Gear cutting and making gear cutters from scratch

[Brent H]

Hey folks,

Has anyone on here made their own gear cutters? There are a few guys on you tube that have made cutters. Some are single point, fly type cutters, others are the HOBB type cutter and others (relatively few) have made the cutters for cutting the involute tooth into a single cutter and then cutting teeth followed by hardening and sharpening.

I have been going over the math and I am going to make up a spreadsheet to calculate the geometry of the cutter and work on doing some custom gear cutters.

Some of the pricing is crazy nuts on a single cutter and I cannot locate 20 degree Pressure angle cutters very easily - most are MOD and do not jive with my Diametral imperial pitch world - LOL.

I am thinking I will just giver a go and see what I can mess up. I cannot do much until I return home, but I will at least get the geometry figured and post my spread sheet of numbers for your enjoyment.

 

[RobinHood]

I think another project just moved onto the top of your to do list: a relieving attachment for your lathe....

 

[Brent H]

EUREKA!

 

[RobinHood]

Yup, that’s the one....

Here is a video link of the tool:

 

[Brent H]

Thanks Rudy, Got the series downloaded and I own the Ivan Law book. Have you made anything like these? I have my tool sharpener and it is jigged out with the gear sharpener so that will be good. Just trying to work out the math for the cutters and put it all into a self calculating spread sheet.

 

[RobinHood]

No, I have not made a relieving attachment ( yet ).

I have a fair number of involute gear cutters. So no need to make my own just yet.

 

[Brent H]

@RobinHood : Roger that - over the next days I will try to transfer the drawings over to Autocad and see about scaling them for 1" arbor cutters.

I will post as I get there. I have the math working out for the button cutter build now with an excell spread sheet - just working on making it more user friendly and have it do both the imperial and metric math. I transferred the numbers to an autocad drawing and all the angles came out bang on - that is at least a good start.

If the Eureka relieving attachment works out well, it will be a pretty cool addition to making some cutters. It looks like by the time I am successful at making the cutters it will be about the same cost in time to buy them....but there is no fun in that....LOL

 

[JohnnyTK]

Gear cutting memorizes me, follow a few on Instagram

 

[RobinHood]

I was actually thinking of modifying the Eureka so that the number of “teeth“ is adjustable. Maybe 12 is a standard for that size cutter?

Then is found this video:

It got me thinking that why not make gears using gear hobs? Only one hob is required for each DP or Module. It also does not matter if you are cutting a spur gear or a helical one - all use the same cutter.

 

[Brent H]

@RobinHood - yes, I have a 12DP 20PA hobb I was hoping to use to fine tune that tooth I welded onto my lathe bull gear..... sigh....

I guess I need a second lathe - haha

linking in the hobb rotation to the cutter is quite the process. There are a few videos of guys doing quite well on a vertical mill with rotary table and a complex gearing selection.

A few better options with a horizontal mill ...... will see what we can come up with. I will post the drawings when I get them done and perhaps, Rudy, you can check them for errors if you have some time.

 

[PeterT]

No sure if this is the same method. Look forward to your results!
http://mikesworkshop.weebly.com/designing-gear-cutters.html

 

[Brent H]

@PeterT : yes bang on for making the button cutters that will cut the profile into the cutter blank.

After a bunch of reading of Ivan Law book - the Mike’s workshop and John Stevenson, I was able to put 2 and 2 together.
Then it was figuring out Excell and getting the formulas input correctly. Next is getting my spreadsheet set so it is a “simple” matter of inputting the data for the cutter you need and it will spit out the dimensions for the cutter buttons, spacing and depth of cut.

The Eureka relief tool is designed to profile the cutter teeth for back side relief so the cutter doesn’t drag through your gear as it cuts. As @RobinHood said the tool right now is designed for 12 cutter teeth. Most cutters now have 14 if they are of the 1” keyed variety. Things will get a bit “modified” to suit I should expect.

 

[Hacker]

It took me over an hour to watch this and I still haven't figured it all out. That is a very interesting video. It makes you want to build one just to cut gears even it you don't need them. I was wondering if using cog belts on the tail stock drive instead of idlers would make for a quicker build and setup?

