# Spark Plug constructlon revisited



## GailInNM (Nov 13, 2018)

Spark plugs always seem too be of interest to the IC  crowd so here is another construction thread on my recently finished d production  run of plugs. These are threaded 10-40 and are just over an inch long overall. They are similar to the plugs I used in my tinyengines which were detailed at:

https://www.homemodelenginemachinist.com/threads/tiny-i-c-engine.7397/page-13

Unfortunately many of the photos in that thread have disappeared, but the drawing remains and  enough of the photos remain to get the idea.  I have made about 35 of these plugs and about  25  of hem are in use withe remainder saves as spares.  Only one of them failed and that was due to an eror on my part during assembly.  These plugs had a long reach nose which I do not need on my current engine design..

The new plugs are of similar design, but with out the extended nose. Construction techniques have changed some what to make construction easier for me.  I am legally blind so hand operations are very difficult for me.  Most of the machining was done with CNC as I can not read the dials well enough to do much manual machining, but all the machining can be done without CNC. I will try to make suggestions on manual machining methods were it might be useful.

Related to these plugs will be molded boots for them, but that will be in a separate thread. For those interested here is a link to the thread on boot molding for previous plugs.  Again , many of the photos are no longer avilable..

https://www.homemodelenginemachinist.com/threads/ignition-boot-molding.14539/

So to start things off here is  a PDF drawing of them.


Z1GPDF-3.pdf


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## GailInNM (Nov 13, 2018)

The body is the most complicated part. On most construction projects I generally start with the complicated parts first, then I can alter the simple parts to fit if I mess up the complicated part.

I started with 1/4 inch diameter 12L14 steel bar. The end was faced off and three diameters wore turned with  a 0 radius righ hand turning tool .  The tip was turned to 0.156 for 0.094 that will be miilled  down to form the groound electrode. Next the section to be threaded was turned to 0.190 and finally the main body was turned to 0.245 diameter. The body diameter was selected so the plug would fit into a .250 counter bore  if necessary.

An 1/8 hole will drilled in the end for the full length of the part. Finally the body was threaded 10-40 with a single point threading tool.  The threading to a shoulder is easy with CNC. If threading on manual machines you may want to invert the threading tool and thread from left to right running the lathe in reverse. You could also use  a 10-40 die but you may need to reverse the die for a finishing cut to get to the shoulder.








And finally the body is parted off.

Gail in NM


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## GailInNM (Nov 13, 2018)

The body was moved to the milling machine where it is held in a 5c collet in a vertical collet closer.  Since I was doing multiple parts I put a stop in the collet. The ground electrode was milled to width with an 1/8 inch 4 flute end mill.  

The milling operation was done in 3 steps 1/32 deep to avoid bending the electrode tap.  Normally I would clime mill with CNC, but to avooid the chance the end mill would grab and bend the electrode I used conventional milling.  





The body was removed and burrs were removed using a needle file and small brass brush.

Gail in NM


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## GailInNM (Nov 13, 2018)

An anvil was made form a length of 1/4 steel. The end was turned down to 1/8 diameter for a length of the body, minus the electrode, plus about 3/64  inch. The edge of the end was broken slithtlllly with a fine file.






The anvil is clamped in a vice using a vee block and  the body is slid on.





I used the face of the 4 ounce hammer to IRON the electrode over the end of the anvil and then gave it one light tap with the hammer to set the bend.






And it looks like this.






Gail in NM


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## GailInNM (Nov 13, 2018)

Back to the milling machine and the 3/16 AF hex is milled on the body. I used the vertical collet closer and CNC for this, but it would be easy to do with either a rotary table of a spindex on a manual machine.






Then back to the lathe to put a slight chamfer on the edge of the hex to make it easier to get a spintite on when installling the plllug..





And some finished bodies.





Gail in NM


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## GailInNM (Nov 14, 2018)

EDIT:
SEE POST #44 IN THIS THREAD FOR AN UPDATE ON INSULATOR MATERIAL.

Next up is the insulator.  I make my insulators out of Corian.  Corian is the trade name for a filled acrylic plastic used in the USA for counter tops. There are some generic versions that work just as well. It machines very and is not fussy about cutting tool angles, although they do need to be sharp.  I used the same 0 radius to make these that I  used to cut the steel bodies. 

I  have been asked in the past about usilng PTFE (Teflon ) for the insulators on small  spark plugs.  It works very well, but I am not a big fan of using it.  First off it is quite flexable which makes it deflect when machining so it is difficult to holding dimensions.  Tools must be very sharp and have high rake angles to machine cleanly. And, it is difficult to get  a good glue bond some means of mechanically increasing firctiion be resorted to.

If you do want to use PTFE, here are a couple of tips.  Fir, after facing of the end, drill a hole the size of the electrode as deep as practical. Insert a length of  your electrode material iln the hhole and griip  it in your tail stock chuck. The PTFE will act as its own bearing and act as a center and stiffen the PTFE for machining. Second, cut some shallow grooves in the area to be glued for the glue to flow into to  increase the frictiion to resist pulling out.

I purchased my Corian on eBay ome time ago.  I purchased it as blanks for making custoom pen bodies. The blanks were about 12mm square. or a little under 1/2 square and not to consistant in size.  They were about 5-1/2 inches long. I found a round collet that they would just fit into and gripped on the corners of the blank with about 2-1/2 inches sticking out of the collet. I tuned this end to about 3/8 inch diameter.  There was a little bit of taper due to the material deflecting while turning.  Changed to a 3/ 8 diameter collet and turned the other end to 3/8 so I ended up with a 3/8 diameter rod. Since there was done a long time ago there are no photos of this.
Gail in NM


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## doc1955 (Nov 14, 2018)

I get my Corian at Menards. I buy a cutting board and the cut it up into pieces. Gail I like your method of bending the tabs. I will keep that in mind on my next run of plug making. I did a few videos on making plugs.


