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Learning how to build Lotus Seven replicas...together!
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PostPosted: Mon Feb 18, 2008 8:47 pm 
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PPAM20 wrote:
Sorry for the rack/box thing if it confused anyone.

But my major point guys is be especially carefull here. Its not a good sign when you can't get through the rack with a bandsaw and then are going to weld on it. Yes it is possible but be carefull - you don't want a fatique crack to get started in the end of the rack itself - it will be a far worse failure than a pinion failure.

The only way I've seen racks shortened (that I would trust) is exactly like zetec7 posted earlier. The rack remaines straight. The body if you are carefull can be straight or straight enough.

I have seen a good variation in zetec7's method where a machined sleeve holding the outside bushing and wiper was pressed and welded to the shortened tube.

Anyhow, I rarely get on a soapbox but I felt I needed to speak up on this one


If that scares you then consider this horror story. My steering wheel is welded to an adapter I made myself. That adapter is welded to the factory plate that has the nut welded in it. (that's 2 welds I did so far)

The steering shaft needed lengthened so I took a piece of 1/8" wall DOM that matched the OD of the shaft and cut the factory shaft and spliced the length of DOM and welded it on both ends. (that's two more=4) the rack needed shortened and welded. (that's two more=6) I also needed to lenthen my tie rod ends so I bought two extra and sleeved and welded them to make two long rods. (for a total of 8 )

So that's 8 welds that I, a non professionally trained welder did with a cheap piece of crap Harbor Freight welder. I fully understand that the failure of any of these 8 welds will result in a loss of ability to steer the car at speed. It is a scary notion indeed. :shock:

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PostPosted: Thu May 15, 2008 5:09 pm 
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I posted some photos and commentary on how I shortened my rack on page 8 of my build log:

http://www.locostusa.com/forums/viewtop ... &start=110

Follow that link for all the details...or if you're the impatient type, this picture pretty well sums it up:

Image

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PostPosted: Thu May 15, 2008 6:31 pm 
Okay, Dave, if I had the tools, skills, and could machine stuff that nicely, I wouldn't have HAD to get it done at a machine shop! :roll:


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PostPosted: Sun May 18, 2008 9:55 pm 
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Are there any compendiums of stock steering rack lengths?

I know it's not Locost, although I am not sure Locost and steering necessarily go hand in glove, but with all the many different aftermarket steering racks out there wouldn't you be better off with a new shorter aftermarket rack than cutting down a stock piece that exactly matches the pivot points of the suspension pieces?

I mean a shorter rack = a longer arc for so therefore within the arc of the suspension movement I can't see it causing any bind.

http://www.pitstopusa.com/SearchResult. ... oryID=1382


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PostPosted: Sun May 18, 2008 10:09 pm 
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Quote:
Its not a good sign when you can't get through the rack with a bandsaw and then are going to weld on it.


Welding on the rack, which is harden-able grade of steel is not something that should be done lightly. I don't know much about this, but in my searching of sites to buy steel, some have descriptions of the alloys. The higher carbon alloys listed as suitable for tasks like machining for a rack, caution against welding or mention welding only by a trained professional welder.

There is likely not much load on these welds, so perhaps that will save the situation. It's not the same as welding mild steel square tubing or DOM tubing. I don't know of any cases of failure, but I don't understand the welding issues really.

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PostPosted: Tue May 20, 2008 12:39 am 
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I used an RX7 manual rack shortened about 5 inches used a tubing cutter on the outer housing. Cut the rack down on a lathe and threaded the end
with a tap.much better than cutting and welding the rack. Made some really nice threads. Looks like a Miata rack Ish... Big tap!! M20 x1.5 as I recall.

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PostPosted: Thu Jul 10, 2008 10:31 pm 
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You know you don't have to weld the rack...

The reason people weld it comes from the fear that taping a hole is weaker than the factory threads. Yes, rolled threads are stronger than cut threads, and guess how rolled threads are applied to an interior hole? With a rolled-thread tap!

So if you don't want to weld the rack, just cut it, drill a hole and use a roll-tap to thread it. You can buy them from mcmaster.com, just search for "roll forming taps". The only issue is how hard the rack is and whether it can be easily drilled and tapped?

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PostPosted: Fri Jul 11, 2008 3:27 pm 
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The Rx-7 Rack I used had machined threads, They were cut, not rolled
it's a 20x1.5mm thread or something like that. I just got a tap from Mcmaster-Carr and used an alignment jig to tap it straight. Don't cut and weld the rack!!!!!!! it's precision ground. Nothing wrong with cutting threads
at all!! I can understand trepidation but if you measure the pull strength
of those threads you would pop the joints out and snap the tie rods long before the threads pulled out. You just need to be careful when machining the threads.

Cheers

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PostPosted: Mon Oct 06, 2008 1:34 am 
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Bringing this thread from the dead.

I've cut down the housing today and just need to do a little bit of cleaning before welding it back together.
I actually cut mine in three slices so when I weld it all up I'm getting rid of both fittings for PS hydraulic lines.

The rubber ring does come off with some more aggressive negotiation :wink: .

I did cut up the piece I had left, ground the edges and test welded it.
Came out fine, full penetration and just as strong.

Moti

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PostPosted: Mon Oct 06, 2008 8:59 am 
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Blackbird wrote:
Bringing this thread from the dead.

I've cut down the housing today and just need to do a little bit of cleaning before welding it back together.
I actually cut mine in three slices so when I weld it all up I'm getting rid of both fittings for PS hydraulic lines.

The rubber ring does come off with some more aggressive negotiation :wink: .

I did cut up the piece I had left, ground the edges and test welded it.
Came out fine, full penetration and just as strong.

Moti


How about some pics Moti?

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PostPosted: Mon Oct 06, 2008 9:18 am 
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While I'm not Moti, I have done essentially the same thing. I also split the steel side into several sections and rewelded 3 pieces back into one to make a cleaner rack and to allow for a wider clamp attachment surface. I eliminated the rubber sleeves for a firmer mount. I welded a mounting U-bracket to the steel housing and made a U-clamp for the Aluminum side. Pay no attention to the shims. They will be replaced with the right thichness steel shim. I wish I had taken more pictures during the depowering and shortening process.

Chuck


Attachments:
rx7 shortened rack.JPG
rx7 shortened rack.JPG [ 77.06 KiB | Viewed 2413 times ]
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PostPosted: Mon Oct 06, 2008 11:27 am 
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Very nice. I have an extra rack that I am considering shortening. I wasn't able to get mine as short as I wanted. (only took out 5 7/8") and I needed to remove about 7" IIRC. It seems to work fine as is, but redoing it is on my "to-do" list. I want to eliminate that big ol metal slug from the end too.

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PostPosted: Mon Oct 06, 2008 2:14 pm 
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If I remember correctly, I took out about 8 inches. The cut-off piece from the rack was re-assigned duty elsewhere. They made my extenders for the tie rod. I drilled and tapped them. I am finding new metric taps added to my tool collection. Another piece from the rack was used to make a mount to relocate the alternator. By chance, the outer tube removed was used to make my trans and differential mounts. I am amazed at how the stuff removed during modifications will find a home somewhere else on the car.

Chuck


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PostPosted: Mon Oct 06, 2008 3:51 pm 
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speaking of steering racks, is there any general length they should be for a book frame?

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PostPosted: Mon Oct 06, 2008 4:58 pm 
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MonkeyNutZ wrote:
speaking of steering racks, is there any general length they should be for a book frame?


Depends on your front suspension design. IIRC, its usually ~18 inches for most designs.


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