Author Topic: Roy Ozouf's Coventry  (Read 19371 times)

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #45 on: November 22, 2016, 03:22:55 AM »
Today I cut out two pieces of aluminum from one of the remainders from making a frame, machined them down to the overall size of the bearing caps.  Then I drilled clearance holes for 5-40 mounting screws and counter-bored them.  This allowed mounting to the tops of the frames.

I discovered that the sides of the caps didn't like up sufficiently well to the frame.  I would have done better to make the caps first and spot the holes onto the top of the frame.  That said, by enlarging the clearance holes I could get the caps pretty close.  However, the bearings themselves have flanges that will impinge on both, so I decided to take off a bit on once side to leave the frames proud of the caps.

That done, back to the CNC mill to machine the pocket for the bearings;  both frames together to ensure alignment.



Afterwards I marked the frames and caps with some punch marks to ensure that they go back together the same way.

Next tasks will be turning the bearings, and then profiling the caps.

The pictures in Ouzof's booklet show oil cups for these bearings, but the drawings don't show a provision for this.  Best guess is a small hole through each bearing that is lined up to match the oil cup and passage in the cap.  The cap clamps down on the bearing to prevent it rotating.

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #46 on: November 22, 2016, 10:53:28 PM »
Today's shop progress:

1) Made the upper bearings from bronze round, but didn't take any pics.

2) Machined a 3/32 square keyway in one of the crankshaft arms

3) Glued up the crankshaft arms to the cheeks using loctite

4) Test assembly to the frames of the crankshaft, bearings, and flywheel.



I also finished the cam link by removing the material between the guides.  I realized the the guides need to go into the channels created in the frame.



Almost ready to assemble the cylinder to the pivot shaft and crankshaft to verify the major motion.   :)

Offline crueby

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Re: Roy Ozouf's Coventry
« Reply #47 on: November 23, 2016, 02:21:45 AM »
Looking great! That is going to be a really pretty model.

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #48 on: November 25, 2016, 12:43:23 AM »
The smaller the parts get, the harder it is for me to figure out how to make them.  These little brackets are a prime example.  To get the 4 needed I started about 9.  Basically I CNC machined the profiles on the end of .5" brass round held in a vertical 5C collet.  Then parted off with some extra on the lathe, and finally trimmed to final thickness on the Bridgeport.



My sense is that these need to be fairly precise with the holes properly centered. The means I came up with is to hold them in the small vise, using a surface plate to ensure that they're mounted squarely.



Then I placed the machinists vise in the Bridgeport vise using a stop for repeatability.  I'd initially zeroed the DRO to the corner of the small vise's fixed jaw.  In this way I could find the proper location of the holes (#43 drill).



A similar reorieintation enabled the second set of holes.



I then made the guide bars as 1.5" of 3/32 drill rod tapped 2-56 in each end.  A sample assembly:



The brackets need to screw into the inside of the right hand frame and allow the link to slide freely up and down on the bars.

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #49 on: November 26, 2016, 12:08:39 AM »
To mount the sliding link one first drills and taps two 2-56 holes in the inside of the right hand frame.  Then the link, it's guide bars, and the four brackets can be attached by screwing the two upper brackets to these holes.  The frame holes for the lower bracket can then be spotted from their brackets once  it's verified that the link can slide smoothly.  These lower holes will wait for another day.

Next I wanted to verify that the tail of the eccentric strap could connect to the upper hole in the sliding link.  I then noticed that I failed to machine the slot in the strap, so that was the next order of business.  With everything back in place, it looks as if everything lines up.  This means that I can loctite the spacer on which the eccentric rides to the crankshaft, as it doesn't need trimming to align the eccentric strap to the link.



At this point the only parts needed to be finished are the small "fiddly bits" that transfer the vertical motion of the slide to the motion of the valve.  I do need to finish up some drilling and tapping for the cylinder assembly before I can attach it to the crankshaft by means of the piston rod.  But the end is in sight.

One fiddly bit I made a start on is the gland for the steam chest.  Here it is as macined onto the end of some .5" brass round.



Next time out I want to fit it to the steam chest spigot before parting it off.

Today I ordered some 2-56 hex screws, nuts, and washers from Godshall;  these will be used to replace the temporary socket head screws currently in place.


Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #50 on: November 27, 2016, 01:26:03 AM »
Today's adventure was sandwiched around the GA-GA Tech football game.  The pre-game activity started with finishing the valve gland and fitting it to the steam chest.



Then in order to assemble the 4 layers above the cylinder to the steam chest cover, it's necessary to drill and tap 6 2-56 holes in the cylinder cutout.  Following Ouzof's advice these were spotted from the port block.  Did the first hole, screwed the port block to the cylinder using this hole, then spotted the rest.



I prefer to tap these small holes by hand on the tapping stand as it's easy to feel the tap pressure and the bottom.  The port block is attached to the cylinder using 4 of the 6 holes.



Post game was mostly about shortening screws.  Two of the these secure the steam chest to the cylinder through the port block.  Then the steam chest cover's twelve screws secure to the port block with 4 screws and to the steam chest itself with the other 8.  I will wait for my order from Godshall before doing any more screw sizing of 2-56s.

I was then ready to assemble the cylinder to the pivot block and pivot shaft, insert the piston and assemble the crosshead to the crankshaft to see how things line up.  Poser shot:



The piston slides pretty easily when the crankshaft turns, but bottoms out on the cover, where I have yet to machine off the extra large spigot I left earlier.  I also haven't finished drilling and reaming the top cover and its gland.  This will be done in the next shop session using the cylinder as the fixture.

