New member looking for help with a mold plug.

[Mountain Man]

I've been building competition model sailplanes for about 60 years. I recently purchased a 3 axis CNC router. (x=6", y="35.5", x=24")
I use the machine to cut ribs & formers and to make mold plugs & negative (female) molds for fuselages and hollow molded wings.
Most of my work, now, is with composite materials like Carbon, Kevlar and Glass.
My most recent project is a fuselage pod 32" long and 2.5" in diameter. It is a basic cylinder, tapered on both ends, with a hatch area cut out. The tough part is.... the cylinder does not have a straight center line. It is "drooped".
The "droop" makes using a normal lathe impossible.
I machined a beautiful plug on my CNC router using epoxy soaked MDF but I would like the plug to be more durable. In the past I have made both steel and aluminum plugs on the lathe and then milled in the hatch area. My router won't handle that.

I'm looking for a machinist willing to tackle the job. I will e-mail .iges/.igs files of the plug. An estimate of cost would be important because I may be asking for something I can't afford.

Jim

 

[brino]

Hi Jim,

I saw your post in the intros, and followed it to here. I have a question about your CNC router.

I have seen many times people treating aluminum much like hardwood; using carbide blades/bits on table saw, mitre saws, and even hand held routers to machine it. I have used my mitre saw on aluminum angle and it did a great job.

You believe that the part you need is beyond your tools, but I wonder.....
Is your CNC router frame "stiff" enough?

Obviously I don't want you or your tools getting damaged, but thought I'd bring it up.
Maybe someone else here has some pertinent experience.

Good Luck!
brino

 

[brino]

ooops one more question.....

What do you mean by "drooped"?

Is it simply two different centre lines, that could be lathe turned using multiple centre holes, or is it a complex, continuous "bend".

Of course, even it it's possible on a lathe with different centre lines, the blending of the joint would be difficult.

Maybe a photo of your prototype would shed some light.

Thanks,
brino

 

[Mountain Man]

Brino,

The router is a Laguna IQ HHC. The frame is quite stiff (3/4" steel plate), the spindle is water cooled & I even water cooled the stepper motors. My concern would be tool lubrication, cooling and chip management. Aluminum also is bad for fouling up tools. My run time for just the top half was over 8 hrs. when I used MDF. I have no idea how long it would take with aluminum.

I don't think I want to push the machine & risk damage.

Jim

- - - Updated - - -

Brino,

Complex sweeping curve.

Jim

- - - Updated - - -

Brino,

I can e-mail files if you think you might want to give it a try.

Jim

 

[brino]

Hi Jim,

My concern would be tool lubrication, cooling and chip management. Aluminum also is bad for fouling up tools.

Yep all great points, thanks for the additional info.

My run time for just the top half was over 8 hrs. when I used MDF. I have no idea how long it would take with aluminum.

Ouch!

I don't think I want to push the machine & risk damage.

Absolutely agreed.

Complex sweeping curve.

I can e-mail files if you think you might want to give it a try.

Jim,

Although I'd really like to help, I believe the project is beyond my skills and equipment.

I was trying to get a better understanding and promote thought and discussion.
It sounds like you have already thought this one thru from all directions.

My last thought would be using your prototype as a pattern to cast the real one. I have done some experiments with green-sand casting of aluminum with a homemade propane burner. However, there's at least two problems with that:
-you'd probably still need to machine the surface for "finish" reasons, and
-due to shrinkage, your pattern needs to be bigger than the final product

Is there any other cast-able material that would meet your durability requirements and not have these drawbacks?!?!?

brino

 

[rangerman]

Wouldn't it be possible to machine a soft aluminum shaft into a tapered cylindrical straight plug on a lathe and then perform a second operation using an arbor press with padded supports and carefully bend certain sections to achieve the required "droop" ?
Pure aluminum even at 2.5" diameter is very easy to bend with a powered arbor press.

Alternatively, you can also carve out an exact wooden or clay pattern of your plug shape and then use that pattern to make a mold for casting the final plug in aluminum, zinc, or even hard plastic.
Any imperfection or roughness could be easily handled using a file, sand paper, scraper, polisher, and other common tools.

Thousands of years ago mankind have been making complex sculptured shapes in metal even without the modern machine tools we now take for granted.

 

[Mountain Man]

Thanks for your interest guys.

I got a response, through another web site, from a machinist in Australia who is going to do the job. Ill have the pod in a few weeks.

JIM over and out