Saturday, February 12, 2011

Kolb Comes Through

Many thanks to Scott Kolb of Kolb Machine for delivering 2 perfectly capped and smoothed cylinder heads.  Scott is a fabrication ace and it is him who I turn to when my ham-fisted hand work simply will not be up to snuff.  He is also an accomplished builder in his own right, having several land speed records under his belt and several more in his sights.  His blog site shows a lot of cool stuff on his LSR project.  There is also some great footage from his visit to the A2 wind tunnel in North Carolina, the heart of NASCAR territory.  The visit was very productive and informative for both learning about his existing partial streamliner and doing tests on shapes for his future 200+mph 125cc full streamliner.  It was my first wind tunnel test and hopefully not my last.

I had 2 sets of ported heads and kit cams purchased from Attack Kawasaki from one of their last Formula Xtreme bikes when that series still allowed significant engine modifications.  These heads were sectioned on a bandsaw and cleaned up on the mill to leave the camchain tunnel and adjacent 2 cylinders.

Bandsaw cutting:

Cleaning up surface on mill with face mill:

I then stripped the paint off the parts and shipped them up to Scott.  He proceeded on the 2 step process first documented in an earlier post, Head Weld Test.  The 2 piece cap is to insure the internal separation from the oil and cooling passages remains separated.

Cutting out the cap plates:


Top cap plate unwelded/welded:
 


We installed extra valves and springs during the process to ensure the valve seats did not slide out of position due to the high heat input during TIG welding.

Fully welded part:

We decided to also fill in the cam bore 1/2 circular cutouts to make the gasket surface a single plane to allow using a waterjet cut Cometic gasket

Filling in cam journal external bosses:

Fully welded:

Trimmed: 

Scott then ground out all the welds giving the part a very clean and manufactured look.



From here I will remove the valves/springs and mount the head on our trunnion fixture to clean up the gasket mounting surface.  Some custom gaskets are on the way from Cometic to keep all the oil inside and we're a few steps closer to having a complete engine.

Until next time...


Thursday, February 10, 2011

Machining the Crankshaft Connecting Rod Journals

I was able to get some more time in on Peter's mill and got the journal machining done on all 3 crankshafts. After the last step the cranks were turned but did not have the offset journals machined, as shown in the following picture:



This step moved the parts from the lathe to the mill.  I hold the right side of the crank in a 3J collet and supported the outboard side with a tailstock with a dead center.  The setup is shown in the following picture:


The process is the same as the aluminum test part, except the spindle speed and feeds were much slower, the depth of cut was less, and I used a roughing and finishing end mill.  The finishing end mill was custom ground to have a flat end which minimized the uneven surface that the test part ended up with.
The roughing end mill has a serrated cutting surface and provides an aggressive edge to remove large amounts of material, allowing the finish end mill to only remove the last .02", last longer, and hold tighter tolerances.  The end mills were purchased from Mari Tool and held in a 3/4 milling chuck for maximum rigidity.

Now on to some cutting shots.  First roughing in a step pattern produces a square journal:


Once both journals are roughed out leaving a square the next operation employs a 4th axis move to create the rounded thrust and journal surfaces:

Here's a couple of videos showing the finishing passes for both the thrust and journal surfaces:
        video
and
        video
The resulting surface finish and accuracy were excellent.  Here's a quick spin of the final part.
        video
The great part about CNC is now I ran the same program 2 more times and ended up with 3 great parts.

Next steps for the crankshaft are to machine the camchain sprocket teeth and drill the oil holes.  Hopefully i'l get to those operations next week and be ready to ship them out for gear hobbing and plasma nitriding shortly after.

That's all for now.

Monday, February 7, 2011

And now for something completely different

After working on all these engine parts I got a bug to shift focus and to make some inroads on the pile of chassis parts that need to be made.  My first choice was to make the upright legs for the front suspension.  These legs are central to the variable flex idea that is incorporated in the front suspension.  Instead of following the current ideas on overall bike flexibility which uses stiff telescopic forks and a slightly flexible chassis, I prefer to have the flex where it is needed-at the wheel.  Telescopic fork equipped bikes don't have much of an option here- the forks needs to be relatively rigid, otherwise they would bind up when flexing under braking load, preventing smooth suspension movement.  With the linkage suspension I am using it is possible to have a very stiff chassis and a-arm structure to allow smooth suspension action and accurate wheel location yet have flex built into the upright legs to accommodate small bumps and irregularities in the surface when leaned far over.

From the years spent campaigning my single cylinder racer I have a good idea of the directional stiffness that will produce good results.  No, I won't go into specifics here on what the stiffness ratios are.  As expected, maximum stiffness is needed in the braking direction and much less needed in the transverse direction.  The initial uprights I designed worked well, but was a bit complex to make quick copies of.  I then moved on to a much simpler design using rectangular steel, some with welded on stiffening plates to tweak the stiffness as testing dictated.  The latest version of the front suspension uses some old and some new to result in a low friction assembly with easily characterized controlled flex characteristics.


First upright design using suspended headstock design:

This design worked very nicely but was a bit complex to make variations on.  The suspended headstock and all ball bearing upright mounts provided smooth action and good feel but at a weight penalty to later, simpler designs.

Second design style using spherical bearings (bearings not shown):
This design had the benefit of being easy to replicate with subtle stiffness variations but I found the spherical rod end bearings reduced feel and required frequent replacement in order to maintain optimum performance.


Final version for the V4 project bike:
This version separates the parts into a bearing carrier and legs that bolt on.  It enables easy modifications to the stiffness by making new leg parts with varying dimensions yet keeps the bearing mount arrangement stiff.  The weight is in between the first two designs, a good overall compromise in my opinion.  The upright legs will be machined today.

As with most billet parts I started with a large plate that both parts could fit in.  I bolted this directly to the CNC table and machined the mounting pads and axle holes as shown in the following image:

I then machined a fixture baseplate that would locate on these premachined features and allow me to complete the part:



The fixture locates on the machine table with dowel pins allowing easy and accurate setup for making more parts.


I then cut out the individual parts leaving extra stock around the perimeter and bolted them to the fixture plate as shown:


Next came the pocketing and chamfer operations:

Resulting in a sweet looking part:



Mirroring the toolpaths allowed me to create the 2nd part with a minimum of hassle resulting in a very stiff looking assembly:  This design also makes use of the latest radial mount Brembo billet calipers for the ultimate in progressive braking feel.


I don't mention it often enough so a big thank you goes out my shopmate to Peter H. for allowing me essentially unlimited use of his 4 axis CNC mill.  Without access to his machine I'd be making much lower quality parts on my old BP 3 axis relic.  And I'd still be figuring out how to fit the engine castings on it!

In the next few days I hope to move on to the upright bearing housing and handlebar mount, both of which need the 4th axis and trunnion table.

Until then.....