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cutting spur gears on a mill

a rogue method?

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Ian Hewson21/09/2021 19:37:14
308 forum posts
25 photos

Brian’s so clever, really in awe of the progress he has made in a few weeks from beginner to absolute expert.

JasonB21/09/2021 19:44:16
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Usually just called X-axis and Y-axis.

Neither Neil's basic method or the CNC method would need any movement in Y except the initial setting of the "whole depth".

Edited By JasonB on 21/09/2021 19:44:45

Pete Rimmer21/09/2021 20:17:46
1069 forum posts
69 photos
Posted by brian jones 11 on 21/09/2021 13:33:18:

Well if a cutter like that had a helix?

It would be a hob.

Roger Best21/09/2021 21:57:52
306 forum posts
36 photos

I can't say I read every word. crook

I did see some very good imitations of severely worn traction engine gears. Modelling to such realistic detail is wonderful.

I look forward to seeing other worn and weathered models.

brian jones 1121/09/2021 23:11:30
347 forum posts
62 photos

Who invented the helicoil insert - life saver for my Lambretta with a stripped spark plug hole?

Obviously someone thinking out of the boxlaugh

Now this rack thing needs more work

I could tilt Doreens pretty little head thru 90deg but this would mean a 1 ft diameter cutting tool - NOT

Does anyone know of a horizontal mill that rotates on the X axis rather than the normal Y axis?

I have joined the Gearheads corner with the gearotic 3 installed - lovely little app free but you have to pay $129 one time for a manufacturing licence - which is probably reasonable if that floats your boat and you need CAM files

You will be pleased to know I have already found faults with their Low PA forms but they welcome eccentric gear designs

You probably know about them already

brian jones 1121/09/2021 23:16:34
347 forum posts
62 photos

Now here's a silly question from SBP

How are gear teeth made with an undercut root?

The SCR CNC wallahs need not stir from comfy chairs

This is strictly old school

AFAIK it could only be done by shaping after roughing out?dont know

OMG you gotta see this

https://www.youtube.com/watch?v=6q0wXore4ow

Edited By brian jones 11 on 21/09/2021 23:50:13

Michael Gilligan21/09/2021 23:52:19
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18925 forum posts
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Posted by brian jones 11 on 21/09/2021 23:16:34:

.

How are gear teeth made with an undercut root?

.

See here for various options: **LINK**

https://www.tec-science.com/mechanical-power-transmission/involute-gear/undercut/

MichaelG.

[ currently in bed ]

brian jones 1122/09/2021 00:14:45
347 forum posts
62 photos

Thats fantastic MG

those animations are what I have been looking for. explains it all

This should be a sticky for all young shavers to understand gears

profile shifting has really done my head in

JasonB22/09/2021 07:09:58
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Posted by brian jones 11 on 21/09/2021 23:16:34:

Now here's a silly question from SBP

How are gear teeth made with an undercut root?

Already answered by Andrew yesterday:

" In theory it should be able to cut small numbers of teeth as well. The undercut arises automatically. In some of the 1930s books I've got on gear cutting there are formulae for calculating whether a hob will undercut or not, even when not needed"

This is how the Sunderland machines do it and what is suggested for the CNC method being discussed except a round rack form cutter will be used instead of a flat shaper type cutter as it is easier for a hobby user to make.

Not sure what you are trying to do with your head on it's side and a large dia cutter? Can't you tilt the work

Dave S22/09/2021 07:20:18
223 forum posts
47 photos

The undercut is an unfortunate artefact of the process of making an involute gear. It limits the strength of the root of the tooth, which can be a bit of an issue. Profile shifting just uses a different part of the involute curve, and so can avoid the undercut. It’s trivial to do in practice - using the same rack form cutter you just move it out a bit (simplification but essentially the process)

I have made some 12 tooth pinions without undercutting by doing just that and they roll against the 144,96 and 90 tooth gears made with the exact same cutter perfectly.

Dave

brian jones 1122/09/2021 07:54:21
347 forum posts
62 photos

Not sure what you are trying to do with your head on it's side and a large dia cutter? Can't you tilt the work

Think of it as a metal saw

https://www.youtube.com/watch?v=KvEUy36u-TI

goto 10.00 to see action

Dave S

Is profile shifting  the same as changing the PA? ie

 

Edited By brian jones 11 on 22/09/2021 08:00:03

Edited By brian jones 11 on 22/09/2021 08:00:46

Dave S22/09/2021 08:08:50
223 forum posts
47 photos

Not really. Design pressure angle stays the same - hence the gear can be cut wit the same cutter, and mesh with gears cut with that same cutter. I believe the actual pressure angle where the teeth meet changes, as a result of being at a different point in the curve.

Read here: Gear Profile Shift | KHK Gears for an explanation of profile shifting. It is fairly common in industry to match the tooth form to the required result.

Edit to add: Introduction to Gears | KHK Gears is a fairly good primer on all things gear related.

Dave

Edited By Dave S on 22/09/2021 08:10:33

Martin Connelly22/09/2021 08:38:35
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1889 forum posts
203 photos

I think trying to use free hobbing for a quick way of making gears is going to be a case of more haste less speed because of the crap it will produce trying to get a usable end result with desirable features. You will soon get to the point where value for money (and time) makes it a waste of time. There is a reason that after the centuries of people making gears it has never been a major method of production. this thread is a reflection of this and should be closed as trying to explain the problems to the OP is best described as flogging a dead horse.

