Cutting Tetrix gears

[Forhire]

Originally Posted by asid61

I saw the Sandvik gear cutters a long time ago, but I have never seen somebody cutting involutes with a slitting saw before! You would probably need a very small diameter saw to cut aluminum without too much chatter at a decent speed though.

Thanks.

The slitting saw wouldn't be my first choice of course. but the code he's using to generate the path is fairly straight forward and should be easily adapted to any cutter.

I quickly tried converting it to the Centroid but it's complaining. I re-numbered the variables but the sub-programs are handled a little differently. Might take a little more to sort it out.

Being able to cut various pitches and tooth count of gears without the expense of many specialty cutters is interesting. Being able to give the kids a programming exercise is a bonus.

It would be very easy to re-write in python and generate the long g-code but doing it directly on the control g-code is more elegant.

[Forhire]

Spent some time on the phone with some really nice folks at Sandvik. I learned a lot.

The Coromill 171 and 172 are profile inserts so you have the same 8 approximate involute shapes you'd find in a typical cutter set. It would be comparable to what were doing now.

The InvoMilling uses the Coromill 161 and 162. The insert is flat bottomed the software generates the involute shape. Single cutter can do any count. A five axis machine is recommended but spur gears can be done with just four. The smallest size the InvoMilling Coromill 161 can do module 2.0. The InvoMilling software is expensive. With the InvoMilling gear cam you can also cut gears with standard end mills and such. It appears the secret sauce is the software more than the cutter.

I was able to talk to a programmer and we discussed the slitting saw method and a few others. He was confident if we could program for the saw then their Coromill 161 would work. The Coromill 161 would be more rigid for sure.

I guess I'll keep working on porting the slitting saw code.

[Forhire]

I re-wrote the slitting saw code in python so I could generate some g-code to play with. This is neat stuff. The rendering is a bit odd looking because of the zero is on the outside edge of the blank and the A axis rotates around the X. It appears to work. I wrote my version to automatically calculate the blank diameter based on the gear tooth count and module making it very simple. Enter the module, tooth count, blank width, and the cutter details, it then spits out g-code.This is a good starting point to play with. I'm definitely going to modify this code to handle standard profile gear cutters also.

The render is for a mod 3.0, 38 tooth gear, and a 30mm face width. The cutter is 60mm diameter and 2mm thick. Similar to the gear in the original video.

[asid61]

I really look forward to seeing this in action!
If you had standard profile gear cutters, wouldn't that be considerably simpler code?

[techhelpbb]

"The Home Shop Machinest" ran some articles on using slitting saws on small CNC Sherline size tools to make aluminum gears. I can dig out issue numbers if someone wants.

If one has an old metal shaper one can also make a carbide cutter for gear teeth for the clapper. Course shappers only cut on the forward stroke so...dead simple tooling...but you pay for it in 40% more cutting time.

[Forhire]

Originally Posted by asid61

I really look forward to seeing this in action!
If you had standard profile gear cutters, wouldn't that be considerably simpler code?

Yes. For milling gears the set of 8 profile cutters is likely the easiest. I'd have to look but I think my code for cutting gears is only about 5 or 10 lines long. The formulas are easy enough to do by hand. Rolling the formulas into a quick python script allows for the code creation with just a few variables.

Milling gears with the slitting saw is just interesting. For me it's a novelty. But, it is very similar to what Sandvik is doing with their Invomilling, so it may well be the future. I think this will be a fun project to play with in the fall. A great introduction to 4th axis programming.

We used Gearotic last season to calculate the gear dimension. Looking at it this morning it appears to also support gear milling. I'll have to play with that some more.

I sorted out the 4th axis at the school last year but I haven't mounted a chuck or center on it yet. Now that we have a use I'll have to get cracking on the 4th axis accessories.

If you don't have a 4th axis, or even if you just have a manual mill you can still cut gears with an indexer. Manual indexers do most counts but are tedious. My Haas indexer is nice because all you do is press a button (or the cnc pulses it).

You can build one using a rotary table and a stepper motor. Here's an Arduino Sherline Rotary Table controller my friend built.
http://www.cnczone.com/forums/arduino/215402-cnc.html

Last year when I needed to cut a replacement 93 tooth back gear for my Lagun I couldn't get my Haas to do it correctly, so I made a new control for it. The 7 wire Haas indexers are steppers and super simple to drive. I ended up using Pacific Scientific 6420 stepper indexer and Python with pySerial. Worked perfectly. The URL below also has some images of making many of the gear cutting accessories required.
http://weldingweb.com/showthread.php...indexer-driver

After all that I discovered the Haas supported circle division but it was a few months after I built my new control.

[Forhire]

Originally Posted by techhelpbb

"The Home Shop Machinest" ran some articles on using slitting saws on small CNC Sherline size tools to make aluminum gears. I can dig out issue numbers if someone wants.