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## GailInNM (Nov 15, 2018)

Hi Doc -- I watched your excellent videos when you first posted them and wanted  to reference them when I started this thread. I was having trouble finding them because of problems on my end.  Thanks for chiming in  and saving me the trouble of finding soI could  llink to them.Our methods are a bit different , but the important think is they both result in the same thing --good pllugs.

On all my previous plugs I hand bent the ground electrode. but I can no longer see well enough to do that.  In retrospect, I should have come up with the anvil method for them as it is much faster and more accurate and repeatable.

On Corian.  I cn no longer safely use a table saw so I bought the pre cut blanks. The seller on eBay offered assortments of different colors so I asked if I gould just get a lot of white ones.  As the pen makers wanted colors he had a excess of white ones.  Said he would send me 50 blanks for US$10 with free shipping. When the package arraved he had stuffed about 70 of them in a flat  rate box along with several usful small sheets.  So overall hey cost me a lot less than I could cut them myself.  For my size plugs that's enough material for over 300 plugs, or about $03 per plug.

GAIL IN NM


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## GailInNM (Nov 15, 2018)

Back to making insulators. With the 3/8 diameter held in a collet the end is faced off with the  0 radius  right hand cutter and the Z axis 0 is established.





To mimimize then cut the 1/8 diameter about 1/2 of its length  using several passes. I then cut the remainder of the 1/8 dimiter, again using several passes. The same procedure was used for the 5/32 diameer, but cutting it longer than the finished part to allow room for a parting tool. Before cutting off i used a small center drill to remove any bump left on the end from the facing operatiion and put a small dimple on the end for  a later drilling  operation. Notice that about half of the length of the 5 /32 is tapered to the end. This taper  can be cut at this time or as separate operation after the part is cut off.  The un-tapered section is to allow chucking on it during later drilling operations.











Gail in NM


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## GailInNM (Nov 15, 2018)

The drilling of the insulator is done on a manual lathe.  One end could have ben done while in the CNC lathe before cut off but for me it was easier to just do in on the manual lathe.

The insulator is held in an 1/8 inch collet. No collet stop is needed as the part will stop when the 5/32 shoulder hits the collet face.  I had turned the taper on the 5/32 diameter while turning on the CNC.  If I had turned the part on a manual lathe I would have just turned the 5/32 end as a cylinder and turned the taper at this time. If turning the taper now, it should be done before drilling as the drilling will make the part more delicate. It is not necessary to face off the end as any variation in the overall length will be compensated for by the grinding operation on the center electrode during assembly. 

Gail in NM


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## GailInNM (Nov 15, 2018)

Center drill and drill the 0.047 hole in the 5/52 end.  This hold does NOT go through the insulator. About 1/16 inch remains undrilled.  The 1/16 inch is not critical and can vary +/-0.025 is no problem.  It is necessary to peck drill this hole to to keep the drill flutes from clogging.





Changing collets to a 5/32 inch, the part is reversed to drill the other end.  As this hole will break into the 0.047 hole, therre is no need for a collet stop as I can feel it break through. I used a #65 drill bit which makes a easy slide fit on the center electrode.  This allows enough clearance for epoxy to be worked in to secure the enc of the center electrode during assembly.

I held the drill in a spring loaded small drill sliding chuck so the drill operation  was very quick as I did not have to wind the tail stock wheel. This drill chuck can in the next post being used to dill 0-80 screws.


be seen

Clean out any swarf in the part an the insulator is done.
Gail in NM


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## GailInNM (Nov 15, 2018)

The 0-80 screw for attaching the spark plug wire to the plug is next.  It is held in a 1/16 collet in the lathe and a #65 hole is drilled through it.  I use a solid carbide printed circuit board drill bit for this.  The point on these drill bits are very good about self centering.  If the screws have a fairly flat head there is no neeed to center drill the screw head.  If the screw head is not flat or if you are using a HSS drill bit it may be necessary to center drill the screw to get  the drill to start  on center. 

In  this photo you can see the sliding small hole drill chuck mentioned in the previous post.





And a little closer photo.






Gail in NM


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## GailInNM (Nov 16, 2018)

The center electrode is made of 1/32 hobby shop music wire. Before starting to cut them I wipe the wire down with a paper towel saturated with acetone to remove oil from the surface.  It's just easier to do the whole length than the individual pieces. Revoving the oil makes the soldering job and  improves the epoxy bond during assemblly later.

The cut lengths should be about 1-1/4 inches ;ong. They will  be cut  down to final length after being installed in the insulator..  The extra length makes it easier to work the epoxy into the insulator during  assembly.  Since the length is not critical they can be cut by hand using an abrasive cut off wheel.  I used a Dremel cut off disc mounted in a Proxxoon IB/E rotory tool.  I like the Proxxon as it has a nice metal bushing at the nose that makes mmountin it easy for use in fixtures and as a tool post grinder.

The cut off disc was adjusted so there was 1-1/4 inch from the tool mount.  The wire was butted against the mount and the wire rotated with thumb and for fingers as it was fed into the wheel. Took about 2 minutes to cut a 36 inch length into 28 electrodes.







