Author Topic: Currin's LTD Stirling  (Read 8387 times)

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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"You can do small things on big machines, but you can do small things on small machines".

Online 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

Online 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.

Online 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 )
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Online 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