CF Spinners - Use Vacuum?
09-24-2004, 07:08 PM
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CF Spinners - Use Vacuum?
Newbie to composites. I have made three CF spinners using the mold I made (4.25 inch diameter). I quality is usable, but not perfect. Each of the three I have made end up with a bubble or two in the surface finish. Only a cosmetic issue, but I'm hoping to do better.
I use 6 pieces of 6 ounce fiber to end up with a two-layer layup. Three pieces are large enough to complete one layer with some overlap. Then the next three pieces are laid over the first three pieces but shifted to cover the seams of the first three. I wet out the CF of all 6 pieces and then carefully spread them into the inside of my female mold. I press all around inside the mold to make sure everything is pressed tightly to the mold surface. But all three have come out of the mold with some areas where the surface has a void in it (like a bubble has formed between the mold and the CF). Do I have to vacuum this to achieve perfection? Seems like a hassle to try to vacuum a part of this shape.
I use 6 pieces of 6 ounce fiber to end up with a two-layer layup. Three pieces are large enough to complete one layer with some overlap. Then the next three pieces are laid over the first three pieces but shifted to cover the seams of the first three. I wet out the CF of all 6 pieces and then carefully spread them into the inside of my female mold. I press all around inside the mold to make sure everything is pressed tightly to the mold surface. But all three have come out of the mold with some areas where the surface has a void in it (like a bubble has formed between the mold and the CF). Do I have to vacuum this to achieve perfection? Seems like a hassle to try to vacuum a part of this shape.
09-26-2004, 10:34 PM
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RE: CF Spinners - Use Vacuum?
Hey Guys,
The reason you're getting bubbles in the finish is because the cloth you're using still has voids in it after saturating it with resin. Using vacuum won't cure this however, since the vacuum required for the typical resins viscocity is beyond the commonly available vacuum pumps capacity. Most of the pumps used in vacuum bagging can pull 26" of vac. You would need more like 29" of vac. to get all the bubbles out. Since 29.4" of vacuum is the max at sea level, the 26" pump just can't do the job adequately. The 29" vac. type of pump costs around $1500.00 used or about $4500.00 new. OUCH!!! You can solve the bubble problem by using pre-preg material, which comes saturated with resin. Keep it frozen till use, and apply heat to cure the resin. Of course you'd need some form of pressure applied to the mold and lay-up until the resin cures, so this is another problem in making spinners. Much more tooling is required. If you are happy with the spinners you're making, and they work for you, smile, you have a lot to be happy about. At least you can make your own spinners without spending a fortune on tooling. To make a professional looking spinner from scratch it costs around $800.00-$1500.00 for the tooling and tools required to do the job right depending on the spinner size of course. That's $800.00-$1500 per spinner size. This of course includes a machined plug, inner amplifier and release tool. All of which must be perfectly molded to produce a true running, professional quality, safe spinner. If this sounds like a lot, it is. Check for makers of CF spinners out there, not many. The liabilty issues for them are serious, not to mention the outlay for the tooling. Think of how many different sized spinners are available verses how many will buy the product.
Just a few thoughts...Glad to see innovaters out there at least trying to make their own stuff. Seems like a dying breed these days.
The reason you're getting bubbles in the finish is because the cloth you're using still has voids in it after saturating it with resin. Using vacuum won't cure this however, since the vacuum required for the typical resins viscocity is beyond the commonly available vacuum pumps capacity. Most of the pumps used in vacuum bagging can pull 26" of vac. You would need more like 29" of vac. to get all the bubbles out. Since 29.4" of vacuum is the max at sea level, the 26" pump just can't do the job adequately. The 29" vac. type of pump costs around $1500.00 used or about $4500.00 new. OUCH!!! You can solve the bubble problem by using pre-preg material, which comes saturated with resin. Keep it frozen till use, and apply heat to cure the resin. Of course you'd need some form of pressure applied to the mold and lay-up until the resin cures, so this is another problem in making spinners. Much more tooling is required. If you are happy with the spinners you're making, and they work for you, smile, you have a lot to be happy about. At least you can make your own spinners without spending a fortune on tooling. To make a professional looking spinner from scratch it costs around $800.00-$1500.00 for the tooling and tools required to do the job right depending on the spinner size of course. That's $800.00-$1500 per spinner size. This of course includes a machined plug, inner amplifier and release tool. All of which must be perfectly molded to produce a true running, professional quality, safe spinner. If this sounds like a lot, it is. Check for makers of CF spinners out there, not many. The liabilty issues for them are serious, not to mention the outlay for the tooling. Think of how many different sized spinners are available verses how many will buy the product.
Just a few thoughts...Glad to see innovaters out there at least trying to make their own stuff. Seems like a dying breed these days.
09-28-2004, 10:01 AM
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RE: CF Spinners - Use Vacuum?
Detail Man
I must agree with the liability issues. Thats one reason I don't sell or give out my spinners or carbon prop blades. Although I test them beyond thier normal use, still a lawyer is not looking for facts.
To avoid bubbles in your layup, in a free atmosphere layup, try multi layers of a lighter composite. It works.
Steve
I must agree with the liability issues. Thats one reason I don't sell or give out my spinners or carbon prop blades. Although I test them beyond thier normal use, still a lawyer is not looking for facts.
To avoid bubbles in your layup, in a free atmosphere layup, try multi layers of a lighter composite. It works.
Steve
09-29-2004, 11:11 PM
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RE: CF Spinners - Use Vacuum?
Very nice job,
If that's not perfect, looks more than close enough to me. I've made very large CF spinners for 50% aircraft and they look just like that. I used a cnc machined aluminum backplate, but I think your spinner looks great! Keep experimenting. By the way, how's the dynamic balance? Have you spun one up to speed yet?
Best Regards,
Dan
If that's not perfect, looks more than close enough to me. I've made very large CF spinners for 50% aircraft and they look just like that. I used a cnc machined aluminum backplate, but I think your spinner looks great! Keep experimenting. By the way, how's the dynamic balance? Have you spun one up to speed yet?
Best Regards,
Dan
10-01-2004, 03:56 PM
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RE: CF Spinners - Use Vacuum?
I have flown the plane (3W100 cap 232) for a few flights and the spinner has performed flawlessly. I have run up full throttle (maybe 6000 rpm) on the ground and see no wobble or vibration. Up close, you can see that the surface is not as perfect as those from Pete's Models, but it is pretty close. 4 ounces overall weight (2 ounces backplate and 2 ounces spinner)
