RKB Kustom Speed
Article by: Rick Bray – rkbkustomspeed@hotmail.com
Originally Published In The April 2015 Issue Of Cycle Source Magzine
One of the most popular topics of discussion I hear when people are looking at my bikes is the amount of detail put into my frames. Quite often people are interested in having me build them a frame, but can’t understand how they go together. Many of the features on them are designed to spawn those exact questions. In some spots the tubing appears to be “slipped” in place while in other crucial mounts look as if they are simply butted against a frame rail or cross tube. However, everything is welded in place and totally structurally sound. These are just details added in during the design process to accent future paint work. These bikes take a hell of a beating going down the road so there is no room to leave any weak links. A quality frame has to be built square and strong enough to handle the day Article By Rick Bray rkbkustomspeed@hotmail.com As you can see my fixture is fairly crude and simple. The only fixed point is for the axle plates. The neck point features adjustable rake and stretch. Every frame starts with a custom neck machined in-house. RKB frames are always one off because to day rigors of vibrating engines, rough roads, and anything else you might encounter while riding. All RKB Kustom Speed frames start with raw American made materials. Though there are cheaper alternatives, I find them to be an inferior product and choose not to use them in my shop. Everything that comes out of the shop is fabricated 100% inhouse and tig welded by myself. In this tech article I will be utilizing my manual mill, lathe, bandsaw, JMR hydraulic tube bender, and Miller 250 tig welder. There are several different brand names of equipment available and many will do an adequate job. It is, however, recommended to use reputable brand named equipment for accuracy and dependability. There are many ways to build a frame and in this article I’ll walk you through the construction of my future Artistry in Iron piece step by step.
As you can see my fixture is fairly crude and simple. The only fixed point is for the axle plates. The neck point features adjustable rake and stretch. Every frame starts with a custom neck machined in-house.
RKB frames are always one off because the fixture does not have engine or tranny mounts built in. Step number 2 is fabricating the seatpost cross tube.
Proper notching and fitting is crucial to weld quality and a square frame. This frame utilizes an I-beam seatpost so the cross tube is larger than normal in order to accommodate it.
The seatpost cross tube is shown here with a pad welded in place for the I-beam to sit on. In the end the I-beam will be structurally sound, but appear to be “slip-fit.”
I prefer to use an engine for mockup while building an RKB frame. This allows for every frame to have unique dimensions. The key to a good looking frame is letting it tell you where everything belongs.
I chose to machine my own I-beam for this frame. It started out as 2” solid square stock and here I used a rosebud torch to add a little curve towards the top of the seatpost.
With the seatpost height calculated I can now start on the backbone. This backbone is 1.5” x .120” DOM tubing that I pressed into an oval shape.
After notching the backbone the fit is fine-tuned with a die grinder.
This frame has accent sleeves on the end of each tube. I plug weld each sleeve to the frames tubing in order to ensure strength.
With the sleeves welded in place and the backbone tacked, the next step is fabricating the downtubes. I chose to use .750” x .156” DOM tubing on this frame, but every frame rail is bent to fit around a specific engine. This is one of the most complicated parts of a frame build because there are multiple axes to compensate for and everything has to be square.
Next up are the axle plates. I hand make my axle plates so they are unique on every frame. These start out as 1/4” 4130 chromoly plate.
Once the axle plates are squared on the fixture I can start on my lower 74 April ‘15 CYCLE SOURCE rails. I-beam was again the material of choice for this part of the frame.
Now that the lower rails are tacked in I can work on the uppers.
After squaring up my engine and tranny for mock-up I build the mounts accordingly. Here is the hand machined tranny mount.
The engine is squared to the centerline of the frame before the mounts are tacked in place. I like to take each connection point in 4 places to make sure nothing moves during fabrication.
Once everything is fitted and tacked the way I like it I sit and stare at it for a while. I’m very pleased with this one!!
I tig weld the frame as much as possible in the fixture then let it cool. Afterwards the frame comes out of the fixture and just to be safe I test fit everything to make sure nothing has moved.
The end result is a clean road worthy frame ready for me to bash the hell out of it……..after it goes to Artistry in Iron.
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