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Old 11-10-2010, 09:37 PM
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Default Cutting new gears on a lathe

Well, after playing for the past week & finally getting the gears for the new toy done..............

Figured some other visitors to the site might be interested in how to do this without a mill. As I don't have a mill, it was a learning experience to say the least.

Cutting gears for a hobby lathe like my Craftsman 12" x 36" is fairly easy once a person wraps their head around the situation. Many gears are cut on a mill with a dividing head, some with CNC, some manually, but the vast majority are more than likely cut on the mill.

Using a lathe is a bit different, but only in the perspective. The actual cutting & moving the gear blank a set number of degrees for each tooth cut is the same. Regardless if using a mill manually or a lathe manually. The only difference is the position the cutter is, regarding the position of the gear blank. On a mill the gear blank is vertical & the cutter is horizontal. On a lathe the cutter is vertical & the blank is horizontal. Really not too much difference once you think about it.

Ok, first of all, a milling attachment is required to do this. Doesn't have to be factory made, it can be something that allows the blank to be held solid, rotated a set number of degrees & raised/lowered to cut the full width of the blank. Once that is out of the way, an adapter to hold the gear blank needs made. This allows the gear blank to be held solidly & the cutter advanced into the blank to cut the tooth.


I'll add some pictures as I go along & explain them here.

(continued)

Pic 1 & 2 - Milling Attachment for a 12" Craftsman/Atlas lathe. Pretty straight forward milling attachment specific to this lathe. (Thanks Cutter, I'm getting some good use out of it)
Pic 3, 4 & 5 - Gear cutting adapter. I'll explain the construction in a bit.
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I haven't always been a nurse..........

Hobart Handler 175
Century AC 230 amp stick welder
Chicago Electric 165A DC TIG
Oxy/Acetylene set
Hand/Power tools
Clark 4x6 Bandsaw
Harbor Freight Tubing Roller
Craftsman 12 x 36 lathe
New to me Enco GL-30B Mill/Drill Thank you 1800Miner
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I don't do nuttin half azzed. I phawk it up completely, given half a chance.
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  #2  
Old 11-10-2010, 09:55 PM
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Ok, the gear cutting adapter needs to be constructed that will allow the gear blank (henceforth called "blank") to be held horizontally & allow it to be rotated a specific number of degrees depending on the number of teeth to be cut.

I used a piece of 1" x 2" strap steel & bolted a piece of 4" x 4" x 1/2" angle iron to it. For the bottom side of the adapter, I used a piece of 2 1/2" x 2 1/2" x 1/8" angle iron that is bolted to the 1" strap through the 4" x 4" angle iron. This second piece of angle needed to be smaller to allow clearance for the cutter to rotate through it's arc to cut the "void" of the teeth.

Once this was made, a 1/2" hole for a short piece of all thread was made in the top angle iron. The all thread was turned down to 3/8" at the bottom & a 3/8" hole drilled in the lower angle iron. This allows the all thread to rotate freely along a single axis.

Pic 1 is the 1/2" angle iron bolted to the 1" strap. It also shows the degree wheel installed on the all thread, captured by 2 nuts/washers.

Pic 2 shows the 1/8" angle bolted to the strap, capturing the 1/2" angle with the same bolts.

Once the all thread has been placed through the upper hole, two 1/2" nuts were threaded onto the all thread. I used a flat washer to allow even tightening on the upper nut. The lower nut will be the top nut holding the blank in place.

Once all this was assembled, the blank was placed into position on all thread & another 1/2" nut was placed below the blank to tighten against the nut directly above the blank.

Pic 3 shows the blank in place. Notice how the turned end of the all thread fits into the hole drilled into the lower angle iron. This locks the blank/all thread spindle into one axis. I did face the lowest nut to about half width, as I thought I would need it for clearance. Turned out I didn't, but that's ok, it still works.

Now the adapter, complete with a blank is mounted into the milling attachment.

Pic 4 shows this & an early attempt at making a hob to cut the teeth. The hob failed & I switched to a single point cutter to cut the gears.

