An experimental V-4 wobbler

[spuddevans]

Some time ago I started designing a little V4 wobbler in Alibre and made a 3d rendering in pdf format to give some idea what I hope it will look like when built.

Click here for interactive pdf rendering

Anyway, over the last few days I have been finalising some of the details and also printing out some plans, and today I have made a little start on this little engine.

The design is to have a V4 configuration, 8mm bore 12-14mm stroke (cant remember which ??? ), double acting wobbler.


I hope to keep a good record of the build with plenty of pics of all the processes, cos I know you all like pics th_wwp Rof}

Actually, today's progress is pretty boring, just some sizing of stock.


Normally, as many other builders, I would have liked to have started on the most complicated part 1st, which on this build is the main frame, but I am awaiting the arrival of some materials for the frame, so I made a start on the cylinders.

I started by putting the ER32 chuck on the lathe, and gripped a length of 20mm round brass bar in it, squaring the end up, then using my patent-pending method of marking up, I traced a mark at 21.5mm from the end.







I then used a thin parting tool to put a cut in at the mark to a depth of around 3-4mm, it's not important what depth, just so long as it is deep enough to be still there when I reduce the bar down to 16mm.




Then I swapped over to a 6mm round profiling tool ( as recommended by Bogs ages ago, and well worth getting ) and reduced to required size, just needing a quick swipe with some emery to clean up.





Then I swapped back to the parting tool and finished parting off. Then loosen the chuck, extend the bar out a little more, tighten, mark up and measure off another 21.5mm, make the initial parting cut, reduce to 16mm, part off and repeat another 2 times, or perhaps 3 times to give you a spare. (as I did knowing that it will be needed :big: )





The reason for making the initial shallow cut with the parting tool was just to give me an indication of how far to reduce the diameter of the 20mm brass bar to each time, and to therefore hopefully stop me from trying to cut too long a section down to 16mm. You might have a firm enough lathe to turn down much longer sections, but on my (as yet, completely unmodified, straight out of the box condition) rubber lathe, I have learnt to keep the minimum stock sticking out of the chuck when trying to keep to dimension, and so the visual reminder that putting on a partial parting cut gives is a helpful reminder to me to only turn down one piece at a time. Plus the parting tool is already in the QC changer from parting off the previous blank, so it only takes a moment to do.


These cylinders are not totally straightforward in themselves, as, just to be difficult, I have designed the bore to be offset by 1mm from the center of the cylinder blank, so I spent the rest of my time in the workshop figuring out just how I am going to machine all the features and also in what sequence to machine it, and of course, how to hold it for machining.

Next up will be machining all the cylinder blanks to the same length (hopefully 20mm), and then machining a pivot on the side of each cylinder before boring out the bore

Anyway, that is as far as I got today, more updates to follow.


Tim

 

[John Rudd]

These cylinders are not totally straightforward in themselves, as, just to be difficult, I have designed the bore to be offset by 1mm from the center of the cylinder blank, so I spent the rest of my time in the workshop figuring out just how I am going to machine all the features and also in what sequence to machine it, and of course, how to hold it for machining.


Tim,
Hope I'm not teaching granny etc.....

You could offset bore the cylinders in the lathe by using a 3jaw chuck with a suitable packing piece in one jaw....

Or you could use a 4jaw with the jaws suitably offset....

Good luck with the build....

 

[spuddevans]

Tim,
Hope I'm not teaching granny etc.....

You could offset bore the cylinders in the lathe by using a 3jaw chuck with a suitable packing piece in one jaw....

Or you could use a 4jaw with the jaws suitably offset....

Good luck with the build....

Believe me, I appreciate any and all advice and wisdom offered :bow: Thank you :bow:

I had forgotten about using a packing piece in the 3jaw, I am intending to bore out the cylinder bores on the mill, so no problem with the offset, plus with the cnc conversion I can get a nice slow powered feed to give a nice finish on the bore using a boring head to bring to the final 8mm diameter. I plan to drill it to about 7.5mm and then have the boring head set up for 8mm and then use the CNC to make a few passes at a slow steady feed to eliminate springing.


The slightly more challenging part of the cylinders is the means that the cylinders will attach to the frame and how they pivot.

