Flapping around... Elmer's Kimble

[arnoldb]

Today's little bit...

From this point on, I'll work a bit slower, as this is the start to the more difficult parts of the build.

First, the engine block. It must be 3/8" (9.53mm) thick. I have some 10mm thick aluminium I could have used, but that bit is from extruded bar and very gummy to machine and tap, so I rather dug a bit of harder 12mm aluminium out of the stock bin:

That was then milled square and to size on all edges. As I felt in the mood for some lathe work, I set it up in the 4-jaw on the lathe - just centered by eye and using a bearing shell as a parallel to the chuck body. Some strips of aluminium drinks can were used to prevent chuck marks, and I used wire to bind down the parallel so that it wouldn't rattle around and damage the chuck face if it did happen to come loose:

Faced one side smooth, flipped the block around in the chuck, and faced the other side down to thickness:

There's a slightly rough bit close to the center, but it does not matter, as that's in an area that will be machined away later.
The block needs to be very parallel, and a check with a micrometer gave me less than 0.005mm (that's 2/10ths of a thou) difference measured in a couple of different locations. My old girl (ML7) may be 40 years old, but she can still do it ;D

Some quick marking out for bits that needed to be milled away and the double marking across is 1mm thick where it must be cut with a slitting saw later:

Cut-outs milled away; just hogged it down close to size with the 16mm end mill and then a light final pass either side to clean it up:

I bought a 5mm edge finder quite a while ago, but it was a bit rough and sticky and didn't work well. Last week one evening I gave it a thorough wash-out with methylated spirits to get rid of the sticky oil that was used on it, mixed some Brasso with thin oil and lubricated the running face with that concoction and gave it a bit of a run, before once again washing it out thoroughly and just giving it some light machine oil. Used it today for the first time, and it works beautifully ;D :

At 800RPM it wiggles around a bit, then smooths out, and then suddenly kicks out positively. On the mill dials this was exactly on the same reading each time; I'll test it's accuracy more thoroughly at another time.

I used the vise stop and the mill's dials to coordinate drill the mounting holes 1.6mm to tap M2 later:

Then I slit the top section off:

As I didn't change the vise stop or dial zero-rings when slitting, I just used the same settings and readings to drill 2mm clearance holes through the top:

Next I tapped the holes in the bottom section. I don't have long enough 2mm screws, so out with some bits of threaded rod:

More marking out. The engine block layout on the plan is quite busy, and it's easy to get some measurements wrong. In addition, the tangent sections are a bit difficult to lay out, as Elmer didn't give easy measurements to get to them. As you can probably see, I ended up with a bit of a discrepancy in the thickness of the tangent sections - a combination of trying to manipulate the protractor and forgetting to compensate for the scribe tip's thickness:

Fortunately, the error is not a biggie; I stopped quite a while ago scribing deep lines on the work, as that's too difficult to get rid of later. Both the scribe and the height gauge tips need a bit of sharpening as well; that's why the lines appear so thick. I'll be using the vise stop to mirror the work as I go, so I only need good layout on one side anyway.

I then started drilling the 1.6mm holes for mounting the "cylinder" covers; these needs to be tapped M2 later. Simple process to get the mirroring; locate a hole on the marked-out side and drill, then flip the workpiece end-over end and drill the mirrored hole on the unmarked side. Here it is ready to be flipped to drill the last hole:

After drilling that last hole I stopped for the day. I'm torn between making both the covers from some 2mm brass plate I have, or making the one cover from perspex so that the vane can be seen in operation. The only suitable perspex I have is 3mm thick, and I'll have to check whether this will fit. In addition, the vane shaft uses the holes in the covers as part of its bearing, so if I make a perspex one, I'll have to think up a way to insert a bush in it, and that's not so easy, as the inside part must be very flat as it is part of the sealing surface...

Time to think a bit...

Regards, Arnold

 

[arnoldb]

Wow - what a hot start to the New Year; it's been consistently in the 38C plus range here for the last 2 weeks, so I didn't even bother to venture into the shop and rather spent some quality time indoors upgrading my computer and a lot of software on it. This morning I grabbed an hour shop before the heat got to me again.

I started drilling the port holes in the engine top:

Half-way through the first hole, the mill started making a funny noise; a quick check and the draw-bar had started unscrewing:

I don't know if the heat could have had an effect on it; I don't over-tighten the draw-bar and it could be possible that the heat allowed it to stretch just enough to come loose... That's something I'll have to remember to be on the lookout for.

