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Cox cylinder/head tap

Old 09-03-2012, 04:46 PM
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Max_Power
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Default Cox cylinder/head tap

Has anyone here ever had or heard of a tap for the 17/32-40 thread in the crankase and cylinder for Cox .049? I'm tinkering with the possibility of some engine projects and figured this to be the most difficult part. Here is a picture of one I made but it is of leaded steel and I'm not so sure it will work properly. I have considered single point threading the cases as well, but that seems very tedious so I figured I would see if any of the halfers here had any ideas. Thanks in advance, Todd
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Old 09-03-2012, 07:56 PM
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Default RE: Cox cylinder/head tap

The taps do exist, but will be spendy. Figure $100.
Old 09-04-2012, 12:13 PM
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Default RE: Cox cylinder/head tap

Hey Todd,

Yes, they are a custom order tap/die (depending upon what you want or need). Dave's estimate is about right for a single one.

These guys bought a bunch of the taps on a custom order a while back and had them for sale around $50. Send 'em an email to see if there are any left, [email protected]

Best Regards, Matt
Old 09-04-2012, 12:39 PM
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Default RE: Cox cylinder/head tap

I had been thinking of doing some needle valves like the KirnKraft remotes too, but I will likely never find a #2 or 3 x 128tpi tap and button die.  I think a 2mm x .25 is pretty good too.  If they were a common standard size they are sometimes reasonable, but no one likes to carry stock any more, then they can get a special order price.
Old 09-04-2012, 01:27 PM
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Default RE: Cox cylinder/head tap


ORIGINAL: aspeed

I had been thinking of doing some needle valves like the KirnKraft remotes too, but I will likely never find a #2 or 3 x 128tpi tap and button die. I think a 2mm x .25 is pretty good too. If they were a common standard size they are sometimes reasonable, but no one likes to carry stock any more, then they can get a special order price.

I am pretty sure Texas Timers still stock a 128 tpi needle assembly for a TD.

We only carry the regular ones (80 tpi) as the machine tooling is too expensive for a very small run of those. My best advice for someone making their own is to check with a local gunsmith. They would be the most likely to make a custom tap/die in those extra fine thread applications.

Matt
Old 09-04-2012, 10:03 PM
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Default RE: Cox cylinder/head tap

Even most gunsmiths would not take on making taps and dies of that sort. It needs pretty special tooling that is simply not that common. For example I don't know of ANY metal lathes that go down to 128 TPI so cutting the tap to make the dies is a non starter for anybody other than very specialized makers.
Old 09-05-2012, 04:19 AM
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Default RE: Cox cylinder/head tap

It wouldn't be High Speed Steel either.  The pitch is only about .010"  That is finer than most feeds.  The dia. tolerances would have to be very close to get a good thread too.
Old 09-06-2012, 06:26 AM
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Default RE: Cox cylinder/head tap

I would be more than happy to check with a couple of our suppliers for an estimated cost on a 128tpi tap/die if anyone was interested.

Best Regards, Matt
Old 09-06-2012, 06:37 AM
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Default RE: Cox cylinder/head tap

Sounds good if it isn't too much hassle.  I have to ship across a border, but it may be worthwhile if I make a few sets.  I am not sure what thread the KK needle was.  Mine was .083" OD which is kind of bigger than a #2.  Maybe I should check the one place here, they were successful for the Turbo plug tap size. I have been using a 2-56 for some needle valves, but a finer one would be better.
Old 09-06-2012, 08:29 AM
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Default RE: Cox cylinder/head tap

I will have a look for you.

The regular Product/Sure Start ones are a 2-80 as well as the Medallion. The TD thread is a 4-80. Both of those sizes I know we can get without much of an issue.

Matt
Old 09-06-2012, 01:46 PM
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Default RE: Cox cylinder/head tap

From my recent experience I don't think the feed of the lathe is the issue, although the "half nut" rates stop at about 80 for most lathes, the normal feeds may start to fit the bill...of course the a the has to be left in gear and reversed between passes then. My lathe will longfeed at between .0197 per rev to .0008 per rev so there is a lot of room there for different thread counts. The real issue I think is finding a appropriate cutte with a small enough radius to make that sharp of a thread without spending a ton of money. That and the losses from flex of that small of material, even if it only 1" long its like having a foot of 1/2 inch stock hanging out of the chuck and its hard to setup to tailstock and thread a object that close to the chuck?One can hand grind a HSS bit to a point, but then you deal with a lower quality cutter as far as durability, etc... My tap actually chases threads decent..I haven't tried to tap a hold yet, but making it leads me to believe a internal thread could be successfully single-pointed for the cylinders. Making a fine needle valve would admittedly be that much harder than this.Of course I am a novice machine St with very modest tooling and knowledge.

Li have contacted James engine to see if they still have tas, but it seems they are out.

