Making a gear cutter

[T_henry]

Hi, I have Ivan Law's Gears and Gear Cutting and want to make a cutter. So my question is what steel should I use for the cutter. I have a 1/4 HSS blank but doesn't hard + hard = crash? Do I have to anneal it then harden and temper or use drill rod? The book does not address the type of material to use for the cutter.
Thanks
Tim

[JCHannum]

I think the Law book calls for the use of silver steel, this is the British equivalent of drill rod, which is fine for the purpose. HSS will be too hard to machine and annealing and re-heat treating is rather involved for the home shop.

As an alternate to drill rod, for limited use or softer materials, mild steel can be used and case hardened with one of the case hardening compounds such as Kasenit.

[camdigger]

HSS is the material of choice, if grinding to profile, IMHO. If you intend to follow the steps to manufacture the cutter spelled out in I.L.'s book (isn't that the one with the two buttons?), use drill rod, or any tool steel in the soft state and then heat treat. (I'd temper to straw color after quenching). IIRC Mr Law mentions silver steel as a material. Simply substitute "drill rod" for "silver steel" throughout the book and you'll be fine.

HSS cutters are fine. Cutters are a compromise between tough enough to take the pounding and hard enough to hold their shape. The material selection for cutters is a source of much angst and endless debate hereabouts.... Brace yerself...

Editted P.S. As JHannum points out, Annealling HSS is a bit problematic for the HSMer as the temps are higher than most tool steels. Not worth the bother, IMHO...

[T_henry]

The books uses drill rod for the buttons to form the cutter so should I use drill rod also for the cutter itself?

[camdigger]

YUP or you can mess with the toxicity of the Kasenit to case harden, then do the heat treat Q&T drill rod would need anyway....

[T_henry]

So my options are, to use HSS and grind the profile or, use drill rod and form the cutter and then harden and temper?

[JCHannum]

Kasenit is non-toxic, it is quite safe to use following the manufacturer's instructions.

Drill rod would be the material of choice, but purchase price and availability might be problematic for one off use. Buying a 36" length of large diameter drill rod to get the 1/2" slice needed for a gear cutter is not the best economics.

[lazlo]

Kasenit with a torch is really easy and doesn't need any special tooling (or an oven): you just coat the blank with the Kasenit, hit it with a torch until it melts, repeat for as much case as you want.

But it doesn't get much easier than A2 drill rod: just heat it up and let it cool. Quench it in a toaster oven.

As JHannum points out, Annealling HSS is a bit problematic for the HSMer as the temps are higher than most tool steels. Not worth the bother, IMHO...

Annealing HSS is the easy part -- it anneals from the heat of a stick welder. The hard part is heat treating it -- you're supposed to do a double- or triple- heat treat in a vacuum salt bath. Drill rod would be much easier.

[camdigger]

Manufacturers recommendation for Kasenit include mechanical ventilation to avoid CO and HCN from pyrolysis (heat decomposition).

https://www.travers.com/htdocs/pdf-msds/81-003-001.pdf

Not particularly deadly in the concentrations and amounts expected, but unpleasant. Drill rod, however does not give off any fumes.

My preference, no Kasenit, just a piece of the drill rod out of shop stock... Handy for D bit reamers and other assorted cutting tools too.

Locally to me hardware and fastener supply stores stock drill rod to 1". I haven't found Kasenit... Haven't looked too hard either.

[gwilson]

Can you just make a fly cutter on a piece of tool steel that sticks out of the arbor at 90 degrees,and is ground to the shape of the gear tooth? Clock makers used hem for centuries.

[Evan]

Kasenite or (Quik Hard in Canada) are sodium ferrocyanide, an approved food additive to stop table salt from clumping. The fumes when heated to red hot contain traces of cyanide gas but not enough to cause problems. At the most all you need is a fan at your back if you are concerned. The material itself is entirely non toxic. It's easy to use and works well.

Incidentally, the threat from overheated teflon lined frying pans is much greater.

[Michael Hall]

For the first time gear cutter check out these youtube videos:

http://www.youtube.com/user/Hobbynut#p/u/15/MItgd-faHFw

I think there is a total of seven or eight videos.

Michael

[Mcgyver]

Hi, I have Ivan Law's Gears and Gear Cutting and want to make a cutter. So my question is what steel should I use for the cutter. I have a 1/4 HSS blank but doesn't hard + hard = crash?

the only way, well not the only way, but the only way in the home shop you're going to machine hardened hss is via grinding. Using annealed drill rod (the state its in when you buy it) you machine to shape with lathe mill etc then harden & temper. What exactly does this cutter look like? single bit, radial milling cutter, hob, fake/faceted hob? etc. what shape it needs to end up will determine whether you start with a hss blank or annealed drill rod

Can you just make a fly cutter on a piece of tool steel that sticks out of the arbor at 90 degrees,and is ground to the shape of the gear tooth? Clock makers used hem for centuries.

you're right, depending on how accurate a profile you can grind. Whether that works would depend on the application i'd think. Clocks are made on purpose with quite sloppy fits and the wheels are slow with light loads. the closer you get to high speed & power the more perfect you want the tooth form

[camdigger]

Can you just make a fly cutter on a piece of tool steel that sticks out of the arbor at 90 degrees,and is ground to the shape of the gear tooth? Clock makers used hem for centuries.

This is exactly the approach I have used in the past to make lathe change gears out of mild steel plate. I used a HSS blank and free hand ground the cutter to match the tooth profile of the change gear with the tooth count closest to the one being made.

If you're doing this, give serious consideration to gashing the blank first to remove the bulk of the material in the gap between teeth. I used a thick slitting saw on a shop made arbor...

The next issue will be dividing. There's a dozen and one ways to do that....

Unfortunately, the last ones I did were not documented with a digital camera, so I can't share them. I'd scan the prints if I could only find them...

[philbur]

This is the method I have successfully used in the past to cut a number of small gears in mild steel.

You only need to make one cutter to be able to produce a full range of gears tooth numbers. If you make the "standard" involute cutter you need to make 7 or 8 to cover the same range. I was quite surprised that Ivan Law's book doesn't even mention this method.

The down side is you need to make a relatively large number of small incremental passes to form the correct tooth profile on the blank. It does however cut more than one tooth at a time. Pre-gashing the blank gear is preferable with this method also.

Phil

For the first time gear cutter check out these youtube videos:

http://www.youtube.com/user/Hobbynut#p/u/15/MItgd-faHFw

I think there is a total of seven or eight videos.

Michael