Rear Bumper Project

[aarcaris]

Originally Posted by WillTheThri11

Looks great...nice that you could import a 3D scan of the van. How did you do that btw? Wondering if I can do this in SolidWorks. Any particular reason you are mounting the bumper on the frame rails vs the stock bumper flanges? Another thought, you may need to box in the "slider" portion from the wheel-well back so it doesn't crush if/when you come down on a rock...Probably also want that square tubing to be same size as your sliders were.

one more thought...you may want to include a cutout and maybe that could double as a hi-lift jacking point...only trying to help take my suggestions or leave them...I love this project!

Thanks for the compliments! The app I used for the 3D scan is called Polycam. It uses the lidar camera and the regular camera on your phone to capture the 3D scan. It works decently for some things, but with most 3D scanners reflections are not their friend, so that's why this scan looks so lumpy and has so much of it missing. From your phone, you can export it into a bunch of different file formats as a mesh model, so I am pretty sure it would work for Solidworks.

I was thinking of mounting to the frame rails and modifying the stock bumper flanges as I felt like the stock mounting points wouldn't be strong enough to keep everything rigid. There is quite a bit of force on the mounting points especially when the swingouts are open as it creates a lot of leverage so I figured if I could mount further back on the frame in multiple spots it may help keep everything really rigid.

The only reason why I didn't box that section on this model is that I am trying to not have to cut the body at that point if I can avoid it. The body hangs down on the sides which prevents me from doing a fully boxed section but you bring up a good point. I should look at it more and probably at least add some extra gussets through there.

I was planning on making the square tube the same size as the connection pieces on my sliders and I'll probably use a similar mounting plate.

I had played around with adding two jacking points on either side for a Hi-Lift but didn't like the way it was looking. So after some searching, I found a product called The D-Lift Adaptor. It connects the jack to the recovery point of the bumper which then allows for the functionality of a jacking point without the look of a hole in the face of the bumper. So currently that is what I was thinking I could use as a jacking point.

I really appreciate the suggestions and comments on the design, and I am glad you are enjoying following along on this one!

Originally Posted by Vanimal

Your pics and idea are great. The main thought should be focused on what kind of wheeling you will do. If you doing beach and 1 to 2 out of 5 trails then you can load and add all you want. With that said your accessories will only be your challenge which ones and where to put them. Sometimes we can over think things.

Thank you! I know that I am probably going overkill on this bumper design. I am not planning on hitting it all the time but I would rather be ready for those harder trails especially if I am going through all this effort and money to build it. No matter what the goal is to find the balance between functionality, strength, and weight.

Originally Posted by boywonder

This iteration looks very nice!

Can you calculate the weight in Fusion360? I'm unclear what Fusion360 offers that Solidworks doesn't......other than it's lots more affordable.

...a couple of comments......

The spindles for the swingarms are going to see large bending moments. Have you played with an aluminess setup that has stuff in the box? Open and close either swingarm, there is a lot of weight cantilevered out there on both sides.

When closed, Aluminess has delrin ramps that help support the arms screwed into the top of the bumper, I did a similar thing.

I would have the spindles extend down through the bumper and welded to the lower bumper surface, you will need that extra "wheelbase" for stiffness.

It may have been discussed in my bumper thread (can't remember) but you could consider using some modern "unit bearing" assemblies from front or rear hubs as the spindle support. They are kind of perfect for this, a dual row set of beefy bearings in a flanged hub with holes in the flange.

I see you have a stiffener across the rear section of the bumper, but you still have a fair bit of open cross section. If you can box in more of the cross section that will increase your section modulus a lot.

I would also triangulate the flanged spare tire support for added stiffness.

Thank you!

So far I have been impressed with Fusion 360. The last program that I used similar to this was Solidworks, but that was probably over 10 years ago so it's been a bit of an adjustment as I have been relearning workflow and process of it. The biggest benefit for me is that it's an Autodesk product and is much more affordable!

I was able to calculate the weight in Fusion 360, and so far with how it is designed it's coming in at around 260 lbs for the bumper and the swing arms. It's a heavy one! Compared to other bumpers with similar designs for vehicles like Tacomas and 4Runners it's about the same weight so considering this one is for a full size rig I guess it's probably right on par. Currently, it's pretty much designed with almost every part being 3/16" or 1/4" steel. I think there are a few areas where I could cut some weight and possibly thin some of the material down to 1/8" in some limited areas, but not entirely sure about that one yet.

- There is a lot of weight on either side for this design. I have tried to do some structural analysis using Fusion, but have yet to figure out how to actually use that stuff. I know it can do that, but I'm still very green on this program. Also, I should mention I am by no means an engineer, so some of these ideas are purely based on me looking at existing products and figuring if "x" product can handle this then this should be able to do that. So I appreciate the input on here from people who are more credentialed than me.

- It's hard to see in the model but I did put in some Delrin pads exactly how you did on your bumper! I figure the more support the better.

- Extending the spindles through the bumper is a good idea. I had thought of doing something like that before, but the biggest problem I saw was that the off the shelf spindle kits only have a depth of +-4". So they wouldn't have enough depth to connect the top and bottom. That is something I will need to look at more closely though.

