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Gear Hobbing/Shaping on CNC Lathe

ranchak

Cast Iron
Joined
Dec 4, 2007
Location
Southern California
I have a three small gears that a customer wants made. One gear is .854" in diameter, .199" thick with 34 teeth. It appears to be injection molded out of some plastic. I would like to make this gear out of acetal. I have a Hardinge Conquest with C axis and live tooling. I originally thought about using a custom ground tool and "shaping" the gear teeth. I saw that WTO makes a hobbing unit Gear Hobbing, but I'm sure the job won't cover the cost of this unit.

I have checked in to a few places that specialize in gears, two have not responded and the one came back with a price of that was what I considered to be high. If anyone here is interested or knows of anyone that specializes in this let me know and I will send you a picture.

But back to the original topic, any thoughts??

The quantities will be around 500 -1000 pieces of each gear
 
Hi ranchak:
I like to refer these kinds of jobs to Zahnrad Kopf who participates on this forum.
He's super knowledgeable and has all the right equipment to do this kind of work efficiently and correctly.
Here's his web site address: https://TheGearMaker.com

There are other good gear makers who participate here too, but he has a fairly small shop and should be a good fit for the scope of your project.
If nothing else, you'll get a great reality check on whether your project is a good candidate for a homebrew solution or if you're better off having it done on a hobber or gear shaper.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
Would it be a repeating order, though? I suppose either way, they are fairly small pcs. We hob gears in a CNC lathe where I work, but the smallest we hob in the lathe is about a 2" P.D., for a length of about 3". Splines, not gears, but likely close enough for this conversation. The limiting factor for us is the RPM of the hob and the machine's ability to sync that with the C axis. Regardless, it's a bit quicker than actual hobbing in the Barber Coleman we have. On some larger parts, and even on "legacy" parts that have had the hobbing process for a while, we're starting to switch over to a single-profile inserted cutter. Cuts much quicker because the live tooling syncing with the C axis is no longer a concern. Some of how you approach this may depend on your tolerance. A single-profile cutter may not be a great fit for a tighter tolerance part, where a hob would really do well.
 
I have a three small gears that a customer wants made. One gear is .854" in diameter, .199" thick with 34 teeth. It appears to be injection molded out of some plastic.
Plastic gears are frequently made with totally non-standard dimensions and sometimes shapes. You probably want to get the prints for the parts or have them inspected by a knowledgeable gear shop before you get too deep into this.

There are many better choices than one of those attachments, unless you have unusual requirements. From your description, I'd go for a #3 Fellows shaper or one of several small hobbers. They'd be cheaper and faster than those attachments and you wouldn't be locking up your nc time doing something the lathe is not really suitable for.

If the quantities are only 500 to 1,000, many people will be able to handle that reasonably. I am surprised you have not found anyone. LA or northern ?
 
Gear hobbing can be done on many CNC lathes with live tooling IF the machine has certain control features. When I worked for Doosan, we routinely did this in the showroom. Results were quite good.
 
Hi All:
I tried rotary broaching gears and I was not able to get them very accurate.
Also, in Delrin, sometimes if the broach stalled I'd strip all the teeth off the part...I don't think there is enough strength in the material to keep the broach turning perfectly in sync with the developing teeth when the teeth are very small especially at the start of the cut.
I had way better success in brass, but I still couldn't make proper gear teeth.
I could make "tooth-like" shapes, but they looked like crap under the scope and they were certainly not usable to transmit motion at speed or tolerate load.
They also weren't very straight.
Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
Hi ranchak:
I like to refer these kinds of jobs to Zahnrad Kopf who participates on this forum.
He's super knowledgeable and has all the right equipment to do this kind of work efficiently and correctly.
Here's his web site address: https://TheGearMaker.com

There are other good gear makers who participate here too, but he has a fairly small shop and should be a good fit for the scope of your project.
If nothing else, you'll get a great reality check on whether your project is a good candidate for a homebrew solution or if you're better off having it done on a hobber or gear shaper.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Thank you very much, Marcus. I appreciate the very kind words. Cheers.

