P&W Wasp Jr. in 1/6th scale

[Mike R]

This is the start of me tracking my build of a P&W Wasp Jr. in 1/6th scale, from drawings by Bob Roach and castings from Bruce Satra.  I started this about 11 years ago when I acquired the drawings and the castings, and about 9 years ago I got a tiny start on building but realized that my skills in the shop were not up to par yet so it sat for a long time.  In the mean time I've played with a few other small projects and dabbled here and there on how to cut the fins on the cylinders.  That was a real challenge for me but I recently figured it out, which has prompted me to post my progress.
So here is the status to date.

• Cylinders are nearly done, need to have bolt pattern drilled for fixing to crankcase, and a pair of flats added to the large flange. 
• 8 connecting rods done (earliest parts made - not perfect but probably good enough for bits that will be hidden.)
• Crankcase done (but may yet get remade).  Has a few discrepancies I may want to address, second (or is it the third one) will go faster.
• intermediate crank support - by far the nicest part I've made to date - from a fit AND finish perspective.

I'm posting this here but as my progress has been so slow that glaciers outpace me don't get too hung up waiting on the next chapter.  Work interferes still far too much.

Attached are a few pics of the current status, one of the cylinders and the connecting rods after I made them.


Mike

[Jo]

You are moving along nicely Mike

I have a few sets of castings that are maturing while I wait for my skills to improve sufficiently that I feel confident to do them 

Jo

[Jasonb]

Lot of work there, this may spur you on. The engine built by Ron Harris that was at the recent London MEX

[Vixen]

Nice work Mike 

It's always good to see someone else embarking on another 'round engine'.

Keep the occasional report coming our way.

Mike 

[Mike R]

Thanks all.

Jo,
I also have other castings waiting their turn (Wright J6 1/4 scale) as well as a locomotive (LMS Duchess 3 1/2" gauge).  Going to keep working on the supporting bits carved from solid until I'm comfortable tackling the castings...

Mike,

Your work on the Bristol Mercury is inspiring, keep it coming! 

Jason,
No need to torture me with that sort of photo to spur me on.  I'm motivated but lacking time due to the need to eat (i.e. work).    Simple math says I need to work 10 more years but I'm aiming for less.  The shop does provide a nice break occasionally but rarely in doses large enough to make real progress, hence the slow pace. Maybe once the kids are adults I'll have slightly more free time.

Mike

[Mike R]

In the spirit of making use of the tools I've collected and modified over the years I decided to put my Emco Compact 5 into service making the 18 valves required.  The Emco is a CNC machine that I've converted to newer stepper motors and modern electronics for fun(Mesa 7i76e Ethernet card and LinuxCNC). 


I choose to make the valves out of 303 stainless after much searching for what material is suitable for small engine valves.  As it appears that just about any steel is serviceable I decided on 303 SS so that there is at least some corrosion resistance for the long periods where this engine will not be running.


The 1st technique I tried was one I'd seen recently on a couple of Youtube videos, where the desired small diameter is turned in one pass from a much larger piece of stock (think 10:1 or more diameter ratio of stock to final part).  This technique failed on first attempt even in 3/8" aluminum due to the lack of rigidity of the Emco - it would grab and then stall.  Next I decided to go at it in steps.


I programmed up the lathe to cut the valve in distinct steps (using Fusion 360 CAM and some hand editing afterwards):
1.  Turn the stem top down to diameter (3/32") for about 5 mm
2.  Machine the retaining groove (home ground tool, 0.44 mm wide (~ 17 thou)
3.  Turn the next 5mm or so down to diameter
4.  Turn the remaining stem length to diameter and shape the head
5.  Part off
6.  Return to start position to help set bar for the next valve.


I initially trialed the program on some 3/8" diameter aluminum and all went swimmingly (sure sign of issues to come ).  Once the 303SS was in I had to make several program tweaks to accommodate the harder to cut material.  The Emco is about as rigid as a wet noodle when compared to my Standard Modern 1340 so I needed to learn more about its capabilities and limitations.


In the end I succeeded in getting a repeatable program but the parting off - even at 3/8" (~10mm) was hard for the lathe. I could actually see the lathe deflect as it tried to cut. Total time per valve was on the order of 20 minutes when taking into account a few programmed pauses I had to let me check on the progress.


