After playing about with several iterations of differing angles to help the spur gear mesh with the newly created worms I realised that I had been angling the spin indexer in the wrong direction. I quickly placed my piece of 3mm rod under the other end of the Spin Indexer so that the nose angled down not up and then cut another gear.

Hey presto, we have a working worm and spur gear.

I also took a little video of it running in my friend’s G5 chassis.

It is a little noisy but I attribute much of that down to the etched gear frame. To confirm this diagnosis, I test fitted a proprietary gear set from Roxey Mouldings that I have in stock and that was just as noisy.

This week has been very much about more learning. First of all, although I reground the 20 degrees cutting tool, I had still left too much of an undercut and the point snapped off again after about five passes.

I did manage to make another worm, the best to date but it was still cut with a standard 60 degrees thread tool – more for the practice at single point threading than an expectation of it actually being used as a worm at some point.

I also made an arbour to hold my gear blanks. I made this primarily because the largest brass bar that I have which is 19mm diameter and is just the right size for a 36-tooth Mod 0.5 gear. I only had approx. 200mm/8 inches, so I wanted as little waste as I could get away with to make best use of it.

The arbor has a short section at 3/16 and then the end is threaded M4 for a locking nut.

With it made I then cut a 36-tooth gear.

After some off line discussion with a fellow member of Western Thunder and much grinding of my cutting tool, I finally managed to get a 20 degrees tool with sufficient support underneath the point and was able to cut a ‘proper’ worm to suit my mod 0.5 gear. On Susie’s advice I wound the lathe over by hand rather than under power to cut the worm. Now I don’t have any kind of ‘handle’ to allow me to turn the lathe over smoothly (I have seen other machinists who make an expanding arbor for their lathe spindle to allow smooth hand cranking) so my effort using the holes in the collet chuck and a tommy bar were quite laborious but I got it done.

I also had another go at making a gear but with a slight angle to the teeth to better mesh with the worm.

My method of creating an angle on the teeth is very unscientific, I started off by adding a length of 0.7mm nickel rod under the front end of the spin indexer to raise it up and it did work albeit not enough and I also forgot to raise the cutter height so I ended up with slightly lopsided teeth and the angle wasn’t quite enough.

Undeterred, I increased the rod size to 1mm and tried again. It was at this point that my learning experience went into overdrive. According to the charts that I have been using* the cutting depth for Mod 0.5 is 1mm thinking I was being clever I increased that by 0.1mm. As soon as I made the first pass, I realised that something was wrong. The cutter had not only cut the tooth but it had also created a much wider channel in the blank which you can see on the right-hand side of my hacked about blank below.

The rest of the teeth on the damaged blank were created by my testing of various cutting depths to determine the point where the cutter cut the tooth without removing any from what would become the adjacent tooth and thus reducing the overall diameter of the gear. After a few test cuts, I determined that for my cutters 0.8mm was the maximum depth before it effectively reduced the height of the adjacent tooth.

*Bob did point out earlier in the discussion that the charts were actually for the cutting of worms rather than gears but we determined that in the absence of any other data that they were near enough for both.

For the Mod 0.3 the data from the chart worked fine and now that I know I can refine my own version based on what I have determined. No doubt that if I do buy a set of Mod 0.4 cutters in the future, I will have to do some tests to refine the Mod 0.4 data to suit the practical application with my set up.

Once I had made that discovery, I cut another gear and although it was successful, it still wasn’t angled enough so I will do further experiments on my duff blank to see how a 1.6mm lift works, before committing to another full gear cut.

Finally, to round off this war and peace update I also cut another worm with the 20 degrees tool in a piece of free cutting mild steel (the others were cut in recycled printer bars) under power and I think that it’s a much nicer worm albeit that there isn’t much visible difference from the ‘hand powered’ example.

Although not strictly speaking specifically gear cutting per, se I had another ‘first’ yesterday. This ‘first’ was single point thread cutting which I have never attempted before. For those that don’t know what single point thread cutting is, it’s the cutting of a thread using a cutting tool in the lathe rather than a traditional threading die (which I used to cut the 0BA worm a few days ago).

The pitch of the thread is determined either by altering gearing via several levers (if your lathe is so equipped) or in the case of many smaller hobby lathes it’s achieved by the use of change gears. Mine is the latter. What the change gears do is alter the rotation of the lead screw so that when the automatic feed is engaged, it moves the carriage a certain distance for each revolution. In my case I needed a 1.5mm pitch so I needed to swap out my standard gear set up for a 30 tooth (A), a 50 tooth(B), a 55 tooth(C), and a 35 tooth(D)

This was the standard gear layout

This is the gear layout for a 1.5mm pitch

Once I had them setup, I put some layout fluid on a piece of nickel bar and did a scratch pass to make sure that I hadn’t made any mistakes.

Then I had a go at cutting a thread using a proprietary standard* 60 degrees thread cutting tool.

*Threads come in many different flavours depending on whether you are using metric, imperial, BA or many of the other thread types. Below is a thread tool gauge designed to assist when grinding your own cutting tools. As you can see US Imperial and Metric use the same standard which is 60 degrees.

I used this mainly because I had never done it before and I wanted to use a known good set up rather than a tool I had ground myself (which proved a wise choice).

I am happy to report that all went as planned, although I did over shoot the thread gutter a couple times because I hadn’t really made it wide enough to allow the machine to stop at this pitch and I successfully cut a screw thread.

