Gear Cutters?

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ELM6061 said:
Thanks for posting this question SMG, so many of my own have just been answered here, and to you Lensman, a great link, and as you stated "even though it is written in German". I have to follow up with; A picture paints a thousand words, and with 46 detailed photos & drawings, it is like reading a book.

One question I do have from that link, if you were going to cut your own HOB'S; What metal/steel would be best to use?

I do have an electric kiln & quenching oil, though apart from Tech school 30 odd years ago, with an oxy torch, I have never tried to heat/soak/temper/harden.

Eddie
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Tubal Cain wrote a 124 page book on heat treatment-------------------
"HARDENING,TEMPERING&HEAT TREATMENT.Page 24 has a very useful para
on on holding time .
Found it very useful.Bought a electric furnace to do heat treatment of die tools. Made and heat treated my die tools for department use.
Tempering can be tough w/o a tempering furnace but some guys found out domestic ovens can used for tempering.A good tempering furnace cost "an arm and leg".But it is worth money spent.
 
G'day and thanks for the replies. The little electric kiln is capable 1800C, so getting hot enough should not be an issue. How even it will be is a different kettle of fish????? Bought it to melt metal in, trouble with being square, there are no heating elements in the door which creates a cold spot and cost me a graphite crucible.
I have read a few different sites about heat/quench tempering and probably the only reason I have held onto the kiln.

I will have to do some more reading in regard to making the cutters to shape a hob.

Eddie
 
G'day Eddie. Can you tell us a bit about the kiln. 1800 deg should be good for melting cast iron I think
 
Cogsy said:
Am I right in thinking that a hob like this will cut any number of teeth, so I would only need one hob per DP? I'm liking the sound of that, rather than buying sets of 8 cutters... Thanks.
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Yes that's correct but the tooth form is a series of small flats rather than a true involute.

IMHO for the gears we use in 95% of model applications this is more than adequate and the gears can always be bedded in with a run in valve grinding compound.

Best Regards
Bob
 
Cogsy said:
Am I right in thinking that a hob like this will cut any number of teeth, so I would only need one hob per DP? I'm liking the sound of that, rather than buying sets of 8 cutters... Thanks.
Click to expand...

Hi,

That is true so long as you understand that the hob will only approximate the involute curve, but in most cases that is more than acceptable.
The trick is to cut the gear in multiple cuts not in one go.

A.G
 
Herbiev said:
G'day Eddie. Can you tell us a bit about the kiln. 1800 deg should be good for melting cast iron I think
Click to expand...
Sorry Herbiev, bit of a miss print and not sure what I was thinking when writing 1800c, it is supposed to be 1200C.
The kiln is a small (square) 240v B&L Tetlow potters kiln, where the door swings up and it has elements on the rear and two side walls.
I originally bought it from a hobby glass slumper, so I could start casting with aluminum. However it cracked my graphite crucible first go and while I had melted aluminum on three sides of the crucible, in the front where the crack appeared, the aluminum had not begun to melt. I immediately put the crack down to uneven heating, as there are no elements in the front (door). I could probably use and get away with using a steel crucible, however I have not bothered to try, and plan to build myself a new furnace, which I will heat using an oil burner.
Electricity is just way to expensive now and by the looks, only going to get worse. Our last bill went up over $200 and we went with out heating for the most part of winter, got rid of the second fridge, led lights for our main lights, power savers in all the main power sockets and I hardly did any work out in the shed.

Eddie
 
Hi Eddie,

I am sure that you know that you'd only need a propane torch to bring the tool to cooked carrot colour, I just use the domestic oven heated to about 250C to temper it. As far as hardening goes you only need to harden the teeth and not the whole length of the tool.


Regards,

A.G
 
An excellent reference is "Gear Cutting Practice" by Colvin and Stanley dated 1937, reprinted by Lindsay Publications.
There is an invaluable article in the Model Engineer by D.J. Unwin, " Simple form relieved Milling Cutters" in issues 21st August 1970,1st October 1971 and 15th October 1971. I have used this method on many occasions to produce my own cutters from Silver steel. If the gear teeth are of a larger D.P. to preclude or make difficult their manufacture at home, e.g. 6 D.P, Tracy Tools in the U.K. supply gear cutters of all D.P. at a very cheap price, some I have purchased were ex WW2, unused, still in the original preservative.
 
lensman57 said:
Hi Eddie,

I am sure that you know that you'd only need a propane torch to bring the tool to cooked carrot colour, I just use the domestic oven heated to about 250C to temper it. As far as hardening goes you only need to harden the teeth and not the whole length of the tool.


