Author Topic: Currin's LTD Stirling  (Read 8474 times)

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.


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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?

Online Vixen

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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
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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