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).

While awaiting the opportunity to make a start on cutting the gears. In spare moments, I have been having a play with the Gear Generator add in, in Fusion 360.

I decided to create myself a working drawing of the Shogun gear replacements that I need and I was quite pleased that Fusion came to the same conclusions about size etc. that helpful fellow modellers (who are far more experienced in the subject than I,) had already worked out.

A friend and fellow Guild member fell soft and offered to have a go at 3D printing my 29 hole division plate.

It turned out really well with all the indexing holes fitting perfectly and the main bore just requiring a little scraping with a 3 cornered scraper to enable it to ease onto the shaft.

Had I been quicker on the uptake I might have added the numbers to the STL file before sending it but it only occurred as I was fitting it to the Spin indexer.

For those that don’t know what a Spin Indexer is, this is mine fitted with the 29 hole division plate.

The eagle eyed will note that the label says ‘5C’ 5C is the type of collet what these indexers come equipped to accept as standard. I don’t have any 5C collets nor am I likely to make use of any so when I saw the Spin Indexer offered at a discount price already fitted with a 5C to ER32 collet adapter I decided that I could make wider use of ER32 collets so I bought the indexer and a set of ER32 collets. Since then, I have added an ER32 collet chuck for my lathe so now I can use the ER32 collets in both the lathe and spin indexer alongside my more often used ER25 collets

This means that I am now set up to have a go at cutting the 2 x 29 tooth gears that I need for the Shogun gearboxes. I am still doing carer duties and Chris doesn’t have her stitches out until next Wednesday. So it will probably be later next week before I take the plunge and have a go.

Discussion over on my gear cutting thread on Western Thunder has had input from several members who are experienced in cutting their own gears and part of the discussion was around worm and wheel gear sets. 

We discussed that it is possible to use a length of say M6 x 1.00 threaded stud to make the worm and use an M6 x 1.00 tap in the lathe chuck to cut a wheel with at least one member having done this in the past. having seen this done in a video sometime ago it was of interest. Then I used a thread gauge to check a Roxey Mouldings Worm and Wheel gear set which came with one of their fold up gearboxes. The metric 1.25 thread gauge fits perfectly but the diameter of the worm is 6.3mm so I think that it’s actually more likely to be 1/4″ x 20TPI rather than M6 x 1.25

We also discussed that using a BA profile of 47.5 degrees would be better than using the standard 60 degree of a metric or US imperial thread. Having checked my BA thread chart I was a little surprised to find that 0BA is 6mm and has a 1.0mm thread pitch. The key difference between Oba and M6 is the angle of the teeth being 47.5 as opposed to 60 degrees. I have lots of 6mm bar recovered from scrap printers and toner cartridges so some trials are in order.

I have been asked if I will do a ‘gear cutting 101’ for those with little understanding of gearsand gear cutting (I count myself amongst them… ) So I will endeavour to share what I have determined so far.

Gear sizes/measurements come in two flavours (as you might expect) Imperial and Metric. The descriptions for these are:

Involute DP Gear Cutters ( DP standing for Diametral Pitch inch size) These come in two pressure angles 14.5 degrees and 20 degrees

Metric Module (MOD) have a declared pressure angle of 20 degrees.

Each Involute DP or Module set is made up of 8 cutters which perversely, the number for each type is reversed from each other

Having determined with help that the missing final drive gears were MOD 0.3 and that MOD 0.3 is a bit fine for 7mm models I bought from Chronosa set of MOD 0.5 gear cutters.

I also bought a single MOD 0.3 No5 cutter which will cut 26-34 teeth from a company in Japan called Gavan Tools but no great surprise that once despatched and I started tracking it, it was coming direct from Shanghai China. That said, the tracking information provided was excellent and it arrived safe and sound.

This is the same image with a little more contrast to all you to better read the details

In my last post I mentioned that a fellow Guild member had a couple of new boxed examples off the Shogun units. He kindly shared some photos of them which with his permission I will share here so that you can see what we are aiming for in the end.

This is the accompanying data sheet

You will note the bit about a ‘special’ axle. I checked mine and the bushes are under the standard 3/16 axles that we traditionally use so I plan to drill and ream mine out to 3/16 making the drive gear to suit.