How to cut Threads using the Left to Right Method.

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===== How to cut Threads using the Left to Right Method. =====

**__//THIS IS WORK IN PROGRESS//__**

Please note that this guide is specific to Bristol Hackspace’s Harrison M250 Metal Lathe.
This guide describes how to cut Standard Metric Threads on the metal lathe such that the carriage moves from left to right during the cutting stage thus avoiding the risk of the carriage crashing into the chuck or headstock.

==== Stage 1. Preparing. ====


Decide on what thread you want to cut:-

Size i.e. M20 by 2.5mm.

Thread direction, i.e. right-handed (the norm), I assume this in the guide below.

With the lathe in its normal operating configuration, prepare your stock that is going to be threaded. 
If you are doing an external thread, your stock will properly need to be as shown in the diagram below. It needs to be the correct diameter to take the required thread; this can be obtained from tables or calculated. You will also need a relief area where the cutting tool can sit before you start each cutting pass This should be bigger than the thread spacing and sufficient that the cutting tool can fit in.
If you are doing an internal thread, your stock will properly need to be as shown in the diagram below. The diameter of the hole should be the correct size for the required thread; this can be obtained from tables or calculated. If the hole does not go completely through the stock, you will also need a relief area where the cutting tool can sit before you start each cutting pass. This should be bigger than the thread spacing and sufficient that the cutting tool can fit in. Note that because of the size of the cutting tools, we currently have the hole must be at least 18mm in diameter.

==== Stage 2. Getting the Lathe ready.====

__**Step 1. Engage the Lead Screw.**__

1.	Remove the cover plate with an M3 hex key.

2.	Rotate the Lead Screw until the edges of the cover become visible. 

3.	Push the edge of the cover upwards to reveal the Shear Pin. You may need to rotate the lead screw further.

4.	Now rotate the Chuck by hand to locate the slot for the Shear Pin to slide into. Make sure you have the Traverse Direction knob set to forward.

5.	When the slot is lined up, slide the unit across, pushing the Shear Pin into the slot.

6.	Slide the cover back over.

7.	Refit the cover plate.

8.	With the lathe in a safe configuration turn on the lathe and check the Lead Screw is turning.

__**Step 2. Select the correct thread spacing.**__

1.	Do I need to change the gears? The lathe should be in the “G” configuration, which is suitable for most metric threads, so you're good. If you're doing a weird thread in banana units. Then you may need to change some of the gears on the headstock. This calculator on the amazing site CGTK can help you here. [https://www.cgtk.co.uk/metalwork/calculators/changegears/m250]. The spare change gears are in the bottom drawer of the cabinet. If you do change the gears, please return the Lathe to the “G” configuration once you have finished. If for any reason you leave the Lathe in any other configuration, please leave a note on the Lathe.

2.	Set the Gearbox Knobs to the correct setting for your desired thread.

__**Step 3. Fit the correct Threading Indicator Dial.**__

1.	If you have set the Gearbox Knobs to an “M” setting you will need to use the Blue Threading Indicator otherwise use the Green Threading Indicator.

2.	To fit the Indicator, ensure the metal bolt is screwed back in to the body. Then place the locating lug in the locating hole on the right hand side of the Carriage and rotate the Indicator to bring the teeth of the cog to mesh with the Lead Screw. Now screw the bolt in to the threaded hole and tighten firmly with 6mm Allen key. Please remove the Indicator when you have finished using it. For more details on fitting the Indicator see……

3.	With the Lathe in a safe configuration, turn on the Lathe and check that the Indicator is going round.

__**Step 4. Select the correct direction of cutting.**__

Set the Traverse Knob to forward.

__**Step 5. Set the Lathe to run in reverse.**__

Set the Lathe to Reverse spin direction. Make sure you set this back to forward when you have finished.

__**Step 6. Select a suitable cutting speed.**__

Start on the slowest speed until you are comfortable, then you can up the speed.

__**Step 7. Mount the cutting tool.**__

Because we are running the Lathe in reverse, the tool needs to be mounted upside down to normal. In order to get the cutting point to be on the centre line of the Lathe, you will need to pack the tool up with some high-speed steel. Then use the adjuster to set the tool up.

__**Step 8. Test well away from everything.**__

Move the Carriage etc., so that the tool is well away from everything. Set the Lathe going and as the Gauge comes around to one of the numbers, gently lift the Threading Handle up and you should feel it engage. The Carriage should move from left to right.

__**Step 9. Set up the DRO.**__













__**Step 10. Test thread spacing.**__

Blacken the surface where the thread will be using a marker pen. With the Lathe running bring the cutting tool in to the lightest contact with the stock at the left end of area to be cut. When the Threading Indicator comes around to one of the numbers gentle lift the Threading Handle and it will engage. A trace of the tread will now be visible on the stock. Check this is the correct spacing either with a ruler or a threading measurement gauge.
 
====Stage 3. Cutting the thread.====





































====Stage 4. Returning Lathe to Standard configuration.====

1. Set lathe to normal forward spin direction.

2. Disengage Lead Screw.

3. Remove cutting tool.

4. If you have changed the gears return them to the “G” configuration.

5. Remove the Threading Indicator.

====Further Discussion.====

This is intended to be a very simply guide just covering the basics; there are many more areas of thread cutting not covered in this guide. The Internet offers lots more information and YouTube videos.

Non metric threads.

Left hand threads.

Tapered threads.

Different thread profiles.

Double Threads.