Cutting gears

Garry,

11 teeth would make what you are cutting a Pinion rather than a Wheel.

The #1 cutter should be fine, but; depending on the application, you may have to adjust the geometry or depthing slightly, to avoid it binding.

MichaelG.

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Edit: This site explains a lot: http://www.hessmer.org/blog/2014/01/01/online-involute-spur-gear-builder/

Edited By Michael Gilligan on 02/05/2018 07:59:33

The number of teeth is set purely by the dividing head. So if you set it up for 11 division you will indeed cut 11 teeth. However the shape of the tooth is set by the cutter. The #1 cutter will be exact for 12 teeth. Depending on your application it may work for 11 teeth, or it may not. If the gear was hobbed it is quite likely that the root of the teeth will be undercut creating clearance. Obviously the undercut cannot be formed using an involute cutter one tooth at a time. One possible way round this is to increase the depth of the dedendum. I calculate that your gear is 8DP? The standard value for the dedendum is 1.157/DP, but for small numbers of teeth it is often 1.25/DP. The better quality involute cutters have the total depth of cut marked so you can work out what the dedendum is. If you're stuck with a particular cutter as MG says you may just need to cut a bit deeper. Be aware thougfh that doing so will increase the backlash.

Technically you're not cutting teeth but the gaps between the teeth.

Andrew

Garry,

What equipment do you have? If you have a horizontal milling machine and a dividing head you are well on your way to making gears.

If you just have a lathe you can improvise but you will have much to do before you can cut gears.

The photo you see below is my gear gear cutting arrangement for a 13t tumbler gear.

It comprises a home made dividing attachment and vertical slide which uses gears to index. the example shown is 52t boxford gear which of course would be indexed every 4 tooth for a 13t gear.

The arbour holding the gear cutter has morse taper and uses a long draw bar to secure it in place. Don't trust a morse taper without a draw bar when gear cutting.

Hope this helps, more details on request Geoff

Be careful when ordering gear cutters to check the numbering system used Garry.

Chinese involute cutter makers seem to have reversed the convention - e.g. Number 1 would be a 135t to rack cutter.

https://www.rdgtools.co.uk/acatalog/WHICH-CUTTER-FOR-WHICH-TEETH-11.html

Regards,

IanT

Edited By IanT on 02/05/2018 08:52:16

Rather than increasing the cutter depth, a better way to solve this problem is to increase the diameter of the gear (profile shift) and correspondingly increase the gear spacing.

If the gears are a fixed distance apart, you can make the larger gear smaller by the same amount as the small gear is enlarged.

It's well explained with diagrams here:

khkgears.net/gear-knowledge/abcs-gears-b/gear-profile-shift/

Neil

If you haven't already done so, it would be well worth your while to buy a copy of Ivan Law's book Gears and Gearcutting. It is one of the Workshop Practice series so quite inexpensive yet invaluable.

Hi,

I too am looking into gear cutting for my new project and was looking into cutters and arbors for the mill.

The arbors seem to be extremely expensive (£50-60).

Am I missing something, are there alternatives?

Craig

Horizontal or vertical mill? You can make cutters and arbors - Ivan Law's book says how, or Mike Cox' website. The latter has a few pages on making cutters.

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This is my personal opinion, and others may almost certainly will argue.

Items that are effectively 'precision' parts of the machine need to be made more accurately [perhaps by an order-of-magnitude] than the components they will be producing.

Therefore; a multi-tooth cutter and its arbor should be made to standards which you might not be able to achieve with the tools at your disposal. ... It is not worth mounting a good multi-tooth cutter on a bad arbor.

You don't mention the £50-£60 arbors by name, or specification, but; for something of appropriate quality, that might be a very reasonable price [*] . ... There are work-arounds, of course; but think about how you would go about making something sufficiently accurate for the job, and how long it would take you.

MichaelG.

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[*] .... Note: There is plenty of tat available, at all sorts of prices.

A few pence worth of gauge plate (before sharpening).

A blank MT arbor

And perfectly successful gear

For a commercial cutter, I would suggest turning your own arbor on an MT blank.

According to Ivan Law's book, a No 1 cutter is for cutting from 135 teeth to a rack, so is most definitely not suitable for cutting a 11 tooth gear.

If you do not have a copy of his book, ("Gears and Gear Cutting" No 17 in the Workshop Practice Series), you would find it a great help.

A No.8 will cut 12 - 13 teeth, so your 11 tooth gear is off the scale of standard Browne and Sharpe type gear cutters.

These are the normal numbers for Browne and Sharpe type cutters.

You can cut 11 teeth with a No 8,but the tooth form will be slightly incorrect. As already suggested, by adjusting the depth of cut slightly you may finish up with a useable gear.

Cutters are available from various suppliers (The last one that I bought, a 1.5Mod No 8 for a 13T gear, cost £22 from RDG Tools)

Arbors are available, or you could possibly make your own. For this you need a stub arbor (possibly plus and adaptor) to suit the spindle on your Mill. Mounting the arbor in your lathe, you turn the plain diameter down to to be snug fit in the bore of your cutter, and tap the end to take a suitable (preferably countersunk head) Allen screw with which to clamp a recessed Washer to clamp the cutter to the arbor.

Armed with this, you clamp the cutter to the arbor, and mount the assembly on the mill.

If using a vertical mill, you will need to bring the centreline of the cutter to coincide with the centreline of the arbor carrying the gear blank.You are then ready to cut the first tooth (or the space between it and its soon to be neighbour), by feeding the gear blank past the cutter. Having once set the depth of cut, and made a cut, (gentle feed!) I would advocate retracting the stationary cutter away from the blank, before indexing the blank for the next cut.

If using a horizontal mill, you will be traversing the gear blank, vertically rather than horizontally, past the cutter, so again, the centreline of the arbor carrying the gear blank needs to coincide with the centreline of the gear cutter. Or you could traverse the gear blank under (or over) the cutter in the horizontal plane.

Howard

Edited By Howard Lewis on 04/05/2018 18:37:14

Howard,

I fully accept that the Brown & Sharpe set has become the de-facto standard, but it's interesting to see Pratt & Whitney's list ... facing p52 in this fascinating little book: **LINK**

https://archive.org/details/teethofspurwheel00macciala

MichaelG.