Equipment/Mini Lathe

Mini Lathe
Model	Seig 7x12 Mini-Lathe
Sub-category	CNC
Status	Working
Accessories	Carbide tooling, HSS tooling, parting blades, 3 jaw chuck, 4 jaw chuck, collets, centres, drill chuck, vertical milling slide
Owner	Joseph
Origin	Permanent loan
Last updated	9 February 2024 17:20:24
Last updated by	Jo
Training required?	yes
Training form	Training Form
Primary Contacts	Joseph, Tails

The Hackspace's Chinese Mini Lathe, aka Jumbo or The Minila The, is used for metalworking and wood-turning. It can also be used as a milling machine, if necessary.

It is probably the most dangerous piece of equipment in the space, both to its operator and itself, and should be treated as such.

Information card: Guide to lubricants, cutting fluids and tooling

Specifications

• Distance between centres: 30cm (12 inch)
• Centre Height: 7.5cm (3.5 inch)
• Motor Speed: 100 - 2500 rpm (in theory)
• Spindle Taper: MT3
• Chuck Diameter: 80mm
• Tailstock Taper: MT2
• Max Drill Bit Size: 13mm
• Cross-slide (radius) and Compound Leadscrew: 1mm / turn (marked in 1/40 = 0.025mm increments)

Training

You must not use the lathe unless you have received training.

We train members to use the lathe. Non-members can operate it under their close supervision.

Please contact a member if you need training. They will show you how to safely operate the lathe.

It's easy to break yourself, the space or the lathe (in that order) if you don't know what you are doing.

Safety

• DO NOT put your hand near the chuck when the lathe is running.
• DO NOT touch the work when the lathe is running.
• Tie long hair back
• Ensure long sleeves will not get caught.
• Be careful when removing work from the lathe – it may be hot.
• If the lathe jams while running, turn it off immediately and then back off the tool.
• Ensure the work piece is secure in the chuck.
• Ensure the tool holder is tight in the tool post.
• Do not turn anything over the diameter of the chuck that is holding it (as an absolute maximum).
• Items that are oversized may be able to be turned on the faceplate.
• Be particularly careful when using the faceplate, as pieces can fly off if not properly fixtured. In particular, longer, heavier parts can easily pull themselves off if the tool jams.

DO NOT TURN:

• Titanium (without discussing it with us first)
• Ferrocerium Rods (sparking rods used to light fires)
• Tungsten
• Cobalt alloys (just don't)
• Radioactive materials
• Food
• The Lathe Monster

If there is any doubt about whether or not a material should be turned, then speak to someone for a second opinion first.

Equipment

Workholding

Currently the lathe has two chucks, a faceplate and a couple of MT3 collets. There are also the dead centres, one MT3 and one MT2, and lathe carriers (also called lathe dogs) for turning between centres.

The chucks and faceplate are attached to the spindle by three or four screws. Screw these grub screws into the back of the chuck, hold the chuck up to the spindle, and screw the bolts onto the grub screws. Ensure these are tight before attaching a workpiece.

Self Centring 3 Jaw Chuck

The three jaw chuck is the easiest way to hold a workpiece. All that you need to do to hold a workpiece is tighten the chuck with a key, much like with a drill chuck.

However, the jaws of the 3 jaw cannot be inverted. If you want to hold a large part, you will need to use the outside jaws, which are stored under the lathe.

The 3 jaw has a run-out of anywhere between 0.1mm and 0.5mm, depending upon the diameter of the workpiece. It is recommended that you do not put a workpiece back into the 3 jaw if it already has precisely machined features. Instead, use the 4 jaw chuck, or a collet (or turn between centres)

Independent 4 Jaw Chuck

The four jaw chuck is the 'universal' chuck. Almost all workpieces (that are smaller than the chuck) can be held in it. In order to tighten this chuck, each individual jaw must be tightened independently. The dial indicator should be used to remove any eccentricity.

It's jaws can be removed and inverted to hold different sized workpieces.

