CD LTD Stirling

[Arthur Dent]

I began working on an LTD Stirling engine about a year or so ago, from the excellent plans from Jan Ridders.  Life happened, as it is wont to do, and I had to set it aside after just barely getting started.  Now that things have settled down a bit I thought it about time to get going again.  Since I am new around here I thought a build thread might be a good way to become better acquainted with all of you fine folks.
I'll start off with a shot of my work space:


This is my 7X12 mini lathe from Grizzly Tools, and the similarly sized mini mill from MicroMark.  My workshop is in a 12' X 24' storage shed out in the back yard.  As you can see I haven't finished insulating it yet.  The spaces between the studs sure make great places for hanging stuff.  Oh well.
I have been looking for some clear plastic container or something to cut up for the displacer cylinder to no avail, and just about decided to order a piece of clear acrylic pipe, when Wife found this really nice carafe at Walmart.  If I am careful I might be able to get enough material for 3 cylinders out of it.  Pretty good for $6.
Here is a photo of the dissected carafe plus the aluminum plate for the top and bottom pieces:


Some quality time with the band saw at work during my lunch break resulted in:


I'm going to have fun fitting those big disks onto my little lathe to bring them down to finished size, but I have gotten a few ideas looking through various build threads, I think it shouldn't be too much trouble.  I'll take pics while setting it up.  That might take a few days though, as my weekend looks pretty full.  I do have a few of the other parts already made, I'll put up some pics of those later.


 

[NickG]

Hi Arthur, looking forward to this thread the carafe was a good find - good idea. 

[Stilldrillin]

Hi Arthur.
Stirling cycle? You got me! 

Your workshop layout, and machine pairing, is just the same as mine. Only a heck of a lot tidier! 

Following, quietly..... 

David D

[fcheslop]

Hi Arthur,
             Stirling engine you got me as well
             I just cannot get enough of hot air engines just love building them or that maybe just hot air
             Watching quietly Now that don't happen often just put that in before Dave did
              Good luck with you're build
kind regards
frazer

[AussieJimG]

Hi Arthur,

That looks like a good start

Jim

[ReFlad]

Arthur,
Watching quietly to learn how this is done. 

Ronald

[b.lindsey]

Nice start Arthur!!  Are you following any particular plans or freelancing the design? LTD's are one of my favorites so will be checking in on your progress as well.

Bill

[Don1966]

Hi Arthur, you have my attention and I will be following along. How do you like you Micro lux mill?

Don

[Arthur Dent]

I won't pretend that my work area is always this tidy.  After a good clean-up one day recently I decided to snap a few shots.  Also, you can see that the rest of the shop is very carefully NOT included in the photo. 
The plans I am working from for this one are the CD LTD Stirling plans from Jan Ridders.  If anyone is unfamiliar with Jan's work you can find his page for this engine here:

http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_ltd_stirling_met_cds/cd_dstirling_frameset.htm

I built my first Stirling engine several years ago, it too was an LTD version.  It was a freelance build based on bits gleaned from various places.  It ran fine, but unfortunately met with a few mishaps during our recent move, and is now a "static model".   To repair it would involve a serious rebuild, so I decided to build a whole new one instead.
The MicroLux minimill is a fine machine.  I will admit however, that I have used it for only pretty simple jobs so far.  Hopefully I will be inspired to get a little more adventurous in the coming months.  I would love to add a rotary table to my collection of accessories, but that will have to wait a while.
Thanks to all for the kind words!  I hope to have an update to post in a few days.

[Bezalel]

I'll be enjoying this build along with the other guys 


Lead on Arty




   Cheers,  Bez

[sco]

Arthur,

I'm part way through a similar LTD stirling based on the plans on Jan's site.  I used a CD 'cake box' for the cylinder wall - bit flimsy but I cut grooves in the top and bottom plates to locate it and keep it round.  I machined the plates on my 1st lathe (Taig / Peatol) by sticking the plates to a face plate with thin double sided tape - provided you take fine cuts it works fine.  You dismount the plates by softening the glue with brake cleaner.