My concerns are that the valve stems are still in need of what I would consider final finishing as they are a couple of thou too large, and the surface finish is not what I want (some are much better than others).  I'll probably end up chucking the head up in a 3/8" collet and lapping the stem to size and finish.  Anyways here are the parts as they sit now in a partially finished state.  There are 22 of them as I will inevitably either loose one, or stuff one or more up in setting up for lapping, etc.   I got distracted and moved on to another part / project after this so I have the lapping to come back to...  (look forward to?).


If you are into boring machining video I took one of the Emco working on one of the valves, its quite slow going as it nibbles away at the metal!  The video is 5 min 46 secs and its only the middle and head profiling portion, with some terrible audio- me talking very little and even then much too quietly to be heard and the lathe squealing at times... You've been warned. 
  <a href="https://www.youtube.com/watch?v=2LJdOdJzXs0" target="_blank">http://www.youtube.com/watch?v=2LJdOdJzXs0</a>
[/size]
[/size]Mike

[petertha]

Very nice. Was this engine ever featured in a magazine like Strictly IC? Or maybe I'm just recognizing the names (Bob Roach & Bruce Satra) from that era. I think there is a 1/4 scale version made by Paul Knapp in the museum. Anyways just curious about the basics - displacement, fuel/ignition type, lubrication.... Also what are your cylinders made from?

[nj111]

That's very nice work so far.  Interested to know your method / tooling used to cut the very fine cyl head fin grooves. With regard to improving the finish of the valve stems I made some in exactly the same way as you have done - but with a little Denford Orac (which I upgraded to Mach3). I finished the stems prior to parting off using some replica external hones that I made some years ago - basically a home made version of a Delapena / Sunnen external hone, this works superbly for valve stems. Nick

[Niels Abildgaard]

  This technique failed on first attempt even in 3/8" aluminum due to the lack of rigidity of the Emco

 The Emco is about as rigid as a wet noodle

 You've been warned. 

From the boring video it can be deducted that overhang- that is distance from spindle bearing to work zone- is at least 100mm.
It is not possible to see the  load path from cutting point to lathe bed and then to Gaia but let me suppose it is some kind of QCTP on the miserably engineered  EMCO tool slide.
My advice is to make or buy a short ER  collet system and a decent compound slide system.
See another boring (but much shorter) video





and less overhang (modified WM180 lathe)

<a href="https://www.youtube.com/watch?v=49ISMaCAB1k" target="_blank">http://www.youtube.com/watch?v=49ISMaCAB1k</a>

[Elam Works]

Mike,

A few thoughts. I see in the video that you are using molded indexable carbide insert tooling. These do not have a very sharp edge, indeed they are manufactured with a slight radius to make the cutting edge stronger. Various coatings increase that radius slightly. They work more like a bulldozer shoving the metal aside than shaving it off. So when you are turning very small diameters like your valve stem it just pushes the work piece aside. Also, as the work diameter gets smaller, and you take shallower cuts, the edge break becomes larger in proportion to the work. You may not even be getting off the edge break on very light cuts, resulting in effect a very high negative cutting angle. Combine that with stainless steel, notorious for work hardening, and it is no wonder the surface finish is poor.

You would be better off with a ground carbide cutting edge. You could take a used insert and grind a new cutting edge on that. It also looks like the insert you are using has too large a nose radius for the light finishing cut you are trying to take. That is working against you by increasing the length of the cutting edge engaged with the work, increasing the amount of torque and rigidity required.

Why not consider using a ground HSS tool bit? It will take a keener edge than carbide can hold, and you can grind a very high top positive rake that will reduce the cutting load (and so reduce torque and work deflection). It will also hold a much sharper tool nose radius. For really small diameters like you are attempting, the nose radius ought to be practically dead sharp, with just a stroke of a fine oilstone to give it a thou or two radius. You are going to be feeding slow anyway, you don't need a big nose radius.

I don't see the cut off tool, but I wonder if it is not the standard 3/32 wide carbide insert parting bit? If so, that is too wide in proportion when you are parting off work that is just 3/8 inch diameter. You want something that is just a 1/16 or little less wide. A ground grooving bit (not molded) would be ideal.

