Now Seal starter motor

[gadabout]

Hi all,
I need to cut a 130 or 140 tooth 64dp gear( doesn’t matter which one as I will adjust centre’s to suit) but I can not find a gear cutter to suit without buying a full set( will never need the others) . Does anyone know where I can get one ? Am told that I could also use a .4 mod cutter ? My eyesight isn’t good enough to grind a single point cutter either at that size.
Thanks
Mark

[Jo]

You do not grind single point cutters you cut them using a pair of hardened buttons. The details are in Ivan Law's book

Jo

[Jasonb]

I have used 0.8MOD cutters for 32DP so you should be able to get away with 0.4MOD for 64DP depending on the gears application, mine were for timing gears on engines, high load or positional accuracy may mean you need the correct cutter. Commercial cutters cover a wide range of tooth numbers at that count so any slight difference in profile will be minute

With a 140T cutter also being suitable for cutting a Rack you could probably get away with a straight sides tool

Single point can be milled or ground depending of the tooling you have and can then be done from an HSS tool bit and used in a simple holder rathe than turning from a disc and relieving it. With the large radius of a 140T cutter and if the material being cut is not too hard you could even set a boring head  to the button radius or 20mm dia milling cutter and cut the tool from Gauge plate or into the end of some silver steel and harden it.

[crueby]

These guys have the cutters individually or sets:
https://www.ctctools.biz/hss-involute-module-gear-cutter-1pc-p54/

[Jasonb]

Don't look to go small enough Chris, I can only see down to MOD1 and Mod 0.4 is what's needed as the closest to 64DP

My goto DP to MOD conversion chart
http://www.davall.co.uk/media/1877/CONVERSION%20DP%20to%20CP%20to%20MOD.pdf

[crueby]

Gotcha, they have down to .5 in the sets, I didn't look close enough.

[BillTodd]

Gear Teeth above 130 or so are more or less straight sided so  a simple P.A grind  will probably do for most things that don't require ground gears.

[Jasonb]

I just remembered the cone drill method that can be used instead of the button method to make single point cutters and has the bonus of relieving the cutter in one go. Still uses the same maths as the button method or you can work it out for a specific tooth count

http://mikesworkshop.weebly.com/making-gear-cutters.html

Though I see you have CNC, it would be easy to cut the single point tool with that using a standard milling cutter into gauge plate or silver steel. If its a reasonable CNC then carbide cutter will cut the tool from HSS. being there is such a small amount of metal to come off to make the small cutter it may even be possible to use a small abrasive tool in the CNC and use that to grind the profile, just set it up for a good number of very shallow passes.

[Zephyrin]

I suggest to make these wheels by a sort off "hobbing" .
this article describes in detail how to make the tool for module 0.5 and can be easily adapted to module 0.4 and smaller !
A single tool for all the wheels !
http://www.metallmodellbau.de/GEAR-CUTTING.php

[RReid]

This is a different but similar article to the one posted by Zephyrin, written in English.
http://david.rysdam.org/machining/gears.html

[Jo]

  I fear we may have frightened Mark off with all of our suggestions as to how to cut one.

Maybe he was hoping for a cheap ready made gear 

Jo

[Jasonb]

Thought he was hoping for someone to confirm that a MOD 0.4 would do which I did as they are more common from the cheaper sources, but there are other ways too as have been mentioned.

Would be nice to know what the gear is for and how mark has decided to proceed

Zephyrin's article translates well with Google and is a good article but a bit chicken and egg as you need to grind a small cutter to form the hob which takes us back to the original problem.

[gadabout]

Hi, still here just digesting it all!
I am not bright enough to work out how to use the button method and it’s calculations . I could make a cutter on the cnc mill I think as it will be as Jason points out a straight side angle ( hope that makes sense) but I have no idea how to work out the angles involved!!
I have a 122 tooth plastic gear 64dp that I free hand ground a 1/4 square hss to fit using a magnifying glass  and a bright light to help , it looks ok to me but it is still quite hard to see properly.
Was hoping to get a proper cutter but not having much luck.
Cutting gears is one of the things I have never done and is on my machining bucket list 😁
Thanks
Mark

[Dave Otto]

If you have a CNC mill you can machine a button generated cutter with out the buttons. Create the profile in your CAD/CAM program; tilt your stock in the vise to create your back clearance.
Use a piece of tool steel like O1 or gauge plate as our friends across the pond call it, and harden after machining.
I have done this for a number of form tools for lathe use and it works quite well, some with very small features.

Dave

[Jasonb]

First pic shows the layout for the cutter, it can actually be just 1/16" wide but I have drawn it 1/4" as that is what you say you used before. As you can see it could be done with a boring head set to the 20.36mm dia or a 20mm cutter would be near enough if you wanted to use a manual mill just using the figures to position the two cuts.

Also step file to import into F360 so you can do the CAM which would be the easier way, tilt the tool point up about 5 degrees and depending on the diameter you swing it at you may want to add a bit more clearance as shown in the second pic but that can be done freehand.