Friday, August 20, 2010

Purge/Heat Sink fitting for Paragon dropouts

Tacking up Chad's rear end, I decided that I needed to spend some time to create a purge/heat sink fitting for the rear hooded dropouts that did a little better job at protecting the underside of the hoods than the foil dams used in the past.  I wanted a piece that would purge the underside, provide a heat sink for both sides, and be interchangable between the chainstay fixture and the frame fixture.  All in the anticipation of creating a tool that will increase the efficiency of building the rear Ti ends and provide a cleaner end product.

Starting off with some 1.75" 6061 stock, I cut some rough pieces to begine turning...
The first part I began working with would be the inside heat sink, an interference fit piece on the dummy axel that would slide tight against the inner plate of the dropout.  Here we are turning it down to the 1.5" od to match the dropout.
 A visual for ya, showing the size...
Next, I layed out the center of the axel line as it sits offset in the dropout, so that when the final hole is finished, my outer diameters will line up perfectly.  Starting with a center drill so that the position does not travel under initial tool pressure, I'll use increasingly larger drill bits and then finish with an endmill to insure the correct size for the friction fit on the axel.

Checking the rough fit on the axel and against the dropout, looks like we did ok...

Working on the inside piece, I'll turn it down to fit the inside diameter of the dropout so that it nestles up under the hood with a small gap for argon flow. 

After I parted off the .75" inside piece, I set up for the axel bolt centerline, then drilled it through. 

The next two processes are for the argon purging...a center bore hole that cuts laterally through the piece, and then multiple air holes that intersect that center bore for the gas to disperse through under the hood of the dropout.  I could not find my tap for the argon fitting, so left the hole undersized to fit the tubing until I can locate that little bugger and thread a larger hole for the quick connect...adapt and overcome I guess :)

Three purge exits that area spaced evenly under the hood's footprint area.

The tool all assembled...ready to begin tacking the rear end together...

Took a bit of time, but a dedicated tool like this is what's necessary to insure a quality finished product.


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