Frame construction

 

After spending a bit of time looking at the motor mounts I decided I didn't like the peaks sticking up, so I cut them off level and capped them while adding the mounting plates. There is no question these will support the engine.

 

I've also added diagonal bracing- the following picture only shows the front additional tubes. I later realized I went the opposite direction with them than most people though the end result will be the same as far as stiffening the frame. The tubes are actually pulled in a little closer to the engine this way but I will still have plenty of clearance with the engine, exhaust, and steering components, so I'll leave them this way for now.

Here's another picture of the bracing.

And I'm now beginning construction on the rear end. Because I'm using a Miata donor I'm designing in an independent rear suspension. This is a tubular version of the Miata subframe and is actually quite easy to build... after spending way too long plugging it into LibreCAD. I really hope it works!

Finally a warm evening to work!

Last night was the first warm evening we've had since last Fall and I was able to spend the entire evening in the garage working on moving some tubes around and making the engine mounts. I've decided to keep the engine offset 1/2" to the passenger's side and lower the engine 1.5 to 2"  below the bottom of the frame. This helps me avoid reconfiguring the top cross tube behind the engine and should help the hood clear the top of the engine more easily.

I decided to make triangular mounts partially because they'll look cool, should easily be strong enough, and allow access to the engine mount bolts if I avoid closing the bottom of the chassis in between the supports. I use 16ga 3/4" square tubing and am considering cutting the top peak off and welding the holes closed. I have yet to add 1/8" sheet to the insides of the mounts.

Recent Progress

More tubes have now been tacked in though progress is a little slower than I hoped due to weather being usually cool. Once it warms up a bit I'll be spending a lot more time in the garage. Here you can see the engine and transmission sitting roughly in place. I think I'll need to lower the engine another inch, move some tubes around a bit, and then fabricate the engine mounts.

The engine is spaced 1/2" to the passenger's side due to the rear differential being offset 1" to the same side. I'm hoping to minimize the drive shaft angle: a little angle is beneficial for keeping the U-joints properly lubed, but too much causes stress.

The design work and planning gets a lot easier when you can use a CAD program. Luckily my previous job taught me how to use AutoCAD. Unfortunately I do not have my own copy, so I had to take a little time to learn LibreCAD which is an open source free CAD program.

Here I mocked up the rear end borrowing some ideas from Matt Rodger's car as detailed on the LocostUSA forum. I also took some measurements on the current transmission output shaft and differential input shaft. Once I get the engine and transmission mounts completed (and moving tubes around a little) I'll be working on the back end of the car. At least the cool weather gave me a chance to iron out some ideas and develop some plans!

Taking shape

The past week was spent tack welding the tubes in place and adding more tubes. I was a little worried about front trapezoid as it requires compound angles to cut, but it turned out well. The top tube is three inches behind the bottom tube.

 

 The build table is 42" wide by 96" long. A nose cone will fit over the front trapezoid and the high angles rear portion is the back of the seating compartment. The back of the chassis will be extended for the rear differential and suspension.

 

 A shot from the front to illustrate how parallel the cross tubes are. If you make a mistake on the basic chassis it will haunt you for the rest of the build by effecting all the measurements afterward and the quality of the finished product.

The car is beginning to take shape although my oldest son thinks it looks like a boat right now. Haha!

After a lengthy break progress resumes...

Since March of last year I have been terribly occupied with repairs and upgrades to my house, repairing daily driven vehicles, and working my tail off at my new job; I install communications cabling at Lambeau Field and there's a lot of work in progress! Work is good. It covers the costs of my hobbies including building a locost. In addition to work selling the Cherokee and Miata (for nice profits) also has helped.

I've now taken the plunge and purchased much of the steel I will need for the basic frame. I've also covered most if not all of the tooling which is required to do something like this. I did have some time and money last summer to construct the build table out of carefully selected 2x6s and a sheet of 5/8" MDF. I used metal bracketing to add some strength and casters for mobility. Luckily I've found a place in the garage which is very level so shimming is unnecessary.

I've begun cutting the frames for the bottom portion of the chassis. I am building this to the "book chassis" dimensions.

A cheap miter saw with a 10" abrasive blade allows me to cut angles with a high degree of accuracy. The bench grinder and a bastard file allows me to dress the tubing ends quickly before laying them on the table. The miter saw was purchased on sale for roughly $70 and the abrasive blade costs roughly $5.  I laid a 2x2 along the edge of the build table to hold the steel even while cutting. As an extra benefit: the 2x2 keeps the tube I'm cutting from moving the pieces around on the build table. The saw/grinder stand is on casters so it can be quickly repositioned as needed.

This is what I mean by "a high degree of accuracy". So far all the joints look like this.

I wanted to test the settings on the welder and pieced some scraps together... the resulting gun-shaped creation delayed getting any work done until I finished (hardly) amusing my wife and kids with James bond impersonations.

After spending years trying to get all the tools and skills together to begin the actual construction I am greatly pleased seeing it underway! More to come soon!