Newbe gear question

[riverrat]

I'm looking to buy a spur gear cutter.
I think I need a 24 pitch cutter #3 cutter for 38 tooth gear and #6 cutter for 19 tooth gear.
Looking to make a 2 to 1 gear
Circular Pitch is .13090 for the 38t gear and 19t gear then will be aratio.06545.
Would this be right or am I way off?
Also can I get to a ratio or pitch the same as 18 thread witch would be like .0555.
This would make larger 38t gear to be Circular Pitch of .1111 and making the smaller 19t gear .0555
Or am I stuck building around the gear pitch and not thread pitch?

Hope I'm not way out in left field.
This would be my first gear.

Can someone help me on this,
thanks

 

[gbritnell]

You're confusing gear terminologies. First gears have diametral pitch. This is the number that equates to the number of teeth in 1.00 inch of the pitch diameter. Yes there is a circular pitch number but that's not used for calculating the desired gear. Involute cutters are made to cut a specific range of teeth, from rack to infinite. In a lot of cases you can get the required ratio and center to center spacing using different pitches, it just depends on the strength of tooth size required, larger tooth, thicker cross section, stronger gear.
gbritnell

 

[Swifty]

This link may be of some help. http://www.hpcgears.com/pdf_c33/27.48-27.60.pdf

Paul.

 

[Philjoe5]

I think I need a 24 pitch cutter #3 cutter for 38 tooth gear and #6 cutter for 19 tooth gear.

This is correct according to the convention in Ivan Law’s book which is used in the UK and US. Be aware, however, that Asian metric gear cutters do not always follow this convention so if you’re making metric gears follow the convention usually engraved on the cutter

Circular Pitch is .13090 for the 38t gear and 19t gear then will be a ratio.06545.

Circular pitch is just pi (3.141) divided by the diametral pitch which in your case would be 3.141/24 = 0.1309. Meshing gears must have the same circular pitch.

Perhaps, if you gave an introduction of yourself along with your background and experience members here can give you more help.

Cheers,
Phil

 

[gus]

I'm looking to buy a spur gear cutter.
I think I need a 24 pitch cutter #3 cutter for 38 tooth gear and #6 cutter for 19 tooth gear.
Looking to make a 2 to 1 gear
Circular Pitch is .13090 for the 38t gear and 19t gear then will be aratio.06545.
Would this be right or am I way off?
Also can I get to a ratio or pitch the same as 18 thread witch would be like .0555.
This would make larger 38t gear to be Circular Pitch of .1111 and making the smaller 19t gear .0555
Or am I stuck building around the gear pitch and not thread pitch?

Hope I'm not way out in left field.
This would be my first gear.

Can someone help me on this,
thanks

Hi RiverRat,
Kindly advise your inventory of gear cutting equipment and background.There are many HMEM gear cutting experts. We have gone beyond cutting simple spur gears.

Ivan Law's Gear Cutting Book will be very useful to have on hand to read up
before getting into serious gear cutting. Gear cutters come in sets of eight pieces for each Module Size gear. Swifty is my Guru for ''Mitre Gear cutting.

In our pursuit ,most of us have a good collection of DIY gears with half tooth.
Part of learning curve. Wrong indexing was the cause.

See fotos of my DIY equipment. Being at the far end of the supply line forced me to cut 20 tooth timing gears for the Webster Engine and Rupnow Hit&Miss Engine and mitre gears too with DIY Dividing Head etc. Welcome to the HMEM Gear Cutting Group.

 

[riverrat]

Thanks all,

I'm retired metal boat building (structural steel).

I have a old logan 9B-17 21 lathe.

Just trying to take a worm gear
rotating at 30 to 75 rpms to spur
gears 19t to 38t to rack to a travel at .0555 per revolution.
( 30 to 75 rpm to travel at .555 per revolution with good tooth size)

I'll buy the Ivan's Law Book.
Thanks,
Riverrat

 

[riverrat]

that should be .0555 not .555

 

[gus]

Thanks all,

I'm retired metal boat building (structural steel).

I have a old logan 9B-17 21 lathe.

Just trying to take a worm gear
rotating at 30 to 75 rpms to spur
gears 19t to 38t to rack to a travel at .0555 per revolution.
( 30 to 75 rpm to travel at .555 per revolution with good tooth size)

I'll buy the Ivan's Law Book.
Thanks,
Riverrat

Worm wheel hobbing can be picked up from the YouTube. Ivan Law's book
has a chapter on it. I regret not cutting 72 gash prior to hobbing with a spiral tap and ended up with a 71 tooth instead of the requred 72T for a
DIY Rotating Table which now cannot be used for dividing.
See fotos.

