The One Man Turbofan

[monty]

Joe,

Yeah, carbide is good for what it's good for.. A lot of people write off HSS as being silly old school stuff. But the cutting action is totally different. Carbide needs a relatively heavy cut to work. It tears and burnishes, while HSS cuts. HSS doesn't leave as good a surface finish because of this-if it's really sharp. But the cutting forces are much lower. I had some really sharp carbide inserts from home, but we didn't have the right holders at work to try it out. It probably would have done the job. That said, HSS is my go to for problem cuts on 4XXX type materials on a manual machine. It's much easier to deal with low speeds, feeds, and cutting forces. Carbide works best on a CNC machine with controlled speeds, feeds, heavy cuts and repeatability. HSS works best on manual machines, one offs, non-hard, non-work hardening, tough materials.

The trick I use to hit the number is: make an oversize cut, measure, then burnish with whatever abrasive I plan to use to the surface finish I want. Then measure again. The difference lets me know how much to leave on the final cut. Then I burnish or hone to final size.

DRO highly recommended!! Measure Thrice....;-)

Monty

[monty]

One more thing....I could have turned a dead center and used a lathe dog, and a dead center in the tailstock....this would have been the best way to get the TIR to the lowest value. The thing is, I didn't have a lathe dog the right size. I would have had to make or order something. I'm impatient and only have a little time before work starts. The holidays make ordering something problematic....

So to any TSK-TSKing old school machinist....I say:

Better is the enemy of good enough!!! 8P

Monty

[monty]

Turned the front spacer/seal today. This grooving tool is pretty handy!

Then I drilled and tapped the pinion gear. If you don't have one of these spring loaded centers for tapping...you NEED one!!

Then I turned down the jam nut and was rewarded with a very satisfying sight!

Now I can measure everything with the DRO and double check all of my CAD models. I got the quotes for the gear machining back, and was pleasantly surprised. I was expecting a ridiculous sum, but it was reasonable. Because of this, I'm probably going to have a pinion made of very high quality material with a + .5 addendum. Should increase the factor of safety for the gear-train to around 2. VERY excited about that.

Family and Christmas activities for a couple days now, but soon back at it to design the castings and forms.

Monty

[dieselguy86]

Hi Monty,

I tried using a lathe dog when i attempted machining my shaft, and found that the weight of it was bending the shaft. Probably wouldnt have noticed with your size shaft, mine is .200”/5.08mm. I like your idea better.

-Joe

[monty]

Dec 20, 2018 22:39:57 GMT -5 dieselguy86 said:

Hi Monty,

I tried using a lathe dog when i attempted machining my shaft, and found that the weight of it was bending the shaft. Probably wouldnt have noticed with your size shaft, mine is .200”/5.08mm. I like your idea better.

-Joe

Joe,

Ha!.....Well, I don't want to do it that way again. I spent the whole morning getting that *&%$#@* thing set up so it ran some what true. The 4 jaw clamping forces kept bending the shaft, and I'd have to whack it back true. Not exactly a precision approach!

I've been thinking about this for the last couple days. I have an idea for the next one. I'm going to machine, or hopefully buy a steel hex bar that is the same size as the turbine nut into a dead center in the three jaw chuck. Onto the hex I'm going to slip a deep well 12 point or 6 point socket with the ratchet drive cut off so it forms a spline sleeve of sorts. (12 or 6 point socket depending on the turbine.) I should be able to position the whole thing so it keeps the turbine from spinning without using a lathe dog. This should prevent the problem you are describing while turning between centers.

Monty

[dieselguy86]

Monty,

My thought was something like a wing nut with really tall “wings” that threaded onto the shaft, with the wings being driven by the jaws. That would atleast provide some balance, and be easy to make.

Im still an amateur, and am really throughly enjoying all your pics. Studying ones experience is easier than learning it yourself. Keep the pics coming.

-Joe

[monty]

Dec 21, 2018 21:06:44 GMT -5 dieselguy86 said:

Monty,

My thought was something like a wing nut with really tall “wings” that threaded onto the shaft, with the wings being driven by the jaws. That would atleast provide some balance, and be easy to make.

Im still an amateur, and am really throughly enjoying all your pics. Studying ones experience is easier than learning it yourself. Keep the pics coming.

-Joe

Joe,

I see no reason why that wouldn't work. The only problem is you will need to use a left hand turning arrangement. I think unless you have a lathe like a Hardinge or Monarch 10EE this is going to be a problem, just like it was for me. The spindle does not stick out far enough, and you run into setup issues with the carriage travel, and the compound. It would be best to keep the turbine against the spindle and use a right hand turning setup. But I would still like to turn between centers to keep things very true. Turning a dead center is the best way to do this. That's why I came up with the idea of using a deep well socket on a hex dead center to drive the turbine. The hex and socket can be loose so it doesn't effect how the turbine or shaft runs true. I'll post some pics when I machine another one.

Right now I'm working on the casting designs.

Monty

[monty]

This is going to be a "fun" casting to produce!

Fortunately I have a method that will work......I think.

[monty]

Design verification in progress.

The mechanical slave has been driven hard and put away wet...

