Author Topic: Currin's LTD Stirling  (Read 8622 times)

Offline Hugh Currin

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Currin's LTD Stirling
« on: June 27, 2017, 05:59:06 PM »
So, this is a journey of the Traveling Sherline Show. Actually a dry run. I described the situation and equipment in this thread. There I mentioned the best way to check the equipment and select tooling would be to build an engine. So this is a log of that build.

I've wanted to build a LTD Stirling for a long time. This seems like a good opportunity. I looked around for a plan set small enough for the Sherline equipment and found the Egg Cup Stirling from Jan Ridders. He graciously sent me a set of plans. I generally work in imperial units (inch) and the plans are in metric so I re-drew them in imperial units. Can't re-draw something without making a few changes, but it is true to Jan's original plans. Too close to give out the re-drawn plans.

With luck it'll look something like this:


I've ordered the materials I don't have on hand and should get started soon. It'll be a slow build for a couple of reasons. First I'm using new equipment and need to learn it. Second I'll have to build some tooling as I go. One reason for the build is to determine what tooling to take along. Finally, things are a little crazy around here, shop time is limited. Hopefully I can get an engine in a couple of months.

You're welcome to come along. Any advise or suggestions will be welcome.

Thanks.

Hugh
« Last Edit: July 04, 2017, 09:18:46 PM by Hugh Currin »
Hugh

Offline b.lindsey

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Re: Currin's LTD Stirling
« Reply #1 on: June 27, 2017, 07:40:07 PM »
Hugh, that should be a good test project for the Sherline. Jerry Howells 1/2 scale Miser is a good one as well but a bit fancier. You may want to consider ball bearings for the crankshaft as they will reduce friction greatly which is critical in LTD Stirlings.

Bill

Offline mklotz

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Re: Currin's LTD Stirling
« Reply #2 on: June 27, 2017, 08:03:51 PM »
You may want to consider ball bearings for the crankshaft as they will reduce friction greatly which is critical in LTD Stirlings.

If you do use ball bearings on an LTD Stirling, it's a good idea to wash out all the bearing lubrication with solvent and use them dry..  Cuts down on the friction and it's not like an LTD is going to put much load on a bearing.
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Online Vixen

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Re: Currin's LTD Stirling
« Reply #3 on: June 27, 2017, 08:07:34 PM »
Hi Hugh,

Is this another coincidence? There are two more Jan Ridders' Egg Cup Stirling engines coming together very slowly in my shop. I seem to copy everything you do Hugh.

My Grandson, Lewis, is showing an interest in engineering and is determined to become an engineer one day. So most weekends we spend time together in my shop building simple engines. My objective is NOT to teach him just to be a model engineer but to give him the wider appreciation of all aspects of mechanical (and electrical) engineering. I am trying to provide him with those precious hands-on engineering skills that do not come with collage courses and books. He is keen and learns quickly, so I believe the time we spend together is well spent.

For Christmas, last year, I put the drawings of several of Jan Ridder's hot air engines into his Christmas box, From these, Lewis decided he liked the look of the small Egg Cup Stirling for his next project. We have made a start, and have completed two fly wheels. Unfortunately, due to his final school year exams, we have had to put the weekend sessions on hold. Exam results are more important than learning skills. We will get back on track any time now.

The first engine Lewis built was a simple oscillating engine, christened the 'Wobbler'. This engine was made entirely by hand on an Emco 4 lathe with a mill attachment (even smaller than your Traveling Sherline Show) The little engine runs well and has already worn the main bearings out, so these will need to be remade. More practice.

The plan for the Jan Ridders' Egg Cup Stirling is to broaden his engineering experience by doing most of the engine using CAD, KAM and CNC techniques. Hopefully he will learn to 'walk the walk and talk the talk' and be well ahead of his peer group at collage. So like you, Hugh, we have redrawn Jan's engine in AutoCAD, we have produced the toolpath code using DesKAM and have machined the flywheel on my Emco F1 mill using LinuxCNC. I know these are not the most up to date software and machines but the thought processes are the same and that's the message I am hoping to get across to him. How to think as an engineer thinks.

Hopefully he will repay me one day with a students low price copy of Solidworks.

The Jan Ridders' Egg Cup engine is very small and may not run too well on the low temperature differential provided by a cup of hot water, so I propose to make a few changes to allow it to be powered by a T light candle, to provide a little more heat energy.

Cheers

Mike
It is the journey that matters, not the destination

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #4 on: June 27, 2017, 10:50:55 PM »
Bill & Marv: It's not as bad as it looks. Jan is using a point contact for the bearings:


The ends of the axle are pointed (60 deg included). It is then supported in set screws that have been spot drilled (90 deg included). The set screws in each post adjust the load/clearance. So theoretically there is a point contact for rotation. I think this is used in clocks and watches? It should work OK??

Mike: Great to hear you are bringing along a young machinist. It'll be a real advantage for his engineering career. Are you doing a build log?

Thanks.

Hugh
« Last Edit: July 04, 2017, 09:20:21 PM by Hugh Currin »
Hugh

Offline crueby

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Re: Currin's LTD Stirling
« Reply #5 on: June 27, 2017, 11:49:26 PM »
Bill & Marv: It's not as bad as it looks. Jan is using a point contact for the bearings:
The ends of the axle are pointed (60 deg included). It is then supported in set screws that have been spot drilled (90 deg included). The set screws in each post adjust the load/clearance. So theoretically there is a point contact for rotation. I think this is used in clocks and watches? It should work OK??

