Helical gear cutting setup

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gbritnell

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Since Chuck Fellows published the drawings for making and using the helical gear fixture I have made quite a few of them. The problem with the whole setup is the indexing/cutting fixture is always at some angle to cut the required gears. At the cutting end of the mandrel is an arbor to hold whatever blank you're going to be cutting. I have posed the question to machinist friends and thought about it myself but couldn't come up with a reasonably accurate way of centering the cutter both vertically and transversely relative to the centerline of the gear blank.

I'm in the process of starting a new project with the completion of the Galion road grader and thought I would like to make another transmission, this one for my flathead engine. My son knows a fellow that has several of them and he offered one to me so that I could take the necessary dimensions. When I built the Borg-Warner T-5 transmission I used spur gears instead of the normal helicals because of the large amount of gear cutting templates required to make all the gears. With this one which has fewer gears I thought I would make the helicals.

Now back to the problem at hand. The gears will all be .250 wide so I made a setup gauge, if you will, that mounts onto the end of the holding arbor. I started by turning a piece of stock that fits the arbor and is .25 wide, the same as the gears. I cross drilled it .093 diameter and inserted a pin in each side, one with a point and one flat ended. I moved the shaft of the fixture to approximately halfway of it's travel and locked it with the locking screw. The next step is to secure the gauge to the arbor and align it horizontally by eye. I then used the dial indicator to get it completely flat. Step three was to use the edge finder to get to the center of the pin. This was done and -0- set on the readout. (X travel)
 

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The home-made gear cutter was secured in the holder and the table (X) was moved to center. The spindle was turned so that the edge of one of the flutes on the cutter was lined up with the point on the gauge. Now the Z was set with a magnifying glass. This is probably the only inaccurate part of the whole setup but for model work it should be very close. This give me the center of travel of the fixture shaft, X position and Z depth, which should be the centerline of the gear blank.
I made some test blanks out of Nylon to test out the setup. The gears are 24 DP, 14 teeth, .660 P.D. and 28 helix angle. A spread sheet was made by Don1966 and it is a great tool when working with gears.
My shaft center spacing is .875 so finding a DP and tooth count for spur gears isn't that big of a problem but when going to helicals the tooth count changes relative to the helix angle. With Don's worksheet you can plug in the variables and keep changing the helix angle until you come up with the proper center spacing. He also expanded on Chuck Fellows contribution by giving the numbers required to create the helical templates.
For a pair of helical gears 2 templates are required, on left hand and one right so this gear box will need 9 templates. Now you see why I didn't go that route with the T-5 trans.
I cut the nylon gears just to verify angles and mesh somewhat then cut one steel gear. I didn't check center spacing but that can be adjusted when I get into making all the steel gears.
 

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The home-made gear cutter
DIY cutter Looks good. Haha dreaming of making one at some point. Book Ivan law "Gears and Gear Cutting" I found already.

How long do you need to align everything?
I was always to lazy to cut helical gears, because of alignment and required extra calculations.
Do you need to align everything twice, for the pair of gears?
It seems you make some gears occasional. Did you consider hobbing them?

Greetings Timo
 
Hi Timo
You can't hob helical gears. Once the setup was where it needed to be it was good for all the gears because they were all the same width.
 
Hi Timo
You can't hob helical gears. Once the setup was where it needed to be it was good for all the gears because they were all the same width.

Hello thank you for the reply.

I thought you need to cut one left helix and on right helix to get a matching pair.

The US military says that I can hob helical gears.



These I pulled out of my collected box of diy gears. It is a pair with 10° ( as I remember ).
Hob that I used is module 1 .
K1600_IMG_3809.JPGK1600_IMG_3810.JPG
As far as I understood it was the hole point to invent gear hobbing Robert Hermann Pfauter – Wikipedia ( but that is dangerous half knowlede on my side )

I think first I try to hob another set, that I have in mind. Then I need to try to understand better what you did on your side.

