Duplex Vacuum, (Heinrici type stirling)

[doc1955]

Nice job Dean!
I'll have to remember the wet paper towel trick. I've always used a wad of modelers clay in the end to stop the ringing. That cylinder looks NICE!

 

[b.lindsey]

Its coming together nicely Dean...its getting to that exciting point ...gonna be a beauty too. As always, an excellent post as well.

Bill

 

[4156df]

Dean,
Very informative post. Nicely done on the liner.
Dennis

 

[cfellows]

Nice job on the cylinder, Dean. How well does that inside micrometer work for you?

Chuck

 

[Deanofid]

Thanks again for looking in, gents. Much appreciated.

Chuck, I've had that inside mic for a little while now, and it seems to do what it's supposed to.
It's from Enco, and was a cheapy (for its type). Kind of rough on the screw, and the spindle lock is
fiddly. The spindle turns backward. The tic marks and numerals are not engraved on.
I have to say it's handy, and now I want a good one.


Now, on to stuff.
This is graphite piston day. It's a simple turning piece, but graphite is a bit soft, compared to metal, and
it's nice if you have a collet to hold it so you don't deform it with the pressure of a three jaw chuck.

This post deals mostly with making an easy split collet to hold the graphite piece, along with a few
general graphite tips. The subject of shop made split collets comes up here now and then, so, might as
well show it being done for any interested builders.

To start on the collet, find a piece of round stock that is somewhat larger in diameter than your work
piece. In this case, my piece of graphite is 1" diameter, so I dug up a piece of aluminum from the
left-overs box that had a diameter of about 1.25" on one end.

The piece is trued up and turned down to 1.20" diameter on the end you see here. The big end will be
cut off in a minute. The diameter of the working end is just a figure pulled out of a hat. The walls of the
piece just need to be thick enough so the jaws of the chuck won't be able to deform them and hurt the
piece that the collet will be holding.

Now the piece is turned end for end, and the larger diameter is cut off. The piece is approximately the
length of the jaws on the chuck. Nothing critical. Just in the ball park. Then the ID is bored for a nice
close fit with the work piece. For this one, .001" over the size of my piece of graphite.

While the piece is still in the chuck, mark it at a point on it's periphery that falls between two jaws, and
put a mark on the chuck body at the same location. If your chuck has a name plate, like the one on
my fortune cookie chuck, just use that as your mark on the chuck.
When you remove and replace the collet in the chuck, put it back in the same place each time.

Now take the collet to the mill, and slit it on that mark just made. The slit can be quite thin. I'm using
a .032" saw here. A hack saw would do fine, too.
After the slit is cut, use a triangle file to remove the burr on the inside of the piece where it was slit.

Now the work piece can be put in the split collet and turned down to the size needed for my piston.

Graphite is filthy stuff, but very easy to cut. When I'm cutting it, I put the shop vac nozzle right over
the tool tip. Saves quite a bit of mess, but it's still going to get every where. Just not as much.

Use a sharp HSS tool with a small radius on the tip. If you don't put the radius on it, the sharp point
can dig in and make little grooves in your work piece.

When I have the piece so it will barely go into the bore of the cylinder, it gets finished up with paper.
The last little bit that needs to come off for it to be a proper fit ends up on the paper, and it burnishes
the surface at the same time. You can take off a tenth fairly quickly using paper.

If the paper gets loaded up, get another piece.

That's my one piece for the day.

Thanks for checking it out.

Dean

 

[Cedge]

Lookin GOOD!! Now I'm the one watching and learning....fascinating so far.

Steve

 

[Troutsqueezer]

I'm impressed when so much work goes into making one piece. I know it's a fairly common thing in this hobby and sooner or later I'll run into a situation where I need to do similar preparation. I hope I can summon enough patience and fortitude when the need arises.

Very nice work Dean, and educational too.

-Trout

 

[ksouers]

Nice tutorial on the graphite, Dean. What RPM do you use?

Actually the subject of graphite came up in a meeting tonight, and how the dust can take out a motor on the lathe. Have you had any problems with it?

 

[Deanofid]

Thanks guys!

Kevin, I turned that piece about 1000 rpm, which is as fast as that lathe goes the way I have the pulleys set up. Faster would be better, I think.
I've never had problems with graphite in the motor(s) on my lathes, but I've heard similar to what you mention here. I don't cut the stuff every day. I suppose if you were going to do it much, might want to figure out some kind of vented setup for the air intake on the motor.

Aren't DC motor brushes make of some graphite compound? Wonder what keeps them going?

Dean

 

[arnoldb]

Very good going Dean :bow: - You're on a roll again.

Kind regards, Arnold

 

[zeeprogrammer]

Great post Dean.

Why graphite? What makes it more suitable than some other material?