If one has an old metal shaper one can also make a carbide cutter for gear teeth for the clapper. Course shappers only cut on the forward stroke so...dead simple tooling...but you pay for it in 40% more cutting time.

It sounds like an interesting read.

I've cut a few gears using a hand ground fly cutter also.

[techhelpbb]

Originally Posted by Forhire

It sounds like an interesting read.

I've cut a few gears using a hand ground fly cutter also.

Article by Jim Hansen, June/July 2009, Volume 22, Number 3, page 4 also made cover. "Machinist Workshop" magazine uses custom manual indexer plate on Sherline headstock with stock Sherline 5400 turning slitting saw.

Marsh Collins did a long article on building a metal shaper which for me is on page 110 of "Projects 8, The Home Shop Machinist" hardcover. A bigger shaper than the hobby size one from the link provided earlier to Martin Model. It is attractive to me to use just a shaper to make gears because it is very predictable in operation and I make so few. Hobber costs add up.

There are plenty of tips in "Tabletop Machining":
https://www.amazon.com/Tabletop-Mach.../dp/0966543300
Page 226 for example they cut a helical gear.

The Sherline 8700 stepper driver rotary table manual has a section on gear cutting.

Now that I scrounged the stuff in grabbing radius .

Here is a HSS bar in a fly cutter body using a 4th axis on a desktop mill to make a replacment gear:
http://www.homemodelenginemachinist....ead.php?t=7246
Keep in mind if you do that you better be darn sure the fly cutter body is mounted firmly. The link above is a manual indexer but that technique works on a CNC 4th axis as well.

Will update when I get to my library later...

[Forhire]

Last fall we downloaded the demo of Gearotic http://www.gearotic.com/ and used it to verify the Tetrix gears we made but didn't really spend a lot of time using it. I've been looking at some of the videos and it does a lot of stuff I didn't realize it does. You can post 4th axis milling code and cut gears using standard endmills. I think we'll play with this some more in the fall.

Anyone using Gearotic for milling gears? How about ratchets?

Gearotic4th
https://www.youtube.com/watch?v=rv77x7I1qQs

I think this is the current Gearotic website. It has a lot more information.
http://www.gear2motion.com/

[sanddrag]

Originally Posted by Forhire

Last fall we downloaded the demo of Gearotic http://www.gearotic.com/ and used it to verify the Tetrix gears we made but didn't really spend a lot of time using it. I've been looking at some of the videos and it does a lot of stuff I didn't realize it does. You can post 4th axis milling code and cut gears using standard endmills. I think we'll play with this some more in the fall.

Looks like a neat piece of software. What are the limitations of the trial version? The website didn't seem to mention it.

[Forhire]

Originally Posted by sanddrag

Looks like a neat piece of software. What are the limitations of the trial version? The website didn't seem to mention it.

I don't think you can export or save in demo mode. I tried to post some g-code and got the license notice. Aside from that everything else appears to function.

[teslalab2]

:cry: so beautiful. Good work!

[Forhire]

Originally Posted by teslalab2

:cry: so beautiful. Good work!

Thanks.

I re-wrote my python script to handle the gcode creation for using standard profile gear cutters on the 4th axis using just a few variables. My mod 0.8 set of cutters are HSS and 32mm in diameter. The numbering is opposite of B&S cutters. It calculates the blank diameter, whole depth, and recommends the cutter based on tooth count. It also calculates feed and speed based on cutter diameter, tooth count, material SFM, and chip load. It saves the gcode to the local folder using the name given.



python tetrix_gear.py
Gear Parameters
Module: 0.8
Pressure Angle: 20
Number of Teeth: 104
Gear Width(I): 0.25

Cutter Parameters
Cutter Diameter(mm): 32
Cutter Thickness(mm): 4
Number of Teeth: 12

Feed and Speed
SFM: 280
IPT: 0.001

Results
Blank Diameter: 3.3386
Whole Depth: 0.0713
Cutter Number: 7
RPM: 849
IPM: 10

File Parameters
Enter Filename: tests2.txt

I sorted my back plotter so it renders correctly.

[Forhire]

If your interested in hobbing gears rather than milling them... you might want to look at this gem. He started out planning to make a mechanical linkage but instead used an encoder on his spindle with a pulse divider circuit to drive a stepper. It fits on his manual knee mill. The details on photobucket should be enough to duplicate.

https://www.youtube.com/watch?v=pzC8eafs2fI
https://www.youtube.com/watch?v=60GGPEZ-xLY

http://s1308.photobucket.com/user/i_...ronic%20Hobber

Along the same lines Andy Pugh over at Linuxcnc has written a custom hal to pulse divide in a similar fashion. I preferred the divider circuit because it can be fitted to nearly any machine... mill or lathe.
https://www.youtube.com/watch?v=ZhICrb0Tbn4