Author Topic: Machining my first miter gears  (Read 6087 times)

Offline Brian Rupnow

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Machining my first miter gears
« on: September 20, 2013, 06:16:15 PM »
I would like to try my hand at cutting a pair of 45 degree miter gears. My cutters are for spur gears, (I have the full set) are 24DP and 14.5 degree pressure angle. I have some round brass stock with a maximum 1" diameter. What I HOPE to do is cut a pair of 45 degree miter gears from this 1" stock. I have Ivan Laws book "Gears and Gear Cutting" and--- :censored:, there's a lot involved in the calculations to cut the blank, even before you start trying to cut the teeth. I am going to fumble away at this, just to see if I can actually do it or not.  This is just a record of how I bumble through it. Don't try to follow me and build a set yourself, based on what I am doing, because I may totally screw this up. First part of the trick will be to use all of the calculations to determine the dimensions of the blank gear form.
« Last Edit: September 20, 2013, 06:26:20 PM by Jo »

Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #1 on: September 20, 2013, 06:16:56 PM »
According to Ivan Laws book, the overall gear dimension will be a resultant, based on whatever number of teeth you decide to use plus some relatively wicked geometry/trigonometry. I'm going to cheat a bit and model it in Solidworks, where by putting in the pitch circle of the small end (which will be the same as the pitch circle diameter of an equivalent toothed spur gear) and an angle of 45 degrees, the computer will calculate some of the unknowns. I COULD do it with trig, but since I have the software I will use it. I am going to guess, to get started, and use a gear with 18 teeth.

Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #2 on: September 20, 2013, 06:18:48 PM »
Some calculations showed that an 18 tooth gear was going to end up being a greater overall diameter than the 1" stock I have to work with. I messed around with the numbers until I found that a 15 tooth 24dp gear would result in an overall diameter of less than 1" so that's what I used. This is the drawing of the blank I arrived at, with a description of how I came up with the dimensions.




Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #3 on: September 20, 2013, 06:20:58 PM »
Okay--based on a direct measurement of my layout, the pitch diameter at the rear side of the cone looks like 0.908, which multiplied by the DP of 24 =21.8, so round it off to 22 teeth.

If I use Ivan Laws formulae and use the number of gear teeth at the small diameter of the come (which is 15t) then the formula gives 1/sin45 x 15=21.2 so I assume it must be the number of teeth on the small side of the cone that gets used in the formula.

My gear cutting charts show that for a 22 tooth gear you use a #5 cutter which cuts from 21 to 25 teeth. It is the calculated number of 22 teeth that determines which gear cutter you use, even though the gear will ultimately only have 15 teeth.


Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #4 on: September 20, 2013, 06:21:30 PM »
Now comes the trick part---The divider plates. My rotary table has a 90:1 ratio. My charts say that to cut a 15 tooth 24 DP gear, I can use any divider plate. 360 degrees divided by 15 teeth =24 degrees between teeth. 360 divided by 90=4 degrees rotation for each full turn of the crank on my rotary tables handle. 24 degrees divided by 4 degrees=6 full turns of the crank on my rotary table. This is fine for the initial cuts, (I think) but then I have to rotate the gear by a number of degrees equal to 1/4 of the tooth indexing angle, to do the next series of cuts. If there are 24 degrees between teeth, then 1/4 of that is 6 degrees rotation of the table. To get 6 degrees rotation of the table, I have to turn the crank on my table 1.5 full turns. I have a 20 hole divider plate. Now one full turn of the crank on a 20 hole divider plate will move the table thru 4 degrees. So--if I turn the handle thru 1 1/2 turns that gives me 1.5 x 4=6 degrees, which is 1/4 of the table rotation between gear teeth. That should mean that by turning the the crank thru one complete revolution and then advancing it another 10 holes when using a 20 hole divider plate, that I have advanced the rotary table 1/4 of the angular distance between gear teeth.

Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #5 on: September 20, 2013, 06:22:33 PM »
This is what may (With the grace of God) become two miter gears. Its a round piece of brass, 1" dia. x 2" long. Since I need something to hold onto with the 3 jaw chuck on my rotary table, I am going to cut a miter gear on each end of it and then split it in half.--Hopefully!!! In the background is the 20 hole divider plate.

Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #6 on: September 20, 2013, 06:23:21 PM »
Here we are with a 0.5" diameter x 0.088" deep counterbore in each end. I used a center drill in each end first because my 1/2" endmill is a 4 flute and doesn't cut right at the center.

Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #7 on: September 20, 2013, 06:24:51 PM »
Both ends are turned to a 45 degree angle, 0.141 back from the end as per the drawing. This newly exposed surface is what will actually become the "tip" of the gears after they are cut. The next step is to set things up in the rotary table. Even though there is an area of reduced diameter immediately behind the tip of the teeth, I don't have to put that in yet. If I did, it would be too difficult to hold properly in the 3 jaw chuck on the rotary table. It can be put in later.

Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #8 on: September 20, 2013, 06:25:46 PM »
Okay--I lied!!! There was one more lathe operation before I head over to the rotary table. I cut the internal 45 degree surface that runs from the front of what will become the teeth in to the .5" diameter which I put in during my first step. This wasn't a perfect match, so I put the end mill back in and cut just a tiny bit deeper until everything ran out properly with no obvious ridges left at the junction.

Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #9 on: September 20, 2013, 06:27:23 PM »
So---Here is my set-up, which at best I can only call "Buck-Shee". After getting everything set up the first time, I discovered that my "Made in India" divider plates were so large in diameter that they wouldn't fit on the spigot of the rotary table without hitting on the table of the mill, so I had to put some 3/4" aluminum spacers under my rotary table and start over again, so that the divider plates and handle would fit in place. My mill doesn't have a particularly deep throat, so the back end of my rotary table is within a gnats ass of crushing the vertical bellows that covers the front of my column. However, I am set up, the rotary table is set at 45 degrees, (or as close as can make it). The centerline of the cutter is on the centerline of the 3 jaw on my rotary table, and I'm about to cut loose. I will cut the first set of teeth tonight after dinner, and wait until tomorrow morning (after good wife has gone to work) to start any of the tricky/funny business.

« Last Edit: September 21, 2013, 02:09:59 PM by Brian Rupnow »

Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #10 on: September 20, 2013, 06:28:43 PM »
That seemed to go well!!! At least when I got all the way around I was cutting air, not a half tooth. It looks a bit weird, but should get better with more steps.


Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #11 on: September 20, 2013, 06:30:24 PM »
This was just too exciting to wait until tomorrow to make my final cuts. I made the second cut all the way around on all teeth, and then the third cut all the way around on all of the teeth. This necessitated raising and lowering the quill by a calculated amount, and I figured out how to make that calculation--its quite easy. --And by God, it does look good. The teeth are parallel on each side of the crest, but the gaps at the root of the teeth are at an angle, just like they are intended to be. Of course, the proof of the pudding will be seen when I cut the teeth on the other end and split the brass round into two separate gears and mount them in a pair of 90 degree bushings to see how they mesh!!!


Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #12 on: September 20, 2013, 06:31:26 PM »
This is the way I calculated how far to raise or lower the quill to take the second and third cuts after the gear was first rotated 6 degrees (1/4 of the angular distance between two gear teeth).



Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #13 on: September 20, 2013, 06:32:25 PM »
I THINK I got this right. Its hard to get a good picture of. Perhaps the edges of the very crest of the tooth are close to parallel, but the actual tooth cross section gets larger and larger as it moves from the center towards the outside of the blank. as far as I know, that is what I wanted to achieve.

Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #14 on: September 20, 2013, 06:33:56 PM »
Ahhh---Sweet Success!!! The gears seen to mesh perfectly. This isn't something I would rush to do again, but I'm surprised at how easy it actually is. I don't really need them for anything---I just wanted to see if I could do it. If any of you have been considering cutting your own miter gears, then rush out and buy a copy of "Gears and Gearcutting" by Ivan Laws, and read thru my thread. -Brian

« Last Edit: September 20, 2013, 06:44:42 PM by Brian Rupnow »

Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #15 on: September 20, 2013, 06:35:06 PM »
Here is a movie of the gears meshing.

« Last Edit: September 20, 2013, 06:50:11 PM by Brian Rupnow »

Offline Tennessee Whiskey

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Re: Machining my first miter gears
« Reply #16 on: September 20, 2013, 07:41:49 PM »
Brian, that's great stuff. You are just great at figuring how to put a piece of metal in position for the tool to do it's work. That's what it's all about anyhow, eh?

Whiskey

Offline Brian Rupnow

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Re: Machining my first miter gears
« Reply #17 on: September 20, 2013, 09:04:56 PM »
Whiskey---After my all summer thrash on the "Rupnow Engine" I needed a simple project that I could complete in a day. I have been wondering about making these gears for some time now. I bought the miter gears that are on the "Rupnow Engine" because I didn't think I would be able to make them.

Offline Pete49

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Re: Machining my first miter gears
« Reply #18 on: September 21, 2013, 04:18:11 AM »
A great how to Brian. Certainly gives the information needed without huge calculus knowledge required :old:. I found Ivan Laws book to be very informative and useful to an old codger like me..
Pete
I used to have a friend.....but the rope broke and he ran away :(

Offline steamer

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Re: Machining my first miter gears
« Reply #19 on: September 21, 2013, 01:00:35 PM »
Nice job Brian...I've never cut bevels before...but we have a good reference now for how to do it should any of us need it! :ThumbsUp:

Dave
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Offline Don1966

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Re: Machining my first miter gears
« Reply #20 on: September 21, 2013, 04:36:33 PM »
Brian I enjoyed following. I haven't made any myself and this will be a good thread for reference. Thanks for sharing. Nice job by the way.

Don

Offline ths

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Re: Machining my first miter gears
« Reply #21 on: September 21, 2013, 10:11:05 PM »
Well done, cracked it!

Hugh.