Mini-Lathe

Updated: First published April 2018

For some while now I have been thinking about extending the capabilities of my home workshop with a small lathe, and have been looking at Myfords and the Chinese mini-lathes that have come to dominate the hobby market. Before looking for a lathe, I made a list of the bits I wanted to make with it to test whether I would really use one. I've made several Ariel motorcycle tools with it, shown here, and a lot of other things besides.

After reading several books and many articles online, I took the plunge with the aid of a bonus from work and bought a RealBull CJ18A from Amadeal. It's a nominal 7" x 14" imperial lathe, perfect for old biking needs.


The lathe comes with a four jaw chuck, as well as the three jaw self centring chuck. I ordered a live centre, a Jacobs chuck and a tailstock die-holder as well. I'm using 10 mm HSS tools from RGD, and I have bought a bar of 10 mm HSS to grind my own tools - so that I have tools available for steel, brass and aluminium.


It's the two speed type, and has metal HI/LO gears in the headstock. You can reverse the spindle at the flick of a switch, which is very useful when machine tapping, and you can vary the speed infinitely. A nifty bit of circuitry forces you to turn the speed to zero before starting the lathe, which is a little safer.

There is a digital display for spindle speed and I have found an app for Android which helps me select the right speed for the job.


There is a cam operated tailstock lock which is useful; I've centred the tailstock using a dead centre against the chuck. The tailstock took a bit of adjusting at first to get the cam lock to work effectively - it's been fine since I adjusted it properly. I bought a revolving centre for the tailstock which was useful when making my Ariel QD hub nut spanner, shown here.

The tailstock quill clamp needs Loctite to keep the tommy bar from vibrating loose as soon as you work the lathe hard, when parting off for example. All the tommy bars on my lathe have thread lock now.


The high/low change lever is behind the headstock, alongside the lever for the leadscrew. I have an 'H-L' label on top of the headstock now - I can't see that one at the back...


I did a lot of research before I bought this lathe from Amadeal, looking at several other suppliers of both RealBull and Sieg lathes. I plumped for Amadeal in the end, because this imperial lathe was available with the metal HI/LO gears, the 4" four jaw chuck and the 4" 3 jaw at a reasonable price. Some of the packages offered with mini lathes include vernier calipers and micrometers, fixed and traveling steadies - things I either have or will never use, which is worth some consideration when buying. I was fortunate enough to have a technical education and am old enough to have had metalwork and woodwork classes in school, with staff who were enthusiastic enough to supervise you in the shop at lunchtime as well. This background, and 30 years as a Chartered Mechanical Engineer helped me understand what to expect and what accessories to shop for.

Amadeal customer service have been very helpful too - I've emailed them with various queries, one of which resulted in a new controller board being provided.

Location


Around the lathe you are going to need some storage. I have my lathe on a steel cabinet which puts it at a comfortable height, and recently I put some shelves above it to keep the workspace clear.


The lathe area is lit in two ways - general ambient lighting at that end of the workshop, and a large LED floodlight which shines directly on the work from above, illuminating the whole lathe.

Tools, Accessories and Modifications


It was clear from the outset that the lathe was going to become a hobby in itself, attracting many enthusiasts with ideas of how to improve and adapt it for other jobs.

The first job was to make a couple of stand-offs to improve the location of the chuck guard, such that it drops into the gap behind the chuck:


I've made a sheet aluminium guard to keep the worst of the turnings off the bed ways and leadscrew. It fits into the travelling steady holes, and is very effective - it's covered in debris most of the time:


While on the subject of preventing chips going where chips should never go, the apron gears have this protective cover. These covers are well documented in several mini-lathe books and websites, but this one is a little different. Instead of the usual acrylic or metal sheet, this one is 3D printed in some sort of plastic. 

I elected to retain it with three panhead M3 screws, because that's what I had at the time; the panhead prevented my bed way chip guard fitting as well as it might. Later I changed them for countersunk head screws. 



Here's the tailstock die-holder from Amadeal. It accomodates several (4) die sizes:


I made this adapter to allow the 1 1/2" die holder to carrier 30 mm dies:


It's an aluminium ring - it has a blind hole to locate the die-holder grub screw, and a steel pin to locate the groove in the die.

Here it is in action with the work in an ER25 collet. I use collet chucks for threading, since there is often too much torque involved for the 3-jaw:


I made a tommy-bar to turn or hold the chuck when hand threading. It has an 8 mm AF end for the 3-jaw and a 6 mm AF end for the 4-jaw. It's made from a bit of scrap 3/8" black mild steel round bar:


I've made a similar thing, with a round end (5.5 mm OD x 7 mm long) to turn the tailstock chuck while threading with a tap. This one has a point on the end to assist when centering the tailstock - I put the tool in the chuck, and bring up the tailstock with a dead centre:



I made several reproduction Ariel toolkit tommy bars as well, shown here.

