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Cross-Twin Engine

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Cobra

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#1
Starting a new engine model.
Plans drawn up over the winter in Mexico.
Two cylinders, Four pistons, no cylinder heads.
Starting on metal.

Cross Twin 1.jpg
 

JimDawson

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#2
Looking forward to seeing your build :encourage:
 

Cobra

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#3
Base of the engine from 3/4" X 14" X 4" aluminium.
Cross Twin 2.jpg

IMG_0001.JPG

About as long as my small mill can handle.
 

Cobra

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#4
Cross Twin 3.jpg

Not much time yesterday for playing in the shop.
Only got the foot for the cylinder done.

IMG_0002.JPG

Want to get started on the cylinder block today.
 

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Cobra

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#5
Started on the cylinder block. I didn't have any 1-1/2" X 4" flat bar so decided to make it out of two pieces of 3/4" X 4" rather than order from the States.
I have just used the aluminium in the past for the cylinder but this time with the split block I decided to make cast iron liners for the cylinders. The initial plan was to have threaded caps on the ends of the cylinders to clamp them into the cylinder block as in the PDF Cross Twin 3a.
Good thing the planning was being done by the Mexican pool with a beer because the second version would just use brass plates on each end of the block to hold the liners in place. Much easier than threading!

CT03.JPG CT04.JPG

Started by milling to two halves of the cylinder block in preparation for bolting them together.


CT07.JPG

Block halves now bolted together and ready to start the boring of the cylinders.


CT08.JPG

Cylinder block ready for the cast iron liners and then the retaining plates.
 

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Cobra

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#6
Cast iron sleeve liners cut from 1-1/2" bar. First time I have tried using liners in the cylinders. Got the cast bar from McMaster-Carr.
Nice stuff to machine but man was it dirty! That stuff gets everywhere!

CT10.JPG CT11.JPG CT12.JPG CT13.JPG CT14.JPG CT15.JPG CT16.JPG

I have hones on order to finish the inner surface of the sleeves.
 

Cobra

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#7
Well the hones arrived this morning. I have to say that, for Canada, I am getting to like KBC almost as much as McMaster-Carr. They have a great selection of products and two day delivery to the door for a lot less than McMaster.
The two hones and some lathe tools arrived for $8 instead of the $40-50 from McMaster.
I ordered two hones, one at 120 grit and one at 240.

CT39.JPG CT40.JPG CT41.JPG

The cylinders are 1.100" and the 1-1/8" hones worked fine.

CT42.JPG CT43.JPG CT44.JPG

That's it for the cylinder block for now. Next will be the bearing blocks for the crankshaft.
Should be straight forward and a little rotary table work at the end to finish the top of the blocks.
 

Cobra

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#8
Completed the bearing blocks for the crank. The crank will be 3/8 so I used a pair of 3/8 X 9?16 X 1/2 needle bearings.

Squaring up the 1/2" stock for the two blocks.

CT18.JPG CT19.JPG CT20.JPG

Drilled and reamed to 9/16 for the bearings.

CT21.JPG CT23.JPG

Needed to use the rotary table for the tops of the two blocks.
At one point in the past I made a taper fitting for the centre of the RT that will accept a 3/8 pin.

CT24.JPG CT25.JPG

The centre pin makes set up of the bearing straight forward. I now have a set of pins that step up or down from the 3/8 in the taper plug.

CT29.JPG

Used the side of the block to set up square at the 0 degree point.

CT30.JPG

I had to get an extended length mill from KBC to reach all the way through the 1/2" material. Decided on double ended and ordered two to cover my uncertainty milling with a 1/8 cutter 1/2" deep.
Turned out that I didn't need the three extra cutting surfaces - the first one lasted and I didn't break it!

CT31.JPG CT32.JPG

Plunge cut in and around the 90 degree arc and out the other side and then did a cleanup climb milling pass to take off the last 5 thou.

CT34.JPG CT35.JPG

Blocks finished and fit to the base.

Cross head guides next.
 

T Bredehoft

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#9
Your mention of Crossheads puts me in an uncomfortable state, not you but my memory. I had a 9" diameter, #156 cast iron crosshead in a lathe, to turn the OD. got done, put the sling on the jib boom around the cross head, took out the center bolt, and the crosshead fell between the ways into the chip pan, taking my right hand with it. Mashed hell out of the first two fingers, end joint only. I spent a month on light duty, taking inventory. This had to be 30 years ago and it still makes my knees weak.
 

