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Old 01-21-2010, 11:29 PM   #1
kcmillin
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Default Involute gear cutter ?'s

Hello everyone, do any of you guy's (or gals) know where i can get a good all around set of involute gear cutters. I know there is a set a parameters for them when you order them, but thats all greek toi me. I have had limited success in the past with homemade gear cutting bits from hss, but i never used any sceince, I would just do it by eye. Including the number of teeth. nothing was certain.
i dont want to get to technicle with it
i just want a set of cutters i can play with and figure it out. anything from 1/4 inch diameter gear with 5-10 teeth up to 2-3 inches in diameter.

Please help, i am incredibly jealous of the most of you , and would like top try my worth by making amazing projects like yours.

thanks,
kel



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Old 01-21-2010, 11:44 PM   #2
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Default Re: Involute gear cutter ?'s


http://www.victornet.com/results.html

Their prices are reasonable....MSC has them also

www.mscdirect.com

A full set will cost you some coin...better to settle on a specific set of gears and maybe 1 or 2 cutters.....


Dave


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Old 01-21-2010, 11:46 PM   #3
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Default Re: Involute gear cutter ?'s

Hi Kel;

Quote:
Originally Posted by kcmillin
I have had limited success in the past with homemade gear cutting bits from hss, but i never used any sceince, I would just do it by eye. Including the number of teeth. nothing was certain.

kel
The first thing that really jumps out here is this; "I would just do it by eye. Including the number of teeth."
Simply put, you will never get a decent gear by cutting them by eye. Gear teeth must be accurately and precisely spaced, and there are no exceptions to that rule that I know of.
This is why you see people using an indexing fixture of some sort for these chores, whether it be a simple spindle with index plates, a dividing head, or RT, or even using another gear as an indexer.

You can buy the best set of cutters in the world and your gears will not come out any better if you think you are going to space them "by eye". Sorry.

To the cutters, you need to prepare yourself to spend some money if you want cut the range of gears you mention. There are a number of cutters in a set that will cut only one pitch on a given set of gear sizes. Those sizes are specific, and you generally cannot just pick a random size and just start cutting teeth on them. If you want to cut a different gear pitch, it means a whole new set of cutters.

I know you said you don't want to get technical about it, but there are some basics that simply cannot be ignored. Before we lay down a load of stuff you don't want to hear, do you wish to continue?

Dean
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Old 01-22-2010, 12:04 AM   #4
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Default Re: Involute gear cutter ?'s

I do have a pretty accurate rotary table and the spacing is always the same, as long as i eyed the first one i knew the steps. I made a crude clock doing this, along with some aluminum gears for a v-4 steam engine, it spins over 4500 rpm no prob.

But yes
I am interested in furthering my knowlede in the matter, i figure if i had success doing this haphazerdly, i should be able to pick up a few basics.

So to answer your question;
Yes, lay it on me!
thanks,
kel

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Old 01-22-2010, 01:27 AM   #5
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Default Re: Involute gear cutter ?'s

get the book "gears and gear cutting" by ivan law. its not very long and will tell you how to make gears that will work 100x better than guessing. its $7.69US at amazon. it even tells how to make your own gear cutters.

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Old 01-22-2010, 02:39 AM   #6
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Default Re: Involute gear cutter ?'s

Okay Kel.
Get the book mentioned in the previous post. I've never seen it, but it seems to be the one people like, judging by how often it's mentioned.

These are the basics I use for my gearcutting.

Diametral Pitch, what we usually just call "pitch". You need to now this in order to size your gears for your projects. Different pitches produce different sized gears for a given tooth count. All gears in a train have to be the same pitch to mesh. Common pitches are 16, 24, 32, 48, 64, and there are lots of others. The smaller the pitch number, the larger the teeth on the gear will be.

The pitch of a gear is a constant, so you can't just pick some random diameter and decide to put a certain number of teeth on it. The pitch and number of teeth you need for a given gear will dictate the diameter of the gear. What that means in real life is that when you design an engine, you don't get to pick the distance between things like a camshaft and a crankshaft. The gears will determine that distance, and you design around it.

To get a smaller or larger gear for a given amount of teeth, you choose a pitch that fits. You don't always get to pick your exact diameter. You pick the pitch that most closely matches the diameter you need. All other gears in that train have to be the same pitch.

Some examples;
Say you want two gears, one about 1/2" diameter with 20 teeth, and one about 1" diameter with 40 teeth.
If you choose 24 pitch for your gears, you won't even get close.
A 24 pitch gear with 20 teeth will be .916", and you can't change it. A 24 pitch gear with 40 teeth will be 1.75".

So, to get closer to the size you want, to go to a higher pitch, which will make the teeth smaller, reducing the size of the gear for the same amount of teeth.
If you choose a 32 pitch, the 20 tooth gear will now be .687" diameter and the 40 tooth gear will be 1.312". The gears are getting smaller, but still have the same amount of teeth because you are changing the pitch.

There are other pitch numbers you might try, to see if they give you the exact diameter of gear you want, but it usually doesn't work out that way. You just have to pick what is close, and build your project around those measurements where they are concerned.

