. That is given for bulk you are only doubling up the PSI as a factor. If not than bulk equals less than tensile strength and the 5/16" bolt would be crossed out. On the other hand since we are also considering sheer strength, we should probably cross out the 5/16" bolt given the Time to get out actual engineering books as it would seem that’s about missing from McMaster.

From Machinery’s Handbook #26 by Erik Oberg, by Industrial Press, NY. 2000 ISBN: 0-8311-2625-6, we learn that a Rockwell hardness scale B is for medium hardness steel verses scale C is for hardness greater than B-100. In other words for anything on the C-chart in comparison to the B-Chart, add 100 to the numbers listed on the C-Chart as they compare to the B-Chart.

Tension is O = F/A 
O = Simple normal tensile or compressive strength in pounds per square inch.
F = External force in pounds
A = Cross-Sectional area in square inches.

Compression is O = - F/A

Sheer is t = F/A
t = Simple sheer stress in pounds per square inch.

(Note the actual symbols do not translate)

This is simple force without other factors into it.

P1476
Preload for Bolts In Shear. - In shear-loaded joints with members that slide, the joint members transmit shear loads to the fasteners in the joint and the preload must be sufficient to hold the joint members in contact. In joints that do not slide (i.e., there is no relative motion between joint members), shear loads are transmitted within the joint by fractional forces that mainly result from the preload. Therefore, preload must be great enough for the resulting friction forces to be greater than the applied shear force. With high applied shear loads, the shear stress induced in the fastener during application of the preload must also be considered in the bolted-joint design. Joints with combined axial and shear loads must be analyzed to ensure that the bolts will not fail in either tension or shear.

General Application of Preload. - Preload values should be based on joint requirements, as outlined before. Fastener applications are generally designed for maximum utilization of the fastener material; that is to say, the fastener size is the maximum required to preform its function and a maximum safe preload is generally applied to it. However, if a low-strength fastener is replaced by one of higher strength, for the sake of convenience or standardization, the preload in the replacement should not be increased beyond that required in the original fastener.

To utilize the maximum amount of bolt strength, bolts are sometimes tightened to or beyond the yield point of the material. This practice is generally limited to ductile materials, where there is considerable difference between the yield strength and the ultimate (breaking) strength, because low-ductility materials are more likely to fail due to unexpected overloads when preloaded to yield. Joints designed for primary static load conditions that use ductile bolts, with a yield strain that is relatively far from the strain at fracture, are often preloaded abouve the yield point of the bolt material. Methods for tightening up t and beyond the yield point include tightening by feel without special tools, and the use of electronic equipment designed to compare the applied torque with the angular rotation of the fastener and detect changes that occur in the elastic properties of fasteners at yield.

Bolt loads are maintained below the yield point in joints subjected to cyclic loading and in joints using bolts of high-strength material where the yield strain is close to the strain at fracture. For these conditions, the maximum preloads generally fall within the following ranges: 50 to 80 per cent of the minimum tensile ultimate strength; 75 to 90 per cent of the minimum tensile yield strength or proof load; or 100 per cent of the observed proportional limit or onset of yield.

P1478
Preload Adjustments. - Preloads may be applied directly by axial loading or indirectly by turing of the nut or bolt. When preload is applied by turning of nuts or bolts, a torsion load component is added to the desired axial bolt load. The combined loading increases the tensile stress on the bolt. It is frequently assumed that the additional torsion load component dissipates quickly after the driving force is remove and , therefore, can be largely ignored. This assumption may be reasonable for fasteners loaded near to or beyond yield strength, but for critical applications where bolt tension must be maintained below yield, it is important to adjust the axial tension requirements to include the effects of the preload tension. For this adjustment, the combined tensile stress (vol Mises stress) Ftc is psi (Mpa) can be calculated from the following:


Ftc = square root of F(2/t) + 3 (2/s)
Where Ft is the axial applied tensile stress in pse (Mpa) and Fs is the sheer stress in psi (Mpa) caused by the torsion load application.


P1489
Working Strength of Bolts.
... the following empirical formula was established for the working strength of bolts used for packed joints or joints where the elasticity of a gasket is greater than the elasticity of the studs or bolts.
W = St (0.55d² - 0.25d)
In this formula, W=working strength of bolt or permissible load, in pounds, after allowance is made for initial load due to tightening; St = allowable working stress in tension, pounds per square inch; and d = normal outside diameter of stud or bolt, inches. A somewhat more convenient formula, and one that gives approximately the same results, is W = St (A-0.25d)
In this formula, W,St,and d are previously given and A = area at the root of the thread, square inches.
Example: What is the working strength of a 1-inch bolt that is screwed tightly in a packed joint when the allowable working stress is 10,000psi? W=10,000 (0.55 x 1 - 0.25 x 1) = 3,000 pounds approx.

Given all of this of the bolts left, we can assume the following with the simple formula:

5/16-24x2" Gr.8 Hex Head Screw (0.2603" id) 150,000psi (0.408862² - 0.078125) = 150,000 (0.1671715 - 0.078125) = 150,000 (0.0890465) = 13,356.975#
3/8-16x2" Gr.5 Hex Head Screw (0.2970"id) 120,000psi (0.4665127². - 0.09375) = 120,000 (0.217634 - 0.09375) = 120,000 (0.123884) = 14,866.08#
1/2-13x2" Gr.3 Military Spec Hex Head Screw of type 18-8 Stainless Seel (0.4056"id) 80,000psi (0.6370962² - 0.125) = 80,000 (0.4058915 - 0.125) = 80,000 (0.2808915) = 22,471.32#
5/8-11x3" Gr.2 Hex Head Screw (0.5119"id) 60,000psi (0.8040669² - 0.15625) = 60,000 (0.6465235 - 0.15625) = 60,000 (0.4902735) = 29,416.41#


Going back to the 1/4-20x3" Alloy Steel Socket Head Cap Screw, it has a tensile strength of 180,000psi. and a minor dia. of 0.1876" for a class 2A fit. This is 180,000 (0.2946727² - 0.0625) = 180,000 (0.086832 - 0.0625) = 180,000 (0.024332) = 4,379.76#.

There is one X factor I have not figured out yet: A = area at the root of the thread, square inches.
Example: What is the working strength of a 1-inch bolt that is screwed tightly in a packed joint when the allowable working stress is 10,000psi? W=10,000 (0.55 x 1 - 0.25 x 1) = 3,000 pounds approx.

You will note that it's (.55 x 1 - 0.25 x 1) above. Where 0.55 x 1 comes from I do not know because it should be 0.622" at the root of a standard coarse 1"-8tpi class 1A bolt. This would give us 10,000 (0.9770065² - 0.25 x 1) = 10,000 (0.9545717 - 0.25) = 10,000 (0.7045717) = 7,045.717#

Something is wrong with my figuring but it would seem that the 5/8-11 Gr.2 screw wins on strength overall. This also means that I got it wrong with I think I guessed the 5/16-24 Gr.8 screw.


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## avkid (Mar 18, 2004)

so complicated


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## miniwyo (Mar 18, 2004)

My awnser, None of the above. Why bolt when you can weld?

RJ
Rock Springs Wy.


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## DMXtools (Mar 18, 2004)

miniwyo said:


> My awnser, None of the above. Why bolt when you can weld?
> 
> RJ
> Rock Springs Wy.



Because you've got to strike it after the show, load it into the semi, drive all night and set it up again tomorrow someplace else.... and the day after that... and the day after that... for the next three weeks.

John


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## HMOcidalmaniac (Mar 19, 2004)

cool i guessed correct


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## Radman (Jun 23, 2004)

whoops I missed the titanium part
hex looks strong when shiny


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## ship (Jun 24, 2004)

Candy questions in addition to being something everyone can and should post to in asking and keeping alive are also something to learn from. If you don’t know the answer, why not especially if it’s a question in a field you are doing? Such questions than should be less intimidating and more a wake up call into something that now realized you don’t understand should be studied.

