# Want to cut helical gears?



## Superburban (Jun 12, 2020)

This is a bit on the slow side, but shows a clever way to make an adapter to cut helical gears on a standard milling machine. Likely a cheaper way to even for those with a universal mill, but lacking a factory universal dividing head.


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## homebrewed (Jun 12, 2020)

Interesting.  Can it be done on a vertical milling machine?


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## Superburban (Jun 12, 2020)

I don't know. You could possibly tilt the head the right angle, and cut from either side with an mount the cutter in an arbor. I'm going to have to sleep on that for a day or two.


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## Lo-Fi (Jun 12, 2020)

homebrewed said:


> Interesting.  Can it be done on a vertical milling machine?



Yep, absolutely. I'll be doing so on my bridgeport quite soon. An excellent write up here:









						Making helical gears on a vertical milling machine
					

go to the home page go to the page above this one “helical gears – links” Making helical gears on a vertical milling machine. It is pointed out elsewhere that most amateurs will n…




					johnfsworkshop.org


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## BGHansen (Jun 12, 2020)

I'm going to attempt it on my Tormach and use the CNC for the motion.  I have an existing gear to reverse engineer from, measured the depth, outside diameter, etc.  I don't know the proper terminology, apologize for my descriptions, plan on figuring out the helix by dead reckoning.

In my case, the blank is at a 45 as the two gears meet at a 90.  I measured the depth at something like 0.315".  Cos/Sin (45) times 0.315" tells me the translation in X and Z will need to be 0.223".  Once I find the rod, will need to move X/Z in the negative direction at the same rate.  

To find the helix (?) angle or rotation during the move, I plan on rotating the 4th axis so the top of the cutter fits into the existing gear.  Then back out the Y, move the X/Z 0.223", then rotate the A-axis and advance the Y.  Keep tweaking the A-axis and Y until the cutter fits correctly at the bottom of the gear.

Suppose it's 70 deg. of rotation during the X/Z move of 0.223".  My G-code routine will be something like "G1 X -0.223 Z -0.223 A 70".

I tried interpreting what to do from Machinery's Handbook and got a headache. . .  Hopefully my reverse engineering will be close enough.

I'll end up cutting a longer length than just 0.315" along the blank.  Below is a sketch of the part I'm making.  Figure once I have the set up, I'll try to machine around 1.4" of gear which will give me two of these parts (after the lathe work).  That'll make my routine something like "G1 X -1.559 Z -1.559 A 490" (7X of one gear).  The stock in my case is brass at 0.558" diameter, hopefully rigid enough for that length of stick out of a 5C collet.

Current hurdle is my 4th axis stepper motor went wonky on me 2 days ago.  Just bounces back and forth.  Hopefully just a cable issue as the motor checks out per Tormach's troubleshooting and the stepper driver has the "green" LED lit.

Bruce


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## benmychree (Jun 12, 2020)

I watched the video recently, and have two comments:
It seems a bit stupid to attempt climb milling, unless of course the machine is equipped with zero backlash feed screw/nut.
There is a distinct discontinuity in the finish of the teeth, they have a scolloped look to them, could be due to the miter gears running crooked when being bored out?
Seems like an awful lot of effort to expend on a lashup of limited usefulness, when proper machines made for the purpose can be had for reasonable prices; any 75 - 80 year old, or even over 100 year old universal mill can preform the task easily.  I had an old B&S #2 universal built in 1906 that I did several of these helical gear jobs on, my present one is 1943 vintage.


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## homebrewed (Jun 12, 2020)

I had wondered how well all the gearing on the setup shown in the video would work.  And it does seem like a lot of work for a one-off with relatively poor results.  If I needed such a thing it would be the impetus to go CNC.  @BGHansen, please let us know how your attempt works out!


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## BGHansen (Jun 12, 2020)

homebrewed said:


> I had wondered how well all the gearing on the setup shown in the video would work.  And it does seem like a lot of work for a one-off with relatively poor results.  If I needed such a thing it would be the impetus to go CNC.  @BGHansen, please let us know how your attempt works out!


Will be making my attempt tomorrow.  Figured out what was wrong with the 4th axis today and it's good to go again.  Now the obligatory long-winded back story. . .

I was entertaining a buddy in the shop making some reproduction Erector set parts.  Crazy looking set up with the 4th axis mounted to an adjustable angle plate.  My intent was to initially make the helical gears.  Then I started reading Machinery's Handbook and didn't feel like going through all of the math and formulas at that time.  

Instead, I settled on modifying the red part in the photo below.  It resembles a steel funnel, job was to drill 10 holes around the perimeter or cut a couple of slots on 180's (two styles of parts).  Was doing it mainly by hand with just a "G0 A0 or A180", then ran a routine for a G81 drill cycle.  It sounded like to motor was trying to move but the table just bounced back and forth.  Ended up turning the eccentric on the motor base which disengages the worm gear with the worm so the table can freely rotate.  Just spun it by hand at that point and manually locked it at 0 & 180.

Pulled the stepper motor and tried to jog it, but it just pulsed back and forth.  Ohm check on the motor was OK.  Ohm check on the cable to the motor was OK.  Hooked the cable to the Tormach control box, pulled the connector on the 4th axis stepper driver and found one lead was an open circuit.  Started tracing the lead back and found a terminal backed out of the female connector in the control box.  Bent the retaining tabs out a bit and pushed it back in place.  From now on I'll pop open the control cabinet when hooking up the 4th axis and look at this connector!

Bruce

p.s.  I'll post a thread on the helical gear.  Will come back to this thread and post the link there so I'm not stealing the thread.


Original intent was to cut some helical gears that meet at a 90 (table tilted at a 45).  Started reading Machinery's Handbook and got lost in the math and formulas.  Worked on a different part instead that uses the same set up.




4th axis stopped working.  Traced it back to this backed out terminal.  Must have pushed it most of the way out when I hooked up the 4th, then vibration finished the job.


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## Lo-Fi (Jun 12, 2020)

I didn't find the handbook very helpful on this subject either. The basics are well set out in that link I posted, which makes it seem like much less of a chore doing the calcs. 

Agreed that the results in the video in the OP are less than great. Some odd choices for how much work went into it! I expect better from the vertical mill setup - the gear train is certainly less torturous and I have gears that mesh correctly. The Tormach setup should yield some great results too. Glad you got the axis sorted!


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## BGHansen (Jun 14, 2020)

Here's a link to the helical gears I cut.  Probably not a model to follow, but I got it to work.  

Bruce










						Erector set part number "FL" helical gear
					

Here’s another Erector set reproduction part string. This one is for part number ‘FL’ helical gear. I shot lots of photos so probably a couple of posts in this thread for the whole story.  First the obligatory history lesson. . .  Gilbert introduced a number of parts to demonstrate different...




					www.hobby-machinist.com


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