 

[Brent H]

@Hacker : I think that is why it is called the Eureka! It takes a few times to figure it out and then .....EUREKA!!!.....LOL...

The math part to do the calculations was driving me nuts and then I got things figured out after I learned that Excel calculates the angles in radians so you have to correct the Sin and Cos for this. Then the drawing on AutoCad all worked out with the new measurements.

I will start drawing the Eureka out after I get some drawings set up for @YYCHobbyMachinist of the follow rest for the 9" Utilathe

 

[RobinHood]

I was wondering if using cog belts on the tail stock drive instead of idlers would make for a quicker build and setup?

That’s exactly what I was wondering.

The change gear method is the traditional way - there is no possibility of getting “out of sync” because of the gear teeth. I think the modern cog belts / wheels have proven to be very reliable, just look at all the timing belts out there...

But first one needs to have a cutter...

The basic principle of the EUREKA attachment is to have a stationary tool and the work “lobes” in and out of the cut. Traditional relieving lathes are the opposite: the tool moves on the X-axis and the work rotates concentrically with the lathe’s Z-axis. The number of “reliefs” per rev is a function of the number of teeth the cutter has.

I am contemplating using the taper attachment mechanism (mostly the telescoping leadscrew) via a timed cam to move the cross slide. I would need the cam to rotate at the number of cutter teeth per one spindle rev. The cam profile would control the relief profile and the stroke length. This way, one could make cutters of various sizes & relief angles. Furthermore, if the cam drive was via a telescoping cardan shaft, one could use the lathe carriage and set up a desired Module or DP and make a gear hob. Gear hobs have straight flanks - eliminating the need to try and approximate the involute curve. And you only need one for all the gears, regardless of # of teeth.





Another thing, if the drive train to the cam was via a planetary, one could drive the ring gear “slower“ than the planet carrier and get a differential function. This would allow for helical cutters as long as the differential per rev is a function of the helix angle. (differential division is the mechanical principle behind an universal dividing head: with each rotation of the crank, the reference point moves backwards ((or forwards)) by the “differential amount” to allow the circle to be divided by a prime number, for example, without using a prime number hole circle plate [like 127]). I digress.

Maybe all this could be done on a Menziken M220? Hint, hint.... Joking aside, I think they fell victim to the CNC revolution, like so many other manufacturers of high quality manual machines.

 

[Brent H]

Some kind of set up like this would work for your hobbing on the vertical mill - the execution might need a bit of improvement but the concept is there

 

[RobinHood]

You know, whatever works. If it gets the job done, why not?

Here is a relieving lathe in action. It’s the kind of set-up I was trying to describe above.

 

[PeterT]

>Next is getting my spreadsheet set so it is a “simple” matter of inputting the data for the cutter you need and it will spit out the dimensions for the cutter buttons, spacing and depth of cut.

I was going to make the spur gears for my radial & was looking at the button method to make cutters. I ended up buying commercial gears & modifying them because they had to be thinned & modified on multiple fronts so I went that route. But one thing I was always wondering about is how to properly attach the buttons to the toolholder. Ideally they should be made from tool steel & hardened if they are going to cut even mild r annealed tool steel gear blanks. I considered drilling a hole & securing with a screw kind of like an insert. But (depending on size) there isn't a lot of room. Possibly silver solder but now the chance of annealing the button hardness is likely. How were you planning on this aspect? Its been a while since I read that Ivan book.

 

[Brent H]

@PeterT : Ivan suggested loctite so you have a bit of open time to turn them so the cutting faces align properly with the relief on the tool holder

 

[RobinHood]

If I am going the button route, I would use broken HSS or even broken carbide tooling and use the surface grinder with the spindexer or the T&C G with the spindexer. Use loctite and a slight press fit into the tool holder, or silver solder the buttons on. The distance between the buttons is controlled by the hole spacing. Then set the completed tool on the grinder again and deck off to the correct rake angle. Lap to finish the cutting edges.