[modeleng] Re: Screwcutting
- From: Patrick Coppens <develop@xxxxxxxxx>
- To: modeleng@xxxxxxxxxxxxx
- Date: Sat, 24 Nov 2007 17:00:04 +0100
Allen Messer wrote:
> Patrick, I have only done it a few times when cutting
> internal threads when I could not observe the tool. I
> was cutting some .750" x 55 Whitworth threads and used
> this method on this one off job.
>
> Question: doesn't your lathe have a threading dial
> mounted on the saddle that engages the feed screw?
> This is what I always use whether threading internally
> or externally---always engage the half nuts when the
> same number comes up to the "mark", dis-engage at the
> end of the cut, wind out the cross feed about a
> hundred thou, crank the carriage back to the end of
> the job, advance the crossfeed screw to Zero, advance
> the compoound feed a few thou, wait for the right
> number to come up to the mark and then engage the half
> nuts again. It takes longer to tell about it than it
> does to do it.
>
> Al
> --- Patrick Coppens <develop@xxxxxxxxx> wrote:
>
>
>> Allen Messer wrote:
>>
>>> It is possible to so mount the threading tool
>>>
>> whereby
>>
>>> the cut can be made FROM the shoulder TOWARD the
>>> Tailstock, eliminating the possibility of a crash.
>>>
>>> Al
>>> --- Patrick Coppens <develop@xxxxxxxxx> wrote:
>>>
>>>
>>>
>> Allan,
>>
>> This is true, and I have done that in the past, on
>> repeat jobs, but it
>> is a bit "of a to do" if it is only for one piece,
>> don't you think so?
>>
>> Patrick
>> MODEL ENGINEERING DISCUSSION LIST.
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>>
>
>
>
>
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>
Allan,
The big lathe does have an indicator, and uses the classical half nuts,
so no problems there.
It is the "smally" that doesn't have one!
The lead screw is mounted under the bed, instead of in front of it.
All in all a very handy and versatile machine, but this is one of its
drawbacks!
That is why I don't disengage the saddle and reverse it back to the
beginning of the thread.
If I wouldn't do that, I would loose my relative position.
The disengaging system itself is great,as it is only by the flick of a
knob, and the saddle stops strait away.
But I want the engagement to stay, so the saddle can go back to its
position.
So, that is why I started to use the retraction tool, as it gave me just
that 1/2 to 3/4 of a revolution more, that I needed to make
the spindle come to a complete standstill.
That is usually done, by retracting the cutter with one hand, while
using "the finger" to flip up the protective perspex, cover over the chuck.
The lathe stops then immediately, and the saddle is still firmly linked
to the lead screw.
I then restart the machine, after having put it in "reverse" and run it
until I clear the piece.
Then the cutter is shifted forward again,by means of the lever, and the
cross slide is moved in, for the next pass.
The machine is taken out of "reverse" and started again.
The next pass is executed....
This too take a lot of writing, to explain something fairly strait forward.
As long as there is there is "some" room left, where the thread is
supposed to stop, there is never a problem.
If you really have to work up to a shoulder with no blank bit left at
all,between the end of the thread an the shoulder proper,
then you have to be really careful, and very, very, very ,very slow.
The first time, I ever had to do that, I didn't even use the motor of
the lathe!
I improvised a crank and rotated the spindle manually...
That was a bit too cautious, but hey what did I know!
*On a different note, and as proof that there definitely is something
funny going on with woman and shoe shops, my better half, just walked in
the door
as I was writing this mail, claiming that she now has seen "boots that
were beckoning her"! Needless to say she bought a pair!!
*
Patrick
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