Best of luck,

Simon.

[zeeprogrammer]

Interesting project Arthur and I'll be watching too.

I have the same kind of equipment. I hope you don't mind a couple of questions/suggestions...

When I use my mill, the chips go flying everywhere. I'm thinking of getting a bit of plexi and making a moveable barrier to try and contain most of the swarf. A bit of slotted wood to hold the plexi.

I'm wondering about that multi-socket on the wall. Could a bit of swarf fly into it? Maybe a cover? Or cardboard/thin plywood as a barrier with a slot for the cord?

[Doc]

Interesting project Arthur and I'll be watching too.



I'm wondering about that multi-socket on the wall. Could a bit of swarf fly into it? Maybe a cover? Or cardboard/thin plywood as a barrier with a slot for the cord?

I had that happen to me when I worked out in the tooling shop wasn't pretty what it did to the wall.

Nice start on project I be here watching.

[Bearcar1]

Watching quietly as well 


BC1
Jim

[Arthur Dent]

It never occurred to me about swarf getting into that outlet.  That's a real good point, thanks for the observation.   
I just tacked it up there temporarily one day when I needed to plug in a lamp for the mill and didn't have an extension cord.  I'll take care of that.   

[Arthur Dent]

Here are the support posts and the cd flywheel hub that I made several months ago, along with a few graphite slugs sent to me by a very kind forum member.



I have never worked with graphite before, this should be interesting.  I haven't yet started looking for the glass for the power cylinder.  If anyone has a suggestion for a US source I'll be interested.  I have thought about making the power cylinder out of brass, but that would loose the visual appeal of the glass.  I do have an Airpot dashpot I could use, but that would be cheating.
The flywheel hub was made from a chunk of an aluminum grounding rod of some sort found by a dumpster diving friend.  The material is very odd, much lighter than you would expect for the size, and the surface has a kind of powdery grainy look.  It almost looks like it has been anodized or sandblasted or something.  I'm nor sure it's actually aluminum, but I don't know what else it would be.  The rods are a little over 1" in diameter and about 22" long.  There is a 1/8" dia steel core down the center, which I presume was to provide a hard tip for pounding into the ground.  There was also a copper connector on the top of each, which my friend cut off to keep for his copper scrap pile.  You can sort of see the grainy surface finish in the photo.  Compare that to the support posts to the right, which are 6061 aluminum.

[wlb]

Not sure if this will work I have attached two photos of my hot air engine which looks like the one on topic. My working piston was plastic. It runs on the heat of a 12V car bulb

[zeeprogrammer]

I meant to ask earlier...how did you go about cutting the carafe?

[Arthur Dent]

The carafe wasn't very difficult to cut actually.  I cut a length of paper the exact width I wanted, taped it around the carafe and drew a line around.  After removing the paper I took it over to the paper cutting bandsaw at work (part of my lunchtime project) and cutting very lightly sawed it off.  Not sure what kind of plastic the carafe is made of, but it wanted to melt into the blade so I had to take it very slowly.  After that, a light touch-up on the belt sander and the cylinder looks pretty good.     

[Arthur Dent]

I did get a little time in the shop today... very little.  Anyway, I decided to play around with turning one of the discs down to diameter.  I put a dimple at the center of one of the discs, then used a live center to butt it up against the lathe chuck (with jaws removed).  A thin piece of cork sheet between the disc and the chuck provided a little traction.



I saw someone do something similar for a flywheel in a build thread somewhere.


 
I had to move the lathe bit out to the outside position in the holder, wind it out all the way, then angle it in a bit, but it worked just fine, as you can see.



I started out just taking off a few thou, but got braver as it went, and eventually found that I could take off .010" at a time without chatter.  This will be fine for the top plate, all it gets is a few holes and a groove for the top of the displacer cylinder to fit in.  The bottom disc however, gets hollowed out a bit to thin down the bottom surface for faster heat transfer.  For that one I'll probably try the double sided tape method.

