View Full Version : Gears
04-18-2005, 12:42 AM
New to the board,and new to machine work.
I would like to know what kind of set up is required to cut small gears in a lath.
I am building a one man helo that has straight cut and bevel gears.Some pix would be good.
Thanx in advance
LES A W HARRIS
04-18-2005, 08:00 AM
Welcome aboard, a start would be GEARS & GEARCUTTING BY IVAN LAW, IN THE WORKSHOP PRACTICE SERIES #17. Available from WiseOwl at
http://www.wiseowlmagazines.com/ all the best.
What Les said...Ivan Law's book is the place to start if you want to learn about cutting gears.
If you want to do it all in the lathe, you'll need a milling attachment and some kind of indexing attachment. Straight cut (spur) gears are pretty easy. Bevel gears are possible...at least in one form. You can't reasonably do the tooth form that's found on commercially-made hobbed bevel gears, but you can do a tooth form that works, which is explained in Ivan Law's book.
Another source of information about cutting bevel gears in the home shop is Kozo Hiraoka's book "Building the Heisler" (or maybe it's in "Building the Shay," or maybe it's in both). Kozo writes the clearest construction instructions of anybody I've ever read. The books are available from Village Press.
[This message has been edited by SGW (edited 04-18-2005).]
04-18-2005, 02:51 PM
You could ask John Stevenson about gears.
He's a genius on that subject!
Ok John, you owe me buddy.
04-18-2005, 06:40 PM
Thanx for the input guys,I'll give the sites a shot.
John dos'nt owe me one but it would be cool if I owed him.
[This message has been edited by Sonnyj (edited 04-18-2005).]
04-18-2005, 10:22 PM
Cutting gears in the typical US lathe is a fussy thankless task.....most milling attachments are not really set up for it, due to non-rigidity. Indexing is a real hassle, as a dividing head won't fit anywhere, so you need a gear just like the one you want to cut.
Reversing the deal using an auxiliary cutter spindle and the main one for indexing is even more hassle.
I tried all sorts of things, and was not happy at all. Never got anywhere useful.
Finally cut my first set of gears on the shaper. They were a set of bevel gears for an atlas shaper ram adjuster.
I have since aquired a horizontal mill.It is so easy on that with a dividing head that I was shocked when I was done so fast and accurately.
Right tool for the job does wonders.
If you don't have it, you make do...been there.
If you have a Myford or similar, you may have a much easier time, due to the table on the crosslide.
04-19-2005, 06:36 AM
Any chance of a few more details on what machine you have size wise and what size gears you fancy making.
Not just for Sonny but anyone who wants to understand more about gears even if you don't cut them is, as others have said, buy the Ivan Law book.
I can't stress enough that this book is the simplist book I have seen that deals with the PRACTICAL aspects of gear cutting.
Too many books out there go off into realms of mathematical calcuations that you have no control over and are well out of the scope of a beginner.
I have shelves full of gear books but this one and the Brown and Sharp books are the ones that I rely on the most.
Many years ago I thought about writing a gear book for the home shop but Ivan beat me to it and to be honest if I did do one it would be so like Ivan's that it would look like a copy.
Perhaps in a few years time as thing progress and hobbing is more realily accepted in the home shop then an updated book may be acceptable.
That electronic hobber that I built is ripe for publication but the original idea was from a guy called Brian Thompson. He's in the process of doing an article for MEW on this and his build up of it.
Because of this I won't do anything until Brian's article has been published. His uses the lathe as a donor machine.
Once Brian's article is out the way I want to do mine based on a horizontal mill and then port to idea to turret mills like the Bridgeport and even the Mill/Drills.
The electronics have moved on from Brian's original Mk1 board. I had a improved Mk2 board built in the States and that is what both of us are using at the moment.
Brian has ported this from a custom board onto veroboard so it's a viable home shop project. We will call this the Mk2-1/2 http://bbs.homeshopmachinist.net//biggrin.gif
I have found an area it can be improved and I'm currently having the Mk2 altered to a Mk3.
[This message has been edited by John Stevenson (edited 04-19-2005).]
04-20-2005, 12:37 AM
Sonny, I'm dabbling in gear cutting. So far i like it the best out of all the things I've tried. I got Ivans book a couple fo weeks ago but haven't had time to really get down to reading it properly. John S and a few of the other guys here helped me a bunch to get started. This is my current setup...it works very well for Alu and Bronze gears. Been buying cutters from Ebay and I've built a cutter that is still a virgin! These will be used for steel gears.
04-20-2005, 09:50 AM
I am in the process of making some gears for a hit-n-miss engine and I am using a hob I created (center of photo). A purchased gear is on the left and a new gear cut with a 3/8" bore on the right. The gear is a 20 tooth 32 DP. The hob is .500 drill rod, hardened and tempered to a light straw. The hob will replace 8 involute cutters and since I took the photo I have made additional gears including a 40 tooth.