Pic 5 shows the failed attempt at cutting with the hob. It just sort of wiped the aluminum away, without really cutting it.
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Mark

I haven't always been a nurse..........

Hobart Handler 175
Century AC 230 amp stick welder
Chicago Electric 165A DC TIG
Oxy/Acetylene set
Hand/Power tools
Clark 4x6 Bandsaw
Harbor Freight Tubing Roller
Craftsman 12 x 36 lathe
New to me Enco GL-30B Mill/Drill Thank you 1800Miner
Papa Lion's Gate Build

I don't do nuttin half azzed. I phawk it up completely, given half a chance.
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  #3  
Old 11-10-2010, 10:10 PM
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Never knew you could cut gears on a lathe. learn something new everyday.
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  #4  
Old 11-10-2010, 10:16 PM
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I can hear everyone thinking "how do you know how far to turn the blank to cut each tooth?" Well, there is a bit of magic in every computer called Excel. Using a spread sheet I created a pie chart. Pretty simple really. The computer does all the work.

First open Excel, in cell A1 enter 360. (this is the number of degrees in a circle)
In cell B1, enter 36 (the number of teeth to be cut)
In cell c1 enter this formula =a1/b1 (answer will be 10, or number of degrees each line needs to be from a starting point)

Then in cell d1 through d36 copy the number in c1 (10). Highlight the 36 cells & using the chart wizard, create a pie chart. Pretty simple isn't it. If are building a replacement gear such as I was, I already know the diameter of the blank, so I machined a blank to that diameter, bored the correct sized hole in the center & cut the gear using the degree wheel.

Pic 1 is the degree wheel
Pic 2 is the degree wheel & a simple pointer. It doesn't matter which tooth is cut first, just keep cutting. The pointer needs to be fairly accurate (I ground a point on it) and the pointer needs to point to the same spot in each degree line each time it's rotated.

Ok, now we talk about relationships. There are 4 that are critical to ensure a good gear is cut.

First is the relationship of the cutter to the blank. The cutter must be 90* to the centerline of the blank.
Second is the relationship of the cutter to the previously cut tooth. This is important to ensure proper gear tooth spacing.
Third is the relationship between the blank & the degree wheel. These two items MUST TURN TOGETHER when rotating the blank. If they do not turn together, the spacing on the teeth cut will not be right & the gear will not work.

(Don't ask me how I know this.)

Fourth is the relationship between the gear/degree wheel/cutter & how accurate does the pointer need to be when rotating the blank. I mentioned before a point ground onto the pointer will help determine accuracy. Make sure when rotating the blank to cut the next tooth the pointer is pointing exactly the same place on the next degree line as the previous degree line.

Pic 3 Notice the nut under the gear blank, there is another right above it to lock the blank in place. Then the nut just under the washer. This is the only nut that gets loosened before the blank is rotated to the next degree wheel line.
Pic 4, the whole adapter less the gear blank & bottom nut. Notice how the degree wheel is captured with nuts & washers, so it's locked to the all thread. This is one of those relationships I was talking about.
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Mark

I haven't always been a nurse..........

Hobart Handler 175
Century AC 230 amp stick welder
Chicago Electric 165A DC TIG
Oxy/Acetylene set
Hand/Power tools
Clark 4x6 Bandsaw
Harbor Freight Tubing Roller
Craftsman 12 x 36 lathe
New to me Enco GL-30B Mill/Drill Thank you 1800Miner
Papa Lion's Gate Build

I don't do nuttin half azzed. I phawk it up completely, given half a chance.

Last edited by MarkBall2; 11-10-2010 at 10:22 PM.
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  #5  
Old 11-10-2010, 10:34 PM
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Last but not least, the gear cutter relationship to the blank.

As I said earlier, I tried a hob, but that didn't work very well. A single point tool works so much better. After I finally figured out how to do it, I was able to cut two 36 tooth gears in about 50 minutes............. one tooth at a time. It actually took longer to machine the blanks, than it did to cut the gear.

