Author Topic: Gamma1-VPA Stirling  (Read 12626 times)

Offline smfr

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Re: Gamma1-VPA Stirling
« Reply #30 on: August 23, 2014, 05:02:21 PM »
Interesting process there, Tim! Too bad about the part being wrong-side-up the first time. This seems to be one of the easiest mistakes we make; I've certainly done it myself at least once!

Simon

Offline fumopuc

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Re: Gamma1-VPA Stirling
« Reply #31 on: August 23, 2014, 06:45:29 PM »
Hi Tim, also following along quietly. A nice runner.
Kind Regards
Achim

Offline Ian S C

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Re: Gamma1-VPA Stirling
« Reply #32 on: August 24, 2014, 12:51:49 AM »
Tim, re the kinked hose; I seem to remember something about a pair of curved brass tubes telescoped together.  Might have been in a Model Engineer article about a Dutch hot air engine.
                                               Ian S C
« Last Edit: August 25, 2014, 02:22:00 PM by Ian S C »

Offline tvoght

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Re: Gamma1-VPA Stirling
« Reply #33 on: August 25, 2014, 02:09:21 AM »
Thanks for your comments Simon and Achim. Ian, it looks like I have a solution for the tube kinking problem, I'm saving it for a future
post since a photo and/or video will be so much simpler than my inarticulate word choices.

The cylinder was machined from a chunk of "Durabar" cast iron 1.25" square.
First in the Bridgeport vise, the end of a 1 foot bar was machined on top,
sides, and end. The width was cut to the finished width dimension of the
cylinder.



6 #2-56 mounting holes were drilled and tapped referencing from the known
locations of the machined end and sides.



The workpiece was then separated from the bar on the bandsaw.



The part was placed sawn end up on parallels back at the Bridgeport vise.
Care was taken to clamp  so that the side with the drilled mounting holes
was parallel to the mill spindle.



The end of the cylinder was milled down to finished length dimension, and
the center of the bore located.




The cylinder was drilled then bored to about .001 less than final diameter.



At the CNC mill, the part was placed on parallels in the vise with the mounting
base on the parallels. A contouring program was run to get a desirable shape.




A separate program written as an after-thought, cut the top of the head flange
to size and rounded the top corners.



I liked the results.




The cylinder still needs to be lapped, and I show here the commercial
lap I used. I'm not offering details but will mention that there is at least
one excellent thread on lapping on this forum to be referred to.
I think here of the thorough coverage by Ramon, whose thread I read at least
twice before undertaking this job.



Thanks again,

--Tim


Online Jo

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Re: Gamma1-VPA Stirling
« Reply #34 on: August 25, 2014, 07:51:40 AM »
Coming along nicely  8)

I am intrigued how does that commercial lap work? I could understand Ramon's with the little screw in the side providing the adjustment  :ThumbsUp: But I can't see how that one adjusts  :headscratch:

Jo
Usus est optimum magister

Offline tvoght

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Re: Gamma1-VPA Stirling
« Reply #35 on: August 25, 2014, 01:33:10 PM »
Thanks Jo. The replaceable barrel on the lap has an internal taper and the screw in the end is tapered to match. I thought Ramon had shown similar shop mad ones.

Note that the one in the photo cost less than $15 US, so I don't mind buying one.

--Tim


Offline tvoght

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Re: Gamma1-VPA Stirling
« Reply #36 on: August 26, 2014, 12:05:15 PM »
The cylinder head was machined from a nice piece of 1/4" thick brass.
A blank was sawed out a bit oversize and the mounting holes drilled and
counterbored.



Once again, the mounting holes were used for mounting to the aluminum tooling
plate on the CNC mill. A profiling program was run to bring the outline to
size.




I had intended to leave the top face as seen in the previous photo, but it
looked too plain, so I whipped up another program to add some fins.



At the Bridgeport, a first hole was made for a barbed tube fitting.



I set up for, and milled an angled channel to go from the cylinder to the tube
fitting.




The threads were turned off of a purchased barbed fitting to fit the
drilled hole in the head. Here shown in the chuck of my trusty Taig lathe.



The head, the modified fitting, and an unmodified fitting for comparison.



And the assembly ready for soft-solder (process not shown).



Check in soon,

--Tim


Offline tvoght

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Re: Gamma1-VPA Stirling
« Reply #37 on: August 31, 2014, 01:06:20 AM »
We take a break from the regularly-scheduled build to a time in the future -when the engine is running-.
I said before I'd originally intended to make the engine's phase angle variable even as the engine was running.
I had some problems with tubing kinking, but I have found a suitable solution to the problem.

