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Posted by DoN. Nichols on April 23, 2008, 1:04 am
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>>>I have a lot of 2 inch by 8 TPI internal threads to cut in cast aluminum,
>>>both left and right hand, and just got the missing parts for an "on end"
>>>style bar thats been in the cabinet for years. I remember someone saying
>>>that they prefer leave the compound 29 degree angle out of it and just use
>>>the cross feed.
>>> Hows that compare to the traditional method for smooth threads?
[ ... ]
>> When you cut threads by feeding straight in, you're cutting both flanks of
>> the thread at once. That produces twice the tool load for a given depth of
>> cut.
> In addition to Ed's comment, formed carbide tools have insufficient
> clearance for cutting aluminum.
That depends. If by "formed carbide" you mean the ones which
bolt the flat of the insert to the side of the tool holder, I'll agree,
depending on the combination of thread pitch and diameter. With 2"
diameter, the clearance angles required for both left and right hand
will be less than for the same 8TPI and 1" diameter.
However -- the "laydown" style of threading tool inserts deal
with the clearance angle by offering a selection of anvils to go under
the insert. Each one has a different angle, in 0.5 degree steps, so you
can achieve a good clearance angle for most combinations of pitch and
diameter.
> You will have much less tool drag and
> loading using HSS. Making good threads easier to acheive. Please refer to
> Ed's comment on machine size and set up stiffness.
Assuming that you grind the HSS to the proper clearance angles
for that specific thread -- requiring two of them if you are cutting bot
left-hand and right-hand threads of the same pitch.
Enjoy,
DoN.
--
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>>>both left and right hand, and just got the missing parts for an "on end"
>>>style bar thats been in the cabinet for years. I remember someone saying
>>>that they prefer leave the compound 29 degree angle out of it and just use
>>>the cross feed.
>>> Hows that compare to the traditional method for smooth threads?