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PostPosted: September 2, 2019, 7:15 pm 
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OK I bought a 95 Miata donor “Kart” so I’m off and running. Any comments are appreciated.
Attachment:
Miata-back lite.jpeg
Miata-back lite.jpeg [ 121.3 KiB | Viewed 3080 times ]

I’m putting this build under “unconventional” because I plan to use the whole Miata roller skate, as several kits and other builders have done in the past. This will require a custom frame.

Here are the basics of this build.

Goals (I like to have project goals being a retired engineer):

  • This will be a street car and probably never go to the track except maybe just for fun to see how it handles. So looks are more important than performance.
  • I’m building the frame rather than buying a kit because I do not want an exoskeleton style body and also because my budget is small ($5k or so)
  • I will probably have to build most or all of the body out of fiberglass
  • I want to complete the project in less than one year. Nothing happens without deadlines.
  • The design will allow the possibility of enclosing the cabin because I live in southern Arizona and may want to add AC later.

I have not done much car work since I restored a TR4 some time ago, so I’m a but rusty. For this reason I want to simplify the build to meet my time and budget goals. So I will use the whole roller skate to avoid building the suspension, mounting the engine, modifying the drive shaft, etc. I will reuse as many components from the donor as possible. I might replace the gas tank with a fuel cell for safety and add racing harnesses as the air bags are gone.

I will build a frame based on the classic Locost design using square tubing (except for the roll bar).

The donor.

My 95 Miata that was being prepared as a Kart by the previous owner. For personal reasons (two small kids and a third on the way) he decided to simplify life and sell his nearly completed Kart. Kart people cut away as much of the Miata as possible to make it lighter. They then reinforce it to make up for the weakened unibody. Google “Miata based kart” if you want to learn more. Here is an example https://jalopnik.com/track-day-genius-b ... 1762775599

I paid $800 for the Kart but it runs and drives well. To transfer the title Arizona DMV made me do an emissions test. It passed!
My plan is to remove the rest of the body and make it Locost-like. It will not look exactly like a classic Locost but will have a similar body style.

Build approach

My basic approach is to strip the rest of the body off, measure and model the roller skate in CAD, then design the frame and body. Rather than creating a large build table I plan to build the frame on the roller skate. I’ll level the roller skate with four small jacks before I start. I will then use a strip of MDF, indexed to the mounting points on the sub frames, to build the side rails. Once I have the base frame built and mounted to the sub frames, I’ll add the rest of the frame while its on the car. This way I hope to keep everything square and lined up with the mounting points and shocks.

To simplify the body I’ll create foam forms on a large CNC machine at my local maker space. The forms will be build up from 2 inch thick foam layers and glued together. This is a common technique. I’ll then apply fiberglass to the foam and, when cured, cut the foam away. So the process does not require making molds. The hard work is smoothing the outside surfaces of the fiberglass.


Last edited by shopmad on November 15, 2019, 11:43 am, edited 2 times in total.

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PostPosted: September 3, 2019, 1:29 am 
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shopmad wrote:
...because I plan to use the whole Miata roller skate...
The only problems with using the complete "roller skate" (the front and rear subframes etc* connected by the PPF) are it puts the engine a long ways forward and the front suspension attachments are quite wide (for a Locost, at least, though they're just right for a Miata).

*I realize that's a pretty big "etc". For those who are new to the rollerskate concept, it includes rear suspension, differential, drive shaft, transmission, engine, blah blahblah.

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PostPosted: September 3, 2019, 5:40 am 
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Nice project - $800 is a great starting point. Would like to see some close up pic of the work that has been done - you have saved yourself a heck of a lot of work already.

Your list looks very pragmatic, especially the A/C!

What software are you doing the CAD work in?

How big is the CNC machine at the makerspace? I am quite envious! Looking forward to your updates. Plus remember that peel ply is your time saving friend on joints.

https://www.youtube.com/watch?v=p9GTYsNBiaE

Cheers,
Marcus.


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PostPosted: September 3, 2019, 2:19 pm 
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Marcus,

I'm using the free version of Fusion 360. You can use it for free if you are a hobbyist or start-up. I'm not sure I would recommend it as it's hard to learn but it does have some powerful features.

I believe the CNC machine is 4 feet wide at the makerspace. I think most makerspaces would have one big enough to make fiberglass forms. You can go longer than 4 feet if you are clever with your gcode and do the thing in sections. These machines are usually 4 feet because they are great for making furniture.

