How would you ....

[dbb-the-bruce]

mill a sawtooth profile with only a mill and a a lathe?
The dimensions don't really matter that much (I'm interested in the technique) but for talking purposes, consider a piece of metal 1" high, 6" long and maybe 1/4 think. The goal is to cut a sawtooth like profile on the top, in crude ascii art:

_/|_/|_/|_/|_/|_/|_/|_/|_/|_/|_/|_/|_/|_/|_/|_
|________________________________|

In reality, the teeth and angle would be flatter, with or without flats between the teeth.
Same question for cutting a gear rack. The catch is that you only have a lathe and a vertical mill.

I can see only two approaches, try to set my lathe up as a poor-mans horizontal mill or make a D-Bit with the right profile and use the vertical mill.

I'm not thrilled about using the lathe as I'd be controlling the pitch with my carriage or limited by the the travel of the cross slide on my compound (or both).

In the vertical, I'd need to make a D-Bit to cut a rack and then mill away half of each tooth to get a sawtooth profile.

Interested in other possible approaches (tell me I need to purchase a horizontal mill!!)

-Dave B

 

[derf]

Vertical mill.....clamp the piece in the vise at the correct angle and use a dovetail cutter.

 

[RJSakowski]

If the mill has a tiltable head, use a tapered end mill with an angle equal to the angle between two adjacent flanks of the teeth. Set the mill head to half the angle and cut. If the head doesn't tilt, set the work at the half angle on a sine plate or angle vise and cut.

If an tool can't be found with the correct angle, select one with a smaller angle and cut in two setups, one for each side.

 

[dbb-the-bruce]

Vertical mill.....clamp the piece in the vise at the correct angle and use a dovetail cutter.

The problem with this method is that your reach is limited by spindle/head and shank on the cutter. It could work for small length racks.
Also, if the piece is at an angle, you need to move in X or Y for each cut.

I'd have to check if I can make this work for my actual part. I had already considered it.

 

[Crank]

Dave,
One way that comes to mind, is mill a slot in a piece of stock (round if you only have a 3 jaw, square or round if you have a 4 jaw) to hold the part. If you make the slot deep enough to bury the part and hold it with grub screws, then you can profile the whole mess and when you are done, remove the part from the holder. Lots of chips, but it saves monkeying with the mill head and re-tramming it. Just a thought to ponder.

Mark

 

[RJSakowski]

Dave,
One way that comes to mind, is mill a slot in a piece of stock (round if you only have a 3 jaw, square or round if you have a 4 jaw) to hold the part. If you make the slot deep enough to bury the part and hold it with grub screws, then you can profile the whole mess and when you are done, remove the part from the holder. Lots of chips, but it saves monkeying with the mill head and re-tramming it. Just a thought to ponder.

Mark

I had thought of this originally but the top of the tooth wouldn't be flat. If that is acceptable, , it is probably the easiest way. Even easier, mount an oversized part between two pieces of flat stock and using either a four jaw chuck and tailstock center or two centers, turn the work. mill the excess off the back edge. Saves milling the slot

 

[dbb-the-bruce]

I had thought of this originally but the top of the tooth wouldn't be flat.

Yeah, flat is a requirement. However as you point out I could just mill off the round part of the profile.

This approach does seem to be about the easiest. I particularly like that I can grind an HHS cutter to whatever profile I need.

I can also handle the carriage advance by making gage block that matches my tooth pitch and progressively moving the carriage stop for each tooth. Should be pretty darn accurate.

I think we have a winner!

 

[homebrewed]

If you need the bottoms (nomenclature??) of the rack or sawtooth to be parallel to the long axis of your stock, I don't see how tilting the milling head can work. The idea of an end mill with the right profile probably is best for a rack, since the profile has to be symmetric. For a sawtooth profile do it in 2 passes -- one to form the angle and then use a smaller straight end mill to produce the vertical side. However, in the latter case the bottoms of the sawtooth will be flat, not a sawtooth form like this:

\ |
\ |
\|
My suggestion would produce something like this:

\ |
\ |
\__|
On the other hand, if you are making a real saw blade you probably don't care too much what the bottom of each tooth looks like. Racks are the picky ones, so to speak.

NOTE: there's something weird about the formatting for my second "figure". It should show a straight vertical but the editor gets rid of the spaces...

 

[RJSakowski]

If you need the bottoms (nomenclature??) of the rack or sawtooth to be parallel to the long axis of your stock, I don't see how tilting the milling head can work.

A tapered end mill with a 15º angle per side will cut a 30º groove. If the mill head is tilted 15º, one side of the groove will be at 30º and the other side will be vertical. If the bottom of the tooth needs to be flat, then a second pass with an end mill equal to the diameter (or more accurately the cosine of the diameter) or less of the tip of the tapered end mill would be needed.

 

[Illinoyance]

First step is to run a regular end mill through each slot to get the right depth and bottom width. If the bottom flat does not match a standard end mill, make it in 2 cuts. Second, tilt the head of the mill and cut the tapered side. Make sure the mill extends to the bottom flat but not beyond. No special tools needed.