Mike: Great to hear you are bringing along a young machinist. It'll be a real advantage for his engineering career. Are you doing a build log?

Thanks.

Hugh
The main shafts on clocks are stepped ends through a barrel shaped hole typically,  this type of point bearing is used on jeweled bearings in watches. I think.

Online Vixen

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Re: Currin's LTD Stirling
« Reply #6 on: June 27, 2017, 11:52:04 PM »
Hi Hugh

I brought up my eldest son to be a fine aircraft engineer, sadly we lost him a couple of years ago. Now, I am fortunate to be able to act as mentor to one of the next generation. It is may way of giving something back.

As to a build log, that will be up to my young protege. I will encourage him to join this wonderful MEM community of ours. However, I imagine he would find the prospect of addressing our community to be very daunting. To a young lad, reaching for the first rungs of the ladder, the established members of the forum must appear like the unapproachable 'Gods of Old'. Maybe the discussions in the '4000 Strong!' thread will find a way to overcome these barriers and make it less intimidating for the younger generation to contribute.

I have seen graphite rod used to make ultra low friction crankshaft bearings for an LTD Stirling engine. Graphite rod is readily available on evil-bay. I never fell compelled to build an engine as per drawing, if a small change can lead to an improvement, it is worth a try. If it does not work out, you can always follow the drawing.

Mike





It is the journey that matters, not the destination

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #7 on: July 03, 2017, 02:02:55 AM »
So, I have the materials needed for the Egg Cup Stirling.


Mostly from McMaster Carr since Online Metals didn't have 12L14 Leaded Steel. I decided to get leaded, free machining, steel because it machines so nicely and the cost is reasonable at this size. The plastic bag contains a short length of 1/4" graphite for the piston. Haven't worked with this before, I hear it machines well but is messy.

You'll notice I've already broken the rules. I used my large horizontal bandsaw to cut the two AL disks shown. Sure didn't want to attack them with a hack saw. I will have to figure out a cut off method for the Traveling Sherline Show. I'll also slice off pieces of the large steel round for a flywheel and the acrylic tubing for the displacer cylinder. More rule breaking.

I've been slowed down. I need to make some tool holders for the Sherline Mill. For a CNC mill I need several holders in various sizes. SO, I'm trying to become friends with the Sherline CNC Lathe. I need to bore, groove and thread to fit the Sherline spindle. Then mount on the spindle and ream for specific tooling (1/4" & 1/8"). Might as well learn enough to make them on the Sherline CNC lathe since I need several.

So I'm still on task but slow. There's also a lot of things going on around the house. And I though retirement would bring more shop time. Think again!

Thanks for following along.

Hugh
« Last Edit: July 04, 2017, 09:21:37 PM by Hugh Currin »
Hugh

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #8 on: July 16, 2017, 04:52:41 AM »
I've been slowed down. I need to make some tool holders for the Sherline Mill. For a CNC mill I need several holders in various sizes. SO, I'm trying to become friends with the Sherline CNC Lathe. I need to bore, groove and thread to fit the Sherline spindle. Then mount on the spindle and ream for specific tooling (1/4" & 1/8"). Might as well learn enough to make them on the Sherline CNC lathe since I need several.

Still planning to build the Stirling, but the above problem is still present. I posted details in another thread. If anyone has insight into cutting specs on a Sherline please chime in.

So I'm on task but slowed down at the first step. Thanks.

Hugh
Hugh

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #9 on: August 15, 2017, 12:36:27 AM »
I believe I have the Sherline equipment tooled up. But I've run out of time. I'll be tied up through September with little shop time. Hopefully I can get a good start on the Stirling beginning October, but life is going to get real busy around then. I haven't forgotten the project though.

But I'll bet you all had forgotten about it. :-) If you didn't thanks for hanging in there, I'll get it off the ground yet.

Thanks.

Hugh
Hugh

Offline b.lindsey

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Re: Currin's LTD Stirling
« Reply #10 on: August 15, 2017, 12:40:03 AM »
We'll be here when you are Hugh. Looking forward to it!!

Bill

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #11 on: December 18, 2017, 04:39:15 AM »
Finally, some progress on the LTD Stirling. We're in Brenda AZ for awhile and able to set-up the Traveling Show. A meager start but thought I'd let you all know I'm somewhat on task.

The first task was to square up the displacer cylinder. I wanted these complete to check the sizing of the upper and lower displacer plates as they are made. Simple turning with a three jaw chuck and HSS insert tooling.


This went well. I had four blanks so squared them all.


To machine the upper and lower displacer plates I needed to use the 1" riser blocks for the Sherline lathe. I hadn't used these before so decided to align the headstock. Put a 1/4" piece of round stock in the 3 jaw and a test indicator in the tool post. First measuring near the chuck, taking center as half way between largest and smallest readings. Then move towards the end of the 1/4" bar. Again taking the middle of low and high readings as the bars center. Adjust headstock to zero at outboard end and re-measure. A few go arounds put alignment within a thousandth or so.


Then using the three jaw chuck I faced and then cut the recess for the displacer cylinder in upper and lower displacer plates. I faced the disks manually (CNC jog commands) but wrote a g-code program to cut the recess itself. The Sherline lathe takes light cuts. I found for this set-up it liked to take 0.005" per pass. That's a lot of passes so I found it easier to write the program that type in MDI codes one at a time.


The plan is to use soft jaws to hold the upper and lower plate for finishing. This for the OD, thickness and machining details of the upper plate on the mill. To machine soft jaws one wants the jaws pushed against the scroll as it will be in use. Grabbing the ID of the plates requires the jaws the be pushed in for machining them. For this I put a twist of wire around the jaws and adjusted the chuck outward to tension the wire. Finally, I faced the jaws and then cut a step in them to hold the displacer plates.