Another good session in the workshop. On the back of this I had another go later in the day, using a piece of steel and the cutter that I had ground. Sadly, as I half suspected, the tip broke off the cutter after about 5 passes. This was due I think, to being ground on a taper, which meant there was nothing under the point to offer any support. Plus being carbide, it was quite brittle.

This actually turned out to be a blessing in disguise as when I started to grind a proper piece of tool steel, I realised that my 20 degrees angle, actually gave me 40 degrees included angle. A mistake that I had also made on the first one.

Thankfully it was a case of taking more off rather than starting again so I just need to finish off grinding it to shape after posting this.

The last two days have been a bit of a milestone in my gear cutting journey as I have managed to cut the missing gears for my two Shogun gearboxes.

I initially test fitted them and ran the motors with the gear rotating on the axle as I didn’t have any small enough grub screws and was pleasantly surprised when they ran freely. Next, I made some tiny grub screws from some lengths of 10ba stud that I had cut off some one inch, 10ba screws. I keep all such things in a plastic Ferrero Roche box as they do come in from time to time. I was trying to be a bit clever by using a very small slitting saw in the Proxxon pillar drill to cut the slot but the blades that I have, are too thick and it ate away half the thickness of the screw. So I cut the slots by hand with a piercing saw.

After chasing them around the workshop floor and miraculously finding them after dropping one grub twice and the other once, I fitted the first one. It all worked as intended and runs as smooth as the other gears. However when I tried the second one it was a bit lumpy and then I noticed that although it seemed to fit okay between the frames it had splayed them slightly so I popped it back in the lathe and skimmed both ends slightly and on the next try it ran just like the first one. Now I really am a happy bunny.

Just for scale this is one of the gears again a 5p piece. They are very small.

Once again, I would like to sincerely thank all who have contributed to my getting this far.

From identifying the gearboxes that I bought at Stafford, to working out via information provided by fellow members that it was a 29 tooth Mod 0.3 gear that I needed to buy or make and all the helpful advice on both the theory and practical aspects of gear cutting. It really is much appreciated.

Later in the day yesterday I stripped down the spin indexer and took the division plate off. I mounted it on the dividing head chuck of my Proxxon mini drill and reamed out all of the holes to 5mm. 

Then, having ensured that the locking collar was tight on the spin indexer and the Y table locked to ensure a consistent depth of cut, I had another go using the opposite end of my aluminium stub.

All went swimmingly and I ended up with a perfect gear.

Now I need to do it for real to produce the missing final drive gears for my two Shogun Gearboxes.

Buoyed by my small successes with the worm and wheel yesterday I decided to take the plunge and set up the mill to actually cut an involute gear.

I took Brian’s advice and did a test cut on a stub of aluminium to take the burrs off and bed in the cutter.

It has to be said I made some mistakes but it was a great learning opportunity and as a number of fellow members asked on the GOG online modellers meeting I recorded a video of the process. I recorded the whole thing which is about 12 minutes long and I suspect may be a little boring in the middle where I was just repeating the cuts.

Here’s a list of the things I did wrong/didn’t do that I should have etc.

1. I didn’t fully tighten the locking collar when I refitted the 3D printed division plate which mean that after a few cuts it stopped moving and I lost my index position.

2. Although I checked some of the index pin holes in the division plate, I didn’t check them all and that came back to bite me as I struggled to get the pin in some of the holes properly this didn’t really affect the indexing too much but it did make it really hard to get the pin out between cuts

3. I forgot to lock the Y axis of the mill table which meant that the cutter eventually pushed away from the workpiece a little.

Taking all that into account I did manage to cut a gear (ish)

The other ‘side’ isn’t quite so pretty…

​Here is the video for those who are interested in the how.

I naively thought, that I had my head around Module/Metric gears. In my mind the Module equated to millimetres pitch or linear spacing. That was until I was idly remeasuring a Roxey Mouldings worm and wheel set, which I had measured up during my original online discussion. But I had understood even less at that point so I figured that I must have got it wrong. When I measured it and the worm pitch was 1.25mm according to my metric thread gauge but the accompanying gear wheel was marked as 40 tooth Which in my head should have equated to MOD 1.25.

While head scratching, I played around with the Fusion gear generator add-in until I worked out by trial and error that the worm and gear wheel were in fact Mod 0.4. At this point my mind was completely blown as everything thing that I thought I understood was in fact nonsense and it proved that I understood very little.

Thankfully when looking in the Ivan Law book on Gears and Gear Cutting, I found a table of reference for Module Gears and although I don’t pretend to understand how the term “Module” relates to anything identifiably metric* I now have something to go on when working things out.

*The nearest thing that I can find which remotely relates, is that the millimetre data under the 14.5 degrees pressure angle column, is almost equivalent to the associated Module reference number.

Further reading of the book confirms (to me at least) that the term “Module” despite being referred to as ‘Metric’, isn’t. It’s based on there being 25.4mm to an inch, which if it’s based on an inch then it isn’t metric.

I took a bit of time and copied out the table into a spreadsheet and then manipulated the spreadsheet into a layout that works better for me – Metric measurements, before imperial equivalents and the smaller modules to the top of the lists (as I doubt that I will ever use the larger modules because I am not equipped to cut such substantial gears).