Boom tube material and fastening

[Jim Allen]

Thanks for sharing, do you mean "FILED" rather than "filled" I am not sure what you mean by that. Seems like I will need to find a shop who can do the proper bending

Yes. Bending the skid fin & mounting the skid fin are both important! Bends need to be parallel to each other & parallel to the water line at speed. The following information was written sometime ago & I believe it still applies.

JA

Aaron,

One important thing I did not mention. All sheet metal materials have a "grain direction". When bending sheet metal materials always bend across the grain & not with the grain.

JA

 

[dwilfong]

Turn fins are not hard to make. Find a pattern you like and scribe some lines on it. As you come to the turn at the bottom (that is the style most use today) make the lines closer as you get to the tip. Put the fin in a vice with some angles in the jaws as this will make a clean break line. As you bend on the fin use a small hammer to tap the bend line in. Start at the top and work your way down the fin. Just eye it up as you go.

I found some .050 Titanium plate on E Bay cheep. If you use Ti just make sure you don't go to far with the bend. It dose not like to be bent back again. A little is all right but don't work it to much. It will snap right of in your hand.

Boom tubes I use goodwinds fiberglass tubes. Thy are cheep and hold up just as good as the $$$ CF stuff.

If you run the boat a lot or race it you WILL replace tubes no mater what thy are made of...................

Thy make sizes that will slide inside each other with just a slight cleanup. thy also make a CF tube that I use if I need some more back bone on the inside tube.

For attachment just drill a hole and use some ss hardware and some Teflon washers so you don't put to much force on the tube holes.

This system holds up to a very heavy boat going very fast in any conditions.

Just figured I would share what works for me.............................

 

[Aaron Lavigne]

Thanks for sharing, do you mean "FILED" rather than "filled" I am not sure what you mean by that. Seems like I will need to find a shop who can do the proper bending

Yes. Bending the skid fin & mounting the skid fin are both important! Bends need to be parallel to each other & parallel to the water line at speed. The following information was written sometime ago & I believe it still applies.

JA

Aaron,

One important thing I did not mention. All sheet metal materials have a "grain direction". When bending sheet metal materials always bend across the grain & not with the grain.

JA

Thanks for the info- I am pretty sure I can cut 7075 aluminum to the overall shape I need with my table saw and band saw (done it safely before), but will probably need someone to roll it for me until I buy a table top roller. I feel filing a knife edge on the turn fin would be a lot of work to make it look good. Maybe I can make a jig for a sander?

 

[Jim Allen]

Aaron,

There are three basic shop files that can be used for most filing operations in a tool room. Learning to properly use any file means that it only cuts as it is moved forward! Carefully scribe the leading edge to give yourself a guide as to where to stop filing.The bottom photo shows a Simonds nucut flat bastard cross cut file which is used for roughing. This file is easy to identify, it is black in color & it has a red colored tang. The next file from the bottom is a Simmonds nucut flat 2nd cut. Both of these files are cross cut types. The third file is a Nicholson mill smooth. It will be used for the finishing of the skid fins tapered leading edge & trailing edge. Files need to be cleaned to cut properly & this is done with the file card shown at the bottom.

All edges including the trailing edge must be kept very sharp. All surfaces of the skid fin, it's leading & trailing edges, as well as any necessary mounting holes will be finished before any bending takes place. Notice the parallel lines on the inside of my skid fin that tell where the bends are to be done. The amount of each bend is important & I used Andy's original fin to duplicate those bend amounts. If you bend the aluminum material in a vise that has beat up jaws, your finished fin will have marks & dings in it also. Look carefully at the photos of the inside & outside of my typical aluminum skid fin. Do no forget about determining the direction of the sheet metals grain. Any tool maker can demonstrate what is meant by this when bending metal alloys.

Jim Allen


Aaron,

If I can find time later today, I'll show how a quality tool room vise, a couple of pieces of aluminum stock & some parallel clamps can be set up to accurately make all the bends parallel to each other. The piece can also be bent without putting any twist in it.