I've done a little more but no pictures yet. The soft jaws hold the plates well for the most part. I have three sets of plates (3 engines) so I'll machine all of them. With luck I'll end up with one or two complete engines. One plate didn't want to catch on the soft jaws. I think, for some reason, the recess is tapered. Next session I'll try to correct this and finish the plates.

I need to get some chip control first though. Some kind of tent to catch chips. Soon as that's set-up I'll try for some more progress.

Till then, have a Merry Christmas and a Happy New Year.

Hugh
Hugh

Offline Kim

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Re: Currin's LTD Stirling
« Reply #12 on: December 18, 2017, 06:09:08 AM »
Interesting technique there with the wire to hold the jaws in position to radius the outside diameter of the soft jaws.
Kim

Offline b.lindsey

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Re: Currin's LTD Stirling
« Reply #13 on: December 18, 2017, 11:28:03 AM »
Glad to see the travellin' shop now in action Hugh. Looking forward to more updates as things happen. Enjoy that warm Arizona weather :)

Bill

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #14 on: January 13, 2018, 03:59:56 AM »
Here is a little more progress on the Stirling. The soft three jaw worked well holding the plates for thinning.


When I cut the aluminum disks they didn't seem to be way oversized. But after cutting to diameter and thickness on the Sherline, they were. It takes many passes and a bit of time to take these to size on the Sherline. But the set-up worked well and I was able to thin them all to size. Per the plans the lower plate had an inset of 0.075" for the plastic displacer cylinder while the upper plate had 0.050". I grabbed the wrong plates and thinned for the lower plate. But I was able to modify the design to account for the error. I even like the new dimensions a little better. So, the lower plates were completed.

The upper plates have a pocket cut out. This is for better heat transfer through the plate and to hold ice/water on this plate to better power the engine. I converted the Sherline to its mill configuration and put on a tooling plate to hold the blanks. I found that I'd loaded CamBam on my laptop but didn't transfer the post processor over. So, it took some time to modify CamBam's LinuxCNC post to my liking. I machined a 0.025" recess in the tooling plate to hold the upper plate. Two tie down holes were tapped using jog and MDI commands.


The program to cut the basic pocket used a 1/4" end mill (slot drill), then a 1/8" end mill to finish up the corners, and a spot drill to chamfer the inside edge. I completed the 1/4" end mill pass. Watching it progress I found the 1/8" end mill was programmed to take a full depth, 0.100", cut to finish the corners. I thought this would cause problems so stopped after the 1/4" end mill pass. Looking at it I liked the way it looked. So I stopped at this point calling the pocket good.


I completed, nearly, by reaming the 1/4" hole in the center and 4-40 threads for the pillars via jog and MDI.


I liked it so much I cut number two the same way.

But since this is for fun, I re-wrote the code to include 1/8" passes and and inside chamfer. To get the chamfer tool, spot drill, to clear the clamps I rotated the part, in CamBam, 90 degrees. If I'd only been thinking correctly from the start. This code took longer to run but I do like the results a little better. Here are the three parts.


The one on the left has the full pocket and inside chamfer. It's also sitting on the displacer cylinder with lower plate in place. The other two are to the right, one upside down to show the bottom.

I need to thread the hole for the power cylinder 3/8-24. Didn't think this was a large tap till recently, but with the Sherline it is. I have a large tap handle at home that would work but would also be too tall for the Sherline mill. I do want this taped hole to be square so will have to figure out a bushing or something to hold it. More minor tooling fun.

Thanks for coming along. Stay warm out there.

Hugh
Hugh

Offline Kim

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Re: Currin's LTD Stirling
« Reply #15 on: January 13, 2018, 06:24:53 AM »
Very pretty looking parts there, Hugh!
Kim

Offline Flyboy Jim

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Re: Currin's LTD Stirling
« Reply #16 on: January 13, 2018, 01:28:32 PM »
Very nice Hugh.  :ThumbsUp:

Jim
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Offline b.lindsey

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Re: Currin's LTD Stirling
« Reply #17 on: January 13, 2018, 02:20:35 PM »
Remarkable work Hugh, and the parts look great!!

Bill

Offline Dave Otto

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Re: Currin's LTD Stirling
« Reply #18 on: January 13, 2018, 05:08:13 PM »
Yes, very nice looking parts coming from the picnic table machine shop!

Maybe a tap guide from OMW? I have one at work and one at home, they get used regularly. Little Machine Shop carries them.
https://littlemachineshop.com/products/product_view.php?ProductID=2571&category=-561984047


Dave

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #19 on: January 17, 2018, 10:45:01 PM »
Maybe a tap guide from OMW? I have one at work and one at home, they get used regularly. Little Machine Shop carries them.
https://littlemachineshop.com/products/product_view.php?ProductID=2571&category=-561984047

Dave

Dave: Thanks. I was thinking of an add on for my spring loaded tap guide. But this looks like a good solution. Seeing your post I remember seeing one before and thinking I need to made one of those, but didn't. I may well order one, it does look handy and is an easy way out of my current set-up problem.

Would be possible to make one on the Sherline but not trivial for me, particularly since I left my garage full of scrap cut-offs at home (bummer). So much easier to order one than order the material and make one.

Hugh
Hugh

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #20 on: January 17, 2018, 11:20:25 PM »
Thank you all for the positive feedback. I do need that!