The cut off operation leaves a small burr on the ends of the electrode which must be removed to make assemblly easier. I use a non-woven light deburring wheel in a bench grinder.  I can hold about 5 wired between my fingers and rotate tem with thumb and forfinger whille pressing them  against the whee. Very quick but the same result can accomplished by rotating the electrode in a folded piece of 400 grit abrasive paper.

Here are a few of the finished electrode blanks.






Gail in NM


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## GailInNM (Nov 16, 2018)

Time to do some assembly.  The 0-80 screw needs to be soldered to the end of the center electrode.  I start by making some solder preforms from 0.015 diameter electronic soft solder.  Don't worry if you don't have any sine solder like ti as other methods work as well and I will talk about that later i. 

I start by wrapping a length of the solder around a center electrode. Then using a #11 hobby blade I  cut off one turn sections to make the  preform.. It iis hepfull to use a new blade that  still has a sharp tip so it will fit into the coil of solder.  I can generally cut two preforms with each cut.  Do the cutting on a piece for wood or plastic to avod dulling the blade.










Flatten the preform with a scrap of metal to  make the  end even with each other.

Dip the end of a center electrode into some paste flux.  If I can see that I have some on it that is enouh. Insert the end  of the electrode into the solder preform. The flux will hold the preform in place. Slide the 0-80 screw on the electrode with a twisting motion to distribute the fllux a bit.







Clamp the other end of the electrode in a small bice leaving a generous amount sticking out from the vice. This assures that the vice does not soak too much heat from the electrode when soldering.  Slide the preform and screw  so the end of the screw and electrode are even.





I heat the screw and electrode with a small butane torch until the solder flows.  Most often the screw will jump away from the end of the electrode.  So, before the solder solidifies I hld a scrap of metal on the end of the electrode and then push the screw back to the end with another scrap. 






Clean the joint up with a bit of alcohol or acetone to rremove any excess flux. 

If you dont have any fine solder, you can solder the screw in place with thicker solder using a soldering iron.This will probably result in a fillet between the electrode and the screw.  You may have to file off some of this fillet so the screw seats on the insulator when the electrode in inserted into the insulator.  It's also fail to  counter sind the end of the insulator a bil to help clear the fillet.

Gail in NM


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## GailInNM (Nov 16, 2018)

Now to gllue the electrode assembly into the insulator.  I use 5 minute epoxy for this.  The epoxy needs to be reasonably thin so it can be worked into the insulator.   My epoxy of choice is  IS made by Bob Smith Industries. and is packaged as two 4 ounce bottles in a package.  It is a 1:1 mix and is very non critical  about the ratio making it easy to mix small batches. Most hobby shops have it with the larger shops having it under their own name.  Amazon and d eBay also have numerous listings for it.  It also has good shelf life.  I have used some that was over5 years old and it acted just the same as wen it was new..

First insert the electrode all way through the insulator  to make sure there is no swar in the insulator blocking the transition of the 0.034 hole ad the 0.047 hole. It should be a free easy fit. I thn lightly clamp the smaller end of the insulator in a small drill press vice vee groove.  Doon't clamp so tightly that you might distort or crack the insulator.  

Mix a small amount of epoxy.  You don't need  much.  Using a piece  of  of wire or stirring stick apply small  amoount of epoxy somey near the end of the electrode and start the electrode in the  insulator.  Continue to apply epoxy  to the electrode as you press in into the insuylator while rotating the electrode and oscillate it back and forth a small distance to work the epoxy into the jjoint.. Easier to do than describe.  When the electrode is almost fully inserted clean off excess epoxy with a paper towel trying to keep epoxy off the screw threads.  Seat the screw on the end of the insulator.  Then clean the screw and joint with an acid brush saturated with acetone and then clean the other end of the insulator with the same brush.












Check that the screw is still in contact with the insulator and set aside for epoxy to cure.

Gail in NM


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## GailInNM (Nov 17, 2018)

With the epoxy cured, it is time to bring the center electrode to length. At this point there is about  3/16 of an inch sticking out from the insulator.  This needs to be reduced to 0.016 inch.  If I try  to just grind this  to length it is probable that the heat from the grinding will damage the insulator.

I did this in two stepsl  First I cut off the center electrode sot here was about 0.030  to 0.040 inch protruding from the insulator using a  Dremel cut off wheel. Then I ground the electrode to the final length with a grinding wheel.  Because I am old. nearly blind and my hands shake I made two simple jigs.  If you don't have any  problems doing fine   hand work you can do this without the jigs, but if you are  making more than a couple of plugs it is well worth m spending the 10 minutes or so to make up the jigs.  

The jig for the cutoff operation is just a piece of 1/4 X 3/8 metal that has an 1/8 hole drilled through the 3/8 dimension.  the 3/8 dimension around the hole is milled down to a point that when the insulator in inserted into the hole the end of the insulator is recessed about0.030 to 0.040 inch.  In operation   the insulator - center electrode is inserted in the hole and  the center electrode is cut off with a cut off wheel. All the jig does is prevents cutting the electrode too short. The jig was held in a small drill press vice.  If the part is rotated when feeding in the cutoff wheel it only takes a few seconds to cut off the excess length.











Gail in NM


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## GailInNM (Nov 17, 2018)

The jig for the final grinding operation is the same as that used for the cut oo except that more materil is milled off so about 1/16 inch of the insulator is sticking out.  I mounted the jig in a drill  press vice and mounted that on my tool grinder.I could then adjust the position of the jig close to the grinding wheel until when i  put the insulator in the jig and twirled it against the grinding wheel the electrode was reduced to 0.016 of the center electrode protruding.  

