My new compound dial & lead screw

I confess to having been very impressed with Doc's Machine rebuild of his Springfield lathe, so much so that I decided to try something remotely similar. Since I started using my 15" belt-drive Sidney, about 10 years ago, I have not been altogether satisfied with the compound dial and lead screw. As I get older, my eyesight hasn't improved. The original dial is 2" in diameter driving a 3/4-8 lead screw so it's .125 per revolution. I decided to make a 3" dial with a 3/4-10 lead screw. All this worked out reasonably well even if I had to make about half the parts more than once.



Here's my question...I finally finished this today and I checked it by putting an indicator up against the front of the compound, setting it at zero and making a complete turn.



When I take up the almost inconsequential backlash and make a complete turn it consistently reads .001 over. One thousandth in 100 isn't the end of the world but now I'm wondering if I made an error somewhere or if this is to be expected. I never checked the original lead screw so I don't know if it was more accurate...

Is that old B&S indicator travel set up parallel with the compound travel axis? Is the indicator point resting on a machined flat surface that is perpendicular to the direction of travel? Do you have a different 1" travel indicator to try? Have you tried checking the indicator on a test stand against a 1" micrometer setting standard or similar thing like a measured 1-2-3 block?

Does your lathe's DRO agree with the dial reading" (Just kidding.)

Larry

Good point. It was not parallel to the compound and it is a very old indicator. I'll try another one...I use that one because it's huge and I can see it easily but I've others.

Thanks very much. You were spot on. I went back to the shop and fitted a newer indicator so it was parallel to the compound and the measurement came out exactly right.

Damn geometry...

marka12161 said:

Damn geometry...

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geometry and physics always getting in the way...

I should have known better. chances are I wouldn't have made that mistake had it not been the end of the day and I was tired. Geometry was actually the only math subject I was any good at.

Not trying to be pedantic (It comes naturally, I don't have to try) but if it's a compound screw it's a feed screw, a lead screw leads the tool to make it follow an idea, like 12 threads per inch.
It really is a tiny difference, maybe more of nomenclature than of it's objective, because when the feed screw moves the compound slide .100" that too is leading it to an idea, a man made concept of distance.

Point well taken! One of my shortcomings is that, since I've never worked in the metal trades, I sometimes mix up the nomenclature but "feed" does make more sense than "lead."

Any language forms the basics of communication and peoples sometimes misuse of it becomes almost common accepted terms. But for machine tools and there parts, I very much agree with partsproduction about there being a definite difference between the lead screw on a lathe used to cut threads and every other axis screw on a lathe or any other machine. And since any conversation about machine tools involves some degree about there stated or unstated accuracy, being accurate with your terms is or should be just as important.Today lot's refer to even the X,Y axis screws on a mill as lead screws. Pedantic? Yeah maybe, but I very much agree that anything but a lathes lead screw should be defined by calling them feed screws since that's what they are. About useless for even mentioning it though as it won't ever change what most people now use as the incorrect terms anyway. Even worse would be some and it seems mostly in the UK who call digital calipers Digiverns, or digital verniers. No such thing I know of and a digital/analog oxymoron if I've ever heard one for sure. Jib instead of gib is another one, but there's at least some evidence jib was at one time and possibly over 100 years ago a recognized and accepted term that was replaced by today's use of gib. I'm unsure and can't verify if that jib term was ever common in North America and again it could be a UK only term. But some still insist on using it.

But my apology's, right now I have intermittent power outages, no water, and no natural gas so no heat in the town I'm in so it felt rather good to rant a bit about something different.

Rant away...
In my real life I edit books about antique arms so I'm well aware of technical terms and how confusing it can be when they are misused. I also hate "nicknames". ("Cast iron" is a good one - it was virtually NEVER used in gunmaking but it's amazing how many of our authors use the term for wrought or malleable iron.) One of my friends once opined that "they use those terms because they can't spell." He may have had a point there. I also like to stay away from trade jargon which, I'm convinced, is only there to keep the uninitiated out. If we want to explain things so that anyone can understand them, the English language has plenty of real words to do the job.

Speaking only for myself, I never try to keep new people out, because I wasn't born with dirt under my fingernails, I had to learn just like everyone else.

I started out with what is considered by many the bottoms of the machine tool offerings, my dad had one of the dreaded "A" lathes, and my own personal first lathe was a Dunlap 109.

That dunlap pulled through for me though, the lever on my reloading press broke off where the thread ended at the shoulder. It was my first attempt at threading since high school, that little lathe and I reproduced the correct thread, and I was elated by it, thrilled.

Now, many years later, I have at least 9 manual lathes.

The point is based on the Golden Rule, "How would I like to be talked to as someone new to the trade?", and why would I rejoice in offending them?
Why would anyone? If it's obvious that someone is playing with a hobby lathe they can be shown a URL for hobby machinists without making them look ridiculous.

Who knows? Maybe in a few years they'll own a huge commercial shop.

In a previous life I ran a printing business and would get lots of calls and visits from salesmen trying to sell me computer systems. My standard reply when they called was "explain this to me in terms I can easily understand, If you can't, I'm not a customer." Sometimes I'd add "I can speak jargon as well as you can, albeit it on a different subject."

But my apology's, right now I have intermittent power outages, no water, and no natural gas so no heat in the town I'm in so it felt rather good to rant a bit about something different.[/QUOTE]

dundeeshopnut said:

But my apology's, right now I have intermittent power outages, no water, and no natural gas so no heat in the town I'm in so it felt rather good to rant a bit about something different.

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[/QUOTE]

I hope your house and MORE IMPORTANTLY your shop and tools are dry and above water! Hang in there.

Lol thanks, but only a true gear head would be thinking about the shop and tools as the first priority. And yeah it's my first priority as well. I'm roughly 20' above the flood level, so a huge bonus there. Shop and tools are damn cold but still nice and dry. There's thousands of others up here right now that are much worse off.

About 15 years ago I bought a new 1" B and S. Checked it against gage blocks and it was off .001 in 1". My cheap one I used while wrenching on machines measured the same for about a $50 difference.
Dave

As to the topic of jargon...
The hot rod world now calls anything made
out of aluminum to be "Billet". They say
it means, "from the billet". Well maybe
in the line of casting and running through
the roll stands, then yes it was one a
chuck of metal that meets the size and shape
of a billet. But the word "billet" used
outside the rolling mill or extrusion mill
is just not correct. But someone who wrote
for a magazine misused the word, and everyone
wants to be kool, right? Easier to talk the
part than actually BEING the part, so laziness
and lack of fortitude breeds adopting lingo
of those who have self-elevated themselves to
kool status because they were able to fool the
editor in their job interview. Brovo! Now we
have trend setters further bastardizing the
language and followers are in no short supply
due to big egos and weak minds. Lesson is to
choose your allegiances carefully.

--Doozer