I think I've competed the connecting rods for the Egg Cup Stirling. Never know till I have the parts they connect but they look workable. I had the mill set up so decided to make these next.

I used the same tooling plate as for the displacer plates, just added another threaded hole. I did take the tooling plate off to use the Tryally vice to put two holes in a piece of 0.06" brass. Then back to the tooling plate. I wrote the code to cut all the rods, for three engines, at once. Then realized I only have one 1/4" drill chuck (and one 1/2"). I needed three for the full program, so I broke the program into four parts. That way I can set the length of each drill between runs. I first center drilled all 12 holes. Then came back and drilled the 1/16" holes and finally the 3/32" holes. I don't have reamers here so simply used a new drill for these, should be OK. Here's the brass being center drilled and after the holes are complete.


I then cut the outside of each rod with an 1/8" two flute end mill (slot drill). There was quite a bit of shaking going on during ramp moves. The CNC enters a cut by ramping in at an angle rather than a direct plunge. The displacer caps I ramped in at 30 degrees. This time I ramped in at 10 degrees and still got a lot of shake. 2 in/min at 3000 rpm. I thought it was conservative but still got a lot of shaking. Maybe just not enough mass? Maybe a four flute would help. I'll keep fine tuning.


I left tabs to hold the parts, three per rod. These can be seen, sort of, on the above picture and the one below. I planned for the cut to go though the brass and into the tooling plate but it was short by an iota. The plate is 0.060" and I asked for a cut of 0.070" but it was still short. The outside two rods were so close to the edge that the edge gave way so the tabs had no structure. So, maybe the lack of depth was OK.


Then I broke the parts from the plate and finished them with a file and emery paper. An hour or so with a file and a Ponderosa IPA from Prescott Brewing gave these finished parts.


I might add an IPA, sitting in a lawn chair, on the porch, in the sun enjoying a perfect day.

Thanks.

Hugh
Hugh

Offline crueby

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Re: Currin's LTD Stirling
« Reply #21 on: January 17, 2018, 11:25:17 PM »
Is your end mill a center-cut style? Some are, and will plunge in fine, others have a small gap in the cutter right at the center, and wont do a plunge cut cleanly.

And yes, those of us stuck up north in the snow are envious of your sitting in the sun!!

 :popcorn:

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #22 on: January 23, 2018, 06:12:30 PM »
Is your end mill a center-cut style? Some are, and will plunge in fine, others have a small gap in the cutter right at the center, and wont do a plunge cut cleanly.

And yes, those of us stuck up north in the snow are envious of your sitting in the sun!!

 :popcorn:

I just checked and my two flute (slot drill) is center cutting. I thought "all" two flute end mills were center cutting, but I'm often wrong?

But any endmill should be able to ramp into a cut. Rather than a downward plunge, angle into the cut moving sideways while lowering the cutter. Hard to do manually but easy using CNC.

I'll try a straight plunge and see if this is any better. Would surprise me but that has happened before.

Thanks.

Hugh
Hugh

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #23 on: January 23, 2018, 06:40:37 PM »
I'm trying to think through this built up crank and need your thoughts.


The parts are small. The main shaft is 3/32" and the crank webs are some 0.80" thick. I'll try to link a *.pdf of the drawing.

Jan RIdder, who did the original plans, suggested soft soldering it together, then grind out the main shaft where the throws are. I don't have a torch with me so I'm considering alternatives. Would loctite work well enough for this crank. The loads in operation are trivial, but those while grinding and handling may not be. I'll likely try to "grind out" with a slitting saw.  I don't think something like JB Weld would get into the joint far enough? I can't easily do a press fit, which was my original though, since I don't have reamers, or a boring bar for a 3/32 hole, or an oven to heat treat a D-bit.

If those don't work its soft solder or silver brazing. Any pick between the two? A small propane torch would likely work for soft but for silver? The parts are very small. I have easy access to large propane cylinders (RV) but no torch (and no oxygen). Can anyone recommend a small propane torch for use with detached propane cylinder? How about with attached cylinder? Also accepting recommendations for soft solder and flux. Likewise recommendations for silver and flux. I'm in the US so any suggestions for small quantity orders?

Thanks in advance to the help.

Hugh
Hugh

Offline crueby

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Re: Currin's LTD Stirling
« Reply #24 on: January 23, 2018, 07:24:47 PM »
On ones like that I have used Loctite in conjunction with a cross pin through the joint, never had one fail with that combination (tight fits are a must). I usually just hacksaw through the bar to remove the section, then file it smooth.

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #25 on: January 23, 2018, 08:35:54 PM »
On ones like that I have used Loctite in conjunction with a cross pin through the joint, never had one fail with that combination (tight fits are a must). I usually just hacksaw through the bar to remove the section, then file it smooth.

Thanks. However I can't cross pin this one. I'm sure some here could but I can't. Trying to drill through and pin a 3/32" shaft is beyond my abilities. Do you think just locktite would be enough?

Thanks again.

Hugh
Hugh

Offline crueby

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Re: Currin's LTD Stirling
« Reply #26 on: January 23, 2018, 08:48:36 PM »
On ones like that I have used Loctite in conjunction with a cross pin through the joint, never had one fail with that combination (tight fits are a must). I usually just hacksaw through the bar to remove the section, then file it smooth.

Thanks. However I can't cross pin this one. I'm sure some here could but I can't. Trying to drill through and pin a 3/32" shaft is beyond my abilities. Do you think just locktite would be enough?

Thanks again.

Hugh
For a Stirling, it should be enough, lots less torque than an IC!

