work on tin can engine

[Ante]

Hello people!

First, I apologize for any mistakes made ​​in the English grammar in writing in the future :)
I am not new member, but my old account is erased...

So.. I am trying to make stirling engine with enough power to move something (boat)
After lots of attempts I am changing direction of building first I am trying to make good piston-cylinder and good displacer rod bushing, to remove all possible friction.
-for piston-cylinder I used copper pipe and epoxy putty, works very well (small friction and very good sealing).
-for displacer rod bushing my plan was to use brass bolt (M5) and for displacer rod bicycle spoke (diameter 2mm)
i don't have lathe so i drill brass bolt on drill press. First i drill clamped wood on table with 5mm drill bit to get center,and I put brass bolt in hole. Because i can drill continuously on first pass, because small drill bit brakes, so I must every 3-4 mm pull out drill bit and clean it. This is reason why I can not get smooth hole. I try with several passes using drill bit 1.8mm and after that fine drilling with 2mm, but always i have great increase in friction when small radial force on spoke is applied .

Thank you in advance to all advices and ideas .

Best regards
Ante

[theropod2]

Hello people!

First, I apologize for any mistakes made ​​in the English grammar in writing in the future :)

No worries on the English use. We'll either get your thinking or ask questions.

I am not new member, but my old account is erased...

Happened to me too. Just hang in there.

So.. I am trying to make stirling engine with enough power to move something (boat)

How big?

After lots of attempts I am changing direction of building first I am trying to make good piston-cylinder and good displacer rod bushing, to remove all possible friction.
-for piston-cylinder I used copper pipe and epoxy putty, works very well (small friction and very good sealing).

Sounds like a good plan. The only thing I worry about with these epoxy pistons is breaking down when heated, but that's my worry as a lot of folks seem to make this system work.

-for displacer rod bushing my plan was to use brass bolt (M5) and for displacer rod bicycle spoke (diameter 2mm)
i don't have lathe so i drill brass bolt on drill press. First i drill clamped wood on table with 5mm drill bit to get center,and I put brass bolt in hole.

May I suggest you drill the brass directly and clamp the brass bolt in place by wrapping it in a piece of leather.

Because i can drill continuously on first pass, because small drill bit brakes, so I must every 3-4 mm pull out drill bit and clean it.

Bits for drilling have different spiral patterns for different materials. You may be using a bit made for wood. Those chips of brass may be resulting from working with the RPM of the press too high. Slow it down as slow as it will go and see if that helps.

This is reason why I can not get smooth hole.

I think you may be seeing the result of too fast a feed, the wrong type bit and not keeping the brass bolt as steady as it needs to be. If that bolt moves just a tiny amount the hole will not be true. Also there are these bits called reamers that are deadly accurate. Get the hole as close as possible undersized and then use a reamer. These make some sweet and smooth holes.

I try with several passes using drill bit 1.8mm and after that fine drilling with 2mm, but always i have great increase in friction when small radial force on spoke is applied .

There should be no radial forces applied at all. The displacer rod needs to travel in as straight a line up and down as possible. Where the displacer rod is connected to the crank there needs to be two bearings. One bearing goes on the crank throw pin and deals with the rotational motion of the connecting rod. The other bearing goes on the displacer rod and allows for a flex point between the connecting rod from the crank throw and the upper/outside end of the displacer rod. If there is any binding at all between these points your engine won't run. Some folks just use a loose fitting loop of the same material as the displacer rod that fits inside. I did this with my first engine, and it works, but a bearing is better.

Here's what I mean (sorry but quick and crude).

Displacer two bearing drawing

displacerloop.jpg (27.92 KiB) Viewed 8139 times

Thank you in advance to all advices and ideas .

Best regards
Ante

You are welcome Ante. Let's get you a running engine ASAP!

R

[Ian S C]

For drilling the way you do, make the hole in the wood a bit smaller, and screw the bolt into the wood, then drill, but only about 1 mm at a time, use a high speed, your drill press won't go too fast, 2500 rpm is the recomended speed for brass. Some brass can be a bit tricky to drill. After drilling, with any luck the hole will be too tight, we can fix that with a tool makers reamer, take 50 or so mm of bike spoke, same as you are going to use, at one end grind / file a bit at about 20*flat, the flat should be about 5 mm long, don't take off too much of the burr left by filing, leave just a little bit, and that will be the clearance. You can put this in your drill press, cut the speed to slowest, put a drop of oil down the hole, now go down the hole with the reamer. For one hole in brass there is no need to harden a reamer like this. Ian S C

[Ante]

How big?

model boat about 0.5 meters
because of some technical problems with solidworks I uploaded only in avi format, some "artistic impression" of boat.
http://img824.imageshack.us/img824/8537/xoj.mp4

I think you may be seeing the result of too fast a feed, the wrong type bit and not keeping the brass bolt as steady as it needs to be. If that bolt moves just a tiny amount the hole will not be true. Also there are these bits called reamers that are deadly accurate. Get the hole as close as possible undersized and then use a reamer. These make some sweet and smooth holes.

I feed very slow, but if i do not clean drill bit it brakes (i broke about 3-4 brass bolts and drill bits). I know for reamers but they are very expensive and hard to find so small, but as I can see Ian S C solved the problem.

