Mini-lathe - shimming the saddle

This is a job I've been intending to get around to for years.

These Chinese mini lathes have a saddle to bed clearance set by two M5 screws providing a clearance between the saddle itself and it's retaining plate. These screws are more or less on the same centre line as the bolts retaining the plates and thus the plates are never parallel to the bed and the contact between the plate and the bed is more of a line than a flat area - something you can see in one of the pictures below.

This leads to poor control of the saddle clearance to the bed which can spoil finish or make your saddle stiff to move. The fix varies - since you don't adjust this very often, I think the easiest way is to shim the plates but various people have shown other options such as a sliding wedge operated by a screw which has the advantage that you can adjust the clearance from outside without having to strip the lathe down. 

As I said we don't do this very often so we will go with shims. The first job is to measure the thickness of the saddle accurately and this is something around 24 mm - actually 24.08 mm.

The next job is to measure the distance between the bottom of the bed and the top of the saddle which will be similar to the first measurement plus a few hundredths of a millimetre (This lathe is Chinese, so we will be talking in metric for this post!) 

The difference between these measurements is 24.33 - 24.08 = 0.25 mm.

I don't have any shim stock but I do have various bits of sheet including a chunk of oil can which is 0.025 mm thick - easily cut with the Wiss snips. Making holes however is extremely difficult - I drilled these between a piece of wood and the saddle plate but it really needs a punch.

It turned out that I had already done the apron side but with a 0.15 mm shim - but I had left the adjusting screws in for some reason. I took them out and replaced the plate with the same shim and found that the saddle wouldn't move at all, so I put a 0.25 mm shim in and reassembled the lathe.

The saddle seems to move smoothly but not have any up and down movement - but it is very hard to tell. Perhaps I'll put a DTI on it and we'll see if we can measure movement.

Model A - that kickstart lever again

 Well, yesterday it was finished. The cotter pin went in way too far and would need replacing, but it worked. However, there was an itch...

I suppose I am a bit obsessive, but I couldn't put up with having to remake the cotter because I had machined the shaft wrongly. I filled the slot up with weld.

A few minutes later, I had re-machined the slot; the shaft is 3/4" within the kickstart lever and the slot has a maximum depth of 0.150" - the easiest way to measure this accurately is from the bottom of the cotter slot to the opposite side of the 0.75" diameter, so you measure 0.600". The slot is bang on the correct depth, and the 0.375" cotter pin fits perfectly.

All I need to do now is cut the spare length off the cotter pin and radius the end, like this:

Now it's finished. Definitely. Apart from the spring cover...

Model A - fitting the kickstart lever

 The last step in the long story of the kickstart shaft project is to machine the flat for the lever cotter pin. We are back on the lathe with the vertical slide and will use this setup to machine the slot:

The cotter pin is about 3/8 diameter so we will use this 3/8 end mill to cut the slot.

This is the last pass of 3/8 end mill - and it's a pass I wish I hadn't made. I was very near the end and used a trial fit to find that the slot I was milling was about 1/32" too shallow. For some reason I decided that it would need another full turn of the lead screw to finish the cut - completely forgetting that the lead screw pitch is 1/16". So now that slot is too deep.

I could weld this up and re-machine it, but the cotter pin still fits and stays in place properly. I guess I will leave this until it becomes a problem - I can't get a 3/8" bolt in there, which would be possible if the slot was any deeper.

So for now, the kickstart shaft is finished.

Model A - positioning the kickstart lever

 As we get towards the end of the kickstart shaft project, it's time to think about where the lever will sit and where the flat for the cotter needs to be machined. This picture mocks up what it will look like eventually: 

The key to success here is to understand the relationship between the mating face of the cotter and the flat on the shaft, all of which combine to determine the position of the lever. The last thing we want to do is to have the lever too vertical or too low in relation to the rest of the machine - worst still that it sits forward of the gearbox! 

We'll use the old shaft to understand this relationship.

What you see here is two pictures of the lever, the cotter and the old shaft. I have used a Sharpie to show the relationship between the shaft and the lever. 

