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Learning how to build Lotus Seven replicas...together!
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PostPosted: Wed Apr 25, 2012 7:45 am 
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Reinforcing the "U" shape brackets or laying the bracket on the side is a common error. You need open sides or if you have already added a reinforcing plate you should cut a slot in the center. The reason is that most to the load from tighting the bolt is used to buckle the reinforcement and is not the actual clamp load use to hold the control arm bushing. Look at any production frame an you will notice that they all have slots that allow for the sides of the bracket to deform around the bushing spacer. The other option is to pack spacers between the wall of the bracket and the bushing center spacer to remove "ALL" the clearance. Dave W


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PostPosted: Wed Apr 25, 2012 10:15 am 
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WelderLee wrote:
Ok i thought of an easier way to explain back stepping. If you imagine you were looking down on the weld like the face of the clock first you would weld from 12 to 3 and then you would back step and weld from 9 to 12 then you back step again and weld from 6 to 9 and then lastly you would weld from 3 to 6. In between each weld you would feather were you started the weld and then self over were you feathered it. For the last weld you want were you started and stopped to be fathered. This is the strongest way to weld this type of joint although all the grinding makes it time consuming. A fun little experiment is to weld up a box with MIG and see if it will hold air, you will find that feathering the tacks and back stepping is one of the only ways to weld that pressure vessal without having leaks.


Thank you, Lee. I'm going to try this out.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: Wed Apr 25, 2012 11:00 am 
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nisseven wrote:
. . . <snip> . . . You seem to obsessed with getting a perfect and while I admire your need for perfection it is not the end of the world if you have a little gap.

. . . <snip> . . . In regard to welding around the round tube, it is not easy. One tip that professionals get taught is to start in the most uncomfortable position and weld through the comfortable to finish uncomfortable and in this way you may get around half the tube. To maintain the correct angle you have to move quite fast as your weld may only be 25-30mm but you hand has to move 200-300mm, for a half circle on 3/4 tube.

. . . <snip> . . .
I like your trianglation except the tube that runs to the middle of the top tube is unnecessary, unless of course you have something in mind that we don't know about. The reason I say this is that it does not intersect at a node as it should.

Bruce


Hi Bruce,

Thanks for responding. The idea of going from the most uncomfortable position to the most comfortable makes sense. I've been doing just the opposite and when you get to that last part where your wrist is really twisted and I know I'm thinking, "Aw sugar, this is where I lay the booger weld."

Switching it around and going from "worst to best" could be useful. I'll just have to learn to make a good start from a bad position.

I wouldn't say I'm obsessed with making a perfect weld. However, when I see work that is really excellent, I genuinely do admire it and I'd like to get as close to that as possible. Most who produce welds and fabrication at a very high level have been doing it for years. I realize I won't get to that level, and if I took the time to do so, I'd never get my Locost done! So, it's a matter of trying to achieve a balance between "good enough" and truly professional.

Check this out (Obviously NOT my work {I probably did not need to say that :lol:}, but what I'd like to do):

Attachment:
File comment: A really good fab job photo I swiped from WeldingWeb.
Fab-Example.jpg
Fab-Example.jpg [ 46.76 KiB | Viewed 466 times ]


The logic (more intuition really) with respect to the vertical piece is two-fold. First, the main diagonal is long and thin, so the vertical is an attempt to reinforce it and reduce flexing although the two other diagonals will obviously contribute there too. The second part is more aesthetic. It just looked funny and unbalanced without the vertical piece and for the few ounces of weight, it added, it is worth it visually. Plus, I know structurally it will give some degree of additional stiffness side to side because if things move they have to bend, compress or stretch the tube too, although clearly not a critical contribution.

The end locations of the diagonals are where I expect the major loads from the suspension mounts to be fed from the outboard sides.

Cheers,

Lonnie

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: Wed Apr 25, 2012 2:46 pm 
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davew wrote:
Reinforcing the "U" shape brackets or laying the bracket on the side is a common error. You need open sides or if you have already added a reinforcing plate you should cut a slot in the center. The reason is that most to the load from tighting the bolt is used to buckle the reinforcement and is not the actual clamp load use to hold the control arm bushing. Look at any production frame an you will notice that they all have slots that allow for the sides of the bracket to deform around the bushing spacer. The other option is to pack spacers between the wall of the bracket and the bushing center spacer to remove "ALL" the clearance. Dave W


Hey Dave,

Could you post a photo of what you mean? It sounds important, but I'm having trouble visualizing it.

Cheers,

Lonnie

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: Wed Apr 25, 2012 2:48 pm 
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Lonnie-S wrote:

Hey Dave,

Could you post a photo of what you mean? It sounds important, but I'm having trouble visualizing it.

Cheers,

Lonnie


And here I thought I was the only "dumb" one.

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PostPosted: Wed Apr 25, 2012 3:10 pm 
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I've been thinking about Dave's comment all morning, and think I got it. Took some thinking though, guess I won't totally box in my brackets....

