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    1. Kit: , by (VIP/Sponsor) gbritnell is offline
      Builder Last Online: Nov 2020 Show Printable Version Email this Page
      Model Scale: 1/8 Rating:  Thanks: 1
      Started: 08-25-09 Build Revisions: Never  
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      One of the recent replies to the fabulous brass T build asked about making the spark plugs. I had mentioned that I had a build tutorial on another forum and several members said they would be interested in seeing it. Rather than post that thread I decided to do a new one that would be more relevant to this forum and the brass T build in particular. So hang on, here we go.
      The first thing I did was to go online and gather some pictures of Model T spark plugs. I couldn't find any dimensions other than the thread size so using that as a guide I found a good photo of a plug sitting in the palm of someone's hand and made an AutoCad drawing. I then scaled it to 1/8th.
      The first series of photos show turning the rod down to the required dimensions. The threaded portion is .099 diameter for 3-56 threads. The hex area was left large enough to get the flats cut later on. One shot shows my dial indicator setup on my 6 inch lathe for setting my long feed depths. The threading die is mounted in a small knurled holder that I made for cutting small threads. This allows for a better feel when cutting them. I die cut down to 1mm. (.039) with no trouble.

      Build Photos

      1/8 Scale Model T spark plug-body-jpg  1/8 Scale Model T spark plug-indicator-jpg  1/8 Scale Model T spark plug-thread-die-jpg  1/8 Scale Model T spark plug-threads-jpg 


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  1. gbritnell's Avatar VIP/Sponsor
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    George
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    The next step is to center drill and drill the though hole for the insulator. I'm using a 1/16th drill which will be .005 smaller than the upper body of the insulator so that when it's inserted it will stop against the shoulder. I do the drilling after the threading because from my experience if you drill first and then thread there's to much load from the die and the thin wall will sometime collapse.


    1/8 Scale Model T spark plug
    Attached Images Attached Images 1/8 Scale Model T spark plug-cent-drill-jpg  1/8 Scale Model T spark plug-drill-jpg 
    QUOTE QUOTE #2

  2. gbritnell's Avatar VIP/Sponsor
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    George
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    With these preliminary steps completed it's on to the mill to machine the hexes on the plug body. I have a collection of threaded hex bushings to hold parts in my dividing head so I found the appropriate one and screwed in the plug body and then mounted it in my chuck. This type of chuck is called a set-true chuck which means after clamping your part you can adjust the chuck so that you workpiece is exactly centered. The first picture show this procedure. The following pictures show the machining of the two different sized hexes. These early plugs had an internal thread so that the insulator could be secured by a threaded bushing.


    1/8 Scale Model T spark plug
    Attached Images Attached Images 1/8 Scale Model T spark plug-indicate-fixt-jpg  1/8 Scale Model T spark plug-hex-jpg  1/8 Scale Model T spark plug-hex-jpg 
    QUOTE QUOTE #3

  3. gbritnell's Avatar VIP/Sponsor
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    George
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    The bushing with the plug body is now removed from the dividing head and put back in the lathe to cut the length and to cut the recess stop between the body and the threaded bushing.


    1/8 Scale Model T spark plug
    Attached Images Attached Images 1/8 Scale Model T spark plug-trim-hex-jpg 
    QUOTE QUOTE #4

  4. gbritnell's Avatar VIP/Sponsor
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    George
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    A little bit of filing and a few rubs with a fine emery board and the body is finished. Now on to the insulator. I used white styrene 1/8 Scale Model T spark plug for the insulator because if this plug were to be mounted it could be screwed into a threaded hole. If it was to be soldered I would have used Teflon for the insulator to take the heat of soldering. The center hole was drilled .04. I wanted to turn the center electrode long enough to pass through the entire insulator to hold everything securely and .04 was about as small as I wanted to go for this length. (.380) The outside of the insulator was then turned down to the needed dimensions, .062 at the bottom to fit in the plug body and .067 at the top to provide the stop shoulder. Along with this I put two spark ribs on the outside. I apologize for the detail picture as the camera didn't focus on the right spot.


    1/8 Scale Model T spark plug
    Attached Images Attached Images 1/8 Scale Model T spark plug-drill-insulator-jpg  1/8 Scale Model T spark plug-insulator-jpg  1/8 Scale Model T spark plug-detail-insulator-jpg 
    Last edited by gbritnell; 08-25-09 at 10:09 PM. Reason: unknown icon popped up
    QUOTE QUOTE #5

  5. gbritnell's Avatar VIP/Sponsor
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    George
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    The insulator was cut off and, cleaned up and set aside. The remaining part is the center electrode. The first turning was the .04 shaft to go inside the plug. After this I detailed the top. The full sized plug had a screw on nut so I put a couple of little steps on the top to replicate this.