We can see that the cotter fits in either direction without affecting the relationship between the shaft and the lever. 

This next rather blurred picture - it looks like it's focused on the bench top - shows the Sharpie mark against the flat on the old lever and confirms that the flat is perpendicular to the axis of the lever. 

We can use this information when we machine the flat on the new shaft. We'll have a look at some of the reference pictures and get a feel for where the lever should be.

Model A - this is getting boring

 While we wait for the long series drills with which we can finally fit the kickstart pawl, we can look at preparing to drill out for the layshaft bush and for the relief drilling that will clear the layshaft first gear pinion. I need to do some measuring to ensure I understand the various dimensions that will be required, but I know that the bore to clear the pinion will be in the region of 1" diameter.

You will recall that in a previous post we machined off the flange that had been used to hold the shaft in the rotary table, reducing it until it would pass through the fixed steady. We see it in use in the picture below during setup:

The short 5 mm hole that has been used for the revolving centre is opened out progressively until we run out of twist drills. This is the 10 mm drill passing right through and into the body of the shaft:

And here it is opened out to 7/8", which is the largest drill I possess - it actually has an MT2 taper and fits directly in the tailstock:

The next job is to part off the stub, but sometimes it is easier to rethink your approach to a job. I set the lathe up to part off this stub after I moved the fixed steady to the 1 1/8" section, but actually I realised it would be much easier to saw it off:

That took less time than setting up. The orange dust is from the saw blade!

This rudimentary sketch shows us what the dimensions of the hole need to accommodate. As I have no wish to bore the hole to over 1" all the way into the shaft, reducing the wall thickness just where it needs to be strongest, I will make a stepped bush to accept the layshaft and provide a thrust face for the low gear pinion. This will be 1" or thereabouts at the inboard end, and reduce to 7/8" for most of it's length. This will give a thin wall over most of the length of the bush since the shaft is about 11/16".

That's the bore done for the low gear pinion - it's 1.010".

I used a depth micrometre to determine the dimensions of this hole - it's a nice tool that I bought from someone at the railway a few years ago:

The whole has two diameters - one for the layshaft and one for the low gear pinion. Both of these diameters will be bushed:

The larger of the two fits the low gear pinion beautifully:

The smaller one clearly fits over the layshaft:

We can also see that the length of the 1 1/8" section is just right:

Now we need the bush, but before we make that the package from Tracy Tools has arrived with the long series drills we need to fit the kickstart pawl and it's pin but before we do that we'll spend the day driving one of these:

Model A - drilling holes

 With the space for the pawl milled out, the next step is to drill some holes for the pawl spring and the pivot pin. When that is done we can function test part of the mechanism.

To drill for the pawl spring we keep the vertical slide setup in the lathe. Getting the height is straightforward because we can use the old shaft to line the vice up with the drill and thus ensure the angle of the hole is correct. 

Since this is going to be drilled in a surface that isn't perpendicular to the drill, I start the hole with a 1/4" slot drill and cut for a few millimetres, finishing the hole to depth with a twist drill.

The twist drill is marked to depth with a bit of tape. A 1/4" drill isn't quite enough - I drill it 6.5 mm to clear the spring and it's plunger:

The holes for the pivot pin aren't quite so easy. I'm going to make a small deviation from the original design here - The original pin is stepped, it's a 5/16" pin reduced to 9/32" for part of its length. Strangely the larger size is inboard, so the step prevents it moving outboard. I want to make the smaller size inboard so that there is no possibility of the pin coming loose and interfering with the layshaft first gear. 

The problem with this approach is that there is no way a conventional twist drill can reach.

I ordered some long series twist drills from the excellent Tracy Tools. They will be here in a few days.

Model A - milling the kickstart shaft

 I can't believe that it's over 2 months since I started work on this kickstart shaft, but I guess plenty of other things have been going on at the same time including railway stuff, making the parts to exchange for the 3D printed gears and other things. However, we are well on the way and this latest post is about milling in the vertical slide set up for the kickstart shaft shaft stops and the platform for the kickstart pawl. 