Heres a video explaining:

<a href="http://www.youtube.com/watch?v=yjcjhlVbio4" target="_blank">http://www.youtube.com/watch?v=yjcjhlVbio4</a>

--Tim

Offline tvoght

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Re: Gamma1-VPA Stirling
« Reply #38 on: September 01, 2014, 05:10:47 PM »
The piston has a graphite outer piece and an aluminum inner gudgeon piece.

The aluminum gudgeon was made from a length of 6061 aluminum held in a collet,
first cutting down a smaller portion.



And in a collet block at the mill, cutting in a slot for the rod.



And then drilling and reaming 3/32 for the gudgeon pin.



Still in the collet block, the piece was sawed off.



With the smaller diameter in a collet, the large end could them be finished.
I wanted this portion to be pretty close to .063 thickness, but I found I
couldn't get a measurement instrument in place to measure it. I "eyeballed" the
thickness by holding a 1/16" drill bit alongside. I got really very close using
that technique.




The piece was then drilled and tapped for a #2-56 screw.



The corner was generously chamfered to allow for a non-square corner at
the bottom of the bore where it will seat.



I have no process shots of the machining of the graphite portion. The shots
here are in fact taken this morning at a disassembly of the broken-in engine.

This shot shows the graphite piece at the bored end. The small screw hole can
be seen at the end.



The components ready to go together. A counterbore for the screw head has been
made, and was drilled by twisting the counterbore bit by hand.



This photo shows how the rod fits and how the gudgeon pin is trapped by the
piston walls.



Thanks for stopping by!

--Tim


Offline tvoght

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Re: Gamma1-VPA Stirling
« Reply #39 on: September 02, 2014, 05:47:43 AM »
The Displacer Rod Gland is made of 932 bronze.

In the 4-jaw chuck, I turned the 1/4" plug-end which will fit in the reamed
hole in the end of the Cooler. The larger diameter was turned, then the rod
hole drilled to perhaps .11 inches and then reamed to .125 (careful that the
reamer did not reach the bottom of the hole).



I see that I am missing a photo which shows that, after cutoff, the plug-end
was held in a 1/4" collet and a boss turned on the other end, leaving a
flange with a thickness of 3/32".

I clamped an aluminum tooling plate on the mill and drilled and reamed a 1/4"
hole to accept the plug-end. By zeroing the DRO at the center of the hole,
the center of the part was thus well-established.

A hole had been drilled and tapped just to the side to allow a 10-32 screw
to act as a clamp on the flange.



I drilled three mounting holes.



The finished part.



Using another purchased lap, I lapped the reamed hole. Here's the cute little
1/8" lap.



--Tim

Offline tvoght

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Re: Gamma1-VPA Stirling
« Reply #40 on: September 03, 2014, 05:07:12 PM »
The crank was built up of 303 stainless steel and held together with loctite
retaining compound.

The first photo shows the beginning of a fixture for building the crank. An
aluminum block was clamped in the CNC mill and faced off to be square with the
machine.



A paper cutout helped me to locate the position where I would drill for the
crank shaft.




A crank disk had already been turned with a hub and a reamed shaft hole (sorry
about the missing lathe pictures). The fixture was drilled and reamed for the
shaft, and the hole was enlarged near the top to clear the hub.
A large chamfer was made to accommodate the radius between the hub and the
crank disk.



Here's the disk in place. You can see how the back of the disk sat nicely
on the fixture block.



A second disk drilled and reamed slightly off-center was placed on top of the
first and was aligned with a .25 mill shank. The fixture had been drilled
and tapped for clamping screws, and a strap clamp held the disks in place.



With the parts thus aligned and clamped, two crank pin holes were drilled and
reamed through both disks. The holes extended well into the fixture block to
be used for later alignment references.



With the bottom disk removed, the previously reamed holes provided for
alignment of the upper disk with drill and mill shanks. The disk was clamped.



The disk was milled to define a small crank web between the crank pins. Note
the thin bridging piece left to keep the larger part with the center hole
intact. Keeping the larger piece attached facilitated fixture clamping and alignment.



The parts were re-clamped, this time with the short piston crank pin loctited
in place. The drive shaft was temporarily used in the center hole for alignment,
along with a drill bit in the yet unused crank pin spot. Also, a 1/8 inch lathe
bit was used to establish the proper spacing between the disks.