By the way with candy questions and what scares the beJesus out of me is that many of the “kids” - all of us being some form of kid in our own self realization, now in charged of their own theater as TD or anyone else also responsible for the tech even on the pro-level in their own program should by way of even which bolt to used or specified have a at least basic understanding on the understanding level of knowing a coating to a bolt does not add much to it’s strength overall - given two people cited this Ultra Coating as no doubt their best guess as to the strongest bolt, but still very wrong, this disturbs me. (Those that chose such bolts should not feel too ashamed you did at least offer an opinion which is when it comes to doing your job as a member of the forum or theater much less a leader also necessary in being a tech person at least more than those who are silent, does specify that more study is necessary in that Ultra Coatin was a red herring.) If it’s of any help titanium also is a red-herring in that while comic books cite it as a very powerful substance able to withstand all kinds of battery on a spacecraft, it’s dynamic abuse ability to withstand in reality is fairly low. For me at least it was bulk in thickness of low grade bolt verses strength of more reasonable bolt volume verses grade hardness as a balance into what’s best able to do the job. I still am without a specific answer. 15 out of how many members and guests? At least in brass ones, all that did vote to date deserve extra credit even if the bolt fails in killing someone you are charged with keeping safe. By the way, did I stress the necessity of knowing what the heck you are doing in general when in charged of such things over the glamor of the title? Any link to my own past posts about title as a student verses someone to learn from?

Having to on a day to day basis being both responsible for and actually understanding even the most basic sense of the question asked as to which bolt to use, these even kids intimadated by such a question by innocence don’t escape from the fact that lack of knowledge does not allow them to escape a broken bolt that could out of innocence in understanding still result in death. You note still after so many members only 15 people have voiced a choice. This amount of people at least voicing their opinion, in addition to those that get it right or at least understand the question enough to get the point worries me in comparison to those that don’t yet understand the need to understand and might than cause someone to die. To me the TD title is sacred. I took it only with the most grave of understanding, and even than I understood much less than now.

For this even in the most complex of questions, I still did have a point in addition to making it even challenging for me to answer because I as a hopefully qualified TD don’t even know the best answer of. Those that take the title as TD thinking they know it all most likely know nothing and that’s dangerous especially if you continue to be innocent of what is really necessary to understand if not know in holding that title of ensuring the safety of those on stage much less the theater and audience..

Radman, good in keeping the topic alive, but hex is just a head type. Given a sufficient washer in dispersing the point loading of this detail, the head of the screw will have little effect on the strength of the bolt shaft. Looking shiny is also not to the point. If of help, it’s good you did vote and reply. Good better still if you cite the difficulty of the question in something that even though we are stage hands and not structural engineers, requires further immediacy and interest in study.


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## Radman (Jun 28, 2004)

By titanium I meant the materials of all the bolts.  
By shiny I meant not rusty.  
By strong I meant less likely to strip, but I change that from hex to phillips/square combo. :x 
By all of the above I meant peer pressure!


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## tjbaudio (Aug 13, 2004)

It is some what late here but I think I may shed some light on the math.

When figuring bolt strenth (tensile) :

area*PSI is the basic answer.
Remember area = pi(R^2)
R = 1/2 diamiter

So for our bolts:
(pi (D/2)^2) PSI

5/16-24x2" Gr.8 Hex Head Screw (0.2603" id) 150,000psi
pi((.2603/2)^2) 150,000=3.14(.13015)^2)150,000=3.14*.01694*150,000=7,982lb

3/8-16x2" Gr.5 Hex Head Screw (0.2970"id) 120,000psi
8,313lb

1/2-13x2" Gr.3 Military Spec Hex Head Screw of type 18-8 Stainless Seel (0.4056"id) 80,000psi
10,336
5/8-11x3" Gr.2 Hex Head Screw (0.5119"id) 60,000psi
12,348lb

Just for kiks a Gr.2 1/4" 60,000psi
1658lb

So in this case thicker is better.

Some other notes (gathered from taking to a guy who made a living selling bolts)

Fine thread helps with vibration lossening of a nut, thats it.

Stanless steel (nut and bolt) when properly torqued will bind and you will have to cut it off (or break the bolt as I had to do with some 1/4" stanless at a gig, not fun) Only use stanless if it has to be weather resistant and not taken apart.

Washers add to shear streanth of the joint by adding more planes of friction.

Something else to consider is saftey. When designing a rigging system most will strive for 10:1 saftey (some go as low as 5:1)

That meens the little 1/4"Gr.2 is "safe" to hold 165 lb. This is not taking into account extra stress other than direct pull.

In building the stairs mentioned in this thread.
Lets say the stairs are 200 lb on there own.
we are using carage bolts up threw the floor at the top.
2 ,200 lb actors stand on it at some points in the show.
that is a total of 600 LB on the top (this is a worst case under normal situations)

Our 10:1 says the bolts need to hold 6,000 LB

that is:
4 1/4" Gr.2
or 
2 5/16" Gr.2

In practice I would probably grab 3/8" if I had them.
That assumes the rest of the parts can take the load.

