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General Discussion of preventative/corrective maintenance and other technical issues regarding your coach that are not covered in other Mechanic's Corner categories (ex. refrigerators, water heaters, and compressors).

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  #181  
Old 3 Weeks Ago
Randy Dupree's Avatar
Randy Dupree Randy Dupree is offline
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Lets fix some Birds,we have about beaten the ramps to death.
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Randy Dupree
2000 LXI 43
Bainbridge,Ga.
Port St Joe Fl.
www.buybyebluebird.com

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  #182  
Old 3 Weeks Ago
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Steelwheels Steelwheels is offline
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Quote:
Originally Posted by CarneyRacing View Post
Okay, I have to draw objection here. People need to be a little more conscious of throwing out the gloom and doom saying "never" in some scenarios.

As with any jacking/lifting/ramping scenario, you need to be conscious of the base you are working on. You working on a pad of concrete or asphalt -- good base. Sand -- bad base, etc. Be smart about what you base is, because without a good base, your ramps will be placed in a bending load, and no ramps are really designed with this in mind. The case where the plywood would fail is when there is not a good base, which is a recipe for disaster with any ramp.

I agree that if someone wants to make jacks or ramps, they either need to really know what they are doing, or simply make them with ridiculous overkill.
The way it was posed from Pairodice, he is proposing to make a set of ramps that are solid laminated plywood 24" wide, wide enough to fully support both of the duals. Solid right? One sheet laminated on top of another? If I mis-understood this, please don't bother reading on.

Now lets look at laminated plywood. on the low end, plywood has a compressive strength of 4,000psi. And we will make some very conservative assumptions:
Axle weight:25,000 lbs
tire contact patch size:10"x11"
# of contact patches: 4
Given this info, the pressure loading on the ramps under the tires is 57psi. Which gives us a safety factor of over 70. Over SEVENTY. That safety factor is at least 10 times higher than the safety factor of the tires, the wheels, the suspension, axles frame, etc. Under this extremely low loading scenario, the only compression in the ramps will be if they weren't tightly glued together, and that would result in slight compression, but nowhere near failure. if a ramp is made of solid wood (not rotten), has a solid base underneath, and fully covers the tire's intended contact patch, it simply won't fail.

There could be a million reasons you don't see ramps like this in a commercial shop, but I can assure you that compressive strength is not one of them.

Wow, you really crunched those numbers, I hope you had a firm base.

Just funnen, now let’s get out there and fix some birds.
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  #183  
Old 3 Weeks Ago
pauleburgess pauleburgess is offline
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Quote:
Originally Posted by brhodes View Post
Coach Craft crew rolled my coach up their ramps made of 8 layers of 1x12 pine glued and screwed together and had no issues as they looked to have been well used.

I agree that the base you are setting up on is very important, no soft earth, gravel, etc. as concrete would be my preference only.

Just my 2¢
They left one of these at my site-- I returned it to them, but was surprised by how light it was. Building something is certainly on my to-do list.
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  #184  
Old 3 Weeks Ago
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CarneyRacing CarneyRacing is offline
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Quote:
Originally Posted by Steelwheels View Post
Wow, you really crunched those numbers, I hope you had a firm base.

Just funnen, now let’s get out there and fix some birds.
I do.

Have to take a little break from bird fixing to spend time with the family and save up for the next up upgrades.
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Pewamo, MI
1979 FC35 SB
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  #185  
Old 3 Weeks Ago
Randy Dupree's Avatar
Randy Dupree Randy Dupree is offline
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Join Date: Dec 2007
Location: Port St Joe,Fl
Posts: 35,622
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Quote:
Originally Posted by CarneyRacing View Post
Okay, I have to draw objection here. People need to be a little more conscious of throwing out the gloom and doom saying "never" in some scenarios.

As with any jacking/lifting/ramping scenario, you need to be conscious of the base you are working on. You working on a pad of concrete or asphalt -- good base. Sand -- bad base, etc. Be smart about what you base is, because without a good base, your ramps will be placed in a bending load, and no ramps are really designed with this in mind. The case where the plywood would fail is when there is not a good base, which is a recipe for disaster with any ramp.

I agree that if someone wants to make jacks or ramps, they either need to really know what they are doing, or simply make them with ridiculous overkill.
The way it was posed from Pairodice, he is proposing to make a set of ramps that are solid laminated plywood 24" wide, wide enough to fully support both of the duals. Solid right? One sheet laminated on top of another? If I mis-understood this, please don't bother reading on.

Now lets look at laminated plywood. on the low end, plywood has a compressive strength of 4,000psi. And we will make some very conservative assumptions:
Axle weight:25,000 lbs
tire contact patch size:10"x11"
# of contact patches: 4
Given this info, the pressure loading on the ramps under the tires is 57psi. Which gives us a safety factor of over 70. Over SEVENTY. That safety factor is at least 10 times higher than the safety factor of the tires, the wheels, the suspension, axles frame, etc. Under this extremely low loading scenario, the only compression in the ramps will be if they weren't tightly glued together, and that would result in slight compression, but nowhere near failure. if a ramp is made of solid wood (not rotten), has a solid base underneath, and fully covers the tire's intended contact patch, it simply won't fail.

There could be a million reasons you don't see ramps like this in a commercial shop, but I can assure you that compressive strength is not one of them.

Very informative post,thanks for doing the math for the rest of us.
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DO NOT SEND PM
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Randy Dupree
2000 LXI 43
Bainbridge,Ga.
Port St Joe Fl.
www.buybyebluebird.com

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