How to cut internal gear?

[timo_gross]

I am not sure if that is a good idea or new. I did not find much about making gear cutters for shaper or slotting head.

A while ago I made a small slotting head for the light weight milling machine.

https://www.homemodelenginemachinist.com/threads/poor-mans-slotting-head.34126/
then recently I looked into the "Arduino Rotary Table for dummies", resulting in me finally getting a small rotary table.


Mounted on the "slotting machine".

I have been reading and seeing videos about "button tools" to make form cutters, to turn gear cutter blanks. Looking at it I had the idea to sort of "reverse" it.

The idea is to keep a "Drill blank" vertical (hardened HSS pieces with rel. precice diameter) to make the slotting tool.
I see a lot of shaper tools that have the cutter perpendicular to a holder, but making them parallel to the cutting motion seems (in my opinion) easier. (downside is the limited stroke, but for slotting it was fine so far.)

• Figuring out the required "button size" that would be used for a similar size gear cutter.
• Getting a piece of round material as a workholder.
• Then two holes were drilled and reamed parallel to the centerline of the stock (required offsets to front and side "CAD")
• threaded holes perpendicular to the reamed holes help to clamp the HSS blanks. (ground little flat on HSS blank to be able to align and clamp)
• two HSS blanks were fittet into the work holder (it makes measuring easier and a spare cutter is produced at same time).
• I put the workholder into a punchgrinding fixture and ground the two bits down to the required outside diameter.

• Then the blanks are swapped (right vs. left)
• 
  
• again ground to same "required" diameter as before on punch grinder (center of workholder is the spinning axis, so alignment is rel. easy) Then each tool looks like this which is basically the finished internal tooth profile.
• grinding some relief angles and put it into the slotting head
• proof of concept seems O.K. The limit is more my ability to set things up as accurate as possible in each of the steps.
• internal gear has 40 teeth module 0.5 (similar to 48 dp)

What do I need the gear for?
I do not need one, just trying the idea

Greetings Timo

 

[Jasonb]

Now you need to make a 4-stroke with epicyclic gears instead of a cam to work the exhaust valve.

 

[Charles Lamont]

I'm impressed.

 

[awake]

Well done!

 

[Steamchick]

Hmmmm... I think I understand? you have made a broach with 2 diametrically opposite cutters?
Or am I completely wrong? - WHich is quite likely on this one!
K2

 

[timo_gross]

Hmmmm... I think I understand? you have made a broach with 2 diametrically opposite cutters?
Or am I completely wrong? - WHich is quite likely on this one!
K2

I try to explain based on the sketch:

• The tooth profile was generated by the cad program.
• blue circle represents the workholder (work meaning the broaches, there are two of them, makes measuring easier, but one is basically extra and not needed for the slotting ) any diameter for the blue circle is fine as long as it fits into punch grinder.
• the two medium size dashed circles are approximating the gear shape, similar to the button tool. (buttondiameter)
• the red circles are the locations of the two broaches. The diameter of the red circle is the HSS blank diameter, they should not intersect and I have 4 or 6 mm holders for the slotter (so 4mm it was)
• The blue circle spins with the two eccentric mounted HSS pins sticking out, the outside area (crossed) is ground away
  
• then the two broaches are inter changed with the already removed sections both facing inwards
• after grinding the two broaches the 2nd time you end up with two similar (same if everything is perfect) workpieces. The left over "blue section" is (more or less) the shape of the gap that needs to be broached.
• making two at the same time makes it easier to check the dimension during grinding, as only the outside diameter (buttondiameter) is target size.

I hope that makes any sense.

 

[Jasonb]

Should result in a nice accurate cutter. When I have done them I just print out the profile and use that to hold the cutter over and compare the shape as I free hand grind it. Your slotting head is also an improvement in the number of times I had to pull the quill lever down

 

[timo_gross]

Should result in a nice accurate cutter. When I have done them I just print out the profile and use that to hold the cutter over and compare the shape as I free hand grind it. Your slotting head is also an improvement in the number of times I had to pull the quill lever down

nice looking workpiece. Was about to ask about the cam, but now I start to understand.