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PostPosted: Thu Apr 26, 2012 7:01 am 
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If you look at the upper control arm bracket in the RH side of the photo you will see a slot in the horizontal surface that allow the side walls of the control arm bracket to deform around the control arm bushing. A bracket with out a slot in the upper horizontal surface can effectively reduce the clamp load by over 80% because the troque applied is really just buckling the closed wall and not clamping the comtrol arm bushing to the bracket. Dave W


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viper 008.jpg [ 433.29 KiB | Viewed 403 times ]
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PostPosted: Thu Apr 26, 2012 7:32 am 
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With respect Dave you are correct if you have to much clearance but using my method enabled me to hang my jig in the correct position with a 50mm bush and the brackets bolted to it. All I then needed to do was shape them to fit to the chassis. The bush that goes between them just fits and I will have no trouble tightening it. As far as I am concerned making a slot would defeat the purpose as I am looking for some braceing, hence the sort of X shape. The boxing in part is only 1.6mm (16G) and at this stage is only on the top.
Lonnie that bracket or what ever it is does look nice and looks to be TIG welded. With a good fit this weld can be done with no filler wire and is surprisingly easy with a little practice and a steady hand. I like the way the holes have been recessed just makes it more professional looking, not sure what it adds structurally in this case but you see little folds all over production cars around brackets etc and they are not just there to look good, but to stiffen up usually thin guage steel.
Keep up the good work.

Bruce


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PostPosted: Thu Apr 26, 2012 10:40 am 
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OK, Dave, I think I see what you're talking about.

Attachment:
File comment: Slotted bracket to allow tightning.
Bracket-Slot.jpg
Bracket-Slot.jpg [ 23.6 KiB | Viewed 386 times ]


It looks to me that in this case there is a hole + slot. No doubt the hole makes sure there is no "stress riser" that allows the metal to tear further under flexing or something like that.

Cheers,

Lonnie

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: Thu Apr 26, 2012 10:44 am 
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nisseven wrote:
With respect Dave you are correct if you have to much clearance but using my method enabled me to hang my jig in the correct position with a 50mm bush and the brackets bolted to it. All I then needed to do was shape them to fit to the chassis. The bush that goes between them just fits and I will have no trouble tightening it. As far as I am concerned making a slot would defeat the purpose as I am looking for some braceing, hence the sort of X shape. The boxing in part is only 1.6mm (16G) and at this stage is only on the top.
Lonnie that bracket or what ever it is does look nice and looks to be TIG welded. With a good fit this weld can be done with no filler wire and is surprisingly easy with a little practice and a steady hand. I like the way the holes have been recessed just makes it more professional looking, not sure what it adds structurally in this case but you see little folds all over production cars around brackets etc and they are not just there to look good, but to stiffen up usually thin guage steel.
Keep up the good work.

Bruce


It sounds like you know what you want to do, Bruce.

Thanks for the compliment. Good luck with your build too.

Cheers,

Lonnie

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: Thu Apr 26, 2012 11:30 am 
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So the slot allows the bracket itself to flex rather than send the force into the chassis?

I thought you were talking about the mounting hole being slotted to allow movement.

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PostPosted: Thu Apr 26, 2012 12:12 pm 
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carguy123 wrote:
So the slot allows the bracket itself to flex rather than send the force into the chassis?

I thought you were talking about the mounting hole being slotted to allow movement.


The bracket should be able to flex, so when you tighten the nut, it removes any play between the bushing and bracket. If there is play, and the bracket is totally boxed in, tightening the nut will not remove the play, and your arm will have some play, allowing it to move fore/aft. Fore/aft movement of the a-arms is undesirable. If there is no play between the bracket and the bushing, it doesn't matter if you box the bracket.

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PostPosted: Thu Apr 26, 2012 4:19 pm 
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Diff brackets are semi-boxed on a live-axle Locost, especially on top if you go strictly book. What's the best way around that?


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PostPosted: Thu Apr 26, 2012 7:40 pm 
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#1) The spacers for a spherical or inner race for a bushing should fit tightly between the flanges. Many oems have serrations on the ends of the inner sleeve on "bushings" that are actually bonded to the inner sleeve and outer shell, so the twisting load is greater than on an actual bushing.

#2) Limit the flange thickness to .125".

#3) A little gusseting goes a long way. Don't completely shroud the bushing.

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PostPosted: Thu Apr 26, 2012 11:34 pm 
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Trochu wrote:
carguy123 wrote:
So the slot allows the bracket itself to flex rather than send the force into the chassis?

I thought you were talking about the mounting hole being slotted to allow movement.


The bracket should be able to flex, so when you tighten the nut, it removes any play between the bushing and bracket. If there is play, and the bracket is totally boxed in, tightening the nut will not remove the play, and your arm will have some play, allowing it to move fore/aft. Fore/aft movement of the a-arms is undesirable. If there is no play between the bracket and the bushing, it doesn't matter if you box the bracket.


That makes perfect sense now that I've seen the pic, but it didn't before.

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