E-gad, he’s making another one of those crazy pop-up things

[Kim]

That is very cool, Craig! 
And I was going to ask the same question Chris just did!  Inquiring minds need to know!
Kim

[Admiral_dk]

Not only that, but can you fit / do all teeth in one setup - or do you have to move the rack relative to your "flatbed on the lathe" ?
I can kind of guess that you will have to move the clamps / remove one at a time ....

Per

[steamer]

Love the sideways thinking on the gear rack fab, and I love Volstro heads!!! 

Nice build!    I'm watching!


Dave

[Dave Otto]

Yup, cool set up to cut the rack!
Nice work.

Dave

[kvom]

Looks as if one pass since height of the tool can't be adjusted.

[Craig DeShong]

Terry, Chris, Kim, Per, Dave, and Kirk; thanks for your interest.  Thanks also for those just stopping by to  see the latest.

Chris and Kim, Kirk is correct.  There is no way to adjust the depth of cut without a completely new setup so the teeth are cut to depth in one pass.  The math calls for a tooth depth of just under 5/32 inch, so these are rather large teeth (at least for the ones I usually cut).  Back when I started making my own gears I read where someone with experience (can’t remember who) stated to just get on with it and cut them to depth in one pass.  I’ve always done this with all the gears I cut.  The notable exception was when I cut the helical gears for the Witte model using Chuck Fellows handy-dandy helical gear cutting fixture.  These were large Diametral Pitch gears and though I used brass I thought trying to manually feed to the full depth in one pass wasn’t practical.

Per: to answer your question…. The problem isn’t in repositioning the work in the lathe saddle, but rather lathe bed length.  Since the rack needs to travel down the lathe bed from one end of the rack material the other (the gear cutter remains at a stationary point) , the lathe bed needs to be at least twice the length of the rack material.  This wasn’t the case with this rack since the length of this rack exceeds twice my lathe bed length.  I compensated by making two tooling bars; the one below was used first with the far end of the rack material just clearing the lathe chuck and the gear cutter positioned to cut the first tooth in the rack.



I proceeded to cut rack teeth until the end of the rack material was about to touch the tailstock.  At this point I removed the first tooling bar that holds the gear cutter and installed the cutter on another tooling bar I had made with the gear cutter located closer to the lathe chuck.  I show this bar below.  This didn’t affect the depth of cut since I’m working from a constant height: an imaginary line drawn between the center of the lathe chuck & tailstock.  For setup, all I needed to do was locate the gear cutter in the center of the last tooth in the rack and then index across to the new location and continue cutting gear teeth.



So, after cutting the remainder of the gear teeth in the rack, things looked as below.



And after cleaning up, below is the completed rack.

[Kim]

Excellent explanation!  Thanks Craig   
Kim

[fumopuc]

Hi Craig, a very interesting set up.
Thanks for showing it.

[Admiral_dk]

Simple and elegant - what more can you ask for ....

I assume that you got a very good idea about the "offset between the two holders", or do you try to 'fit the cutter into a previous cut slot" (so to speak) to know where to continue the cutting process ...?

[Craig DeShong]

Thanks for stopping by to see the latest.

Kim, Per, and Achim; thanks for your interest.  Per, it was a simple task to place the gear cutter in the just finished tooth and center it.  Then I just needed to offset to the next tooth position and proceed.

With the rack complete it’s time to install it in the engine and make whatever adjustments are necessary (hopefully few) to obtain a smooth movement of the piston as it traverses the cylinder and the rack engages with the drive gear on the clutch.

To do this I’ll need to make the rack guide that sits atop the table.  This is mostly another job of trying to machine something to look like a casting.  Below is my CAD rendering of the rack guide.




This is another opportunity to machine myself into a corner where I don’t have a way to hold the part in order to finish it.  I stared at the drawings for quite a while before determined a path to follow and what steps to take in what order to accomplish making this part.

I started off machining the top of the part.



Then completed most of the top and drilled the mount holes used to mount this part to the engine.


At this point the part is about ½ complete.  If time allows I’ll try to finish it tomorrow.

[Craig DeShong]

Thanks for stopping by.

Work continued on the rack guide.  This part sits atop the engine and supports the rack as it moves up and down through the engine stroke.  In the photo below I’ve cut out the area through which the rack will pass.  I’ll be making a brass bearing for the rack to ride in further down in this post.


The casting has a curved top edge.  I’m cutting this with my rotary milling head.


Finally a little profiling on the bottom of the part.


And it is complete.


The rack is sandwitched between two brass slides.  This is the slide that fits in the cut out area three photos up.



And this is another brass slide that confines the rack to a pocket within the two bearings.



Here is a photo of the entire assembly so far.  I have the piston and rack installed, the rack guide with its slide bearings in place, and the main shaft with clutch and contained gear in place.



Now for a test to make sure everything is moving freely and as designed.  The rack and piston must move freely through the entire length of the piston travel.  Gravity alone returns the piston to the bottom of the stroke.
<a href="https://www.youtube.com/watch?v=B-4JW9QaoXI" target="_blank">http://www.youtube.com/watch?v=B-4JW9QaoXI</a>

[crueby]

Great looking parts, as usual.   

[Craig DeShong]

Thanks for stopping by to see the latest.  Thanks for the compliment Chris; almost as pretty as the parts you make  .

If you’re a REALLY attentive follower of this build you might remember my previous attempt to make the secondary shaft drive gear.  If you do, you’ll undoubtedly remember that, for lack of saving five  minutes, I didn’t put a keyway  in the arbor I used to hold the gear blank and when I cut the gear it rotated on the arbor and I didn’t get a gear with consistently spaced teeth.

Since then I placed a keyway in the arbor and then used it to cut the secondary shaft driven gear which you can see up-thread.  The material to re-make the secondary shaft drive gear has been delivered for a while but I’ve been busy in other areas.  Now I’m cycling back around to try making this gear again.

The first task was to face off the piece, turn it to the correct diameter; drill, bore, and ream the hole for the drive shaft; and then profile the front face of the gear blank as you see below.


With that accomplished I turned the gear blank around In the lathe and finished the back side of the gear blank.



I cut the keyway in the gear blank and then placed it on the arbor; you can bet I’m using a key this time to prevent rotation of the gear blank on the arbor  .  I then commenced cutting the gear teeth.  There are 49 teeth on this gear; I’m about 1/3rd of the way around on this photo.

[Kim]

Second time's a charm!

Always painful to do things over - both in wasted material and time. But it does go faster the 2nd time around, and I try to remind myself how much I'm learning and how much fun I'm having! Which is mostly true!   But it sure feels good when it's done!

This one is looking good!
Kim

[Craig DeShong]

Thanks for stopping by and Kim: thanks for the encouragement.  They say “three is the charm” but I’ll take “two” any time.

Progress continued in cutting the remainder of the teeth on this gear.  Things went without a hitch this time around and I ended up with a very serviceable gear as you can see below.



Next was installing it in the engine to check the “fit”.  I’m pretty happy with everything so far.  The gears have just a tiny “tad” of backlash but it’s very acceptable.  Any tighter of a fit and I might have some binding.


I’m at a loss on where to proceed next.  I could continue with the mechanism on the secondary shaft or I could machine the flywheels.  I’m leaning toward making the flywheels.  With the flywheels mounted I can get a pretty good idea of just how free everything is and when I machine the secondary shaft parts, I can judge just how freely everything turns.