DIYbanter - View Single Post

(DoN. Nichols) wrote in
:

O.K. The easiest to get is the pipe tapping high-sulfur oil ...

I'll try to pick up something today.

... MSC I seldom get off an order
smaller than $100.00 once I have decided that I'm going to call them.
:-)

I feel your pain :-) For me it's BusyBee machinery and KBC tools.

... I hadn't thought of allowing for the helix angle.

For a 40 TPI with a 3/8" OD, I come up with only 1.22 degrees,
so your side relief should be sufficient here. With the 1/2", it is
even less.

It's a rather easy change to make, so I may do this anyway. Then I'll be
sure that it's not contributing to the problems.

[ ... ]

Hmm ... for 16 TPI, I start out with 0.010" per pass, and
reduce
to perhaps 0.002" for the last pass or two. I also make two or
three repeats at the final depth.

Knowing that I had trouble already, and that my Atlas lathe is not
very rigid I wanted to minimize deflection/vibration.

O.K. One thing to consider, however, is that too small an
infeed results in the tip burnishing and sometimes work-hardening the
workpiece on one pass, and then digging under after one or more extra
passes.

Unless the depth of the thread is truly critical, I would check
depth of subsequent passes, and try to adjust the feed so you can take
a full depth pass (whatever works for you) for the final pass.
Following it with another pass at the same setting will burnish the
finish a little, if there was no spring to catch up to.

You may be on to something, see my comments at the end.

(I'm used to
my 12x24" Clausing being rigid enough for pretty much any cut that I
am willing to risk.

While my experience is limited, it is mostly on much heavier equipment
than the Atlas. In school we used 12" swing Standard Modern-Lathes which
would probably be similar to your Clausing in rigidity, and from there I
went to running a 24" swing Monarch for a while before returning to
school. At the same time I am enjoying the challenge of learning to work
within the limitations of the 10" Atlas.

... there are the various interfaces
between the carriage and the tool (cross-slide ways, pivot for the
compound, and compound ways) all contributing to give. Have you
pulled the compound out at the pivot and made sure to clean out any
chips before re-installing it? IIRC (and based on my old 6x18
Atlas/Craftsman), the Atlas design has a boss projecting from the
cross-slide, with a dovetail turned on it, and the compound has two
setscrews pushing in bronze or brass angled pushers to contact the
dovetail. The Clausing, by contrast, has a hole in the cross-slide, a
cylindrical plug on the bottom of the compound, and two holes 180
degrees apart going through the flange on the compound and T-bolts in
a circular T-slot surrounding the hole. A much more rigid mount.
Since Clausing and Atlas combined at some point (I hear stories saying
that A bought B, and others saying that B bought A), hopefully the 10"
has the more rigid design.

I am not familiar with the 6" Atlas, but it sounds similar to the setup
on the 10" Atlas. It is a known weakness of the lathe.

Also -- what size of tool stock did you use for the threading
tool? I generally go for at least 1/2" on my Clausing (where the
quick-change toolpost and holders will accept up to 5/8" shanks.)

1/4" clamped as short as possible in the toolpost. It's what I had on
hand. I agree that larger would be better I among other things it would
allow me to let it project a little more.

... you may want to pick
up a half-center (actually a bit more than half) to give you more
elbow room. *That*, you will have to use with a lubricant on the
center, as there are no live half centers. :-)

The ideal lubricant for that is a lead compound, which is of
course very difficult to get these days. Older machines often had a
cavity in the tailstock holding some, with a dauber to transfer it to
the center. Lacking that, I would suggest an extra pressure lubricant
for the center -- perhaps a lanolin based case sizing lube from a
store which deals in reloading equipment.

I have the case sizing lubricant on hand. I'll add a half center to the
shopping list.

Next -- what shape are the jaws in? A common wear pattern on

[ ... ]

I presume that I don't need to mention being careful to keep the
abrasive grit from reaching the bed of the lathe. Cover with a cloth
or newspaper or aluminum foil. At a suggestion -- the newspaper wet
with oil will help to keep the grit on the paper.

OK, wetting the paper with oil sounds like a good idea.

It is a babbit bearing headstock. I must admit I have had concerns
here, since it is an older lathe which is known to have spent part of
it's life in a low production environment. I lack the skills to
confidently determine it's condition.

O.K. The trick for this is:

1) Remove the chuck.

2) set up a dial indicator mounted on the headstock and measuring
the
register of the spindle.

3) Take some wood dowel (broomstick is the common suggestion, if
it will fit into the spindle), and push down and pull up, noting
the change in reading of the indicator. Someone who owns a
plain bearing lathe should chip in here -- but I think that the
reading should be on the order of 0.001" deflection when dry
(e.g. after sitting overnight), and much lower when the spindle
was just being run, and thus has a good film of oil.

Lacking a wood dowel, I would consider aluminum or brass rod, so
it is unlikely to damage the spindle.

I guess my concern here is how hard to push. I want to find any play, but
I don't want to damage anything. A little leverage goes a long way :-)

You can find web based information on pouring a new Babbitt
bearing in place, and whatever scraping may be needed.

While it would be really interesting, it is probably more of a project
than I can undertake.

... Nope -- The only 12L14 listed on their page is machinable
expanding collets, so I guess that the online places are your best
bet. Not too many industrial places stock the 12L14.

I am in Toronto frequently, so it's not a really big deal I'll call
around the metal suppliers. I see now that I was spoiled in my youth. My
dad had a screw machine shop, and always had LOTS of 12L14 on hand in
many sizes, as well as an assortment of brass and stainless rod.

2) Any ideas why I get the rough thread, especially at the right
end?

At the very end suggests deflection of the workpiece, though it
could be play in the gibs of the cross-slide or the compound. Or a
combination of them all.

I ran a couple of trials last night:

The first attempt was the same setup as before, but at around 600 RPM. My
reactions are still adequate, but I wouldn't want try it with 16TPI :-)
There was no noticeable improvement.

Next I tried with a live center supporting the right end at 40 RPM. Due
to interference between toolpost and tailstock I had to go back to the
lantern toolpost. This improved the thread at the right end, without
making the rest any worse. Now the roughness and tearing are evenly
distributed.

I think your comment about work hardening may be the key. One would
expect to get progressively larger chips if the infeed is the same for
each pass. Instead, it was noticeably variable, as if it occasionally
"dug in" and took a larger amount on some passes. I am going to try
cutting it more agressively to see if that helps.

Rob