Next up - gear cutting/ gear cutters!

[Chris152]

We have a B&S dividing head, which we bought a while ago. We want to learn to use it, but don't actually need to cut any gears so I'm reluctant to buy specific cutters til we do. They're not cheap, especially if we buy individually. Cheap sets go for about £70, no idea if they are any good - so far, most of our kit has been old, good quality and relatively cheap.
I'm wondering about mounting a steel disc in the chuck and just marking it with a milling cutter at the edge in the correct positions, just to get the idea of locating the cuts. I've watched a few videos on how to make the rotations, and we have three discs to select them.
Does that make sense as a method for learning the tool? Or would we be missing a whole other dimension of gear cutting? (Speed/ feed/ depth, of course.)

I'd appreciate any advice.
Thanks, Chris

 

[ChaiLatte]

I'm wondering about mounting a steel disc in the chuck and just marking it with a milling cutter

Glue a piece of paper to the steel disk and use a sharpie held in the machine's spindle to mark it. If you end up with a 'gear' having 29 1/2 teeth, you know something has gone wrong. Change the paper and try again.

When confident, substitute paper for plywood or MDF and sharpie for something more sharpier.

 

[Chris152]

...substitute paper for plywood or MDF and sharpie for something more sharpier.

Great idea. Thanks.

 

[J-G]

but don't actually need to cut any gears

Dividing heads are not just used to make gears. They can be used to create 'flats' at specific angles to each other, specifically squares and hexagons, but actually and polygon you happen to need.

Gear cutting often requires an odd number of 'turns' plus 'holes' depending upon the number of teeth and which index hole ring you select. To learn the basics I would recommend that you set it up to mill a hexagon. If your head is a 'normal' 40:1 ratio then having cut one side, you'll need to turn the 'handle' 3 and 1/3rd turns - so if you use a plate with 30 holes that becomes an easy 3 turns plus 10 holes, if you have a 60 hole plate then it's 3T + 20H - - - - and so on.

 

[Chris152]

We'll definitely have a go at a small hexagon, J-G. Ours is indeed 40:1.

Didn't have a Sharpie as such, ChaiLatte, but we have some whiteboard markers which wipe from the steel, even easier to start with. This was just direct indexing to get the idea. I'm genuinely excited that it works - our first go!

Which oil is best for these - ISO 68 or 32?

 

[ChaiLatte]

...if you use a plate with 30 holes that becomes an easy 3 turns plus 10 holes, if you have a 60 hole plate then it's 3T + 20H

In principle, you are correct, In practice, it would be most unusual for a dividing head (especially one with a 40:1 ratio) to be supplied with either a 30 hole or 60 hole plate as they add no useful prime numbers to the dividing range.

The foundation below what you saying is that the hole circle must be exactly divisible by three.

---

To the OP: have a look on the Internet Archive. There are two books called 'Treatise on milling'. One is by Brown and Sharpe, the other by Cincinnati. There is not a lot relating to dividing heads that they do not cover.

 

[J-G]

In principle, you are correct, In practice, it would be most unusual for a dividing head (especially one with a 40:1 ratio) to be supplied with either a 30 hole or 60 hole plate as they add no useful prime numbers to the dividing range.

I agree that 30 or 60 plates are unlikely to be available, I was trying (and apparently succeeding) to give the OP the basic principle. I ought to have used 27 and 21 which would have given 3T9H and 3T7H - hindsight is always useful

 

[Chris152]

I agree that 30 or 60 plates are unlikely to be available, I was trying (and apparently succeeding) to give the OP the basic principle. I ought to have used 27 and 21 which would have given 3T9H and 3T7H - hindsight is always useful

9 points, I think we've got the hang of it - the tables at the back of the booklet make the indirect maths easier!

I'll keep an eye out on the bay for some old gear cutters and post once we've cut a gear of some sort.

Thanks all.

 

[Dalboy]

I use a rotary table to cut my gears, it comes with three discs for gear cutting. If you need to go around two or three times depending on gear size to cut the teeth, the dividing head is well worth learning. Luckily, the teeth I cut only needed to be none with a single pass. I know the cutter are not cheap so buy as you need. The gears below needed two separate cutters

 

[J-G]

9 points, I think we've got the hang of it - the tables at the back of the booklet make the indirect maths easier!

I'll keep an eye out on the bay for some old gear cutters and post once we've cut a gear of some sort.

Thanks all.

You appear to be approaching this subject from an academic viewpoint - rather than a 'need to make' one.

