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Learning how to build Lotus Seven replicas...together!
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PostPosted: December 5, 2018, 7:07 pm 
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Location: Carlsbad, California, USA
There is still some final noodling to do with respect to the rear axle suspension. My original plan was to make the axle-side of the Panhard rod mount a double shear affair. The big RHS piece in the photos from my last posting (just above) would have supplied that. However, their really isn't enough space to do it the original way and still be able to adjust and maintain the Panhard rod with reasonable effort. It's getting crowded back there.

The axle clamp itself fits nicely. I have about 2-1/2" clearance on droop between the bolt heads and chassis. In reality, no more than 2" is expected, so I should be OK.
Attachment:
File comment: Axle clamp trial fit on axle in correct location.
DSC04664.JPG
DSC04664.JPG [ 98.78 KiB | Viewed 163 times ]

In place of the double shear implementation, I'll be doing single shear as shown here.
Attachment:
File comment: Axle-side Panhard rod mount re-done in a single shear design.
DSC04663.JPG
DSC04663.JPG [ 133.26 KiB | Viewed 163 times ]

The design consists of the weld-in, tapped, bushing I machined, and a 5/8" Heim joint dropped to 1/2" diameter by a set of high misalignment bushings, plus a grade 8 flange bolt and a thin retention washer. In truth the Heim joint can't go over the head of the flange bolt, but the thin washer supplies a little "belt and suspenders" reassurance. I'll need to use the semi-permanent Loctite compound on the threads of the tapped bushing. The flange bolt threads 1-1/4" into the bushing and I think that should be adequate.

The weld-in bung and jamb nut will secure the Heim joint to the 1-1/8" DOM tubing of the Panhard rod itself.

I'm making a second axle clamp which will accept a triangulating tube going from the DOM tube on the axle mount to a tab on the second axle clamp. That's where I plan to absorb lateral forces from the DOM tube of the axle-side mount pictured above. So, I still have some fab work to do.

The adjustable coilover mounts I ordered came today by UPS.
Attachment:
File comment: Adjustable coilover mounts.
DSC04675.JPG
DSC04675.JPG [ 102.48 KiB | Viewed 163 times ]

The general product is of really good quality, but there is one issue I'll have to solve. As shown in the vendor's parts catalog, the threaded tubular boss (you weld it to your chassis) goes all the way up and down the threaded shaft. However, as shipped, the threads on the boss are such that the shaft only goes as far as you see in the photo below.
Attachment:
File comment: Threads cut limit the travel of the shaft to what you see here. I need the shaft to come all the way through.
DSC04676.JPG
DSC04676.JPG [ 137.01 KiB | Viewed 163 times ]

That's not going to work for me. I need to have 1" adjustability on either side of the boss so I can adjust the height of the car without pre-loading the coilover springs. It's 5 days for shipping each way if I send them back to the maker to be fixed. I can get a 1" x 8 UNC tap in 2 days. I think I'll just finish the threading myself.

I'm trying to buy parts where I can instead of making everything myself as a means of cutting down on the time necessary to complete my build.

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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: December 6, 2018, 6:25 am 
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Another option is to use a carbide rotary file in a drill to open up the id on the end where the threads stop, so the shaft can go through.You can get single cut rotary files at most hardware stores but double cut aka (b*stard cut) used for cylinder head porting work best. A mini-lathe is another option but a tap is important to have to chase after welding around threads, which I assume you will be doing.

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PostPosted: December 6, 2018, 10:27 am 
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@MV8
Thanks very much for the tip on opening up the threads. Unfortunately, it looks like the smart thing to do is send the two collars back to the vendor and have the threads tapped all the way through.

After I posted last evening, I researched a tap from McMaster-Carr. A suitable tap for through-hole use is $74.80 plus tax of $5.61 and shipping of about $5. That makes $85+ for a tap I'll likely use one time.

I wrote the vendor an e-mail last night and I'll follow up with a phone call today. They are the manufacturer of all the component parts. It's just going to be smarter to send the collars back and have them corrected. I'll take measurements from them and just go ahead with my design work while I wait to get them back (10 days?). I have other things to do, so I won't be sitting still.

Thanks again,

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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: December 6, 2018, 11:24 am 
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In case you change your mind, a $10 bottoming tap works fine. I'd be surprised if the id of the end was not already sized for tapping those last couple threads that you need. Just fyi.

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PostPosted: December 6, 2018, 1:23 pm 
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Miatav8,MstrASE,A&P,F wrote:
a tap is important to have to chase after welding around threads

Very good advice.
Yes this is a must nearly every time you weld an internal threaded component. Welding can shrink the piece plus welding spit may contaminate the threads.

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PostPosted: December 7, 2018, 9:21 am 
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I would check the O.D. of the threaded rod end. It is possible that when broaching the internal square drive that the very end of the rod expanded. Also I would add a locking nut on the threaded rod to prevent fretting between the two. There will be constant movement as the suspension works. It is not consider best practice to put bending loads into threads. Plus you have the added leverage of this design. Hopefully you have rolled threads Vs cut.
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PostPosted: December 7, 2018, 12:48 pm 
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@MV8
Right again. I thought finding a $10 tap in 1" - 8 UNC would be as likely as finding a 5¢ Havana cigar. Wrong. There's a place in New York that has a through-hole, plug taps for $14 and change. Oh well, the collars are already on their way back to the maker via UPS.

I could end up needing both a tap and a die (see davew response below) in future, however.

@horchoha
Thanks for the pointer, Perry. I actually do that now when I can, which means SAE taps of 1/2" or less. For larger sizes, I'm SOL as we used to say. I would buy a larger tap & die set if I used larger sizes much. but they're pretty rare applications for me.

@davew
Argh! I didn't even think of that, Dave. Actually, I could have purchased a 1" nut locally and tried threading it all the way down the threaded rod. Since the first part of the collar goes on, that probably isn't the issue, but if it wouldn't start on easily, that could indicate bad threads on the rod.

The threads are sharp-edged, so I believe they were cut. I know how rolled threads are made, but they are not common. I'd expect they'd be smoother than the ones on this piece.

Because I have a narrow spring base, I'm inclining the rear coilovers inward 5°. To keep the axle-side coilover bracket centered on the axle tube and have the chassis side bracket centered in the structure (my preference), I need to incline it and forward 1° too. I haven't done the math, but that's 5 & a fraction degrees off vertical overall. I'm feeling OK with that in terms of bending forces on the threaded rod. At my ride height, the plan is to have the collar half way down the rod. That will leave 1-1/2" exposed below +/- any future adjustments I make.

Thanks for pointing that out as a consideration.

Cheers all,

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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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