Cobra

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#10
Oh crap. Makes me cringe just thinking about it.
 

Cobra

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#11
Started the Cross Head guides the other day by starting on the spacers required under and between the guides.
Soon ran into problems keeping all of the spacers the same length using my long spindle stop.
Took a deviation from the Cross Head to make up a 5C Collet stop shown in one of the other posts.
Much better results with the stop in the collet.

CT46.JPG

With the eight spacers completed, I could move on to the actual guides.

Started with 0.25" Aluminium flat brought to dimension and then just skimmed to flatten the faces. Unfortunately that then meant go back and do the spacers again as the guides were now no longer 0.25" thick.
Made new spacers to accommodate the very slightly thinner plate.

CT45.JPG
CT47.JPG CT48.JPG

Started with the centre cutout. Every time I do this kind of cutout in the middle of a piece, I thank Tom Griffin for the hints on plunge milling instead of using the side of the cutter to do the bulk of the metal removal.

CT49.JPG CT50.JPG CT51.JPG

Cut the 1/2" wide tracks with a 7/16" mill. Ran down the centre line first and the stepped over to each side and climb milled the finished edge and the last 3 thou of the depth.
Slots came out nice.
Drilled the four corner holes to finish each guide.

IMG_0002.JPG IMG_0003.JPG IMG_0004.JPG

Start on the crankshaft next.
 
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Cobra

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#12
Started on the crankshaft.
You can tell that hobbyists (at least me) have a low value of time! I needed a piece of 5/8" flat to make the web of the crank shaft.
All I had was a piece of 1" flat, 6" wide. So cut it roughly with the 4X6 and then start milling!
CT53.JPG CT54.JPG CT55.JPG

Eventually got it to size. NEXT TIME GO BUY A NEW PIECE OF MATERIAL!!!

CT57.JPG

Done and ready to start drilling the three shaft holes.
Decided the best way to ensure alignment of the three pieces of the web was to drill in one piece and then cut it apart for the three pieces.

CT58.JPG CT59.JPG

Drilling and reaming for the 3/8" shafts.

CT60.JPG

Nice slip fit on the 3/8 drill rod used for the shafts.
Didn't try to do a shrink fit as they will be Loctite glued and pinned with spring pins at each joint.

CT61.JPG

Cut the first side piece off the main block. Notice that to preserve registration among the holes, they were marked to maintain the same orientations.
As a result of the saw cut, I now have one machined face on the TL side and a saw cut face. Before cutting the second side off, the saw cut face on the main block had to be machined to allow me to keep the square orientation of the holes in the main block. After milling the cut face it was returned to the saw to remove the other side piece.

CT63.JPG

Re-milling the centre block to keep the face square to the holes.

CT64.JPG

Cutting the second end piece off the main block. Had to set up blocking to clamp the short piece in the saw!

CT65.JPG

Milled both end pieces to keep the same thickness. (and save some time!)

CT66.JPG

Three blocks completed and ready for trial fitting. Note that I did manage to hold the orientation the same. (Major win!)

CT67.JPG

Trial fit with the three shafts.
The centre block will now have to be cut down to the angled connector.

IMG_0005.JPG

Angle cuts laid out on the centre block. The block was set in the vise using a 1/8 parallel laying flat on the jaw to align with the scribed line.
The second cut is done with the initial cut face on a parallel.

IMG_0006.JPG IMG_0007.JPG

Ready to start the assembly. All parts will be washed in acetone and then the two small shafts will be glued to the end webs using Red Loctite. They were left over night to harden before using the adhesive on the centre web.

IMG_0008.JPG

Crankshaft all glued together. It will sit overnight before trying the drilling and reaming for spring pins at each of the seven joints.
 

Cobra

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#13
Getting back to posting some photos.

CT77.JPG

Drilling and reaming each joint for 3/32" spring pins. Amazed at how much personal stress is removed by moving to a spotting drill instead of the centre drills!


CT78.JPG

Pressing in the spring pins. need to make a smaller nose for the press so I can actually see that the pin is going in straight.


