How close is close enough?

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

Moderators: GlennW, Harold_V

whateg0
Posts: 1114
Joined: Sat Mar 28, 2009 3:54 pm
Location: Wichita, KS

How close is close enough?

Post by whateg0 »

It's a rhetorical question. I don't want to hijack another thread so I started a new one to discuss it.

I have watched quite a few Adam Booth videos over the past few years, and noticed that almost everything he does gets dialed in on the 4-jaw. Now, as long as it's in the 4-jaw, why not dial it in as close as possible, right? Before I had a 4-jaw I had the 3-jaw with bell-mouthed jaws and while it wasn't great, or really even good, it did hold work. I never dialed anything in on it because I couldn't. I know that work wasn't always perfectly centered because on the first pass, I'd often only cut on one side of the part. After I added a 4-jaw to my tools, I went back and checked the runout of a given part in the 3-jaw and had almost 5 thou TIR. Not absolutely awful, but not close, either. As long as I wasn't going to remove a part from the lathe and put it back in, I was able to make parts this way.

For the past few months, I have been in the process of making a few pieces to make my 3-jaw adjustable. So, I've been using the 4-jaw almost exclusively. Even when I am making a part in one setup well below the diameter of the original stock, I still find myself getting a part close, then thinking, eh, I can dial it in better than that. I never did that before. I would generally get a part under 5 thou and then move on. Now, I can't help myself from getting closer.

I watched a Keith Fenner video a few days ago where he was "dialing" in a part using a scriber on a height gauge to visually get close. It wouldn't have been possible to get closer, as I think the part had been cast, but still it was plenty good. Harold has described the attributes of softjaws, and while I don't have the ability to use them on any of my chucks, if the gripping wasn't a concern, wouldn't "close" be good enough here? One of the things that softjaws are great for is repeatable concentricity for a given size. In theory, since these handwheels aren't perfect, does that reason really apply here?

Watching SteveHGraham's thread about the handwheels, I kind of wonder, especially since the part isn't perfectly round to begin with, are we overthinking this?
User avatar
SteveHGraham
Posts: 7788
Joined: Sat Jan 17, 2009 7:55 pm
Location: Florida

Re: How close is close enough?

Post by SteveHGraham »

One of my problems was that the part had to be counterbored on both sides, and I didn't want one counterbore to be 20 thousandths off the axis of the other one. I will have to bore one side, flip it, and bore the other, and I don't want to lose too much accuracy when I do that. I think I would have to screw it up pretty badly to affect the function, though.

Sometimes I deliberately try to make parts better than they have to be, so I'll be in practice when I actually need to do something right.
Every hard-fried egg began life sunny-side up.
User avatar
WesHowe
Posts: 176
Joined: Sat Sep 19, 2015 9:52 am
Location: Huntsville, Texas

Re: How close is close enough?

Post by WesHowe »

I am no Adam or Keith, but I always try for a thousandth. If I was interested in production work, I would probably be happy with less precision most of the time, because when you're reducing something by 20 thousandths, it doesn't really matter if a few more chips come off one side that the other.

You can have more than 0.001 variance in a few inches if your lathe leveling or tailstock alignment isn't well done (or have loose gibs or excessive wear), and chucking to a tighter tolerance won't change those errors.
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: How close is close enough?

Post by pete »

I see a whole lot of threads started more so on the U.K. based forums than over here about people being overly concerned about the runout there 3 jaw scroll chucks have. For a lot of what there doing the parts may be quite small and usually at some point the part might need to be swapped end for end to finish so I guess there's some logic about there concern. But a lot just don't seem to want to use a 4 jaw to improve things either. My best guess is both Keith and Adam use the 4 jaw independants as much as they do simply because the normal 3 jaws don't repeat well enough to make the minute or two saved worth it. If you watch Keith real close in that Bar Z 4 jaw competition you'll see he's got one hand on the part while rotating it and feeling how concentric it is so it can be rough adjusted before putting an indicator on it for the final adjustments. Indicating in a previously machined surface pretty much demands either a 4 jaw or face plate to get things concentric. If the work can be fully machined without moving it and if your stock is oversize enough to fully clean up on all the surfaces then it doesn't really matter what chuck type you use other than a 4 jaw will hold round shafts much more securely. Some really odd shaped parts are still easier to hold on a face plate and tapping them into position imo. For really concentric shaft type work that can allow centers to be drilled I don't even use a chuck at all other than to hold a piece of scrap so a concentric center can be turned on that. It's still the easiest method and even more so for work that has to be moved to check a fit or swapped end for end. Rhetorical answer I guess would be the work requirements set what's close enough or not good enough. I usually do the same as Wes and aim for about a thou with a 4 jaw as good enough if I'm not trying to get a previously machined surface dialed in. Using a 10ths indicator can do a great job of using up your time and patience. :-)

I've got a book first written in 1907 about tool & gauge work. They show boring and grinding master gauges for a typewriter manufacturer on a sleeve bearing lathes faceplate using shop made hardened and ground tool maker buttons and a shop built dti and locating the holes to well under a 10th. All done by hand tapping the part into position and fixtureing it on the face plate. My guess is jig borers and grinders weren't invented yet, but that's how they got close enough to what they needed. I could probably measure to the limits of what they were doing, but not a hope I could locate and machine to those tollerances on my lathe even if I had a good tool post grinder.
User avatar
SteveHGraham
Posts: 7788
Joined: Sat Jan 17, 2009 7:55 pm
Location: Florida

Re: How close is close enough?

Post by SteveHGraham »

What I have been told is that the 4-jaw is supposed to be the standard chuck, and the 3-jaw is really for convenience.
Every hard-fried egg began life sunny-side up.
User avatar
Harold_V
Posts: 20232
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: How close is close enough?