For cross drilling the holes, if your hole is first started through the web, then the web itself will act as a drill guide for the round bar. To the drill, it will just look like a single drilling through the rectangular web cross section. Even if it is off center a smidge, it wont matter as long as you loctite the webs on and THEN drill for the pins. This assumes the webs and shaft are the same alloy metal, otherwise it could dig in differently and wander.

Offline b.lindsey

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Re: Currin's LTD Stirling
« Reply #27 on: January 23, 2018, 09:00:47 PM »
Hugh, for a LTD Stirling, Loctite alone should be sufficient. You could even pre cut the 3/32" stock and make a simple fixture to make sure each crank is aligned first and then to make sure they are 90 degrees to each other and not have to cut the center sections out. As long as the holes through the crank throws are a good close (maybe even snug fit) things should stay in alignment overall as well.

Bill

Offline zeeprogrammer

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Re: Currin's LTD Stirling
« Reply #28 on: January 23, 2018, 11:07:50 PM »
You'll notice I've already broken the rules.

Good man. I tend to follow the rules (thank you my parents)...often to my detriment.

Breaking the rules is often a win-win. It either goes better than expected...or you learn something.

(We're talking rules here...not laws.  ;D )
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Offline Dave Otto

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Re: Currin's LTD Stirling
« Reply #29 on: January 23, 2018, 11:31:38 PM »
Hi Hugh

I can't imagine ramping at 30 degrees, I typically ramp at 1.5 degrees. Even at 3 degrees I get some rubbing on the back side that I don't like.
On the crank shaft; many years ago I built 3 Moriya hot air fans. These all have crankshafts assembled with loctite and not pinned. Not wanting to have to cut out the center what I did was to put a pair of v-blocks in the milling vise leaving enough space between the for the throws. Everything was cleaned and assembled, clamping the main shafts in the v-blocks kept everything in alignment. I can't remember for sure but I most likely assembled the crank pin first while passing a shaft through both throws. Then after that was cured the rest of the assembly was finished. I just can't remember for sure.

My little fan has many hours of run time on it with out any crankshaft issues. You most likely saw it running at the GEARS show.

You continue to make good progress on your engine.

Dave

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #30 on: January 24, 2018, 01:45:26 AM »
OK. I think I've got it. Both Bill and Dave suggest locktite should be OK for an LTD Stirling. I agree. Both also suggest cutting the shafts to length to avoid "grinding out" the main shaft between crank throws. I thought of this but wasn't sure I could align the parts. They think it's possible so I'll give that a try. It's by far the easiest solution, if it works.

I'd though of using the mill. Mount a bar in a 3 jaw on the milling table. Then drill that bar 3/32". Move the spindle up without moving X or Y. Finally clamp one end of the main shaft in the spindle and the other fitted into the bar in the three jaw. Should be as square as the mill is trammed and its TIR. As Dave said, assemble the crank pins first, then the whole assembly. (I don't have any V-Blocks with me.)

Thanks all. I at least now have a direction.

Hugh
Hugh

Offline b.lindsey

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Re: Currin's LTD Stirling
« Reply #31 on: January 24, 2018, 02:05:06 AM »
Hugh, that should work as long as the 3/32 hole is drilled straight. For fit purposes, drilling undersize (still straight of course) and reaming 3/32 might give a better fit if you happen to have a 3/32 reamer on hand.

Bill

Offline NickG

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Re: Currin's LTD Stirling
« Reply #32 on: February 04, 2018, 02:46:17 PM »
Hugh, I agree locktite will be fine for this, Iíve it is what I used on the flame licker engines with no problems. There will be zero forces from cutting out as long as you grip the shaft in the vice or chuck, not the webs. You donít need to touch the webs.


Sent from my iPhone using Tapatalk

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #33 on: February 27, 2018, 08:27:35 PM »
Well, I think Iíve crawled my way back from a 3 week sickness (cold). They usually put me down for some 2 weeks, but this one was particularly nasty. Glad I didnít have to work during it.

On the Stirling, Iíve made some ďprogressĒ. I cut out the crank webs for one engine. Using the same techniques as for the connection rods, I put some new holes in my current tooling plate. Then screwed the stock in place with two screws. Again I broke the CNC code into three parts due to lack of tooling. First run, center drilled the 8 holes and the second to drill out those holes. The third, using an 1/8Ē end mill, was cutting the profile of each web. A roughing cut stepping down to depth and then one full depth finishing cut. Three tabs were used to hold the parts to the parent material. I wanted to use a four flute endmill, but found I have one 2 flute with me. So itís a 2 flute (slot drill).


After removal from the tooling plate.


The four holes beside the mounting holes are trials. I wanted to find the number drill to give a good fit to the 3/32Ē rod. Then I cut the webs free at their tabs. Before I started this adventure I picked up a cheap Harbor Freight 3Ē bench grinder mainly for grinding HSS bits. Wasnít sure it would be of any use, but it is sure great for cleaning up these tabs, much faster than a file. So, a little grinding, filing and sanding gave four crank webs.


The crank pins and main shaft were simple lathe work. The backside cut off tool holder for the Sherline even worked well cutting the 3/32Ē drill rod. I decided to leave the main shaft in one piece while applying Loctite. That keeps everything aligned while the offset between the cranks was set by eye to 90 degrees.

The loctite caused some problems and may have ruined the part. The connecting rods need to be installed while the crank is glued. Very hard to loctite the pins without getting some on the connecting rod big end. I put grease around the big end to protect it. The result is the connecting rods turn but have some resistance. I suspect any resistance in a LTD Stirling is death, but I continued on.

