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How can I cut a 9 inch, recessed, 1/2 circle groove in ... - 8/20/2003 11:31 AM   
rsieminski



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From: Sarasota, FL, USA
Status: offline 		Kinda hard to explain. I've been working on an airboat hull plug forever. The problem is in accurately cutting the groove for the prop. It starts about 1/2 way from the front, and extends out the back. It's a sunken area about 1/3 the circumference of the 9 inch prop, so the engine will sit lower in the hull. Wire cutting everything else works fine, but this detail always gets butchered.
Thanks,
--Rick

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How can I cut a 9 inch, recessed, 1/2 circle groove in ... - 8/20/2003 12:25 PM   
ohcustoms



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From: plymouth, OH,
Status: offline 		use some fine grade sand paper and a wooden dowl, that's my suggestion.

good luck


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Or... - 8/20/2003 3:14 PM   
Mike James



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Status: offline 		You can make this contraption (in the image) out of some stiff wire, so that it can be used as a "tip" in your soldering iron, then cut the foam with heat. Only small grooves remain in the top surface, to be filled later.

I didn't invent this idea, and I haven't done it that way, so I don't know the details about what size wire to use, etc.. You might be able to do something similar with a wire-holding device and your foam cutting machine, if you have one.

I have done this job with a phenolic or fiberglass wing tube, with small "teeth" filed in the end. Just rotate it to cut.

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How can I cut a 9 inch, recessed, 1/2 circle groove in ... - 8/20/2003 4:26 PM   
canadianjosh


 

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From: victoria, BC, CANADA
Status: offline 		Tricky, tricky, you could build a jig from some pieces of wood in a shallow circle shape and use a router with a straight shank bit to cut it out. While i hate to ruin experimentation, i can see one problem with this design where the prop travels 1/2 inch into the hull. That is the prop will unload in this section and speed up creating some horrible vibration. This will occur because believe it or not the prop will create a vacuum in this notch, have you ever covered up the back of a hair dryer?? it starts to rev higher when you do, now that's ok because the speed increase is uniform over the impeller in the dryer, but when you unload a section of propeller it will create vibration. A solution to this would be to taper the notch behind the propeller quite a lot, i would say at about a 25-30 degree angle to allow air to continue on behine the propeller, and do the same for the front to allow more air in, you still may run into some probs, let me know how it goes.

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All Forums >> RC Airplanes >> Composites Fabrication And Repair >> How can I cut a 9 inch, recessed, 1/2 circle groove in foam?
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