All set up to cross-drill the long port holes. I used a small square as both a parallel and a way to keep the block square vertically. The wire is to feel when the hole breaks through into the other passages:

As I was peck-drilling these deep 1.6mm holes without any lubrication, so I kept a careful look-out for the drill tip clogging up like this:

Whenever that happened, I stopped the machine and cleaned the tip thoroughly. If one don't, that's a sure-fire way to break off a drill in a deep hole.

At that point, the shop got too hot again, and I moved inside. Out of pure idleness I made a short video on using the wiggle-wire:
[ame]http://www.youtube.com/watch?v=D_XQvD-rRts[/ame]

At least this afternoon some cloud cover came in, and there's the rumble of thunder in the distance. A good rainstorm would help to break the heat spell, so hopefully it might be cooler tomorrow so I can actually get something done.

Kind regards, Arnold

 

[Ken I]

Its hot here in Cape Town as well (33°C) so work in the shop has been unpleasnat - like you I just finished drilling some deep holes - a little nerve wracking.
Your edge finder looks just like mine - I gave it a clean and lube once and it lost its repeatability - cleaned it all out and it was fine - ungrateful edge finder.

Ken

 

[arnoldb]

Ken, I was once in Cape Town when it went up to 35... Camping in a caravan... High temperatures in CT is really unpleasant :wall:
:big: I'll have to keep an eye on this edge finder then; if it get ungrateful, I'll just clean out the oil.

;D It's been cooler here the last couple of days, and after a run-around to shops this morning I got some more done on the Kimble, though I fluttered around all over the show. Must be residual heat-stroke or something...

Instead of checking exactly where I ended off last week, I jumped in with a bit of perspex hacked off a salvaged old line-printer "window":

The perspex is 4mm thick, but that's not a problem as the one side of the engine where I want to put the clear engine cover can accommodate it. I'd decided to make an insert from 2mm thick brass plate to act as the bearing.

To protect the perspex, I just coated it with masking tape, leaving the section that I wanted to mill out for the insert open:

The mill was still set up to drill holes all over the engine's top, and fortunately I thought to check if I'd finished all the holes in the top last Saturday. Good thing I checked; I'd forgotten to drill the exhaust ports; in fact, I'd never even laid them out on the top. So that was done first. Then I had to drill the holes. There was no way to get in close enough to spot drill first, so I just had to take the plunge and drill with the 1.6mm drill and hope it wouldn't wander:

As I couldn't drill straight through for both ports in one go, I had to flip the workpiece and drill from the other side as well. I don't know if I was purely lucky, or if I'd spent enough time to set up accurately, but both holes intersected perfectly. Looking through it, it's impossible to see that it was drilled as two separate holes.

With all the holes ( :) in the top completed, I started on the brass insert for the perspex cover, purely because I'm lazy and it's easier to make it first and then mill away the perspex cover and use the insert to check the fit. Holding smallish bits of plate is always a bit of a problem, so I opted for the tooling plate to hold it down to mill to width:

The perspex cover followed to cut out the insert space:

While I was set up on the tooling plate, I also looked for a nice piece of flat 2mm brass plate for the other side-cover, and squared up two sides of that as well:

I nearly started tapping all the 2mm side-cover mounting holes on the block and top, but then remembered that it would be easier to spot all the holes in the side covers using the block and top. Then I saw some more holes I'd forgotten in the top; the 1.6mm mounting holes : - So I drilled those first:

Three down & one to go; just a flip away...

And done:

Cleaned the burrs off all the holes, and then glued the insert to the perspex plate. I wanted to use epoxy glue, but when I found the tubes, all the hardener had leaked out, so I used superglue. I hope it bonds with perspex. Stopped for the day with this bunch 'o bits; not much to show for quite a bit of work ::

Regards, Arnold

 

[arnoldb]

This afternoon I clamped the covers and block together. The perspex cover is sandwiched between the brass cover and the block, and the masking tape on it helps a lot to keep things from moving:

Off to the drill press to drill the 1.6mm holes. With a small drill like this, I'm comfortable, yet very careful, to keep the workpiece firmly pressed down on top of the vise jaws with my left hand and operate the quill with my right. Because of the different layers in the sandwich, I peck-drilled the holes to keep swarf in them to the minimum while drilling:

When needing to move the clamp to a different position without letting things come apart, I just clamp the lot in a spot where the old and new clamp position wouldn't interfere. Sometimes I do that with another toolmaker's clamp or in this case I used my small milling vise:

Here I wanted to flip the clamp from the left to the right to be able to drill the holes on the side where the clamp was before changing.

