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Learning how to build Lotus Seven replicas...together!
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PostPosted: November 20, 2018, 5:11 am 
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Coming along slow, will hopefully speed up a bit during winter.

Finally got the inboard front shocks figured out (mostly)

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PostPosted: December 10, 2018, 2:57 am 
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Went a little frame crazy this weekend. Probably should have asked before, but I bought some steel tubing from a local steel supplier, A513 is what I got. Did I need to specify something more specific? For my "napkin calcs" I figured about 30,000 in-lb max moment at the center of the chassis (from gravity) and with a 10" height center to center on the main rails using the middle as a "neutral axis" gives 6000 lbs compression on the top rail and 6000 lbs tension on the bottom rail. The top 2 tube have a total cross section of about .6 in^2 ((1.25^2-1.125^2)*2) which gives 10,000 psi. I think the lowest yield strength steel is around 30,000 psi. Am I in the ball park? Not trying to land on the moon here.

And I would assume since all the weight is NOT right on the center and with all the added triangulation that makes the number even better (for safety and flex).

Also the shocks I've got are about 1000lb/in springs with a travel of 1.9",but the wheel rate is about 3.5:1 (adjustable on the rocker). But at full compression that's about 2000 lbs on the shock mount. Seem right?


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PostPosted: December 16, 2018, 2:09 am 
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Some more rendering fun, and an attempt at a "vintage" Brabham style body.


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PostPosted: December 18, 2018, 1:47 am 
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Looking for a steering rack and I completely spaced out that this is a "front" steer. This seems like a decent rack, but I'll need about 21.5" pivot to pivot. I guess you can just add whatever spacer plate to this rack, I kind of like that. I'd like 4" travel, but 3.5" is probably fine.

https://www.mechanicsurplus.com/product ... jXEALw_wcB

Thoughts?

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PostPosted: December 20, 2018, 5:23 pm 
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Drill press didn't work for notching, too much chatter, so much that the chuck kept falling out. However the Mini lathe cut them like butter!

I gotta get a metal band saw.


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PostPosted: December 20, 2018, 7:21 pm 
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Johnsinski wrote:
However the Mini lathe cut them like butter!


Why didn't I think of that? :cheers:

Tough choices for an affordable rack that is center load when it needs to be wider than 20 inches. That is probably your best option without making your own. You could also use one of those traditional style racks that are really narrow by adding extensions and a bolt-on bushing support for each end, inside the boots of course.

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PostPosted: December 21, 2018, 4:09 am 
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I can't take cred for the mini lathe technique, I saw a video somewhere of somebody notching a tube with an endmill in the chuck of a lathe. The tool post slots (with large chamfers) seem to hold a tube clamped to it at the same axis of the lathe chuck.

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PostPosted: December 21, 2018, 9:50 am 
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It looks like you have a program going for notching. However, with larger, thicker tubing, the mini-lathe might be a challenge to use due to vibration.

No doubt, you're aware of the notching fixtures sold by many vendors including Harbor Freight (https://www.harborfreight.com/pipe-tubi ... 42324.html) now on sale for $60. I have one, but there are better ones out there.

I think there may even be some examples of DIY notchers on http://www.homemadetools.net too.

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: December 21, 2018, 11:50 pm 
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I "sort of" knew there were drill press jigs, but I think my drill press is so crap, it still may not have worked. I did use a 1 3/4" hole saw in the mini lathe today and it was a bit sketchy, just had to be careful with the feed. A finer tooth saw would probably help a lot.

This plate is milled on my CNC router in hopes to be a wishbone welding jig, where's the fire extinguisher?! Other than fire, the other downside is it can only be tacked from one side. It should at least work well to fine tune the length of the wishbone tubes. You can see they're a bit long still by the small gap between the board and the long tubes. The short tubes are just aluminum place holders right now as I need to get more steel tube. Notice my awesome identification system, FUT1 = Front Upper Tube 1, clever eh?


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wishbone_outer.jpg
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PostPosted: December 22, 2018, 9:42 am 
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That's a very clever idea with the CNC router. You can't get much simpler that "falling into a hole", so to speak. If they end up accurate to the degree you desire then you're done.

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: December 29, 2018, 4:32 am 
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I think I've settled on the brakes, Wilwood has some small light calipers that are for single seat formula type cars. I think the rotor I was looking at is 12" x .350" or .380" thick and there is a brake hat that fits to a Chevy hub. That'll blow the wallet up, but I think it'll be more robust than the motorcycle brakes I was thinking of.

Does this seem like a reasonable way to mount the lug style caliper to my upright? It's basically an angle with 4 holes in it. This design also allow the same upright and caliper bracket to work on left and right sides. Do clearances seem reasonable? Top view shows about 1/8" from bracket thread boss to rotor and about 1/8 from the rotor bolts to the bracket outer face.


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PostPosted: January 2, 2019, 5:39 pm 
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Working on the suspension bushing mold and camber adjust tube/sleeve nut.


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PostPosted: January 3, 2019, 6:40 am 
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Johnsinski wrote:
I think I've settled on the brakes, Wilwood has some small light calipers that are for single seat formula type cars. I think the rotor I was looking at is 12" x .350" or .380" thick and there is a brake hat that fits to a Chevy hub. That'll blow the wallet up, but I think it'll be more robust than the motorcycle brakes I was thinking of.

Does this seem like a reasonable way to mount the lug style caliper to my upright? It's basically an angle with 4 holes in it. This design also allow the same upright and caliper bracket to work on left and right sides. Do clearances seem reasonable? Top view shows about 1/8" from bracket thread boss to rotor and about 1/8 from the rotor bolts to the bracket outer face.


Clearances are adequate if the hardware is correct. There should be a washer under the head and allow for safetywire bolt height in case you want to go that route instead of just red loctite. Brackets look good to me imho.

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PostPosted: January 3, 2019, 12:07 pm 
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Location: Duxbury, MA USA
Where are you located?
I am thinking about getting back at my project, which has sat for a little over 2 years and there are enough similarities that we might collaborate and move both cars along.
I am in Duxbury, MA. The car I am referring to is the "Duxbury Hodgepodge Sequel" http://www.locostusa.com/forums/viewtopic.php?f=36&t=15956
As far as racks go, take a look at a used Porsche 914 rack. That is what I am using.
Paul

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PostPosted: January 3, 2019, 4:33 pm 
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Hi Paul, I'm in Wisconsin, but that doesn't mean we can't bounce ideas around. You have a really cool build going, definitely keep working on it, that body is so cool. 914 rack sounds like a good plan, I'll look around.

I knew this was going to be alot more project than maybe I could handle, but it's really satisfying as it progresses, albeit slowly.

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