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torker
01-23-2005, 09:05 PM
I just made a simple gear with aluminum for a blank. I'd like to make some gears out of steel in the future but I'm wondering about cutters. I used a flycutter, single point, hand ground cutter for the aluminum and I'm sure the same setup would work for steel...except the cutter would dull a lot faster and need frequent sharpening. I can't see this working with a 100 tooth gear where there will be many sharpenings and the chances of screwing up the profile are huge. I'm just wondering because there was a whole pile of new cutter gears(7/8" bore) on Ebay awhile ago that could have been had for about $150 for the works. Would this be a better way to go with a light machine? Thanks!
Russ

JCHannum
01-23-2005, 09:18 PM
The downside of buying gear cutters is that each pitch requires 8 cutters to cut the range of tooth count from 12T to rack. This virtually guarantees you will never have the cutter you need for the gear you wish to cut.

Get yourself a copy of Ivan Law's Gears and Gearcutting. It is in the Workshop Practice Series avalailable from several sources, including Brownells.

It is an excellent book on the fundamentals of gearcutting for the HSM, and offers a couple of methods of making cutters.

Wtom
01-23-2005, 10:53 PM
<font face="Verdana, Arial" size="2">Originally posted by torker:
I just made a simple gear with aluminum for a blank. I'd like to make some gears out of steel in the future but I'm wondering about cutters. I used a flycutter, single point, hand ground cutter for the aluminum and I'm sure the same setup would work for steel...except the cutter would dull a lot faster and need frequent sharpening. I can't see this working with a 100 tooth gear where there will be many sharpenings and the chances of screwing up the profile are huge. I'm just wondering because there was a whole pile of new cutter gears(7/8" bore) on Ebay awhile ago that could have been had for about $150 for the works. Would this be a better way to go with a light machine? Thanks!
Russ</font>

Torker: Check this out
http://homepage.ntlworld.com/peter_harrison/workshop/gearcutting/index.htm

Tom

torker
01-23-2005, 11:27 PM
JC..Thanks! I wasn't sure about the cutters on Ebay...I was sort of worried that I'd end up with a bunch of cutters that where no good to me. That IS the book I'm ordering on Monday. Busy Bee tool company sells it.
Tom...Thanks for the link! That's a pretty neat way he made his cutter. More reading....
Russ

SGW
01-24-2005, 08:05 AM
There is little point in buying a pile of random gear cutters. Odds are they will be the wrong diameteral pitch, or the wrong pressure angle, or the wrong number cutter, for any particular gear you want to cut. When you want to cut a particular gear, buy THE cutter you need. You don't need to buy a whole set.

As far as doing it with a single-point tool: you can make that work better by gashing the tooth positions with a slitting saw as much a possible before cleaning up with the single-point form tool. You're right about a single-point cutter taking a beating in steel. I made a couple of small gears (16 and 32 teeth) that way, out of leaded steel, and my single-point tool just about survived. I neglected the tooth-gashing step, which would have helped a lot.

Ivan Law's Gears and Gearcutting is good.

[This message has been edited by SGW (edited 01-24-2005).]

John Stevenson
01-24-2005, 08:22 AM
Ivan Law's book has got to be the definitive for home shop gear cutting.
I have shelves of books here on gear cutting but they all go off into realms of advanced maths, trig, involute tables and spells.
90% of this information I have no control over.

I buy a gear cutter and I expect it to be made to spec, I don't need to know all this spec.

Ivan's book cuts right down to the bits you need to know and the bits you have control over, depth of cut etc.

None of this mumbo jumbo spells that's in all the other books.
Lets face it where in Nottingham am I liable to find three wise men and a virgin ?

John S.

torker
01-25-2005, 08:26 PM
Thanks again guys! I was wondering if any of you looked at the page Wtom pasted? What do you think of his cutter idea? Thanks!
Russ

JCHannum
01-25-2005, 08:50 PM
The hob as suggested is another approach to gearcutting that will work well.

In the Other Methods link, you will see John Stevenson's method of making a gear cutter with tool steel discs to form the cutter. Ivan Law's book also goes into this method.

Gears can be easily cut on the milling machine with home built cutters.

J Tiers
01-25-2005, 10:22 PM
Hobs are even more filthy expensive than cutters.