JA

 

[Aaron Lavigne]

Very nice and once again informative, I like the idea of learning how to play with metal since I mostly cut wood. I have a solid vice at home and would like to attempt to bend the 7075 aluminum myself. I guess I would have to heat it up first? And I assume i'd hold the fin in a vice while filing

 

[Jim Allen]

Very nice and once again informative, I like the idea of learning how to play with metal since I mostly cut wood. I have a solid vice at home and would like to attempt to bend the 7075 aluminum myself. I guess I would have to heat it up first? And I assume i'd hold the fin in a vice while filing

No heat is necessary, even if you are bending steel & yes, you need to hold the piece when filing.

JA

 

[Aaron Lavigne]

I was thinking of buying the vice attachment in the link below to bend the fin

Didn't mean to turn the tube thread into a turn fin thread, but why not Im sure many can benefit

http://www.grizzly.com/products/4-Vise-Brake/H3243

 

[Brian Sorgente]

That's pretty sweet.

 

[Tom Foley]

I like that attachment , now I need the $ 800.00 Wilton vise !!

 

[Jim Allen]

I was thinking of buying the vice attachment in the link below to bend the fin

Didn't mean to turn the tube thread into a turn fin thread, but why not Im sure many can benefit

http://www.grizzly.com/products/4-Vise-Brake/H3243

Aaron,

The grizzly H 3243-4" vise brake is intended for making 90* bends. A 90* bend in high tensile strength aluminum can be made if the radius of the bend is large enough & if the bend follows the grain rule. None of the bends needed to make an aluminum skid fin for our purpose would be greater than 15*. I also believe the parallel alignment of the bends to each other would be difficult with this die set. Keep in mind, there are aluminum alloys stronger & stiffer than 7075-T651, available in sheet form, which are .090" to.100" thick, which would be ideal for a rigid skid fin.

The red scribe lines on the inside of my skid fin are 1/2" apart. They indicate where the fin is to be bent & where it is to be clamped in the vise by using the sharp edge of the vise's jaw for alignment. I start with the bottom bend first & securely clamp the material above the vise jaws between two 1/4 thick pieces of aluminum. I use pieces that are 12" long X 2'' high. The long length keeps things aligned so that there is no twist in the bend. I use a 12" adjustable wrench to bend the fin at this point. You will find that it will be easy to bend & you will be able to make bends that are parallel to each other without twisting the part. Each bend is the same amount, approximately 15*. This is really a "piece of cake" with simple tools & a little fore thought.

JA

Aaron,

Note: There is a simple method that can be used to mount any flat type, unbent skid fin, to the vertical inside wall of any sponson at any angle desired. Unbent, flat type skid fins never present the type of problems that can be found with bent skid fins??????

JA

 

[dwilfong]

Now that is a cool tool........................................It will do the job for sure........................

You can get the 4 1/2 Wilton like I have for about $400 or less.

 

[Aaron Lavigne]

Keep in mind, there are aluminum alloys stronger & stiffer than 7075-T651, available in sheet form, which are .090" to.100" thick, which would be ideal for a rigid skid fin.

What aluminum would you suggest?

I use a 12" adjustable wrench to bend the fin at this point.

How dou you use an adjustable wrench to bend it? Can you post a picture of the jig setup

 

[Jim Allen]

Aaron,

These are the aluminum pieces & clamps I use to bend .060" to .125" thick aluminum type skid fins when there is no bending brake available. The vise shown is a 6" Magnum Machining vise which is mounted to my milling machine table. It costs about 1/2 of the $800.00 price mentioned for a Wilton vise of comparable size.

Notice the position of the fin once it is located with a marked bend line & the vise has been closed. All the bend lines have been marked on the inside of the fin at 1/2" intervals. A 1/8" X 1" X 12" spacer shim is placed beneath the front side clamp bar to give that clamp bar enough room to move downward when bending takes place. The spacer shim is removed after the clamps are applied. I apply a very little pressure with the 12" adjustable wrench on the center parallel clamp. It doesn't take much force to bend even .125" thick 7075 T 651 aluminum.

Jim Allen

Note:

There is an aluminum alloy which is stronger than any 7075 grade. Thus far it is only available in the bar or rod form, but this was also true of the 7075 alloys when they first appeared. The alloy is 35% stronger than 7075. When considering its strength to weight performance it is 33% better than 7075 & 28% better than 6 AL-4 V, grade 5, Titanium.

JA

 

[Aaron Lavigne]

Perfect thank you for the great detail. I am going to try all of that soon using as much of the technology you posted as I can