The jig could also be mounted in a lathe tool post and a grinding wheel on an arbor be used in the spindle.  In either case a 46 grit grinding wheel works well, but this is not critical.






Unless the burrs from grinding are laarge they will not have to be remove, but a folded piece of 400 grit abrasive paper will remmovve them quickly if desired. Clean the end of the electrode and  insulator as any matalic particals here may short  out the plug.






Gail in NM


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## GailInNM (Nov 17, 2018)

A moment of truth approaches.  Slip te insulator all the way into the body. If all the machining dimensions have been held the center electrode should be about 0.025 inch.  from the ground electrode.  Minor variances can be taken care when when setting the gap later by bending the ground electrode.   If there is a major variance then it may be necessary to alter a  part.

If the gap is OK, then the insulator assembly is glued into the body with epoxy n the same manner that the electrode was glued intoo insulator.






Any excess epoxy is removed with paper towel and acetone before the epoxy starts to cure.  

The join and the electrode end are cleaned with an acid brush saturated  with acetone.  To function  properly the electrodes must not have any epoxy left on them.





This  completes the spark plug assembly I set my gap at 0.025 inch by bending the ground electrode. Hint: Most 6 inch flexable machine rules make in the USA  0are .25  thick. some import rules are 0.5mm thick.

Now all  that is left are a the nut to secure the spark plug wire and the washer to seal the plug to the engine.

Gail in NM


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## Johno1958 (Nov 17, 2018)

Thank you very much.
Sooner or later I'll have to have a go at making some long reach plugs and maybe sooner than i think. The little engine engine I have been making (stalled at the moment) have plugs that are buried very deep inside the head and will benefit from a longer reach option.
I have been on Ebay to find Corian but here in Australia without paying massive postage from the US a bit hard to find but I have bought some Peek from China which I can say is a very hard and firm
type of plastic by to feel of it, which is suppose to be heat resistant. I guess I'll find out. 
Cheers
John


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## ruralearl (Nov 17, 2018)

Hi Gail,  Thank you for this post.  Regards,  earl


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## Blogwitch (Nov 18, 2018)

What a very nice and informative post Gail, very similar to the OLD STYLE posts that were the norm on here.
Rather than just a next bit picture, a FULL explanation of what needs to be done to obtain the final result.
A real joy to read.

Keep it up

John


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## GailInNM (Nov 18, 2018)

Thank you John (both of you) and Earl for the kind comments.

John1958: PEEK should work just fine. Here in the US we use Corian because it is easily available, chaeap and adequate for the application, not because it is the best material.  For the type of engines that I build, small low speed cool running hit and miss, I think that even plain clear acrylic rod would work fine.  It is available everywhere but it is not too pleasant to  machine because the strings wind up on it when turning. For appearance it think the exposed section   could be painted white with epoxy appliance  touch lup paint before the electrode is glued in.  I say epoxy paint because most other paints would come off. when cleaning up the excess epoxy during assembly.  

Blogwich: John, you and I are both of the same generation  and nearing the end  of  our active model building days due to physical limitations. But since we both still have active minds we can still contribute to the hobby by sharing some of the information that we have acquired during the last 50 or 60 years.  I think we are of like minds on this.

Gail in NM


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## GailInNM (Nov 19, 2018)

The nut used to attach the spark plug wire can take many forms or even be optional in some cases.  The easiest nut is of course to use a standaard 0-80 nut. Since my fingers don't work all that well I have trouble with them sometimes so I make a knurled nut.  An easy alternative to a knurled nut is to drill a tap a short length of 1/8 hex brass.  

I make 0-80 knurled nuts out or either  1/8 or 5/32 brass rod.  As I had enough nuts  on hand I did not make up any for this run of plugs., so there are no photos of the process.  But I will describe the process a bit.

I use a scissor knurling tool. When properly adjusted scissor type tool applies very low side pressure on the stock so several inches can  be knurled at once. About 1-1/2 inches of 1/18 diameter brass with no support on the end.  I have a small live chuck that I made many years ago and  if I use it in the tailstock I can knurl 5 or 6 inches of 1/8 stock can be knurled.

The knurling increases the diameter enough that I change collets to 1/64 inch over  the stock diameter.  I can then drill and cut off the nuts. I then tap them in the lathe using a tap driver in the tailstock.

A simple threaded sleeve with a groove cut in it can be used with a clip on wire connection similar to what is frequently on old model aero engines.  Looks nice. but I don't know of any commercial clips small enough for this size  plug. Clips can be made, but they are a pain to make in this size.

One 'no nut' option is to  make a straight in connector  out of 3/32 OD brass tubing about 1/8 long and is split  along the length.  It is  then swaged down to be a snug slip fit  on the screw threads and the wire soldered to the side of it.  As they are not very pretty the are best used if a boot is used on the  plullg to  cover them  up. I will probably use this on  the engine I am  working  on as I will be using a boot on the plug and will include details when I  do the pllllulg boot thread.

Gail in NM


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## JtH (Nov 19, 2018)

Gail,

Thank you so much for a gin clear posting on a subject which as been a mystery to me for years.  I am presently in Panama, but when I eventually return to Australia I will be following in the footsteps of John to try peek..

Kind regards

John (another one..)


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## GailInNM (Nov 21, 2018)

JTH: Thanks John.  I am  glad you are finding this thread useful.  