One more thing. The threads of a bolt gives us mechanicle advantage. That is why a 1/4" bolt (breaking strenth 1658lb) can be snaped off with a 6" wrench.

Tom B
ps time for bed.


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## ship (Aug 13, 2004)

Stainless steel bolts also have the advantage of being more heat resistant such as in conditions of fastening a lamp base to a fixture. In general I use Stainless Steel top lock nuts with normal screws if not actual ground screws for ground terminals, or stainless steel screws with Zinc coated top lock nuts for lamp base attachment. Given it’s a one time use deal because the Stainless will deform the normal steel threads on installation. This as opposed to all Stainless or all Zinc where at best you can’t rely on which will strip out or both will strip if not break in tightening in the case of Stainless. Reason for using top lock nuts being that Nylock nuts will melt and degrade under higher temperatures, and lock washers don’t always work.

Washers in general also add to the torque you can add in that they act as if a ball bearing in friction of nut against surface. Rigging is 10:1 on stage, in the industry it’s frequently 5:1 for construction safety standards.


Carriage bolts are normally grade 2 but can be found as grade 5. This would be a factor. Overall and including what you say, very good without checking the math. Tensile strength is a factor but so is sheer strength for this application which is a different formula. The sheer strength of say a gr.8 by 3/8" bolt might be similar to that of a gr.2 by 5/8" bolt given tension upon lumber tends to be less a factor such as on a slightly loose bolt or that the lumber compresses with movement. It’s also shown that choosing the bolts used in general becomes very difficult without a ready reference to them. Interesting there is no pre-figured chart ever developed. Any chance you might go for one dependant upon the application dead hang, sheer torsion etc?


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## Mayhem (Aug 13, 2004)

Not familiar with 'top lock' nuts - anyone care to give an explanation?


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## ship (Aug 16, 2004)

Top Lock and Side Lock nuts are what’s called thread deforming nuts. Remember how when you get a nut tight, it’s a question of the friction caused by jamming nut to threads of the screw to keep it in place? What happens if there was some movement or nut were not made tight by means of lock washer or thread locker? The nut would come loose... A nylock - Nylon thread lock nut uses nylon to prevent this movement but the nylon does not take to temperatures well. 

A Top Lock nut has it’s last thread out of alignment with the rest of them so that in screwing it on, the last thread by way of friction is already preventing the nut from coming loose no matter the position. This is given that the top locking part of the nut faces outboard so it’s the last to engage the screw’s threads. Otherwise since it when working properly is almost even tearing up the treads of the screw as it passes by them, the threads of a nut following the top lock would not have much to grab to when it does get tight.

A side lock nut is similar except the deforming part of the nut is in the center of the threading by way of some dings in the nut which scrape. It is normally a little abrasive to the screw as it goes on but still has the same effect.

On these nuts, infrequently the ding to the threads will either not be deep enough to hold or wear out just as a nylock nut in it’s nylon can wear out and thus do nothing. All such nuts which don’t hold should be thrown out. Upon removal of the nut from a screw as above and especially if there is a significant difference in the grade between nut and screw, check the threads on the screw for stripping. This is possible to happen. Such are not to be used on something which is going to come off a lot.

P.S. Check out your McMaster Carr website for other forms of lock nuts and perhaps better descriptions.

Typical uses beyond lamp bases would be the bolt holding yoke to fixture on a PAR can - which should be reversed so you can see when it's unscrewing. Nylon nuts on a PAR fixture are kind of counter productive due to the heat. Other uses for them would be in fastening the fixture to a lamp bar though I'm not sure of why the place I work do this nor want to get into that battle. My guess would be that a top lock nut in this case would both be shorter in not requiring a lock washer or the extra height of a nylock nut, withstand more heat, and given the fixture is designed to swivel, it won't have problems in doing this but still staying in place unlike a nylock nut after time.

Note also with all nuts, you want at least three threads of the screw extending beyond the nut, this is especially important with a top lock nut that relies upon that end part of the nut to keep it in place. Should there be a little movement in the nut, it otherwise would become a normal nut.


