Mini-lathe - slitting saws and lightweight milling attachment

 Why do I always choose the difficult path? All I needed was some slots in the heads of the clutch spring screws and the clutch dome screws which I suppose I could have made with the hacksaw but no, there must be a difficult way, a better way, a more challenging way - a Simon way. 

The screws looked quite good when they came off the lathe: 

I've had a slitting saw and a suitable arbor for quite a long time, bought for some long lost reason. The problem with slitting saws in the mini-lathe is that is difficult to get work into the right place to use them. Screw heads can of course be slotted with end mills or slot drills or hacksaws but actually a slitting saw is the best way - an end mill or slot drill is always going to be a delicate creature at that size and a hacksaw is not going to produce a very tidy result. 

I thought about setting up a jig and using the milling table somehow but it never really gelled until I thought about holding the work in a tool post and using the compound slide vertically. I thought I could do this with a simple bit of angle so I bought a chunk of 3" x 3" black steel angle, 4" long and set it up on the cross slide with a few holes:

It works rather well and could be arranged to put the work in the right place relative to the slitting saw and to be able to span the slitting saw with the stroke of the compound slide.

You use the lead screw to drive the saddle and get the work centralised - but this reveals that there is a lot of end float in the lead screw which will need to be adjusted out.

I used a piece of scrap hex as a test piece, and you will notice that the chuck has been replaced by the ER25 collet holder which will not only grip the slitting saw arbor more effectively but also allows considerably more space to approach the work.

You set the depth of cut with the cross slide, and make the pass with the compound slide:

The result of the first test was a nice slot that didn't go across the middle of the hex, despite my efforts to line it up properly. The problem is clear once you strip off the tool post and put a square on the lathe bed:

Well you remember I said it was a bit of black mild steel, not known for keeping it's dimensions! I put a shim in the appropriate position to square the tool post to the lathe bed.

Weeks later, the angle plate was properly modified to obviate the need for a shim.

For this next test I have a 1/4" CEI hex head bolt in the workholder that I made earlier, centred accurately.

Here's a close up. The slitting saw is set to cut downwards pushing the work into the lathe bed to minimise movement of the saddle, the cross slide, and the assembly holding the compound slide:

This results in very nice cut, perfectly centred. This is actually made with three passes, each of 0.5 mm depth.

The next step is to make a similar cut in one of the real clutch spring screws. This saw is 1/16" wide so will be fine for the clutch centre screws but I think it will be too much for the clutch dome screws.

Other possibilities for this same setup are to use a similar work holder with an end mill and make odd sized hexagon fasteners - for example, CEI nuts in brass which are usually unobtainable.

Model A - mudguard bolts

 Way back in the dim and distant past I made these mudguard stay and rack retaining bolts copied from the ones on the W/NG. I didn't realise at the time that the ones I removed from the W/NG had a thick spacer attached to them - and I had faithfully copied the bolt with the spacer in place.

With the collet still in place on the lathe, we'll remove these spacers:

That's better:

The proper length of these bolts allows the stays for the rear half of the mudguard to sit much closer to the frame such that the one on the near side no longer fouls the brake lever:

Model A - gear control rod

 In the last few years I've made a few bits for the hand gear control, including parts of the tank lever, clevis pins for both ends of the rod and the clevis itself for the gearbox end.

All that remains is the rod itself. This is made from a piece of 5/16" 316 stainless steel which can be made to be very shiny but isn't fun to machine. At least all it needs is a thread and at each end.

We'll use the lathe to get the thread square and to put a small undercut on the short 5/16" thread at the tank end.

This looks quite neat but I'm surprised to see that one of the tank end clevises has obviously been painted - or perhaps chemically blacked. More on that later he says mysteriously!

This is the gearbox end clevis. That reduced hex full nut doesn't look very good - I'll make a new one.

That's a job for later though - right now the gear control rod fouls the carburettor bellmouth. It needs a little bend.

There is always scrap on the bench such as this piece of scaffold tube which is used bending things sometimes.

That's much better. The part that comes down from the tank is parallel to the centre line of the bike and then the rod bends inwards towards the gearbox. It works beautifully.

That's it for the moment - we'll polish up a bit of 303 stainless hex for that lock nut.

Model A - clutch dome 2

 The clutch dome has received something of a battering from the sheet metal hammers in recent weeks and is now almost usable. I partly welded up one of the splits in it but as we are coming to the end of the primary chain guard project it's time to repair the two broken screw lugs and finish welding the split.

This is the setup. Hidden under there is a piece of 2-in angle held vertically in the vice with two magnetic welding clamps attached to it. The clutch dome is sitting on top of a pair of clamps with the remains of the screw hole on a copper plate on top of the vice.

I've cut the old lug off and use the linisher to create a straight edge. I've butted it up to a scrap of 1.2 mm sheet steel tightly enough to make an autogenous weld:

Here's the dome with two lug repairs cut to somewhere near the right size, with an accurate template copied from one of the good lugs.

These shape up quite nicely. The holes are drilled with a step drill to avoid the three-sided shape you'll get drilling sheet metal with a twist drill.

The next step is to make some proper screws...

Here's the dome back in place with all the lugs drilled and shaped.

Model A - primary chain cover

 As I've said, probably more than once, the primary chain cover and it's associated parts - the clutch dome and dynamo chain cover - have a number of problems mostly associated with splits and broken welds. Nothing fundamental is missing apart from a couple of brackets and there's nothing we can't fix.

