Milling with a lathe

Page 4

Modifications and hints to help you

If you are milling several slots or holes to a set depth, a carriage stop is highly desirable.

If the carriage handwheel does not have an indexable scale, use a digital or dial indicator to advance the carriage the correct amount when setting up for the next cut.  

I designed a magnet backed travel indicator (Micro DRO) to make this easier.  It can also be used on the cross slide and the mill slide.  It cost less than $10 and works very well.

If you're intending to mill on your lathe then I recommend you make one.   It's dead accurate and great for setting up increments and alignment.

lathe DRO

Click here to see how I made it.

You can also use the ram in the tailstock to advance the carriage (recommended), and read out from the graduated ruler on the quill, or the handwheel indexing collar. 

Change gears

I disconnect/split the change gear train when milling at high speed - to reduce wear and noise.

When milling with very large carbide cutters at maximum lathe speed, the shock loadings transmitted back through the change gears from the spindle can be quite severe.  In extreme cases this can chip/damage change gears if left in mesh.

Milling with HSS at much lower speeds is a safer alternative, and overcomes this issue.

Align work

Use a square to align the workpiece on all three planes (vertical, horizontal, and across the ways).

I use the Micro DRO seen above to check the across the ways (cutter) alignment.  This makes it quick, easy, and is dead accurate.

The video below shows how.

By bringing each end of the work piece up against the mill bit and comparing the two readouts, you can see if it is misaligned.  Both readings should be identical.

When setting up your rig for the first time, it is also beneficial to run a light facing cut across the top of the vice jaws to get them parallel to the mill bit.  This will make it easier to visually align work.


A piece of hard scrap steel is milled below with carbide to see how it all performs.  A pretty good result.

er32 collet

A steady feed speed and light passes work best.  No lubricant is required with carbide - the hotter the better, so keep the spindle revolutions as high as the lathe will go.

With HSS cutters the opposite applies - speed must be reduced below 900 RPM and lube used to prevent overheating and chipping of the cutter tips.  

In the smaller sizes I purchased some HSS end mills rated for hard stainless steel work from Ebay, and they have proven to be good quality and durable.  Not expensive.

Below is a range of basic mill bit styles and types.

end mill

Left to right are double replacable tip slot mill, single replacable tip slot mill, HSS countersink mill, HSS end mill, HSS slot mill, HSS keyway cutter, HSS fluted side mill.

Most of these were bought from on line stores at much cheaper prices than through local suppliers.

HSS slot and end mills have several advantages over carbide as they:

- can have four cutting edges as against the two (or even one) of carbide,
- t
he cutting edges are generally wider than a carbide tip,
- and you can cut the full depth of the mill bit in one pass, mainly to finish off, if required.

All of this helps
give a cleaner cut, and as they spin at a much slower speed than carbide there is very little noise.  In comparison, running a lathe at high speed with carbide screams.

Carbide puts a lot of shock loading on the spindle drive system, particularly with very large mills or fly cutters.

Belt drive lathes can easily handle this, but light weight geared head lathes may not fare so well.  I'm just being cautious on this, and raising it as a possibility.   HSS is the safer option.

With HSS you have to use coolant for harder metals, but the finish is as good as you can hope for.  I often use HSS in preference to carbide.

I spray the coolant on with a plastic squirt bottle at regular intervals.  You don't need much, just enough to keep the temperature down.

The coolant I use is simply a 1 to 4 part engine oil/ kerosene mix.  It smokes a bit, but won't cause rust, take the paint off the lathe, or give you dermatitis.  It's also cheap and readily available.  There are various commercial products available.

HSS mills are relatively cheap to buy and for very small lathes, may be the best option.

You can see how easily I re-sharpen them below.

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