Turn down shaft of tap

B

BarryMcM

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Hello folks,
I am new to machining (7x12 benchtop), and I am looking for advice.
I have to tap a hole 35mm deep.
The hole is deeper than the threaded part of the tap's shaft (~25mm).
The shaft is of a larger diameter than the hole.
I want to turn down part of the tap to fit into the hole.

chipped.jpg
The very first piece of anything I turned was a hardened steel shaft out of a plunge router base.
I used a parting tool to trim off the end with the rough cut.
It was ugly sounding, but worked.
I made the cut dry at a few hundred RPM (no indicator as of yet, so I am guessing).
On this tap shaft, however, the flute passes through the cutting path.
This sounded very ugly, and as you can see, I have barely made a mark in the shaft before chipping the carbide insert.

Any suggestions on how I could turn this down would be appreciated.

thanks,
BM
 
I would think the interrupted cut of the flutes in the extremely hard tap will just shatter the tip of the carbide insert. 'Specially the pointy D profile. Rather than damaging the tooling, I would think it cheaper, and possibly quicker, to just buy a reduced shank tap.
 
I have some taps that have been ground on the shank for clerence , you can get longer taps though so might be worth looking for a cheepy on ebay :)

Stu
 
A pulley taqp has a turned deown shft as well s longer length for threading deeper holes. I woulde modify a conventional tap by grinfing. It oesn't have to be precise. You just need a smaller diameter than the tap drill.
 
They sell undercut taps . ;)
 
Grinding is the only practical way to reduce the shank- it's way too hard to machine, as you discovered
-Mark
 
I too have done as you described. A wider included angle insert will be stronger for example a square insert with a 90 degree corner will be stronger than the 50 degree included angle on your DCMT insert.

I recommend NOT reducing the shank smaller than the tap drill. The tap can cut crooked more easily if the shank is reduced too small.
image023.jpg
 
macardoso said:
I too have done as you described. A wider included angle insert will be stronger for example a square insert with a 90 degree corner will be stronger than the 50 degree included angle on your DCMT insert.

I recommend NOT reducing the shank smaller than the tap drill. The tap can cut crooked more easily if the shank is reduced too small.
View attachment 365836
Click to expand...

I machined my tap with a SCGT09T0304 insert. Spindle speed was adjusted to give a light blue chip. Dark blue or black is too hot/fast. No Coolant
 
You might try eBay and look for a nut tap or a pulley tap.
 
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