During discussions regarding the Headstock spindle thread form, some concerns were expressed by members regarding the difficulties of employing 1″ Taps.

I promised to elaborate on my recent experiences

EW Stringer Lathe Spindle Thread

First task was to choose which material to use:
Traditionally back plates are fabricated from Cast Iron.
Mild Steel Round Bar or Cast Iron Bar Grade 250 are perhaps the most obvious choices.
Both are easily sourced in 65mm diameter and costs are very similar.
I chose to use 65mm Bright Mild Steel Round Bar 080A15/EN3A
Of all the mild steels available this grade has the most suitable properties for our application (in my opinion). However, a cast iron version will probably be my next project and may well turn out in the end to be a better choice of material?

I preferred to rough turn the backplate blank and finish bore to tapping diameter which gives better control of diameter rather than purchase a special tapping size drill.
My stock drill is a 14mm MT1 taper shank for direct mounting in the EW tailstock.
This is the max diameter drill available in MT1 taper shank form (Tracy Tools) and allows entry of a 10mm Boring Bar + CCMT060204 Tip (arceurotrade 060-325-39510) to bore to finished size.

The 1″ diameter is obviously tough going so I had previously purchased a full set of 3 taps: Taper, Second and final Plug all in HSS (Tracy Tools). They came with a centre drilled square drive end which is essential for proper alignment.

My heavy duty SCT Tap Wrench for Taps 1/4 – 1 1/8 inch (SKU: 12102004) was supplied by Mark at Chronos Ltd. (thoroughly recommended):
The fixed handle is screwed & can be removed for storage in it’s box but also enables use in the lathe when tapping a bored component. It allows a tailstock centre to engage with ease and there is enough space to reposition the wrench as the work progresses.
This is where great patience is required as progress is very slow. Only very small cuts are best (max of 15-20deg of handle rotation) and then back off to clear the cut swarf. Advancing/retracting the tailstock feed to maintain centre engagement.

In conclusion, as stated in my previous post:

EW Stringer Lathe Spindle Thread

“Have no fear, tapping a 1″ thread should never require brute strength”…

I hope this additional information is of use to EW owners who may like me have felt unsure of how to proceed.

Andre