You've already seen that I've made a start on the clutch dome in a previous post so today we are going to start on the chain cover proper. 

The chain cover supports the forward end of the rear chain guard and the bracket for this has cracked and been repaired with a piece of thick sheet and several ugly rivets. Fortunately it has been fixed in more or less the right place:

What we will do, to start with, is retain it in this correct position with a short weld:

Next we will remove the rivets and start to reshape the bent and twisted metal. This is a simple as using a centre punch and a series of progressively increasing twist drills until the rivet head comes off leaving the stem still in the hole, when the part will come off with a little tweaking and no damage.

With that lower bracket removed we can dress out the distortion in the chain cover .

The next job is to make a new bracket in the style of the existing brackets at the front end of the chain cover. In common with those brackets this is cut from 2 mm thick steel sheet on the bandsaw, linisher, and pillar drill. Here it is in position for a trial fit:

It is supposed to fit inside the curve of the chain cover and be retained by two spot welds, the holes for which are still there. This is quite a weak design and I'm not at all surprised that the welds failed.

The new bracket needs a bit of bending to get it to fit properly at both ends.

That's it for this part of the repair. What you can't see is that I have made a short weld along the edge of the clutch aperture to retain the outboard edge of the bracket.

The last bit of this job is a split along the bottom edge which has opened out probably due to the stresses remaining in the part after it was pressed to shape. I've used three clamps to draw this together again for tacking:

This is not the most tidy job, but I realise now I had the current too low. I try to keep it down to avoid blowing through the thin metal but you need it high enough to make the metal flow! I laid too much filler rod onto this to make sure I wasn't burning holes.

It will grind out ok, and the penetration is perfect. 

Getting near the end now - two holes to fill. A thin copper backing lets you puddle in some filler rod:

I've not taken a picture, but with a copper backing there is virtually no dressing to do on the back of this weld.

Back to the rear chain guard mount again, with the rivets removed and the holes plugged we can just weld up the seam along the edge of the main primary chain guard:

This is a tiny little autogenous butt weld with a little bit of filler rod part way along.

That will do.

Quite a bit of cleanup though - we will do that tomorrow.

I'm calling this done.

Model A - dynamo chain cover

 I've mentioned the dynamo chain cover more than once and it's now risen to the top of the list for repair. I'm part way through the repair of the primary chainguard and I want to make sure that all of the items that affect its position are in place before I finalise the welding.

The dynamo chain cover is in pretty good shape really apart from the fact that the chain has at some time worn through one of the feet and it has disappeared.

It's a simple matter to make a new one out of a bit of 16 gauge steel sheet using the pillar drill and the linisher. More difficult is to drill out the old spot welds and release the remains of the original foot. Here's the new bit in place with 5/16" holes where the spot welds used to be:

It takes a surprising amount of material to make a plug weld into those holes. The tricky bit is to support the work on the copper heat sink and make the welds without burning the original material away. However it soon done and fitted back in place for testing prior to clean up:

Model A - crankshaft shock absorber 2

 Well the Lambretta cush drive spring has arrived and fitting it up you can see why AOMCC singles expert Peter said that it wouldn't fit with the '26-'27 pattern shock absorber, which is what I have here. There is no way that you can get the nuts on to start this compressing the spring.

Fortunately, the 1930 pattern shock absorber is available from Karol Burger of the Slovak Ariel Klub.

Even more fortunate is the fact that Karol stocks two types of sprocket, one with 19 teeth and one with 23 teeth. What I have here is a '26-'27 19 tooth engine sprocket which is obviously for sidecar use: 

We know from experience with both the Huntmaster and the Square Four that bikes of this era are usually low geared (even when specified for solo use) so we do not want to compromise our budget and our riding experience by buying the wrong sprocket. This makes me feel a lot better about having the wrong crankshaft shock absorber!

We won't do anything else in this area until we have the new bits from the Slovak Klub.

Model A - crankshaft shock absorber 1

 It's all go here. The latest investigation is to look at the crankshaft shock absorber, which it turns out is missing a few vital parts!

These are the sections of the parts book that deal with the crankshaft shock absorber. I had assumed, wrongly, that because there was a shock absorber in the clutch there would not be one on the crankshaft. However club member and Black Ariel spares coordinator Lee, who is currently restoring a 1928 Model E (which has a Burman box) tells me that his bike has a shock absorber in the clutch as well. Therefore I am now given to believe that all the bikes have a crankshaft shock absorber.

I'm missing the spring and both the collars that it sits in. I'm told that a Lambretta spring may be useful and I have a dimensions for that and I actually I have ordered one. 

The spring collar A6/714 is missing and I have no picture at the moment. However the function of these parts is fairly obvious so I'm confident that I can make something up.

This is the bit that Sturmey Archer call the spring retaining collar. It's listed at Draganfly but unfortunately out of stock at the moment. I'm sure we can make one of these.

This is the A6/712 sliding member:

As you can see, the spring sits on a 33 mm diameter. The Lambretta spring dimensions are:

• Free length = 37.5mm
• ID = 35mm
• Wire dimeter = 6.85mm

The diameter should fit nicely. It looks like this:

As you can see, there is only two wire diameters in that 37 mm length, so it should compress considerably - maybe to the 20 mm I have available!