Next off to the mill to get rid of excess stock on the covers:

Silly me... I'd put the studs and nuts on the top on the wrong side. That made milling excess stock off the top more difficult, as I'd originally planned to just remove the nut and stud on the alternative top parts to finish to size. The nut was too big to rotate, so I had to go around its back:

Next I turned up 1.6mm pins from some 4.3mm aluminium rod I have. The toolbit is set up to leave a very slight taper on the aluminium, and the entire thickness is turned down in one go. I used the small ER11 collet chuck, as it has a 4.5mm collet that can easily clamp down to 4.3mm - thus saving strain on my 5mm ER 25 collet:

The four completed pins/plugs. As you can probably see, I just used a side-cutter to clip them off at just over the approximate length needed. The two longer pins are to plug the holes right at the top of the engine top; they need to be long enough that their inside ends will be machined flush with the valve bore later on:

Here I installed one of the side plugs - a tiny dab of loctite on it, and hammer it into the hole with a small ball-peen hammer. I knocked it good and flat, so that the plug will properly fill the hole, and once the excess is filed off, the plug will be completely invisible:

The two top pins knocked in and then filed flush; as you can see, they "disappear":

Same with the pin on the side; just lightly cleaned up here:

There are still tool marks on the sides of the block; these will be removed later in the build.

At this point I called it a day, as a big thunderstorm with high winds broke. I'd left a lot of doors and windows open in the house, so I had to go and attend to a bit of mop-duty ;D:

Regards, Arnold

 

[arnoldb]

A bit of a boring update today...

The cover plates were still sticking together after last weekend's work - this was a result of using some old gummy masking tape to protect the perspex cover, so I lightly clamped them together just to make sure they didn't come apart, then opened the holes to 2mm for clearance for M2 screws, and then countersunk all the holes - easy to do by getting one hole to the correct depth and setting the drill press depth stop:

I had a bit of chatter in the holes; after a careful check,I found that these holes are actually a bit small for the countersink I have and it can barely open them up, so I'll have to buy a smaller countersink at some point.

Next up, tapping the M2 holes in the engine block. My M2 taps are too short to tap the holes right through, so I had to tap the holes from both sides. I used my tapping guide to limit the depth to tap too to half of the engine block depth (Apologies for the out-of-focus photo):

Then I set about tapping all the holes. For aluminium I use methylated spirits (rubbing alcohol) as tapping fluid, so I poured some into a spray-can top to make life easier. The meths easily washes off any chips stuck to the tap, so it's easy; tap the hole; swash the tap in the meths and it gets both cleaned off and "lubricated" for the next hole:

The dark bits in the meths are chips that were washed from the tap.

Next a quick check, and as I thought, the shortest M2 screws I have are too long for the thin cover:

They are OK for the perspex cover though.

I've had to shorten M2 screws in the past, and it's a bit of a pain in the rear :. Usually it was just one or two screws at a time so I'd fiddle along, but I was in no mood to fiddle ten of them... So I diverted and built a little tool.
I just chucked up some 8mm hex brass, drilled it 5mm diameter (for M6 threading) 15mm deep, and followed the 5mm drill with a 2mm one another 4mm deeper. Then I tapped it M6, and parted the piece off 17mm long. On to the mill, and with a 2mm slot mill, I milled a slot to the center of the 2mm hole, and a perpendicular slot wide enough to allow a 2mm screw's head to pass through far enough from the end to leave the cone section left by the 5mm drill intact.

To my horror I discovered I'm out of 6mm silver steel to make the rest of the tool , so I used a cap screw with the head sawn off and the end section of the thread relieved to clear the last bits of thread in the brass bit:

I wouldn't recommend using the above tool under power on the lathe, as the screw will easily deflect into the slot while machining. I just used it chucked up in the lathe (with motor off) to saw off the excess length of the screws with a junior hacksaw with a fine blade:

It is convenient to have the tool in the lathe, as it's easy to clean up the cut face with a small file, and also file a slight taper around the cut face by rotating the chuck by hand. These screws are stainless steel, and just outside the size for my favourite electronics cutter, if they were within it's size I would just have clipped off the ends with it and cleaned off with the file.
Ideally, I should have "relieved" the seat for the screw in the brass bit to 90 degrees rather than using the 118 degree cone left by the drill bit - but that would have meant making up a d-bit reamer and I wasn't in the mood for faffing around with that today.

