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Attaching Delrin Low Drag buttons with wood screws?

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Underdog

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Do wood screws go into the bulkhead without splitting the plywood? I purchased AMW/ProX's 1010 Delrin low drag rail guides (very nice buttons) BH type that come with wood screws. I'm trying to install them on a Madcow Mozzie however there is a concern that the wide wood screws will split the narrower plywood bulkhead. The plywood is nice but not terribly thick. Am I missing something?
delrin.JPG
 

Bat-mite

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Can't really tell from the picture.... How thick is the CR, and what size screw? If the diameter of the screw is less than half the thickness of the wood, then I don't see a problem. But I would drill a hole in the wood that is slightly narrower than the screw, so that all the screw has to do is thread itself.
 

samb

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Do wood screws go into the bulkhead without splitting the plywood? I purchased AMW/ProX's 1010 Delrin low drag rail guides (very nice buttons) BH type that come with wood screws. I'm trying to install them on a Madcow Mozzie however there is a concern that the wide wood screws will split the narrower plywood bulkhead. The plywood is nice but not terribly thick. Am I missing something?
View attachment 297927
If you have a small target like that I would double the thickness of the ring. You can double a small section to cover just the length of the screw all the way up to doubling the entire ring.

Here's an example of my LOC Doorknob where I tripled the thickness for my u-bolt attachment point and button placement area. I didn't want to miss my target ! :) More than you need I would think but you get the idea.

centering ring.jpg
 
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K'Tesh

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If you have a small target like that I would double the thickness of the ring. You can double a small section to cover just the length of the screw all the way up to doubling the entire ring.

Here's an example of my LOC Doorknob where I tripled the thickness for my u-bolt attachment point and button placement area. I didn't want to miss my target ! :) More than you need I would think but you get the idea.

View attachment 297929
I agree with samb on this one. However, even with doubling or tripling the thickness of the ply, I'd be leary of using wood screws. Machine screws are cheap, and if (say your not in China) you can probably find what you need at a local hardware store. If you are in China, you could probably find them... 1) if you can fit inside the store, and 2) can overcome any language barrier.
 

Underdog

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The wood screws are the same thickness as the 1/8" thick plywood CR. Madcow's instructions say to install the second lug at the Center of Gravity. That may not be the same location as the centering rings.
cg.JPG
 
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jimzcatz

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I attach a small block of wood on the ring or bulkhead, giving the screws something to bite into.
 

Underdog

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I attach a small block of wood on the ring or bulkhead, giving the screws something to bite into.
Oh, so I don't have to worry about throwing the rocket "out of balance" by putting a small block on just one side? I was under the impression that the rocket would veer off to one side if not kept perfectly balanced. I guess it does not make such a difference (same with those 808 key cameras). But I have to wonder why? Weight distribution is so critical in an airplane.
 

samb

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Well I think opinions vary on the types of screws and location. I can't give you a good reason not to use the supplied screws unless you are adding significant weight an/or upgrading the motor. I used machine screws on my Doorknob because thats what came with the buttons. I do like to have one guide at or close to the cg but l want a strong attachment point more. Do you have an idea where your rocket will balance ? How close to the forward centering are you ? Within one caliber, I say good enough. You may have some leeway to place the forward ring where you want it but I'll bet the stock placement will be fine. You could do a dry fit to get the approximate balance point or look for Mozzie threads here or on rocketreviews.com to see what other builders came up with.
 

jimzcatz

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Oh, so I don't have to worry about throwing the rocket "out of balance" by putting a small block on just one side? I was under the impression that the rocket would veer off to one side if not kept perfectly balanced. I guess it does not make such a difference (same with those 808 key cameras). But I have to wonder why? Weight distribution is so critical in an airplane.
Seriously? If you are that worried, put a second block 180° out. We are talking milligrams here, I don't see the problem.
 

samb

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Oh, so I don't have to worry about throwing the rocket "out of balance" by putting a small block on just one side? I was under the impression that the rocket would veer off to one side if not kept perfectly balanced. I guess it does not make such a difference (same with those 808 key cameras). But I have to wonder why? Weight distribution is so critical in an airplane.
A 1/2 inch or so square block of basswood or some other hardwood wont upset the applecart. :) Don't let my picture throw you off, you just need enough so the screw stays in the wood.
 
