# Drills and a Cox tap



## Kludge (Aug 16, 2008)

Once again the Kludgemeister combines two subjects into one post!

Fisrt off, I have a bunch of drills that have 1/4" threaded ends on them obviously intended to screw into the electric/air/bench drill. (These came from a military base closing somewhere and are just a handful of what was actually available.) There are several number sizes plus several 1/4" and a 5/16" - all except the last in some small quantity. I have no clue what these are supposed to fit so any thoughts would be greatly appreciated. Also, I measured the shaft below the flutes and found all to be undersized. (Across the flutes is pretty much right or a gnats eyelash small.) Is this normal or some sort of special case?

Second, I know I've seen a tap somewhere to allow threading Cox .049 cylinders into homemade crankcases (Questions related to 2-stroke engines made from these will appear later.) but I cannot remember where. If someone could point me to a vendor, I'd greatly appreciate it. (I guess finding vast quantities of .09 or larger pistons & cylinders and the taps to fit them is pretty much an ain't-gonna-happen thing.)

BEst regards,

Kludge


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## Mike of the North (Aug 16, 2008)

I think the drills are used with a drill like this.
http://www.tightfittools.com/riganat.html

Mike


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## Kludge (Aug 16, 2008)

Mike of the North  said:
			
		

> I think the drills are used with a drill like this.



Could well be. Airplanes are full of all sorts of unpleasantly awkward to reach places. A right angle head like that would make life a lot easier and threaded bits would make losing them somewhere in the various abysses larger aircraft have less an issue. 

If no one has any objections, I should like not to continue that line of thought lest embarrassing moments from bygone days emerge causing me to go off to curl up in a corner and twitch for a while.

Anyway, I should be able to make an adapter to fit my Taig lathe for drilling items secured (more or less) in the milling attachment. Some of the bits are very short so flexing will be a lot less a problem. 

Thank you for the help.

Best regards,

Kludge


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## GailInNM (Aug 16, 2008)

James Engine has the tap for the Cox Cylinders. Not cheap, but he may have had to have them made up special.
http://www.jamesengine.com/index_files/Page435.htm
Gail in NM,USA


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## Kludge (Aug 16, 2008)

GailInNM  said:
			
		

> James Engine has the tap for the Cox Cylinders.



Cool! That's the one. I didn't have it bookmarked before which puzzles me just a bit. Many thanks for the assist.

You're probably right about having them specially made. I know of a place in England(?) that does that sort of thing and isn't cheap but when it's the difference between having and not having in an environment where competition is limited, it's often worth a few extra pretty stones and bits of shiny metal. Dependent on need, of course.

Best regards,

Kludge


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## GailInNM (Aug 16, 2008)

Kludge,
What is it you are up to with the Cox cylinders? I have built up several engines around them. Fun little projects. You should be aware that the thread size given in several references is not correct. It is listed as 17/32-44. The 44 pitch reference is close enough that if you make the threads really sloppy you can make them fit. Some one made the error early on and the error kept getting copied by other authors.

Information for the Cox cylinder variations is at:
http://en.wikipedia.org/wiki/Cox_hobbies

And some plans for Schroeder's engines are for sale at:
http://modelenginenews.org/rsch/index.html
Go to the bottom of the page. 
I think that both of these engines had construction articles on them, with plans, in Model Engine Builder. 

If you think about building up a Simple Single, I think I have an extra crankcase you can have for the cost of postage. Threads in it were single pointed. A few other extra parts are here too.

Gail in NM,USA


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## Kludge (Aug 16, 2008)

GailInNM  said:
			
		

> What is it you are up to with the Cox cylinders?



This is all part of my effort to take over the world, one Twinkie at a time. ;D

I've been thinking about multicylinder engines built up using Cox cylinders & pistons - and maybe other parts as well. I have a particular fondness for round engines, in part because I love the sound and in part because I have time on them as both a pilot and a mechanic. (I've also got "flat engine" time but that's not half so much fun.) While I may to build a horizontally opposed engine or two down the line to fly in a smaller (than the B-25) R/C airplane, the whole idea of a multicylinder and, by necessity, multibank radial has been nagging at the back of my mind for a while. The full 9 cylinder 3-bank engine will probably not get built but putting together 1/3 of it - a 3 cylinder engine - isn't outside the realm of possibility. 



> You should be aware that the thread size given in several references is not correct. It is listed as 17/32-44.



Do you know what it should be? I tend to ... ummm ... push limits just a bit and having a jug fly off at an inopportune moment would probably make me even more unpopular with the building association than I already am. ;D



> Information for the Cox cylinder variations is at:
> http://en.wikipedia.org/wiki/Cox_hobbies
> 
> And some plans for Schroeder's engines are for sale at:
> http://modelenginenews.org/rsch/index.html



Tagged 'em both. Thanks! I've subscribed to MEB since inception (with my latest renewal delayed due to helping my daughter with her expenses) so I'll go through the back issues to find them. 



> If you think about building up a Simple Single, I think I have an extra crankcase you can have for the cost of postage. Threads in it were single pointed. A few other extra parts are here too.



I may take you up on that. I need to see what it's going to take to have Murphy give me back my workshop. (Long story)

Again, many thanks.

