Cutting Tetrix gears

[Forhire]

Originally Posted by asid61

Ah, that's what you meant by "pulsed manually". I was thinking of you keeping a really close eye on the students every time they cranked the indexer. I missed the part where you said "Haas 5C"

I was thinking about using a geartrain to keep them in sequence. If you have to gash the gears then there's no point to doing the hobbing over just buying involute cutters imo. I actually had a spreadsheet that had all the gears that were needed to be bought from Vex to generate most non-prime-tooth-count gears from 1-100 teeth and beyond. The hobbing machine that I designed required a lot more machining than I was comfortable with, unfortunately.

Yeah, making a hobber would be a lot of work. Have you seen the Jacob's hobber? http://www.lathes.co.uk/jacobs/ Castings use to be available and you see variants now and again online. For small FRC and FTC gears something about that size would be perfect.

I wonder if anyone has devised a cnc hobber on the cheap?

[asid61]

Originally Posted by Forhire

Yeah, making a hobber would be a lot of work. Have you seen the Jacob's hobber? http://www.lathes.co.uk/jacobs/ Castings use to be available and you see variants now and again online. For small FRC and FTC gears something about that size would be perfect.

I wonder if anyone has devised a cnc hobber on the cheap?

Yes, I have seen that, and I really want to buy it, but the only site the castings are available from is in the UK and the thing is expensive enough already.

A CNC hobber is called "CNC mill + automatic indexer", I believe. To my knowledge (a few weeks of on-off research) nobody has made a dedicated CNC hobber, although it should be easy to set up if you already have a CNC mill.

[Cory]

Originally Posted by asid61

Yes, I have seen that, and I really want to buy it, but the only site the castings are available from is in the UK and the thing is expensive enough already.

A CNC hobber is called "CNC mill + automatic indexer", I believe. To my knowledge (a few weeks of on-off research) nobody has made a dedicated CNC hobber, although it should be easy to set up if you already have a CNC mill.

If you Google "cnc gear hobber" you'll find tons of examples. Not the same as a cnc mill with 4th axis at all. A gear hobber has to vary the angle the hob is presented to the work at in order to make different kinds of gears.

When not done on a dedicated hobbing machine, hobbing mostly occurs on y-axis equipped cnc lathes, minus some homebrew setups people have built with mills. I know 368 at one point had setup their mill to hob sprockets. I think there were pics on here somewhere, but you need to mechanically slave the rotary axis to the spindle.

[asid61]

Originally Posted by Cory

If you Google "cnc gear hobber" you'll find tons of examples. Not the same as a cnc mill with 4th axis at all. A gear hobber has to vary the angle the hob is presented to the work at in order to make different kinds of gears.

When not done on a dedicated hobbing machine, hobbing mostly occurs on y-axis equipped cnc lathes, minus some homebrew setups people have built with mills. I know 368 at one point had setup their mill to hob sprockets. I think there were pics on here somewhere, but you need to mechanically slave the rotary axis to the spindle.

It's the "on the cheap" part that's not in google. Industrial gear grinders and the like are beautiful things.

[Forhire]

Originally Posted by asid61

Yes, I have seen that, and I really want to buy it, but the only site the castings are available from is in the UK and the thing is expensive enough already.

Martin Model has the castings available based on Tom Hammond's patterns. They appear more robust than the original Jacob's castings. Ships from Oregon. 14 Piece Gear Hobber Casting Kit + Drawings $495.
http://www.martinmodel.com/MMPtools.html

Here's a video: https://www.youtube.com/watch?v=ZpJOEj-kX_o

[Forhire]

I'm going down the gear cutting rabbit hole... I've been watching some of the Sandvik InvoMilling videos. Cool stuff for sure! Here's a simple spur gear.
https://www.youtube.com/watch?v=vDf0lEN3ekg

Poking around Sandvik's site I found the CoroMill 171 which can do "Gear module range: 0.8–3 mm (DP 31.750–8.467)"... which got me thinking about how cool would it be to do it all with one cutter.

Then I wondered about how to program it.

Sandvik had a link to Euklid GearCam. It looks cool and spendy. I'm sure the Coromill isn't cheap either.
http://www.euklid-cadcam.com/en/soft...vomilling.html

Then I happened across this video of Wilfried Smekens cutting gears with a slitting saw.
https://www.youtube.com/watch?v=HI27vSoxCeo
https://www.youtube.com/watch?v=gWdBunio5aI

He posted his "Involute spur gear free gcode wizard using O codes" source in the comments of the first video. I assume it runs in LinuxCNC. I wonder if I can make it work with the Centroid? I'll have to study it some more.

Now I'm intrigued. I think we could do this. We have a 4th axis on the Centroid CNC at the school. This would be a perfect use in the fall.

[asid61]

Originally Posted by Forhire

I'm going down the gear cutting rabbit hole... I've been watching some of the Sandvik InvoMilling videos. Cool stuff for sure! Here's a simple spur gear.
https://www.youtube.com/watch?v=vDf0lEN3ekg

Poking around Sandvik's site I found the CoroMill 171 which can do "Gear module range: 0.8–3 mm (DP 31.750–8.467)"... which got me thinking about how cool would it be to do it all with one cutter.

Then I wondered about how to program it.

Sandvik had a link to Euklid GearCam. It looks cool and spendy. I'm sure the Coromill isn't cheap either.
http://www.euklid-cadcam.com/en/soft...vomilling.html

Then I happened across this video of Wilfried Smekens cutting gears with a slitting saw.
https://www.youtube.com/watch?v=HI27vSoxCeo
https://www.youtube.com/watch?v=gWdBunio5aI

He posted his "Involute spur gear free gcode wizard using O codes" source in the comments of the first video. I assume it runs in LinuxCNC. I wonder if I can make it work with the Centroid? I'll have to study it some more.

Now I'm intrigued. I think we could do this. We have a 4th axis on the Centroid CNC at the school. This would be a perfect use in the fall.

I just finished giving you rep for the last post... time to find 10 more people to give rep to.
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.

[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?

[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.

[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 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...