    1/8 Scale Model T spark plug
    Attached Images Attached Images 1/8 Scale Model T spark plug-elect-jpg 
    QUOTE QUOTE #6

  6. gbritnell's Avatar VIP/Sponsor
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    George
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    As I was getting ready for my next segment I noticed an icon had popped up in my previous post. I don't know where it came from. Anyway, now that all the bits are finished I took a couple of pictures with them on a penny so you could get an idea of the size. I then pushed everything together and took several more shots of the finished plug. If anyone needs a model T spark plug in 1/8 scale I have one laying around.


    1/8 Scale Model T spark plug
    Attached Images Attached Images 1/8 Scale Model T spark plug-jpg  1/8 Scale Model T spark plug-finish-jpg  1/8 Scale Model T spark plug-finish-jpg  1/8 Scale Model T spark plug-finish-jpg 
    QUOTE QUOTE #7

  7. xken's Avatar VIP/Sponsor
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    Kenneth
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    Great tutorial! I do hope some people appreciate the effort you put in to doing this. I know what kind of time it takes to stop and document.

    One question and I may be showing my lack of thread sizes, you mentioned you cut the threads to 3-56 size; I am familiar with 2-56 1/8 Scale Model T spark plug and have tap and die for 2-56 1/8 Scale Model T spark plug . Is 3-56 just the next size up that you machinist's keep away from the rest of us?

    Being a modeller first and a self taught on machines I still have a great deal to learn.

    Bring it to Glenmoor and we could have some fun with people with it.

    Again great job and keep up the great work you are doing!

    Ken
    QUOTE QUOTE #8

  8. gbritnell's Avatar VIP/Sponsor
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    George
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    Hi Ken, 3-48 is the next size up from 2-56 1/8 Scale Model T spark plug in the course thread sizes. 3-56 is the fine thread for this diameter. I have course and fine taps and dies for each size from 0-80 1/8 Scale Model T spark plug to 3/8-24 with numerous special threads in between.
    George


    1/8 Scale Model T spark plug
    QUOTE QUOTE #9

  9. xken's Avatar VIP/Sponsor
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    Thanks for the insights, I will have to find a thread chart somewhere. Where do you get the taps and dies for these sizes?

    Ken
    QUOTE QUOTE #10

  10. Deuces-wild's Avatar VIP/Sponsor
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    Hey Ken, You might want to try J&L Industrial supply. They carry a machinist's hand book that has all the tap/drill size charts for watch makers and also the bigger stuff. The hand book is about??? 4 inches thick and packed with lots of valuable info. The book costs about 30 bucks last time I looked. The one I have at work is the 24th edition which I bought in the mid '90's.
    Be nice or else ~1~**
    QUOTE QUOTE #11

  11. Hi George , wonderful tutorial on making spark plugs. Like ken I'm also a self taught model engineer and still have alot to learn , I have my own way of making spark plugs but this is invaluable information and I will take it on board , great clean result Thankyou for sharing.

    Sean
    QUOTE QUOTE #12

  12. strevo's Avatar VIP/Sponsor
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    Steve
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    Quote Originally Posted by Deuces-wild View Post
    Hey Ken, You might want to try J&L Industrial supply. They carry a machinist's hand book that has all the tap/drill size charts for watch makers and also the bigger stuff. The hand book is about??? 4 inches thick and packed with lots of valuable info. The book costs about 30 bucks last time I looked. The one I have at work is the 24th edition which I bought in the mid '90's.
    Guido,
    A guy I work with is a tool maker by trade and has a copy of the machinists handbook from the 60's. The funny thing is, even though they keep releasing new editions, for the most part, it's all the same stuff. It really is like 4" thick!
    -Steve
    "Success and failure are the same choice; only attitude determines the difference." Ross A. Halliday
    QUOTE QUOTE #13

  13. Deuces-wild's Avatar VIP/Sponsor
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    You got it Steve!!! I"d still like to find out where those micro taps are sold at. Maybe www.smallparts.com has them??? It might be worth a look....... Yep! They got'em. Check it out!
    Last edited by Deuces-wild; 08-26-09 at 12:16 AM.
    Be nice or else ~1~**
    QUOTE QUOTE #14

  14. chuckylane's Avatar Member
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    chuck
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    [QUOTE=gbritnell;36887]As I was getting ready for my next segment I noticed an icon had popped up in my previous post. I don't know where it came from. Anyway, now that all the bits are finished I took a couple of pictures with them on a penny so you could get an idea of the size. I then pushed everything together and took several more shots of the finished plug. If anyone needs a model T spark plug in 1/8 scale I have one laying around. [/That is THE COOLEST,I can not wait to tell a friend of mine about it,Fantastic]
    QUOTE QUOTE #15

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