The little tool works quite well. Slip a screw in, tighten up the brass section on the arbor, saw off the little screw, file the nose flat to remove the burr from sawing, file a slight taper around the end of the treads then loosen the brass nut with a hand under it to catch the screw as it falls out... It took me less than a minute per screw to get this lot shortened:

All the little screws in place - I need to make all the countersink holes about 0.1mm deeper though ::

And the perspex cover screwed on:

To compensate for the thickness of the masking tape that was on there, I countersunk the holes slightly deeper. Unfortunately, I over-compensated : - these are slightly too deep.

Hopefully, I'll have more interesting progress to report tomorrow.

Regards, Arnold

 

[bearcar1]

Looking good as always Arnold Thm: You have provided me with something new to try next time I am tapping Ali, rubbing alcohol. (who knew) I've used WD-40 in the past but will definitely have a go using your spirit of choice. You have the hot temps to deal with while I just came in from ridding ours and the neighbors drive way of the 5-6" of snow that dumped itself on us yesterday and last night. Have I ever mentioned how much I hate shoveling snow? %&^$%# the stuff anyway.

seasons greetings .... bah humbug ;D

cheers

BC1
Jim

 

[arnoldb]

Thanks Jim
:big: The alcohol's not my spirit of choice, but it works on the ali. I wouldn't waste my spirit of choice on tapping - after all, it has to be imported from Scotland at great expense. Fortunately it arrives without bagpipe music, haggis and snow

We had a beautiful day here in Windhoek today; cool with light rain. Great for shop time... Unfortunately, my tummy decided it wasn't taking any part in a great day, so it was a bah-humbug for me too :

Kind regards, Arnold

 

[Blogwitch]

Arnold,

Your little device that you made for shortening your screws is in fact called a LANTERN CHUCK.

If you have more than a dozen screws to shorten or modify, it pays you to make one as you did. But you made the mistake of cutting away the side so that you could put the screw in. Normally, you just have a hole in the end and the screw is fed in from underneath the hole.

I'm sure that if you put a search in and look for images, you would get a few pictures of what I am on about.

Looking good.


John

 

[arnoldb]

Thanks John - I knew I'd seen something similar somewhere, but could not remember it's name or precise design. Now I won't forget; the next one I make will be a proper lantern chuck, as it's obvious that one can be used under power.

Kind regards, Arnold

 

[arnoldb]

Finally, a bit more done. I'm taking things a bit slow on the engine block, as I don't want to make a mistake.

Last weekend I ended off with the countersink screws on the brass cover side still sticking out a bit. For some of the machining operations to follow, I needed them flush - or just a tiny bit below the surface, but I also didn't want them countersunk too deep, as I think that looks plain ugly.

So after a careful measurement, I determined that they are sticking out just about the thickness of a business card. So I used the plate just lying on top of the drill press vise jaws to set the drill press depth stop with the countersink bit engaged in one of the holes, then shoved a business card below the plate and touched up each hole:

Screwed up, all the screws are far enough below the surface; I could even rub the block over some emery to clean up the face a bit:

It would look even better if all the screws were "timed" so that their slots lie the same way... That's a project for one day when I try and do an "advanced" build :big:

On to one of the most important holes for the project; the main pivot hole. This has to be very square to the engine body, otherwise the engine will be near-certain to bind as the vane will twist around in the block... When I built my tooling plate, I marked it so that it go back in the mill vise in the same orientation that I faced its top, So I used that - did a quick check with a DTI to make sure that it was still level and square, and clamped the engine block to it, leaving it over-hanging just enough to clear a 6mm reamer passing through:

Then I drilled the hole through with a 3mm drill. This was followed by a 5mm end mill. The reason for the end mill is that it will true up the hole in case the 3mm drill had wandered a bit. This was then followed by a 5.9mm drill; my theory being that it would follow the hole left by the 5mm end mill and not wander off course. Finally I ran the 6mm reamer through the hole to get it to size and smooth:

Next the perspex cover was removed, and I set up the piece in the mill vise so that I could drill and ream for the rotary valve. It was left raised enough out of the vise so that the cover plate could be removed without disturbing the set-up - then I drilled 2.9mm and reamed 3mm through the lot for the valve shaft:

The cover was removed, and I drilled the 3mm hole out to 9.8mm:

Next it was reamed to 10mm. The plans call for a 3/8" hole for the valve, and I could have done that by boring the hole, but I had a careful look at the valve plans, and its easy to adapt it to 10mm:

The plans call for the "plugs" in the holes that were inserted from the top of the head to go in deep enough into the valve hole to be machined flush when reaming/boring the valve hole... ;D I must have done something right, as they did "disappear".

I left off there for today. Another important bit of machining is next, and I'd like to do that in one full shop session.
Back of block:

Front:

Overall progress... I never coated the base with some oil, and it picked up a bit of surface rust from the damp weather we've been having. Fortunately, nothing major, as it still needs some surface finishing and paint:

Regards, Arnold

 

[Ken I]

Damp weather ? - it thought it only rained steam in your neck of the woods.

Ken

 

[Foozer]

Very nice so far, countersinking can be fun. gizmo to get em nuts on

http://www.panamericantool.com/countersinks/micro-stop-countersinks-cage-needle-bearing.html

I'm gonna gain 20# with the chips and Twinkies watching this build

Robert

 

[bearcar1]

What terrific therapy it is to watch as you work Arnold. (cheaper than a trip to the dentist as well ;D) It's going to turn out to be another fine piece of art, I just know it. Thm:

BC1
Jim

 

[arnoldb]

:big:, Ken, that's the problem... It doesn't make puddles and run off; it just permeates the air and hangs around rusting things...

Thanks Robert - I like those doo-dads you linked to, but at that price, I might just make my own at some point! Hmm... Chips & Twinkies... Is the weather still keeping you from your shop; I thought you had a rotating cylinder engine going stickpoke ;D

:big: Thanks Jim. Don't mention that Den... word; I'm not scared of many things in life, but of them Most Definitely :

;D Today was one of those golden days in the shop that makes me love model engineering so much. Just the right amounts of challenges, head-scratching, problem solving, lots of chips, and that whole kaboodle coming together in a nice end result. Not really much to show as the end result, but the journey was the fun part.

For the next step in the machining process, I needed a sacrificial plate. A bit of flat wood would have done as well, but I wanted slightly more accuracy than the wood would have given. A while ago, the storage term for a whole lot of these ran out at work:

Anybody remember those? As I'm responsible for IT Security at work, I signed them off for responsible destruction - told the bosses what would happen to them, and brought them home. Taken apart, it's easy to snip the tape into thousands of pieces, and I get nice bits of tempered aluminium plate and a lot of precision pins out of them to use in projects. Bosses are happy, and so am I.

I was spoilt for choice on how to do the next part... Work on the lathe face plate, or boring head on the mill... As there was quite a bit of milling to come, I decided on the face plate, as it's fun to change between machines for different jobs.
With a suitable bit of plate sawn from the old tape, I started setting up things on the face plate. I find it easier to start setup on a table, and then mount the face plate to the lathe later:

For the next step, the lot had to be mounted on the lathe, with the workpiece centered on the reamed hole. Normally that would be done by sticking a pin in the hole and using a dial indicator or DTI to clock it up, but I know a pin chucked up in my lathe's tailstock is spot-on, so thats the method I used. Face plate mounted on the lathe and the pin in the chuck:

Not a bad job of eyeballing on the table before-hand ;D

With the workpiece loosened slightly, it was easy to lightly tap it into position to fit the pin:

Then I added one more clamp - just to be safe, and to allow me to remove either of the side clamps so that I could get at the screws holding the engine body to the top:

: I'd forgotten to lay out the cut dimension for the top... Not so easy with a hole where the center should be either... The small lathe is not mounted properly yet, but this is a very light job, so I fired it up and faced and lightly center drilled a bit of 6mm rod:

That was then sawn off and inserted in the hole in the block:

Next, I set my compass to 31.75mm. Well, the photo shows that it was slightly less than that, but the camera's macro mode is much better than my eyeballs. The reason the reading on the rule is 41.75mm is that the other end of the compass is sitting in the 10mm groove of the rule:

Target cut-line scribed:

Then I added some counterweights to the face plate; No fancy math was used; just the fact that I have a fairly good feeling for how heavy the bunch of clamps and retaining nuts are - the gears were selected to approximate that. And a final check from the top as to whether there would be any clearance issues:

And a view from the side - with the cutting bit set as deep as it would go:

Then I started putting some cuts on... The cutting bit was honed super-sharp, but on the second cut I heard the dreaded sound... A high-pitched squeal each time the cutter cut... Chatter... Stopped, and yes there it was (you can click on the image for a larger picture):


The finish in this cut must be smooth as silk; there would be no easy way to lap it accurately once done... So I tried a stiffer toolbit; same thing - slightly finer chatter, but still there.
As the chatter was very fine, it would not take much to damp; I tried pressing on the back of the toolbit during the cut with a toothbrush handle, and the chatter went away ;D:

After the final cut with the toothbrush in position (once again, clickable for a larger photo):

;D That's the finish I was after ;D

Some more lay-out followed:

Then a quick bit of hogging in the mill:

I just used some threaded rod screwed into the mounting holes to set the piece to mill out the angled sections:

A little while later:

Then with both covers mounted on, a bit more lay-out:

More milling - a bit more careful this time so as not to break out chunks of the perspex - and lots of brass, aluminium and perspex chips all over the show:

Finally I ended up with this:

I left the outer edges of the block slightly thicker than the plans show - they are purely cosmetic, and the extra thickness is to help prevent the perspex from cracking.

Overall progress:

;D Looks more like it. There's still some work left on the block - a hole to drill and tap in the top for air supply, and a bit of clearance milling on the bottom for the vane - then a final flat-lap and cosmetic work, but the hardest part is over.

Regards, Arnold

 

[Foozer]

Thanks Robert - I like those doo-dads you linked to, but at that price, I might just make my own at some point! Hmm... Chips & Twinkies... Is the weather still keeping you from your shop; I thought you had a rotating cylinder engine going stickpoke ;D

Regards, Arnold

Took a left turn from the rotating cylinder, had this Airpot sitting around, and well,

Robert

 

[Ken I]

Arnold, I always get something out of your posts... a toothbrush handle as a harmonic damper - who'da thought :bow:

Ken

 

[arnoldb]

Thanks Ken - that was just one of those "Oh well, let's try this out of desperation" moments.

: My work life has been keeping me pretty busy of late, so shop time is hard to come by.

This afternoon I drilled a 2.5mm hole through the center of the engine top:

That was tapped M3 for the air inlet.

I next milled out the excess metal that was still left on the bottom of the engine:

The bottom mounting holes were not tapped yet, so I also tapped those M3, and gave the block a final flat-lap on both sides. That pretty much completes the engine block part of the build.

Next I started on the vane; I milled a section of 4.8mmx12 brass flat bar down width of 9.65mm - that's the same thickness as the engine block. I didn't quite get it, and ended up at 9.7mm. I wanted the vane 0.01mm thinner than the engine block, so I sat down and flat-lapped it down to 9.64mm on some 600 grit paper, frequently checking with a micrometer that I was keeping it parallel and not lapping one end down more than the other. Quite a bit of manual work, but it turned out well in the end:

Next I faced the one end square, cut it of just over length (the bit of flat bar was more than twice too long), and then squared up the other end as well. The vane top needs a slot where a seal with a small spring will be installed, so I started cutting that with a 2mm cutter. after about the 7th pass, a bit of a disaster; just a second of inattention and I increased the rate of feed just too much:

Oh well, that poor end mill has been doing duty for more than six months now, in everything from plastic to a bit in stainless; it was getting a bit blunt. So I fetched a new one from my stock and finished the job. There's only one left now, so it's time I fired off an order to RichOn - I need some other cutters as well...

Back when I started this project, I mentioned the fact that Elmer's plans has a measurement error with the mortise and tenon joint. I was still undecided whether I was going to use this method for joining the vane to the main shaft.
This joint is most likely the weakest link in the engine, and would see quite a bit of torque transferred through it, so just soft-soldering the vane to the shaft without some form of additional strengthening would very likely lead to failure.
Many moons ago, John Bogs suggested that silver soldering the joint would be his way to do it - I agree, but then there's one teeny little problem for me; this joint has to be done ultra-neat as any excess would be very difficult to clean up, and that's something I'm still having problems with when silver soldering.
So it was either the mortise and tenon for me, or I had to find another solution. I did the latter, and decided that three pieces of 1.5mm piano wire running between the shaft and vane would be just as strong - if not stronger than - a mortise and tenon made from brass. The main loading on the joint is radially, and the wire would cope well with that - while loctite would be more than adequate to keep things from coming apart.