Normally, wobblers use a spring to hold the cylinder in place. On this wobbler I intend to use rare-earth magnets that are glued into recesses in both the frame and the cylinder. It is the recess and the means of pivoting that is a little more challenging, for me anyway ;D

It's kinda hard to explain, but the next time I'm working on this I will be machining these parts, so all should become clearer. (or I will be posting up about how I am re-designing it all :big: :big: :big: )


Tim

 

[T70MkIII]

Looks like a very interesting design, Tim. Can't wait to see your progress.

 

[bearcar1]

I'm intrigued by your method of cylinder retention Tim. Your design has a pleasant appearance to it, although I must admit that the 'batwing' base looks to be a challenge.

BC1
Jim

 

[spuddevans]

I must admit that the 'batwing' base looks to be a challenge.

The lower part of the frame, ie the legs, should (he says hopefully) be fairly simple to machine. It is just made of 2 radiuses, radiai, radii, Curves :big:


I got another couple of hours in the playroom workshop today, and started by mounting my new vice onto the mill, and then clocked it square with a dti, I didnt go crazy, but just got it down to +/- 0.05mm ;D




I then mounted all 4 cylinder blanks on some parallels and with two pieces of ali at the front and back to compensate for the minor differences of thickness on each cylinder. If you dont put some soft material between the jaws and the workpieces then the slight differences will cause the multiple pieces to not all be gripped the same, which is perfectly fine unless you actually want to machine any of them. The Ali not only protects the brass from the steel vice jaws, but also will squish a little to compensate for the minor differences.

Anyway, I then I worked back and forth with a flycutter to get all 4 to the same length, 20mm.




I then turned the cylinders on their sides, gripped them in the same manner, and made a few more passes with the flycutter. Here's a shot after I cut the flat down until the required thickness ( 14mm ). Others might prefer to switch to an endmill to get the bulk removed, but as there was only 2mm to remove, and on brass I am able to take 0.25mm depth of cuts with this flycutter, it was quicker to keep using the flycutter. Plus it leaves a lovely silky smooth finish. Don't let the curved lines fool you, they cannot be felt by my fingernail.





Not having a lot of time left I started to set up for the next machining processes. The next thing will be to bore out a 2mm deep, 10mm diameter recess in the center of the flat section, and I will probably drill the inlet/exhaust holes at the same time. Because this has to be done on all 4, I'm going to use my sophisticated vice stop system shown below.




And for making sure that the cylinder flat is positioned true and flat I use another patent-pending system...




It wasnt until I had released the vice after flycutting all the flat sections that I realised that I should have kept them in place and just drilled and bored all the relevant holes using my edge finder on each cylinder and then moving to the right coord's for the holes :wall: :wall: :wall: :wall:


Oh well, you live and learn.

So next will be a boring post ( oh come come! this post has been pretty boring anyway Rof} Rof} ) and then some silver soldering.


Tim

 

[spuddevans]

I've made a little more progress on the cylinders.

According to my plans I have to drill the 2 inlet/outlet holes, and also a central 10mm diameter hole. The small inlet holes pose no problem, but the 10mm diameter hole is a little more tricky for me as I found that I do not have a 10mm endmill, and this hole must be flat bottomed. (wasnt that a queen song, "flat bottomed something-or-other" :lol: )

I could've made a 10mm D-bit, but I figured out another way. I do have a 3/8" endmill which is 9.51mm approx in new money, and I also have a boring head that I can set to 10mm.

So here are my tools for this task,




Center drilling the holes,




Boring out the majority with the endmill,




Drilling the 1.5mm steam passages,




Then I swopped the ER32 chuck and mounted the boring head in the mill and then bored out to 10mm, I left the boring head locked at the needed diameter.





Repeat the above steps another 3 times, til you have this.




Then I turned the cylinder upright in order to bore out the bore

Using my expensive vice-stop to position the cylinders to make a little production line, first up after centering up was center drilling all 4 cylinders,




Then following through with drills up to 7.8mm,




Then I reamed all 4 out to 8mm, I was going to bore them with my boring head but I realised I didnt have a slim enough boring bar for it ( something for the shopping list )




Next I turned up 4 little rings of brass, 10mm OD, 8.1mm ID x 3.5mm depth.




And this is where they fit,




And here are the pieces all together with 4 8mm x 2mm neo' magnets sitting in place.




The magnets will be epoxied in place, and I am considering leaving the rings unfixed, they will fit into corresponding 10mm recesses in the main frame, and the magnetic attraction should keep them all in place.


While I have the vice stop set up, I will probably next drill the 4 holes on each end of the cylinders for fixing the endcaps or glands, then that should be all the cylinder machining operations done.


