Gear Cutting

[simister]

Hi,
I am about to start building the Kerzel Hit & Miss. However, I wanted to practice cutting some gears.

I purchased the indexing plates for my rotary table and set it up on the mill.

I have had 3 attempts and can't quite get it correct.

I am trying to replicate the small tooth gear on the Webster Engine for practice.

This is my set- up

24 teeth

0.8 module Number 4 cutter.

Cutting depth 1.8 mm

20 hole index plate - 3 full turns plus 15 holes.

I am getting 24 teeth and 23 of them look good, however, the last tooth is too wide. I am not sure what I am doing wrong.

Any help on this would be appreciated as I am very new to gear cutting.

I have attached a photo.

Regards, John

 

[Leswato]

Looks like the thicker tooth would take another cut so I would say that it's indexed for 24 cuts which would give you 25 teeth
Les

 

[Leswato]

Sorry 25 cuts lol

 

[Jasonb]

Are you definately moving 15 holes? You need 16 holes between the fingers one to take the pin and 15 actual holes to move.

This would give you about a 4 degree error by the time you reach the last tooth and it looks like about that

 

[Leswato]

What's the ratio of your dividing head

 

[Jasonb]

Easy enough to work out from the quoted turns used 90:1

 

[SmithDoor]

Do you have a 60, 72 or 90 tooth work on your rotary table
What are you number of hole in your index plates

I have test all my indexing with marker first to avoid 1/2 tooth

Dave

Hi,
I am about to start building the Kerzel Hit & Miss. However, I wanted to practice cutting some gears.

I purchased the indexing plates for my rotary table and set it up on the mill.

I have had 3 attempts and can't quite get it correct.

I am trying to replicate the small tooth gear on the Webster Engine for practice.

This is my set- up

24 teeth

0.8 module Number 4 cutter.

Cutting depth 1.8 mm

20 hole index plate - 3 full turns plus 15 holes.

I am getting 24 teeth and 23 of them look good, however, the last tooth is too wide. I am not sure what I am doing wrong.

Any help on this would be appreciated as I am very new to gear cutting.

I have attached a photo.

Regards, John

 

[Leswato]

Are you removing any back lash within you rotary table

 

[Brian Rupnow]

One thing to watch for and be very careful of--if your directions say 3 full turns plus 15 holes, that means 15 holes visible between the sector arms. If you put the pin in the fifteenth hole rather than the sixteenth, you will end up with an accumulated error at the last tooth.---Brian

 

[canadianhorsepower]

Hi,
I

This is my set- up

24 teeth

0.8 module Number 4 cutter.


Regards, John

24 teeth is a number 5 cutter

 

[P.J]

In addition to what's allready been mentioned about using the correct cutter, based on the picture it looks like you might be cutting the teeth too deep.
To calculate the cutting depth we multiply the module of 0.8 with the magical number of 2.157 which gives us 1.7256mm, lets call it 1.73. So, in old world money you're 3 thou too deep, which might not sound like much but 0.8 module is a delicate little thing.

 

[fencer]

John I always before I cut teeth use a pencil mark on the centre of the cutter the full circumference of the gear and check that I have not made a mistake.Tedious I know but time well spent.Beat of luck with the next one
Frank

 

[Jasonb]

Too deep a cut or the wrong number cutter won't give an odd size last tooth, they will all be the wrong profile but the same size. As I said and Brian confirmed the common mistake is not to have #of holes plus one for the peg between the arms.

In this case each tooth should be 15degrees apart (15 x 24 =360) but by missing one hole each tooth will be 0.2deg too small (1/20 of a turn) so by the time you get to the 24th tooth you will be 4.8degrees short (24x 0.2)which is why the odd tooth looks bigger.

J

 

[simister]

OK, thanks guys for all your help. It looks like I have made a few mistakes on this cut.

1: My notes say that the depth should be calculated by: 2.25 x Module = 2.25 x .8 = 1.8 mm. Is this correct or should it be 2.157 as suggested by P.J?

2: It also looks like I have made the classic mistake of not moving forward the extra hole. I was doing 3 full turns and when I counted the 15 holes I was including the hole I was already in. This would certainly be the cause of the bigger tooth at the end.

3: the ratio head is 90

4: the tip to check the cuts with a pencil before starting makes a lot of sense and I will be doing that next time to avoid wasting time and material.

5: Back lash is another important point I will be more aware of that.

6: My notes definitely say that a number 4 cutter for 21-25 teeth. However, I notice that my notes are in reverse, for EG no 1 cutter for 12-13 teeth. This is different from canadianhorsepower's table.

I will have another go over the weekend and see how it turns out using all of your advice.

Thanks again guys.

John

 

[Jasonb]

For Gears 0.25Mod to 1.0Mod you should be cutting 2.4xMOD ((Dedendum + Addendum) x MOD) so in this case

1.4 x0.8 + 1x 0.8
1.12 + 0.8 = 1.92




http://www.hpcgears.com/pdf_c33/27.48-27.60.pdf

MOD gear cutters are often numbered the opposite way to DP which is why you have diferent numbers to Luc's table

 

[simister]

For Gears 0.25Mod to 1.0Mod you should be cutting 2.2xMOD ((Dedendum + Addendum) x MOD) so in this case

(1.4 + 0.8 ) x 0.8
2.2 x 0.8 = 1.76mm.



http://www.hpcgears.com/pdf_c33/27.48-27.60.pdf

MOD gear cutters are often numbered the opposite way to DP which is why you have diferent numbers to Luc's table

Jasonb,

I had a look at the PDF you linked and I am confused.

It says "Whole depth = Addendum + Dedendum

In My case:

Dedendum = 1.4 x MOD

Which will be: 1.4 x .8 = 1.12

Whole depth will therefore be 1.12 +.8 = 1.92 depth.

Am I missing something here?

John

 

[Cogsy]

Jasonb,

I had a look at the PDF you linked and I am confused.

It says "Whole depth = Addendum + Dedendum

In My case:

Dedendum = 1.4 x MOD

Which will be: 1.4 x .8 = 1.12

Whole depth will therefore be 1.12 +.8 = 1.92 depth.

Am I missing something here?

John

You're not missing anything, Jason has made a slight math mistake, adding 1.4 x MOD to the actual MOD of 0.8 rather than 1 x MOD (easy mistake to make and somewhat confusing I know).

The Dedendum is 1.4 x MOD, the Addendum is 1 x MOD, so adding them together we get 2.4 x MOD so 2.4 x 0.8 = 1.92mm total depth (this is only for MOD 1.25 and under, over that use 2.25 x MOD).

 

[P.J]

Now I'm confused. I've been using this for years with satisfactory results:
http://www.micro-machine-shop.com/module_gear_data.pdf

 

[Cogsy]

Now I'm confused. I've been using this for years with satisfactory results:
http://www.micro-machine-shop.com/module_gear_data.pdf

From what I understand this is the theoretical total depth and should equate to identical tooth and gap widths at the PCD. In practice I believe the figures given above (2.4 and 2.25 depending on MOD) are real world figures. Your figure would work, as you've discovered, but you probably get slightly different shaft centre values than someone who uses the larger depths.

In practice it wouldn't make a whole lot of difference, my gears running in place of yours would work fine but would have a little extra backlash. Yours running on my machine might be a little tight but may be able to be 'run in' to suit the closer shaft centres.

Of course this all goes out the window if the cutter manufacturer has specified a different overall depth of cut. They can make cutters with extra clearance built in I believe.

 

[Jasonb]

Yes my error, I've gone back and corrected it.