A little over a month since the first parts produced, so I'm definitely moving faster on this one than is my habit.  I think my month's layoff in October plus wanting to finish it for Cabin Fever has something to do with it.






Offline Dave Otto

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Re: Roy Ozouf's Coventry
« Reply #51 on: November 27, 2016, 02:30:30 AM »
Nice progress Kirk!

Dave

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #52 on: November 28, 2016, 12:51:07 AM »
Thanks for looking in Dave.

I had only a couple of shop hours today but managed to get the top cylinder cover and gland drilled and reamed.  With them on the cylinder the piston moves up and down very smoothly, so everything seems well centered on the bore.  I discovered I should have drilled the holes for the glands at 45 degrees to the plane of motion, but I don't believe that will cause any problems as the crosshead won't hit the gland screws.

I may have an issue with adjusting the piston travel.  When the piston rod is at BDC it still is barely touching the bottom cover spigot.  I can't adjust this with the crosshead currently as it's screwed all the way down.  At TDC I have about 1/4" of space between the top of the piston and the top of the cylinder.  Not sure what the optimal spacing should be.  Clearly I can face off a bit from the cylinder bottom, but to reduce the top clearance I'll need to add a couple of threads to the piston rod.


Offline crueby

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Re: Roy Ozouf's Coventry
« Reply #53 on: November 28, 2016, 01:08:41 AM »
That is looking wonderful!

Since the cylinder rocks during the stroke, how does the steam get in? Does it come through the bottom pivot rod? Or does it use a flexible hose?

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #54 on: November 28, 2016, 01:38:47 AM »
Chris,  the air and steam enter though the left side of the pivot shaft to passages in the pivot block and then through the lower cover.  The exhaust exits via a similar set of passages to the right side.

For testing I'll just use tubing with a press-on adapter, but eventually there should be a globe valve on the side, and the supply pipe will need to be a slide fit with packing to the pivot shaft.

I did some calculation knowing that the length of the swept volume is 2*crank throw + piston length.  Subtract from the length of the cylinder divided by 2 gives the design space at the ends of the stroke, in this case 1/8".  Since my space at the top is > 1/8", either the piston is too short (pretty sure that's not the case) or the cylinder is too high.

The height of the piston can be affected if either the pivot block or the bottom cover are too thick, so that will be checked next time.  I'm pretty sure the pivot block can use a trim anyway.

Given how short a distance the valve moves, I suspect that it's sensitive to the sum of all the movements in the "fiddly bits" that connect the eccentric to the valve rod.  I know Stan had some issues with timing adjustments.

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #55 on: November 29, 2016, 12:01:12 AM »
After disassembly and measurements, I determined that the cause of my piston travel issue was the piston rod.  I didn't thread the crosshead end far enough so that the crosshead was 1/8" or so too high.  The simplest fix was just to reduce the unthreaded portion with a grooving tool to less than the minor diameter.

In most of my prior builds the plans called for extra threads and a jam nut to adjust the piston travel.  However here the crosshead descends right to the gland.  In fact, I may need to relieve the gland a bit if the packing causes some contact.

Aside from that, today's shop time accomplished the following.

- Marked, drilled, and tapped the bottom mounting holes for the guide bars on the right hand frame.  The link slides pretty smoothly with the bars screwed down on both ends, so I'm quite happy with that delicate job done.

- Made the rocker shaft in two parts, loctited together.  Pics next time

- Ditto on the die block

- Did the drawing and CAM for making the valve rod end, which should be the first task tomorrow.

Offline sshire

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Re: Roy Ozouf's Coventry
« Reply #56 on: November 29, 2016, 02:37:05 PM »
It is a fiddly engine. So many different movements it seemed to be a constant "adjust this, which changed something else. Fix that, which changed some other movement." Eventually it all comes together.
Once I had it running, I made the mistake of taking it apart for paint and polish. Reassembly required the Repeat-the- "adjust this" step.
Best,
Stan

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #57 on: November 29, 2016, 06:22:33 PM »
Stan,  I remember that at NAMES it wasn't running.  Good to hear that you've gotten it running since then.  Don't bring it to CF, or at least keep it far away from mine.  I will name it "Lady Godiva's Ugly Sister".  I doubt I'll paint it.

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #58 on: November 30, 2016, 12:23:36 AM »
Took me all day to make the valve rod end because of various idiocies in setups.  My plan was to cut the profile in some round stock and then turn the collet block sideways to cut the slot with a 5/64 endmill.  Third time was a success although the slot came out slightly off center, which I suppose had something to do with the work sticking out so far.  I doubt it will cause any problems since the position of the rocker arm, that fits into the slot) is adjustable.



Here's the 3 fiddly bits I've worked on the past 2 days:



That leaves only the remake of the rocker bracket and the the rocker arm to complete of all the valve motion pieces.  I'm waiting for my order of Crystalbond to show up to make finishing the arm easier, but I can cut the profile in advance.  I also need to start on the frame spreaders plus a means to attach an air supply to the pivot shaft before a test can be contemplated.

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #59 on: November 30, 2016, 11:33:13 PM »
Today was remake the rocker bracket day.  If you remember I made it in mirror image previously, so I modified the CAD file and basically followed the same process.  The main difference was clearing the material around the profile, where I tried out a new trochoidal pocket machine operation now available in CamBam.  Here's the pocket:



Using this operation, the tool is at full depth and uses a series of arc moves to remove material.  My stepover was .025 using a .25" endmill, so 10% radial engagement, 11 IPS feed rate.

The finished part: