A quickie Turbine

[Bogstandard]

I started on this one today, I couldn't find any suitable plans for the type I wanted to make so I decided to make it up as I go along and hope it all works out right. Again it is a junk engine made from bits and pieces about the workshop.
The first pic shows the bits and bobs I'm going to use. A bit of stainless rod from an old printer, a couple of flanged bearings from the same source, some 3/8" bullet proof macrolon that I've had for years (turbines have a bad habit of coming apart so I thought I would use this as a bit of a safety factor) and a chunk of ali plate. Also I had a 'ring' of brass that was no use for anything so the smaller bit of brass is going to be persuaded into the centre by use of a toggle press and that will give me the material for the rotor itself.

I forgot to take pictures of the lathe work on the rotor (a friend called round and disturbed me, and I just forgot). But I will mention that it has to be very well secured to the spindle by force fit, and the turning has to be very fine to attempt to keep some sort of balance, no wobbly bits here, otherwise you will really regret it.
This shot is putting in one of the twenty 'pockets', again it has to be very critically machined to keep balance. I used my DRO to make sure every pocket was the same. After this machining it was back onto the lathe and cleaned up again.

Here we have the finished rotor, I have spun it up on air to about 20,000 rpm and seems to be very well balanced, it sounds just like a jet engine at that speed, had the neighbours looking over the fence to see what it was.
The bits in the background are what I hope to drive with this beast, one is a fantastic swiss made precision ballraced 12 volt motor that hopefully will make a good generator to light a few bulbs, and the square black lump is a variable gearbox that gives output from 1 to 200 to one just by turning a little knob. The generator will be driven when in forwards motion and the gearbox when it is running slightly slower in reverse. The way hopefully I am going to do this is with one way drive bearings ( these are on the rotor shafts), I just hope that they can withstand the speed.

Tomorrow I hope to get the outer casing made, complete with end covers, then if I can get the nozzles in I should be able to get it on the tacho to see just what it can get up to. The only problem as I see it is my digital tacho only goes up to 29k.

John

 

[rake60]

It's looking like a good design me me John.
ed miles is our resident bearing expert, but I do have 10 years experience
in that field as well. The bearings could be your limiting factor.
A bearing spinning at supersonic speeds will fail in a very graphic way.
I have seen injuries caused by the rolling elements breaking through the
outer races of bearings that were being cleaned my a mechanic blowing
them out with an air nozzle and allowing the outer race to spin.
It cost him his left thumb and left eye.

I'm being over protective again....
Just be careful. If it doesn't look right, shut er down!

 

[Bogstandard]

Hi Rick,
Thanks for your concerns.
I looked at this problem with the bearings, hence the makrolon 'shield'.
I didn't fancy forking out for high speed ceramic bearings, so I will go with these and limit the output by restricting the air pressure.
I don't even know at the moment whether it will have enough power to turn over with the motor and gearbox attached. Maybe I will have to restrict it to just one. I should know later today.

John

 

[ed miles]

John, the accident injury from spinning a bearing with air is because it was not mounted in a housing that would hold the thing together. By the looks of the pictures, the bearing you are using is small. If you could give me the number, I can give you a maximum speed range in grease. We have bearings with steel balls, 85mm shaft at 10,000 rpm with grease lubrication in CNC milling machine spindles. Above that they use oil air systems for lubrication and cooling.

Ed

 

[Bogstandard]

Hi Ed,
Not much info I am afraid.
The smaller race I considered was a double SS shielded flanged. The only markings are NMB (on the shield). 5mm bore, 4mm wide, 13mm main size and 15mm flange size, the flange is 1mm thick.
I have decided to go with a 6mm bore by 5mm wide, all the other is the same. As far as I know these are a German made bearing designed for use in hard disc drives, and I've got hundreds of 'em.
The smaller one was made for use in commercial grade dot matrix printers.
These bearings may be a special produced for a certain job. No packaging markings either, they come in a vacuum packed bandolier designed for production runs.
Here is one with the shield removed, 8 balls held in place by what looks like a SS cage. Sorry about the quality of the pic.

John

 

[ed miles]

John, the bearing number from Koyo is F695-ZZ and from NSK it is the same Bore 5mm, O.D. 13mm, Width 4mm and Flange diameter 15mm with two shields. Maximum speed with grease is 43,000 rpm. Your only possible problem will be the age of the bearings. The shelf life of the grease in sealed or shielded bearings is 5 years. Try rolling the bearing on the bench top holding the inner ring and loosen the grease up a bit before you start to run the turbine.

Regards Ed

 

[tattoomike68]

I borrowed a rotary table from my brother in law and am building one too. Mine will be ugly and scary and have plain brass bushings.

I plan on running it outside to test it and let it rap out full blast, if it melts down or dies then I will fix it. 8)

 

[Bogstandard]

Ed,
Many thanks for the info, it has put my mind at rest. I was contemplating limiting it to about 50,000 anyway, so it looks like it will be a little less, so I will take it just a bit further when my tacho stops reading at 29K.
Supposedly this design of pocket can get up to about 350k rpm, god knows what bearings it would use.

Mike,
Be careful, and don't stand too close, in fact as far away as possible.
But I can see you having problems with using a plain bush, even well greased the friction alone will most probably cause it to seize up with the heat generated. I hope you prove me wrong.

John

 

[ed miles]

John, ball bearings would never stand up to 350,000 rpm even if you had ABEC9 bearings with ceramic balls and rings at a price only NASA could afford. Normally the bearings for that kind of speed are Hydro Static bearings which are plain bushings with oil feed under preasure so the shaft never contacts the bushing. That type of lubrication is very expensive and requires very accurate alignment of the bearings to the shaft so you do not get edge loading of the bushing bores. If you stay down aroung 30,000 rpm you should not have any problems, but please keep a keen ear for sound level changes that could mean a bearing problem in the making.

Ed

 

[Bogstandard]

Don't you just hate it when relatives call unannounced. Dragged out of the workshop while still halfway thru a job, go and get a good scrubdown and sit there for hours making out you are enjoying yourself. Anyway, that all slowed me down today so I didn't get as far as I wanted to, but here is the latest update for those that are interested.
Just to give you a bit of info on the major parts.The rotor is 60mm diameter and 6.5mm thick at the bearing journals and then reduced to 6mm outwards, the pockets are 5.5mm wide and are spaced at 18 degrees apart, a total of 20 pockets. The clearance around the rotor is 0.5mm (the hole it fits into is 61mm diam). It uses a 6mm force fit shaft running in two flanged stainless sealed bearings. The nozzle is a step down from 2.5mm, thru 2mm to final size of 1.5mm and is directed tangentially to hit the pocket where the vertical face hits the horizontal. The exhaust ports are 5.5mm diameter and tangential to the rotor rotation and enter the 'cylinder' at 0, 10 and 20 degrees. It seems a bit long winded but this is basically all the information you need if you want to build one.

Now this is what I have been up to today.
The first thing done was to mount the casing plate into the four jaw and bore the 61mm hole. I placed a pair of thin parallels at the back of the plate while setting up to give me clearance to bore thru without hitting the jaws, the parallels were removed before turning on.

This next shot is the same boring process but 'stopped' by the flash

After the hole was bored and before doing anything else I skimmed across the face, this gave me a datum face that is truly square to the bored hole, After this it was flipped over and skimmed down until the plate was 12mm thick.

I didn't take any pictures of the next bit, but all it consisted of was friction turning two pieces of makrolon to a disc shape, drilling a centre hole of 6.5mm. Boring out a recess to fit the bearings and forming a spigot on the face to a very good fit in the bore and to a depth to allow no end float of the rotor between the bearings ( this required a bit of slick maths, but the dog came to the rescue).
Here are the bits so far. The white on the back of the makrolon discs is just tape to protect the surface finish. The nozzle length is that it sits just not quite reaching the periphery of the main chamber. You can see the tangential exhaust ports and the recess on the bottom of the plate that they connect to and allow the spent air to escape.
All that is required now for a working turbine is to drill and mount the end plates.
There are no drawings for this as I made it up as I went along but if anyone wants to make one just ask your questions.

