Questions about standards (measuring rods) for micrometers

[mmcmdl]

I very rarely have to hold anything under .0005 now unless it's bearing related . If I make something for myself , I design the G-job so it doesn't have to be a close tolerance . For my "work" these days , I usually have to hold +/- half a broomstick . Best bet for learning , always aim for your nominal dimension . Shoot for the middle .

 

[middle.road]

"I am just having fun in the shop" -- That is the main thing. Be it whatever, as long as you're having fun doing it.
Try making up some of the mechanical puzzles that are out there. Good experience and fun to create.

I get my money from my job which has nothing to do with machining, so all of the work in my shop is hobby stuff. I have the most fun when I am challenged; the more challenging, the more fun. The best day is when I fail because I make sure to learn something from it.
Generally, after I make something it goes out on the “metal” shelves which is a euphemism for the scrap area.
In machining school, they recommended to shoot for a thou tolerance and expect to fall short. They also said that if a tolerance is not written on the drawing, then assume .005”.
Understanding that I am just having fun in the shop, my target tolerance was chosen as .001” for now because I don’t think there will ever be any temperature control out there. My best case scenario of .0003” is probably optimistic, considering the lack of a controlled climate.

So my goal of .0003”-.001” tolerance is chosen, and not required by any means. To be honest, I would be very pleased if I hit a thou.

 

[mmcmdl]

In machining school, they recommended to shoot for a thou tolerance and expect to fall short. They also said that if a tolerance is not written on the drawing, then assume .005”.

Form , fit and function . Don't mill if a saw cut is adequate . Finish specs also determine what is needed . Never give a customer " more than what is needed " , it'll quickly eat up your time and profit .

 

[erikmannie]

1) I use Mitutoyo mic standards and they're pretty okay for a quick check but they are not good enough to calibrate a mic.
2) I always clean the mic faces with Kim Wipes and gently close them to make sure the mic is zeroed before use. I could probably dispense with this because the mic always reads zero.
3) Mic standards (rods) are not used often so if you buy good ones used, they will probably be okay. If you really want to know if they are accurate, send them to a calibration lab and have them report their lengths so you know what they really are. Because a mic standard is marked 1" or 2" or whatever, it doesn't mean that is the actual length to a millionth of an inch. If you must know how long they are, have them measured by a lab. You just have to keep in mind that that rod was measured in a lab and its length may/will be different in your shop and in your hands ... but it will be damned close.

Your unasked question is actually about trust. Can you trust the rods to be accurate enough to give you confidence in your measuring tool? This is not about the level of work you can actually do; it is about trusting the readings you get.

Just so you know, calibrating your tools is a personal choice. Calibration refers to the act of evaluating and adjusting the precision and accuracy of measurement equipment. This is different from Certifying it, which is done by a lab; they will tell you if the instrument falls within the acceptable standards for that tool. Certification is done in a controlled environment by techs who know what they're doing, using equipment that is far more accurate than most of us own.

I calibrate my own mics and calipers. I now use a Mitutoyo Cerastone Grade A set that is specifically made for calibrating micrometers and is accurate to between 4-6 millionths of an inch. I follow the standard procedures to check my tools and this gives me enough confidence in them to trust them. I do not need to certify them or have them certified; I just need to know I can trust their readings. How accurate I can work is a separate thing.

I don’t know if I’m doing it right, but I clean the anvils and check zero on a 0-1” or 0-25mm mike before an important measurement (as opposed to roughing). I use a standard on a, e.g., 1-2” or 25-50mm mike in the same manner. Does anybody ever just take a large mike out of the box, clean the anvils and measure the work? Maybe I am wasting time by using a measuring rod to check the zero each day.

I don’t think I would have the money for any calibration services.

 

[erikmannie]

I give a lot of credit to you machinists who have customers. I get enough of that at work.

In my shop, I am too selfish about my creative freedom to allow in others who might alter the path that I want to take. Again, I get more than enough of that at work.

Having said that, I retire in a little over 11 years, and I might change my tune when I need customers’ money.

 

[mmcmdl]

No need to check everyday Eric . Even in DOD shops , they only require tools to be calibrated every 6 months . Clean your anvils when the job is finished , just for storing tools .

 

[mmcmdl]

In my shop, I am too selfish about my creative freedom to allow anyone else to restrict what I do. Again, I get more than enough of that at work.

Me too ! I haven't had a customer in 25 years . I send them to a machine shop . I got tired of spending days making parts for neighbors that they could purchase for a buck . I had plenty of those type of jobs .

 

[erikmannie]

Me too ! I haven't had a customer in 25 years . I send them to a machine shop . I got tired of spending days making parts for neighbors that they could purchase for a buck . I had plenty of those type of jobs .

Customers can be great, but they can also be very annoying!

I stopped taking work when a few people haggled on the price. They did not appreciate the investment in time, money and effort that I had made. This is why I have so much respect for people who do paid work. They have to put up with a lot of foolishness.

 

[mmcmdl]

Customers can be great, but they can also be very annoying!

Machining is annoying when doing it for money , that's why my shop has been " shut down " for many years . My worst customer was my neighbor with his Gravely addiction !

 

[mikey]

No need to check everyday Eric . Even in DOD shops , they only require tools to be calibrated every 6 months . Clean your anvils when the job is finished , just for storing tools .

I agree with Dave. Also, make sure the faces of your 0-1" mic are NOT touching when you store it.