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Underdog

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A 1/2 inch or so square block of basswood or some other hardwood wont upset the applecart. :) Don't let my picture throw you off, you just need enough so the screw stays in the wood.
I was also concerned about keeping the inside of the body tube smooth and free of obstacles, so the at the parachute could discharge without snagging on a protruding wood screw or block of wood.
 

K'Tesh

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Depends on where you put the block... If the block is part of the motor mount, and located on the side away from the recovery gear (presuming here that you're mounting the shock cord to the engine mount), then no problem... Even if it's on the same side, it shouldn't be a problem. However, if you're doing one mid airframe, then yes it would be a problem. T nuts and machine screws present a smaller profile for snagging. Especially if you make it smoother by covering the back of the T nut with epoxy putty.
 

samb

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I was also concerned about keeping the inside of the body tube smooth and free of obstacles, so the at the parachute could discharge without snagging on a protruding wood screw or block of wood.
I share your concern. Any kind of mods I've done like we're taking about here are placed like K'Tesh describes, on the aft side of the forward ring.
 

Underdog

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I share your concern. Any kind of mods I've done like we're taking about here are placed like K'Tesh describes, on the aft side of the forward ring.
I'll check the "center of gravity" location for the launch button and see where it ends up with respect to the centering ring.
 

samb

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I'll check the "center of gravity" location for the launch button and see where it ends up with respect to the centering ring.
Ok. Keep in mind the instructions were written with the stock 1/4 inch launch lugs in mind. I wouldn't be that concerned about a deviation in the placement of the forward button if it was my build. It appears that this model doesn't have a lot of extra room for the recovery system so I would prefer not having any protruding screws in that space, faired in or not. :)
 

mkadams001

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you could use well nuts. It looks like the CG is in the area of the motor tube so there would be no obstruction.
 

tab28682

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I have been retrofitting a few older 2.6"-4" dia cardboard tube rockets with rail buttons and wood screws.

These all have 1/8" ply centering rings. On one model, the night before a launch, I installed the aft button so that the screw came out just below the aft centering ring. Mixed up a batch of 30 min epoxy with milled glass to make it thick enough to stay in one place and not run. Built up a smooth epoxy fairing over the screw, blended out to the centering ring, potting it into place.

After that epoxy kicked, I installed the forward button just above the forward centering ring. Used a long stick to apply the filled epoxy over the exposed body of the screw in the same manner as the aft screw, only not quite as neatly. Looks and feels to be more than strong enough for this 4" x 78" rocket in any flyable wind situation while on the rail.

There are obviously other and better methods when building for rail buttons from the get go, but this is a pretty easy and quick way to retrofit an old model with launch lugs.
 

CORZERO

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Threads like this should be in the "Beginners" section.
 

Underdog

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I have been retrofitting a few older 2.6"-4" dia cardboard tube rockets with rail buttons and wood screws.

These all have 1/8" ply centering rings. On one model, the night before a launch, I installed the aft button so that the screw came out just below the aft centering ring. Mixed up a batch of 30 min epoxy with milled glass to make it thick enough to stay in one place and not run. Built up a smooth epoxy fairing over the screw, blended out to the centering ring, potting it into place.

After that epoxy kicked, I installed the forward button just above the forward centering ring. Used a long stick to apply the filled epoxy over the exposed body of the screw in the same manner as the aft screw, only not quite as neatly. Looks and feels to be more than strong enough for this 4" x 78" rocket in any flyable wind situation while on the rail.

There are obviously other and better methods when building for rail buttons from the get go, but this is a pretty easy and quick way to retrofit an old model with launch lugs.
I will give this a try.
 
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