Author Topic: Currin's LTD Stirling  (Read 8548 times)

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

Online 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

Offline Vixen

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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

Offline Vixen

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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