Thanks for the tip on peel ply. I looked at a few videos on it and it seems it would reduce the finishing stage of the fiberglass. This is just the phase that I hear can be long in frustration. I'll look into it further as I just have an idea of how it works so far.

thanks.


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PostPosted: September 3, 2019, 2:25 pm 
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I'm not sure how to reply to specific people on this forum so please excuse the order of these posts.

This is to JohnMcCornak.

Yes, I know the geometry is different and it's possible I may not end up Locost-like enough to suit me. My plan is to measure the rollerskate and model both the frame and body in CAD and see how it looks. I may even 3D print a model to get a better feel of it. If I don't like it I may change my plans. I know some people have used the rear subframe and suspension, at least, to make things easier.

My preliminary fooling around with not-very-good guesses at the layout shows that indeed the front would be wider than the traditional Locost.


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PostPosted: September 5, 2019, 9:50 am 
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As Marcus asked what work has been done to the Kart and more pictures. Here is a list:
  • No performance work except for new shocks.
  • It has a roll bar which I will try to reuse.
  • The owner stripped wiring harness to the minimum and rewrapped it
  • It has front lighting but needs better stop and running lights.
  • The owner removed the power steering pump and depowered the rack — the rack needs a plug however.
  • It needs new ball joints, control arm bushings (the owner gave me some), tie rod ends and alignment
  • Needs a set of custom instruments as the instrument pod and that part of the harness are gone
  • But title is clean, not salvage.


Attachments:
dash-lite.jpeg
dash-lite.jpeg [ 153.66 KiB | Viewed 3717 times ]
roll-bar lite.jpeg
roll-bar lite.jpeg [ 99.35 KiB | Viewed 3717 times ]
head lights - lite.jpeg
head lights - lite.jpeg [ 152.07 KiB | Viewed 3717 times ]
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PostPosted: September 17, 2019, 4:45 pm 
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While I'm disassembling the Kart I'm researching some things I need for my frame design. One is the windshield -- how to do it.

Found one place, so far, in Tucson that will supply my windshield glass — Speedy Glass near Kolb and Broadway. They were extremely helpful and even gave me a sample of the molding and locking strip. Here are their points.
  • They can’t cut down an existing windshield because they are curved and it will crack. They can only cut down flat glass
  • Arizona demands laminated glass and you can’t use a used windshield.
  • Don’t bother to try and salvage the old windshield. They are bonded in such that even the pro’s almost always break them when they remove them.
  • The glass they use is 1/4 inch think and the metal strip on the frame is assumed to be about 1/8th thick.
  • The radius of the molding can't be too small or the rubber distorts.
  • Cost will be between $80 and $250 depending on what type of glass coatings such as tinting.
  • Yes, can do split windshield but I need to either put a bar down the middle or figure out how to bond the glass (but what about the radius issue).
  • If I bring in the frame they will install the glass. But I should bring in my design and or a template before I build it for them to check.
Attachment:
Moulding-end copy.jpeg
Moulding-end copy.jpeg [ 85.54 KiB | Viewed 3087 times ]

I bent their sample molding as much as I could before it distorted and got a minimum radius of about 86mm. I might want to do a split windshield but I need to talk more with them about how to do the junction such that I can avoid a center bar.
Attachment:
Min radius copy.png
Min radius copy.png [ 747.22 KiB | Viewed 3087 times ]

My research confirmed that it is hard to cut a curved windshield and even when you do so you can expect to ruin some windshields in the effort. Some people sandblast them down to size. You can send a curved windshield template away for a custom curved windshield but that will cost 1 to 3 grand.

I could not find a small windshield, like from an MG Midget, that was small enough even though they are not very expensive.

So flat or split it is for this car.


Last edited by shopmad on November 15, 2019, 1:19 pm, edited 1 time in total.

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PostPosted: September 17, 2019, 6:09 pm 
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Try a super beetle windshield.

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PostPosted: September 17, 2019, 6:20 pm 
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Welcome to the forum shopmad :cheers:

Sounds like a fun project and very doable.. Love sourcing Miata stuff as it's so plentiful and easy to work with..