By whose standards ? :)
No way you're going to touch a gear machine for cutting teeth. If other requirements of the part make using a gear machine non-optimal, then it can be worthwhile.
But not for just cutting teeth.

Yep.

I've written a fair amount about this, based in personal experience. In fact, I literally just went through this again, not two months ago.

Bottom line is that if you purchase ( or have ) the machine, purchase the extra plug-in from the MTB to do Hobbing ( $Kxx ), purchase the specific Hobbing attachment they approve of ($10K - $15K ), have them install it and set it up ( yet more $Kxx ), and purchase the tooling they approve of, they will tell you that they guarantee you can achieve AMGA 7/8-ish. ( old std ) That is after they take 4 weeks ( most actually take longer ) to consult with their applications group. Yes, this included Doosan.

Of course, when it comes time to actually sign papers, they will not actually put that in writing. Not one single one was willing to put it in writing, much less make the payment contingent upon successfully achieving it. Even with them setting it up and doing it.

So... you're on your own... :rolleyes5:



Think about that for a minute. :skep: :confused:



Sounds ridiculous. And it is. :nutter:


As I have written a few times in this forum - The bottom line in my experience and opinion is that the machines and tooling are simply not rigid enough to even begin to compete with actual gear machinery. At such point that they do start becoming rigid enough, you are well into the range of machine size and price that makes it plainly stupid to be making gears upon them, save for some very limited circumstances.

Now, having spoken with the OP, they evidently do not actually need them to be that accurate of a gear. However, it does very much appear to be very non-standard. And, he does very much need the Pinion part of the Compound Gear to be Shaped. ( if they are to be cut ) There _are_ other options here for him, but unfortunately there are other concerns that may make the whole effort a bit of a non starter.
 
... they will tell you that they guarantee you can achieve AGMA 7/8-ish.
7 to 8-ish ? seriously ?

For comparison, a few years ago (okay, ten) I helped a place that had a bunch of clapped-out 1940's #7 Fellows shapers. With a bunch of work tuning and adjusting we got them making very good AGMA 8's to poor 9's. (Higher is better, 14-15 would be ground gears, 9 was an average automotive gear back then. Automotive is better now.) This was real, honestly measured in production on lead and involute testers, not seat-of-pants qualificating. Cut on, basically, junk.

AGMA 7-8 is not very good for $12,000 plus :(
 
AGMA 7-8 is not very good for $12,000 plus :(

Well to be completely fair, they are all almost universally able to achieve AGMA 7-ish when all the conditions are perfect. And so as not to be misleading, the total is more like ~ $18,000.00 - $20,000.00, depending on which MTB and peripherals one chooses.


So... there's that... :rolleyes5:


As well, it is important to realize that this all assumes best case scenarios, all the time.


The best was the time I had a face-to-face 4 hour plus conversation with the head of the Mazak Gear Cutting Applications group. I was gobsmacked that he was so brutally honest with me. Most places count upon the fact that the shops that they are selling this capability to are looking at it because they are not gear shops and have no clue about making gears. Strictly my opinion - it is that very set of facts that allows them to make such claims without fear of having feet put to the fire. A shop that has no real gear making knowledge cannot put them to task without enlisting the aid of outside assistance. And once third parties are involved and parts travel to and fro, the finger pointing and blame shifting can begin. However, a shop that can legitimately inspect the gears properly and gauge AGMA class, right next to the machine?

There is a reason that they will not put it in writing.

Let me put it another way - We are actively looking to purchase a building to move into, and expand. The money for a turning center with live toys ( and thus, ability to Hob ) has already been accommodated for. If any MTB is willing to put their money where their mouth is and put it in writing, with payment based upon achievement of uniformly and commonly achieving AGMA 9/10, ( without resorting to a machine the size of the actual building** ) we will take delivery the day we sign the papers for the building.

** - Meaning: a typical 6"/8" chuck, 2" - 3" through bore, 16" to 18" diameter envelope, & 12" - 24" length envelope, in the 6K-lb - 12K-lb range.

So far, we have spoken with Haas, Doosan, Mori Seiki, Okuma, and a handfull of others.