The main shaft was cut out using a slitting saw. Worked very well.


So the final assembly looks like this.



The loctite seems to hold. The big problem is the friction in the connecting rods from some errant loctite. Iím going to put some lapping compound in the joints and spin them awhile. I tried this a little and it loosed up some. Has a long ways to go for a LTD Stirling though.

If I canít loosen them up I may have to go to soldering the crank together. We joined the Gem and Mineral Club in Quartzsite where they have a jewelry making shop. There are some very small acetylene torches for silver soldering jewelry. Might work better than loctite. So I plan to cut another set of crank webs with a raised shoulder around the crank pin. That should prevent any binding between the rods and the crank webs.

Jan Ridders suggested soft soldering the crank. Any thoughts on using soft solder vs silver? Also any suggestions to keep the solder away from the connecting rods? Those brass rods would love to soak up some solder, likely more than the steel parts. Any other suggestions greatly appreciated.

Thanks for coming along.

Hugh
Hugh

Offline crueby

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Re: Currin's LTD Stirling
« Reply #34 on: February 27, 2018, 08:56:23 PM »
Wow, those are some small crank webs! Looking very good, hope you get the friction worked out.

 :popcorn:

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #35 on: March 10, 2018, 10:50:17 PM »
crueby: Thanks for looking in. They are small, but it's a small engine. Small tools, small engine what can I say. :-)

In spinning the crank to loosen the connecting rods the Loctite failed. It was a medium strength and should have work, I thought. The joints were clean but not laboratory clean. Don't know what went wrong. The connecting rods weren't loosening up adequately anyway. SO, I pulled the whole crank apart and cleaned the parts up.

I made two additional sets of webs. For these I left a small shoulder around the connecting rod big end. I think this will help in leaving the rods free moving. I also decided to try silver solder (or soft solder) on these. I used a spot drill (90deg) to cut a small fillet around the outside of holes in each web. Also tapered the crank pins at the ends with a file in the lathe. The fillet and taper are to allow a small bowl for the silver solder to flow into. You can see these features on the pic below. I left the main shaft one piece again to maintain alignment.


For silver soldering I painted the connecting rods with white-out, typewriter correcting fluid, which I understand will resist the flow of silver. I also put a wet sponge over the connecting rod thinking it would keep the brass connecting rod cool and prevent silver flow. (I only did this once because the sponge burned.) Then put flux on the web being worked on and a small piece of silver solder at the two joints. You can see the silver sliver in the following pic.


I then heated the web and shafts with an acetylene/air torch. I tried my best to heat the steel without melting the silver. When the steel heated enough the silver melted and (usually) flowed nicely around the shaft. The  silver worked so well I didn't try the soft solder.

I ended up with two cranks out of three tries. I think I heated the third one too much and the silver flowed into the connecting rod joint. Couldn't get it apart again so a re-build on that one. But two out of three is great in my book. Here are the two working cranks. The round very shinny object is a seriously over exposed penny for scale.


The pic below shows representative silver solder joints, after a little cleanup.


I think the trick was heating the metal just till the silver flows. The middle of the webs don't get hot enough to flow the silver. So, it flowed around the shafts and fill the fillet area without penetrating further. Even without full penetration they'll be more than strong enough, and the rods spin.

So some progress, but slow. Thanks for looking in.

Hugh
Hugh

Offline Kim

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Re: Currin's LTD Stirling
« Reply #36 on: March 10, 2018, 10:58:47 PM »
Nice looking crank shafts there, Hugh!

Isn't it fun when the silver solder works!  I just love it :)
And I agree completely, 2 out of 3 is outstanding!

Kim

Offline crueby

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Re: Currin's LTD Stirling
« Reply #37 on: March 10, 2018, 11:00:36 PM »
Wow - nicely done - don't think I would have ever tried soldering with the conrod in place, quite a feat!

Bet you were glad you were outdoors when that sponge burned, probably a nasty smell. I wonder if using a large clamp or other bar on the conrod  close in to the web would act as a heatsink?

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Re: Currin's LTD Stirling
« Reply #38 on: March 10, 2018, 11:10:09 PM »
Very clever and neat bit of silver soldering.

Did you get to use the very small acetylene torches from the jewelry making club?

What flux did you use? You were lucky it did not lift the white-out on all the conrods.

Go safe

Mike
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Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #39 on: March 10, 2018, 11:19:30 PM »
I can't imagine ramping at 30 degrees, I typically ramp at 1.5 degrees. Even at 3 degrees I get some rubbing on the back side that I don't like.

Dave
Dave: Thanks. I've been meaning to respond.

I've always ramped in at 30deg or so, sometimes even 45deg in aluminum. My thinking has been it's much better than a straight plunge. It speeds up the program execution and seems to work. I've typically done a tangent entry, an arc into the part while ramping. I've thought it gives a smoother surface, but with a shallow ramp angle the lead in arc gets long and causes interference problems. But this is all on a large machine with some rigidity and mass. The Sherlines seem to be different.

I cut the new set of crank webs using a 2 degree ramp angle. This helps quite a bit, but I still get what I interpret as complaints from the Sherline mill. The parts were better though, less gouging. I even tried one with 1 degree ramp which wasn't noticeably better than 2 degrees. So I'll likely use a 2 degree ramp angle for the Sherline. Thanks.

The code did some strange things at these shallow ramp angles. Though I did learn how to use a shallow ramp using tabs in CamBam. Some of the code seemed non-sensical. It would act as if it had very little distance for the ramp, so oscillate rapidly with a ramp. I think too short back and forth to give a real ramping. Other times it would oscillate for no apparent reason. It gave good parts so the code worked, but a long ways from optimized.