 

[barnesrickw]

Looking forward to taking care of house things so I can give gear Hobbing a shot. Also, I found a prototype model of a gear cutting machine at the museum I work at. I'll get some pictures of it and post. From the early 1900's.


Sent from my iPad using Model Engines

 

[BronxFigs]

I have (found it in a scrap-yard) a commercially made spur gear. I want to mount it on the crankshaft of a model engine. I know the OD, the mounting hole diameter, the width of the teeth, the material (steel) the gear is made from, and the number of teeth. I need the matching spur gear, but with twice the number of teeth, for a 2:1 ratio. The center-to-center distance(s) is not important. I will build to suit.

Some questions:

1. What do I need to know to either, order, or, machine the mating gear? (Honestly, I would rather not machine the matching gear).

2. Assuming I now have the two matching gears....how do I find the center-to-center distances for mounting, and correct meshing?

These gears will be very lightly loaded and will be used in a crankshaft to camshaft application for a model engine. Is the backlash, and exact center-to-center distances critical?

3. In this kind of application, would it be easier to just use a set of 2:1 sprockets and chain, in lieu of the gears?

Pardon me....my ignorance is showing. Help!


Frank

 

[Philjoe5]

Frank,
The gear that mates to the one you found must have the same diametral pitch. To calculate it, count the number of teeth on the gear you have, add 2 to that and divide by the outside diameter of the gear. That should give you one of the common gear pitches. If you get a number that doesn't match, like 20.3, then divide that by 25.4 which would give a result of 0.8. That's a common metric gear pitch.

The center to center distance is (N1 + N2)/2P where N1 = number of teeth on gear 1, N2 = number of teeth on gear 2 and P is the gear diametral pitch. For smooth running gears you should be close to that. But you're right, the usual load on a cam operating a valve on these small engines is light so you can tolerate a bit of play.

Cheers,
Phil

 

[BronxFigs]

When I don't know something, my default position is to ask questions and get answers from those who know far more than I. So I find myself asking forum members, and asking, quite often.

Thanks for the gear information. I will do some quick calculations and start looking for a matching spur gear. I have a friend that has a gear tooth gauge. I guess I will need information about tooth shapes, too.

I suppose I could probably make the matching spur gear in my friend's shop....but it would be less of a headache for me, if I just bought a matching gear.

Many thanks for the help.


Frank

 

[gus]

Looking forward to taking care of house things so I can give gear Hobbing a shot. Also, I found a prototype model of a gear cutting machine at the museum I work at. I'll get some pictures of it and post. From the early 1900's.


Sent from my iPad using Model Engines

Please post fotos. Looking forwad to make a miniature hobbing machine.
A gear train required to hob to tooth count. Hobbing with spiral tap got me hooked to hobbing.

 

[gus]

Looking forward to taking care of house things so I can give gear Hobbing a shot. Also, I found a prototype model of a gear cutting machine at the museum I work at. I'll get some pictures of it and post. From the early 1900's.


Sent from my iPad using Model Engines

Please post fotos. Looking forwad to make a miniature hobbing machine.
A gear train is required to hob to tooth count. Hobbing with spiral tap got me hooked to hobbing.

 

[gus]

Hi Riverrat,
CTCtools.com sells very low cost HSS Gear cutters. Best to buy in sets of 8 pcs. I bought Metric Module 0.8 and 1.0 at US$75
per set. Newman tools have info on cutter size selection to cut ''no of teeth".

 

[crueby]

I think that is www.ctctools.biz, not .com. The .com address goes to a placeholder page (maybe they changed?). I had bought a set of gear cutters from them a couple years ago through thier ebay store - took a couple weeks to arrive from Hong Kong, but they were good cutters, have used them on several projects so far to cut brass gears.

 

[gus]

Frank,
The gear that mates to the one you found must have the same diametral pitch. To calculate it, count the number of teeth on the gear you have, add 2 to that and divide by the outside diameter of the gear. That should give you one of the common gear pitches. If you get a number that doesn't match, like 20.3, then divide that by 25.4 which would give a result of 0.8. That's a common metric gear pitch.

The center to center distance is (N1 + N2)/2P where N1 = number of teeth on gear 1, N2 = number of teeth on gear 2 and P is the gear diametral pitch. For smooth running gears you should be close to that. But you're right, the usual load on a cam operating a valve on these small engines is light so you can tolerate a bit of play.

Cheers,
Phil

Hi Frank,

Metric Module 0.8 is my favourite for cutting i.c. 20t/40t timing gears.
I use a stack of gears 20---------80t to direct index gear cutting. This way
I have no half tooths. Have yet to DIY a Dividing Head with Indexing Plates to extend tooth range beyond 80.