These photos shows the progress after the loctite cured on the first crank pin.




Shown in this photo is a fixture to help hold the displacer crank pin in
alignment. The crank pin is seen protruding out of the aluminum alignment fixture.



Here's the assembly with the displacer crank pin being loctited in. The aluminum
alignment fixture obscures the pin itself. Note the crank shaft is still inserted
to ensure alignment of the two disks during loctite cure.



After the loctite had cured, the main shaft was loctited in its proper position
in the lower disk.




Finally, the extraneous fixturing part was sawed away with a jeweler's saw
to leave just the small web between the crank pins.



A note about the shaft and crank pins. They are made from 303 stainless
steel "Miniature Drive Shaft" material purchased in 3 inch lengths from
McMaster-Carr. The diameter and straightness tolerances are excellent.

--Tim

Offline tvoght

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Re: Gamma1-VPA Stirling
« Reply #41 on: September 05, 2014, 01:33:28 AM »
The Cylinder Frame Clutch (for want of a better name) is the part which traps
the Cylinder Frame against the Bearing Stand and allows the Cylinder Frame to
rotate in order to effect phase angle change.
A pad made of thin Teflon sheet is trapped between the clutch and the Cylinder
Frame to provide a smooth adjustment with a tendency to hold place once set.
Is there a term for the kind of action I'm trying to describe?

I started by turning and parting a .125" thick washer of 1144 steel (chosen
because I had stock of appropriate diameter). At the Bridgeport, I drilled and
countersunk for 3 #4 flat-head screws.



I mounted the part on a store-bought expanding mandrel and tapered back the
face for appearance.



I mounted the part on a tooling plate on the CNC mill and ran a program to shape an outer contour..




The finished part. The 3 holes match the holes tapped on the face of the
Bearing Block seen before. The three "arms" which extend past the screw holes
lie over the Cylinder Frame, with the Teflon pad between.



Thanks for looking,

--Tim

Offline Roger B

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Re: Gamma1-VPA Stirling
« Reply #42 on: September 05, 2014, 02:08:40 PM »
Coming along nicely  8)

I am intrigued how does that commercial lap work? I could understand Ramon's with the little screw in the side providing the adjustment  :ThumbsUp: But I can't see how that one adjusts  :headscratch:

Jo

Jo, it looks like one of these:

http://www.acrolaps.com/

The price list is attached.

I ordered the 15mm and 25mm sizes along with two spare laps in each size. Postage was 28 USD
Best regards

Roger

Offline tvoght

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Re: Gamma1-VPA Stirling
« Reply #43 on: September 06, 2014, 12:41:15 AM »
Roger, I'm quite certain that is the source of the laps I use. Thanks for posting the link.


Photographic evidence of the connecting rods is woefully inadequate, but I'll
show what I've got.

First the piston connecting rod. Starting with 360 brass, I made an end cap
by drilling for 2 0-80 screws in the end, close fit through the cap and threaded
in the larger rod portion. The cap was then sawd off with a slitting saw and
then screwed back on.

In this first photo, you can see the rod in the Bridgeport vise with 5 holes
drilled. The hole the the left is the big-end crankpin hole and you can see the
split where it was sawn. That hole is reamed 3/16. The 3 middle are lightening
holes which double as clamping holes in a further operation. To the right is
the gudgeon pin hole which is also reamed 3/32. The milled portion reduces the
thickness of the rod everywhere except at the big end. There is a matching
milled slot on the other side.



At the CNC mill, the part is clamped to the tooling plate with cap screws.
There's a reference hole in the tooling plate to align the part to a known
mill reference (so the programmed cuts are made with reference to the crankpin
hole).



Here's the part after the contour is cut.



The displacer connecting rod was made in the same way, except that it does
not have a detachable end cap. I have no process photos.

Thanks for watching,

--Tim



« Last Edit: September 06, 2014, 12:49:20 AM by tvoght »

Offline Ian S C

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Re: Gamma1-VPA Stirling
« Reply #44 on: September 06, 2014, 01:07:21 PM »
Tim, I,m a bit uncertain about the reason for the separate crank pin for the displacer, was tis required to attain the correct ratio between the two sides of the motor?
      My first Stirling Engine was a V type, with a single crank pin, the displacer driven by a Scotch Yoke.  The ratio was obtained by increasing the diameter of the displacer.  I did, at one stage think of making an adjustable phase angle on it, but it ended up getting pull to bits, and converted into a Ringbom motor.
                                                          Ian S C