4-40 shear pins for PML Phenolic tubing ?

[rocket1017]

Hi Guys:

I am finally finishing up my 7.5" dia Little John. It is made with PML tubing covered with 2 layers of fiberglass cloth. The nose cone is a PML fiberglass cone that I filled with high density foam.

The question is I always used 2-56 nylon shear pins on my loc paper tube rockets. But i afraid this cone is too heavy for those. I was thinking of going for qty 4 4-40 nylon shear pins on nose. . Also I want to use then on the coupler section for the drogue. But I am nervous they may damage the phenolic or crack it ? Anyone have any experience good or bad with this tubing and 4-40 nylon shear pins ?

I taken a lot pic's during build as it for my level 3 project. I guess I should post some kind of post build thread if folks would be interested in seeing the build process.

Cheers
John Sicker
TRA 1017
NAR 49422

 

[CarVac]

Hi Guys:

I am finally finishing up my 7.5" dia Little John. It is made with PML tubing covered with 2 layers of fiberglass cloth. The nose cone is a PML fiberglass cone that I filled with high density foam.

The question is I always used 2-56 nylon shear pins on my loc paper tube rockets. But i afraid this cone is too heavy for those. I was thinking of going for qty 4 4-40 nylon shear pins on nose. . Also I want to use then on the coupler section for the drogue. But I am nervous they may damage the phenolic or crack it ? Anyone have any experience good or bad with this tubing and 4-40 nylon shear pins ?

I taken a lot pic's during build as it for my level 3 project. I guess I should post some kind of post build thread if folsk would be interested in seeing the build process.

Cheers
John Sicker
TRA 1017
NAR 49422

If both the coupler and the tube are fiberglass reinforced, it should be fine.

If you're worried, you could just use a greater quantity of 2-56 pins.

 

[rocket1017]

Coupler is not fiberglass reinforced. it is just standard Phenolic PML coupler. Yes i thought of using more 2-56 I might go that way.

 

[dixontj93060]

You can do 4-40s I use them on my 6" PML Bulldog, but I put brass flat stock at coupler areas to get a clean shear.

 

[Rocketjunkie]

4-40's will work on phenolic tubing but will damage it. You will have to drill new holes every 2-3 flights.