Regards,

A.G
Click to expand...

Hi A.G.

Heat Treatment of gear cutters. Your expert advice is sought.
I am wondering would it be the same as heat treatment for gears where only the gear tooth/teeth is hardened using high frequiency coils. Back in the Painted Post and Ahmedabad plants we us this process to case harden piston rods so that they could survive the oil scrapers and metallic packings.

Youtube has a video of a DIY High Frequency Induction Coil Heaters.
 
SMG said:
Dumb question, what does the # mean or designate on different gear cutters. I understand the pitch, I just don't understand the difference between a #7 48 pitch gear cutter compaired to a #8 gear cuttter. I"m sure its somthing really simple, but I am in the process of purchasing some gear cutters online and I need some advice.

Thanks
Steve
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Hi Steve,
Please include Gus too.
Just got myself educated thru brousing Internet suppliers.:):)
Gear cutting books were not very helpful. Have no idea one cuttter will not cut the entire O.D. Range .Ha Ha. :wall::wall:
My gear cutting experience was cutting one 4 " spur gear using involute gear cutter as specified on print. Using the dividing head was kind of mysterious to a seond year trade school student. Workshop instructors were not best. Some of my mates had half tooth.Ha Ha:wall::wall::wall:
This was way back in 1961/2.

Now planning to gear up to cutting spur gears. Will post.:cool::cool:
 
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The shape of gear teeth change according to how many there are. TO visualize this, compare the teeth on a 12-tooth gear (very rounded flanks) with the teeth on a rack (straight flanks). Strictly speaking, any given gear cutter is correct for cutting one tooth count. A cutter will be approximately correct, however, for a range of tooth counts near that one "exact" tooth count. I don't remember the numbers offhand, except that #8 is 135 teeth to a rack. #1 is something like 12 to 14.

There are, I believe, gear cutters available in sets of 15 to give better approximations of the correct tooth form.
 
Mainer said:
The shape of gear teeth change according to how many there are. TO visualize this, compare the teeth on a 12-tooth gear (very rounded flanks) with the teeth on a rack (straight flanks). Strictly speaking, any given gear cutter is correct for cutting one tooth count. A cutter will be approximately correct, however, for a range of tooth counts near that one "exact" tooth count. I don't remember the numbers offhand, except that #8 is 135 teeth to a rack. #1 is something like 12 to 14.

There are, I believe, gear cutters available in sets of 15 to give better approximations of the correct tooth form.
Click to expand...

Hi Mainer,

Thanks for the expert advice. Gear cutting will happen in the later half 2013 when I get a simple dividing head done from Harold Hall's prints and the first complete set of cutters from UK.Same cutters are Chinese Made. Hope they last.

Way back 1981 ,went to the Leblonde Singapore Lathe Plant to make pre-delivery inspection of the 18" Swing x 8" Precision Lathe. Was shown how they cut precision gears and lapping.Plus "running in" gear box. Opportunity missed. The Gear Cutting Module Supervisor was a Canadian with many years of gear cutting experience. Same would have been my best "Guru".

Gus Teng
 
I think I may have gotten the numbering of the cutters reversed (what I said was #8 is really #1, etc.) so don't let that confuse you.
 
With a universal mill you can use 1 cutter to cut all gears. The cutter is called a hob and is a spiral rack profile and the spindle and the indexer arbor have to be mechanically synchronized. Cutter is both more complex, and simpler, but the setup is more complex.

Though, in this day of stepper motors and computers it is really quite simple. Either mechanical gearing (the old way, needs lots of gears) or electronic gearing (the new way. all the gears are in software...).

Here's an example.
[ame]http://www.youtube.com/watch?v=ZhICrb0Tbn4[/ame]
 
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