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.

Model A - rear brake pedal

 The rear brake pedal shaft is one of those areas where you see the horrors perpetuated on old motorcycles through years of neglect and changes of ownership with varying levels of skill. Having removed this one to rebuild the footrests and replace the brake pedal spring we realise that it is in fact a bit mangled.

To start with, we can see that the thread has been cut to a BSW form - Ariel would not have used BSW here, the thread would originally have been CEI. We will build it up with weld and cut a new thread to the right size.

That pin across the right hand end as we look at it forms both the stop and the fixing point for the end of the spring. Part of it, the fixing point for the spring, has broken off. It proves impossible to knock out though it is listed in the parts book as a separate component, so we drill it out.

Here it is, illustrated in the 1930 parts book:

The other curiosity which I didn't understand initially is how the shaft is lubricated. There was no obvious grease nipple but under all the gunge a hole appears half way along the shaft, which is clearly to let grease into the central reduced area - and an ex-nipple on the end which has had some attention from a hammer.

I've said many times that the AOMCC is a wonderful club to be associated with and a few questions posted on the Facebook page yielded this drawing from 1925 and signed by Val Page himself. The drawing clearly shows the same formed nipple on the end of the shaft that the later Ariels used until the end of four-stroke production in 1958.

The difference between this and the later bikes is that whilst the later bikes use a nut to retain the brake pedal on a parallel fixed shaft, this application uses a nut on a taper to retain the pedal on a rotating shaft. Therefore when you want to remove the pedal for adjustment, you have to undo the nut and knock the end of the shaft to free the taper. Guess what happens? The nipple gets flattened...

To start with we're making a new pin on the lathe. I didn't intend to use a piece of stainless, but at the time I couldn't find a quarter inch piece of mild steel round bar - but no one will ever see this, so it doesn't matter if it's the wrong colour.

I've cut a semi-circular channel in the end of the short bar to locate the brake pedal spring. It's a simple matter to chamfer both ends and press it into the pedal shaft.

This is how it looks.

This is apparently the correct spring - I got it from AOMCC Black Ariel spares some while ago and I'm assured it is the right one, though it looks very stretched when it's in position.

See what I mean?

The next step is to build up the mangled thread and nipple. This is none too tidy but hopefully there will be enough material to turn it to 7/16" without firing up the TIG set again.

The first pass at turning to size shows, as it often does, that more building up is required:

That done, we can start forming the shapes according to the drawing with a radius tool to form the curve and shape the grease nipple:

I seem to have missed out a step here - I've forgotten to photograph the drilling out of the grease hole, which is 5/32" per the drawing. The next step is to cut the 7/16" CEI thread. 

Here it is on the bike with the brake pedal attached:

We will need to be very careful when moving the pedal - using a socket or something over the nut to avoid damaging the nipple!

Here's an overall view. That pedal is very high!