The good news is that they will cut ANY gear of the same DP, if you have correct change gears to work the hob and gear, and a setup to connect them.

Now for the bad news....you have to be able to set the hob at an angle to a travel axis, so that it will cut a straight tooth. On a ram type vertical mill (Bridgeport), that is not a real problem, but on a horizontal, you can forget about it unless yours is a "universal".

John Stevenson
01-26-2005, 04:09 AM
Russ,
The pasted link will work and it's reasonably quick and cheerful.
Plus side is you only need one cutter for all pitches.

Biggest drawback is the shape won't be an involute but it will be formed with a series of small steps to the side of the teeth.
Depending on the uses you want the gear for will restrict this method of cutting.

Something like your dial gear or screwcutting gears on a lathe that run at low speed would be fine but two of these running together at higher speeds may make an unaceptable noise.

Obviously as they wear in they will generate a true involute profile by the running action.

John S.

[This message has been edited by John Stevenson (edited 01-26-2005).]

torker
01-26-2005, 07:01 AM
Thanks guys! John...I like your method but I'm a little concerned about how the cutter will stand up to the abuse it will most certainly get from me http://bbs.homeshopmachinist.net//biggrin.gif I'm pretty sure to build a cutter over the next couple of days that will be made out of a truck axle or another piece of mystery metal that I have. Both are pretty tough to turn even in an annealed state. The fellow who did the writeup about the cutters more or less says that his isn't a true involute but was proven in use. Hmmmm...You say the gear noise will decrease in time as the gears wear together but I suppose at the same time the clearances will increase as well. Sloppy fit and (under the right curcumstance) the possiblity of heat generation? The gear I made for the threading dial is for very low speed, very low pressure...as Evan said..."it could be made with a file". However, the reduction unit that I want to build is going to be a whole differect ball game. The primary gear coming off the motor is really going to be spinning fast so now I do have concerns about noise/fit. I can see this may be a longer learning process than I thought. Ha...I may be sticking with aluminum gears for longer than I thought also!
Russ

JCHannum
01-26-2005, 09:33 AM
<font face="Verdana, Arial" size="2">Originally posted by J Tiers:
Hobs are even more filthy expensive than cutters.

The good news is that they will cut ANY gear of the same DP, if you have correct change gears to work the hob and gear, and a setup to connect them.

Now for the bad news....you have to be able to set the hob at an angle to a travel axis, so that it will cut a straight tooth. On a ram type vertical mill (Bridgeport), that is not a real problem, but on a horizontal, you can forget about it unless yours is a "universal".

</font>

Hobs are easily made on the lathe as was described in the provided link.

The problem of setting the blank angle on a horizontal mill is easily overcome by fabricating a sub-table like torker's that has the index and tailstock on a base that can be positioned at any angle on the mill table.

Overcoming the series of flats problem John describes is the major problem of hobbing one tooth at a time. This requires a gear hobber with both hob and blank powered and turning.

There are kits and plans available for making HSM useable hobbers, and John was working up a servo driven one a while back. This can get involved, but if some quantity is to be cut, it is worth looking into.

J Tiers
01-26-2005, 01:32 PM
<font face="Verdana, Arial" size="2">Originally posted by JCHannum:
The problem of setting the blank angle on a horizontal mill is easily overcome by fabricating a sub-table like torker's that has the index and tailstock on a base that can be positioned at any angle on the mill table.
</font>

Is that totally equivalent?

In one case, the table is traveling parallel to the hob teeth. In the other, it is moving at an angle to the teeth.

If you have the two geared together, as the gear moves towards the hob, it seems the gear must shift rotationally relative to teh hob to stay in proper engagement if the table does not move parallel to the teeth.

If the table moves parallel to the teeth, the engagement does not change...they turn together and remain in proper mesh at any point in the feed without requiring slip.

Did you mean a sub table with feed?

John Stevenson
01-26-2005, 01:59 PM
Yes it has to be a sub table with feed set to the helix angle of the hob.
If you do have a Universal mill where the table swings then this isn't needed.

Going onto vertical mills something like a Bridgeport can do this by tilting the head but a fixed head mill drill will also need a sub table but set 90 degrees to the bed.

Clear as mud ?

John S.

torker
01-26-2005, 02:03 PM
John...I understood the "mud" part just fine! http://bbs.homeshopmachinist.net//biggrin.gif