Post by Harold_V »

In many cases, the degree of precision is more a thing of personal pride than need. If any of you have struggled in the process of mastering machining, you may understand. That's how one sets himself apart from those who can, and those who can't. Besides, striving for perfection serves one hell of a good purpose, that being the skill level achieved to perform tasks that would be daunting for those who work with a "good enough" ethic.

The day comes when each of us is called upon to perform difficult machine work. It can manifest itself in the way of tight tolerances, but there are other operations where tolerance may not be tight, but the operation itself is difficult.

I struggled in ways some may find hard to believe. I was told I wasn't worth keeping after my 90 day probationary period had elapsed, but one individual thought I had promise, so he encouraged upper management to reconsider. Thanks to this individual, I did achieve the goal---but it took several months of effort, and his constant encouragement and advice. He, and other supervisors, instilled in me the pride in doing a job well, and I carried that forward to the day I operated my own humble business, and it served me exceedingly well.

So then, when you do a project, consider that when you are finished, it represents you. How do you wish to be seen by others? Do you hope to have their respect, perhaps their envy, that you can do it right, and do it quickly? That's one of the things that comes from mastering machining. It often takes little more time, if any, to do it that way once you've mastered the process.

Patio commented to me some time ago that I show nothing---that I talk, but don't machine. Well, yeah! I don't. It's not that I don't, but I've spent the last 20 years busting my butt building my shop and house---where I also carried forth the idea that "good enough" wasn't. It may have been a mistake in building the house and shop, as it cost me one hell of a lot of time, but I am proud to show the work I did (along with the able hands of my very good wife, Susan). I do not apologize, because I know I did the very best job I could with the equipment I had, and the limited knowledge at my disposal. I am not a house builder---I am a machinist.

I like "pretty work". I've done a lion's share of it in my day, the bulk of which was in tooling and/or production parts. I rarely did any machine work for the common man, as that wasn't my goal, but I did make one thing that turned out great, and I'd like to share it here (I've shown it before, but it's been a long time. We have many new readers since then).

This focusing device was built for an 8" telescope, for a gentleman who worked at the planetarium in Salt Lake City.
Attachments
Telescope1.jpg
Wise people talk because they have something to say. Fools talk because they have to say something.
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: How close is close enough?

Post by pete »

I'd be proud of that if I'd done something half as good Harold.
User avatar
Harold_V
Posts: 20232
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: How close is close enough?

Post by Harold_V »

Thanks, Pete. The story is long, but the owner was so pleased with the focuser that he had my name engraved on it as the builder. It was a fun (although frustrating) project. The telescoping portion was made from 3" stainless steel tubing, .062" wall. It had to be round, and it was prone to moving while being machined, the result of stresses being released. I turned it three different times to get it round, then polished it under flood coolant, to keep it cool. Even slight heating caused it to move out of round. On the average, it was only about .045" thick after machining.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
User avatar
SteveHGraham
Posts: 7788
Joined: Sat Jan 17, 2009 7:55 pm
Location: Florida

Re: How close is close enough?

Post by SteveHGraham »

Harold, you're always on me about soft jaws. Here is a product YOU need to start using: a digital camera. If you're too cheap to get a new smartphone and a smartphone account, you can pick up a used smartphone for nearly nothing, use it as a camera, and upload the photos to your computer using USB.

http://www.ebay.com/itm/Samsung-Galaxy- ... SwAPVZJ658

I have this feeling you're using a 1997 Nokia.
Every hard-fried egg began life sunny-side up.
Mr Ron
Posts: 2126
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: How close is close enough?

Post by Mr Ron »

Harold_V wrote:In many cases, the degree of precision is more a thing of personal pride than need. If any of you have struggled in the process of mastering machining, you may understand. That's how one sets himself apart from those who can, and those who can't. Besides, striving for perfection serves one hell of a good purpose, that being the skill level achieved to perform tasks that would be daunting for those who work with a "good enough" ethic.
I wholeheartedly agree with your assessment of the "good enough" ethic. I always strive for perfection when others tell me "it's good enough". I don't always (never) attain perfection, but that doesn't stop me from trying. It is something that drives me. It takes me a long time to do any project and I won't be hurried. I think my work, although far from perfect, speaks for itself.
Mr.Ron from South Mississippi
User avatar
Gary Armitstead
Posts: 279
Joined: Sat Mar 02, 2013 12:35 am
Location: Burbank, CA

Re: How close is close enough?

Post by Gary Armitstead »

When I first started in the die sinking trade and became an apprentice over fifty years ago, an old journeyman (an excellent one at that) once told me a little saying. A few simple words to put all these "close enough" comments in perspective........

There are three types of die sinkers (any tradesman can fit in the spot). One uses his hands. One uses his hands and his brain. The third uses his hands, his brain and his heart. The third one is a Craftsman.
Gary Armitstead
Burbank, CA
Member LALS since 1980
Member Goleta Valley Railroad Club 1980-1993
User avatar
Harold_V
Posts: 20232
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: How close is close enough?

Post by Harold_V »

SteveHGraham wrote:Harold, you're always on me about soft jaws. Here is a product YOU need to start using: a digital camera.
I do, although it's ancient by today's standard. It's a Sony MVC-FD97. The picture shown was taken before digital cameras were on the market. It is a scanned picture, one I did with my scanner, years ago.
If you're too cheap to get a new smartphone and a smartphone account, you can pick up a used smartphone for nearly nothing, use it as a camera, and upload the photos to your computer using USB.
I'm pretty cheap, of that there is no doubt, but owning a smart phone, for us, isn't in the equation, as we live in a shadow and get no signal at all with our Tracfone. We use it when away from home, however. Some folks seem to get mixed results when here, with their cell phones, however.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Post Reply