While the nut was  optional in some cases a sealing washer to bo between the plug and engine is not optional. The washer needs to be made from a malleable  but stable material that is softer than either the plug or  the engine (usually head).  PTTFE does not work well because it creeps (not stable) under pressure.  Alloy aluminum is too hard in many cases, but near pure aluminum will  work. Tradition dictated annealed copper for the washer and that is what I use.

The ID of the washer needs to be a close fit  on the plug threads and the OD needs to be at least equal to the body of the plug.  For the plug as drawn these are 0.190 ID and 0.245 OD.  The thickness should be at least the pitch of the thread, 0.025 in case of the 10-40 thread. 

A  quick note on plug threads.  10-40 was chosen as it is a quasi-standard for the next size down from the almost universal standard of 1/4-32 for model engines.  Rimfire makes 3 excellent plugs (the Z series) with 10-40 threads.  Unfortunately due to limited demand and production run size they are a bit expensive.  This plud as drawn is roughly the same as their Z1 plug.

I will describe two different methods of making the washers.  The first method is specific to the the #10 threads and will probably apply mostly apply to USA  builders because of available materials. The second method can be used for different size threads and is a little more work if you are only making a few washers. 

Gail in NM


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## GailInNM (Nov 21, 2018)

Getting staarted on the first method.  Sometimes, not often,  things just seem to work out our our way. I needed 0.245 minimum on the OD and 0.190 ID.  It just turns out that the most common 1/4 copper tube in the USA is 0.250 OD with a wall thickness of 0.030 resulting in 0.190 ID nominal. It is available at many smaller hardware stores cut to length which is convenient since a foot is enough for more washers that you will want to make. The big box DIY stores also sell it, but most of them want to sell you a 25 foot coil. A few of them sell cut lengths.

If you buy a new piece it will probably be fully annealed and vey  soft. If you have some that has been setting around the shop for a few years it will probably be work hardened by just being moved around.

I had about 10 feet in a partial coil that I had for some time so it was work hardened.  After roughly straightening the end I cut off a few inches.  You will get about a dozen washers er inch plus you need half inch or so to clamp on.






To anneal it I just heated it to a dull red and let cool.  Some people say to quench it in water, but the results are the same as if you let it cool in air.  If you have over heated it water quenching will wash off some of the fire scale that may have formed.





After it cools I clean it up a bit with abrasive paper . To straighten it I place it on a hard   surface and roll it with a bit of flat metal. This will most of the bend out of it.






Gail in NM


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## GailInNM (Nov 21, 2018)

While not perfectly straight thee tubine is straight enough to be usable. The tube is clamped in the lathe with about 1/2 inch protruding.  If using a chuck. it may be advisable to insert a piece of 3/16 rod in the tube to prevent the chuck jaws from deforming the tube. A collet is preferable if available.  

If the tube was cut using a standard tubing cutter as I used the end will have been swaged in to  a  smaller  ID  on the end.  About 1/16 inch is cut off to get past this section.  Use a sharp  tool and very llight cuts.  Copper does not play nice because ii 
is  soft that the tool will dig in.





Lightly deburr the ID of the tube with a countersink and the OD with a fine file.






Check to see if your spark plug will fit inside the tube.  It probably will not as the tube will be slightly out of round.  If it does  not fit, run a #12 or #11 drill about 1/2 inch into the tube.  and again check to make sure the plug fits.










Gail in NM


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## GailInNM (Nov 22, 2018)

All that is left now is to part off the washers to about 0.030 thickness.  I use a 0.o30 wide parting tool that has the tip ground to  a 15 degree angle so side nearest the  part cuts first and the parent stock side last.  This reduces the burr on the  part to make clean up easier.  You will have to look hard in the photo to see this. but it is there.





Then part off the washers too thickness.  I catch the washers on a piece of wire so I don't have to find them in the swarf tray. Lightly deburr the ID and  OD  of the parent stock with a  countersink and fine file between each  parting off operation. I get about 5  or 6 washers and then feed out some more tubing  and repeat the operations.   






The washers will have a burr  on the cut off side.  The straighter the tube the less burr.  I pick off the major part of the burr with a hobby knife or tweezers and then give them a rub  on abrasive paper  or with a fine file. If you are making more than half a dozen or so washers you will save  some time and fingernails by making a pocket about 0.020 deep in a scrap of metal to drop the washer into to hold them while filing the burr off.  I just plunge a 1/4 inch end mill into the jig and wobble it plus and minus a couple of thou on each axis so thelle washers fit easily in the pocket. 





That's it for method one of the washers.  Method two will follow , probably in a couple of days as I will be busy with the USA Thanksgiving holiday and family gathering  (today) the rest of  today and recovery  tomorrow. I  wish all my USA friends a happy holiday.

Gail in NM


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## GRAYHIL (Nov 22, 2018)

When I make small spark plug  I put a small under cut in the plug body first at the end of the thread.(_not very deep only a few thou_)
The washers are made as you say but the bore is _tapped _not as quoted :

Check to see if your spark plug will fit inside the tube. It probably will not as the tube will be slightly out of round. If it does not fit, run a #12 or #11 drill about 1/2 inch into the tube. and again check to make sure the plug fits.:

The washer will the screw on the plug and settle in the undercut and not come off or be lost.

Grayhil


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## GailInNM (Nov 22, 2018)

Grayhhil: Thanks for joining n.  Your method has a lot of merit and I can certainly recommend it.  If a #12 drill is used the washer will barely slide on the threads.  When building my engines I countersink the plugl hole to the major diameter of the thread.  This makes it easier to start the plug ans makes sure the plug will seat on the head.  The first time the  plug is installed the washer swells into this countersink then has  to be  unscrewed from the plug to remove itt.

