Programming Setup 1 on the Lathe

The first step in converting CAD to chips is to plan ahead, and it should happen very early in the design stages, otherwise you run the risk of having an unmachinable or hard to machine part.  What we are doing here is step 2, converting 3D CAD to 2D CAD to G-code CAM.  The 3D CAD provides complete surface information of the part.  Since at this stage the part is a simple revolved shape, we can reduce it to a 2D profile and not lose any information about the shape.  From this 2D profile the CAM software creates a series of 2 dimensional moves along the X axis (diameter) and Z axis (length of part) that create the part profile from solid bar using appropriate cutting speeds and feeds.

3D CAD:

2D CAD:

2D CAM:

Now we can go to the machine, which is currently busy.....

The CAM package is told the shape and position of the various tools needed to cut the part, it is told the shape of the part, and it is told the characteristics of the machine.  Doing what computers do well, crunch numbers, it uses all of this hopefully accurate information to calculate the appropriate motions to generate the desired part profile.  As with all computer programs, garbage in=garbage out, except instead of the BSOD or an inaccurate spreadsheet, you get twisted metal and a large repair bill.  It is a very good incentive to make sure all the info input is correct and also carefully check the output.  The output of this 2D CAM process is a text file in what machinists call a G-code format.  A sample g-code file in a format usable by my Siemens control looks like this:

%MPF52
G70 G90 G40 G54
(TOP-CAP-3-rec2-rad PR=3.745 Z1=8.075 )
(T-2 O-6)
(DCGX IN SDJCR-123)
T02 D06
G0 X0.825 Z.5
Z0.
M3 S1000
G96 S1000
M8
G1 X-0.0357 F.005
G0 X0.6316 Z.155
G96 S1500
G1 Z-2.99 F.008
X0.6864
G0 Z.11
X0.5567
G1 Z-2.4417
X0.5625 Z-2.4475
G3 X0.57 Z-2.4656 B.0256
G1 Z-2.99

The format is relatively simple and once you have used it a bit reading it is pretty straightforward.  The G-Code file is sent to the machine over the network and then after machine setup the program is run.

Once my current lathe job is complete the crank goes right in.  I hope to have another blog update sometime this week.

Starting on the Crankshaft

Now that the engine case patterns are approved and the production order placed I can move on to the crankshaft.

It will be a 180 crank to exploit the reduced variations in reflected crankshaft inertia that this configuration provides, similar to Yamaha's cross plane crank in the M1 Grand Prix bike and the R1 Super Bike.

I will be initially testing 2 different versions of the crank- one with pork chop counterweights and one with full circle counterweights. The main testing variable is the overall weight/inertia vs. aerodynamic efficiency of the 2 versions.

Full circle configuration:
Pork Chop configuration:


The manufacturing process will be as follows:

Material blank:

• 3 3/4" diameter x 9.7" long
  
• 4340 steel
• 28-32 Rockwell C hardness
  

In house:

• Machine crank on lathe in 2 steps blank leaving .01-.02 stock on surfaces to be ground.
• Mount lathe blank in mill 4th axis and rough machine crank throws
• Rough and finish machine the two silent chain cam drive sprockets with custom form end mill cutters.

Outsource:

• Hobbing of primary drive gear and starter clutch/crank sensor spline will be done by Eagle Machine, Inc. of British Columbia. They have experience to properly deail with custom low production crankshaft.
• Final Grinding of main and rod bearing surfaces will be done by Lopez Crank Shaft of Santa Fe, CA. They are another custom crank specialist and can provide the accuracy and surface finish needed.
• Plasma nitriding will be done by Accurate Ion Technologies, a specialist in steel hardening and advanced surface finishes. We are using plasma nitriding for it's low process temperature that enables proper multilayer surface hardening of the part with no distortion.
• Once we get the part back from Accurate Ion it is ready for use.
  

The process will involve 2 lathe setups and one milling setup.

The lathe first lathe setup will hold a 3 3/4" x 9.5" long material blank in a 3 jaw chuck. we'll machine one end of the crank, the middle main bearing journal, and various smaller features on one end of the part.

End of first lathe setup:

Once I finish some client lathe work currently running this is next in line. The next post will detail programming and cutting of this first lathe operation.

Long Block Assembly Shots

Now that we have a girdle, top, and a couple of heads the time is ripe for some assembly shots. I'll let the images speak for themselves...


Short Block:




Long block:



The overall engine assembly is very short front to rear to enable a long swingarm in a short wheelbase. The resultant slight additional height compared to a normal I4 is easily accommodated by the unique chassis needed for the Hossack-style front suspension.