All that and maybe more (or less) on next weeks show.....



Tim

 

[Brian Rupnow]

Very cool idea with the rare earth magnets. I will be interested to see how this works.---Brian

 

[spuddevans]

Very cool idea with the rare earth magnets. I will be interested to see how this works.---Brian

Thanks Brian Thm:

You're not the only one, I'm pretty keen to see just how this turns out :big: :big:

Actually, doing some rough experimentation with the 8mm dia magnets this afternoon, I am a little concerned that they will provide too much of a pull, thereby creating too much friction. But I am building in some adjustability to the frame, instead of using a magnet on the frame as well, I intend to use a little disc of steel, and I can vary the size of the disc to suit the magnetism needed.


Tim

 

[bearcar1]

Hello Tim, nice concept engine. To solve your friction problem, would a thin washer of Teflon between the magnets help reduce the drag of the metal on metal you are experiencing with using two magnets back-to-back. I rather fancy the idea of the two as opposed to one attracting an unmagnetized piece of steel. Teflon sheets can purchased in supet thin sheets from McMaster Carr. It's a concept that will be interesting to see how it unfolds. Thm:

BC1
Jim

 

[spuddevans]

Hello Tim, nice concept engine. To solve your friction problem, would a thin washer of Teflon between the magnets help reduce the drag of the metal on metal you are experiencing with using two magnets back-to-back. I rather fancy the idea of the two as opposed to one attracting an unmagnetized piece of steel. Teflon sheets can purchased in supet thin sheets from McMaster Carr. It's a concept that will be interesting to see how it unfolds. Thm:

BC1
Jim

Thanks Jim, I have got some teflon sheet, but my plan is to have a small gap between the magnet in the cylinder and the steel disc, probably about 0.15mm-0.3mm. The friction I was mentioning was the friction between the cylinder port face (the flat face) and the face of the frame.

I made a Elmers #25 wobbler ages ago, it runs really sweetly, and I used a spring to hold the cylinder to the frame, comparing the pressure needed to pull the cylinder off the frame, and the pressure needed to pull two magnets apart, I had great difficulty pulling the magnets apart, and even pulling the magnets of the end of a 8mm steel rod was greater than pulling the cylinder off the face of my wobbler.

I do remember that when setting the tension on the spring on the wobbler, when it was too tight it really slowed down or even stopped it from running. Hence my thoughts about using a steel disc in the frame that would be replaceable with alternative sizes to "adjust" the pull of the magnets if needed.


Tim

 

[spuddevans]

I got a little more done today, namely the drilling and tapping the 32 holes in the cylinders for the packing glands and endcaps.

Having a DRO with a bolt hole function does make the drilling a lot easier, combine that with a vice-stop for repeatable workpiece positioning makes for a relatively easy time.

I got a little carried away with that and forgot to take any in-progress shots of the drilling, Oops :doh:


Then I mounted all 4 cylinders in a vice placed on my tapping stand, and I was really glad to have it. Tapping 32 holes with both M2 taps ( 2nd and bottom ) by hand would've been a nightmare.




As it was, I was able to tap a hole every 20secs, which I thought wasnt to bad. But after tapping 16 holes on the top, then turning them all over and tapping the bottom 16, I started to think if there could be a way to speed the process up a little.

One thing I noticed was that withdrawing the tap seemed to take longer and caused more ache in my arm. Then inspiration hit ( or perhaps it was a particularly bad case of wind :big: ) and brandishing a hacksaw I made this little mod to my tapping stand.




Then I put a slot screwdriver bit in my cordless drill and selected reverse. Then I would wind the tap into the hole until it reached full depth (just before the squeek) backed it out a quarter turn, then it was just a case of slotting the screwgun onto the newly made slot and 2secs later the tap was out, much easier on the arm!!


So at the end of that I have 4 (hopefully) finished cylinders.



Then I had to retire back to the pc to redo some of my plans to adjust some dimentions on the main frame.


Tim

 

[spuddevans]

I got a little more progress today, not much to show, just some preperation work really.


I started off by making a little angle plate, this is needed for milling and drilling the internal steam passages in the "V" section. I have got some angled parallels (now there's a funny thing), but I didnt want to stack up 8 of them to make 45 degrees !!!

So I marked up a scrap of 10mm ali plate and rough cut it on the bandsaw, then mounted it on the mill table using a V-block to align it for finishing it.

