Thursday, September 8, 2011

Clutch cover machining

Now that I'm done with the pockets on the primary drive gear there is some empty space on the mill bed so I'll get in come clutch cover machining in while the setup is available.

After machining the 4340 steel going back to aluminum is a pleasure.  The 4340 steel is a high strength steel that requires a rigid setup with speeds (how fast the spindle/cutting tool spins around) and feeds (how fast the cutting tool is advanced through the material) about 1/3 that of aluminum.  If cutting aluminum can be compared to a hot knife going through butter you can describe cutting high strength steel as a butter knife going through steak.  A tough stringy steak, not a nice tender filet mignon.  One that quickly dulls even the hardest coated carbide cutting tools.

Back to the topic at hand, cutting aluminum.  As usual we start with a large flat plate clamped to the table and gradually whittle away all the unnecessary material.

Careful clamping and slightly thicker stock will allow me to leave a thin bridge of material around the perimeter making it easy to clamp and machine without clever fixtures.
All the programming was correct and this operation went off without a problem.

The large circular island in the middle of the part is where the clutch will go.  This island was left to allow me to use the hole as an initial clamping point for the second mill operation.  When the last facing operation is done the round dropout will become scrap.

I ran two parts and checked fit of the starter shafts and gears that this cover houses and everything fit properly.

I now have to program and run the fixture plate for the second mill operation then program and run the front side of both parts.  That will finish the part and allow me to start mocking up the starter gears and right hand side engine components.  Hopefully I can get to that in the coming week and put up another post.

Wednesday, September 7, 2011

Finishing the primary drive gear

After the two lathe operations to create the primary drive gear blank I need to do one mill operation to create the clutch basket mounting holes and various weight reduction features.

Switching from machining aluminum to machining steel is like getting a 2 flat tires.  With aluminum you can spin the spindle as fast as it can go and then just push the end mill though the material with little regard for cutting forces or temperature.  Chips fly and progress is made, quickly.  With steel, especially this high strength 4340 material, the spindle needs to slow down a lot and the feed rates seem to be just above a crawl.  End mills wear quickly and if you're not careful with the cutting parameters you will be treated to the sight of a glowing end mill spitting out glowing chips.  Pretty, but not good for material integrity.

To hold the part I machined soft jaws (similar in concept to the lathe ones) in the Kurt vice, clamped the part, and indicated it for concentricity just to be sure.
After setting up a set of the same tooling used to machine the crankshaft journals we're ready to run the program.  It is not too complex a program, just some holes and pockets.  The finished part looks like this:

and after repeating a few times we have a nice group of parts:
The parts are now ready to be sent out to the gear house who will cut the gear teeth on the outer diameter of the part.  It will then go for plasma nitriding to surface harden it and after that the part is ready for use.

Tomorrow I'm going to switch back to aluminum and start machining the clutch side cover.

Tuesday, September 6, 2011

Making parts again....

After a couple of weeks of turning these
into a bunch of these

and a lot of this
the lathe is open and I am more than ready to make some bike parts!

Today we're making the blank for the input shaft primary drive gear.

This is the large spur gear that the clutch basket bolts to.  It meshes with the crank drive gear which is machined directly onto one of the circular crank counterweights.  This is a highly loaded part and therefore made from the same 4340 material that the crankshaft is made from.  The plasma nitriding hardening used to harden/strengthen the tooth surface is the same process used for hardening the crankshaft plain bearing journals.  Due to the higher surface stresses encountered by the gear tooth the part will be left in the plasma nitriding chamber for a longer time which creates a deeper layer of hard material.

The process will start with round blanks sliced from a 7 1/2" diameter bar.  The material was sourced from Grammer Dempsey & Hudson, a ferrous metal (steel) supplier located close by in Newark, NJ.  They are old school to the point that they don't have a website!

Here's a few blanks of material are ready for the first and second lathe operations:

After machining soft jaws to the appropriate diameter the stock can be held in the 3 jaw hydraulic chuck.  Soft jaws are replaceable clamping jaws that can be easily machined to hold a specific part diameter or profile.

I then ran the first lathe program which cut the clutch basket mounting face and pilot, the needle bearing bore, and the outer diameter that the gear teeth will be formed  from.  Machining all the crucial features in one setup ensures a high degree of accuracy.  Since this part is responsible for the transfer of all the engine power from the crank to the transmission accuracy is essential to minimize frictional power loss.

After machining several parts I then recut the soft jaws (they are replaceable once cut down as far as the mounting bolts) to hold the part by the newly machined outer diameter in order to clean up the back face of the part.

The back face machining is for weight reduction only so accuracy requirements are much lower than for the front functional surfaces but I still take care to minimize reclamping errors..

Repeat a few times and we have enough for a first run of engines:

The part now needs one mill operation to create weight reduction pockets and the clutch basket mounting holes.  I should have some time this week to do that.

Monday, September 5, 2011

Cross Pollination

Just letting the blog viewers know that there is a new thread on the project over on the ADV Rider Forum.  The forum is mainly focused on Adventure riding.  They describe their mission as 'created to support the horizon-chasing adventure motorcycling community.'   It's a far cry from roadracing but it uses motorcycles and it's practitioners are more likely to take a hacksaw and wrench in hand to improve functionality than most riders are.  Also, adventure riding is fun as hell and a lot more accessable and cheaper than roadracing.  Pick a dirt road and go.

The site's new 'Some Assembly Required' forum is a perfect place for the project and so far it has gotten a warm welcome.  Take a few minutes to browse and you'll see an interesting collection of projects and maybe get the bug to find the horizon.

I have a bunch of pics to put into a couple of posts but my camera is still making its way back to me after our Indy trip, which was a ton of hard work with barely a second to relax.

Check back in a day or so for more.