Unrelated to building of plugs butt related to plugs I just  conducted an interesting experiment with supprising results. I took one  of my test hIt and miss engines with a 3/8 bore and 1/2 stroke and fired it up and adjusted the fuel mixture to get it running smoothly.  Had to readjust it a little as I had last run it in June at about 6600 feet elevation.  I am about 5300 feet elevation so the mixture changes a little bit. The head  on this engine is thick so it had an extended nose  plug in it.  I replaced   to plug with one of the short reach pllugs from this run and installed.  It is about 0.280 inch shat the plug I was using.  I just wanted to see if it would run at all.  It started right up and without adjusting anything I could not tell any difference in performance from the original   plug.  This ment that the spark was about 0.28 inch up an 1/8 diamater hole from the combusttion chamber.  It was just s happy at full load as it was at idle. This result was totally unexpected.  Photo shows the two plugs.  I will clean the long reach plug before re-installing it.  It has about 250 hours on it since clleaniing.






Gail in NM


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## GailInNM (Nov 29, 2018)

OK, back to making washers.  This time out of flat sheet copper.   The first problem is acquiring some copper sheet the right thickness.  You can buy copper sheet but most of the time they want to sell you far more than you need.

For washers this size What I use is copper pipe as used for water plumbing .  Looking at the specifications for copper water pipe in the USA. The wall thickness for "1/2" pipe is right in the middle of the thickness range I want.  I   put "1/2" in quotes because there is no dimension on the is  pipe that is 1/2 inch. Going back in history, they started of with 1/2 inch usable ID.  Then they added an allowance for scale and  mineral build up and then round up to to the nearest neat fraction for the ODn.  The result is that "1/2" pipe measures 5/8 inch OD.  You don't need much.  A 3 inch length is enough for 30 to 30 washers.  If you have a friend in the  plumbing business they will probably have a short cut off that they will give you.  If not, the big box DIY stores usually have short length in the 1 to 3 foot length at reasonable prices.

I first cut the pipe into about 3/4 long sections.





Then split the sections length wise.  I put them in  a small drill press vice tightening them  only enough to hold them lightly and cut them on the band saw.







Gail in NM


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## GailInNM (Nov 29, 2018)

The copper in the split part is in full hard state from work hardening during  the manufacturing process. It will be annealed to a soft state before  unrolling it.  If you have not worked with copper I suggest that you try to open the piece up a bit before annealing using the method in the second photo of this post so can get a feel for the difference between dead soft and work hardened. 

To anneal just heat it up to a dull red and then let it cool. I use a DIY style propane torch for this.





It is soft enough to open with you fingers at this point but it is easier if you open it up most  of the way by inserting a pair of needle nose pliers  in it and then opening up the pliers. 





Then finish opening it using your fingers. After it is mostly open  turn it  over and press it down on a hard surface.  It still will not be flat but it will be close.





There will be fire scale on both sides of the copper.  In the above photo the copper had been over heated so there is lots of fire scale .  Brush off the fire scale with a brass or stiff  fiber brush. This is to keep the scale from being pressed into the copper during the final flattening operatioon.

To finish flattening the copper blank I insert it into a mill vice with flat jaws and clamp it.  To make it easy I do it is several stages so I have something to hold on to.







Gail in NM


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## GailInNM (Dec 3, 2018)

With some flat blanks in hand it is time to make the center 0.190 diameter hole.s  I have used 3 different methods at  different times so will describe all three.

The first  way is to use a CNC milll.  The blank is supported on a pair of thin parallels in the mill vice.  Only a moderate clamping pressure can be used as the copper is soft and will buckle if  to mulch pressure ils applied.  Check that the vice griiips both ends of the blank bp llightly clamping and  then checking that both ends are being gripped.  If  the pipe was cut squaare then it normally OK. but if not a few strokes of a file will square it up. I plunge in slowly with a 3/16 4 flute center cutting end mill and then open the hole up with circular i orbit with a radius of about 0.0015.  Repeat spacing the holes at least 3/8 apart.  Note in the photo that I am holding the blank down with the handle of a chip brush.  Cop[per grabs when the mill breaks through and may try  to pull out of the vice.  Don't even think about using a finger for this!!!






Gail in NM


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## GailInNM (Dec 3, 2018)

The second method is the same as the first as far as setup but done  on a manual mill.  Put 3/16 holes in the blank with an end mill then  finish the hole to size using a 0.180 drill.  This will leave mmore of a burr than the first method but it is not  too bad to  remove.  If you try to drill the hole with out using an end mill first the blank will probably pull out of the vice  and you will have a large burr to remove.

Gail in NM


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## GailInNM (Dec 5, 2018)

Just to show how out of date I am with the technology of on line shopping I looked on Amazon with a search for copper sheet and found many listing for 23 and 24 gauge copper sheet.  23 gauge is 0.025 inch thick and 23 gauge is 0.021 inch.  Either would work OK but I  would prefer the 23 gauge.  Prices range from US$ 12  to US$ 20 for a 12 inch square sheet.  Smaller sheets are also available.

This would save you some time and effort from cutting from a piece of pipe as I did.

Gail in NM


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## GailInNM (Dec 5, 2018)

Moving on to the third method of putting in the 0.190 holes.  The holes are punched with a very simple punch and die set. I have a foot press, AKA Kick press. that I normally use.  As these are not common in most home shops I set the punch and die up on my small manual mill which has a 6x24 inch table with a a R8 spindle.  Smaller mills than this would struggle with punching this hole.

