Shoptask owners?

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VelocityDuck
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Re: Shoptask owners?

Post by VelocityDuck »

I get 9.25mm between across 3 teeth. Across 4 teeth is 12.3mm.

When I plug the diameter, teeth and 9.25mm into lines 29, 30 and 31, it shows the PC over 4 teeth as 9.366 and 9.370 (20 and 14.5 PA). Which confirms that I have no idea what I'm doing. :(

I don't get how the PC over 4 teeth can only be about .1mm greater than the PC over 3 teeth.
TomB
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Re: Shoptask owners?

Post by TomB »

Did this note get separated from some other notes that explains the objective?
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Harold_V
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Re: Shoptask owners?

Post by Harold_V »

TomB wrote: Thu Dec 10, 2020 1:03 pm Did this note get separated from some other notes that explains the objective?
No, it did not. If you'll review the previous page, you'll see the reason for his comments.
To avoid confusion, it's a good idea for the quote function to be used when responding. That way there's some kind of reference to posted comments that, otherwise, may not make sense. This is a good example.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Torch
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Re: Shoptask owners?

Post by Torch »

I did not realize just how precise the measurements become at that pitch. I guess it works better on coarser tooth pitches. I tried it myself with a 27 tooth module 1 gear and it is very difficult to be accurate even at 20x magnification on an optical comparator.

If I had to guess -- and at this point, I do -- I would bet on the gears being a 20°pressure angle. That is by far the most common for modern gears and is commonly used on similar machines.
VelocityDuck
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Re: Shoptask owners?

Post by VelocityDuck »

Torch wrote: Fri Dec 11, 2020 8:21 am I did not realize just how precise the measurements become at that pitch. I guess it works better on coarser tooth pitches. I tried it myself with a 27 tooth module 1 gear and it is very difficult to be accurate even at 20x magnification on an optical comparator.

If I had to guess -- and at this point, I do -- I would bet on the gears being a 20°pressure angle. That is by far the most common for modern gears and is commonly used on similar machines.
Thanks.

So with this information, where does that leave me? Is it possible to find someone who can cut a gear like this?

I do have an old 63 tooth gear with some broken teeth. Its diameter is obviously much greater than a 27 tooth gear so I'm thinking it could be cut down. That way the shaft and splines wouldn't have to be cut.

But I'm (also guessing) that these gears are hardened and I have no idea if it's possible to un-harden it.

Pardon the beginner questions because about 99% of what I work on is aluminum with about 1% being mild steel so this is uncharted territory for me.
curtis cutter
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Re: Shoptask owners?

Post by curtis cutter »

"Pardon the beginner questions because about 99% of what I work on is aluminum with about 1% being mild steel so this is uncharted territory for me."

I appreciate your asking as there are a lot of guys like me out here who read and learn from the responses to even what many would believe the simplest of questions.
Gregg
Just let go of it, it will eventually unplug itself.
Torch
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Re: Shoptask owners?

Post by Torch »

VelocityDuck wrote: Fri Dec 11, 2020 8:38 am So with this information, where does that leave me? Is it possible to find someone who can cut a gear like this?
Yes. There are companies out there that can cut custom gears -- for a price. It is also possible to cut your own. You might need some additional equipment. Depending on what you have already, you can make some of the tools yourself.
My first foray into cutting gears is documented here:
https://www.chaski.org/homemachinist/vi ... =4&t=87790

I made my own cove-cutting tool post, used it to make my own gear cutters. I used O1 tool steel and used an oxy-acetylene torch to harden them. I did buy a 90:1 6" rotary table with indexing plates -- a worthwhile investment with many other uses. I already had a 4-jaw lathe chuck, which I modified slightly to mount it to the rotab. And I did eventually buy a set of HSS module 1 gear cutters (reasonably priced through Ali Express) to save time when making robot gear trains. Making arbours is easy with your lathe. You'll need at least one for the gear and another for the cutters.
VelocityDuck wrote: Fri Dec 11, 2020 8:38 amI do have an old 63 tooth gear with some broken teeth. Its diameter is obviously much greater than a 27 tooth gear so I'm thinking it could be cut down. That way the shaft and splines wouldn't have to be cut.

But I'm (also guessing) that these gears are hardened and I have no idea if it's possible to un-harden it.
Let's deal with the second part of that question first. Do a file test to check for hardening. If the file skates over the material, then it's hardened and recutting may not be possible for you with your equipment. However, if the edge of the file cuts easily into the material, then I don't think it would be a problem. Given the way the teeth are stripped, I doubt they are hardened.

Now, on to the first part: You will need an arbour to mount the gear on while machining. The gear needs to be rigidly mounted to the arbour so it can't lose index. Since your gear is already broached with splines, you will need to find a way to key the gear blank to the arbour. There's not a lot of rotational torque to be applied, so it doesn't have to be really fancy. Maybe a small chunk of steel screwed to the flange of the arbour? Anything to keep the blank from rotating under light to moderate rotational force.

It is also possible to mill the splines after milling the gear. Bore the id as required. Broach a standard machine key for mounting to the arbour. Mill the gear teeth. Unmount the 4-jaw from the rotab and mount the 4-jaw flat on the table. Then mount the gear in the chuck and mill the splines with a small diameter (<1/8") end-mill. Smaller is better for the corners, and you will probably have to finish the corners with a hand file, depending on how sharp the corners are on the shaft. Or run the corners to the centre of the mill, so the flats are proud of the rounded corners.

You would first centre the gear and bore the minor diameter. Next, offset the rotab by the 1/2 width of the spline - 1/2 the mill diameter to the right, mill the left edge of the spline to the major diameter, then offset to the left 1/2 the spline width - 1/2 the mill diameter to do the right edge. Then centre the table, mill out to the major diameter -1/2 the mill diameter and use the rotab left and right to cut the outer circumference between the first two cuts. Remember, tiny mills require high speeds and shallow cuts. Rotate the rotab 90° to do the next spline and repeat until you have 4.

Will it take time, care and precision? Yes, absolutely. Be prepared to start over if you screw it up. (Maybe cut spare blanks so you have spares). I find I am most likely to make a mistake 1/2 way through the project with something repetitive -- like counting the handwheel turns between each gear tooth. But it is a great way to learn and if you are a hobbyist then you can probably afford to spend the time more than the money.
Torch
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Re: Shoptask owners?

Post by Torch »

You could also check out this post:

viewtopic.php?f=4&t=91985

An alternative to making a cove turning tool post.
Torch
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Re: Shoptask owners?

Post by Torch »

And here's a link to my post about the HSS cutters from China:

https://www.chaski.org/homemachinist/vi ... =4&t=98250
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Harold_V
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Re: Shoptask owners?

Post by Harold_V »

A comment in regards to the gear in question. The photo appears to be of a gear made of gray iron, with an absence of any sign of chilling. It is most likely dead soft. Gray iron readily breaks when in tension. A poor choice for gears, although it's very easy to cast and machine, so it is commonly used.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Torch
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Re: Shoptask owners?

Post by Torch »

Good point about the material. I really like 1144 stressproof for gears.
VelocityDuck
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Re: Shoptask owners?

Post by VelocityDuck »

Torch wrote: Fri Dec 11, 2020 10:44 amLet's deal with the second part of that question first. Do a file test to check for hardening. If the file skates over the material, then it's hardened and recutting may not be possible for you with your equipment. However, if the edge of the file cuts easily into the material, then I don't think it would be a problem. Given the way the teeth are stripped, I doubt they are hardened.
You called it! File cuts into both the 27 tooth and old 63 tooth.

I'm going to read through the references and see if it's something I might be able to do.

Thanks!

Don
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