04-21-2005, 09:21 AM
John, without breaking your vow of silence can you tell us what an electronic hobber is? I'm (theoretically at least) familair with mechanical hobbing but am curious what an electronic hobber is - control cutter path (ie replicating the shape of the hob via cnc) or relative speeds of the shafts or both? I understand if you're not able to reveal much, but no fair mentionning it if you can't say anything http://bbs.homeshopmachinist.net//smile.gif
Jim, that hobber looks fantastic. can you tell us how you made it? I've always wondered, short of devising some link & cam between the crossfeed and the spindle how to get it backed off behind the teeth.
[This message has been edited by Mcgyver (edited 04-21-2005).]
04-21-2005, 03:22 PM
I took a few photos of the setup I used and will try to post here. Basically, I used a 40 degree 'threading' tool to form the teeth on the lathe. Then I put the cutter in my index chuck on my vertical mill and cut to the depth of the tooth using a 1/6" slitting saw with one edge centered on the cutter (hob) centerline. After indexing for 10 teeth, I then used an end mill and rotated the cutter (hob) about 18 degrees to cut the relief. I also rotated another 5 degrees and skimmed just behind the cutting face and you can see the two surfaces on each tooth. Hardened to a non-magnetic state and water quenched for W-1 drill rod. Cleaned throughly, honed to a fine edge and then baked in the oven at 410 degrees for 45 minutes. Shut off the oven and let everything cool overnight. Next morning it had a beautiful light straw color which the pictures don't do justice.
For what it's worth, this is my first experience with making hobs and making gears. Machining and machine work is just a hobby now that I am retired from a desk job. For those that have spent many years in this profession I am sure they have other ways of doing this.
The last picture is a shot of the 2 gears I made. That was the easy part. I ended up making 4 hobs until I could get the results I wanted which was to give me a gear that would match one of commercial quality. As you can see, the straight sided hob tooth *does* form an involute tooth curve.
I hope this helps. I spent a great deal of time researching this before I got to the final result. Eventhough it has been time consuming, I have enjoyed the journey.
04-21-2005, 03:54 PM
Here's a link to two artiles on the electronic hobber that were discussed previously.
The pictures are still there from the links but the movie has been removed.The pictures noe go up to 26 in number, just keep swapping the last number.
04-21-2005, 08:23 PM
Jim, that helps my understanding, mind if ask a few more?
I was aware that the straight sides generated the involute form, presure angle determines the threading tool angle doesn't it? Don't you have to rotate hob and blank on perpendicular shafts, geared together? I'm curious how you did that - purpose built hobber or interesting set up?
John, just went through those links, very cool, encoder -> stepper basically did away with the need for a hobber. Plans for a good orrery and that set up and we'll be makin gears like crazy!
[This message has been edited by Mcgyver (edited 04-21-2005).]
04-22-2005, 07:57 AM
The setup to cut the gear is the same as in the center photo of my earlier post except the hob replaces the slitting saw and the gear blank replaces the piece in the chuck.
The chuck is on a dividing head and setting on the table of my vertical mill. Cut - index, Cut - index. Its a manual operation. I only need 6 gears and can get that from a $0.50 piece of drill rod. John's setup is best for lots of gears. It's only a hobby for me.
Here is a link you may find useful - I certainly did:
Thanks to Pete Harrison.
04-22-2005, 11:14 AM
Just a note to clear the differences up.
Jim's method of using a hob with no helix, in other words a stack of single rack cutters will cut a gear in a series of steps.
To cut an involute you have to roll the hob and blank in sync with one another.
The Pete Harrison link that Jim put up explains it very well and you can see the small steps present in the work.
I think this is a marvelous idea and far quicker and easier to do for the majority of people.
As you gear sizes get bigger the steps are far smaller, in fact once you get above 135 teeth the single brown and sharp cutter is virtually a rack cutter.
Where these won't hold up so well is doing a small number pinion but you can get round this to a great extent by rotating the blank 1/2 a tooth and move one way by 1/2 the circular pitch of the gear.
This will then double the number of steps cut in the sides of the teeth.
It's a method well worth cutting your teeth on http://bbs.homeshopmachinist.net//biggrin.gif
04-22-2005, 11:31 AM
that really helps, I hadn't study the photos enough and hadn't noticed that the hob was individual teeth and not a helix. I think it’s a great solution over a set of cutters.
I guess it would be fair to call a faceted approach to generating a gear?
I'm still puzzled on making hobs though and often have trouble imagining it in 3d. For each tooth to have side clearance, wouldn't the thread cutting tool have had to move in and out as the thread was being cut, thereby creating back off all around the profile?
Perhaps it was not a factor having no side clearance with the facet cut, but if it was in a hobbing set up (electronic or mechanical) would a hob made this way work?