Milling the end stop took two attempts to get the angle right but I'm very satisfied with where this is now:

This is the other end which is a bit more difficult because it's a completely enclosed corner. I started this with a 3/8" end mill and finished with a 1/4"  slot drill to remove as much material as I could. It may yet need to clean up with the Dremel.

The next step is to rotate the shaft and start with the flat area where the pawl sits. I've marked the edges of the area using the original shaft as a guide and I've tried to set up the new shaft in the vice such that the virtual area defined by these lines is in a vertical plane. I used a pointer in the collet to line up the marks as shown below - this is a later picture, but it gives you an idea:

Cutting at around 0.5 mm per pass, we start to define the flat area:

Many passes later and we are nearly there. The finish is fine, despite the grumbling vibration from the lathe. I tightened up the gib strips during this operation, but I really must look at the saddle retaining strips.

Soon afterwards, we are done. The platform for the pawl is 10 thou narrower than the original.

Next step is the holes for the pawl and the pawl spring.

Model A - changing setup

 I do believe we have come to the end of the milling that we are doing on the rotary table. Both the slots are finished as far as I can tell at the moment, so we need to have a look, have a measure, and think about the next steps. 

Fitting the shaft into the gearbox cover this time, I have discovered that the inner 1 in or so of the shaft is around 0.002" oversize - it is dead on 1.125 in, but needs a little bit of clearance. The main part of the shaft is 1.122 in and fits perfectly.

Again both ends of the slot that the stop fits into will change shape when we get the shaft onto the vertical slide.

You can see here the vast difference in length of these two parts!

Comparing old and new:

I've made some simple stiff card templates to make sure that the shapes of the slots are correct and to help me place the beginning and end of the flat area the pawl sits on:

Model A - still milling

 It's been a busy week what with one thing and another but one thing that did happen was a delivery from Tracy Tools - 2 milling cutters and a slot drill which enabled me to finish the first slot and start the second. 

This is how it looks in place:

Note that the edges of the slots are currently radial - they will have more of a tangential slope once we move to the vertical slide setup.

This is the same view with the original kickstart shaft:

And for the record, from the other end of the kickstart travel:

Next we are back on the lathe to mill the long slot that goes most of the way around the shaft:

That picture shows three 0.5 mm passes.

This next one shows progress after another three 0.75 mm passes:

Model A - milling the kickstart shaft

 Milling starts with the realisation that I only have long-series end mills, and the largest one is pretty blunt.

We crack on anyway, to get a feel for it, test the setup, and try out the rotary table.

Learning about the state of the 3/8" mill, I press on with a new 1/4" cutter.

Shortly after I took this picture, and having spent some time sharpening a cutter, I broke the 3/8" mill by feeding it too hard. I pressed a dovetail bit into service and got a lot more material out.

Model A - Kickstart Shaft, setting up for milling

 After a turn on the railway and with the grandchildren coming for the weekend there's not much time for workshop stuff, but I'm inching closer to finishing the setup for milling. 

Some countersunk M6 screws have arrived to clamp the right angle plate to the cross slide, underneath the rotary table:

Using the slot that we milled a few weeks ago, we can adjust the rotary table to align with the centre of the lathe spindle: 

The tap follower I'm using as a pointer here looks like it might be useful for marking out the parts of the work we are going to mill away.

A little while later, after all the preparation for the visiting little ones is done, I venture back to the workshop. I've reduced the diameter of the 2" section to the required 1.990" to match the original, and increased the length of the 1 1/8" section by about 0.040" such that it protrudes from the kickstart shaft bush by 0.020" rather than hiding inside it. I've also changed the carbide tool inserts for new ones.

I've also made a new set of clamps, but I've made them a bit big - I think we might have to do that again... That's development work for you!

In the same package as the M6 screws for the right angle plate came some button head M6. These are to replace the cap heads on the cross and compound slide handles to avoid skinning our knuckles: 

They look a lot neater as well.