[Bezalel]

The flywheel hub was made from a chunk of an aluminum grounding rod of some sort found by a dumpster diving friend.  The material is very odd, much lighter than you would expect for the size, and the surface has a kind of powdery grainy look.  It almost looks like it has been anodized or sandblasted or something.  I'm nor sure it's actually aluminum, but I don't know what else it would be.  The rods are a little over 1" in diameter and about 22" long.  There is a 1/8" dia steel core down the center, which I presume was to provide a hard tip for pounding into the ground.  There was also a copper connector on the top of each, which my friend cut off to keep for his copper scrap pile.  You can sort of see the grainy surface finish in the photo.  Compare that to the support posts to the right, which are 6061 aluminum.

Hi Arthur


Your description is identical to what one would expect to see for a magnesium sacrificial anode out of a solar hot water storage chamber.


there are two ways to confirm it ( well it is only one if you actually intend to use the material for some thing else )


1. scratch a piece down to clean bare metal add a few drops of white table vinegar, if the vinegar bubbles up it is indeed magnesium.
2. this one is not recommended but fun for confirmation, if you have a few spares.
Ignite the end of the bar in a very hot timber fire or furnace or blowtorch. once alight you have a hand held torch good for about 10 to 15 minutes with the brightness about the same as a 3000 Watt light bulb.   


This is an out doors activity in the clear absence of kids, pets and spouse.

[Arthur Dent]

   You might well be right about the magnesium.   Every time I pick up one of those rods that little voice in the back of my head says "this isn't aluminum".  I just never followed it through.
I suppose that is the danger of using "mystery metals". 
If I get the chance I'll test a sample of it after work tonight.

[Arthur Dent]

I have been thinking about the glass for the power cylinder.  Several months ago I read a long thread somewhere discussing the suitability of various types of test tubes and syringes for this kind of use, though of course I can't find it now.  There are lots of online suppliers for such things, but being a creature of habit I of course first turn to:
Amazon.com 
Wow, what a variety of choices.  16 X 150mm rimed Pyrex test tubes look good.   That would give me a lot of material to play with, and hopefully out of a dozen or so I'll end up with a piece round enough to make a good cylinder.   So now while waiting for those to arrive I have plenty of other work to do...

[rleete]

Are you also known as "Rocketcaver" on that other forum?

[rleete]

Also, for test tubes that are the right size for this (as well as most of Jan Ridders engines), try Edmund's Scientific.  Buy several, as you will find some aren't round, some are tapered, etc.  Of course the ones that are perfect you will break while cutting, so you need a selection.  I bought about 6 of each size, and got enough usable to make several engines.

[Arthur Dent]

Yes sir, that's me.  (I thought you might recognize some of my photos)
I haven't ordered the test tubes yet, but plan to in the next day or so.  Have been looking at the Corning Pyrex Vista series. 
I hadn't thought of Edmund's, will take a look.  Thanks!

[Arthur Dent]

Bezalel, you were right.  It's magnesium.

[Dan Rowe]

Arthur,
One of the demonstrations at the fire fight training I had was to take a double handful of oily magnesium swarf and set it on fire in an open field. We used a  three way nozzle and hit it with fog first and it really flared up. Then we switched to high pressure and the swarf became a 20 foot ball of flame. Wow that was impressive.

The machine shop was only too happy to donate the swarf to the school as it is a real hazard.

Dan

[Arthur Dent]

Thanks for the warning.   
I am well aware of what magnesium can do, I used to make rocket engines with magnesium powder and... other stuff.  I just never had a big solid chunk of it before.
Rest assured that I don't plan to machine any more parts out of this stuff.  I'm not sure what I will do with it, but it has already been removed from my metal working area.