Summary: Sharp, ground edges (the keener the better); positive rake; and minimize the length of the cutting edge engaged.

Nick, I like those external hones; thanks for posting the pictures. I have a project that would benefit from something like that.

-Doug


[fix typos. 18Mar20. -Doug]

[Mike R]

Hi Nick.


I appreciate the external hone pictures, I was planning on making something and that has given me some good direction on what I'm doing.  I'll fill everybody in on the cylinder fin cutting in a proper post, basically involved using a slitting saw on the mill and rotating the work.  The heads are as purchased so no credit to me on that work except perhaps having the foresight to buy them while they were available. 


Hi Neils,


I do realize that the overhang from the spindle bearing is quite long.  I briefly looked at an ER collet chuck for the lathe (cheap Chinese version) that would bolt in place to the chuck adapter I have fabricated and surprisingly it provided almost no benefit in terms of shorter overhang.  That leaves customizing my own ER collet onto the strange nose of the Emco.  Doable but I just wanted to use the lathe for once, not take on yet another non-engine project.  I may revisit but as I don't have any smallish ER collets I'd need to buy them as well and its just not something I'm interested in at this time.
It does have the Emco tool changer - not sure if its miserably engineered but it certainly has its shortcomings.  I did reduce the stick out of each tool to a bare minimum, I could have maybe gained another 5mm but with more effort.  Again I wanted to use the tool changer as that is the appeal of the CNC - it can in theory make the whole part in one go, changing tools as needed.  So changing out the tool changer for a compound is not in the cards, I'd like to learn what the lathe is capable of and how I can maximize it through better choices of tooling, tool paths and setup.


Hi Doug,


I appreciate the feedback.  I was being a bit lazy in terms of using what was available to me on a few fronts. 
I recognize that the insert was maybe not ideal.  I've actually ordered a set of inserts designed for aluminum which at least provide the sharp edge but not the smallest nose radius so that gets 1/2 way there.  I had actually gently lapped the insert on a diamond sharpener to try and get a sharper edge but may have made matters worse rather than better.
I was using the tool changer on the lathe and it has positions for 3 square shank turning tools and 3 round positions (i.e. drills etc).  I needed 1 for the groove at 0.44mm,  1 for the majority of the turning and 1 for parting off.  In hindsight I could have left the valve attached and parted off in the manual lathe, freeing up a tool position for a "roughing" tool and 1 for fine finish. 
The parting tool is ground from a HSS bit, and its about 0.055" wide (under 1/16").  I could have made it narrower but again my laziness prevailed as I thought it was small / thin enough.  Maybe one day I'll learn...   
This was one of the first times I've tried setting up the lathe for "production" parts and if I'm so inclined I can have another go at the valves as the material was cheap in this size and I consumed less than 2 ft (about $6).  Might be worth it just to learn how to setup the lathe better to get parts that are "ready to go" off the lathe. 


- Mike


 

[Mike R]

Pertha,

I don't believe it ever featured in a magazine.  Ron's Model Engine News had a few mentions of it but I've never seen a full magazine / blog / thread on a build.

[Art K]

Mike,
Just wanted to say hi! and that I am following along, or at least I am now. I look forward to your work on Your Wasp Jr. I do like round engines and have 2 on my bucket list.
Art

[Niels Abildgaard]

It does have the Emco tool changer - not sure if its miserably engineered but it certainly has its shortcomings.

- Mike

Hello Mike
Found it on Lathes

http://www.lathes.co.uk/emco/page8.html

Was not aware that Emco had made such a thing

Kind regards

Niels

[Jasonb]

can't you use some tailstock support, I always use a very small BS 0 ctr drill on the overlength valve stems and then turn the full length rather than in steps. Excess length turned off later by holding stem in collet or a split bush.



DCGT insert will help a lot and also angle the toolholder or get one that presents the insert so there is more clearance when cutting the shape of the valve head as the larger engagement width is when you are getting chatter.



I'd saw up your stock into 2 x valve + 25mm then you can keep the ctr section to hold then if you need to lap the valve stems ( I have not found the need to) and also when lapping the valve into it's seat

If it won't part off well then saw off and hold by the stem to face head to thickness with light cuts, again hold stem in collet or split bush.