Two-cylinder, double-acting wobbler

[ths]

Great going , Simon. I'm glad to hear of the router bit success as well.

Cheers, Hugh.

[b.lindsey]

You are making some good progress on this one Simon. The base looks great and that router bit sure did a nice job!!

Bill

[zeeprogrammer]

Nice Simon.
It was good to hear about the router bits too.
Seems like several people were interested in that.

[Don1966]

Nice Simon, I love the way the base turned out with the router bit also. Project is looking good bud.

Don

[smfr]

Made some good progress today, with only a minor hiccup. I cleaned up the top of the standard around the glued-on pieces, and gave them a nice radius on the lower face with the ball-end mill (and the glue held for this part...)



Then the hole for the bearings was drilled and reamed:



Ack, I knew that glue wasn't going to hold!   



Actually what happened is that I didn't go all the way through with the drill just before reaming, so the reamer pushed off the cap. No biggie, I'll just glue it back on when fitting the bearings.

Next was cutting the big slot for the flywheel. First I drilled a cross-hole near the bottom of the slot, so that two saw cuts would free the middle piece:



then took my biggest saw, a 4"er, to it:



The max depth I could go was just a hair under what I need, so I might have to clean out the bottom of the slot later.

Now it was time for some lathe work. I started with the bearings, turned from bronze, then made the shaft and crank pins from 303 stainless. I left final reaming of the bearings for when they are fitted to the standard. The big hunk of rod in the photo is prepped for the crank disks, which I'll do on the rotary table later.



While set up for lathe work, I also started on the flywheel. One side was cleaned up, then I flipped it around in the 3-jaw and trepanned the other side:



That's all I had time for today. I think I'll have to fit the soft jaws to the chuck to finish off the flywheel.

Tomorrow the brown van arrives to deliver various bits of brass rod which I'll be using for the cylinders. I haven't quite decided on how put the cylinders together, but I suspect it will involve some soldering 

Simon

[Johnmcc69]

Thats coming along nicely Simon, nice design.
Can't wait to see it run.

John

[smfr]

Here's the flywheel flipped over, after fitting the soft jaws to the chuck, and machining a small shoulder to fit the diameter of the flywheel:



This way I was able to finish the second side with the trepanning tool, and drill and ream the center. All that's left is to do a finish cut on the outer surface, which I'll do once I've drilled and tapped for a grub screw.

Now onto the cylinders.

They started as some 1" brass bar. It needs a bit of profiling, to make flanges to hold the screws that attach the cylinder covers, so after taking it down to flange diameter, we mark the part to turn down further:



A bit further along; here the outside profile is done, I've started the parting cut to mark the final length (more on that later!), and am hogging out the bore, which will be 5/8".



About that length; somehow I managed to make this cylinder about 0.05" too short (I think I forgot to add the parting tool width), but am kicking myself for not double-checking the length. Brass ain't cheap! So it seems that I have a practice cylinder, which isn't a bad idea given than I'm not really sure how the next steps are going to turn out.

My plan is to mill out a slot and solder in a rectangle of brass. I was careful to choose the dimensions of the slot so that it does not intersect the final bore, since I don't want to be boring over a solder join. The rectangular part ended up about 3/8" think by 0.6" wide. Here I've saw-cut three from some 3/4" square bar, one for my test cylinder and two for the real things:



Now the slot is cut:



and the fit checked:



I put 4 light center-punch marks on one of the parts to leave a gap for solder, and then set it up with flux and silver solder:



I just have a length of solder on each end, on the little shelf left by the over-long rectangular part. This seemed to work quite well; I really only care about solder penetration near the ends, to seal the ports.

Soldering went well; I was careful to put most of the heat on the larger part, so the whole thing came up to temperature. It also helped that I'd drilled out the center, to reduce the thermal mass, and allow the flame to be played through the bore.

I decided to do the boring in the 3-jaw, since I can hold the part nicely (with some drinks shim can to protect the part from the jaws). First we take a skim off the ends:



Note to self: leave the real cylinders oversize so there's material to trim away here!

Now the boring which was done with an insert boring bar; it worked well with no chatter:



The bores will just need a bit of a hone, so I left them about a thou undersize.

A small chamfer on the bore, and we're done:



Note how the solder seam is invisible

I'm quite pleased with how this went, and will proceed with the actual two cylinders next.

Simon

[Don1966]

Hi Simon, I can relate to your cylinder mishap, I had the same thing happen on my Epicyclic Steam engine some very expensive mishaps. Glad to see you have made some progress and she is looking good. Do you foresee any problems in your design yet, are you just correcting as you go?

Don

[smfr]

Thanks Don. I haven't found any problems in the design, yet, but I suspect that they will show up once I hook up the piston rods to the crank, and try to turn it over.

One thing I'm a little worried about is that my piston volume is pretty high (5/8" bore, 3/4" stroke) given the size of the ports (0.113" diameter). That might limit the speed.

Simon

[Bearcar1]

Nicely done Simon    The cylinder turned out very well and I like your methodology in its making.


BC1
Jim

[steamer]

Looks great from here Simon!   I wouldn't worry much about the port size...it'll breath all right.    They're nice when they run slow and you can see them anyway...

Nice job on the cylinders!.......and I like roughing mills too!