Finishing the Girdle Machining

This blog post is dedicated to Chris Hodgson from San Jose BMW. I saw Chris and his crew at the BUB Bonneville motorcycle speed trial event last week while helping wrench for Scott Kolb on his 125cc partial streamliner. Scott set a new 2 way record of 146.7mph on the last day of the event after lots of tweaking. There's an article over at Hell For Leather on the effort. The trip was lots of fun, especially when a record is set. Every speed lover needs to go to Bonneville. It's only 2 hrs outside of Salt Lake City and besides having no speed limit also presents an awesome vista in any direction.



Back to the topic at hand, I had the short block with me for display purposes and Chris Hodgson was like 'when did you do that machining, the blog is not up to date, what are you waiting for!!!!!' Being chastised by an internet follower compelled me to get my ass back in gear. That fact that it was a person who is a world renowned BMW tuner made it go into high gear! Chris and crew also took a record with their BMW HP2 so it was a happy pit area all around.

Chris, this update is for you and hopefully I will be able to work on the project and update the blog regularly.

Now on to our regular programming...........

After the last post, which was machining the girdle split surface, we are up to the balance of machining on the girdle part. We were up to this point on the part:

Oil gasket and split surface machined:


The next step is to machine the girdle subplate then complete the part machining. The subplate screws to the oil pan surface and is accurately aligned to the trunnion table with dowel pins.



The first set of features to be machined is the crankshaft main bearing split surface:

Facing:


Drilling/tapping.......


Then the 4th axis is indexed 90 degrees and the clutch side is machined. there is a bunch of profiling for the cassette transmission side plate, trans and oil shaft bearing bores, gear clearance, and misc threaded holes.

Cassette mounting flange:

Gear clearance:


Roughing the bearing bores:


Once these deep bores and pockets are done the 4th gets rotated -180 degrees to machine the output sprocket side. The features on this side are the generator cover surface, oil filter mount, oil pump drive and pressure chambers, and starter bore. Yes, a starter motor! No rollers, no bumping, just press the magic button.


Facing gasket surfaces:

Some operations are pushing the limit of tool stability, like this 1" dia x 8" long insert end mill:


Starter motor mounting hole:

Gerotor porting:

The oil pump is a gerotor supplied by Melling, a high quality OEM/aftermarket automotive parts manufacturer. This style pump is highly efficient and compact when properly packaged. A lot of design assistance for the entire oil pump circuit was provided by Marc Goulet of Melling. Marc is also a motorcyclist and was kind enough to donate his time and put up with my unending questions on the subtle details of high performance oil system design. Marc has been involved in the design of some top level F1 engine oiling systems so he is definitely the person to ask in this field.

Inner and outer oil pump gerotor:


These parts fit into dual eccentric pockets that have CNC porting designed to allow high flow with minimal power losses.

Those 3 machining positions contain all of the high tolerance operations. Now on to some less critical ones:

Oil drain hole:


The position of the subplate is then indexed 90 degrees on the trunnion table and we machine the:

Upper engine mount:


Lower engine mount:


Starter mount:


That covers the majority of the machining on the girdle. Bearing bores will be finish machined as part of a complete crankcase assembly.

It ends up being one sweet looking part:




Stay tuned for more soon!

Machining the Gasket Split Surface

Now that we've gotten accurate mounting features and a matching fixture plate we can start machining the rest of the part.


These operations are relatively simple, some facing, drilling and a bit of spot-facing. I'll be machining the following features:

• face the main gasket surface

• drill/main bearing stud holes

• drill/tap crankcase attachment bolt holes
• drill cylinder head oil drain holes
• spotface/drill oil passage in filter area

That's all I have for now. I hope everybody has a fun 4th of July holiday. Until next time.


Chris

Machining the Girdle

Now that the girdle has been scanned and determined to be accurate, I can reference known location features to accurately position and clamp the part to the mill bed.



Once rigidly clamped onto the bed, chips will start to fly.

Literally.

• machine fixture plate and mount part
  

Now we're ready to machine the rest of the features using the 4th axis setup. Unfortunately, it's time to shift to some customer work for a few days.

QC on the Crankcase Girdle

The sample casting for the crankcase lower section just came in. This part contains the crankshaft lower bearing caps, oil pump/filter and drive system, and the transmission and clutch. Although it looks visually more complicated than the crankcase top, it is a simpler piece to cast in that there is only one internal passages requiring a buried core, namely for the oil pump pressure area.

The placement of this core is less critical than those for the cylinder bores because of the lower pressure and thermal stresses this area experiences. This core forms the pump inlet and outlet ports, high pressure chamber, pressure relief valve port, and oil filter mounting boss details all in one piece. One of the benefits of the casting process is that part complexity is not penalized as it is with billet parts.


The QC process used on this part will be the same as for the crankcase top:

• scan

• overlay to CAD to verify fidelity to the CAD model.
  

This sample part was dimensionally excellent. There are a couple of areas I may modify after going through the part's CNC programming process. I'll know more as the part moves through the various machining stages.

That's all for now.

Chris