What am I doing wrong.

[Roger HulettParticipant @rogerhulett83124]

I am trying to cut a 16 tooth gear. The Warco chart for 16teeth on a 90:1 ratio shows 5turns and 10/16 extras. I set it up as instructed with 11 spaces between the sector arms. With the gear cutter in position and starting from the first hole adjacent to the left hand sector arm then I rotated the chuck 5 turns + the 10 remaining holes between the sector arms until the pin reached the right hand sector arm. I then marked the gear blank at the point where it would be cut by the gear cutter.I proceeded to do this until I reached the starting point. I then counted the pencil marks and found I had 18. I have tried this several times and each time the result was 18.

What am I doing wrong?

[Roger HulettParticipant @rogerhulett83124]

Warco RT + dividing plate + Warco Tailstock + horizontal mill

[Michael GilliganParticipant @michaelgilligan61133]

Roger,

The instructions sound entirely logical

(5×16)+10 = 90

… So I really don't know what's going wrong.

MichaelG.

[Phil PParticipant @philp]

Firstly

90/16 = 5.625 = 5 5/8 = 5 10/16

Are you sure you are using a division plate with 16 holes ?

I would have expected there to be 10 "spaces" between the sector arms not 11, there will be actually 11 holes visible between the sector arms.

So that gives you 5 full turns and 10 out of the available 16 spaces per division.

Phil

[Roger WoollettParticipant @rogerwoollett53105]

You need five complete turns plus 10/90th of a turn. Thus you need one hole in a 9 hole plate, 2 holes in an 18 hole plate etc. You will have to find a plate where the number of holes is a multiple of 9.

[Halton TankParticipant @haltontank]

Roger,

I think you are not resetting the sector arms to new position after each 'cut'. I.E. after five turns plus 10 holes you have advance the sector plate so that the left arm is now touching the pin.

Phil,

I think 11 holes showing is right as you want 10 segments between the holes.

 

Regards

Luigi

 

Edited By Halton Tank on 03/11/2015 17:21:05

[Phil PParticipant @philp]

I dont agree with 18 holes.

You can do it with the 16 hole plate as I said above.

Or you can use 5 full turns and 15 spaces of a 24 hole circle

Or you can use 5 full turns and 20 spaces of a 32 hole circle

18 holes does not work.

Phil

Edited By Phil P on 03/11/2015 17:24:21

[AjohnwParticipant @ajohnw51620]

Look on the bright side – you did right marking the divisions rather than cutting the gear.

John

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[Roger HulettParticipant @rogerhulett83124]

I think Luigi has hit the nail on the head. After marking out the blank,I disengaged the chuck and moved the pin back to it's original position.Then re-engaged the chuck,moved the pin 5 turns + 10/16.I didn't realise that one moved the sector arms each time. First thing in the morning,I will retry. Thanks everyone and especially Luigi.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Halton Tank on 03/11/2015 17:20:02:

… advance the sector plate so that the left arm is now touching the pin

.

… Clear and Concise advice ^^^

Quoted, with emphasis, for the benefit of future visitors.

MichaelG.

[Brian WoodParticipant @brianwood45127]

Hello Roger,

It is the gaps you count, not holes and the sector arms are moved as a locked pair after each cut. You don't need to release the chuck, in fact you could easily lose count or position that way.

I found a cocktail stick on the other side of the sector arm when it has been moved into contact with the pin as a useful reference to return to if you lose count. Move it up to that arm again after each resetting of the sector arms.

Try another 'air-cut' to check it through as you did.

Brian

[brickyParticipant @bricky]

I have cut numerous gears,but I always had to concentrate on the number of turns as I was sometimes unsure on the count.I solved this by getting a hand held number clicker.

Frank

[Neil WyattModerator @neilwyatt]

Going back to thw original post:

I am trying to cut a 16 tooth gear. The Warco chart for 16 teeth on a 90:1 ratio shows 5turns and 10/16 extras. I set it up as instructed with 11 spaces between the sector arms.

Surely with a 16-hole plate it should be 11 holes or 10 spaces?

But the only way to get 18 with 90:1 ratio is to make 5 full turns + NOTHING, so I am sure that LUigi has the real problem – the sector arms aren't being advanced after each division is made.

Neil

[Swarf, Mostly!Participant @swarfmostly]

I'm obviously missing something here but, if the OP is wanting to cut a 16 tooth gear and has a 16 hole plate, why not use direct indexing???

Best regards,

Swarf, Mostly!

[AjohnwParticipant @ajohnw51620]

Does anyone know what the advantage of 90:1 is?

I wonder if there is one really. Coming from industry I had used 40:1 for dividing plus compound at times. I went to buy a worm and wheel and they only had the 60 as that is what people want so bought that. Turns out that with the usual standard plates 60 is ok. On the other hand I saw some new Vertex bits available and do want to make a bigger dividing head or maybe / rotary table at some point I wondered about buying them to save making a few bits and pieces. When I checked the hole counts in the plates I found that they wouldn't cut 2 primes that I will probably want. Leaves me wondering if 90:1 is just bigger number must be better. 90 also needs to be a bigger wheel to achieve equally strong teeth,

John

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[JasonBModerator @jasonb]

Posted by John W1 on 03/11/2015 20:14:18:

Does anyone know what the advantage of 90:1 is?