In the interests of keeping the space around the lathe tidy, I made this tool block from a chunk of sapele windowsill:


Accessing the slide for adjustment was always a problem because you have to remove the splashback. This is easy enough but as standard it is retained by five short M5 screws, which are a pain to replace. I changed these for studs and long sleeve nuts, which means I can remove and replace the splashback by hand, without moving the lathe at all:


More details on this modification are shown in this post:

Toolpost

I bought a quick change tool post for the lathe quite early on:


It's held in place with one of those long cap screws - I will practice screw cutting and replace the cap screw with a long stud, so that I am not wearing out the compound slide thread and so that I do not need an Allen key every time I want to move the toolpost. It came with four tool holders including a parting tool holder and a boring bar holder - I have added three more tool holders to my collection. It's very useful - jobs would take a lot longer if I was shimming each time I changed tools, but it is not very rigid. There is a sleeve which clamps the tool post to the top slide, but in standard from it's central bore allows the whole toolpost to move slightly.

I've replaced the 10 mm cap screw that is provided with the quick-change tool post with a stud, so that I can use the original hand nut and operate the tool post without reaching for the Allen keys:


The first attempt was about 5 mm too long, so I had to trim it again. The short M10 thread in the compound slide is undercut to provide a good fit.


Job done, and much easier to use, though as I said the toolpost itself is still quite prone to unwanted movement. 

Part of this is due to the sleeve which is seen under the new hand nut and which clamps the toolpost down through the cuboid body to the compound slide: The issue is that the hole in this sleeve has an OD of almost 11 mm to clear the 10 mm stud and allows the toolpost to move, its rigidity relying only on the clamping force. This next picture shows my toolpost with a new sleeve, made to a closer tolerance in the cam, and with a 10 mm central bore. This provides just enough clearance over the 10 mm stud and is much more rigid. As you can see, it looks much like the standard one, though there is slightly more clearance to the cam than necessary and the flange on the top it thicker and has a larger diameter.


It's got a 1024 needle roller bearing under the clamp nut, just to make sure the torque goes to clamping force and not friction!


Milling in the Mini Lathe

The next step is to set the lathe up as a milling machine, sparked off by the desire to make a locking ring spanner for the hub bearings on my Ariels, shown here

I've made this base plate, which replaces the compound slide. Its made of 12 mm thick plate and it's fixed to the lathe using the two M6 cap head screws that retain the compound slide. I've added two further screws at the far end of the cross slide, to prevent it turning:


The plate is large enough to allow the milling slide to be mounted in several positions. It will need a modification to the saddle clamp since that is now obscured by the plate.

I have this vertical milling slide and vice, which I bought from Chronos. It has a 50 mm vice (50 mm jaw width & 50 mm opening) and the slide travels 80 mm:
The plate serves to allow the milling slide to be solidly mounted to the cross slide, be centred on the spindle axis, to move with the cross slide and saddle and provide XYZ movement for the work piece. The slide is bolted down to that 12 mm plate with a pair of M8 cap screws and a suitable clamping plate:


Since I took this picture, the plate has had several extra holes such that milling can be carried out at up to 45 degrees in either direction from the lathe centre line.


I've used a small cast handwheel to provide manual operation of the lead screw, for feeding during milling. It's got two M4 grub screws to retain it to the M8 thread on the end of the 16 TPI lead screw, and allows you to advance the saddle by 0.0625" per turn. The aluminium graduated dial is divided into 60, so you can advance the saddle by around a thousand of an inch if you need to:



The saddle has a graduated dial as well, divided into millimetre increments. Slop in the saddle pinion means that you can move the saddle handwheel to the equivalent of about 0.5 mm of saddle movement, and therefore the dial is graduated in millimetres. There's no point in subdividing that any further:



The dial has a spring loaded friction pad and a grub screw to lock it in position.

Rotary Table

To extend my milling capability, I bought a small (3") rotary table. It can be fitted on the lathe with the axis vertical or horizontal and you can set it at 0-90 degrees to it's mounting surface, so it's quite versatile. It has a 58 mm base to table height though, and that is above the 12 mm milling adapter thickness so it will most often be fitted on the vertical slide like this.


In this position, you can centre the rotary table on the spindle axis.

