View Full Version : Gear Cutter

03-17-2005, 05:59 PM
I just received the 18 DP gear cutter I ordered from E-bay. Only, it is not what I though it would be. I thought it would be a form milling cutter that would cut away the material between the teeth one at a time. Instead what I recieved was something that more closely resembles a large knurl. It is about 4 1/16" O.D. 11/16" thick, has a 45 Degree champer and about 10 degree bevel to the largest dia. It says "speed steel" on it. Has anyone heard of making gears by a knurling process?

Gary P. Hansen

Ted Coffey
03-17-2005, 06:54 PM
Sounds like you were sent the wrong item. Is there a picture of what you ordered on e-bay?

03-17-2005, 07:15 PM
It is Ebay item number 3879593429 There is no question that they sent me what was in the photo but this is not what I think of when I think of when I think of a gear cutter. It could be just a gear but why would it be made of HSS? The only way it could be used to make a gear is as a knurl. Knurling to form a gear? I guess there would be no need of indexing. Just cut the gear blank to the right size and knurl it! Were gears ever cut this way?
Gary P. Hansen

John Stevenson
03-17-2005, 07:41 PM
What you have bought is a gear shaper cutter.
It works by being driven up and down, like a vertical shaper and at the same time rotating with the blank.
Here's a picture of the machine.


The cutter is the 'gear' on the left, the blank is on the right.
In use the cutter reciprocates part the blank and generates the involute as they both rotate.

John s.

03-17-2005, 07:43 PM
Looks like a gear to me not a cutter??

03-17-2005, 07:59 PM
John Stevenson: Thank you for clearing that up for me. Now I wonder if I have one of those in my workshop. LOL Was that a comon way of making gears? Or is it still?

Gary P. Hansen

John Stevenson
03-18-2005, 02:57 AM
It still is a common way but probably not so much now that hobbing machines have evolved.

There are three general ways to produce gears commercially, actually more but we'll keep it simple.

[1] hobbing where the blank is moved across a rotating hob, like a worm with teeth, whilst being geared to it.
Advantages are accurate, very quick.
Disadvantages are hobs are expensive and you can't do gears next to a shoulder because of the run off area.

[2]Gear shaping like your cutter.
described in the post above.
Advantages tooling is cheaper, can do gears up to a shoulder and handy for small runs and specials.
Disadvantages, can only do spur gears without expensive additions to the machine and usually a face width limitation.

[3] Gear planing where a tool shaped like a piece of rack planes across the face of the gear s it revolves. The produces anything from 3 to 5 completed teeth at a time due to the length of the cutter. The cutter then backs off, the blank indexes round and the job repeats again.

Advantages, cheap tooling and able to do very large gears with large face widths. Can also do helical gears with just machine adjustments. Other than a specialised machine it the only way to produce herringbone gears as used in big turbine reductions.
Disadvantges: none really, they have been called slow but they can cut on both strokes is setup with double cutters and the operation is pretty automatic.
It's one of those machines that seem to have ost favour.

John S.

kap pullen
03-18-2005, 11:21 AM
Some internal gears are broached now a days.

Coupling shop I worked at had pull type broaches, broaching gears, and finish bored/keywayed coupling hubs.

Some hardened gears are wire cut edm'd.

Gear tooth profiles is a mastercam programing system option.


[This message has been edited by kap pullen (edited 03-18-2005).]

Dave Opincarne
03-18-2005, 01:16 PM
John left out good old fashioned milling and shapers with a form cutter, but these are no longer practical for production and he did state he was limmiting his remarks to commercial production. Shaping has the advantage of having the cheapest tooling (single point form ground). For the home shop this can also be done on the mill using a fly cutter setup. A form cutter is usualy the tool of choice for a mill but the cutters are expensive for the amount of use they usualy see. Of the methods John mentioned hobbing (with the hobb and plank indexed via a gear train) has the advantage of producing a true involute for any given preassure angle and pitch using only one cutter. A form tool will cover a range but will only be an aproximation, and reindexing throughout the cut will produce facets on the gear face. For most everything a hobbiest is going to do this is irrelevent, but for high speed, high preformance applications the true involut tooth will mesh better and reduce wear on the tooth significantly. In a true involute there should be no tooth to tooth wear since the line of contact rolls along the tooth face.

[This message has been edited by Dave Opincarne (edited 03-18-2005).]

John Stevenson
03-20-2005, 09:24 AM
It was just a generic post.
The subject of gearcutting would and does fill many volumes.
I have often thought that it may be a good idea to do a book on gearcutting for the home shop but Ivan Laws book had just about summed it up.

I can't impress enough that this is THE book for anyone interested in gears.
True there are other books out there Dudley, Jones and Buckingham come to mind but they do get into the subject in greater depth at the expense of loosing the beginner.

It's no good spending pages explaining about obtuse gear theory when the guy in the home shop can't do anything about it.

Simply put you need to find the size of the gear either from a drawing, by recomendation or by calculation.
You then need to obtain the cutter needed.
Make a blank to size then index and infeed to the depth either on the cuttere or a chart.

Terms such as addenium and deddenium although useful have no part in making the gear. These calculations were the concern of the cutter manufactures.

Where Ivan Law scores is that all this un-needed information is mentioned as a reference then moved on.
His main points are points that the home shop user has some control over.

Possible in the future as this hobby progess's there will be a space for a more detailed book or at least one that covers operations like hobbing that were once out of the realm of the home shop guy but are now being introduced.

John S.