I was wondering too why it was important to mark the collet prior to splitting it and making sure the collet was placed back in the same place. Does it make a significant difference in keeping it true? Or is it just important if you are going to remove/replace once cutting (on the part being held) begins?

Thanks.

 

[SAM in LA]

Dean,

Thanks for the education.

I needed a collet like yours the other day.

I'll have to remember it.

Good idea about having the vacuum cleaner near the tool bit when cutting graphite.

I am awaiting the next lesson.

Thanks,

SAM

 

[kcmillin]

Great Post Dean, I am learning allot. The paper trick on the graphite is a good one. I used 1200 grit and it was too much. I will definitely use paper next time.

I have the same question as Zee. How well does marking the Collet keep it true?

Kel

 

[mklotz]

Very nice description, Dean.

I would add only two points...

Make the collet in the shape of a top hat. The "brim" will prevent the collet from pushing back in the chuck. Save these collets when you make them. You'll use them again and again.

If you need to be a bit more aggressive "sanding" your graphite workpiece, use paper cut from a brown paper grocery bag. Being a cheaper grade of paper, it's coarser and cuts more quickly.

 

[b.lindsey]

When turning graphite, I usually put the nozzle of the shop-vac near the cut so the fine dust doesn't collect on the ways or het pulled into the motor, more precautionary but it does keep things cleaner for sure.

Coming right along Dean...how many parts to go??

Bill

 

[Deanofid]

Arnold, Zee, Sam, Kel, Marv, Bill, thanks much guys.

Why graphite? What makes it more suitable than some other material?

Zee, this engine has to be a pretty low friction job to run at all. Graphite serves three purposes in that regard. It's one of the best self lubricating substances us mortal hobby types can get our hands on. Really slick, and stays that way. It's thermal stability is a plus. It won't expand enough from heat to cause friction in the bore. It's really light for it's exterior dimension, meaning less mass to cause friction on the bearings and such.

I was wondering too why it was important to mark the collet prior to splitting it and making sure the collet was placed back in the same place. Does it make a significant difference in keeping it true? Or is it just important if you are going to remove/replace once cutting (on the part being held) begins?

Thanks.

Zee and Kel;
When the collet is made to size in the chuck, you're getting rid of any runout inherent in the chuck scroll and jaws, since it's bored in place. Putting it back in the same orientation each time puts it back where it was when it was cut. The outside of the thing may have some runout because it was being held by jaws that for sure had runout. I put it back in the same place to keep its bore on centerline.

It's not perfect, but if you have a three jaw with .003" runout, (who doesn't?), and you bore the collet in place and put it back the same way, it will do better than your chuck.

Marv, I like the "top hat" idea. I have made some in kind of a reverse way to that, cutting a stepped recess inside to act as a depth stop. The collet has to be put all the way into the jaws, against the chuck face. The top hat thing would keep it out on the end of the jaws. That's a handy tip, to me!

Bill, 18 parts to go!



I got to do the piston wrist and displacer shaft bushing today. Both of these pieces will become an
integral part of the piston when they're done.
Quite a few pics, so I made some of them a little smaller so the page won't take too long to load.

The bushing is a simple turning with a hole reamed through its center.
In the shot above, I once again used the piece as its own support while step cutting the
length of the bushing end that will go through the hole in the middle of the piston.

This is the piece just off the lathe. The long slender part has been left over-long. I think the piston
needs to be finished down just a bit more than it is, and this will give me something to hold on to
once it's mounted into the piston.

The other part for the piston is the wrist, being parted off here.

The bushing is drilled and counter bored with a shop made cutter.

The wrist is milled to take the end of the con-rods. The end mill is 1/16" diameter, spindle speed is
5000 rpm, and down feed is .020 per pass. I use canned air to puff the chips out of the cut so they
don't build up and break the end mill.

The last thing for the wrist is to drill the cross hole for the wrist pins.

The busing is put through the piston and set into its recess, then the previously drilled holes are
used as a guide for hand drilling the holes through the piston.

This is how it all goes together. The wrist (on the right) goes completely inside the piston.
I know this piston looks rough as a cob, but it is really, really smoooth. And slikery.

The wrist is pinned to the con-rod.

Then it's all screwed together. This shows how the displacer shaft goes through the center of
the piston.

Checking things for fit.

Here you can see the assembly from the top end. The piston is just peeking above the cylinder liner.

The group shot, and that's it for another day.

Thanks again for looking in.

Dean

 

[Twmaster]

Now that is really coming together. I wanna be just like Dean IF I grow up!

 

[kcmillin]

You have a nice pile of parts there Dean. Not much left to make it seems.

Kel

 

[zeeprogrammer]

Thanks for the answers Dean.
Looking good!

 

[ksouers]

I like the way the piston is assembled. Both of them, now that I think about it.

How much clearance is there between the displacer piston and cylinder?