Centering a gear cutter

[Sunset Machine]

I've never been real confident in the method I've been using to "center" the cutter - using indirect measurements taken from one side of the cutter body to the side of the blank or arbor.


I found an old book called "Planing and Milling" by Franklin D. Jones written in 1915 and in it is the following method that actually centers the cutter properly and includes a simple test. This was a headslap for me, so obvious it is. Due to the time period the text refers to horizontal mills but the method applies to vertical mills as well.


Patched together from 3 pages into an odd size, I hope it's still legible after the upload...

[TomG]

Interesting.

My first inclination would be to take the difference between #1 and #2, divide by 2 and add the result to #2, but their method accomplishes the same thing with one less step.

Thanks for posting this. Now the challenge will be to actually remember it for future use.

Tom

[awemawson]

I use a 22mm bearing mounted on a 1/2" shaft for centring - a technique copied from John Mills (Doubleboost) :

Slow rotating spindle. Bring bearing up to one side of work until it's outer race just stops spinning as it rubs the work. Zero DRO. Then approach other side until bearing just stops spinning. Half the DRO reading is your centre point.

No reason same method cannot be used with a gear cutter with a bit of ingenuity.

[Sunset Machine]

Give it a good filename and use the file searcher when the time comes.
I couldn't let it die in an old book.

The other lesser method. There's a ground flat c-clamped to the cutter (barely) and a tissue paper feeler in use. The problem mostly in the extension of the flat, it could be sitting on a hair that levers the end out. Or here, it's barely held by the c-clamp for lack of enough surface. Add those errors up.

Sorry about the ugly mill. I have a can of paint for it somewhere.

[Dr Stan]

I've used a pair of angle plates, one on each side of the gear blank, and gage blocks to find center. This of course assumes the cutter is properly ground.

To double check rotate the first cut (about 75% depth) to 90 degrees and then to 270 degrees. Place a dowel pin in the slot and check to see it it is same at both angular locations with a test indicator & a surface gauge. Split the difference and move the table the appropriate amount. Rinse & repeat.

[Pete O]

Thanks for posting the article, I hope to get a chance to use it sometime!