CT79.JPG

Back into the mill to remove the unneeded ends of the two outer arms.


CT80.JPG

Crankshaft completed.


CT81.JPG

Installed to the bearing blocks with Teflon spacers to centre the shaft.
 

T Bredehoft

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#14
Those pinned shafts look scary. I can't imagine they would last very long running. I've only turned cranks from solid. It's really a great exercise, however.
 

Cobra

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#15
Those pinned shafts look scary. I can't imagine they would last very long running. I've only turned cranks from solid. It's really a great exercise, however.
I am sure I wouldn't use that method for the Cobra, but I have never had a problem with steam engine models.
 

Cobra

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#16
In preparation of the piston work, I needed to finish off the cylinders. The outer surfaces were completed and the ports for the steam valve were added.

CT082.JPG


CT083.JPG

Finished the sides and the top surface.


CT084.JPG

Used a 5" Sine vise to cut the 45 degree edges.

CT086.JPG

With the cylinders finished, on to the four pistons.
 

Cobra

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#17
There are four pistons, two per cylinder. The outer pistons are connected to the crossheads by 1/8 rods and the inner pistons will be connected via stuffing boxes and cross links to the crossheads.

CT087.JPG CT088.JPG

Turning the two pairs of pistons from 1-1/8 aluminium bar.

CT090.JPG CT091.JPG

Completed piston sets.

CT096.JPG

Pistons installed and waiting for the crossheads.
 

Terry Werm

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#18
Nice work so far Jim. Thanks for sharing it with us. Is your engine per chance inspired by Elmer Verberg's engine of similar design?
 

Cobra

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#19
Nice work so far Jim. Thanks for sharing it with us. Is your engine per chance inspired by Elmer Verberg's engine of similar design?
Exactly Terry. I have built a number of his designs.
Lately I have started using his design as a start and redrawing, modifying and figuring out how to make.
Gives something for an activity while hiding from Canada's winter down south.
 

Cobra

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#20
Cross heads for the two cylinders.
Made as a single piece and the cut in half and trimmed to size.

CT092.JPG CT093.JPG CT094.JPG CT095.JPG CT097.JPG CT099.JPG CT100.JPG

Cross heads attached to the outboard pistons.

CT101.JPG

Cross heads fitted between the upper and lower guides.

CT104.JPG
 

Cobra

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#21
Blanks made for the connecting rods. As seen on the top bland the cap has been cut and re-attached in preparation for drill and ream for the large end of the rod.

CT107.JPG

Large and small ends drilled and reamed.

CT109.JPG

Centre drilling the small end for the tailstock centre. They will also function as oil holes for the small end.

CT110.JPG

Thinning down the blanks prior to turning the shafts.

CT111.JPG CT113.JPG

Turning down the shafts.

CT114.JPG CT117.JPG

Connecting rods fitted to the crank and to the pins in the cross heads.

CT118.JPG CT119.JPG CT120.JPG
 

Cobra

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#22
Stuffing boxes for the inboard pistons made in a similar fashion to the cross-heads. Made in a single part and then cut apart.
Packing gland nuts for each of the pistons for sealing the air chamber.

CT121.JPG CT122.JPG CT123.JPG CT124.JPG

Cross link arms for the inboard pistons cut from flat stock pieces stuck together with double sided tape.

CT125.JPG CT126.JPG CT127.JPG CT128.JPG CT129.JPG

Cross links fitted to the cross heads and the stuffing boxes.

CT130.JPG CT131.JPG

Links are soldered on the stuffing box and pinned on the cross head.

CT132.JPG CT133.JPG
 

Cobra

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#23
Support bracket for the valve train.


CT134.JPG CT135.JPG CT136.JPG

Crank rocker arm for the valve train.

CT137.JPG CT138.JPG
 

Cobra

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#24
Starting on the valve body. Turned from 1-1/2 inch brass.


CT139.JPG

Milling the valve slots after the arm had been attached to the top side.
Arm was attached with a fastener so that the length could be adjusted if needed.

CT140.JPG CT141.JPG CT142.JPG

Threading the two ends of the valve pivot.
Switched to single pointing when I discovered that I need a new 1/4-20 die. Old one was too dull to cut well.

CT143.JPG CT144.JPG CT145.JPG CT146.JPG

Link arm from the crank eccentric to the valve link.
Soldered and installed.

