Gear Cutters

[mklotz]

Marv---i'm running a 14.5 degree pressure angle. You know that if you keep on doing this I'm going to have to fly to California for some hands on Dos lessons, right??? ;D ;D ;D

You don't need DOS lessons to use my programs. You just need to understand how to run a DOS program under DosBox, which does all the DOS work for you. Get one of your granddaughters to help you out.

The ideal solution, of course, would be to convert all my programs to run on 64 bit Windoze. I make no money off my programs so that isn't going to happen if I have to do it. Writing them the first time was fun. Porting is my idea of hell.

Over the years I've had numerous folks ask my permission to port my programs to other systems. Given that my stuff is in the public domain and the code is available in the downloads, I've always told them to go right ahead. Sadly, I have *never* heard of anyone following through on these promises. They must detest porting as much as I do.

Porting isn't going to happen so DosBox is the best alternative. At least it's free.

 

[Dan Rowe]

Brian,
Steamer posted a good gear book in the download section a while back. It has all the formulas that Marv has programmed in DOS. The calculations are really not difficult.

http://www.homemodelenginemachinist.com/index.php?action=tpmod;dl=item280

Dan

 

[gmac]

Dan + Steamer;
Thanks for posting the reference to the spur gear book - perfect timing for me!
Cheers
Garry

 

[mklotz]

Books and formulae are fine if you never make calculation errors. I know that most of you are infallibly accurate with your math but there may be a few in the future who lack such expertise.

The programs, once debugged, always compute everything correctly. That fact, plus the fact that many folks are completely baffled by mathematical formulae, are two of the reasons I wrote many of my programs.

 

[Dan Rowe]

Marv,
Yes programs are wonderful. I just checked and there is a DOS box for the Android operating system. I have not tried your programs with my phone yet, but I will.

Books explain things with words so one can use a program with out a garbage in garbage out error.

Dan

 

[Brian Rupnow]

No gears yet, as the machinist who is going to modify my arbor is off sick. I did however, set up both shafts which are supporting the "gears to be" in the lathe and put a centerdrill into the cantilevered end so I can use my "Tailstock thingy" to support the end of the shaft. This is a "posed" picture, as I have never used this "Tailstock thingy" since I bought it 3 years ago with the rotary table. (What the heck is it called, anyways???) I have to chase down some 12 mm T-slot bolts to bolt it down with, and adjust the center height to be correct. It may not be needed at all, but I am assuming that anything that can make for a more rigid set up will be a good thing.

 

[chuck foster]

the tailstock thingy is just that...............a tailstock

hope you feeling better

chuck

 

[Brian Rupnow]

Thanks Chuck---Its not me thats sick though. Its one of the younger machinists where I'm working right now, who has volunteered to cut down my arbor for me on one of the big shop lathes.----Brian

 

[dgjessing]

You guys have (again) inspired me! Did a little research and made some rough drawings:

I don't have a dividing plate so I've stuck with tooth counts that divide into nice "even" numbers of degrees which I can do easily on the rotary table. I ground a fly cutter bit into a rough approximation of a gear cutter:

This opens up a whole new world of fooling around ;D

 

[Brian Rupnow]

dgjessing---Very nice work. Far nicer than my attempt with a hand ground cutter.

 

[Blogwitch]

There are really three things that scare the living daylights out of new machinists.

Parting off, which really is a personal thing that you have to conquer the fear of, screw cutting and gear making.

These last two, once you get over the initial trepidation and actually carry them out, then become things that hold no fear at all. You soon realise that they are really easy to do, all you need is a bit of maths, a bit of equipment plus a bit of understanding and away you go.

John

 

[dgjessing]

Thanks guys ;D

It's so darn easy that I've done the 36 tooth from scratch since the last post:

Now I need to make some sort of gizmo that uses them to take so "show and tell" with my real machinist buddies :

 

[John S]

Careful, this is what happens before you get good

Video.

[ame]http://www.youtube.com/watch?v=zOmSrePm_UM[/ame]

John S.

 

[dgjessing]

Careful, this is what happens before you get good

Yikes! What am I getting myself into?

 

[Brian Rupnow]

Now there's a beautiful thing!!!!---My professional machinist friend turned the shank on my arbor fromTravers down from 3/4" to 1/2" so that it would fit in my 1/2" collet (pictured on the left). He told me something interesting as well. That arbor has a 1/8" x 1/16" keyway in it, and so do the individual gear cutters. Mike said "Whatever you do, don't use a key in there." Their plant safety comittee had a meeting with all of the machinists concerning an incident where a dull gear cutter had jammed in the blank being cut, and since it couldn't slip on the arbor because of the key, the gear cutter had split and shrapneled, cutting the operators face quite badly. There policy now is to not use a key, just tighten up the threaded nut that holds the gear cutter in place, snugly. Better to have it slip than split and possibly explode. Mike says that a sharp cutter will never slip without the key in there anyways.

 

[tornitore45]

Hobbing requires a "rigid" linkage with a defined gear ratio between the spindle and the rotary table, not a feature available in many home shops.
Cutter only requires a rotary table or any indexing method.

A gear cutter or a singlr point cutter "a la flycutter" requires to be shaped correctly.

A hob has straight flanks at the PA and the cross section looks like a rack.
Losely speaking, a true hob is basically an Acme screw with flutes and relieves cut in. The Sctew leads equal the gear circular pitch.

There is an aproximate method to use what I call a pseudo hob, the theet are groves not forming an helix, in other words they look like a honey dipper but cylindical rather than egg shaped.

The pseudo hobb cuts one complete thoot and a few adiacent teeth partially cut.
When the blank is advanced one tooth, the pseudo hob cut the next tooth and nibbles away to the other a little more.
The final toot shpe is a number of small facets approximating a true involute.
No linkage required.

 

[Brian Rupnow]

Danm!!!---Just lost a whole post for some reason. I am now going to approach the operation of setting the correct cutter height. I simply don't trust my eyes to do this. Contrary to what the Chinglish instructions and diagrams say about my rotary table, the backing from the mill table to the center of the 3 jaw chuck is exactly 4.021" (measured about 3 different ways!) The gear cutter hub is 0.157" thick, so if I divide the thickness by 2, I get .0785". Then if I subtract 0.0785 from 4.021", I get 3.9425" from the mill table up to the underside of the cutter hub. Since I have no good way to measure this. I will turn a piece of round stock to exactly that length with both ends faced, set it on my mill table and lower the quill untill the bottom of the hub hust "kisses" the end of my home made height gauge.

 

[Brian Rupnow]

Here we have the large gear blank all set up in the mill. Cutter is mounted on arbor, safety stops are set up to limit carriage travel, and depth of tooth cut is dialed in. Lord help me---I'm going to cut a gear!!! (Well, actually I see that I only had one carriage travel stop set up when I took the picture.---the other was adjusted before I started any cutting.)

 

[Brian Rupnow]

And---"OH MY GOD----ITS A GEAR!!!----

 

[Brian Rupnow]

And near as I can tell, its perfect. ---At least when i went one more cut beyond the last pass between teeth, it didn't proceed to eat the next tooth.!!! ;D ;D