My latest thought is that i'm thinking of trying to just make a 4 cylinder long head that uses studs to clamp the head and whole cylinder to the crankase and will likely just turn the threads off the "jug" , seal with brass washers and make a head for all four cylinders as one piece, perhaps even using regular glow plugs. This would eliminate the need to do any fine threading. This is a winter project I am just trying to overcome the cylinder mounting hurdle ahead of time so I can design around it. It seems like a cool looker too. The next difficulty is figuring out how to make a crankshaft with seperate "chambers" for each cylinder so that they do not have to be all on a common journal and can be fired 90 degrees apart. A set of broaches to make nice square holes might be needed I'm sure HMEM might be a better outlet for this thread, but I like picking the brains of folks here too. Still a bit of flying weather this year so after I see if my tap works on a bare hole I will put this project back to the "design" stage while I burn what fuel I can with the weather I've got left. If anyone has any ideas on a crank/crancase that would still allow seperate chambers for intake/transfer I'd love to hear them.

Has there ever been any other method of model engine fuel control besides threaded needles? Todd
Old 09-06-2012, 03:21 PM
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Default RE: Cox cylinder/head tap

If you centre drill the back of the tap you made, you can use a centre in the drill chuck or collet of the mill and chase the threads if it has just been drilled and not moved, or if it was indicated. Otherwise a CNC is better. Why bother with the Cox cyl. why not use a Norvel or AP .09 cyl.The AP has the bypass ports milled in the cyl. already.It is much easier to make, schneurle ported, ABC, maybe muffler friendly, and not a Cox. Another note. I can get a #4-80 tap for $11, but not the die at the one supplier I sometimes use. They never heard of a finer pitch than that. As far a a needle valveless needle, you can surround a piece of tubing and run a screw in to squish it fairly well.. It won't leak, and if you go in at an angle it is like a finer thread. It needs a rad. on the bottom so it doesn't cut the tubing.
Old 09-06-2012, 06:17 PM
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Default RE: Cox cylinder/head tap

Most of the reason I chose the Cox is that this is mostly a "zero dollar" project and I have a bunch of new sure starts in a bucket as donors, most the metal..., and besides the tap, all of the tooling. It is less of a project to power a specific project and more to learn new skills and practice them. Like many right now the budget is tight so I have been hopping around a lot doing what steps I can do with the materials or parts I have on hand...then moving to something else that needs more labor than time. I look at a back room full of hobby items, and I have found myself in the past "75 bucks"'ing myself to death on projects when accumulation of skills will probably help me do more cool things in the long run LOL. in short: I'm cheap and just entertaining myself killing time and I'll make one with optimal parts after I prove I can pull off a simple, loud one Todd
Old 09-07-2012, 03:56 AM
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Default RE: Cox cylinder/head tap

The AP .09 is only about $30.  It is cheaper than a   new   Surestart, has bearings, carb,  and a muffler.  But I guess you don't have a box of them in the basement, and they don't come up at swap meets as often as the Cox stuff.
Old 09-07-2012, 06:35 AM
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Default RE: Cox cylinder/head tap

Try this supplier to see if they can get what you need: http://www.victornet.com/tools/Speci...-Taps/199.html
Old 09-07-2012, 12:18 PM
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Default RE: Cox cylinder/head tap

They have the Turbo plug tap(m8 x .75) cheap,and an m2 x .25 tap and die which is useful for a needle, a tap but no die for an m2 x .2 which would be better. The # taps go to 80 TPI. Good place though, and most stuff says it is in stock. Oh they don't have the Cox cyl. size that I could find.
Old 09-17-2012, 08:53 AM
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Default RE: Cox cylinder/head tap


ORIGINAL: aspeed

Sounds good if it isn't too much hassle. I have to ship across a border, but it may be worthwhile if I make a few sets. I am not sure what thread the KK needle was. Mine was .083'' OD which is kind of bigger than a #2. Maybe I should check the one place here, they were successful for the Turbo plug tap size. I have been using a 2-56 for some needle valves, but a finer one would be better.

One of our suppliers came back with a quote that was much too expensive (over $300). I have another pending quote from another one still.

Best Regards, Matt
Old 09-17-2012, 01:53 PM
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Default RE: Cox cylinder/head tap

The M2 x .2 tap is good, but there is no die that size.  I still have 1 remote KK needle  left. 
Old 09-18-2012, 10:19 AM
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Default RE: Cox cylinder/head tap

Max Power, since you already made ONE tap to this thread size why not simply make another. But this time make it from drill rod and then harden and temper it following all the shaping operations?

I've done a few of my own custom sizes in that way and it's not that big a deal.

With the picture in the first post you're on the right track but you need to make the gullets a LOT bigger. The cutting teeth will not be relieved on a home made tap similar to how they are on factory ground taps. So the key with a 17/32 diameter tap with fine threads of this sort is to cut away 5 or 6 gullets so you leave about a 3/32 to 1/8 wide set of threaded "lands" to do the cutting. Even then I like to lightly releive the peaks on the trailing edges.

To get a good start you'll also want to lightly chamfer the first couple of teeth with a file before you cut the gullets out.

