CAM help for Radial Diffuser

[doctorklein]

Hi,

I just made my account today because I am looking for help making the radial diffuser for the miniature jet engine some friends of mine and I are building. We have access to a 4-axis machine (FADAL CNC 88HS) but I am having a lot of trouble with the cam. Does anyone here have advice on how to use mastercam for 4th axis operations such as cutting the fins out on a radial diffuser.

Below I included the engineering drawings for our diffuser as well as a video showing the specific operation we are having trouble with.


www.youtube.com/watch?v=fjFjHVy1fGM skip to 1:27 

[turbotom]

Sorry I cannot help you with the CAM issues but you should really revise your design of the axial part of the diffuser. The vanes at the periphery form convergent passages so they act as a nozzle and not as a diffuser. You should definitely only have those vanes that need to contain a threaded hole designed massive, all the others should just be slim airfoils. For your engine's rigidity, you won't need mroe than five or six of these vanes to be threaded.

[praendy2203]

Hi,

also there are 12 diff wedges in your plan.
So you can get in trouble with aerodynamical problems.
Better to design the diff with 11, 13 or 17 wedges.
I use 12 wedges on my diff, but I use a 11 bladed comp wheel.
Andy

[doctorklein]

turbotom praendy2203

Thank you for the feedback, I will absolutely take your advice into consideration. Honestly I think making those design changes will be easier than doing the cam/learning how to run the 4 axis machine.

[jetjeff]

Hi,

I would just continue the wedges to the outer case (like the Kingtech turbine). Much simpler design.

The wedges can be made slightly curved.

Regards

Jeff

[doctorklein]

jetjeff I'm not sure what you mean. can you send a photo?

[wannabebuilderuk]

Sept 13, 2021 20:31:39 GMT -5 doctorklein said:

jetjeff I'm not sure what you mean. can you send a photo?

I believe he means something like this d2t1xqejof9utc.cloudfront.net/screenshots/pics/8cfcf80b92d1aeef433fda7884bdc18b/large.bmp

[jetjeff]

Hello,

Yes, the reply with the image link, is what I mean.

I got a new Mac in 2014 and most of my photo's from this build (2nd Kamp build) is on my old Mac, which won't boot up.

You might seriously consider this style of compressor diffusor. You should have no problems making it on a 3 axis mill.

Regards

Jeff

[doctorklein]

jetjeff I redesigned the fins on the side of the radial diffuser so they no longer create a nozzle, however I am worried that the triangular fins on top of my diffuser may be too tall. In the photo I sent the top fins are 0.27 in and the side fins are 0.18 inches. I am thinking about changing these dimensions. I would love to hear your take on this.





Thanks again for all the advice!

[jetjeff]

Hi Doctorklien,

You're in the ballpark. The almost .010" of difference would allow to machine the wedges shorter if needed. Or even make the wedges slightly taller.

Regards

Jeff

[doctorklein]

Hi jetjeff

You mean 0.1" difference right? And just to confirm, you're saying I could either make the triangle wedges shorter or leave them be? If I take them down, I'm thinking about making them 0.24 to match the height of the edge of the compressor give or take 10 thou. Also I seriously appreciate your help on this.

[racket]

You're creating a "nozzle" at the "corner" , the diffuser wedges need to be 0.240" to match the comp exducer flow passageway height and your axial vanes need to at least the same height or greater to continue the diffusion process.

[dieselguy86]

doctorklein,

Here's a cut away of the diffuser I'm working on, you can see how the flow path continually grows bigger. 



-Joe

[doctorklein]

Thanks for all the help on this one! Here is the final product! Take a look!

[racket]

That right angled edge as the air leaves the diffuser channels needs to have a radius on it