I 1st up aligned the V-block,


this is taken before milling, and yes I did notice that one edge is not fully fitted into the V-block, I adjusted it and re-tightened it before milling.



Here's the result. I know that it is a little rough looking, but it will do just fine, it will only be used 2 or 4 times, and each time will only be for aligning the frame in the vice, the angle itself will have no pressure applied to it.



Then I turned to preparing the Ali for the main frame. I cut off a piece of 1/2" thick Ali' in the bandsaw, then cleaned up and squared the 4 edges. This just left the front and rear faces to clean up and bring to 12mm. My present flycutter has about a 30mm sweep, so it was not enough for this, so I sharpened up a new piece of hss and mounted it in the larger flycutter ( I have a set of 3 flycutters, up til this point I have only used the mid-sized one )

Tooling ready I took a couple of shallow cuts off each side (0.25mm doc), then checking with mic I reduced the thickness to 12mm. The last pass took off 0.1mm and left a really reflective finish.



Then I spent a while marking out the positions for all the holes to be drilled in the face.




Next time things should get a little more interesting, I will be drilling all the thru holes and then boring on each face the 10mm bore's that the cylinders pivot on, plus some bores for the crankshaft ballraces, then will be drilling the long internal air/steam passages (longest is 46mm)


Tim

 

[maverick]

That little 45 degree angle block is very handy, don't be to sure you'll only use it 2 or 4 times. I've got 2 or 3 of various size
that are just the ticket every once in a while. Great looking engine also.

Regards,
Mike

 

[spuddevans]

Thanks Mike, you're probably right, I'll find many more uses for the 45deg angle.


I've got a little more progress made of the frame.

I mounted the frame in the vice on the mill on some parallels and then using an edge-finder I zeroed on the bottom of the frame (actually I zeroed off the jaw of the vice) and then zeroed off one side of the frame blank. I then moved in to the center of the frame and zeroed there. This is because of the way I have marked the dimensions on the plans, working from the center of the frame rather than from one edge.

Then I put a little center drill ( I really must get some proper spotting drills ) in the chuck and center drilled all the holes using the coords off my plans.




Then I set about drilling all the thru holes, and all was going well until a little "plink" sound. Grrrrr, I broke a 1.5mm drill halfway thru leaving a small segment of drlllbit stuck fast. :wall: :wall:






I finished off drilling the rest of the thru holes with a fresh bit, and bored out the larger blind bores for the cylinder pivots and for the ball-races for the crankshaft. Then I turned the blank over and bored out the larger blind bores on that side, then very carefully drilled the failed 1.5mm hole from the other side until I heard and felt the drillbit start to catch the stuck fragment.

I then spent an hour or more digging it out using various methods with not much success until I tried using a pointed V carbide burr. I then very gradually fed the burr into the stuck drillbit until I had bored most of the way through the stuck bit, then I took the remainder of the broken drillbit, ground the broken end flat and then I applied a little persuasion with a hammer and the stuck bit popped right out.


Then I took a couple of pieces of 6mm steel rod for the next step.




These 6mm rods fit into the blind bores for the ballraces, and are used along with the 45degree angle I made earlier to mount the frame vertically in the mill vice as shown, the two HSS lathe bits are there to raise the frame up enough to allow me to get the right angle




Then (once the vice was tightened up) I touched off the 6mm rod with a 16mm endmill, zeroed the DRO and then raised up the Z-axis by 38.87mm (according to my plans the distance from the center of the crankshaft to this edge of the frame is 41.87mm, subtract half of the 6mm rod brings you to 38.87mm) and zeroed again.




Then it was just a case of raising the cutter up and then nibbling my way back down to zero. Then I loosened the vice, rotate the frame and align using the 45degree angle and tighten the vice. Then nibble away the 2nd corner.




I did think about shaping more of these upper arms while having it in this position, but I have some long holes to drill, and want to do that before spending any more efforts, just in case I totally mess up the long boring. The shaping of the outsides of these arms are not critical, so the shaping can wait til later.


Next up will be boring these 4 long steam passages between 38-46mm approx deep, then if nothing snaps or gets stuck, I will be shaping the outer edges of the frame.


One handy tip I have learnt from snapping the 1.5mm drillbit, when I started using the new bit I began rubbing a pencil up the flutes. This seemed to stop the ali welding itself into the flutes, and I re-applied the pencil a couple more times per 12mm deep hole, this seemed to work really well, good old carbon lubrication.


