Cutting my first gear

[Brian Rupnow]

With a little judicious grinding, I can get most of the profile required in two steps, as per the drawing---

 

[Brian Rupnow]

So, I start with a piece of 3/16" square HSS and grind it as per the drawing--

 

[Brian Rupnow]

Then I dress a mounted point (small mandrell mounted grindestone) to 0.298" dia. and blast away on the sides of the cutter as per the drawing---

 

[Brian Rupnow]

So, Captain Gerry---Am I close so far to what you did?---And if I am, how much relief angle did you add in?-----and did you add relief angles to the large radii???----Brian

 

[kvom]

I have been wondering if there is any disadvantage (other than tedium) of using a RT as a dividing head without plates.

It would be easy to write an Excel spreadsheet to calculate each interval's degrees/minutes/seconds. You could then just move the RT directly using the dials. Obviously slower than the plate method, and you'd have to manually locak the table each time.

Comments? (FWIW, my RT doesn't have the plates)

 

[kustomkb]

Nice job describing your thought process Brian.

Kvom,

I think your eyes would get a pretty serious work out dialing a rotary to the second for every tooth. It's the plates which give you the accuracy.

Brian,

Here is a nice write up on how top use your plates, there's not much to it, if you take the time to read it. In the end you will have much more accurate gears and the process will go much quicker;

http://igor.chudov.com/manuals/Troyke-Rotary-Tables/UsingARotaryTable.pdf

 

[Brian Rupnow]

Kvom--Are you reading my posts? That is exactly what I am proposing to do----Not use the divider plates.

 

[Captain Jerry]

So, Captain Gerry---Am I close so far to what you did?---And if I am, how much relief angle did you add in?-----and did you add relief angles to the large radii???----Brian

Brian,

You are right on track. That looks good. I did add relief to the large radius. If you don't, the cutter will drag its heel through the cut. There must be at least that much relief added in the long dimension. Side clearance is also important. You can do both at the same time with the setup that I used.

Left Side:

Right Side

With the table angle set to 10 degrees and the toolbit in the small vise, if you were to point the tool parallel with the front edge of the table (pointing straight up the slope) the resulting grind would leave you 10 degrees of relief in the long dimension. By angling the tool so that it points uphill at about 30 degrees with the slope, The resulting grind provides side relief at the same time. You only need to watch the profile on the top of the cutter. The relief angles take care of themselves.

The last step is to point the bit straight up the slope into the stone and take the heal of the end, leaving a 10 degree relief at the tip. I found it easier to grind the small radius as the final step (after the last step).

I knew when I showed this method in the donkey build thread that I was giving it a once lightly, and since it didn't draw any questions, I was pretty sure I hadn't explained it very well. I hope I have now but don't hesitate to ask if its still not clear.

Jerry

 

[Brian Rupnow]

Jerry---thanks!!! How did you establish your angles? The field of play is too small to lay things out on the 3/16 piece of HSS (other than perhaps a centerline.)---Brian

 

[Captain Jerry]

Brian,

I just realized that the gear you are making is closer in size to the pinion that I cut. These pics show the same thing only using a smaller diameter stone closer to the one you will use,

You will really like the dividing plates. They are a bit of a mystery but once the light comes on you see what I mean.

Jerry

 

[Captain Jerry]

Brian,

The table angle sets the front relief. I just eyeballed the side angle. Its not so critical. I guess you could clamp a straight edge to the table if you want.

Jerry

 

[Dan Rowe]

Brian,
Thanks for posting your gear cutting adventure. I bought a shaper for this type of gear work but I have never put it to use yet.

Jerry, I think that I followed your first explination but thanks for adding it to this thread with more detail.

Kvom, The plates I have for my RT do not have every division between 2 and 100. It has most of them but not all so if an odd prime number gear was needed the only option would be by degrees.

Dan

 

[Brian Rupnow]

Jerry---I am setting here reeking of gasoline (I was out of Varsol) from cleaning the cosmoline off the divider plates which I bought with my rotary table 3 years ago. I am reading the Chinglish literature that came with them and scratching my head trying to make sense of it.---Again, I ask---How did you establish your side angles when you ground your HSS? surely you didn't lay them out on the HSS and "grind to the line"???

 

[Brian Rupnow]

Gerry---Sorry---We were both typing at the same time I guess.

 

[mklotz]

Kvom, The plates I have for my RT do not have every division between 2 and 100. It has most of them but not all so if an odd prime number gear was needed the only option would be by degrees.

Dan,

You don't need a hole circle for every division. As an example, given an RT with a 90:1 gear ratio (what Brian has) you only need the following hole plates...

Hole plates required for all divisions up to 50
3,5,13,14,16,17,19,22,23,29,31,37,41,43,47,49

to obtain all the divisions between 2 and 50.

 

[Brian Rupnow]

And here we have a prime example of the "quality" of imported Taiwanese machinery. My rotary table, purchased thru BusyBee Tools in Canada, and proudly manufactured by the Tzu Yen Industrial Company Ltd. trademark "Yiyen" with a nameplate decrying "PRECISION MACHINE TOOL" sells a set of divider plates with their rotary table which only vaguely matches the tapped holes in the rotary table. Damn, Damn, Damn!!!! The only good thing here is that the center bore on the divider plates is a very good fit on the spigot of the rotary table. I guess that before I do anymore set-up with my divider plates, some hole slotting will be in order.

 

[Captain Jerry]

Brian,

There are some guidelines that could be layed out on the top of the tool bit. If you coat the bit with dye you could mark the centerline and the two cross lines at each end of the large radius. I did not do this but it has been recommended on other threads. You might find them usefull. See the attached PDF.

Lets see the holder that you will be using for the bit.

Jerry

View attachment Alibre Design Drawing.pdf

 

[Brian Rupnow]

Thanks Jerry---I'll probably be doing some of that---I'll post a pic when I get that far.---Brian

 

[Brian Rupnow]

I am sure that there must be some great irony involved in using an imported Oriental milling machine to correct the mistakes in an imported Oriental indexing plate, however, its done. All the parts assemble just like in the pictures in my Chinglish brochure, and fortunately 18 divisions is one of those numbers that you can use any of the dividing heads for. I won't be using both arms of the brass sector?? part, but will use one of the arms as a "witness" to make sure I always get the pin back in the same hole after 5 revolutions. My rotary table gear ratio is 90:1, so 5 full rotations of my handle will give exactly 20 degrees, which is 1/18 of 360 degrees.

 

[Brian Rupnow]

Here we have a piece of 3/16" square HSS, with the requisite layout lines on it.---Pretty darn small, isn't it. I think I'm going to build a simple jig for the 22.5 degree angle on each side and grind them on my bench grinder, using the fixture I made up to grind lathe tool bits.