Propeller challenge

[rbarrowATmembankDOTcom]

I am attempting to cut a 27" propeller with the bot. I have ArtCam Pro and have imported the STL model into Pro. Since this is a double-sided process on a 3 axis machine, I am trying to fixture this block in such a way to permit it to "flip" to finish the backside.

I have tried creating a "negative" of the prop (think mold cavity) to serve as a fixture for supporting the partially machined block. I guess I am a bit frustrated with the time involved so far. I seem to have a problem with toolpath about 1/2 through the finish pass (roughing pass already completed), it suddenly shifts everything to a lower x value. It's as if the home position of the bot jumps .75" negative... Windows V3 - PRT 96..

Looking for comments/ideas/Shotbot destruction intervention or the like...

Thanks,
Roy

[windsor@muskoka.com]

I just did a simmilar cut for a boat stem .I cut the rabbet on one side then milled a pocket into a spoil board to hold the flipped over stem for milling the other side. I did the design in rhino , toolpaths in visualmill and used the windows v3 software with a prt control box . I had no problems . ----Is it possible you offset the part in the cad program when you flipped it ?

[mrdovey]

Roy...

I think I'd be strongly inclined to leave blocks at the tips (to be removed as the final step) and to support the workpiece primarily at the hub and at the tips.

To minimize flexing, I think I'd try leaving a "spine" from hub to tip block, front and back, down the center all blades. This could provide additional "stiffness" and could be removed as the next-to-last step.

Are the roughing and finishing passes part of the same file or are they performed by separate files? Have you examined the code in the area where you're experiencing the x reference frame jump?

Don't ever attack a machine that weighs more than you do and/or has sharper teeth than you do. :-)

Morris

[gbatten]

Roy,

May I ask why you are making a propeller? I assume it is an airplane propeller? I am a pilot and aircraft owner and someday hope to build a plane.

...Gene

[artisan]

I agree with Morris. Trying to create a cavity to hold your carving is infinitely harder and inherently less accurate than leaving tabs or blocks attached, which can then be flipped on bolts and checked for height. In other words, you need a jig with bolts that will "register" your piece when you flip it. The tabs can be cut off on the final pass. This strategy may change slightly depending on the material you are machining...I don't think you mentioned it. Good Luck....D

[rbarrow@membank.com]

Thanks for all the suggestions...I had not considered the blocks at the tips approach but that certainly makes good sense and might prevent blood loss as well.

This prop is for a giant scale aerobatic radio controlled plane and this one is made from hard maple. I am going to try beech as well just for comparison...assuming I am successful at creating something other than firewood.

I don't know why the code has created a jump but with over 140,000 lines, it can be a bit difficult to dig through. I think I am going to re-path this thing with the blocks and see what happens...

Thanks...will keep you posted!
Roy

[b.allanson]

For your propeller project, I would try a product called deskproto.
You can download it for 30 day trial it has a processor for shopbot. (full access for 30 days) and it automatically creates double sided toolpaths, and allows for blocks on the ends or tabbing.
very easy to use it is wizard driven. It only requires you select your machine in the beginning.
Good Luck,
Brian Allanson

[rbarrow@membank.com]

Wow...where has this software been kept! I downloaded the trial and had a toolpath in 10 minutes ready to go (except for a bit of FE cleanup)...

If I didn't already have ArtCAM Pro, this would be the ticket for these things!!!

Thanks Brian..

Roy

[trentjordan@machinecnc.com]

I'm trying to cut propellers also. Check out the effort so far at http://www.machinecnc.com. The website has a good description of my failures so far, but I haven't given up.