Gear Maker-Be aware of these limitations:

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FixitMike
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Gear Maker-Be aware of these limitations:

Post by FixitMike »

(This has been submitted to Vectric Support)

The Gear Maker Gadget has a major problem. It draws gears with a sharp inside corner at the bottom of the teeth. If the outline is drawn as shown and cut with a round end mill, the inside corner uncut material can interfere with the tips of a mating gear. The dedendum should be at least equal to the addendum (of the mating gear) plus the cutter radius if the mating teeth have sharp outside corners.

The solution is to cut a gear form with the dedendum large enough that the cutter radius will fit in. A full radius root will maximize the diameter of an end mill that can be used. The form should include the option to add a radius to the inside the corners equal to the cutter radius, or a full radius root. The radius must start at a point below the pitch circle by the amount of the addendum of the mating gear.

Unfortunately, the Gear Maker gadget does not permit changing the dedendum or adding a radius.

Another, more sophisticated, solution is to make sure that the outside corners of the mating gear have a fillet at least as large as the radius of the end mill that is used to cut the gear. This can be done by using the fillet tool to change all of the corners after all of the gears are drawn.

A combined solution is to use the Vectric Inlay toolpath to cut the gears. This will put the proper radii in both the inner and outer corners. And, it will be obvious if the end mill diameter chosen is too large for the job.

FYI:
Normally, the addendum of the mating gear will be the same as the gear being drawn. There are exceptions, but they would not occur if the Gear Maker is used to draw both gears.
(Dedendum = distance from pitch dia. circle to the bottom of the space between the teeth.)
(Addendum = distance from pitch dia. circle to the tip of the teeth.)
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Re: Gear Maker-Be aware of these limitations:

Post by Tailmaker »

Good point. I have another method:
- move the gear center to x0/y0
- tweak one tooth/one notch in node editing mode as desired (I usually extend the notch bottom round)
- cut the vector at the beginning/end of this tooth/notch segment and delete the vector with the unmodified teeth
- rotate/copy the modified tooth to make a whole gear again
- re-join the vectors
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Re: Gear Maker-Be aware of these limitations:

Post by jimandi5000 »

You are talking about these two places (See the little circles)

Should someone try to fix this?
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GearIssue.jpg
Thanks,
Jim

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FixitMike
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Re: Gear Maker-Be aware of these limitations:

Post by FixitMike »

jimandi5000 wrote:
Wed Jul 21, 2021 12:50 am
You are talking about these two places (See the little circles)

Should someone try to fix this?
That is my opinion as a fairly experienced gear designer. However, the work-around of cutting the profile with the inlay toolpath is a fairly easy solution as long as the user knows about it.

And take into account that Engineers want things done perfectly when they start critiquing.
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Re: Gear Maker-Be aware of these limitations:

Post by GEdward »

The Gear Maker gadget is not necessarily flawed from the standpoint that most gears are made with specialized machines that use a gear hob to cut the profile. What the gadget fails to do is to accommodate the limitations imposed by cutting a profile with an end mill using a CNC router. Thank you Mike for the work around. But as you say, "as long as the user knows about it". And even at that, it is not a perfect solution.
It seems to me that the most straight forward solution would be to have the gadget ask for the diameter of the end mill that will be used and simply draw the gear root deeper by the amount of the radius. I suspect that is what Tailmaker is manually doing if I am reading his work around correctly.
FixitMike also points out that the tops of the gear teeth could be rounded by the amount of the end mill radius as well. While that would work, and at the same time have a more pleasing appearance at the mesh interface, it would mess with the functionality of the gear a little bit. Given that most gears being cut with a CNC router are not intended for industrial performance, I suspect that is not really an issue.
Regardless, I hope Vectric Support can work out a solution within the gadget.

Ed

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Re: Gear Maker-Be aware of these limitations:

Post by Nox Ferocia »

after looking at it's current output there is at least one notable flaw... the dedendum (the space from the pitch circle to the bottom of the tooth valley) is too short... for the default Diametral Pitch of 5 it should be 0.25in, but it's actually 0.2321, at least by standard gear sizing. Although I'm not sure it would be enough of a difference for cutters close to the width of dedendum, but for smaller cutters (<1/2 the dedendum width?) it might be enough. For wood or similar I'd still recommend rounding off those sharp tip corners (unpolished materials bind more there)

There's a quick overview of the standard (listed as ANSI B6.1, but it's the same as the current ISO) at https://www.engineersedge.com/gear_formula.htm. I 'believe' the reasoning for the extra dedndum spacing is to allow oil/grease/dirt/debris to more easily flow out without any grinding/compaction adding additional wear/stress.

FWIW even as an american I really wish people would abandon Diametral Pitch in favor of Module (M = 1/DP). module is both more direct (almost no division, bigger is... bigger) and more informative (tooth spacing = PI * M, Pitch Circle diameter = M * teeth, addendum = M, dedendum = 1.25 * M, etc)

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