1/4 scale Porsche 917 180 degree V12 Build

[crueby]

Oh, the way you mentioned it in the earlier post,  "40 tooth cam gears with vernier holes", I thought there was something special on the gears themselves.
 

[Vixen]

One of the cam gear towers.....Additionally, there are (2) 40 tooth cam gears with vernier holes....

There are 4 oil pump gears

And there are the distibutor gears  ( cross helical )

So ......cutting gears for a while!

Dave

When you said  "40 tooth cam gears with vernier holes" I thought you were referring to the ring of 17 bolt holes that you can see on the end of each camshaft on the 917 cross section shown below. These holes allow for the vernier adjustment of each Camshaft with respect to the Crankshaft. When you build up the whole camshaft gear train you will probably find the camshaft position may be out by part of a tooth width (that could be as much as 9 degrees). The vernier holes allow you to rotate the gear on the camshaft in 1/17 of a tooth increments until the timing is spot on, to within 0.5 degree. It's quite normal to only fit only five or six bolts into the available vernier holes.



There is a similar vernier adjustment on the Mercedes Benz W165 camshaft gears. You can see the uneven bolt spacing.



Mike

[steamer]

One of the cam gear towers.....Additionally, there are (2) 40 tooth cam gears with vernier holes....

There are 4 oil pump gears

And there are the distibutor gears  ( cross helical )

So ......cutting gears for a while!

Dave

When you said  "40 tooth cam gears with vernier holes" I thought you were referring to the ring of 17 bolt holes that you can see on the end of each camshaft on the 917 cross section shown below. These holes allow for the vernier adjustment of each Camshaft with respect to the Crankshaft. When you build up the whole camshaft gear train you will probably find the camshaft position may be out by part of a tooth width (that could be as much as 9 degrees). The vernier holes allow you to rotate the gear on the camshaft in 1/17 of a tooth increments until the timing is spot on, to within 0.5 degree. It's quite normal to only fit only five or six bolts into the available vernier holes.



There is a similar vernier adjustment on the Mercedes Benz W165 camshaft gears. You can see the uneven bolt spacing.



Mike

Yes we are talking about the same thing

Sorry Chris missed that point......Ive got the vernier on the VDH on the mind.....

[crueby]

Ah - now I understand!  Thanks Vixen/Dave!

[steamer]

And two more

[Vixen]

"That's another fine mesh you've got us into, Stanley"   

Yesterday you gave a master class explanation of the intricacies of using a dividing head and index plates to set the number of teeth on the gear wheel.

Today's question is. How do you decide the depth of cut to form the gear teeth?    Do you
A.     Use some a formula from a text book (such as Ivan Law's 'Gears and Gear Cutting')
B.     Do use use a look-up table
C.     Use then D+ value etched on the side of the involute cutter
D.     Another way

I tend to use option C above and it seems to give good results in my gear trains.

Mike

[steamer]

I usually use the hand calculation as there are a lot of points of error not the least of which is gear run out and cutter runout , to say nothing of getting the cutteron center.    All of my 48 dp cutters are different widths by up to 1  mm...and  .005" run out..so worrying about tenths seems silly..   at least with Chinese cutters and shop made arbors.  I usually wait on fitting the gears till I can set them on tool makers bushings and confirm a good mesh.      We can start a thread if we want to get into it.

Dave

[Jasonb]

That's what I tend to do to just depth the gears and set the backlash and fit at what that PCD ends up being. Initial cut is to formula for me.

[john mills]

i have cut gears usually turning the blank to the calculated od  often on the drawing then i cut to the depth which is on the cutter
mostly my gear cutting was on hobbing or a shaping machine a fallows type.but the only way is to cut the first ones and check
if the gears are heat treated try one first and check how it comes out after it has been heat treated .i only had limited
information  about these processes but the ones i did work .miner adjustment can be made to improve the fit .referd to machinery's hand book  old ones.
john
 

[steamer]

I made dedicated arbors with 1/2" shank to fit a specific 3C collet that I save for gear cutting.  These arbors are clocked to the "G" in Hardinge on the face of the collet and final turning was done then.   When they are used, I always clock them to that spot with some emphasis on rotating the arbor in the collet as I close it.  I typically get less than 0.0005" runout of the arbor in both the lathe and the dividing head..      The gear blanks are mounted on the arbor and final OD is done just prior to cutting the teeth and without dismounting them from the arbor.   I consider these arbors expendable, as they can sometimes get cut when cutting the gears, and as they get more or less worn, I make new ones.   I also make brass arbor bushings that I also consider expendable.   Currently I have arbors for  3/8,  7/16, 1/2 and 19/32.  all with 10-32 threaded holes for a clamp screw.    They are pretty trivial to make, and I can make them as long or as short as is needed.      This constitutes my "system" for cutting gears.

If we would like to continue this discussion, please start a new thread so I can keep this for the 917 project.     Thank you.

Dave

[steamer]

"That's another fine mesh you've got us into, Stanley"   

Yesterday you gave a master class explanation of the intricacies of using a dividing head and index plates to set the number of teeth on the gear wheel.

Today's question is. How do you decide the depth of cut to form the gear teeth?    Do you
A.     Use some a formula from a text book (such as Ivan Law's 'Gears and Gear Cutting')
B.     Do use use a look-up table
C.     Use then D+ value etched on the side of the involute cutter
D.     Another way

I tend to use option C above and it seems to give good results in my gear trains.

Mike

Your way is the best Mike.   I've dug into this a bit and it is truly the best way to determine cut depth...as it includes the Pressure angle, the DP and any small error in the gear cutter....what remains is the amount of clearance you desire.  So this cut is called the minimum depth.

Dave

[steamer]

Progress today!   One more gear and the cam drive line gear cutting will be done!
I have a bunch of holes to put in....but I'm gaining on it    family portrait  but you can see the gear train layout...all of this is driven from the gear at the center of the crankshaft.   The two last gear blanks straddle the crank.    After this I'll be cutting the pump gears and the pump drive gears.  After that distributor cross helix gears...but those can wait...

[Kim]

Them's a LOT'o gears, Dave!  A lot of meticulous work represented in that last shot! 

Kim

[Vixen]

Nice work. You are making good progress 

[RReid]

Excellent!