- I hadn't been looking at using a unit-bearing setup, but it's a good idea and something I will have to look into more. I was planning on using a dual tapered roller bearing setup as they are serviceable and already have lots of off the shelf options for spindles.

- I appreciate the incites on this! My goal was to add some strength while also minimizing the weight as much as possible. I may have gone too far to the minimizing weight side of that scale. I was thinking that since it was all 3/16" steel it would still be strong enough, but that is something I will have to look back at. Now if only I could figure out the structural analysis part of Fusion360.

- Adding a triangulate flanged for the spare tire support is a great idea and something I am going to for sure do! Looking back at it I think there are a few areas in which adding some gussets would be a good idea.

Thank you again to everyone for your questions and suggestions! As I have said before I am out of my depth on this project but that is part of the process that I enjoy. So really any and all suggestions and comments are super helpful and much appreciated.

[boywonder]

3/16" steel seems like a lot....

My bumper is 3/16" Aluminum and that was intimidating enough.

Is there any way you can determine the thickness of other steel bumpers?

The elastic modulus (stiffness) of mild steel is roughly 3x the modulus of aluminum.

..and the density (...and weight for same thickness) of steel is also about 3x that of aluminum....

That (very roughly) implies that if you reduce the steel thickness to 1/3 that of aluminum you'll end up with (very roughly) similar weight and stiffness as an aluminum part. There are lots of assumptions and details in that statement but you get the idea.

Also, in general a thinner walled closed (boxed) cross section will be a lot stiffer than an open section constructed of thicker material.....lots stiffer.

[E-350]

Just a very small, but important, thing I‘m not it was mentioned before: bottle opener and a place to park your can [emoji23][emoji23] I love the corner of my UJoint bumper where I can park my beer (just for a short moment of course!)
Someone must have had that in mind during the design phase!

[Lilnuts2]

To the OP I'm so jealous of your modeling skills.

I like the Ujoint bumper. It has a steel structure with a replaceable aluminum skin if damaged.

[aarcaris]

Originally Posted by boywonder

3/16" steel seems like a lot....

My bumper is 3/16" Aluminum and that was intimidating enough.

Is there any way you can determine the thickness of other steel bumpers?

The elastic modulus (stiffness) of mild steel is roughly 3x the modulus of aluminum.

..and the density (...and weight for same thickness) of steel is also about 3x that of aluminum....

That (very roughly) implies that if you reduce the steel thickness to 1/3 that of aluminum you'll end up with (very roughly) similar weight and stiffness as an aluminum part. There are lots of assumptions and details in that statement but you get the idea.

Also, in general a thinner walled closed (boxed) cross section will be a lot stiffer than an open section constructed of thicker material.....lots stiffer.

Thanks for the explanation. I appreciate the insights from someone who actually knows what they are talking about!

I had originally had it pretty much all at 1/8" thickness but when I showed my fabricator buddy who works at a local company that makes Dodge suspension and bumpers he suggested bumping it to 3/16" and adding the extra internal "webbing" design.

Since there are a ton of companies making bumpers for other rigs I searched around and gathered some data points and used them as a reference point to see what material thickness they were using. Here is a rough list of companies and the thickness they were using on their bumpers.

• C4 Fabrication - 3/16" for main shell, 1/4" for mounting plates (Toyota Tacoma)
• BAMF Fabrication - .188" for main shell, mounting plate brackets .50", Swing arms .188", Tire support .134" &.188" (Toyota Tacoma)
• Relentless Fabrication - 3/16" for main shell, mounting 1/4", Swingarm 3/16" arm, 1/8" panel, and 1/4" mounting plate. (Jeep Gladiator)
• Expedition One - 3/16" for main shell and 1/4" for mounting plates 3/16" (Ford F250 Bumper)
• Chassis Unlimited - 3/16" for main shell 1/4" mounting plate (Dodge 2500 Bumper)
• Backwoods Adventure Mods - 7ga for main shell 1/4" mounting 3/16" and 1/4" Aluminum for swingouts. (Mercedes Sprinter)
• Buckstop - 1/4" and 3/16" for shell or 3/8" and 1/4" aluminum (Ford E350)
• Aluminess - 3/16" Aluminum with 1/4" Aluminum at mounting points (Ford E-350)
• U-Joint - 1/4" For base structure/ mounting unknown thickness for aluminum skin. (Ford E-350)
• Thuren Fabrication - 3/16" for the main structure. (Dodge 2500)

I appreciate the simple explanation of the difference between aluminum and steel. I honestly was surprised to see so many of these companies are using 3/16", especially in comparison to how Aluminess makes almost everything out of 3/16" and obviously it holds up well. I've seen some people's Aluminess bumpers after hitting deer at 60mph looks like nothing happened! I guess the biggest difference between Aluminess and others is that most of these other bumpers are made to take a beating on rocks so they are overbuilding them to withstand repeated abuse. That's just a guess though.

Based on the simplified explanation you gave I should probably look back at it and see if I could lighten up the design some by going to 1/8" for the main shell which would probably drop it enough that I could box the shell and help add some rigidity to it. As I said I am out of my depth so I really appreciate your input!