I am not sure, if I would have success with free hand grinding. I am not an experienced free hand grinder (lack of practice hours and clumsy).
These cutters were small (I think) tooth gap is only 1.2 mm deep, tip of the cutter is roughly 0.25 mm and the tooth gap is 1 mm wide.

What is the module of the gear from your video?

Greetings Timo

 

[Jasonb]

That one is 1.75MOD so a bit easier to see when grinding, I've also done a smaller engine with 1MOD. Both are 12T spur and 24T internal which gives the 1:2 ratio needed for a 4-stroke and having the internal gear eccentric to it's outside diameter provides the movement that a cam would normally do. The Robinson is as per the original design the RMC is Freelance.

 

[Steamchick]

I also like the clever curved shape of the "regulator" arm.... on the RMC engine. - Or is it a photographic distortion? I guess it puts the hand-end of the arm just where the hand needs it?
K2

 

[Jasonb]

Just angled to add a bit of interest as much as clear the pully, it pivots a disc with one of the ignition contacts so advances or retard sthe ignition timing.

 

[Steamchick]

Jason, Timo, you both qualify as a "Clever lad".
Thanks for the educational posts.
K2

 

[TSutrina]

I am not sure if that is a good idea or new. I did not find much about making gear cutters for shaper or slotting head.

A while ago I made a small slotting head for the light weight milling machine.

https://www.homemodelenginemachinist.com/threads/poor-mans-slotting-head.34126/
then recently I looked into the "Arduino Rotary Table for dummies", resulting in me finally getting a small rotary table.

View attachment 153575
Mounted on the "slotting machine".

I have been reading and seeing videos about "button tools" to make form cutters, to turn gear cutter blanks. Looking at it I had the idea to sort of "reverse" it.

The idea is to keep a "Drill blank" vertical (hardened HSS pieces with rel. precice diameter) to make the slotting tool.
I see a lot of shaper tools that have the cutter perpendicular to a holder, but making them parallel to the cutting motion seems (in my opinion) easier. (downside is the limited stroke, but for slotting it was fine so far.)

• Figuring out the required "button size" that would be used for a similar size gear cutter.
• Getting a piece of round material as a workholder.
• Then two holes were drilled and reamed parallel to the centerline of the stock (required offsets to front and side "CAD")
• threaded holes perpendicular to the reamed holes help to clamp the HSS blanks. (ground little flat on HSS blank to be able to align and clamp)
• two HSS blanks were fittet into the work holder (it makes measuring easier and a spare cutter is produced at same time).
• I put the workholder into a punchgrinding fixture and ground the two bits down to the required outside diameter.

View attachment 153576

• Then the blanks are swapped (right vs. left)
• View attachment 153579
  
• again ground to same "required" diameter as before on punch grinder (center of workholder is the spinning axis, so alignment is rel. easy)View attachment 153580 Then each tool looks like this which is basically the finished internal tooth profile.
• grinding some relief angles and put it into the slotting headView attachment 153581
• proof of concept seems O.K. The limit is more my ability to set things up as accurate as possible in each of the steps.
• View attachment 153582internal gear has 40 teeth module 0.5 (similar to 48 dp)

What do I need the gear for?
I do not need one, just trying the idea

Greetings Timo

Great use of a button gear. A pinion gear shaper tool is used that is geared to rotate with the ring gear bank on commercial machines. (larger OD for cutting root of ring gear and only nee a few teeth on each side of the center) This could be make with the DIY gear cutting approaches found here and hardened. Make first passes to cut center full depth. Multiple teeth will be cutting to achieve the involute profile. Some trig can be use if need more cuts by moving ring gear center. Note the fewer number of teeth the more secondary cuts will be needed to approach a involute for both the tool and the ring gear. Red is primary involute cut and green, blue and light blue are improving involute cuts made by other teeth of the pinion gear. A rack multiple tooth cutter can be used to make the pinion. To get clearance tilt axis a few degrees both direction which doubles passes for cutting the tool. Note for planetary ring gear slightly deeper cut need, increase pitch diameter and angle, to be made since this is where clearance can be created.