With sufficient time, it is possible to remove all measurable eccentricity in a part. It can be expected that with enough time, a workpiece can be 'dialed in' to 0.02mm without significant difficulty.

Faceplate

The faceplate is a useful way to hold oddly shaped, or relatively large diameter workpieces on the lathe. You clamp the workpiece to the surface, using T-Nuts and bolts.

If it is not possible to hold a workpiece on the faceplate due to there not being a hole in the right place, a hole can be drilled and tapped on it. Please only do this as a last resort.

Holding work on the faceplate has a higher risk of throwing the workpiece off. Be particularly careful.

ER32 Collets

We have a full set of ER32 collets for the lathe, along with a chuck. These can be used to hold cylindrical stock of an diameter between 2mm and 20mm.

They are attached to the lathe via the collet chuck, and a large collet nut. You must place the collet into the nut, and then use the nut to insert the collet into the chuck.

Do not put a workpiece that is oversized into an ER32 collet. It will damage the collet.

The ER32 collets should have an absolute maximum run-out of .2mm, though it has been measured to be significantly less, depending upon the workpiece and which collet is in use. The maximum run-out of the chuck itself is 0.07mm. They also hold the workpiece very straight, so the amount of run-out should not significantly increase for long workpieces, assuming there is a full-collet length of material in the collet (though still use the tailstock for support).

Morse Taper 3 Collets

There are a number of collets for the spindle bore of the lathe. These can only hold a cylinder of the diameter that they are labelled with. They are probably most useful for holding endmills for milling operations

Do not put a workpiece that is oversized into an MT3 collet. It will damage the collet.

These collets are held into the spindle by a drawbar, which is currently a long M12 bolt with a washer on the end.

Toolholding

There are currently two toolposts for the lathe, a fixed, 4 way tool post and a Quick Change Tool Post (QCTP).

The vast majority of the time, the QCTP is preferred, as it allow the user to adjust the height of the tool easily. With the new wedge type tool post, most of the rigidity problems should be solved

The 4 way is more rigid, and better results may be possible than with the QCTP, if you can be bothered to shim the tools correctly.

Turning with the Lathe

The lathe is a relatively simple machine but extremely versatile. As such, it would be difficult to write a full set of instructions for it's use. This being said, here are some instructions on how to perform some basic operations.

Step Turning

Step turning is the simplest form of lathework. You make a cut parallel to the line of rotation by pushing the cutter along the length of the work piece, up to a particular point, and repeat at increasing depth to create the correct diameter of work piece.

The appropriate depth of cut depends upon the material, the tool and the spindle speed. As a general rule, set it to 0.25mm in from the outer surface and see how well it goes.

Until the electronic 'gearbox' is fitted, the lathe carriage has to be moved via the large, black hand wheel. During turning, do not attempt to feed the cutter too quickly, or you are likely to chip the tool and/or cause a significant amount of chatter.

Taper Turning with the Cross-slide

Taper turning is another relatively straight forward operation. However, it requires a certain level of preparation over step turning. It is significantly easier to turn a taper towards the headstock than away from it.

First, remove the cross-slide from it's ways to expose the screws that hold it in place, then rotate it to the desired angle. This can either be done with a protractor (if precision is not required) or via trial-and-error using the dial indicator. Wind the cross-slide back on and check that the gibs are correctly adjusted. Square the tool-post against the workpiece.

Adjust the position of the carriage and slides so that the tool is positioned against the edge of the workpiece. Lock the carriage in place.

The appropriate depth of cut depends upon the material, the tool and the spindle speed. The depth of cut should be shallower than with a step-turning operation.

Use the cross slide to advance the tool along the workpiece, instead of moving the carriage.

Common Problems

There are many problems that may occur when turning parts on the lathe. However, these are the ones that are common, and can be fixed with relative ease by the user.

Loose Top-slide

The top-slide can sometimes work it's way loose. This can be fixed by tightening the middle grub screw. The problem usually causes a ridged effect on a part whenever the top slide is used. It can also cause a poor surface finish, even if the top slide is not being used.