The Sherline seems to go though end mills faster than the kneemill. The "jumping" of the Sherline can't be good for tools. I'll pull out a new endmill and see how it lasts with shallower ramps. That could help.

Thanks for the note. Anything else you note please speak up. :-)

Hugh
Hugh

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #40 on: March 10, 2018, 11:54:19 PM »
Kim: Thanks. It is fun watching the silver flow, particularly when it goes where you planned.

crueby: I wouldn't have thought to solder them with the con-rods in place either. But the original plans by Jan Ridders had them this way. I couldn't figure a good way around it. Ya, about that outside part..... A chunk of aluminum or copper clamped on would have worked better. Where were you when I was planning this??

Mike: I did use the jewelry torch and it was just right for this small job. I did it in the jewelry shop at the local club. They charge $4 per 3 hour session which I think is reasonable once in awhile. They even had two stations with Foredom flexible shaft grinder/polishers. They have a nice set up for this. The flux came out of a small bottle on the bench. So no clue whatsoever what type or brand. Worked well though. I was careful with the flux and only put it where I wanted silver, so didn't get any on the white out.

Thanks for the help and encouragement.

Hugh
Hugh

Offline crueby

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Re: Currin's LTD Stirling
« Reply #41 on: March 10, 2018, 11:58:01 PM »
...
crueby:  ...  Where were you when I was planning this??
...

I was out to lunch? Napping? One of the two!  :Lol:

Offline Steamer5

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Re: Currin's LTD Stirling
« Reply #42 on: March 11, 2018, 09:00:17 AM »
Hi Hugh,
 Nice work! Don't say much but have been following along. But this time I have something to add....

The old gent I started out playing this game with commented once that the BEST thing ( now you can take this with a large pinch of whatever) to use as a heat sink when silver soldering is a potato!! I would suggest that once you finish your silver soldering you don't eat it  :naughty: & you don't let somebody else grab it & put it in the pot for tea!

Cheers Kerrin
Get excited and make something!

Offline Ian S C

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Re: Currin's LTD Stirling
« Reply #43 on: March 11, 2018, 11:20:00 AM »
It means that the cranks are closer together, but a good way to build a 90* crank is to have two plain cheeks on the outside, and one in the centre in an L shape.
My smallest motor has a fabricated crankshaft 3 mm diametre with ball bearing big ends, the webs are 2 mm thick, I can't remember which Loctite grade I used, it may have been 641.
Ian S C
« Last Edit: March 11, 2018, 11:30:16 AM by Ian S C »

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #44 on: March 18, 2018, 05:15:19 PM »
Hi Hugh,
 Nice work! Don't say much but have been following along. But this time I have something to add....

The old gent I started out playing this game with commented once that the BEST thing ( now you can take this with a large pinch of whatever) to use as a heat sink when silver soldering is a potato!! I would suggest that once you finish your silver soldering you don't eat it  :naughty: & you don't let somebody else grab it & put it in the pot for tea!

Cheers Kerrin
That sounds like a great solution. Enough moisture in the potato to absorb heat and enough heft to keep it in place. I might even throw it in the stew pot afterwards, don't tell anyone.

I will try this next time. Thanks.

Hugh
Hugh

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #45 on: March 18, 2018, 05:18:39 PM »
It means that the cranks are closer together, but a good way to build a 90* crank is to have two plain cheeks on the outside, and one in the centre in an L shape.
My smallest motor has a fabricated crankshaft 3 mm diametre with ball bearing big ends, the webs are 2 mm thick, I can't remember which Loctite grade I used, it may have been 641.
Ian S C
Ian: That does make sense, and would make for a more compact crank. Following Jan Ridders plans have the power piston and displacer far enough apart this wouldn't work well however. But would make construction easier in the right engine. I'll keep it in mind.

Thanks.

Hugh
Hugh

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #46 on: March 19, 2018, 02:40:48 AM »
We have a crank so need some way to hold it and its bearings. The engine has two columns for this support. Let's make those.

The columns mount onto the upper plate with set screws. A pair of holes in the plate are threaded 4-40. Also the base of each column is drilled and threaded 4-40. Threading of the column bases was done on the lathe and fairly simple. Each column was cut to length, also on the lathe. Then the top was brought to diameter with a bevel around the edge.

Now the fun begins. Flats and a threaded hole are cut in the column top, as per the plans. The 4-40 threads at the base have no orientation. The only way I could figure to cut the tops square was to mount them to the plate and mark the orientation of the flats. I put the columns on and squared those to the mill X axis using a parallel and test indicator. After being fixed I felt tip markered the insides and took a very light cut to mark where the flats are to go.


The columns are now assigned a location and need to stay there. The clamping to cut the flats and put in the threaded hole is pretty convoluted. I used a toolmakers vice on the Sherline table. A six sided "collet" block is held in the vice. Since I have no collets large enough for the 3/8" columns I used a three jaw chuck as shown. The block allowed me to flip it 180deg to cut both inside and outside flats.


A through hole and 4-40 tap completed the top of each column.


And that completes the first part of the column construction.

Thanks.

Hugh
Hugh

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #47 on: March 19, 2018, 03:23:00 AM »
SO, the columns are finished top and bottom. They would likely work this way but don't look very elegant. Let's cut the center 3/8" section to a nice visually attractive taper. They were kept at 3/8" till now so they could be held easily to finish the ends.