Greetings Timo
 
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You can certainly hob helical gears using standard hobs but you need to be able to adjust the relationship between the feed and rotation of the workpiece, not all hobbers have this feature
 
Draw filer is correct. I should have been more specific. Hobbing can be used but you need a gear hobbing machine which most home shops don't have. If you had a hobber then you would need the hobbs to go with it.
 
Draw filer is correct. I should have been more specific. Hobbing can be used but you need a gear hobbing machine which most home shops don't have. If you had a hobber then you would need the hobbs to go with it.
Now this guy has a horizontal boring mill bu the same could be done on a vertical mill, not by me but I'm pretty sure there are some here that could.
 
Now this guy has a horizontal boring mill bu the same could be done on a vertical mill, not by me but I'm pretty sure there are some here that could.
Yes LSCAD has some very good videos on the subject without getting too crazy on the equipment side. It does not really matter that he is using the horizontal mill. It has the advantage that the hob is supported on both ends, but as you see below, a vertical machine can also do it.

Draw filer is correct. I should have been more specific. Hobbing can be used but you need a gear hobbing machine which most home shops don't have. If you had a hobber then you would need the hobbs to go with it.

It requires quite some modification or extra equipment, but is not impossible. It is not ideal, but it is a home shop project ( work in progress ). Better a bad machine than no machine :). I did not have a rotary table or dividing head, so I made the stepper driven ER20 collet holder. Originally I wanted to use it for dividing and cutting every tooth separate. Then I could only find a 2nd hand hob, but no disc cutters. I ended up trying to figure out how the hob works.

setup.jpg
  • Rotary axis with the blank on the right. It had a belt drive but the torque was not enough. Now it has a 1/7 gear reducton that it cut for itself.
  • The gear blank rotates a fraction (1/20 for todays two gears ) of a full circle, when the hob rotates one full rotation. That is synchronized by the controller it measures the hob rotation with an encoder and then the blank is rotated by the stepper motor. The number of teeth is entered in the software before the spindle is switched on.
K1600_P1000800.JPG
  • The workhead travels according to the set angle to the left and down at the same time. sin(46.95°) multipied by travel in -X direction down. That is a little cheating, but it is CNC after all and can be done in that simple way, without having to adjust the machine geometry.
Outcome:

Today I tried to make these two gears out of AL with same helix angle of 45° to see if I can get a 90° relation between the axis. Foto shows them on the drill press just to check if they would theoretically work.

K1600_P1000802.JPG
It was more a proof of concept did not need them for a project, they are the project.

The hobs cost between expensive and unaffordable, but price was in the range of a set of eight disc type cutters. One Module ( or Pitchdiameter) is covered, so the hob replaces a complete set, I think because of that it becomes accepteable. One hob covers already a lot.


Greetings Timo
 
Since Chuck Fellows published the drawings for making and using the helical gear fixture I have made quite a few of them. The problem with the whole setup is the indexing/cutting fixture is always at some angle to cut the required gears. At the cutting end of the mandrel is an arbor to hold whatever blank you're going to be cutting. I have posed the question to machinist friends and thought about it myself but couldn't come up with a reasonably accurate way of centering the cutter both vertically and transversely relative to the centerline of the gear blank.

I'm in the process of starting a new project with the completion of the Galion road grader and thought I would like to make another transmission, this one for my flathead engine. My son knows a fellow that has several of them and he offered one to me so that I could take the necessary dimensions. When I built the Borg-Warner T-5 transmission I used spur gears instead of the normal helicals because of the large amount of gear cutting templates required to make all the gears. With this one which has fewer gears I thought I would make the helicals.

