Gear cutter question

[V 45]

I'm having an issue trying to figure out what involute cutter to buy to make some gears.
What I'm trying to accomplish...one gear with 40 tooth with O.D. of .824", another 20 tooth with O.D. of .431", these mesh together. Then another set that mesh one with 15 tooth O.D. of .444" and the other is 27 tooth O.D. of .758".
I have not cut any gears prior but I do have a rotary table with a index attachment that I can use.
Any help is greatly appreciated.
Thanks again... V 45

 

[dnalot]

Hi

This might help

http://scriptasylum.com/rc_speed/two_speed.html


Mark T

 

[V 45]

That's a good for connecting gears but ... the ones I'm trying to make don't all mesh together. Just the 2 each in separate areas. I'm looking for the cutter size if I stated it wrong.
Thanks again

 

[gus]

Hi V 45.

The Involute Gear Cutters comes in a set of 8 per Module. Each cutter will cut a range of tooth count and no more or less. For example No. 1 will cut 135 teeth to a rack. No. 2 will cut 55-----134. Please refer to Gears and Gear Cutting by Ivan Law. Chapter 9 page 65. With the correct cutter ,the cut gears will mesh. By now there are about 10 HMEM Members cutting DIY Gears for our 4 stroke Gas Engines. See attached table foto. Gear cutting is not difficult but be prepared to scrap some gears as part of learning curve. Scrapped DIY Gears make very good paper weights or fishing sinkers . Book by Ivan Law is recommended for beginners.

 

[Cogsy]

Rather than buying cutters you can easily make a single cutter per DP that closely approximates the correct involute shape. Lots of info on calculating, making and using them at this link. Lots of us have used them and they work just fine for timing gears, etc.

 

[xpylonracer]

Hi V45

From the info given it seems your gears are not exact commonly used DP, closest to the 40T and 20T is 48DP, this DP would need diameters of .875" and .458" respectively. To cut these you will need 2 different cutters.
For the 15T and 27T gears the closest commonly used DP is 36. Diameters for these 36DP gears is .472" and .805" and again you will need 2 cutters.

FYI DP=(N+2)/OD where N=number of teeth
so OD=(N+2)/DP

Checked again and seems likely your 40 and 20T gears are MOD .50, the other pair don't come exactly MOD .6 but are close. If you don't make your own cutters you still need to buy 4 cutters, could make them expensive for just a one-off.

Emgee

 

[steve-de24]

V45, you don't say where in the world you are located but here are my thoughts on your gears,

I think your 40 and 20T gears could be metric Module=0.5
For the 40T gear : OD = 42 x 0.5 = 21mm = 0.827"
For the 20T gear : OD = 22 x 0.5 = 11mm = 0.433"

And the 15T and 27T gears could be 38DP
For the 15T gear : OD = 17/38 = 0.447"
For the 27T gear : OD = 29/38 = 0.763"
And before anyone says 38DP is non-standard, I agree, but it was the standard DP used by Meccano, a very popular machine modelling kit in the UK aimed at kids of all ages.

Regards,
Steve

 

[Charles Lamont]

Rather than giving the ODs of the gears, Is the centre distance between the shafts fixed? If so, this would allow a more accurate suggestion to be made.

 

[kvom]

Rather than giving the ODs of the gears, Is the centre distance between the shafts fixed? If so, this would allow a more accurate suggestion to be made.

Agree with this. If you're trying to replace some old gears with fixed shaft positions and required ratios, then the shaft distance is the critical factor. There may be pitches and tooth counts that will do what you want with cheaper cutters.

 

[canadianhorsepower]

Hi V45

From the info given it seems your gears are not exact commonly used DP, closest to the 40T and 20T is 48DP, this DP would need diameters of .875" and .458" respectively. To cut these you will need 2 different cutters.
For the 15T and 27T gears the closest commonly used DP is 36. Diameters for these 36DP gears is .472" and .805" and again you will need 2 cutters.

FYI DP=(N+2)/OD where N=number of teeth
so OD=(N+2)/DP

Emgee

I'm a little confuse here:wall:

you are saying OD=(N+2)/DP
and on the site that Cogsy sujest they are not.

 

[V 45]

Hello all,
Thanks for the help !!
Here's some more dimensions that might help.
Center of shaft to shaft for the 40T (Teeth cut .047") and 20T is .589" (Teeth cut .048")
Center of shaft to shaft for the 27T (Teeth cut .068") and 15T is .550" (Teeth cut .065")

These are fixed dimensions of the shafts the gears would be on. This is on a print and not making replacement gears but new for a project. The original print was scaled down to fit my small machines.

Also added my location.

 

[kvom]

You are getting into the realm of watch gears. My math might be a bit suspect, but here goes:

1) The pitch circle radii of the two meshing gears together equals the shaft separation, or .589
2) The tooth ratio is 2:1, so the larger gear's radius is twice the smaller. Thus 3*B = .589, B=.196
3) The resulting PCD for the large gear is .784 and the smaller is .392
4) This results in a diametrical pitch of 51.

As stated earlier, a .5 module cutter = 50.4DP would be close enough. Note that the tooth depth is 2/DP = .04".

You might also choose a smaller number of teeth. 30 and 15 would be 38DP. The teeth would be larger.

 

[xpylonracer]

Hi LUC

I quote OD (outside diameter) the highlighted part in the article posted is describing circular pitch (PCD).
OD is more useful because that's the calculated dimension of the blank gear with a known DP and number of teeth.

Emgee

 

[V 45]

The highlighted figures are the O.D (Outside diameter).

 

[xpylonracer]

Afraid not, highlighted figures refer to Circular Pitch not OD, check the drawing again and you will see the arrow pointing to CP which is almost centre of addendum and dedendum.

Emgee

 

[V 45]

I highlighted the number. On the drawing the arrow is pointing to the very tip of the tooth. I attached the page I'm working on.

View attachment SHEET 12 Gears.pdf

 

[xpylonracer]

The highlighted text is in an earlier post by Canadianhorsepower (another forum member), there is confusion because I think you mean I am referring to your BOLD text for the OD of your gears in your post.

Emgee

 

[V 45]

Sorry for the confusion.

Still looking for help with a cutter !
Thanks again

 

[steve-de24]

V45, the drawing explains a lot. Because this design is a scaling of a previous design the gears have ended up being defined by
(a) number of teeth
(b) outer diameter
(c) depth of tooth.
This is very non-standard way of doing things but ok if you are making your own gears ( and your own gear cutters if you want to be exact!).
Close enough cutters would be metric Module = 0.5 for the timing gears and DP = 38 for the kicker gears (if you can find them).

Alternatively you could play around with the design a bit (by changing tooth numbers and minor changes to the distance between centres) and see if it is possible to use something like DP=40 cutters for both sets of gears. I'm assuming DP=40 will be easier and cheaper to obtain in USA.

Steve

 

[V 45]

I have a cutter drawing, it's been almost impossible for me to make. That's why I am looking for a commercial made cutter. I've made several but it's still not right.