OK, I just took the time to do a sketch. Shown here a 17/32 thread and using a 3/16 chainsaw sharpening file it looks like you'd get a good tapping form from using 5 gullets. Note the arrow showing that you don't want to simply plunge straight down. It'll cut much more effectively if the teeth have a slight hook angle which you can get by starting with a straight plunge and then push to the side as shown by the arrow to get the hook shape. Note that you need to sink the file in a little past half it's diameter to get this.

I didn't show it on the sketch but with 5 gullets the resulting cutting lands are .1 wide if you shape the gullets as shown without a lot of excess opening. That's about perfect for getting a good "follow" during the thread cutting but without creating too much drag.

You'll likely want to make TWO taps like this. One for a starter and one for bottoming if you will be running down to a flat stop like the Cox heads. So take careful notes of your numbers on the first tap so you can replicate it for the second.

For measuring the thread cut depth for things like this I'm a big fan of the "3 wire" method. This is where you use wires that fit down into the "V" of the threads so the wire sits on the walls of the "V". For 32TPI this means you want to use something like .018 wire. The idea is that the wire sticks up over the peaks so you can get a meaningful measurement of the pitch diameter that you can use for comparison when cutting the threads on the taps. Whatever you get on the glow head threads add .002 to ensure some play to be able to spin the heads in.
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Old 09-18-2012, 11:42 AM
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Default RE: Cox cylinder/head tap

I think we are on the same page Bruce. The drill rod is a bit harder to get a clean cut that small though, so I'm still figuring that one out. I did cut a female thread in aluminum single pointing..., and it turned out pretty well. I'm considering doing this and then having a sleeve press into the case after threading so that when I cut threads it will he l be a through hole with a open space behind to make it a bit less tedious. Looks like James engine is out of the taps so I'm gonna have to figure it out this way....what kind of tool do you think you would use to make this cut? HSS or the small carbide I'm using? Its a shame a old Cox cylinder isn't harder or I would consider splitting it and using a plug to stretch the OD a bit. Todd
Old 09-19-2012, 11:35 AM
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Default RE: Cox cylinder/head tap

With a good thick sulphurated cutting oil and a stoned HSS single point I have no trouble getting a nice shiney result when cutting the annealed drill rod.

The key is setting up the cross and compound slides correctly. I don't know your ability level so bear with me if I repeat the obvious.

You want the compound set at 29 degrees from the cross slide so that the trailing side of the cutter drags lightly on the back side of the thread you're cutting. Also for obvious reasons you want to do your last few cuts a thou at a time. I also find that a final pass with the setting at the previous pass does a nice polish cut run by using the spring in the machine to supply the cutting pressure. Another hint is that I like to run a smooth cut lathe file lightly over the crests to remove the sharp burrs between my last cut and the "polishing pass" which is set to the same as that last pass.

If you try this I think you'll find that it leaves a pretty slick finish.

Oh, one other thing that isn't always obvious. The leading side of the thread cutter needs a little more rake than you think it needs. This is because of the advance rate used in cutting threads. You want enough clearance rake that it makes up for the angle of the thread spiral along with a little clearance for the cut. So the cutting tool ends up with a 10 to 12 degree rake on the leading side. If that's not there you may find that it's dragging the thread just cut along the front ridge as it rotates down and away.

Again, sorry if this is already well known.
Old 05-22-2014, 06:57 AM
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I am starting a radial 9 cox engine proyect. I foudn an online shop with all the piston and heads I needed, and agreed with the seller, he will specially order some 17/32-40 thread taps to sell on his web site at a "decent" price of $55. Keeping in mind that I have received quotations of $200 euros, $50 is a good one. Hope this opportunity of getting cheaper taps can make others start new cox proyects. http://www.exmodelengines.com/cox-.0...-head-tap.html
Old 05-23-2014, 04:03 PM
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10 years ago I was looking at doing the same thing. Andrew Coholic from Canada was in need of a TD .09 glow head at the time and traded me for a tap he had made.
Below is his response to how he made it. Good luck, Greg

--- Andrew Coholic wrote:

---------------------------------
To make the tap, I cut the thread first, then mill the
grooves, and then lightly hone to remove any burrs, and then
finally case harden the cutting surface using Casenit compound.

Remember, cut only aluminum and non-ferrous metals, it is not
hard enough to cut steels.
Old 05-24-2014, 01:13 AM
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It can be done, but you need threading skills, a good lathe that can handle such thread, trial and error, etc. For a $200-300 tap I would try it, but for $50-60 best to buy a professional one made.

Gsw1, did you made any progress on your radial?
Old 05-24-2014, 05:53 AM
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Remember that when you make a tap, the pitch diameter is a couple of thou. larger than a screw or whatever part is going in for clearance. There are charts, measurement over wire MOW, and best wire size BWS charts or calculations. there are also thread micrometers to make it easier. Personally, I think $50 is a lot for a tap, I would make one if my lathes had the capability.

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