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    • Machining 1/8th Scale Engine Components

      as you can tell. while i was making the injector hat, i make quite a few other important engine components. we'll start with the offset mag drive for the pro mag 44. not very complicated so we'll breeze through it's construction.

      drive and the mag.


      finished and installed.


      here's the belt tensioner. to make it correctly is a bit of a challenge. i made this piece on the rotary table.
      initial adjusting slot and mounting holes are placed in a large round of aluminum. there is alot of measuring and drawing involved with making most of my parts. you'll see why.


      roughing the outside profile and the counter bore in the center is for clearance around the fuel pump drive. for ths to be concentric when done you have to know exactly where all the mounting holes are.


      just needs to be parted from the parent round bar.


      finished piece.


      checking for fit and concentricity to the fuel pump drive


      here are the rest of the parts for the belt tensioner assy.


      here is the tensioner installed.


      along the way i also made the belt guard / starter mount.


      the blower pulleys were also made from timing pulleys i purchased along with the blower belt. the allowable overdrive on a PSI screwblower in an NHRA alcohol dragster at present is 2.28:1. i acheived an overdrive ratio of 2.25:1.


      i also put a mag clamp and support rods on the offset drive and made spark plug wires and boots. the silver rings around the spark plug are plug retention devices which are mandatory to keep a flying spark plug, out of your skull.


      hope you enjoy.

      1/8 scale t-bucket-193-jpg
      This article was originally published in forum thread: Scratchbuilt 1-8 scale top alcohol dragster started by comp1839 View original post
      Comments 75 Comments
      1. ronr's Avatar
        ronr -
        Hi, Very nice build... Ronr
      1. comp1839's Avatar
        comp1839 -
        you are welcome mark.

        thanks ron. glad you like it.
      1. BrassBuilder's Avatar
        BrassBuilder -
        Quote Originally Posted by comp1839 View Post
        i'm sure no bodies really all that interested in making the rim or the beadlock.
        I think you will find that we have absolutely no problem with lots of pics and lots of details

        I'm just getting back into my builds after a 7 year break because of school. Hoping to start posting some stuff here within a week or so. I'm opposite of you and Dan, I have a CNC mill and lathe that I prefer over the manual way of doing things. At least I think I prefer a CNC lathe....I just got the conversion done last week and trying to figure out how to run it now.
        I have no idea how you do all of that manually...fantastic work.

        Mike
      1. 3.Star's Avatar
        3.Star -
        Magic!!
      1. comp1839's Avatar
        comp1839 -
        mark and micheal, thank you and i'm glad you like the build so far.

        so i guess i need a set of front wheels. these will be Gibson dragster front wheels. i start off with a piece of 1/4" thick flat bar that i cut some discs out with a hole saw. the hole saw did not have a centering drill bit in. the hole you see in the middle i added later on the rotary table. it is a #43 hole.



        in the rotary table i used a ball end mill the counter bore the front surface. this provides a nice smooth transition on the front face of the wheel. the back of the wheel is counterbored with a standard end mill so i have a lip with which to grip the wheel in the final stages of machining.



        next the material between the stars is systematically removed. first a cut on the radius between each spoke. then an off set diagonal cut to produce the spokes of the star.



        a series of holes are then made to clear the way for the end mill. this keeps the end mill from walking around and making those random goofy cuts.



        an offset diagonal cut then creates the taper cutout inside the spoke of the wheel.





        the center is then tapped for a 4-40 thread. nexrt the wheel is gripped on the inside back lip and a groove is put in the center of the wheel for the tire (o-ring) to seat.

        finished product.



        next i'll get the chassis going.

        hope you enjoy!
      1. comp1839's Avatar
        comp1839 -
        i thought i'd add these photos of the real wheels i am trying to duplicate so you can see if i am close or not.

        gibson front wheel.



        american racing pro series trakstar rear wheel.



        hope you enjoy.
      1. Interceptor's Avatar
        Interceptor -
        Once again great work David, and very informative.
        Everything clearly explained and documented with pic's.
        I enjoyed it again (as with all the previous...)

        Thanks and keep it up.

        Mark
      1. comp1839's Avatar
        comp1839 -
        always a pleasure to help, mark.

        so.....here's the chassis. i constructed a jig to build the chassis on out of a inexpensive aluminum extrusion from a company called 80/20. attached to the jig are some pieces to locate the rear at ride height. also some plates to locate the motor to the rear on a centerline and up front some machined aluminum rod to locate the king pins at the proper angle, wheel base and offset.







        here are 2 shots of the initial jig and set up.





        here the chassis has the shoulder hoop / upper rail installed with most of the uprights.





        here is a shot to give you an idea of the length of this car.



        this is why i use a chassis jig. note how straight the car is even though it's wheel base is over 36" long.



        here is a better view of the alignment of the rear to the rear motor plate (sometimes referred to as a mid plate).



        here is a shot of the rear end chassis mounts.



        the rear bolts to these mounts with mounting plates.



        here is a mock up of the rear and the motor/ trans to check for alignment issues. there were none. you have to love planning and jigs!





        here we can see the king pin bosses at the proper angle. you'll hear king pin angles from 15 degrees to 30 degrees. i use 15 degrees. also note the obligatory 2" offset in the front wheels. 2" is the max. the rules allow. the left front wheel is always leading. right front is always trailing. the a-arms are made of areo tubing.





        here is the "x" brace in the front of the driver area.



        roll cage is installed.





        these little gizmo's give the driver a place to put there arms to assist in exiting the car.



        here is the mounting for the puke tank.



        here are some of the pieces for the clutch linkage.



        i'll stop here and pick up later on.

        hope you enjoy!
      1. Interceptor's Avatar
        Interceptor -
        Great work, as before David.
        Can you give a rough idea of the length of this machine ? My glasses aren't strong enough to read the end of the ruler.
        Very informative once again. I like the pic's.
        Keep those updates coming.
        Thanks.