–

It's easier to rotate work against a cutter than with a 40:1 ratio, thats why its used on a rotary table. In the home shop a rotary table often has to double as a dividing head

[Dennis DParticipant @dennisd]

On the Arc site there is a link to a guide by Cletus Berkeley on setting up and using a rotary table.

**LINK**

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Den24171 on 03/11/2015 20:28:38:

On the Arc site there is a link to a guide by Cletus Berkeley on setting up and using a rotary table.

**LINK**

.

Yes, it's a very useful guide … but note that he discusses 72:1 ratio

[which might lead to some confusion]

MichaelG.

[Enough!Participant @enough]

Posted by Roger Woollett on 03/11/2015 17:12:15:

You need five complete turns plus 10/90th of a turn.

No, you need 90/16 turns = 5.625 turns

So 5 turns plus 5/8 of a turn (or 5 turns plus 10/16 of a turn) …. a plate with a multiple of 8 divisions.

[AjohnwParticipant @ajohnw51620]

Posted by JasonB on 03/11/2015 20:20:40:

Posted by John W1 on 03/11/2015 20:14:18:

Does anyone know what the advantage of 90:1 is?

 

–

It's easier to rotate work against a cutter than with a 40:1 ratio, thats why its used on a rotary table. In the home shop a rotary table often has to double as a dividing head

Thanks Jason. I had wondered. My dividing head is the Dore Westbury design with 60T wheel but he used his own idea of hole counts on the 2 plates to go with it. 14 circles of holes and unusual primes so it misses a fair few tooth counts so I had a look at what happens if 60T is used with B&S plates which have been pretty popular and it comes out like this

That's just up to 100 'cause I got fed up. Coverage is more important the lower the count anyway. If I do one I think I will stick to 60T and fit a bigger handle.

I was rather surprised by the hole counts on the vertex plates. As some primes aren't there they couldn't offer the same coverage.

I'd guess the dividing heads I used at work were 40T so that the worm form was strong to allow them to be geared from the table on a miller. They had us make a 1" twist drill and mill some square threads.

John

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Edited By John W1 on 03/11/2015 23:27:37

[Phil PParticipant @philp]

I think the 90:1 has got more to do with the physical size of the actual worm gear under the table.

By default the rotary table is usually larger in diameter that a dividing head, so the gear will also need to be bigger, if it only had 40 teeth they would need to be huge ones, so they went up to 90 as standard on most commercial rotary tables I have come across.

In reality it does not matter too much what the ratio is so long as it is an even number that can be divided into easily.

I tend to use plates from my 40:1 dividing head on the 90:1 rotary table and vice versa when required.

The GHT dividing head is 60:1 and that is quite a useful bit of kit as well. But to be honest most times for general use I use a 24 hole direct indexing plate on the back of my Tom Senior dividing head.

Phil

[Roger WoollettParticipant @rogerwoollett53105]

Posted by Bandersnatch on 03/11/2015 22:03:46:

Posted by Roger Woollett on 03/11/2015 17:12:15:

You need five complete turns plus 10/90th of a turn.

No, you need 90/16 turns = 5.625 turns

So 5 turns plus 5/8 of a turn (or 5 turns plus 10/16 of a turn) …. a plate with a multiple of 8 divisions.

You are of course quite right. A total of 90 turns is required. Five complete turns for each of 16 teeth takes up eighty leaving 10 turns. Thus 10 holes of a 16 hole plate times 16 teeth gives 10 more turns.

[Martin KyteParticipant @martinkyte99762]

Do it all in division plate hole steps.

Multiply the 90 by the 16 of the division plate giving you 1440 for 360 degrees.

you need 16 teeth so divide by 16 which is 90.

you have 16 holes on your division plate so 90 is 5×16 + 10

or 5 whole turns plus 10 holes for each tooth.

regards Martin

[AjohnwParticipant @ajohnw51620]

Posted by Phil P on 04/11/2015 00:04:21:

I think the 90:1 has got more to do with the physical size of the actual worm gear under the table.

By default the rotary table is usually larger in diameter that a dividing head, so the gear will also need to be bigger, if it only had 40 teeth they would need to be huge ones, so they went up to 90 as standard on most commercial rotary tables I have come across.

In reality it does not matter too much what the ratio is so long as it is an even number that can be divided into easily.

I tend to use plates from my 40:1 dividing head on the 90:1 rotary table and vice versa when required.

The GHT dividing head is 60:1 and that is quite a useful bit of kit as well. But to be honest most times for general use I use a 24 hole direct indexing plate on the back of my Tom Senior dividing head.

Phil

That makes sense. One thing I didn't use at work was a rotary table.

The GHT head adds a 40T wheel plus worm to drive the 60T worm. It's possible to get just about any division ratio any one might realistically want using that by averaging the errors – the 40T worm is driven by a graduated handle rather than a division plate. 0.15 degrees per turn so suppose it could be graduated to 0.001 degrees. More intended for vernier scales I suspect.

John

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[Michael GilliganParticipant @michaelgilligan61133]

Just for completeness: I should mention that my BCA has a 180 tooth wormwheel, cut on the periphery of its 8" table.

The dial is scaled 0-60 0-60 so that's minutes of arc … half a turn per degree.

I shall [in the fullness of time] probably add the facilty to drive it with a Stepper Motor.

MichaelG.

Edited By Michael Gilligan on 04/11/2015 11:34:57

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