Before I could use it in anger, I needed to make a chuck mount on it for which needed to make an adapter plate. This took a while:


Tool Post Dremel Attachment

I made this attachment to allow me to attach my Dremel to the mini lathe as a tool post grinder:


It was quickly made from scrap 3/4" ply, and it allows me to use the Dremel for grinding, milling or drilling jobs in the tool post. I used it to cut the slots in this expanding arbour:



Dividing Attachment

This arbour is actually part of the dividing attachment I made to David Fenner's design described in his book 'The Mini Lathe'. It's a simple tool that enables you to increment the chuck in as many steps as the standard change wheels allow - actually twice as many, because it's designed to increment the gear teeth, as well as the gaps between the teeth since the peg can be set to span a tooth as well as settle in the gap between two teeth. I used this to make the graduated dials for the lathe.


I've used the rotary table to make additional wheels for dividing - this one has 31 teeth:


It's used to make serrated shafts like this:


Wide Feet

Out of the box, the mini lathe is provided with four rubber feet, of about 40 mm diameter. There are two under the headstock and two under the extreme right hand end of the bed. The thing is, they are mounted very close together - actually on a 72 mm pitch, which allows the lathe to rock when you are using it in anger, making parting cuts for example. I'd thought about mounting it to the bench, but I realised after a few months use that I would be wanting to adjust the slides regularly and bolting down would make it very difficult to get to the back. I opted for spreading the existing feet to a 160 mm pitch and leaving it sitting on top of the bench.

I made these spreader beams out of a bit of bar (actually an old door threshold), 6 mm x 20 mm. There are two 8 mm holes to attach to the bed, and two holes M6 for the feet:


I mounted them using some M6 screws with shallow heads which I think were originally part of the kid's bunk beds. The bars are designed such that the feet don't protrude beyond the drip tray:


Collet Chucks

Struggling to hold work in the chuck while threading, I've invested in a set of collet chucks. 


I bought two - an ER25 and an ER40, both with MT3 tapers to go in the headstock. The ER25 covers 1-16 mm and I have collets for all those sizes; the ER40 covers 3-26 mm and I have collets for 20, 22 and 26 mm to cover most of the larger imperial and metric sizes I use.


Both the chucks have M12 threads for the draw bar. I've made a draw bar from an old stop-cock key (which had an OD of about 14 mm) turned between centres, a 25 mm 303 stainless offcut and a spare handwheel. I cut the M12 thread on the drawbar in the lathe - my first attempt at screwcutting, though I did finish it off with a die; the stainless part is turned to loosely register with the spindle internal diameter. It's retained to the bar with a circlip. The handwheel, while a bit small, was in stock. It's retained to the bar with a 4 mm roll pin.


Reversing Gear

When attempting screw cutting for the first time, I found out a couple of things relating to running the lead screw at relatively high speed. When the lead screw is running slowly, torque requirements from the motor are low, because of the gear settings. However, coarse threads (like the 1.75 mm pitch I was attempting) require the lead screw to turn much more quickly and this increases the torque required from the motor.

I found the tumbler gears would persistently pop out of engagement.

I did a couple of things to address this:
  1. I removed the control box and made sure the lead screw pillow blocks were properly aligned and lubricated with a light oil.
  2. I modified the detent mechanism on the reverser, to make it stay where I put it.
If you look at the picture below you will see the reverser detent pin drops into shallow recesses in the belt cover. Any kind of tangential force or torque on the tumbler gears has the reverser disengage part way through the thread, stopping the lead screw and ruining the thread.


I removed the belt cover and made these detents much deeper, using a centre drill and a countersink. Works beautifully now:

Cutting Fluid Feeder

The latest modification to my lathe is to provide a cutting fluid feed to the tooltip, shown in detail here. It’s a simple device with a copper tube feeding fluid from a bottle hung on the wall through a clear PVC hose with an isolation valve:



Jobs on the Mini-Lathe

I've used the mini-lathe for quite a few jobs on the bikes since I've had it. You can find some of them here:

Reference Sites


There are some good mini-lathe websites I've found. I'll list them here:


There's a mine of information online and in literature, some of it quite old - my lathe is of much better quality than some of the books and websites would have you believe. I use it almost daily - it's incredible how useful it has become but it is a bit of a hobby in itself.

I could probably write a lot more on this subject but it's getting late.

3 comments:

  1. I have the same lathe and it works fine but lately the spindle speed readout cuts off.have you any idea why?

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    Replies
    1. I'd go and look at the sensor and the wiring in the control box. You can take the end cover off to see the sensor; it's wiring leads into the control box to a connector on the control board.

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