For those who have never done any press work here are some very brief comments on punch and dies.  I say very brief as whole books are devoted to the subject.

Clearance is needed between the  punch and die.  If punching a hole, the punch is made to the desired hole size and the clearance is applied to the die.  If punching out a a disc, or part, the die is made to the desired size of the part and the clearance is applied to the punch.  This clearance  is specified between each side of the punch and side of the die As a rule of thumb the clearance is from 6 to 10 percent of the material thickness.  The greater the clearance the the larger the burrr on the part or hole. As the clearance is reduced a smaller burr will be formed but the pressure required to punch the hole will increase.

The punch will stick in the parent material so it is a good idea to polish the sides of the punch to reduce the friction and resulting effort to remove the punch.  The slug will also stick in the die so the area below the cutting edge of the die is relieved so the slugs can fall free without having to be pressed through the thickness of the die.

Gail in NM


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## GailInNM (Dec 5, 2018)

Since the washers are being made of  soft copper the  punch and die can be made of any mild steel and does not need hardening of any kind. Unhardened it would be good for at least 500 holes and then a touch of the die on a belt sander would make it  good for another 500.

I made the punch by first milling a concave on the end of  a 1/4 inch diameter rod and then turning about 1/2 of it down to  0.190.  The concave makes the punch shear the hole and reduces the pressure required to punch the hole to about 1/4 the pressure that is that would required if the end is made flat.  This reduces the wear and tear on the milling machine quill rack and pinion and also on the arm muscles. I mill the concave first as the milling operation distorts the end of the punch making it slightly larger.  The turning  then removes this distortion. Making the punch long enough so a couple of inches protrudes from the chuck that holds it makes it easier tor align the punch and die.  

I made the die from a piece of 1/4 x 3/4 cold rolled mild steel.  I drilled the larger diameter (0.201) hole by touching off the point of the drill and drilling to a depth of of the material so the tip of the drill just touches the bottom side.  Then I drilled through with the 0.194 drill.  This difference of 0.004 on the diameters of the punch and die gives 0.002 per side clearance.  

The die was removed and a flat file used to remove the burr caused by drilling.  This gives a sharp cutting edge on the die. 

The die was clamped with the cutting edge up in the milling vice on parallels. The punch was held in the drill chuck and aligned so it would enter the hole in the die. The Z axis stop was set so the notch in the punch would enter the die about one material thickness.  It can enter more but that makes it more difficult to remove the punch from int the stock .










Gail in NM


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## GailInNM (Dec 6, 2018)

A couple of holes are punched.




And then a bunch. Notice n the photo that I got some of the holes too close to each other.  This will make cutting the parts apart  with snips or a saw difficult while leaving enough material for the OD. This will only affect one of the methods that I will describe for producing the OD in a following post.

Also notice the stripper mounted above the punch.  This is  optional  but lit  will save a lot of time and irritation in  removing  the  punch from the stock  if making a quanity of washers.





And an overall photo of the setup showing the temporary llash up  for the stripper .






Gail in NM


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## Rocket Man (Dec 6, 2018)

I buy small spark plugs at O'Riely auto parts store.  After using them in my rockets engines they get 1400 degrees.  Copper gaskets soon become loose fit.  I can tighten the spark plug several times soon the copper gasket needs to be replaced.  I buy flat sheet roofing copper at Lowe's I use a punch set to punch out blanks.  I had to make my own punch set for the diameters that I need.  I punch out center hole first then use another punch with a guide pin on the tip to punch out the finished rings.  If I want copper rings to be softer metal I heat them with my propane torch.  Work hardened copper gets soft again if you heat it to about 1000 degrees.


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## nel2lar (Dec 6, 2018)

I had the need for some copper washers some time ago and made them from a piece of tubing. Copper tubing comes in several OD's. I took the tubing slipped it onto a mandrel that was a snug fit then used a tubing cutter to cut my washers to the desired thickness. Worked a charm for me just try not to cut into the mandrel.
Thanks for sharing
Nelson


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## GailInNM (Dec 18, 2018)

Thanks for the comments. All are welcome.  If you have a different way of doing things please post them.  
I apologize for the time lapse in this thread.  Life has a way of getting in the way of  playing with  toys.,

There are a couple  of ways of cutting the OD of the washers.  The first way that I will illustrate takes the least  amount  of  tooling but is slow to make the washers.  Still it OK for a dozen or washers. A mandrel is made from 1/4 diameter rod by turning the end down to a smooth sliding fit on the ID.  Make spud about 1/2 inch long and keep the inside corner sharp.  A clamping sleeve is made out  of the same material. It is about a 1/4 inch longer than the spud, about 3/4 inch long.  It is drilled through so it is a sliding fit on the spud.  Face off both ends so they are square and sharp.  

The washer blanks are rough cut out with metal snips and then the corners are nipped off. 







Here is the   rough cut washers but the corners have not been cut.






The blanks are loaded on the mandrel.  Up to a dozen can be put on at  once.  I have put on 6  in the photos. As copper does not machine well so the blanks are filed to be  sort of   round and then turned to about .005 over size.  The copper will have smeared enough that the washers will be stuck to each other.  Removing the last 0.005 with a file will remove this smearing so the washers will separate. 















Gail in NM


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## GailInNM (Dec 18, 2018)

Another method of producing the  OD is by punching with a setup similar to that done when punching the ID.  The punch is made from 1/4 stock and has a pilot turned on it that is a close sliding fit in the ID  of the washer.  It  would be possible to drill the rod and  insert  the pilot, securing it with Loctite. The taper on the  piloot just makes it easier to get the punch started in the ID of the washer.

