Can a Single Cutter tool cut X profile shifted gear?

[makary]

Cannot find answers to my dilemma anywhere: can I use a single cutter tool to cut a gear with an X profile shift?
I believe a single cutter would shift the entire involute which is not what the X shift is about. I think in the case of the X shift, it is the Major and Minor that shift while the position of involute remains unchanged vs. nominal involute for X=0.
Another words - the tooth profile uses different portion of an involute but does not shift the involute towards or away from gear center.
Could anyone let me know whether I am correct?

If I could use a single cutter to cut my X-shifted gears I would be able to do it myself on a CNC instead of contracting the job outside.
I have a pinion to cut with X=+0.35 and a meshing gear with X=-0.35.

Thank you

 

[gearcutter]

A single cutter 'rack shaped' (straight sided) tool can do it if the tool is fed tangentially through the job in a reciprocating shaping motion.........look up MAAG Gear Shapers.

You could also do it by feeding in the axial direction with a fly-cutter type tool but you'd need to use a form tool that has the same specific profile as a corrected tooth gap.
You could create the profile in software and then use the coordinates to EDM wire-cut a form tool with the correct profile.

 

[makary]

Thank you Gearcutter. By Single Cutter I did mean what you call a fly-cutter type tool. Our gear cutting tool supplier calls them Single Cutters (may look up: Single Cutter gear cutting tools). It looks like a slitting saw blade but with a gear groove profile instead.

I would not be able to rotate my gear on a CNC to use shaper cutters such as the Maag or the Fellows cutters. The only type of cutter we could use on our CNC would be the Single Cutter (fly-cutter type tool). From your reply I understand that I was correct and this type of gear cannot be made with the cutter in question, unless it is shaped to the X shifted profile it needs to cut.
Thank you!

 

[gearcutter]

"A single cutter 'rack shaped' (straight sided) tool" is not a disk shaper cutter.
You can do what I'm suggesting in any modern turning or milling centre. The tool remains fixed (does not rotate), similar to a tool holding bar on a slotting machine.

The rotating tool you are referring to is generally known as a 'form milling cutter'. I'm not sure why some call them single cutters. Perhaps it's to do with the fact that an individual cutter will only cut the one pitch & pressure angle.
They do not produce true involute profiles. The actual profile they cut is a combination of involute & cycloid, known as 'composite form'. Here too I don't understand why some call them involute gear cutters.

 

[tbuelna]

The type of milling form cutter and technique being described would machine the opposing flanks of a tooth space at the same time. This is different than what a generating technique would produce. Applying profile shift to a gear changes its flank profile shape, as shown in the image below. Thus, if an accurate tooth shape is required, you would need to make a form cutter for each specific gear design if you intend to use the machining set-up described.

 

[makary]

Not sure how to use a "rack shaped" cutter on a 3-axis vertical CNC mill. The gear to be cut was meant to be fixed in a horizontal rotary table (gear axis horizontal along X). The rotary table is fixed to the mill's workable so the only place to attach a cutter to is the spindle.
Can't really attach a rack shaped cutter to a spindle.
Since when cutting with a rack cutter the next cut is done after work (gear) is rotated by one tooth, this indicates to me that is is also a form tool just like the disk single cutter I referred to in the beginning.
Couldn't use a standard cutter made for X=0 correction.

I guess I should get busy programming the CNC so it can cut with a hob-cutter mounted to the spindle
This X=-0.35 is making things a bit difficult...

 

[gearcutter]

As I tried to explain in my previous posts; the 'single tooth' rack cutter does not rotate.
What I'm talking about is a generating process, it is not a form cutting process.
MAAG gear shaper machines are capable of doing exactly the same thing.

The spindle is fixed from rotating (braked). The quill is programed to reciprocate like a slotter.......up & down. If you were doing it in a turning centre, then the tool turret would reciprocate L to R.
The gear blank has a motion that is both rotary and tangent to the cutter. When one tooth gap is completed, the blank is withdrawn from the cutter, the blank is then indexed to the next tooth gap's position and the process begins again.
The cutter is not fed into depth like a form cutting operation.

One of my customers found themselves in a similar situation to yours some years back. Thinking that they would produce the gear on their own CNC mill, they purchased a 250mm diameter form milling cutter in the hope that it would reproduce the sample gear's profile. Upon receiving the $3000 cutter and comparing it to the sample's profile, it quickly became evident that it was not the same profile. After contacting me; we found that the 3 meter diameter gear had a -0.65 addendum correction. This is when we came up with the idea of using the mill like a MAAG gear shaping machine is used. One of their programmers was really 'switched on' and straight away understood what it was that we were trying to achieve. He programmed the whole setup in MasterCam. The gear's face width was around 180mm and the mill's quill extended just past 200mm............so perfect for this job.
I created the tool's 25deg PA rack profile in gear software and the customer sent the file out to have several HSS tools EDM wire cut. 3 for roughing and 1 for finishing.
In the end they got the job done but swore that they would never try manufacturing their own gear again. Next time, they said, well just get a gear shop to do it..........too much messing around, they said.

 

[tbuelna]

makary-

In you first two posts you seemed to be asking about a true form cutter like the image shown below, where the entire tooth space (opposing flanks, fillets & root) is cut at the same time, while the blank is fixed about its axis. After milling one complete tooth space the blank is indexed to cut the next tooth space. This is slightly different from hobbing, which uses synchronized rotation and translation motion between the cutter and blank to "generate" the flank, fillet and root surfaces of all teeth progressively.

In your OP you asked whether the form cutter could be used to mill two spur gears with balanced amounts of profile shift. The answer to your question is "maybe".

First, what are the number of teeth on each gear? In the attached image you will find an excerpt from J.R. Davis' Gear Material, Properties and Manufacture that provides guidance on what range of tooth numbers can be produced from a given form cutter. However, make sure you note the qualifying statements about the compromised accuracy from using this approach

Second, form milling is a miserable way to machine gears since it gives poor tooth index accuracy. So if your application requires even a modest level of accuracy in the gears, form milling would not be suitable.

Third, in your OP you correctly noted that simply adjusting the radial offset of the standard form cutter will not provide the theoretically correct shape of an involute flank with profile shift. The correct shape of an involute flank with various amounts profile shift is illustrated in my post above. Obviously these three flank profiles cannot be produced with the same form cutter simply by adjusting the radial offset.

Lastly, unless you use a machining method for your gears that provides decent accuracy you won't see the benefits of the profile shift. You might be able to get sufficient accuracy from form milling, but as a minimum you will need to have a custom cutter made for each gear with the adjustment for profile shift.

Good luck to you.
Terry

 

[mfgenggear]

Makary

we form grind by means of multi tooth index plates which could be replicated by a milling form cutter, a 4 TH axis precision rotary table & chuck. and can manufacture AGMA class 8 or 10 gears by this method.
we can form Gring an AGMA class 15 master gear , and we can do it often

Mfgenggear

 

[makary]

Thank you all. You've helped me tremendously!
As a result we've contracted the job outside from a gear maker. In the future however I will attempt to cut some gears in hose - those gears that require no accuracy.

Tbuelna - I had to go with a profile shift to avoid heavy tooth undercut in the pinion that has 13 teeth only. The large gear has 133 teeth.
One person insisted in cutting the large gear with a form cutter - just the type you are showing in the picture (don't know why our tool supplier calls it a Single Cutter). I was almost certain that this would not work for an X profile shift. Glad I asked...
If in the future I use a hob, I will synchronize the CNC spindle speed with the rotary table speed so both the hob and the gear blank rotate at the same time.

 

[mfgenggear]

a form cutter can cut any shape required.

Mfgenggear