I drilled three 1.5mm holes spaced 2.5mm apart in the bottom of the vane:

Next I cut a section of 6mm silver steel to length ( I restocked earlier this week) and cleaned it up on the lathe. Then I drilled matching 1.5mm holes in it - offset to compensate for the one thicker cylinder cover so that the ends sticking out from the engine would be equal:

I used the Dremel with a cut-off wheel to slice off three sections of 1.5mm music wire, and pressed those into the vane with some loctite, and with more dabs of loctite, pressed the lot into the shaft. The middle hole on the shaft had wandered a tiny bit, but this actually helped things; I had to use the mill vise to press it together the last bit - and the vise aided in getting everything nice and square. It won't come apart easily, but if needed, I can get it apart again with some heat. Some of the excess loctite running between the two pieces also help to make the seal air tight:

and

A quick assembly, and things are looking good; some oil smeared on the vane gets distributed evenly everywhere on both the rear and front covers, and there's no binding ;D:

Regards, Arnold

 

[lazylathe]

Another great build thread with lots of pictures and problem solving!!!
Excellent as usual Arnold!!

Looks like another winner on the go here!!! ;D

Andrew

 

[arnoldb]

Thanks Andrew - I'm having quite a bit of fun building this one; I just hope it runs when I'm done :big:

Got to the rotary valve today. The plans for the valve itself is a separate chapter in Elmer's book.
I went about making it quite differently from the way Elmer describes - in fact, I did not do a single bit of marking out...

As I'd made slight dimensional changes to the engine block in the valve area to suit my available reamers, I had to re-calculate some of the dimensions of the valve. Most importantly, it's slightly bigger at a close 10mm fit compared to the 3/8" (9.53mm) the plans call for. This meant that some of the porting cut-outs had to be slightly deeper than those shown on the plans - all by 0.235mm ~ 0.24mm. The 1/8" shaft section was re-sized to a running fit for 3mm.

First I turned down a bit of 1/2" brass rod. A 8mm long section 2.98 mm thick to match the 3mm reamed hole in the the back engine cover and the next section 9.99mm thick for a close fit in the reamed 10mm hole the engine top:

I got a nice smooth finish just turning to size, so no lapping needed here.

Off to the mill with the dividing head mounted in the vise, and the edge finder and hand-wheel zero-rings used to locate things - from this point, all operations were done according to mill dial readings:

The valve needs a 1.6mm hole drilled accurately through it's center, but on one side, the hole is connected to a 2.4mm slot. Rather than have the drill bit wandering on a curved surface, I first milled the slot, and then drilled the hole - much easier this way:

Another small change to Elmer's design follows - this time to correct a booboo that crept in when I drilled the port holes in the engine top; the drill wandered a bit on both holes, and they are pretty far off axially compared to the valve center line. The original valve design uses just the 1.6mm through-hole to supply air to the ports in the engine top - meaning everything have to align pretty darn accurately, and I don't have that... So to compensate, I milled a short slot 1.6mm deep axially on the other side of the workpiece (rotated 180o since the last operation):

After milling the slot in the photo above with a 1.5mm cutter, I followed it with a 2mm cutter - which might be a mistake... I'll see if this is OK later.

The exhaust cut-outs followed - taking care to cut them both from the correct side; one had to be done feeding in on Y, and the other feeding out on Y:

Back to the lathe, and parting off - an action photo for a change:

The finished valve:

Well... not quite. Seeing as I have this one transparent engine cover, and one of the most difficult things to explain to people when they're looking at my little engines is always how and where the air or steam goes inside the invisible bits of the engine, I decided to add a cross-section of the valve cut-outs on the "visible" face of the valve. I just free-hand milled this lot with a 1.5mm cutter 0.1mm deep:

The 1.6mm drill bit sticking through there is what I used to estimate level and orientation when I clamped up the workpiece :big:

With the milled out bits on the valve face coloured in with a permanent pen, it'll look like this in the engine top:

Regards, Arnold