Originally Posted by E-350

Just a very small, but important, thing I‘m not it was mentioned before: bottle opener and a place to park your can [emoji23][emoji23] I love the corner of my UJoint bumper where I can park my beer (just for a short moment of course!)
Someone must have had that in mind during the design phase!

Attachment 46592

Those are good ideas! Even though I don't drink having a spot for a bottle opener for others is a good idea to incorporate into the design.

Originally Posted by Lilnuts2

To the OP I'm so jealous of your modeling skills.

I like the Ujoint bumper. It has a steel structure with a replaceable aluminum skin if damaged.

Thank you! It probably wouldn't seem as impressive if you knew how much time I've spent on the model, I'm slowly figuring it out though. The U-Joint bumper is a nice design with the best of both aluminum and steel construction. I had tried to do something similar at the start of this process, but couldn't get the look and constructability to work well on this design.

[deserteagle56]

Better plan on adding an extra leaf spring to your rear suspension!

It may not matter to you - but that design will not allow the van's rear doors to open fully. Which reduces the opening by about 8". Same problem with the Aluminess which is why I couldn't use it as I ride my quad into the back of my van.

[1der]

Serious consideration should be given to strengthening the bumper mounting flanges attachment to the ends of the frame C channel. Those need to be really, really strong, especially if considering jacking up using the bumper. l

[boywonder]

Originally Posted by aarcaris

I appreciate the simple explanation of the difference between aluminum and steel. I honestly was surprised to see so many of these companies are using 3/16", especially in comparison to how Aluminess makes almost everything out of 3/16" and obviously it holds up well.
Based on the simplified explanation you gave I should probably look back at it and see if I could lighten up the design some by going to 1/8" for the main shell which would probably drop it enough that I could box the shell and help add some rigidity to it. As I said I am out of my depth so I really appreciate your input!

Yes it's a good approach to use the material where you need it, and if you can design closed sections with thinner walls that usually gives plenty of stiffness.

There's lots of torque/bending moment on the swing arm spindles, if you don't want to connect to the door hinges they'll have to be very stiff.

[Vanimal]

Regarding the spindles. In post #19 you can see the spindles on my bumper I envisioned. I started with a simple structural backbone. The spindles go thru the tubing and welded on bottom and top of tubing. The box was a cut down Jet ski trailer box and the ladder double as the cradle to Rais and lower the spare tire. It obviously needs repaint but it's been on the van for years no issues with the spindles. The arms swing roughly 80* before the stops to avoid tail light contact.

[aarcaris]

Originally Posted by deserteagle56

Better plan on adding an extra leaf spring to your rear suspension!

It may not matter to you - but that design will not allow the van's rear doors to open fully. Which reduces the opening by about 8". Same problem with the Aluminess which is why I couldn't use it as I ride my quad into the back of my van.

Luckily I have 2 extra leafs that I had to pull out of my leaf pack when I did the 4x4 Conversion plus I am still sitting a little high in the rear. So at least hopefully I can take care of the added weight if needed.

As for the door that's true that I will look for some functionality, but luckily for me it's not a deal breaker. I have two drawers in the rear and since they are inset from the sides the doors don't even have to be at a full 90 to get them open. Since I have the pivot point pushed further out I am hoping that helps maintain the most opening angle as possible.

Originally Posted by 1der

Serious consideration should be given to strengthening the bumper mounting flanges attachment to the ends of the frame C channel. Those need to be really, really strong, especially if considering jacking up using the bumper. l

Yeah, I am 100% not relying solely on the stock mounting brackets. As of right now, I plan on modifying the mounting plate so I can use the two holes on the inside of the plate and cut off the outside of the frame rails part so I can run the plate back along the frame rails to connect into the factory hitch mounting holes. I think this should give it a lot more area for it to grab on to in multiple planes rather than the single plane of the factory mounts.

Originally Posted by boywonder

Yes it's a good approach to use the material where you need it, and if you can design closed sections with thinner walls that usually gives plenty of stiffness.

There's lots of torque/bending moment on the swing arm spindles, if you don't want to connect to the door hinges they'll have to be very stiff.

That's a good point. I have started to re-design the pivot point to help strengthen it up by adding more structure under the skin of the bumper that it will tie through. Also have started playing with the possibility of adding an additional pivot up on the upper Brush guard similar to how Aluminess does it. This would also give me the option to tie it back into the door hinge as you said.

Originally Posted by Vanimal

Regarding the spindles. In post #19 you can see the spindles on my bumper I envisioned. I started with a simple structural backbone. The spindles go thru the tubing and welded on bottom and top of tubing. The box was a cut down Jet ski trailer box and the ladder double as the cradle to Rais and lower the spare tire. It obviously needs repaint but it's been on the van for years no issues with the spindles. The arms swing roughly 80* before the stops to avoid tail light contact.

That's a good idea! The last swing out bumper I built (about 10 years ago) I did a similar thing and it worked pretty well. So far if my model is working correctly I should be able to get 110-120 Degrees of swing with this design before there starts to be any interference. Obviously, real world may yield a different result.