I hope to get a vid tomorrow and scare the neighbours to death in the process.

John

 

[Bogstandard]

Here is a pic of the finished motor, with a little bling added.

And here is a short vid to show that it runs.

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Job done!

John

 

[rake60]

That one is a little too scary for me John, but you certainly did a
beautiful job on it!

Excellent craftsmanship as always!

Rick

 

[Bogstandard]

Hi Rick,
I doubt if ever it will run at that speed again, I have decided to load it with a generator to slow it down.
By the way, for the video I loaded the bearings to make it slow down a lot quicker, it normally takes about 3 minutes to run down from a fairly high speed run, otherwise it would have taken about 10 mins to get the three free wheeling runs done.
Here in the UK they put small turbines on the model steam locos to run the lights from, they build on a small stator and rotor onto the end, so to me it isn't scary because I've seen them used a lot with no problems.

John

 

[Bogstandard]

Just a reflect to the quickie turbine.
Finished it off today and it has changed a little since I first conceived and made it.

The end with no power takeoff has had a solid endplate made and a spinner has been fitted to the protruding shaft, this can be removed if I want to take another feed off the turbine.
The other end is now coupled through a very light grip silicone coupling to a high precision swiss made ballraced motor to act as a generator.
The output from this is a constant 17volts, so five high brightness LED's works out perfectly for the voltage produced.
All in all a nice educational package.

<object> <param> </param> <embed src="http://www.youtube.com/v/KW6V7JWbQwk" type="application/x-shockwave-flash" width="425" height="350"> </embed> </object>

John

 

[wareagle]

That is cool! I love the sound!! And really great craftsmanship!!

I really wished I had the guts to make one, but I am afraid that I would have that thing exploding into a million pieces and be picking metal toothpicks out of me for the next twenty years! :shock:

 

[Bogstandard]

Hi Wareagle,
If you read the full post on the build, there were a fair amount of safety issues involved, with reference to the bearing speed and the correct material for the transparent viewing window, I made light hearted fun about it, but with something like this, safety is paramount. Normally the rotor would be enclosed in a full metal casing just in case anything goes wrong. But I needed it viewable.
This one, now that it is loaded with a generator, on 30psi, will limit itself to around 34-35k rpm. Unloaded it will run to destruction.
If you are not happy doing something like this, don't do it.

John

 

[tattoomike68]

I am still working on one and mine is very simple, ugly and I intend on running it till it comes unglued and will video it running.

Im going to hit it with 175 psi and let it wind out and see what happens.

I am making the rotor a 24 tooth gear looking deal in .125" aluminum with a .250 hub running on an armature thats .125" running on brass bushings with a good .002" slop.

I want to see it run 100,000 rpm but if it dont make it I dont care. I hope mine blows up so I can see the point of failure.

Its all fun for me.

 

[Bogstandard]

Hi Mike,
At that sort of pressure, in an enclosed turbine you might have a bit of trouble getting rid of the spent volume of air. The way I did mine with a tangential exhaust, it sort of 'scrapes' the spent air off the rotor.
If you are doing the 'sawtooth' type of rotor maybe a series of holes or a large slot at the bottom of the side plates on both sides might help, following and in line with the radius of the sawteeth, otherwise the rotor just might stall and refuse to move at any sort of speed.

John

 

[tattoomike68]

Hi Mike,
At that sort of pressure, in an enclosed turbine you might have a bit of trouble getting rid of the spent volume of air. The way I did mine with a tangential exhaust, it sort of 'scrapes' the spent air off the rotor.
If you are doing the 'sawtooth' type of rotor maybe a series of holes or a large slot at the bottom of the side plates on both sides might help, following and in line with the radius of the sawteeth, otherwise the rotor just might stall and refuse to move at any sort of speed.

John

Thanks for the tip,I bet thats why my first turbine failed, I think you nailed it, my first was a .375" 6 tooth rotor with a fly wheel made from a dime. it did not run but I was a little too ambitious.

 

[rangerssteamtoys]

I just found this while looking around on the forum, yeah yeah 120 day warning thingy.
I have seen this video on youtube so many times, fascinated by the turbine. Little did I know it was you.

Great video.