About the windshield.. surely split/flat will work and will likely be the easiest route, but if you do want a curved windshield, it's something that can be done.. Most streetrod guys will cut down an existing windshield- and they seem to be quite successful at it.. Conventional wisdom is to cut the glass down first, then make the frame/surround to fit the glass..

I'll be facing exactly this challenge on my project in the next year or so.. I've sourced an Austin-Healey 100-4 frame, and I need to cut a windshield down for my needs.. In my case, the glass must be flat top to bottom, but a curve A-pillar to A-pillar is ok.. My research so far has led me to source a 1999-2014 F150/F250 windshield to cut way, way down to get what I'm after..

I've never done this, so it will likely be a steep learning curve (Read: I'm likely to break one in the attempt).. I am looking forward to developing the skill though, and even if I lose one or two, it's still cheaper than having one made or paying someone to do it..

For what it's worth.. A few years ago I did in fact have an obsolete OEM windshield made.. the first one was $1000.00, and as several of us went in on a group buy, the price fell to 500.00 each (it's the one-of-one where the $$ comes in)

**one last option: google 1948 chevy truck one piece glass(??)... I could be wrong, but one of the popular late 40's split-windshield trucks now has a one-piece aftermarket option that has a 'crease'/fold in the middle of the actual glass that eliminates the need for the OEM center post.. you could take that and have your shop cut it down for your needs as it's a 'flat glass' (sort of :lol: )

No matter how you tackle the glass issue, keep us apprised on your progress- on the whole project actually, with lots of pictures and updates

--ccrunner

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PostPosted: September 17, 2019, 8:29 pm 
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If you have the 3D cad profile it can be cut using abrasive waterjet from an existing windshield, will still cost a fair whack of folding stuff but not as much as making from scratch. I have a cardboard template cut out for my projects front glass that I take around the shopping malls and try up against various potentials - so far not even close but perseverance is the key.

Appreciate the photos, looks good.


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PostPosted: September 17, 2019, 10:09 pm 
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I had a flat, laminated windshield made for my Truckster about 2 years ago for $68. If I remember correctly, the corner radii were about 3 inches. I can't remember and that project has moved on to a new owner. I reused the original rubber glazing. I saved some dollars by giving the glass shop a paper template for them to cut to. Just a point for your reference. YMMV.

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PostPosted: September 18, 2019, 12:00 am 
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shopmad wrote:
This is to JohnMcCornak.
A common error. I have an aircraft in the National Air and Space Museum that mislabeled the designer as "John McCornack" for about a decade, on the assumption that Jack was a nickname for John.
shopmad wrote:
Yes, I know the geometry is different and it's possible I may not end up Locost-like enough to suit me. My plan is to measure the rollerskate and model both the frame and body in CAD and see how it looks.
I think that's a great idea. A CAD rollerskate would be a valuable design tool for Miata-based folks. Please include the wheels.
shopmad wrote:
I know some people have used the rear subframe and suspension, at least, to make things easier.
I think it's a great way to do it. I'm no fan of the front subframe, but the rear subframe is a splendid little plug-and-play unit, and I'm sorry I threw so many of them away in my first decade of Locost life.

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PostPosted: September 18, 2019, 12:28 am 
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The waterjet cutting is a good idea. I could buy small windshield for about $140 and have someone cut it. There are several places in Tucson that do waterjet but I'll have to call around and see what a one-off small job would cost and if they can cut a windshield. It might be cheap of I give them the CNC gcode rather than have them generate it.

Re the radius. Thanks for letting me know that a 3 inch radius worked. My guess at 86 mm (I work mostly in metric since it's a Miata) is 3.4 inches. Pretty close.


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PostPosted: September 18, 2019, 12:44 am 
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Sorry Jack,

I was able to get the front and rear suspension off GrabCAD and I guessed at the rest. But I know it's not right so I'm not posting it yet. When I pull the remains of the body off the kart I plan on refining the roller skate model. I'll post it it and give credit to those whose parts I got off GrabCAD. Maybe I will put it on GrabCAD and put the link here.

I'll be happy to post my chassis and body as I develop them but people should know I am not designing for the track and I am not doing any stress analysis. I don't know how. I plan on beefing up the chassis by imitating published Locost chassis designs as much as possible. Then I will cross my fingers and drive off.


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PostPosted: September 23, 2019, 6:03 am 
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Grabcad helped me get models of coilovers - handy resource, thanks for the idea!


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