CT150.JPG CT151.JPG CT152.JPG


As I was installing the arm, I got to thinking about Tom's comments on the assembled crankshaft.

Those pinned shafts look scary. I can't imagine they would last very long running. I've only turned cranks from solid. It's really a great exercise, however.
I had never turned a crankshaft from a solid piece so thought I would give it a try.
 

Cobra

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#25
Turning a crank from solid turned out to be a little more tasking than I had originally imagined.
Started with the idea of using a parting tool to cut the slots for the two journals.
Started making up the blank from some hot rolled flat bar.

CT154.JPG

Face milled down to 5/8 inch.

CT158.JPG

Centre drilled each end for the three rotational axes.

CT159.JPG

Cutting the first journal.

CT161.JPG

Got part way and decided that this was a very scary way to make these slots. That blade is sticking out a long way.
About two seconds after that thought, the edge of the blade caught the blank and everything went to hell in a handbasket.

CT163.JPG

Time to re-think and start over.
Decided that a new tool was in order. I purchased some rectangular tools 1/4 X 3/8 and 1/4 X 1/2

CT165.JPG

Ground two ends of one of the 1/4 X 3/8 tools to be what was essentially heavy parting tool ends.
One end to cut left and the other right. I put about a 1.5 degree angle on the face of the tool with the idea that the actual journal could be finished by cutting from the centre to each side.

CT166.JPG

Finished side view of the double ended tool.

CT167.JPG

Also thought that bandsawing the blank ahead of turning would help the cause.
Sawed out the first journal area and then started on the other before thinking that it would flex.
Made up a spacer to eliminate the width of the saw cuts.
Started cutting with the new tools. Cut very well down the sides of the slot.

CT168.JPG

Getting near the dimention for the journal and the wide tool dug in and the blank lasted not at all!

CT169.JPG

Back to making another blank.

CT170.JPG
 

Cobra

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#26
Decided that the wide end to the tools could be improved on so ground the ends to leave just a small (1/16") flat on the face.
Again bandsawed out the journal space to get started. No additional saw cuts this time!

CT173.JPG

Everything was going well for the first little bit. Got the slot cut to the proper dimension, leaving the journal at 0.625" and then started reducing it to the target 0.375" finished dimension.
Just a little in-attention and there went another blank after about another two hours of work. Getting somewhat frustrated with this stupid idea of cutting cranks from solid pieces. This time it tore up the dog and the centre in the headstock.

CT174.JPG

Starting again on the first journal slot.
Cutting the sides is getting to be routine now.

CT176.JPG

Switched back to a 1/4" flat nosed tool to finish the journal to the final 0.375" dimension.
To avoid it digging into the job, I put the lathe out of gear and turned the spindle by hand. The freshly sharpened tool would shave off less than a thou at a time, leaving a nice finish.

CT179.JPG CT180.JPG

Made up an aluminium spacer for the first journal slot and started on the second.

CT181.JPG CT183.JPG

Finishing off the final dimension of the second.
Now, just need a second spacer and I can get started on the centre shafts.

CT185.JPG
 

Cobra

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#27
I cannot tell you how relaxing it was to be turning the outboard shafts!
Cut the webs to dimension and then just brought the shafts to their 3/8 size.


CT186.JPG CT187.JPG CT188.JPG

Finishing up the faces of the crank.

CT191.JPG CT192.JPG

Removed the extra material on the webs.

CT193.JPG

Thanks Tom! It was a great learning exercise that I would not have done without the push from a member of a great site!

CT194.JPG
 

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#28
Thanks Tom! It was a great learning exercise
Watching your efforts, I think if I were do to that I'd bandsaw much of the work away before starting on the lathe. But you (and I) learned quite a bit from your experience.
 

Cobra

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#29
Final assembly and test running.

CT195.jpg CT197.jpg CT198.jpg CT199.jpg
 

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MikeInOr

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#30
That is a very cool project!... But what I really appreciate is your photos of the machining in action! As a complete novice I am learning a lot from your posts and seeing how you are setting things up and how you are doing the machining. And the blank that got ruined... very cool that you shared that! There always seems to be more to learn from something that went awry then when everything works out perfectly the first time.

Thank you for your posts!
 
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