Primitive gear cutting method

[Andy CarruthersParticipant @andycarruthers33275]

I've read with interest various ways to cut gears, read Ivan Law's book on the subject too, and thanks to Neil for his excellent advice on cutting gears also

Then I saw this: https://www.youtube.com/watch?v=J0o3W4_LRBw which strikes me as an elegantly simple way to cut gears – I don't have a need for a specific ratio, just 8 gears with meshing teeth for a project I am working on, I will program the arduino to scale the stepper motor speed so 4 pinions of 9mm and 4 larger gears of 18mm would suffice. I appreciate using this method the gearing would be concave – I am planning to create thin gears so I anticipate this will not matter

Anyway, I'm the novice and you my esteemed audience are the font of all knowledge so I'd like your opinions please

Edited By Andy Carruthers on 15/09/2017 16:38:12

[Andy CarruthersParticipant @andycarruthers33275]

[JasonBModerator @jasonb]

I think you may need a left hand tap to make one of the pair as you can't do a mating pair with just a regular right hand tap.

This is really meant for worm wheels where the "gear" teath need to be on an angle to mate with the helix angle of the worm

Not quite sure what you are doing with the Arduo and steppers but the gear blank does not need to be rotated the action of the helical teeth on the tap will drive the gear blank round so you just need the mill spindle to turn the tap and work out how the tap pitch divides into the circumference of the blank to get the number of teeth. If you try to control the rotation of the gear blank you will just get a concave groove around the edge as the tap then becomes little more than a ripper or roughing endmill

Edited By JasonB on 15/09/2017 16:48:29

Edited By JasonB on 15/09/2017 16:50:48

[Andy CarruthersParticipant @andycarruthers33275]

Thanks Jason – always something new to learn here!

I had imagined the rotation of the blank commensurate with the cutting action of the tap would result in straight cut gears

[Andy CarruthersParticipant @andycarruthers33275]

On re-reading my first post I can see I have introduced scope for mis-understanding

The gears on cutting will free-wheel as demonstrated in the video, when fitted to my project, they will be driven by stepper motors

[Mick B1Participant @mickb1]

What if the pitch of the tap doesn't divide exactly into the circumference of the blank at the bottom of the cut?

[SillyOldDufferModerator @sillyoldduffer]

A Meccano Gear Cutting Machine using Andy's method is described here.

[Neil WyattModerator @neilwyatt]

Posted by Mick B1 on 15/09/2017 17:14:31:

What if the pitch of the tap doesn't divide exactly into the circumference of the blank at the bottom of the cut?

It will undercut the teeth. Actually the PCD should be an even number of tap pitches, it will always cut the tops of the teeth a bit thin and the root spaces a bit wide, just as a rack form hob does, this is what creates the involute gear shape.

[Neil WyattModerator @neilwyatt]

The problem with this method is it is for producing worm and wheels, not gears that run together.

Also, unless you gash the blank first you are just as likely to end up with an extra tooth space over the theoretical number, because the OD is one extra tooth larger than the PCD. Once its started cutting (say) 61 teeth instead of 60 it will just squeeze them all onto the PCD by cutting narrow teeth.

Don't ask how I know.

[Andy CarruthersParticipant @andycarruthers33275]

Actually Neil, I'd appreciate some more detail on your home made cutter used to hob the gears on your Orrery please…

[Mick B1Participant @mickb1]

I'm guessing that you'd need a spiral-flute tap if you were trying to hob thin gear-wheels by this method, so that you'd always have a tap thread point in at least one of the toothspaces to give drive? IIRC purpose-built hobbing machines drive the blank spindle in a set ratio from the hob spindle, and you don't have that here.

Perhaps even the spiral-flute tap might not work if the flutes were wide enough to miss all the teeth currently being cut.

Edited By Mick B1 on 15/09/2017 19:24:22

[Alan Johnson 7Participant @alanjohnson7]

There was an article "Gear Cutting With the Shaper" published in Model Engineer on the 14th. September, 1950, written by "Base Circle," a nom de plume, but I do not know for whom. It uses a very simple system to copy gears. No dividing head is required, and a cutting tool ground to the pressure angle which is very simple to make. It does use a shaper, but if you don't have one a fly cutter on the mill would probably work. I have a pdf copy of the article, and I am happy to send it to whoever wants, and I have converted it to jpg and place the four pages into my photograph album.

Hope this gives you a few ideas.

Regards,

Alan.

[HopperParticipant @hopper]

Posted by Andy Carruthers on 15/09/2017 16:37:48:

…I don't have a need for a specific ratio, just 8 gears with meshing teeth for a project I am working on, I will program the arduino to scale the stepper motor speed so 4 pinions of 9mm and 4 larger gears of 18mm would suffice….

Sounds like readily available cheap gears for radio controlled model cars would suffice. Ebay is full of them.

The method in your posted video will not make gears that mesh together. It makes worm wheels, which mesh with a screw thread the same as the tap used in the cutting process.

[RobinParticipant @robin]

I am so out of date with this model stuff. Just out of curiosity I typed "involute gear cutter" into eBay to see if prices had come down since the 1980's and then quickly added that magic word "set" to the search box. Now I've gone all trembley. So much to do, so little time

[IanTParticipant @iant]

Haven't got around to doing it yet but the Base Circle generation method will be my approach to gear cutting – as once the basic shaper accessory is made then different sized gears just require a simple 'pitch-circle' part to be turned and the ability to step/divide the work the required number of teeth. A single straight sided tool can be used for all gears of the same pressure angle (say 14.5 degrees). This method is capable of generating very accurate involute gears.

This recent YouTube (the last one of a set of four) shows an accessory based on the Base Circle method in operation.

Regards,

IanT

[IanTParticipant @iant]

Robin

My horizontal mills have 1" arbors and MOD gear cutters to suit are currently just over £20 each (and there are normally eight per set).

One of my gear box designs needs four different gears in two MOD sizes (and there are four boxes per engine). Buying in gears would cost over £260 whilst the four cutters needed would only be about £84 (plus material). However, other projects planned need different sized gearing and then cutter costs start to mount up. Hence the attraction of generating the gears…. but you do need a shaper!

Regards,

IanT

[John HaineParticipant @johnhaine32865]

Ian, or a hobber, or you can make approximate involute cutters by the two button method?

[Neil WyattModerator @neilwyatt]

Posted by Andy Carruthers on 15/09/2017 18:16:39:

Actually Neil, I'd appreciate some more detail on your home made cutter used to hob the gears on your Orrery please…

What do you want to know?

The cutter was made to the same profile as the equivalent rack, I then cut grooves at the correct spacing, but a tad deeper.

Neil

[Andy CarruthersParticipant @andycarruthers33275]

@Neil – something hasn't stuck yet – am I correct in assuming the cutting tool is 20 degrees? and if so, what is the spacing between each tooth of the hob?

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