Treading a Trapezoid Nut for my Deckel FP2 X Axis Spindle

This entry documents part of my journey in restoring a Deckel FP2 Milling Machine, I will  share the story on how I got the machine in a separate post, a rare tool in Africa. It does not help that this is my first on making a boring bar for threading, grinding the HSS tool with 30 degree included angle, adding side relief,  and finally cutting a deep internal thread. I could not find any information on dimensions on the internet so I have taken  the decision to share my experience.

The boring bar was made from a length of 15mm drill rod, with a 4mm hole for the HSS tool bit. The flex in the bar made me think a line boring setup might be better suited for production runs, not sure if this is standard practice.

The Trapezoidal Thread for my Deckel FP2 X Axis Spindle, dimensions are close to DIN103, although my machine sports a 4mm pitch. My readings indicate this is not standard to DIN103. Initially I started with ISO 2904-1977 but soon realized the bore of 19mm does not fit the Deckle Spindle, then had to re-bore :/

Ks measured at 19.5mm

Kn (Nut bore diameter) should be 20mm

Dn kept at 24,5mm



For Inside Threads, the correct bore size is important, before threading commences.

Step 1 – Ensure inside bore size is correct on entire length of bore. Difficult to fix bore after threading has started, would require new setup/feed speed changes etc. Not good.

Step 2 – Boring bar is parallel to work, insert is at correct height, for brass bronze no back rake. i.e. tool should be perpendicular to work.

Step 3 – tool post is clamped down hard, (with deep internal thread this caused a problem since boring bar shifted, and had to be realigned. Compromising thread quality)

Step 4 – compound should be at 0,5deg less than half the included angle of thread, see infeed methods below. – 14,5 for Trapezoidal internal thread. Slanted back /.

Step 7 – scratch pass, to establish if feed is correct.

Step 6 – Use boring tool to outside diameter of nut to determine thread depth. Subtract tool height.

Keep going until measurements get close, start fit testing.BoringMeasurement

Outside dimension – (( B – H )  * 2 ) = thread depth

soll wert ist wert
outside diameter  45 50,457
boring bar to outside 16,8785 17
Tool height min 2,5 3,9
Thread depth 24,5 24,257



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