Cutting threads (well grooves) with taps

Just to prove I finally made it out of the armchair:
This is one component of a mod to add a "boring and screwcutting" speed
range to my sieg C6.
http://www.btinternet.com/~steve.withnell/lathe/pulley/Bpulley.jpg
JS suggested using a diehead chaser for cutting Poly -V grooves. I didn't have the correct diehead chaser, so I "converted" a tap to achieve same. The pulley is made from cast iron bar and as you can see the trick works like a charm despite me having about 2% of John's experience.
I have one more pulley to cut and once the new drive belt arrives the C6 should have two ranges of decent grunt - 240 -> 2400 and 40 ->400 for boring and screwcutting.
Another question. The pulley "V" is 11mm deep - how can I get a clean flat cut in the bottom to eliminate the chatter marks in the picture? I know it doesn't matter, but I know its there...
Thanks
Steve
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wrote:

Two ways, [1] Ignore it nothing runs on the bottom unless the belt is tattered. [2] use something like a parting tool that's 1/4 to a 1/3 the width of the bottom and take a light facing cut. The chatter is there because it's too wide a tool for the lathe, job support etc. Increasing stiffness [ or so Gert says' I wouldn't know ] or reducing width of cut achieves the same result.
Nice job on the pulley BTW, better than mine as mine is in alloy as it was to hand. -- Regards,
John Stevenson Nottingham, England.
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On Mon, 19 Jun 2006 21:22:22 GMT, John Stevenson

Don't know if this is a question or a suggestion. The tool with which you are cutting the groove, of necessity, must overhang its holder a considerable amount. Can you rig up something, almost like a super-slim version of a machinist's jack, that sits on the cross-slide and supports the underside of the tip of the tool?
I think I've seen pictures of something similar in conjunction with turning rolls (for a rolling mill) out of chilled iron [ICS reference series?].
Thanks.
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Steve wrote:

Looks good! I'll remember that..
Out of curiosity how did you use the tap, or the remnants of it? I'm guessing you ground off the tapered end to allow cutting up to the pulley shoulder, then ground two opposing edges flat, so it could be clamped in a toolholder...
Guy
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Not as sophisticated as that. The tap is 5/8 so quite chunky. I sliced the end off with a slitting saw on the angle grinder then tidied up one set of teeth to use as the cutting edge. The tap went straight into the toolpost packed to height.
The tap can be used for cutting internal threads in a similar fashion. The advantage is that you get a much better thread form than when using a single point tool.
Steve
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[cut]
Old hand thread chasers work quite well in this respect too and I've found them also useful when cutting external threads on a screwcutting lathe in stainless steel (where my experience with single point tools has been poor). They also come with the correct form ground in, which isn't easy to do free-hand on a grinder for a single point tool.
It is slightly catch-22 -- I happen to own chasers because my lathe is plain; but I've made use of other lathes in the past!
Alan Bain
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