The plan was to grab the top in a four jaw on the lathe. Also put a small block at the base screwed on with a set screw as they mount to the plate while in use. The other end of the short block was center drilled for a tail stock center. This plan had a couple of problem. There is little space left at the top for the four jaw when space is left for the lathe tool. I had trouble grabbing the top adequately. At the tail stock there were other problems. The block tended to un-thread pushing the part towards the spindle and eventually coming loose. The coming loose part was pretty exciting, even on the Sherline.

I finally found a 1/4" collet that would grab the top better than the four jaw. I just used the threaded hole in the base for the tail stock center. It is just decorative so a few thousands isn't critical, and the center didn't harm the threads. The set up used is like this.


The G-code that CamBam produced reduces the diameter by 0.005" depth cuts. This gave a nice finish and didn't take too long. The taper was approximated with steps, then cut smooth. One finish pass further smoothed things out. In this pic you can see the stepped taper approx. nearing the end of the cycle.


Here is a picture of a column before thinning and one after.


I'm still building three engines, although I'm down to two cranks right now. Here is a picture of the three top plates with columns.


And finally a pic of one up to this point. I haven't cupped the screws to hold the crank, but this give an idea of the assembly.


Still a ways to go but they seem to be coming together.

---------------------------------------------
But I fear I've run out of time for this winter. The Traveling Sherline Show is going into storage till next fall. It takes up quite a bit of space on the road, but the tent to catch chips is too big to take. It's quite involved to set up the tent, so we need to be fixed for at least a few weeks. I don't see this happening till fall. So the Stirling is on hold till then.

Thanks for coming along.

Hugh
Hugh

Offline b.lindsey

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Re: Currin's LTD Stirling
« Reply #48 on: March 19, 2018, 11:02:45 AM »
I will miss your updates Hugh!  The traveling Sherline Show has been fun to follow and you have made some good progress on these three little engines.

Bill

Offline tvoght

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Re: Currin's LTD Stirling
« Reply #49 on: March 19, 2018, 01:43:56 PM »
Looking very good Hugh. It's too bad you have to fold up operations for so long.
I have a question about your use of the Sherline chuck in the collet block. Do you have some kind of straight shank adapter or something?


--Tim

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Re: Currin's LTD Stirling
« Reply #50 on: March 19, 2018, 04:08:42 PM »
Nice looking engine parts Hugh.
I am sorry to hear that the road show will have to go on hold until autumn. I thought you had found the answer. But it's those damn chips that cause the problem every time.

Mike
It is the journey that matters, not the destination

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #51 on: March 19, 2018, 04:13:21 PM »
Looking very good Hugh. It's too bad you have to fold up operations for so long.
I have a question about your use of the Sherline chuck in the collet block. Do you have some kind of straight shank adapter or something?


--Tim

TIm: Thanks. It is depressing to fold up shop for over six months. I may be able to pick it up sooner, but it's nice to know the traveling shop is available.

The chuck adapter is called a Index Block Set #2045 from Sherline. One with 6 sides and one with 8. The head of each is a copy of the Sherline spindle so collets and chucks will fit. The set came with the Sherline shop I picked up a few years ago. Pretty handy.

Thanks.

Hugh
Hugh

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #52 on: March 19, 2018, 04:25:43 PM »
Nice looking engine parts Hugh.
I am sorry to hear that the road show will have to go on hold until autumn. I thought you had found the answer. But it's those damn chips that cause the problem every time.

Mike

Mike:

Thanks. The parts are rough by the standards here, but I'm pleased with them. I have fun trying and learning.

The chip problem is partially solved. The "tent" solves the problem but takes awhile to set up and is really big to store. It is all CNC so I may be able to build an enclosure. Some plexi walled box that collapses into 5 sides for storage. It'd be smaller than the tent but too large for our current vehicle. Always thinking.

Thanks.

Hugh
Hugh

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #53 on: March 19, 2018, 04:31:28 PM »
I will miss your updates Hugh!  The traveling Sherline Show has been fun to follow and you have made some good progress on these three little engines.

Bill

Bill:

Thanks. But there is an up side. By fall everyone here will have completely forgotten about this build. So you all will "get" to reread the entire thread just to come up to speed again.  I know you'll all thank me for this, well maybe.

I'll be looking in as Internet service allows.

Thanks again.

Hugh
Hugh

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Re: Currin's LTD Stirling
« Reply #54 on: March 19, 2018, 04:36:14 PM »
Hello Hugh

My Emco F1 Mills all have clear plastic enclosures. They keep most, but not all, of the chips inside. If you can source some 3mm (1/8") Polycarbonate sheet it will be far more crack and shatterproof than Plexiglass. All you need is 5 pieces with holes drilled along the edge and a bunch of those tie wraps. Whatever did we do before they were invented?

Mike
It is the journey that matters, not the destination

Offline Hugh Currin

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Re: Currin's LTD Stirling
« Reply #55 on: April 01, 2019, 04:25:14 PM »
This winter has been a bust for machining engines. It was cold and wet the whole time here in Brenda, AZ. Not cold like north of here, but cold enough to make working in an unheated tent undesirable. I've made no progress on the Stirlings and it's time to pack up for the summer. Bummer.

I did build an enclosure as Mike (Vixen) suggested just above. I found some 1/8" press board and plywood from local dumpsters with plastic from Lowe's. Mainly to see how it would work.


From the little machining I've done with it, it works very well. Cut the zip-ties and it'll fold flat for transport and storage. I'll likely throw this one away (except the plastic) and build a nicer one when we pass by my wood working equipment.

Have a great summer. I'll be checking in as I can.

Hugh
Hugh