[Arthur Dent]

My diamond coated glass cutting discs and test tubes arrived a few days ago, so I logged some more shop time.
Here you see me set up to cut a test tube.  Most folks pad the test tube with paper or tape or something to keep the chuck jaws from crushing them, but I found that un-necessary.  A light touch on the chuck key and the tube was securely anchored.
 
Mr "out of focus" decided to visit for a while, sorry about that.   

The lathe is set to run in reverse, so the the tube and cutting discs rotate in opposite directions.  I'm not certain that this is really necessary, but it made me feel better.  Also, lathe and Dremel running at full speed.  A few drops of 3 in One oil every now and then, plus a very light touch on the hand wheel, and...

This particular tube was a culture tube that I happened to have a whole bunch of.  The culture media had expired and the lab was going to pitch them, so I got permission to "liberate" them from the waste bin.  I was just using this for practice before cutting up a Pyrex tube, but the culture tube turned out to be quite a bit more "in round" than the Pyrex tubes I got, so I'll try it in the engine first.  In this low temp engine the heat tolerance won't matter, so the lime glass should be fine.  I got a few different sizes of Pyrex tubes, I'll save them for use in my Ridders high temp "Stirling Bas" when I get around to building it.  Some of them just happen to be the right size.   
I turned down a slug of delrin to see how good a seal I could get with this tube, and the results are encouraging.  With my thumb closing one end of the tube the slug barely moves down the tube... when I release my thumb it falls through freely.  I'm actually tempted to use the delrin for the power piston.  But I have the graphite, so I HAVE to use it, right?
Back to the top plate, I thought I would be clever (or lazy) and use a parting tool to make the groove for the displacer cylinder to fit into, but because of the way the parting tool holder is made, there is no way to mount it so that I could crank it into the proper position for the groove.  So, I ground up a quick tool to do the groove. 

You can see that it worked ok, but after I got in a few thou in it started squalling like a scalded cat (no actual cats were harmed in the process).  Yes, I was wearing hearing protection, and it's a relativity shallow groove, so I just kept going until I reached spec depth.  But I would be interested to know how to properly grind a tool for this purpose.  I did search first and didn't find anything, so just did what I thought would work.  It worked fine, other than the squalling.  I'm sure it was caused at least partly by the outside wall of the groove rubbing on the side of the tool, I can see the side of the tool is rubbed dull by this action.  I thought I had allowed for that while grinding it, obviously I was incorrect.

[b.lindsey]

Nice to see more progress on this Arthur...i am following along with much interest.

Bill

[zeeprogrammer]

Nicely done Arthur.

Would it have been helpful to place paper towels or a rag underneath to catch the debris? I know this is done when sanding on the lathe but I don't know about glass.

[steamer]

Try

Slow down the speed
Increase the feed
Decrease the top rake of the tool
Provide just enough front clearance and no more
Make sure your tool has enough side clearance...consistant with strength

ELIMINATE ANY AND ALL TOOL OVERHANG WHERE EVER POSSIBLE!

Dave

[Arthur Dent]

Zee, maybe some paper towels would have been a good idea.  There really wasn't much mess though.

Steamer, I probably made the undercut a bit too steep.  You can see the chatter marks in the bottom of the groove in the photo.  I was focused on outer the side rubbing.  If I make another one of these I'll play with that.  Thanks for the advice.

[Arthur Dent]

Sorry for the long hiatus.  I found out I had prostate cancer and have been dealing with that.  A date with a good surgeon seems to have me fixed up, so far everything is going fine. 
Watch your PSA fellows, and make friends with a good urologist.
It's amazing the "stuff" that can get piled up in the workshop when it's not being used regularly.  I'm going to have to mount another cleanup campaign before long so I can get back to the machine work.  I really want to get this little engine running by Christmas.

[b.lindsey]

Arthur,

Glad to hear that things seem to be going well with the prostate issue. And you are right as to the PSA test. Though it is being debated in the medical circles lately, it is a simple blood test, and should be done annually if only as a precaution or early warning test.  Will look forward to your return to this interesting project too!!

Bill