Dave

[smfr]

Weekend means shop time! Except for the two yard sales and famers' market that I had to hit up first... I did score some nice small files, hand tools and a couple of hunks of mystery metal though. 

Managed to finish the machining of the two cylinders today. Here they are pre-milling, and a bit longer than the stubby one on the left:



My soldering approach was exactly the same as before, and it seemed to work fine. As before, I chucked them up in the 3-jaw to finish the ends, then bore:



Note how I've written how much to take off (1314 thou) on the end; I've started to do this, and it means fewer mistakes. The only other handy tip here with boring is to mark the face that was outermost when doing boring; this face is true to the bore, so should be the top of the cylinder.

All done:


Something that was a bit odd was how one face seems to have been distorted after soldering:



I rubbed the face on a file to remove burs a few times, and note how the file only touched the ends of the right-hand cylinder. No biggie, I'll be turning those faces flat later.

Next (actually, earlier!) I made an expanding mandrel to hone the cylinder bores, and also to hold them for later machining operations. I turned a taper on the end of an M8 socket cap screw, which itself required a fixture to hold the bolt in the collet:



and set up for the taper cut:



Note how I'm turning backwards; the thread would unscrew the other way around. The taper was done with the top slide set at an angle, and I kept it at the same angle for the later mandrel boring step. (Luckily, cutting on the back side here made the angle work for both operations.)

Here's the mandrel:



The bore was drilled down with a small drill matching the small end of the taper. Then it was drilled part-way at M8 tapping size (17/64") for threading, then countersunk for the socket cap. Then, using a small boring bar, I cut a taper to match that of the screw, starting from the bottom of the tap-size section; the taper was roughly in the center of the turned section. This was mostly done by feel, as it was impossible to see down the bore. Finally, the thread was tapped. The last step was cutting some slits:



Now I could use this mandrel with some Timesaver lapping compound to hone the cylinder bores, using the socket cap to control the tightness. The bores ended up almost exactly the same diameter.



Post honing:



With Timesaver, you're supposed to use a lap that's harder than the material being honed, as it doesn't embed, but this Al lap seemed to work well enough.

Tomorrow it's time for cylinder caps and the piston glands!

Simon

[Kim]

Neat work Simon!  Nice soldering job.
I'm going to have to figure out how to lap a cylinder like you did here.  Your expanding mandrel is pretty neat!
Kim

[smfr]

I've got a few more bits and pieces done on this engine over the past few weekends, but it's hard to find shop time in the spring when the garden sprouts weeds!

Anyway, here is a bottom cylinder cover being parted off:



and a top cylinder cover being reamed. I reamed in the same setup as machining the cylinder side of the cover to ensure that the ream is perpendicular to the faces that mate with the cylinder:



I then finished the parting off with a hacksaw to avoid accidents, and flipped it around to hold it in an ER25 collet (so useful!):



With this setup, I could finish the outer diameter of the boss, and drill and thread for the piston rod gland.

Here's one of the glands being machined from hex rod:



I had to go back and forth a few times on these parts, because the cylinder cover + gland ended up too long, and would interfere with the crank throws. You can see one shortened set on the left here:



I won't be able to do a final check until I have the crank throws done, and be able to fit the cylinders to the body, so these parts may still need a bit of work.

Most of the cylinder parts done:



You can see I made a few tries at the piston glands, and that I still have some flux to get rid of on the cylinders. I think I need a stronger pickle than the oxalic acid bath that I've been using.

Now onto the crank throws. A bit of 1" bar of what I think is 1018 steel was cleaned up on the outside, and had a 3/16" hold drilled and reamed. It was then marked up for the throws, and held vertically in a vice. Note the clamp on the V-block; you'll see why I had that later.



I then went at it using a 2-flute endmill (aka slot drill), at fairly low speed with 1/4" depth of cut:



and I did a final pass with a 1/8" endmill. Finally, I located the center hole, offset by the crank throw (3/8"), and drilled and reamed for the 1/8" crank pin. Here we are after that:



So, about that clamping setup. The side forces when milling here are considerable, and on my first try, I just had the part held in a vice against a V-block, in the smooth vise jaws. The end result was this:



The endmill caught on the part, and pulled the part and V-block sideways in the vise    Hence the extra clamping on the second try, which went without incident.

OK, now to part off two throws from this rod. If I had a bandsaw, I might have used it here, but don't trust my hacksawing abilities to get a staight cut through 1" of rod. So I went with an HSS parting tool, since it would do better with the interrupted cut than carbide. That works pretty well:



but I did finish the cut with a hacksaw, since bad things could happen when breaking through with a non-cylindrical part jamming against the tool. After parting off the first, the revealed face was cleaned up before parting off the second throw.

The throws were then held in the 3-jaw for a bit of cleanup on the parting face, using some parallels to get them square to the chuck and protecting the finished surfaces with some Coke-can shims. In this way, the nub from parting could be faced off and a final cleanup pass taken:



After a bit of elbow grease on a few grades of wet&dry paper with some oil, and some filing of the machined edges, we have two throws:



Simon

[chuck foster]

looking good simon 

i like watching your projects unfold and the neat and interesting set ups you do to hold some rather irregular shaped  parts.
your fit and finish and attention to detail is very admirable.

keep up the good work and looking forward to your next installment.

chuck