There should be no radial forces applied at all

Radial force always exist, beam end crankshaft make path of circle, so connecting rod is parallel with motion only in two points in cycle, but if angles are small radial forces are also small, don't get me wrong

Thank you very much for advices

For drilling the way you do, make the hole in the wood a bit smaller, and screw the bolt into the wood, then drill, but only about 1 mm at a time, use a high speed, your drill press won't go too fast, 2500 rpm is the recomended speed for brass. Some brass can be a bit tricky to drill. After drilling, with any luck the hole will be too tight, we can fix that with a tool makers reamer, take 50 or so mm of bike spoke, same as you are going to use, at one end grind / file a bit at about 20*flat, the flat should be about 5 mm long, don't take off too much of the burr left by filing, leave just a little bit, and that will be the clearance. You can put this in your drill press, cut the speed to slowest, put a drop of oil down the hole, now go down the hole with the reamer. For one hole in brass there is no need to harden a reamer like this. Ian S C

I tried to taper bolt in wood but it showed that the better way to center bolt is to put nut on other side of plank (I have hole on center of table on drill press)
I am afraid that high speed will brake drill bit, I broke 4-5 drill bits till now. Yes, brass is tricky!
I am not sure did I understand way to make tool makers reamer so I attached picture, please confirm it is that right way.

I forgot to ask two more questions:
what is recommended length off bushing
and Ian you think that I drill immediately with drill bit diameter 2mm or smaller?


Thank you in advance to all advices and ideas .

Ante

[theropod2]

Radial force always exist, beam end crankshaft make path of circle, so connecting rod is parallel with motion only in two points in cycle, but if angles are small radial forces are also small, don't get me wrong

snip...

Thank you in advance to all advices and ideas .

Ante

Perhaps my crude drawing isn't clear, but the two bearings eliminates these side loading issues. The beam end has an arc range of motion. This arc imparts a side load at the middle of the up and down motion that one bearing will not eliminate. I think if you look at the image gallery here you will see every single walking beam engine has some method to deal with this.

Here is an image of Boyd's engine. Note the little bright spot between the displacer end of the beam and the displacer rod.


Here is my engine, and note that there is a loop of brazing rod at the same place.


I don't think one of these engines will ever run without this second pivot.

R

[theropod2]

Ante,

A better way for me to explain this is to examine a conventional internal combustion engine and how the crank, connecting rod and piston is arranged.

The crank throw has a bearing on that end to deal with the rotational movement of the off center throw of the connecting rod.

The connecting rod also has a bearing at the wrist pin of the piston.

If the wrist pin connection was not allowed to pivot the piston would bind in the cylinder as a result of the angle change between the crank throw and the cylinder alignment. This is exactly what's going on with the displacer rod. The displacer rod must travel in a straight line within the gland/rod slide just like the internal combustion engine piston/cylinder arrangement. The only way to get that job done is to build in a pivot point that will not interfere with the rod travel limits.

Hopefully this is more clear than my other efforts.

R

[Ian S C]

There is a sketch of a tool makers reamer on my pic gallery, have not worked out how to get it on here yet. Ian S C

[jimlarsen]

These things can be hard to figure out all by yourself. It is always better to start with plans and instructions that have a proven track record for success. Have you tried building the Walking Beam engine from Boyd's website?

[Ante]

@theropod2
I understand you everything, and I am familiar with lots of types of mechanical motions, and I did not want to philosophize :)
I wanted to say ... A picture is worth off a thousand words so here it is, picture: http://img855.imageshack.us/img855/2702/drawing1.png , I deliberately wrote short beam..
I hope that you are now understand what I want to say about forces in links.
And I agree with you totally.

The easiest way to totally remove radial force from bushing and any sliding surfaces is to use James Watt parallel motion link (http://en.wikipedia.org/wiki/Watt%27s_linkage and http://www.animatedengines.com/watt.shtml), but it is complicated. Compromise is to use beam , or ross yoke and reduce side loadings - reduce friction...

theropod2 thank you very much on your efforts

@Ian SC
Thank you, everything clear! you will be informed how bushing works
P.S. in meanwhile i made "polishing machine"for bushing but without great influence on bushing.


@ jimlarsen
yes of course that I will go step by step with use all of gathered knowledge from internet.

Thank you all
Ante

[Ian S C]

Anti, your diagram is very nearly another useful tool called a D bit. the flat should be on half diameter, or maybe .002" more, there is a little to do with shapeing the front end. These are best made of silver steel/ drill rod, and hardened and tempered. Ian S C

[Ante]

I drilled brass bolt with advices of Ian SC

New detail is tapered bot , I used it to make thread in wood with drill press, so I have nice centered bolt for drilling

here few pictures




brass bolt is still tight for bike spoke but I need to repeat drilling with sharpened tool maker reamer because it is not tempered...

Ante

[Ian S C]

Ante, just file the flat on the reamer, it will form a burr on the edge, just leave that and use the reamer by hand the brass is softer than the steel. Ian S C

[Ante]

Ian I was cutting with reamer 2/10 mm of diameter (drill 1.8mm reamer 2mm)is it to much for reamer it was damaged after first drilling..
and tight hole is (I think) because of high temperature, so brass was little widen.

I could not test hole yesterday because I did not have new bike spoke. So I need to repeat drilling

Ante

[Ian S C]

How tight is the bike spoke in a hole drilled with a 2 mm drill? If the 2 mm hole is tight put the ream through that.Maybe a 1.5 mm drill as a pilot before going through with the 2 mm one. Did you put the reamer through by hand, don't use power on the drill press, but after the drill goes through change the drill in the chuck without moving the bolt, then wind the chuck around by hand as you slowly feed the reamer into the work. IanSC

[Ante]

I did not drill with drill bit 2mm, I drilled with drill bit 1.8mm and after that with bike spoke reamer 2mm on drill press on small speed, heat was enormous so that lubrication oil was instantly evaporated and reamer was damaged.
But last night I sharpened reamer and polish new bike spoke and after little finishing bike spoke slides perfectly.

Next drilling will be with drill bit 2mm and reamer.

Thank you very much on advices.