Best regards,

Kludge


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## GailInNM (Aug 16, 2008)

Kludge,
The correct size is 17/32-40. I found some variation in the early Cox cylinders on the cylinder base thread diameter. Not a lot, but enough that I had to redo a crankcase because the later cylinder was too tight. I used an early one for a go gage when I cut the threads, then the later one would not fit. That's what I get for making things to fit with no allowances. It was only about a thousandth of an inch, just enough to screw me up. I have never measured the actual size, but I do remember that the Cox engines cylinders actually measured smaller than the 17/32 by a few thousandths. 

It hard to do a radial two stroke engine because the crankcase pressure required to for fuel transfer is hard to generate. Not many success stories there. Most common way is to mount three engines on a plate and gear the outputs together. That can be improved on by making a crankcase with three cavities in it and three reed valves fed by a manifold with a single needle valve. Looks better, but hard to get the mixture right for all three cylinders.

I will quit talking about it now however as I don't want to screw up your creative talents by telling you what others have done. 
Gail in NM,USA


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## Kludge (Aug 16, 2008)

GailInNM  said:
			
		

> The correct size is 17/32-40.



Cool, thanks. Since I need some other taps (and dies) made anyway, I'll add this to the list. Maybe several of them to sell at a rediculous profit. ;D



> I found some variation in the early Cox cylinders on the cylinder base thread diameter.



I'll probably be using all Sure Start cylinders & pistons since they're cheap and available. I think it's cheaper to buy the whole engine that just the cylinder & piston. If the cylinders are a touch small then it's all good. I just have to watch my tapping start point so they line up nicely.



> It hard to do a radial two stroke engine because the crankcase pressure required to for fuel transfer is hard to generate.



Yep. All one crankcase makes a round engine unpleasantly icky since there really is no crankcase compression to speak of. A V-block engine with both pistons on the same crank throw stands a better chance but even it's a bit of a challenge without extreme cleverness and maybe a little Jamesons in the coffee.



> That can be improved on by making a crankcase with three cavities in it and three reed valves fed by a manifold with a single needle valve. Looks better, but hard to get the mixture right for all three cylinders.



Actually this is kind of the approach I had in mind but without the reed valves. In one of my demon-chasing mental exercises, I thought about a common rotary valve on the back of the engine (This was before I decided that more banks would be fun.) that would only be open for around 120 degrees of rotation for each cylinder (actually a touch less unless its design is horridly clever) but I could use the same rotary valve for all three cylinders. Assuming the shaft the individual engines are geared to runs at the same speed as the engines (just backwards with simple gearing), it can drive the rotary valve instead of the crankshafts doing so. This got a little complicated when the 2nd & 3rd bank popped into my mind but not impossibly so. I think.

As you mentioned, balancing the cylinders can be a bit of a trick but again, I think not an impossible one. Hmmm ... I wonder if there's a way to provide a positive pressure (or at least a really really good swirl) at the rotary valve(s) to give a slightly better opportunity for balancing. Something to think about the next time the demons hit.

Are we having fun yet? 

Best regards,

Kludge


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## DICKEYBIRD (Aug 17, 2008)

Hi Kludge,

Here's a couple links with a little info on Ralph Barnette's 5 cyl radial with Cox 1/2A cyls. I 've seen these run at various meets a couple years ago and they run well. They sound more like a squadron of angry bees than a P&W Wasp though!

His radials use a rear mounted 4 vane blower and a single Enya .09 carb.

http://www.rcuniverse.com/forum/m_3...ALPH%2CBARNETT%2CRADIAL/anchor/tm.htm#3366168

http://www.modelenginenews.org/gallery/p8.html (Scroll down to the bottom)

I saw his Trimotor with 3 of the radials do some high speed taxi tests at the Little Rock S.M.A.L.L. fly-in a couple years ago which was quite an impressive feat. It was too heavy to fly though.

Milton


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## Kludge (Aug 17, 2008)

DICKEYBIRD  said:
			
		

> Here's a couple links with a little info on Ralph Barnette's 5 cyl radial with Cox 1/2A cyls.



I took a look at the links then at a link on the Model Engine News site to another page discussing multicylinder 2-stroke engines. I'd like to find more detail on the vane-type blower he used to see how he designed it. (This also goes back to the Ryobi 2- and 4-stroke engines for the B-25 project and getting more power from them.)

I wonder if the Enya carb was what he had on hand or if there was some selection process. I couldn't tell but I may have missed something.



> They sound more like a squadron of angry bees than a P&W Wasp though!



That in itself is an endorsement! Even a wasp knows not to be around when bees are swarming. ;D



> It was too heavy to fly though.



Reminds me of a story Arthur Godfrey told some years ago which I won't go into now but has to do with Bathtub Aeroncas and airplane rides. 

If he doesn't mind a little redesign, there are materials other than balsa that might help him lighten the ship so it can get airborne. It won't be a stunt plane but "once around the pattern" is far better than fast taxi tests. If nothing else, it's a good proof of concept - that Cox-based radials built with a master rod and a single crankcase rather than individual engines geared together can fly. After that, it's a race to see who can get the best performance from such an engine. That's when the real fun begins. 

Thanks for the urls, Milton. Now I've got more possibilities to consider. This is a good thing.

Best regards,

Kludge


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## barnesrickw (Jul 17, 2013)

Any chance an SM05 tap will work for a Cox .049 cylinder?  SM05 is 0.535-40. So it is larger by almost .003. This is assuming that 17/32-40 is the correct size of the cylinder thread.


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