Tool Height

The lathe is fitted with a quick change tool post. This allows for quickly changing the tools, and also adjust the height of the tool in-situ. However, the tools may not be set to the correct height. This can be adjusted by unlocking the tool holder and adjusting the thumb nut on the tool holder to raise or lower the tool. A tool that is at the incorrect height will produce a poor surface finish. If the parting tool is too high, it will rub and not cut correctly. If it is too low, it will likely jam the spindle.

Milling on the lathe

It is not necessary to have any additional training (beyond the normal lathe training) to use the vertical slide. However, if you are not confident in it's use or have not used it before, ask for help before attempting it.

It is possible to use the Mini Lathe as a milling machine, by attaching the vertical slide to the carriage. This is significantly safer, easier to understand, and more versatile than using the faceplate to perform many of the same operations.

To attach the vertical slide, wind back the top-slide, as is done for taper turning, but remove the rotatable base too. Using the screws stored with the vertical slide, screw the angle plate into the rotating part of the carriage. Tighten the nuts downwards to secure it in place. Take care to ensure the vertical slide is as close to parallel with the movement of the cross-slide as possible. If necessary, hold the dial indicator in the 10mm collet and move the cross-slide back and forth to until you have aligned the vertical slide.

The chuck should not be used for holding end-mills. Instead use an MT3 collet and drawbar to hold it securely in the spindle, as it is a far more rigid way of holding the tool. However, it may be necessary to remove the chuck guard.

Feed and Speeds

The feeds/speeds are a bit complicated, as it depends upon the tool geometry, size of stock and exact grade of material. For that reason, refer to a copy of the Machinery's Handbook (we don't have one).

However, here are some general rule of thumb:

• Larger diameters should be run slower than smaller diameters
• HSS tooling should be run slower than carbide tooling
• Harder materials (like steel) should be run slower than soft materials (like brass)
• Harder materials should be run at a lower feed rate than soft materials
• If cutting threads, run the lathe relatively slowly (without stalling)

Maintenance

If anything breaks, shout at Joseph.

The tailstock can be aligned by loosening the screw on the bottom, and the grub screws in the sides. Unless you know what you are doing, please don't attempt to adjust it. It takes a reasonable amount of time and effort to line it up.

The last full overhaul was performed on the 5th December 2022.

• The headstock was aligned to point 0.08mm downwards, and 0.015mm towards the user.
• The tailstock was set to be as flat against the bed as possible, and the headstock shimmed to be as close to parallel with the tailstock as possible.
• The drive belt was replaced.

The motor and power supply were replaced on the 19th October 2023 with a treadmill motor and supply. The main drive pulley was replaced at the same time in order to fit with the existing motor pulley, and to increase torque.

Additional resources

There is a large amount of information available, online and on paper, on the operation of the lathe. Here are some websites, books and videos that may be useful:

Blondihacks' lathe skills playlist - This is very useful for demonstrating the use of the lathe.

Mini-Lathe.com - This is quite a useful resource for general reference, along with various instructions on how to make tools, turn specific cuts, and how to modify the lathe to work better. Remind the owner of this lathe to actually implement some of the upgrades at some point.

Little Machine Shop - Useful for approximately correct tool cutting geometries

Choosing Inserts - Helps explain the difference between different carbide inserts. Less relevant to this lathe, as the tool often isn't as much of a limiting factor, but worth bearing in mind. Ideally inserts designed for low chip loads should be chosen, or use relatively sharp HSS tooling.

Books:

The Workshop Practice Series - Not all of them are tremendously relevant to lathework, but others are very helpful when learning how to use the lathe. Also, there are several books of toolmaking projects, if you don't have any ideas of what to make, but want to use the lathe.

The Amateur's Lathe - An old book on the use of small lathes. It predates the era of low(ish) cost milling machines, and so describes some of the less orthodox ways in which you can use a lathe.