RCU Review: David Johnson on: How to Cut Carbon & Fiberglass Spinners

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    Contributed by: David Johnson | Published: June 2005 | Views: 40543 | email icon Email this Article | PDFpdf icon
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    By J. David Johnson

    A short time ago I found myself n the position of needing to cut out a spinner for a recently completed Extreme Flight 87" Yak. After much research I found some beautiful carbon fiber and fiberglass spinners available from Bisson Custom Mufflers. The fiberglass spinners cam in both a gel coat white and silver weave. Simply beautiful. Yet none of the spinners were available pre-cut.

    O.K., more research... I found little on the net to help me here, but just enough to put me on the right track.  The method that follows is my interpretation of how best to cut a spinner to fit nicely around the prop of your choice. It, at least, worked very well for me. This same method can be used for basically all spinner materials including aluminum and plastic.

    First let's get the disclaimer stuff behind us...
    Fiberglass and carbon fiber are not materials to be casually played with. Always wear safety goggles and a good quality mask to prevent inhaling particles. A good pair of gloves might not be a bad idea either. When cutting, it's best to do so outdoors with the wind blowing away from you.

    While I have done my best to make this tutorial as clear and concise as possible, should you decide to attempt cutting your spinner using these techniques, RC Universe and the writer (uh, that would be me) are NOT responsible for any harm or damage incurred. In other words, proceed at your own risk.

    With that said, the process is much more simple than it appears and most people will have a perfect, factory looking cut spinner.

    Well... if you don't already own a contour gauge, your local hardware store should have them in stock. I got mine from Lowes. The first step is to drill your prop. I normally position the prop on the engine with the logo up and at about 5-10 degrees past (clockwise) the sensor. This usually allows the prop to just be coming off my hand as the magnet passes the sensor and the compression stroke has taken over the "flip". This is an important step as if you just start cutting and drilling, you may find that when you are all done the prop is not in a safe or convenient position for hand flipping. Once drilled, position the prop in the spinner backplate making sure the prop does not touch any of the screw tabs, mark one hole, then using your prop drill guide, drill the backplate.

    Now you can align the spinner with the prop using the prop bolts. Take the contour gauge and press it firmly down over the prop at the approximate location the spinner cone will be located. Note how perfectly the fit is around the prop.

    In fact, it's too perfect. We need to allow some room. So... Take the shape left in the "pins" of the gauge and transfer it to a piece of posterboard or some other semi-flexible stock. Most spinners have a small lip where the cone rests. Make sure to mark where the bottom of the cone will be NOT the bottom of the spinner backplate. Then cut out the pattern you just traced. Using the small "hole" piece, lay it down and trace around it on a flat edge of another piece of card stock. I add about 1/16"-3/32" to the short side and the same to the bottom (note the shaded areas). This allows the extra clearance we will need.

    Cut your new template from the cardstock and leave some on each side to wrap around the prop & set down on the backplate. Check the fit and adjust as necessary. Remember not to take too much from one side or the other as you could possible miss a screw location.

    If your spinner is already drilled for the screws, put them in before marking the cutout location. If not you should mark and drill them now. This is done similar to the method used for cowl mounting where you tape a tab to the bottom of the spinner, bend it over the edge and mark the hole position. Attach the cone and transfer the hole and drill.

    Mark on both sides of the backplate where the close edge of the prop meets the backplate. Remove the prop. Attach the spinner cone to the backplate, then align your template to the marks allowing for the 1/16"-3/32" gap and mark the cutout locations. Transfer the cutout by tracing the inside of the template. If you are marking a CF spinner, you might want to apply some masking tape to the area to give you a lighter area to mark and see. In addition this will help keep the edges cleaner when dremeling out the opening.

    Once the opening has been transferred, it's time to get the dremel tool out. Again... make sure you use a mask and goggles, and make your cuts outdoors or in a well ventilated area. Dremel out the cutout using a small sanding drum attachment and a medium grit sleeve. For best results, only go up to line itself and leave the line where you can see it. Then finish the cutout by using a 1/4" hardwood stick with sandpaper glued to it and a small rattail file. It doesn't take long at all, and you want to sand/file till the line is JUST gone.

    The result is a clean, perfect looking cutout. Attach the backplate, prop and spinner to your engine and double check the cutout for fit... you might need to make a very fine adjustment and remove a little more material. But when complete, you'll have a spinner that's custom cut just for your prop and will add that much more to the appearance.

    I hope you find this tutorial helpful. Should you have any questions, concerns or find any mistakes, please feel to PM me here at RCU. My username is Maudib.

    Comments on RCU Review: David Johnson on: How to Cut Carbon & Fiberglass Spinners

    Posted by: cloudancer03 on 06/10/2008
    thank you thank you..I thought I was stupid not to figure things out.lol and I have a contour guage and always wondered what to do with it.thank you.you made this problem an easy fix..so glad I have a college degree lol.
    Posted by: on_your_six on 10/05/2010
    I think that you should mention spinner balancing. A properly cut spinner needs to be balanced before running it on an engine or electric motor. We have found brand new spinners to be so badly out of balance that they almost tear the bearings in the Motor/Engine. Make a mark on the spinner and keep removing material from the bottom half of the low prop cut-out until the spinner will rotate and stop randomly. This is a static balance and you might have more work to do when you spin it up to 8000 rpm and hear a lot of vibration.
    Posted by: on_your_six on 10/05/2010
    Scoff if you will, but a properly balanced spinner makes a huge difference in how the engine/motor performs. I have taught this method to several guys at my local field and they now see that it is just as important as balancing a prop. Spinners on electric motors are easier to tell a difference because you hear all the vibration noise, where a gas engine will mask it. It can be done with a dremel tool in about 1/2 hour using the dubro prop balancer.
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