# 2 sided machining a propeller



## Chris Prouty (Nov 10, 2016)

Perhaps you guys here can help me. I've been racking my brain and burning through prototypes trying to machine a working propeller. I have VCarve pro and I've imported a 3D model that I want to cut. The problem I'm having is tricking the machine into cutting it. I say trick, because the propeller file is not a symmetrical propeller so the top down profile is different on each side. Hard to explain some photos of one of the prototypes and the model in the import screen in VCarve. As you can see from the first photo, I'm almost there. I just want to be able to thin the blade out. Anybody have experience in this sort of thing? I would appreciate any advice.


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## Cherryville Chuck (Sep 28, 2010)

Hi Chris and welcome. I'm not a CNCer but unless your machine was capable of flipping the prop over to do the reverse side then I think you would have to treat it as two separate objects with the same outer dimensions and outline in a plan type view. I don't think the curve should present a problem since every plot point in the drawing has an x, y, and z coordinate.


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## old55 (Aug 11, 2013)

Welcome to the forum Chris.


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## MEBCWD (Jan 14, 2012)

Chris,

Looks like you already figured out that you will need to flip the model so here are a few pointers that might help.

First thing you need to remember is VCarve Pro limits the number of imported 3rd party models to one import where it allows multiple vem files. You need to start 2 identical design projects and import the face into one project and to back into the other project. When you import the models (front and back) make sure you use a standard views so you can flip the model without moving it (on the import screen, depending on the model, use Front and Back or Right and Left). Don't move the model around use the center button only. Make sure you are on the bottom of the model before you import the model. After you have the models imported center it in the project (do not rotate it or resize it). 
After you have the models imported into the two files you need to use the "Center in Material" button and center the models in the material. If you need to resize the models then you should use the "Set Selected Object Size" button and make sure you re-size both models the same amount.
You will need a way to align the board after you cut the first side so you need to decide what you will use for alignment pins. Say you will use 1/4" pins, locate a 1/4" circle on the project where it will not be cut out by machining the model or cut out toolpath and is on the longest dimension of the model and centered to the Axis. Now use the "Mirror" function and create another pin location flipped about the job center. You will calculate a Drilling Toolpath for the holes. Only the first file needs these. When you run the job machine the first side then you will drill the holes in the board, then after the board is removed you will drill the holes on the spoil board. Use your pins to locate the board to the spoil board then machine the other side.


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## furboo (Oct 12, 2015)

Chris, welcome!

I can't help you, but I'm very interested in how you solve this. I have several antique propellers that I've collected over the years, the most interesting off of a 1920's Consolidated PT-1 Trusty. So far, your prop looks very nice.


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## Chris Prouty (Nov 10, 2016)

*Progress so far*

So here's what got me to this point.

I took the model in to VCarve and set the model height the same as my material height. In this case, that was 1.65"

I then adjusted the zero plane to where the bottom of the blade starts being an undercut. For the top, this was 1.33" and for the bottom it was about 1.5". Note, I created two different jobs, one for the top and one for the bottom. I kept the model at the top of the material. 

I created my toolpath for the roughing and finish and a profile which was only as deep as the difference between where the zero plane was and the material thickness. So for the top, the profile toolpath was only set to cut .15" and the bottom profile was set to cut .32". This ensured I wasn't cutting into the other side of the model. 

This got me close. I had to finish the cutout with a jigsaw because of the middle section. 

I'll continue to refine on small scale until I'm comfortable going bigger.

Below are the results.


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## Cherryville Chuck (Sep 28, 2010)

Chris you say in the first post that this is to be a working propeller so do you have a way to balance it when you are done?


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## MEBCWD (Jan 14, 2012)

I'm not really sure why you are using a jigsaw to cut this out. You can add tabs, just remember you need to trick the cnc into thinking the tab is in the middle of the job or lowest point on the first side when flipped. Set your tabs up so they will be thick enough they won't be cut out. You may have to build 3d model tabs, not sure unless I set the whole thing up first.


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## Jbird22 (Oct 24, 2016)

My limited experience with two-sided machining has been with Cut3D. I can insert my Solidworks .stl files into the program and calculate top and bottom toolpaths. Like MEBCWD said earlier, the key is aligning it perfectly when you flip it.


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