The blanks were bored to accept 1/2" ID bronze bushings. The originals don't have bronze bushings, but then again they aren't aluminum, but an alloy called Zymak. The alloy is a zinc/aluminum amalgam that is fairly soft. The aluminum is much harder & I was afraid it would gall on the shoulder bolts, so I put the bronze bushings in the gears.

Pic 1 & 2 are the 3/8" hole drilled to hold the all thread in alignment
Pic 3, 4 & 5 is the single point cutter held in an end mill holder.
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Mark

I haven't always been a nurse..........

Hobart Handler 175
Century AC 230 amp stick welder
Chicago Electric 165A DC TIG
Oxy/Acetylene set
Hand/Power tools
Clark 4x6 Bandsaw
Harbor Freight Tubing Roller
Craftsman 12 x 36 lathe
New to me Enco GL-30B Mill/Drill Thank you 1800Miner
Papa Lion's Gate Build

I don't do nuttin half azzed. I phawk it up completely, given half a chance.
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  #6  
Old 11-10-2010, 10:39 PM
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The finished product mounted in the reverse tumbler of the Craftsman lathe.

They are a bit noisy, because I didn't cut the gear at different angles like a real involute gear should be cut. I just cut a "Vee" to form the teeth. Eventually after enough use, they will wear in & form their own "multiple angle" involute.


I did this little tutorial for new members or others that might need gears cut that happen to have a lathe, but not a mill. Figured I could pass on some knowledge I learned in a weeks worth of work.

Pic 1 & 2 final product installed.
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Mark

I haven't always been a nurse..........

Hobart Handler 175
Century AC 230 amp stick welder
Chicago Electric 165A DC TIG
Oxy/Acetylene set
Hand/Power tools
Clark 4x6 Bandsaw
Harbor Freight Tubing Roller
Craftsman 12 x 36 lathe
New to me Enco GL-30B Mill/Drill Thank you 1800Miner
Papa Lion's Gate Build

I don't do nuttin half azzed. I phawk it up completely, given half a chance.
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  #7  
Old 11-10-2010, 11:00 PM
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I had read about cutting gears on a lathe, but I always wondered how you could get accuracy within .002 that some gears require. I see for the type of gears you made that level of accuracy isn't required. Can you also cut the teeth to any configuration/shape by special grinding a cutter to the shape you want? I would guess that helical gears can't be done on a lathe???
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  #8  
Old 11-10-2010, 11:01 PM
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thanks. another question answered for me without much work on my part.
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Old 11-10-2010, 11:05 PM
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Nice job on the tutorial Mark.

If you add a pawl of some sort on your rig to engage the first tooth after it's cut, then you don't have to rely on lining up the pointer on your degree wheel by eye. The tooth to tooth relationship will remain constant based on the accuracy of the the first turn on the degree wheel.
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  #10  
Old 11-10-2010, 11:07 PM
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I've been thinking about helical gears, but a person would have to be able to rotate the blank as the cutter is running. I don't know how I would cut them on a mill, but if that could be figured out, the plane of the cut is just moved 90* & the same process could be used.

Hobbing worm gears is done on the lathe quite a lot. The blank must be allowed to rotate with the hob as the hob turns, kind of like threading. I tried to make a hob, but wasn't successful. Maybe because I didn't understand the process well enough.

As far as accuracy, it can be done, a cutter can be turned with the appropriate angles, then the teeth cut. About the only difference how these were cut vs a mill cut is the angle of the blank & cutter. And these gears don't require or hold nearly the torque a set of gears like a differential/transmission. But they weren't designed to work like that, so this process for small gears will work quite nicely.
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Mark

I haven't always been a nurse..........

Hobart Handler 175
Century AC 230 amp stick welder
Chicago Electric 165A DC TIG
Oxy/Acetylene set
Hand/Power tools
Clark 4x6 Bandsaw
Harbor Freight Tubing Roller
Craftsman 12 x 36 lathe
New to me Enco GL-30B Mill/Drill Thank you 1800Miner
Papa Lion's Gate Build

I don't do nuttin half azzed. I phawk it up completely, given half a chance.
Reply With Quote
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