That's about as clear as I can possibly put it.


There is a reason that places like our very own Woodward, places like Andrews, and others that are in the gear biz still use actual gear making machinery to make gears, despite having turning centers that "could" ( air quotes ) do it. :rolleyes5:

But, it will come up again in 6 months... :cool:
 
I have a three small gears that a customer wants made. One gear is .854" in diameter, .199" thick with 34 teeth. It appears to be injection molded out of some plastic. I would like to make this gear out of acetal. I have a Hardinge Conquest with C axis and live tooling. I originally thought about using a custom ground tool and "shaping" the gear teeth. I saw that WTO makes a hobbing unit Gear Hobbing, but I'm sure the job won't cover the cost of this unit.

I have checked in to a few places that specialize in gears, two have not responded and the one came back with a price of that was what I considered to be high. If anyone here is interested or knows of anyone that specializes in this let me know and I will send you a picture.

But back to the original topic, any thoughts??

The quantities will be around 500 -1000 pieces of each gear

Just out of interest what vintage of Hardinge Conquest ? year / model etc.

Ta.
 
If you want to do it yourself, a #3 Fellows can be had for much less than that attachment - less than half, probably less than a quarter. It takes up about 2' x 2' by 4' tall, and will kick out those teeth much faster and better than any lathe attachment. It's a no-brainer, to me.

If one of the parts is a compound gear (which you did not mention) you can't hob it anyway. So there is that, too.
 
Bear in mind I've never seen a gear shaper in person, let alone run one. I did look up some videos on YouTube and saw some gears being shaped. All of the videos I saw the gears where a few inches in diameter. The thing I'm having a hard time figuring out is how to shape a gear that is 0.415" in diameter. Are the gears held by an internal mandrel?
 
You said the originals were molded. Like other widgets, you can mold things that cannot be machined if in the same configuration. This is true when cutting gears also- you need to give some thought to how you are going to hang onto them to cut the teeth. You usually have two choices- like a lot of other parts- a hole thru the center so you can put them on an arbor or between centers or a combination of the two.
The size of the part does not usually change this basic requirement.

We got some gear blanks one time from a customer with no hole thru them- about 14" diameter. We ended up pretty much standing on our head to fixture them for cutting. When the customer got the bill, he complained a bit, and we discussed the issue. His response was "oh- we just put the bores in later- we just assumed it did not matter".
 
Bear in mind I've never seen a gear shaper in person, let alone run one. I did look up some videos on YouTube and saw some gears being shaped. All of the videos I saw the gears where a few inches in diameter. The thing I'm having a hard time figuring out is how to shape a gear that is 0.415" in diameter. Are the gears held by an internal mandrel?

Really just depends on the constraints of the job or parts. This particular Compound Gear is approximately 0.500 Outside Diameter and happens to be a very custom Diametral Pitch and Pressure Angle. ... and no through hole... :rolleyes5: At this size, it really wouldn't matter if it had one. The arbor is not going to satisfy any rigidity requirements. So, we had to come up with a way to hold them, somehow.

We were "lucky" in that a few of the diameters were held to +/-0.0002", so we made a custom fixture to hold by those diameters. Grinding and Honing were required. :cool: I want to say that the diameter that is being engaged by the Vee ( at the top ) was around 0.075", if that gives you any idea on scale. It was more than 48 hours ago so I really don't recall any longer... No room to keep old data among the detritus...

 
Of course, when it comes time to actually sign papers, they will not actually put that in writing. Not one single one was willing to put it in writing, much less make the payment contingent upon successfully achieving it. Even with them setting it up and doing it.

So... you're on your own... :rolleyes5:



Think about that for a minute. :skep: :confused:



Sounds ridiculous. And it is. :nutter:

Typical unfortunately. But sad.

R
 
@ ranchak, this is what a #3 Fellows looks like. It's not very intimidating. Parts go on the spindle in front, cutter goes on the spindle in back, there's change gears between the two to couple their speed. That's pretty much it, if you are only making a few different parts.

22210a.jpg
 








 
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