The bearing fits nicely:

A little work with some scrapers and epoxy later:

Fan fits like it should:

Of course no sooner had I printed the stators than I found about 4 things I wanted to change! I don't care how long you've been using CAD or doing design work....nothing beats holding the thing in your hand!!

If only I had a 3D printer that produced aluminum parts!!! life would be so much easier. Can't wait to fire up the foundry! But first I have to finish the diffuser and NGV design:

[Johansson]

Awesome printing Monty! So this is a casting pattern, right? Will you cast it with the lost-PLA method then since the part looks very difficult to cast in green sand.

[pitciblackscotland]

Nice big 3D printer I can see a couple of rotary housings in the first photo, do you repair rotary engines

[monty]

Jan 3, 2019 1:19:50 GMT -5 Johansson said:

Awesome printing Monty! So this is a casting pattern, right? Will you cast it with the lost-PLA method then since the part looks very difficult to cast in green sand.

Thanks Anders.

I Love having a 3D printer! I've been using the technology in my day job for 20 years, but it was out of reach cost wise for my personal projects. It's become something I can afford to use at home in just the last couple years. Right now I'm just printing the parts to make sure everything fits the way I want, and to discover any gotchas in assembly. It also is uncanny how many little details I discover that need tweaking no matter how good I think the CAD model is.

I experimented with some lost PLA stuff, and initially that was my plan....but there are some problems. It's really hard to get a good burn out. There is always some ash that is hard to get out of the shell. It's also a LOT of work to create the shell. It takes a long time to print the form, and although not terribly expensive, the plastic isn't free. That fan case probably has about $20-30 of material in it. The burnout is difficult because the shell needs to be rapidly fired, but the PLA doesn't just melt out the bottom super fast like wax. It expands and wants to crack the shell. The ceramic shell stuff isn't cheap either. I have access to a shelling room and a burn out kiln so that could be an option....but I have a better method.

I started using the RPM process while trying to make a piston for a 2 cycle project. Casting a very high quality piston is no small feat, especially for a high rpm highly stressed engine. I spent almost a year developing the methods I use now. I tried everything. Sodium silicate sand, green sand, wax investment, you name it.....RPM is what I finally landed on. RPM (rubber-plaster-mold) is used for bridge tooling in industry for low or initial run castings that must be die cast quality. It works really well with a 3D printer. The advantage is once you make the forms using the printer, multiple copies of the mold can be made, just like sand casting. That is a huge advantage when doing development work. I never get things done to my satisfaction the first time, so I like being able to make multiple parts. That way I can screw up once and a while and all is not lost! You can also get away with low to no draft, or undercuts unlike sand casting, because the rubber is flexible and does not stick to the plaster.

The basic process is to print the cavity and core that I want in the end. Then make a rubber mold from that. Then cast the mold cavity and cores in plaster. Plaster mixed with silica sand is used. The molds are fired in an oven to drive off water. The chemically bonded water must be removed as well, so it takes a while to dry the molds.  The molds only need to be heated to around 250 C -not nearly as difficult as firing a traditional investment. I use an oven to dry overnight. Then I pour the next day. Much faster than shelling a wax. I also found that the shrinkage with lost wax is really high. If you are making parts to be machined, it's a real problem. I've got the rpm process dialed in so I only need a couple millimeters of machining allowance. It would take a couple tries to get there with lost wax.

I usually try to make the gate area an insert in the rubber tool so I can play around with the gate size without having to make the whole thing over again if my initial guess is too small or too big.

Stay tuned...I'll post some pics when I get to it.

Monty

[monty]

Jan 3, 2019 1:35:06 GMT -5 pitciblackscotland said:

Nice big 3D printer I can see a couple of rotary housings in the first photo, do you repair rotary engines

You can also see a BMW V12 if you look closely... I really need to clean up the shop!

Let's just say my interest in aircraft engines is wide, deep, and longstanding.

The V12 would be great if a constant speed prop didn't cost a small fortune. I'll get around to making that 3/4 Spitfire one of these days..maybe in retirement.

The rotary is good, but it spins too fast for a prop and not nearly fast enough to make a fan happy. Plus it needs a pesky radiator.

I have plans for this little turbofan, but first it must be built and tested!

Monty

[pitciblackscotland]

Jan 3, 2019 8:12:13 GMT -5 monty said:

Jan 3, 2019 1:35:06 GMT -5 pitciblackscotland said:

Nice big 3D printer I can see a couple of rotary housings in the first photo, do you repair rotary engines

You can also see a BMW V12 if you look closely... I really need to clean up the shop!

Let's just say my interest in aircraft engines is wide, deep, and longstanding.

The V12 would be great if a constant speed prop didn't cost a small fortune. I'll get around to making that 3/4 Spitfire one of these days..maybe in retirement.

The rotary is good, but it spins too fast for a prop and not nearly fast enough to make a fan happy. Plus it needs a pesky radiator.

I have plans for this little turbofan, but first it must be built and tested!

Monty

Yes i did see that very large engine,good that you have some other interest. I have a couple of Sachs Wankel engines that i am playing around with and slowly working on a 12A single rotary engine.

[Johansson]

Monty, I am very interested in your progress with the RPM casting! As you might know I am casting a bit myself and if there is a method for us hobbyists that produce better/easier castings than the green sand or lost PLA I am all ears!