Gear Cutters for use with a dividing head come in sets of 8 - FOR EACH DIFFERENT DP or MOD. Dependent upon the manufacturer, the one for a Rack is either N°1 or N°8 with each N° handling ever decreasing tooth count. Each one is a 'compromise' as to the tooth form, and none with cut an accurate Involute form - as achieved by 'Hobbing'. - If you want to cut Cycloidal Form that's another subject entirely!

Just buying random Gear Cutters won't give you the option to simply cut gears with different tooth count. You need to determine whether you need Imperial (DP) or Metric (MOD) and then what size gears.

I tend to work with small to medium sizes and Metric, I also use a Hobbing Machine (rather than dividing head) so I have Hobbs with MOD 0.4, 0.5 & 0.7 along with 20DP & 40DP for some Imperial needs (Myford change-gears mostly). Those 5 Hobbs will cut every tooth count within the physical constraints imposed by the Hobbing Machine, using 'Gear Cutters' I would need 40 (35 if you ignore the fact that the Rack cutter wouldn't be used on a dividing head) cutters.

[EDIT] - - - - Ooops!! Rack cutters WOULD be used on a dividing head - for gears with a relatively large number of teeth (why can't I find an 'Embarased' emoji ? )

 

[ChaiLatte]

I hope I am not reading between the lines here, but if we look at Chris' other post on the kingpin reamer, it may be he wishes to learn this skill with a view to applying it to an automotive application.

AIUI, most automotive gearing is highly non-standard (i.e. does not fit into an integer DP or 'nice' Mod number). Hence, even commonly available cutters would be of no use for this application.

A good introduction to gear cutting as a subject is "Gears and gear cutting" by Ivan Law. Dodgy pdf copy also available at the Internet Archive.

 

[Chris152]

Thanks both. It is kind of academic at the moment - we don't need a gear cut so we're just looking to learn how, so that we can make them when needed, along with any other uses for the kit. (I say 'we', but it's actually my lad who's needing to learn, he's studying welding and fabrication, wants a career working with classic vehicles and is fascinated by machining - my interest is just to help him along the way, tho I'm really enjoying the process.)

So now we've got the idea of using the indexing head, we're going to cut some gears - something that's pretty clear is that doing these things settles them in the mind/ hand better than just knowing in the abstract.

Somewhere in the mess that is my house, I have a copy of Law's book, but can't seem to find it, it'll turn up soon I hope!

I didn't know about the non-standard nature of automotive gearing, we'll look into that. Thanks.

 

[J-G]

A good introduction to gear cutting as a subject is "Gears and gear cutting" by Ivan Law.

Imperative reading for anyone who has any interest in gear-cutting.

@Chris152 You may be interested in looking at a program I wrote a couple of years ago called [Involute] which displays the true image of an involute form gear tooth which can also be printed for use as a shadowgraph template.

It takes your input with regard to tooth count, DP or MOD and PD and calculates the various other dimensions. It can handle any DP or MOD - integer or not - though getting hold of non-integer DP cutters is somewhat debatable

You can find it [HERE] - it needs no 'Installation' as such, just copy it to your hard disc - I suggest in a folder with a name that makes sence to you rather than the [Downloads] folder - and run it. For accurate results you do need to calibrate both your monitor and printer but there are graphic buttons to facilitate this.

 

[Chris152]

Imperative reading for anyone who has any interest in gear-cutting.

@Chris152 You may be interested in looking at a program I wrote a couple of years ago called [Involute] which displays the true image of an involute form gear tooth which can also be printed for use as a shadowgraph template.

It takes your input with regard to tooth count, DP or MOD and PD and calculates the various other dimensions. It can handle any DP or MOD - integer or not - though getting hold of non-integer DP cutters is somewhat debatable

You can find it [HERE] - it needs no 'Installation' as such, just copy it to your hard disc - I suggest in a folder with a name that makes sence to you rather than the [Downloads] folder - and run it. For accurate results you do need to calibrate both your monitor and printer but there are graphic buttons to facilitate this.

That's great - thanks J-G. I need to load it on a different computer, turns out the old one I'm on (Mac OSX) isn't supported by Microsoft Windows. Does it actually need to be on a PC? The lad's Mac runs either.


eta: Tadaaa!

 

[J-G]

That's great - thanks J-G. I need to load it on a different computer, turns out the old one I'm on (Mac OSX) isn't supported by Microsoft Windows. Does it actually need to be on a PC? The lad's Mac runs either.

Ah. - appologies, I should have said that it is Windows only - I don't have the nouse to write for the dark side