Now back to the problem at hand. The gears will all be .250 wide so I made a setup gauge, if you will, that mounts onto the end of the holding arbor. I started by turning a piece of stock that fits the arbor and is .25 wide, the same as the gears. I cross drilled it .093 diameter and inserted a pin in each side, one with a point and one flat ended. I moved the shaft of the fixture to approximately halfway of it's travel and locked it with the locking screw. The next step is to secure the gauge to the arbor and align it horizontally by eye. I then used the dial indicator to get it completely flat. Step three was to use the edge finder to get to the center of the pin. This was done and -0- set on the readout. (X travel)
Wow i have a edge finder with a flat !? i wonder why ?
 
I'm at a little bit of a loss here. You initially had some questions about cutting helical gears then the use of a hobber but already had equipment to do so. My setup is based on the Chuck Fellows design whereby any home shop machinist could make the occasional set of gears. I watched the whole YouTube video and while very enjoyable for a machinist such as myself I don't think there's going to be many building a machine to that degree for a couple of gears. Just saying!
 
Hi Alec,
Did I upset you with my post? Your comment "Wow I have an edge finder with a flat" kind of borders on the sarcastic. Just for clarification I purchased it that way. It makes an audible click when the edge is found.
 
I'm at a little bit of a loss here. You initially had some questions about cutting helical gears then the use of a hobber but already had equipment to do so. My setup is based on the Chuck Fellows design whereby any home shop machinist could make the occasional set of gears. I watched the whole YouTube video and while very enjoyable for a machinist such as myself I don't think there's going to be many building a machine to that degree for a couple of gears. Just saying!
Hello,

Nothing to get lost :) I was ( still am ) curious how you made the gears. There are so many ways to make gears, or just get some gears. I already found few more method in this conversation that you started.
Buying a hob is not really a big achievement. Making a working cutter is a different skill altogether.

How that fixture works I slowly start to understand from the other Post by Chuck Fellows. (not entirely there yet, how you make the helix template)
I am still trying to figure how a left and a right helix without changing the setup are made.
( One thing which seems to be impossible with the hob )
The steep 45° helix angle gears was the an experiment that I did just after I saw your pictures.

My question was if you considered hobbing as alternative, assuming you make enough gears to justify it as hobby project.
Hobby projects: Always a question if the gear is a part that you want to have. Or if the process to get the part is the project.



LSCAD I think does a mixture of Hobby and teaching aid. I guess he is doing it together with engineering students. See such a device working is very different from reading it in a book.


Cheers Timo
 
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To make left and right helicals requires 2 different templates. The template is calculated by the lead angle at the pitch diameter.
 
What is the advantage of a helical gear over a spur gear? Correct me if I'm wrong. I thought helical gears in vehicles ran quieter than spur gears. But spur gears are stronger than helical, that's why racing engines use spur gears. They don't care about noise, just strength.
Grasshopper
 
But spur gears are stronger than helical, that's why racing engines use spur gears.
Spur gears aren't stronger, because of the angled contact helical gears are smoother and quieter and they last longer particularly in high load applications because there are more teeth in contact as well as the load being distributed in more than one axis. They can also transmit motion in non-parallel axes.
The downside is that they are less efficient due to some of the load being transferred to side thrust and sliding friction on the teeth which results in more heat and all that means they need better/more lubrication than spur gears. Commercially they're more expensive to make as well though for the racing application I suspect the efficiency is the deciding factor.
 
I'd better point out that spur gears -can- transmit more power because the area of contact as they roll across each other is across the entire width of the tooth. Helical gears only have a rolling -point- contact, moving across the teeth as they run. This is why they are quieter.

I'm keen on air-cooled VW engines; from the factory the cam/crankshaft gears are helical; the drag racing boys with the heavy cams and 400lb valve springs use spur gears instead. They still need replacing after 50-100 quarter mile races.

Side thrust can be an issue; this was resolved by industrialist Andre Citröen with the herringbone gear. Hence the car company logo of two chevrons. The VW cam satisfies its thrust requirements with one of the two bearing shells having a thrust face from the factory; engine rebuilders usually buy two sets, so they can have two thrust faces instead!
 

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