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## Mayhem (Aug 16, 2004)

Thanks for that Ship,

I have never seen them before, only nylock, which as you point out are not suitable for heat applications. 

To test for wear on the nut - is this done in a similar way to testing nylock nuts? In fact, what is the correct way to test either of them?

The method that I use (past visible inspection) is to see if I can turn one without using a wrench.


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## ship (Aug 16, 2004)

That's normally the way to see a problem, otherwise if it just screws on with a wrench far too easily.
On top lock screws, I have found say 1 or 2% of a lot of 100 especially once you get into the smaller screw sizes that for some reason don't have a good hold on the screw, the dimple is not dimpled all the way.

In industrial conditions, I have seen it before that a cold chisel and mallet have been used to dimple a nut. This could work on say a grade 2 nut in general but one would not want to do it for less than perminant installs, nor for structural applications where a Grade 2 nut would not be used anyway.

Also, should you stock such things, be careful not to mix the side lock nuts in with the normal ones or you will have troubles with those not knowing the difference.


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## tjbaudio (Aug 16, 2004)

ship said:


> Tensile strength is a factor but so is sheer strength for this application which is a different formula. The sheer strength of say a gr.8 by 3/8" bolt might be similar to that of a gr.2 by 5/8" bolt given tension upon lumber tends to be less a factor such as on a slightly loose bolt or that the lumber compresses with movement. It’s also shown that choosing the bolts used in general becomes very difficult without a ready reference to them. Interesting there is no pre-figured chart ever developed. Any chance you might go for one dependant upon the application dead hang, sheer torsion etc?



I agree that a chart would be nice. With most of what I build I go by what feels right. Now granted that most of it is(Edit NOT) rigging that may be ok. Looking at the math I think I over size any way witch is also a good thing. It would be nice to have a simple chart that could be put up in the shop for standard bolt sizes and applications. This may be a good project for CB. One thing to worry about though is libility. We would also need to take into acount varience in manufacuring. Perhaps we should also track down some bolt manufatures and ask them.

Tom B

Edit: Most of what I build is not rigging. When rigging I do do the math and look at ratings.


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## ship (Aug 18, 2004)

Very good concept, I would definitely trust a domestic brand most (them little triangles and other markings or stamps not designating grade designate manufacturer.) I believe it is however getting more rare for domestic manufacture of bolts however in general. Bolt grading still should have a general factor in tolerances between one bolt to another.

Given Crosby group for instance has a chart for their wire rope clips, as with most other things, it's surprising that there is not something like three ready access charts. I’m thinking tension, compression and sheer, but torsion might also be an extra factor.

Any college kids out there looking for a term paper in their theater engineering classes? I have enough of a loadstone project going on with just lamp specs. Stacks and stacks of paperwork to type into the files and more to research yet. Even starting to add LED lights with screw bases to the notes. Our architectural club install department is starting to sell them putting me both in charged of finding fixtures and lamps, plus knowing the difference thus they have to get added to the notes.

One lamp for instance that came up Monday was on a note from Martin tech briefs that the HMI 1200w/S is no longer the primary lamp for a Mac 2K. It's now the upgraded HTI 1200w/D7/60 also by Osram. Little detail that requires a lot of work to change in the notes. It needs to find it's way to my lamp/fixture combinations page - both of them (one for shop inventory and one for fixtures in general.) Needs to be added to the lamp pricing spreadsheet and I need to start getting quotes on how much the new lamp is going to cost me. 

Finally and granted I have been aware of this lamp for almost a year now and was wondering besides the available cooling fin what the difference was or if it was suitable. It was only added to the specifications page of my notes with the preliminary data available from Osram which did and still does not include a part number beyond the temporary one of FO 5166. Short of having a part number, much less as a lamp being added to the Sylvania part of the companies's website, it's going to be very difficult to get the lamp.

This requires constant monitoring of the Sylvania website to see when it gets added in getting a part number and in seeing if the specs change as frequently happens between preliminary data and permanent specs.

This is only one of thousands of lamps I'm tracking developments of constantly. Part of my job at work to be the go to guy on such things. A bolt project thus for me at least is way not realistic now that my periodic vacation from doing lamp specs is over and I’m back into updating the notes again something like three to 20 hours a day every day. Just started to do them again after taking the last month or two off and I have a lot to catch up on. Only about two years behind in some cases now.


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