        Mark
      1. comp1839's Avatar
        comp1839 -
        thank you, mark. the wheel base is 36 1/2". the overall length, including the wheelie bar, will be just under 4 feet.
      1. Interceptor's Avatar
        Interceptor -
        Wow David, that's a real Big Boy (or Girl if you prefer) then.
        You must have a large enough space to keep your models on display.

        regards,

        Mark
      1. FineModelCars's Avatar
        FineModelCars -
        Dave, you are absolut crazy. Amazing!!Karsten
      1. BrassBuilder's Avatar
        BrassBuilder -
        David,
        What process are you using to polish your wheels to get rid of the milling marks?

        I've been needing to build a framing jig and been searching around for material. I never thought of using that 8020 stuff. That will be perfect! Off to ebay...

        Mike
      1. comp1839's Avatar
        comp1839 -
        mark, i do have a pretty big set of shelves. good thing it takes a long time to build these! hehe. luckily i'm not keeping this one. it's a present for a very good friend of mine.

        thank you, karsten. coming from a talent like you..........means alot to me.


        hi, mike. first thing i'll say is use a good sharp cutter to keep as much of the tooling marks out of the work piece from the start. good machining goes a long way to doing a little polishing. from there i spin the piece in my lathe while sanding with wd-40 and 600 wet dry. next 1000. next 2000. i do not go that fast either, maybe 200rpm or so? let the paper do the work. only use moderate to light pressure. i use a generous amount of wd-40. then i use aluminum wheel polish and a nice soft clean rag. you'll have to clean the wheel in soapy water and re-polish. i'm sure there are a lot of different ways. this one works for me.

        glad the 80/20 suggestion works for you. i find the stuff indispensable.
      1. comp1839's Avatar
        comp1839 -
        now to the interior tin work. first i made a seat. i made a aluminum buck and fit the aluminum pieces around it by hammering and filing it to fit. then i tig welded the .022" aluminum together and ground down the finished weld.

        the seat.








        the head protector was made in the same fashion.







        this pic shows the floor pan, front foot panel and the equipment panel above the legs.



        here is a pic of the TDR butterfly wheel w/ hand grips. i thought it was a fun little piece to make.



        hope you enjoy.
      1. Interceptor's Avatar
        Interceptor -
        Once again great craftsmanship David. I like what I see.
        Truely enjoyed it (and the great pic'sofcourse).
        Are you employed in the metal working branch ? Or did you learn all this by yourself in going along the builds ?
        I don't see myself doing "tig-welding", let alone "normal" welding...

        Keep it coming, I'm still enjoying every bit of this thread.

        Mark
      1. comp1839's Avatar
        comp1839 -
        always glad to hear you're enjoying the build, mark. i started out in the automotive trade as a tech (20+ yrs.). i learned all of my metal skills for working on my race cars. i have since gotten out of the auto trades and i work for a company that makes packaging equipment for mostly the drug and beauty industries. now i'm using all the things i learned to build my racing stuff on machinery.
      1. ScaleMotorcars's Avatar
        ScaleMotorcars -
        I'm a happy guy. I just won a combo mill/lathe on eBay for $250. My old mini lathe has seen its last and even though this is one of the Harbor Freight mills its still far better then what I had. Besides $250 for a mill/lathe with power feed, I couldn't pass it up.

        Finally Ill be able to get some of these projects done.

        Keep posting away David this is great stuff....
      1. comp1839's Avatar
        comp1839 -
        dan, that's great! set 'er up, plug 'er in and git to making some chips.
      1. comp1839's Avatar
        comp1839 -
        i'll breeze through the first body i made since i wasn't happy with it and made another. after the pics i'll explain my displeasure.











        this body was made from 23 gauge aluminum (approx. .023" thick). while thickness wasn't the real issue it didn't hurt my decision to scrap it. the body also sat high off the ground in one spot almost 4 scale inches. it should be 3" from the leading edge to 1 foot behind the front axle center and 2" from there on back. so needless to sat i put this in the scrap bin and started again this time i would also try 27 gauge (.015") aluminum. getting much thinner just isn't practical for me as i don't have a delicate set of hands and neither does the guy i'm building this for........and to answer the question on every ones mind as to how thin it should be to be perfect scale the body would have to be .004-.005" aluminum depending on how thick the body is on the real car.

        this is another shot of the original body for comparison.



        here is the new body.





        i also worked with tim at TDR to come up with a r.p.'d nose w/ canards.





        here is some close up detail of the windshield mount.



        drilled and primed.





        i am currently waiting on some NACA ducts to arrive. again i worked with tim at TDR to produce these. when the ducts arrive i can finish the body work and paint this puppy. then it's final detailing.

        hope you enjoy!
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