Martin C

John Haine22/09/2021 09:24:43
4170 forum posts
242 photos

On the PA / undercut question, Mike Cox has published tables for the button method of making involute cutters, and can supply the background spreadsheet. One can insert the pressure angle as a parameter in these. For clocks in the motion work (driving the hands) one can use involute just as well as cycloidal gears (in the train too probably) but it is nice to be able to use small pinion tooth counts (8 or fewer). One can use the spreadsheet to explore how the pressure angle affects the undercut, and use goal-seek to find a PA which gives no undercut. If you are making both gears, and where there is minimal torque, this can be quite a good option.

brian jones 1122/09/2021 09:25:45
347 forum posts
62 photos

Kind of missing the point here MC

this thread has opened up a treasure chest of valuable insights from experienced members sharing their knowledge

The noob to this complex sphere has to battle through all manner of rubbish from google and YT

For example there is the self style expert on Gears sponsored by AGMA

https://www.amazon.co.uk/Dudleys-Handbook-Practical-Design-Manufacture-ebook/dp/B0933KCRD6/ref=sr_1_1?keywords=dudley+gears&qsid=261-0563408-7179466&sr=8-1&sres=0367649020%2C1498753108%2CB01HDMKKIE%2CB01BLEILKE%2CB01H3R3GK8%2CB018IDQBN0%2CB00B0PHMW8%2C0241464501%2CB008C8T66Q%2CB00N5TYLBW%2CB00ERXMRWU%2CB07MMZZ2HW%2CB09BHYQ98X%2CB0711LLJ7T%2CB00002438O%2CB01BF9I4O8%2C0070179026%2CB007F9L4SQ%2CB0892VL1N4%2CB00Y3PJMES

Browse the Fundamental Laws of gearing at the beginning and you will get the picture

I do appreciate the Japanese link from Dave S

https://khkgears.net/new/gear_knowledge/introduction_to_gears/

OBTW

I did produce a perfectly serviceable plastic gear for modellers with light duty use in mind. Might work even better in Delrin. If it helps some modeller knock something up quickly then maybe it has a use despite the sceptics

img_0760.jpg

OBTW its a pity we cant rate these posts because some of them really are 5* solid gold

You cant make an omlette without breaking eggsdevil 

Edited By brian jones 11 on 22/09/2021 09:30:39

Martin Kyte22/09/2021 09:42:43
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2558 forum posts
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Posted by Dave S on 22/09/2021 07:20:18:

The undercut is an unfortunate artefact of the process of making an involute gear.

I have made some 12 tooth pinions without undercutting by doing just that and they roll against the 144,96 and 90 tooth gears made with the exact same cutter perfectly.

Dave

Are you sure about that.? With low pinion counts undercutting provides clearance for the tip of the mating gear on the tooth exiting engagement. 12 tooth pinions and wheel counts of 90 96 and 144 sounds like clock wheels to me. I'm sure they can be made to work as you say but only by decreasing the engagemant. When a rack (or a hob) is used to generate an involute form it must of neccessity create the clearence it requires and with low tooth counts teeth are undercut.

regards Martin

Dave S22/09/2021 11:00:41
223 forum posts
47 photos

Yes it’s a clock, and no I’m not sure.

These are the first gears I’ve ever cut, and I suspect that I should have profile shifted the wheels the opposite way to thin the teeth.

Still it’s all learning, and if they are depthed ok then they mesh ok - even if it’s not quite correct…

Will do better next time

Dave

brian jones 1122/09/2021 11:12:37
347 forum posts
62 photos

does this help

http://hessmer.org/gears/InvoluteSpurGearBuilder.html?circularPitch=1.954&pressureAngle=30&clearance=0.1&backlash=0.2&profileShift=0.2&gear1ToothCount=12&gear1CenterHoleDiamater=0&gear2ToothCount=144&gear2CenterHoleDiamater=0&showOption=3

Martin Kyte22/09/2021 11:40:54
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2558 forum posts
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Posted by Dave S on 22/09/2021 11:00:41:

Yes it’s a clock, and no I’m not sure.

These are the first gears I’ve ever cut, and I suspect that I should have profile shifted the wheels the opposite way to thin the teeth.

Still it’s all learning, and if they are depthed ok then they mesh ok - even if it’s not quite correct…

Will do better next time

Dave

No need to appologise, for many clock making situations tooth form will not matter a jot. Personally I like to use Thornton cutters and do use pinion cutters for pinions. Firstly because its easy and secondly I like the traditional cycloid tooth shape and flat bottom. I remember Alec Price lecturing on making clockwheel cutters and pointing out that old clocks had a variety of tooth profiles all made with shop made cutters and they all worked for many years successfully. If you are doing challenging horology like making watches or year going clocks then optimisation of friction really starts to matter otherwise so ling as you depth properly which basically means gettin each pair to run sweetly then you won't have too many issues. Swiss standards are more about allowing mass manufacture to function with interchangeble parts than anything else.

regards Martin

Dave S22/09/2021 12:18:27
223 forum posts
47 photos

I’ve gone involute for the clock because I wanted to explore the use of the “rotary Sunderland rack method” as a way to make gears.
That plus many naysayers telling me that a clock couldn’t possibly work with involute gearing as it’s not possible to gear up with involutes… I’m not sure how the gear knows

Dave

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