If the die has a flat top as shown in the lower left of the following sketch it will take a fairly large amount of  pressure to punch the washer. out.  It two or three  strikes on my small mill,  Thiss pressure can be reduced by producing a shearing angle  on the die as shown in the lower right part of the sketch.  Although it  would be easy to put a shearing angle on the punch using  an  inserted pilot the washer produced would be neither round or flat. Also notice that increased the side clearance from 0.002 to 0.003 inches.  This also reduces the pressure required.  This is 12% of the material thickness so a small burr may be produced.  This burr can be easily removed if desired but as it is  outside of the pressure sealing area of the washer it will not hurt anything if it is left  on.




Gail in NM


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## GailInNM (Dec 20, 2018)

A third method of making the washers is really just a rehash of the punching of boh the ID and OD.  The punches are the same but the die has a guide for the punches built in.  This allows the punch/die set to be used in an arbor press  or the the punches to be driven with a small hammer.  The difficulty with this method  is that the punches are difficult to remove after punching. A few ways of to remove the punches iare:
 1. G grip the punch with pliers and twist while pulling.
 2. Cut some shallow grooves in the punch body so a pry bar can give extra force.
 3. Leave the ID punch flat and drive the punches out with a small brass punch.

The bottom of the die uses the same relief as before.  The upper  portion has holes that gives a smooth sliding fit on the punch body. A little side play is  OK as the punches will try to center on the cutting part  of the die as soon as the punch starts to enter of the stock. 

Another advantage of this method is that no set up is required so  you can punch out a few washers and store the tooling.  Then you can pull out the tooling and  punch out a few more if required at a later date.

No photos as I have not done this since I got my kick press 30 years ago, but I did use it prior to that.
Gail in NM


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## GailInNM (May 24, 2021)

I have made many plugs using Corian and it works fine but is quite brittle. Also it is difficult to find in some overseas countries. I went searching for a replacement material and fount that pulltruded fiberglass epoxy rod has slightly better high voltage insulating qualities and better heat and flame resistance. It machines easily and the swarf is fine and does not pack up as bad in the flutes of small drill bits.
Best of all it is easy to find as it is used as the shaft for bicycle safety flags. Most of the time the flags  are sold with the flag glued to the shaft so when the flag wears out the old shaft is thrown away. So if you ask around you may find one for free. But even if you have to buy one they can be found on Amazon or Ebay  for $10-15 for a 6 foot one with bike mount and flag. And that i s several lifetimes supply.  All that I have seen are 1/4 inch diameter and have come from China so should be available in most countries. 
I have only made a few plugs with it so far. All have tested OK.  I ran one of them in an engine for about 25 hours. Then, I inspected the plug under a microscope and could not see any depredation of the insulator.
GailInNM


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## simonbirt (May 25, 2021)

I have made them using PTFE insulator, I know that it gives off nasty gases if it melts. I would not use it in a high performance application but recon it is OK in my hit and miss engine. The combustion temperature is clearly above the melting point of PTFE but the cylinder head is an effective heat sink. In fact the whole engine is made out of material with a lower melting point than the combustion temperature. The advantages of PTFE is that it is easy to machine and it seals easily arround the electrode.


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## Steamchick (May 26, 2021)

I heard someone say they simply used fuses from the domestic plug. The insulator ceramic tube can be machined (carefully), but 2 of 3 made good plugs (or so I believe). But maybe different countries use different fuse bodies and different ceramics. If you can work glass, you may be able to glaze a wire core, then glue it into the steel body? Or use exhaust pipe sealant clay to seal a ceramic tube around the core wire and into the body?
Lots of options!
Let us know what is best?
K2


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## Jasonb (May 26, 2021)

I've done them using glass tube as the insulator and a tungsten tig electrode down the middle all put together with Locktite "Black Max" as per Nick Roland's design.


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## Steamchick (May 26, 2021)

Nice one Jason! Should work I think - and you can tune the mixture by flame colour with this one!
K2


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## Steamchick (Aug 1, 2021)

Brilliant! Thanks for the explanation.
Considering using PTFE, I like your idea of the grooves so the epoxy forms a structure that resists the sheer from the internal engine pressure on the insulator. Have you considered making the assembly so the shoulder is on the inside part of the insulator, and assembly from the inside? - Of course, this means the side electrode must be bent after the insulator is installed. But obviously your method is successful, so no reason to change. What engine do they run in?
K2


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## simonbirt (Aug 1, 2021)

Here are the drawings and construction notes. 

The photo shows the tooling used. Left to right top to bottom: 

Screw gauge for single point thread cutting
Swaging tool
Block to support insulator and electrode while punching over top
Gauge for body
Finished bodies
D bits for body and insulator
Punch to attach cap
Form tool for cap- radius, groove and parting 
Mandrel to hold bodies
Prototype plug


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## GailInNM (Aug 1, 2021)

Great ideas and methods Jason, Steamchick, Simon and others.
Very nice constructions plans Simon.

By sharing our ideas and methods novices builders can see that spark plugs are not really "spooky" and that as long as a few basic techniques such as spark gap, adequate electrical insulation and sound mechanical strength  are met they will work. So designs can be mixed and matched to suit the builder's tools, tooling and material availability and with confidence that the plug will work. And experienced builders can also get new ideas to incorporate in their next build.

Thanks for sharing everyone.


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