Math Challenge.

[Rhapakatui]

So my dad has a problem at work.

1. I got a new job and am not there to help with the tough math stuff.

2. he has a short deadline and his bolt holes aren't lining up.

 

I've noticed some engineer types on here and thought maybe you could help.

Dad is building a staircase around an oil tank. The tank is 30' tall with a 60'1'' diameter. Rise and run on the steps is 8" and 8" so its on a 45degree angle. Staircase is 30" wide. He had all of his flat bar and angle rolled to fit the staircase, laid out and drilled the holes. When he got his stair treads bolted to the outside part of the staircase, the bolt holes do not line up with the inside part. I'm not there so that's what I got over the phone. If there are any math wizzes on here or auto CAD guys, help me out and see if you can figure out what he did wrong.

 

I figure this is as far from a Datsun discussion as possible, but I was on here when I got the call and I don't know any engineers. I ussually solve this stuff for Dad if he can't figure it out. We make a pretty good team, but I quit on him to take a better paying temporary job and now he has a problem. Thanks for any help.

 

Jerm.

[INDY510]

Is it multiple choice?

 

 

I can't see the pics

[fastdadd]

jsut bolt it togehter then weld in a piece to make it look right.....that is the ratsun way

[Laecaon]

Seems like some information is missing. Not lining up what way. Like the first step was right and the rest were wrong?

 

The inside track is running a circle with radius 360.5" and the outside is at 390.5".

 

Are the steps rectangular? If so then either there is some overlap of the steps or there is gaps in the steps. Of course I am assuming the steps wrap around the tank.

[INDY510]

I also don't understand what your question is????

 

 

 

 

 

So if the goal is to climb 30 ft......... 30 x 12 = 360.......... 360 / 8 = 45

 

 

So you need 45 stairs to get to the top

[Laecaon]

The problem is that both the inner and outer track were ordered at 8run8rise. This is true for the outer track. The inner is going to me more of a 6run8rise. Exaggeration of course.

[Rhapakatui]

Steps are rectangular I know that much. Only info I forgot was a 6" gap between tank and stair structure. I'm sure if I was there I could figure out the problem. As I am not though, there are no pics. I think he needs to subtract a little on the run for the inside set of bolt holes to make it spiral. My mom called to ask for help. She's not a structural fab hand but she's trying to help. I told him to slot the inside holes and run with it.

[nismo dr]

so thats why he was the lowest bid

[Rhapakatui]

Yeah, he kinda got screwed when my new job started a week early. I was supposed to help him this week and start the shut down Tuesday. They decided to call us in early so we could get used to the place. Stupid Exxon Mobil refinery.

[Laecaon]

I would help, more, like do some actual calculations, but I need to go work on my car. And I dont have my handy dandy notebook to help me at the moment. I do math better on paper than the computer.

[Rhapakatui]

Yeah I'm supposed to be dismantling an altima tonight and scavenging a sentra for usable parts. Instead my wife has me at the beauty parlor so I can tell her what to do with her hair. The stair job should've been finished today but now it looks like I'll be helping on that tomorrow instead of enjoying my last weekend off til Halloween.

[INDY510]

My calculations show that if the inside of each step is 8 inches wide,,,, ,,, then the outside of each step needs to be ~9.066 inches wide

 

 

Well there's your problem

 

 

 

The staircase will wrap around a little more than 1/4 of the tank....... ... the outside railing will be about 4ft longer than the inside railing

[INDY510]

That's only if the inside track of the staircase is always 6ft from the outside of the tank.....

 

 

And the staircase is 30" wide

[Rhapakatui]

That's only if the inside track of the staircase is always 6ft from the outside of the tank.....

 

 

And the staircase is 30" wide

 

 

The gap is 6 in not ft. Other than that wow thanks. I hadn't done any numbers on it so I didn't think the difference would be that big outside to inside. I don't think my dad allowed for any difference at all. Guess he was in a hurry.

 

I'm amazed at how many responses I've gotten. You guys rock. I'm about to call and check his progress and I'll let you know.

[INDY510]

Don't forget my member title...... .......... I'm a indiot

 

 

There is a big probability that everything I said is totally wrong....... :lol: ......... I'll recalculate for 6inches not 6feet

[Thomas]

The outer length shouldn't be too difficult to find using the ratio of sides from similar triangles:

 

L_{outer} / 8" = 396.5" / 366.5"

 

L_{outer} = 396.5" /366.5" * 8" ≈ 8.6548"

[Rhapakatui]

Think we solved it. Indy was the closest. We drew it out full scale on the shop floor and it comes out to where the outside is about 8" x 8 5/8" rise and run if we leave the inside 8 x 8 like the prints call for. Punched our holes. Gonna test fit after lunch.

[INDY510]

Indy was the closest.

:hyper: ........ :crying: ............ :blush:

 

 

I figured it out an easier way this morning:

 

The tank: 60ft

 

Gap to stairs: 6" ................ 60ft + 6" on each side = 61ft diameter for the inside rail of the staircase

 

 

Staircase: 30" ............... 61ft + 30" on each side = 66ft diameter for the outside rail of the staircase

 

 

Circumference:

 

61ft x 3.14 = 191.54ft .. ... x 12" = 2,298.48 inches is the circumference of the inner rail of the staircase

 

66ft x 3.14 = 207.24ft... ... x 12" = 2,486.88 inches is the circumference of the outer rail of the staircase

 

 

 

2,298.48" / 8" = 287.31 ... 8" steps to go around the inner rail

 

2,486.88" / 8" = 310.86 ... 8" steps to go around the outer rail

 

 

287.31 / 310.86 = 0.9242

 

 

 

 

So if the inner side of the steps are 8" ...... . the outer side should be about 8.65"

 

 

 

 

 

8" x 8 5/8" rise and run if we leave the inside 8 x 8 like the prints call for

 

8 5/8" = 8.625" ............. I guess I could have been alot closer if I was thinking clearly...... :hmm:

 

 

 

Did this equation make any sense?

[INDY510]

The outer length shouldn't be too difficult to find using the ratio of sides from similar triangles:

 

L_{outer} / 8" = 396.5" / 366.5"

 

L_{outer} = 396.5" /366.5" * 8" ≈ 8.6548"

 

I think Thomas is smarter than all of us....... .. :lol:

[Rhapakatui]

Oh yeah, I guess so.. Sorry Thomas for totally overlooking your awesome math skills.. Thanks again for all the help on what may have been the nerdiest thread in Ratsun history...

BTW

Success on the first section of the stairs

 

I had things to do and I'm not really on the payroll anymore so I didn't hang out to see the entire staircase through once I saw it was working.

 

Thanks again guys.. I totally owe you one. Next time ya need something welded let me know.

[Rhapakatui]

so thats why he was the lowest bid

 

I told my Dad, and the shop owner Troy, that this was my favorite reply. They both laughed and proceeded to tell me that they bid the job 2k over the other guy, but the customer liked their past work so much that they gave it to them anyway.