To figure out what the diameter of a gear will be for a given pitch and fixed tooth count, use this simple equation.

Diameter = Number of teeth, plus two, divided by the diametral pitch (DP, or pitch)
For a 40 tooth gear with a 24 pitch it looks like this:
40T+2/24DP = 1.75"

You can use that to find out how large your gear blank needs to be so when you cut the appropriate number of teeth on it, they will come out spaced exactly right. No left over spaces, or half teeth, etc.

To figure how deep to run your cutting tool into the gear blank when cutting teeth, use the constant of 2.157. Divide the gear pitch into that number and it will give you the depth of cut for gears of that particular pitch.

Learning to make your own cutters may well prove worth your while, once you've seen what follows.

Each pitch of gear takes a different size of cutter, of course, since different pitch means different sized teeth. The big deal about this comes from the fact that a cutter is not only unable to cut any pitch other than what it was designed for, but that it will only cut a certain tooth count range on a gear. To be able to cut all the gear sizes in one gear pitch, such as 24DP, you need eight cutters. If you want to cut 32 pitch gears, none of your 24DP cutters will work, and you will need another set of eight cutters to cut 32DP. It can add up quick.

The cutters are made to cut a certain range of tooth numbers. A 24DP no. 8 cutter will only cut 12 or 13 tooth gears. If you want to cut 14 to 16 teeth of that same pitch, you have to buy another cutter. If you buy a whole set of eight, you can cut from just a few teeth, (12, I think) to as many as you want. But only in that one pitch, unless you buy another set.

You have an RT, so you can divide a circle into any number of teeth you want, for cutting your gears. Make sure you know before hand what all the different settings on the RT should be for all the tooth locations on the gear, before you start. Work it out on paper, and keep a list of subsequent settings near the mill as you cut.

Make sure your gear cutter is set dead center to the gear blank. If you don't have it right, it will show up in the gear having teeth that appear to lean to one side, and they will mesh tight, or not at all.

If you need to know more about this, ask. The few basic things here will tell you how big to make your gear blank, how deep to cut the teeth, and how to figure different sized gears for a given pitch.

Read up on it some, and don't get freaked out by the stuff you don't really need to know. There seems to be more math theory to it than actual machine shop practice. You don't need to know the same stuff as an engineer who gets his jollys drawing out involute curves, but many books include that type of thing. Learn how to calculate the proper diameter for a given gear pitch/tooth count, and the correct depth of cut, and you will get along.

Dean



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Old 01-22-2010, 03:17 AM   #7
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Default Re: Involute gear cutter ?'s


thank you VERRY much for this info> I was totally lost before.
I am so glad I found this forum.
you know I did not even know what a metal lathe was until I bought one at a Cummins tool show. and for 5 years I used a drill press with an x-y table on it. I finally bought a used mill/drill this fall from a local hobby shop owner. and WOW WOW WOW I did not know what a mill actually could do. I never seen one in action till I bought it. and then a month ago I finally broke down and got the internet, its an incredible wealth of knowledge that I wish I had a long time ago.

Once again THANK YOU Dean for the great info, and I will definatly check out that book.

Thank you my internet pals,
kel
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Old 01-22-2010, 04:22 AM   #8
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Default Re: Involute gear cutter ?'s

You bet, Kel.
There are others here that know a lot more about this stuff than I. If you have more questions, a good place to put them is in the "Questions and Answers" section nearer the top of the forum home page. I think more people read that part of the forum, so you might get more answers.

You've got the enthusiasm for the job!

Dean

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Old 01-22-2010, 05:25 AM   #9
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Default Re: Involute gear cutter ?'s

Dean, You Hobb any gears yet? That video I got shows how to make them and use.

Matt

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Old 01-22-2010, 05:32 AM   #10
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Default Re: Involute gear cutter ?'s

I know this post is about involute cutters, but I thought I would just mention another method, using gear hobs.

Rather than having a 'set' of cutters to do all sizes, a hob uses just one cutter to do the whole range. They work out cheaper buying just one cutter rather than the whole 'set'.

When eventually I can get a round tuit, I will be experimenting with these hobs to cut gears very easily on the mill. I have the system worked out, and if theory is to be believed, then these hobs will cut any size gear in a matter of minutes.

This is a hob of the correct size to cut any size of change wheel on my lathe.



And how they are held on the mill. It isn't the hob that is the difficult bit, it is getting it to the correct cutting angle and holding the blank. But if my calculations are correct, it will be a very easy method of cutting gears.



Hopefully later on in the year, I might be able to shed a little more light on it.

This is where I obtained my hobs from.

http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Gear-Hobs

I will be using module sizes (metric), but some normally used DP (imperial) sizes are available as well.

I got my ideas from watching the Jose Rodriguez's DVD, obtainable from here

http://littlemachineshop.com/products/product_view.php?ProductID=2057&category=

And a box of matches to hold my eyelids open while watching it. He has a very 'put you to sleep' drawl. I would suggest watching it in stages.


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