Model A - getting into the gearbox

 I've now completed the footrest and brake pedal area and I have the lathe up and running again after the feed gear upgrade so it's time to get back to the gearbox and particularly the kickstart shaft. 

I've not had the gearbox out before so given that the clutch is off I'll go in there, clean it up and do a few jobs. The first step is to remove the oil tank and the battery tray, then you can remove the four nuts under the gearbox and lift it out.

It's in pretty good shape externally - there's no major damage and aside from the kickstart shaft nothing missing. There are a couple of little jobs: 

• One of the 5/16 studs retaining the frame bracket is missing, 
• There is some damage around the gearbox casting for these studs 
• The gearbox adjuster bolt is broken

First, a couple of general views:

With the gearbox out, we can attend to the bent bracket that the adjuster locates in. Somebody has obviously forced the gearbox adjuster without undoing the nuts underneath, bending the plate and breaking the adjuster - it's astonishing how ham fisted some people can be!

Five minutes with a hammer sorted that out.

The outside is a little bit grubby, but more worrying is the state of the bearings on the main shaft and the sleeve gear. I'm told that the sleeve gear bearing is available, but expensive - I doubt if you can get the bushes for the mainshaft though...

The next job is to remove the broken adjuster bolt. Fortunately it drills easily:

The bolt is not seized in place and comes out quite easily with the EZ-Out:

I have a new bolt available from AOMCC Black Ariel spares and after I have run a tap into the hole it fits back on with some Copper-Ease:

Apparently there is supposed to be a spring under that screw adjuster.

The next job is to sort this out. All we need here is a new stud - 1-in long with a 5/16 BSW at one end and 5/16 CEI at the other. 

What is a bit more puzzling is that the lug on the gearbox does not line up with the engine plate so perhaps there is a thick washer in here:

And as if by magic, a new stud appears courtesy of the mini-lathe and some 5/16" round bar:

And later, a 1" diameter, 1/4" thick spacer:

All I have to do now is sort out the mixed-up 1/2" diameter engine studs - or 'tie bolts' as Ariel call them and we are done with making & mending on the outside of the gearbox.

Mini-lathe - first commercial job!

Part of the deal to get the larger lathe feed gears printed was that the owner of Regenerate3D, James, needed some aluminium parts machined for a radio controlled glider. The bit he needed was an adaptor to go between a motor shaft and a printed propeller. I agreed to make the bits to his drawing and we corresponded for a few days refining his design.

One of the most interesting bits of machining anything is working out the best sequence of operations and I'll show you what I did here but I can't pretend it was the best sequence!

The first step was to cut a chunk of 1" 6021 round bar, face one end in the lathe and reduce it a little so that it would go further into the chuck. I then turned it around to machine the other end to something close to the finished state:

Next step was a face knurl, which I had never done before. I used an existing wheel and made a little holder for it with a bit of 10 mm round bar. The washers are there to prevent the wheel contacting the work. The issue is to get the knurl close in to the centre means you cannot have anything protruding beyond the wheel - so there is no room for a nut or screw head to retain the knurling wheel.

I was very pleased with how it came out, and turned the work around to finish the other end to the same standard. At this point I still had a half millimetre oversized on the journal that would carry the propeller.

I replaced the chuck with the ER25 collet to hold the work whilst I parted it off - this was a mistake, because there was not enough length available to hold the work in the collet to withstand the parting off loads. I should have sawn them in two. Fortunately I hadn't taken any of the diameters down to size and I was able to remove the scuff marks caused by the work moving in the collet. 

Once I had the two bits separated, I could drill the holes for the grub screws. There's a chamfer behind that flange which is out of shot here and I made sure that the holes were drilled and tapped before I formed that chamfer, to give me enough room to hold the part for drilling.



This is the 3D printed propeller that will be used to launch the glider into the sky:



Here is the rear view. You can see the chamfer that I was talking about earlier:



The propeller is actually in two parts - there is an M8 nut hidden inside which retains the prop to the aluminium adapter.

Mini Lathe - feed rate upgrade

 As I started to machine the kickstart shaft for the Model A it became apparent that it was painful in several ways - partly due to the hot swarf coming off it and partly due to the fact that it was taking ages!

What I needed was the automatic feed. This is dead easy to engage and is always available on the lathe but I quickly found that the lathe couldn't cope with the feed rate given by the 20:80:20:80 gearing that the standard setup offers. 

The Ted Hanson book suggests replacing the last 80 tooth wheel with a 3D printed 127 tooth wheel - but they are not commercially available. 

Some browsing revealed that reduced feed gear wheels for the mini lathe are not commercially available on this side of the pond in any shape or form. Some posts on the 7x Mini Lathe Facebook group suggested that the best option was to go to Thingiverse.

As predicted I found some suitable STL files which I could print for free. However not being equipped with a 3D printer I resolved to look around Norfolk to see what I could find, and made contact with Regenerate3D in North Walsham who in exchange for some machining work and a spot of cash produced these lovely gears:

The black ones are made from PPA-CF and the orange ones from PA6-GF. They are both very strong and hard. Both sides needed a little bit of fettling to make fit properly - a 12 mm reamer for the lead screw gear and an 8 mm reamer for the intermediate gear.

Contrary to what some folk have written about this gear size, the cover will fit without modification so you do not have to have your gears exposed while working.

The only negative side of this that I have found so far is that with the increased ratio from motor to lead screw, I can no longer turn the hand wheel on the lead screw and so we'll have to remove or disengage the lead screw hand wheel for milling.

FH - test ride

 I took the Huntmaster out on a nice little test ride today, 25 miles around North Norfolk to buy samosas from a nice family run department store in Holt.

It went beautifully - no problems other than the usual sweating from the base gasket! I think we also have to admit that the number two exhaust guide is probably leaking - probably too much clearance. There's wet oil at the silencer.

It's idling very nicely - I stopped to reduce the speed at one point, and to take a few pictures, and the idle is certainly more reliable than it was.

FH - pilot circuit

 No pictures, but this afternoon I've drilled out the fixed size 20 pilot jet in the Huntmaster's MK1 Concentric carburettor.

It's now got a size 30 pilot fitted, which reflects the size 35 specified for the BSA Road Rocket (fitted with a Monobloc) and the fact that Concentrics are supposed to run richer than Monoblocs...

Time for a road test.