Tim

 

[spuddevans]

It's amazing just how things go, when I was designing this engine, the part that puckered my cheeks the most was thinking about drilling the long narrow internal air/steam passages, close to 50mm long with just a 2.2mm bit, drilled into Ali' which I know from experience just loves to gum up a drillbit, break it and weld the broken bit deep in the workpiece.

But what do you know, the deep drilling went without a hitch, no breakages, no gumming up, and no breaking through where it shouldnt.

Here's a picture when I'd drilled the last of the 4 deep holes, and I've drawn on it to show where the internal passages meet. Because the passages are offset from each other the passage on the front (green) is not connected to the rear passage (purple) (I just know someone is going to make a joke about that !!! Get your minds out of the sewer and into the gutter with the rest of us :big: )

I drilled the first 30mm of each hole with a 2.5mm drill, then finished the hole off with a 2.2mm bit. The reason was not only for ensuring the bit wouldnt break, but also made sure that these long holes would break through into the 1.5mm cross drilled cylinder ports. Then by switching to a slightly smaller bit gives a little more room for error on drilling without breaking into the central crankshaft bore.







Then I moved the frame into a vice on the tapping stand to tap the central hole on each arm M2, this is for attaching a cap to cover and seal the ends of the long internal steam passages.




Once that was done I couldn't resist fitting the cylinders and pivot rings to see how it looks.






Next I will be making some steel inserts to fit into the 10mm pivot bores in the frame to give the magnets something to pull onto. There will probably be some experimentation with the sizing of the steel inserts to get the appropriate "pull force". Then I will be moving back to the cylinders, or rather, to the end caps and packing glands and pistons.


Tim

 

[bearcar1]

Tim, I can only imagine your relief of having gotten over the deep drilling without incident, way to go. It is always a pleasure to get over the anxieties that we drum up in our minds over some step or procedure, only to find it to be a piece of cake and all of the worrying was for nothing. You know, I'd be willing to send you a proper pencil sharpener if you wished. :big: I'm anxious to see how your magnet attachment method works out, so far a terrific looking engine. Do you have a plan "B" in mind just in case your original idea doesn't work out as well as hoped?

BC1
Jim

 

[spuddevans]

You know, I'd be willing to send you a proper pencil sharpener if you wished. :big:

:big: :big:

I was going to tell you that I had been chewing on the wrong end of the pencil while drilling the deep holes, but the truth is that I was using it to rub in the flutes of the drillbits to prevent the ali welding to the drill. It worked too, absolutely no problems with ali sticking in the flutes.

I'm anxious to see how your magnet attachment method works out, so far a terrific looking engine. Do you have a plan "B" in mind just in case your original idea doesn't work out as well as hoped?

I'm anxious too :big:


A plan "B" scratch.gif Hmmmm! I dont really have a plan B, just from the initial testing of the magnets, I cant forsee there being not enough "pull", if anything there was way too much pull using 2 magnets attracting to each other, that's why I'm going to try using a steel insert in the frame, then I can vary the diameter of the insert to adjust the "pull" factor.


Tim

 

[ChrisB]

A really great thread Tim,

Wonderful to see some really nice pics to go along with the great explinations too. A really very interesting looking engine. Looking forward to seeing more progress soon.

Chris

 

[spuddevans]

Thanks Chris,


I got started on the Endcaps today, and started by chucking some 20mm brass bar in the lathe, and then turning down a section to 13.8mm (the OD of the endcaps) and then turned a tiny 8mm spigot (to fit the cylinder bore). Then I marked up the bar to show a 1.5mm line.




Then I parted off at the line, then repeated 3 more times.

Then I had to clean up the little pip left on from parting, my plan is to mount them into a 14mm ER32 collet and then skim off about 0.1mm off the face. However, as I have tried to chuck up thin items before in my ER32 chuck and have found that without something the same diameter in the rear of the collet, when you tighten the collet up it tends to pull out of true, so I just used one of the endcaps in the other end,




Then I used a plastic handle to "nudge" the endcap into alignment while the collet is only hand tightened with the lathe rotating slowly, then stop the lathe and tighten up.




All four,




Then I took the ER32 collet off the lathe and mounted it on the mill, and drilled the mounting holes.




Then after drilling all 4 holes in the endcaps I couldnt resist mounting one on a cylinder.




Next up will be the packing glands.


Tim