Bike Bobber

[massdrive]

Another bike another coaster brake arm needed to fit around a rear sprocket on an adaptor. I started with 1" x 1/8" cold roll box tubing. Why such a stout choice of material for a coaster brake arm? Because I had a 10 ft. length literally laying around on the floor. I lopped off 20", just eyeballed it. Then I split it length wise about 1/4" thick, again I just eyeballed it. At this point it is hard not to notice that my work piece warped as I split it on the saw. This is to be expected when ever you apply friction and/or heat to thin metal and will be easily dealt with later in the process.
So now I have turned a piece of 1" box steel into a piece of 1" x 1/8" x 3/16" x 20" steel u-channel. I eyeballed the u-channel and sawed it in two. I chucked each 10" length one at a time onto parallels in a power lock vise and milled them 3" at a time down to 3/16" thick. Than using a belt sander I de burred the u-channel's and ground a 1/16 x 45 degree chamfer along the length of the outside edges. Again I just eyeballed it.
NEXT INSTALLLMENT

 

[massdrive]

Re: Bike Bobber Welding thr Brake Arm Together

Welding the Brake Arm Together

Again let me say that if I had some lighter gauge steel lying around I would have used it. Also there are many different fabrication methods that can be used. I'm using the slit and weld method. If I had a pipe bender, or break press, or a torch set I would use other methods to shape the brake arm. Some might say what I'm doing is crude, yep it is... crude and effective.
So the two half's of the brake arm are ready to butt weld together. MIG welding is easier and faster, but in this case TIG welding will be more effective. I aligned the two strips of u-channel in a bench vise and squeezed them together securely. Squeezing them together while welding and letting each section cool in the vise will straighten the arm out with no fuss.

 

[massdrive]

Cupping the Brake Flange

Cupping the brake flange is critical. Without this the arm will simply twist and brake off of the flange. I cut out a small rectangle from the left over piece's of box tubing leaving the 1/8 radius. I slit the radius about every 1/4 in. and eyeballed it into position centered on the edge of the flange. As I tacked it together I tapped the heated metal around the flange with a hammer to form a cup. After tweaking the cup walls straight I finished welded both sides and than rough ground them.

 

[massdrive]

Attaching the Cup to the Arm

First I eyeballed and cut two slit's on opposite sides of the arm and bent it to create a crookneck to go around the rear sprocket. I than tacked the cup and arm together and made a test fit... so fare so good. Next I made two crude gusset's to help support the arm on the cup and welded them in place on both top and bottom.

 

[2door]

Like your previous one, Mass, that arm isn't going anywhere. Bullet proof and functional.
Too bad most of the chrome plating shops are out of business today. But maybe just a coat of paint color matched to the bike will look good too.
Thanks for the tutorial.

Tom

 

[massdrive]

Well ya know its not done yet so how do you know where it is going? I don't really know yet. lol Thank you for helping me decide if I was going to keep it simple and plain, or fancy and ornate. You will have to come back and see what happens... I think you will like it.

 

[2door]

LOL. Clarification: "isn't going anywhere" means it won't break, fall off or fail. Guess I should have been more precise and stayed away from slang.
Looking forward to seeing the finished product.
Tom

 

[massdrive]

Ohhhhhhhh... no harm done either way 2door. I took no offence it made me chuckle. And you are right it's not going anywhere. I admit it is a lot of over kill. I'm going to lighten it up a little and dress it up at the same time.

 

[massdrive]

Grinding the Cup

I rough ground the gusset's top and bottom and than sawed off the excess metal. Next I finished ground the entire cup assembly. It came out nice

 

[massdrive]

So the brake flange cup is finished and the brake arm is ready to shape. I'm using the slit and weld method to bend the brake arm into a nice smooth 3 1/4 in. arc. Why 3 1/4 ins.? Because I'm installing a 40t rear sprocket that is... 6 1/2 ins. in diameter. It is little things like this that can make the components of your bike mesh together.
To start I made a simple template out of poster board to follow when bending the arm. As you can see unless you do this everyday it can be difficult to gauge the width and frequency of the saw cuts. So I've made some more work for myself, but it will all work out in the end. After tacking it together on one side I welded the inside diameter first. This will help stabilize the piece when I finish weld the side I tacked.

 

[massdrive]

Using minimal heat I finish welded the tacked side of the arm. After letting it cool while clamped to the table I set it up on the mill to quickly remove the excess weld bead. Yes it is faster and easier and yields better results than grinding however I did fry a 3/4 in. 4 flute end mill in the process. I can get it re-sharpened.

 

[Tang]

Nice work for eyeballing it.

Tang
The trail life for me.

 

[massdrive]

Thanks Tang. As I said in the beginning of the thread I'm using material I have laying around and this is just one method of fabrication. As fare as eyeballing everything on this project I do it because precise measurements are not necessary. It has become sort of a personal joke for me and you will see why soon enough...

 

[2door]

Well, I'd say your 'eyeballs' are working just fine. Show us the finished product.

Tom

 

[massdrive]

With the wide side of the arm milled flat I ground the inside and outside of the arc on a belt sander. When ever this type of fabrication is done there is bound to be some pits and pin holes in the metal. Pits are easy to fill and blend in, but pin holes are like ice bergs in that most of the hole is under the surface. You can spend a lot of time and resources welding and grinding chasing them around, or you can simply grind them out with a carbide bit and a dremel, fill them in once and be done with it. If you plan on painting than pits and pin holes can be filled in with body filler and or primer. However I'm having the brake arm powder coated so the metal finishing is critical to ensure a smooth uniformed powder coat surface.

 

[massdrive]

After roughing in the pit repairs with a dremel tool I finished blending them in by hand with a crescent moon shaped bastard file. A die grinder with a sanding disc or barrel will do the job too, but in this case a file can work just as good or better, and cheaper too. A good quality file properly used can last for decade's or more. To blend in the pit repairs I used long rolling twisting strokes of the curved side of the file. I worked both sides of the entire arc at once not in sections. Always use a bastard file with forward stokes only. Dragging the file backwards against the work surface only serves to dull the file prematurely. Also use a file card to keep your files clean and you will produce better results and your files will last longer, oh and your tool box drawer will stay cleaner too.

 

[allen standley]

Thanks MD, I had brake arm issues in the past. No doubt I'll reference this again in the future.

 

[massdrive]

You are very much welcome Allen. I'm glad that you're inspired to make some mods to your bike. There is much more to come.

 

[massdrive]

Time for a test fit... opps not enough clearance between the crook neck of the arm and sprocket. Grrrrrrrrrrrrr... I guess I should have eye balled twice and cut once. Long story short, I cut out the crook neck and replaced it with an arc. In retrospect this is what I should have done to start with, it looks much better this way.

 

[massdrive]

Now it's time to secure the brake arm to the frame rail. Unfortunately this frame has already been powder coated so there will be no welding on the frame. I'm going to make a cool little bracket that will clamp to the frame and allow the arm to be moved fore and aft to adjust the chain with out loosening the bracket and dragging it on the frame rail. I decided to make the bracket out of aluminum. Why? Well the frame is aluminum, but mostly because aluminum is softer than steel and there for easier on my cutting and grinding tools and supplies. Oh yea I have some flat stock laying around.

I won't be doing much eye balling on this bracket. It has to be a precision fit to hold the brake arm in place and not damage the frame. I'm starting with some 1/4 in. x 1 1/4 in. flat stock.