Max & Min Dimensions

[ModulusCT]

Simple question... When is the use of MAX or MIN appropriate?

When would a dimension like .060 MAX be preferable over .060 +.000 / -.010?

Am I telling the machinist by applying a MAX dimension that don't care if the dimension is .000? 9000 ft for MIN? My guess is yes... But then why would anyone want to use these terms?

 

[SDETERS]

We use these terms a lot. For Example of threads and a tap drill. We specify A max depth for the tap drill and a min full thread depth for threads. This way we can control the thread depth but leave it up to the machinist on how deep to run the tap drill with in our max limit.

 

[drawoh]

ModulusCT,

I have used the MAX dimension when I draw something that looks like an aluminium angle. I specify a radius of 12mmMAX. The minimum acceptable radius is zero, as you noted above. This allows the fabricator to use stock aluminium angle, if he has any lying around.

JHG

 

[ewh]

I also use the terms frequently, when specifying a fillet radius for example. If stress is not an issue, I see no reason to tie the machinist to a tolerance unnecessarily.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[PeterStock]

I do not like to use MAX and MIN dimensions. Used like Sdeters states for threaded holes is good, but otherwise I prefer to explicity give an acceptable range. If the dimension is .060 MAX, then 0 needs to be acceptable. If the dimension is .060 MIN then 99999.999 needs to be acceptable, if the part will allow it. The min dimension for the full thread in Sdeters example was limited by the depth of the tap drill. If that dimension was not given, then it must be acceptable to drill and tap thru the entire part.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

 

[ModulusCT]

OK -

So use carefully... And probably sparingly, in only a handful of situations. I like the thread depth use and the min radius sounds like a handy application for me.

Thanks.

 

[ewh]

Agreed, use sparingly. I also agree with Peter's point that extremes must be acceptable to use the terms. There are situations where extremes are allowable.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[ctopher]

If you measure from an edge to a center of a hole, then indicate "max", the machinist could give you half of a hole on the edge.

Chris
SolidWorks 09, CATIA V5
ctopher's home
SolidWorks Legion

 

[PeterStock]

And watch what you use for a nominal. If a vendor takes you model and runs with it that R.060 MAX fillet could easily come in .070 or so and cause an interference. Yes it is not to the print, but you would have needed to inspect that feature to find it.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

 

[ewh]

If in doubt regarding the use of the terms, you could always indicate allowables in your tolerance, i.e. "R.06 +.00/-.06" is essentially the same as "R.06 MAX"

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[ctopher]

It also determines what type of fit you need.

http://www.caddownload.blogspot.com/2009/06/learn-gd-basics-with-examples-limits.html

Page 28:

http://engineering.dartmouth.edu/mshop/pdf/introdr.pdf

Chris
SolidWorks 09, CATIA V5
ctopher's home
SolidWorks Legion

 

[looslib]

We used a min/max value on a radius for glass headlight molds around the lugs that orient the lamp into your car. We didn't have it at first, just had the finish shop do a blend with no spec called out. On one batch of molds the finish guys over worked the radius and the glass was failing inspection because the radius was too large and wouldn't let the lamp seat properly. Modified the drawing with a min/max radius and the problem was solved.



"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[SDETERS]

We also have use it in a tapered core in a die casting or any process that one needs to have draft. You call out the top of the core a Max Diameter and at a gauge dimension depth, call out a min diameter. So we let the manufacturing process Die casting help in determining the min max. So one can have a straight walled die casting or a one with draft with in the limits of the max call out at the top of the core.

 

[powerhound]

looslib,

You bring up a major point of contention I've had with a customer I used to have to deal with. With the original print there was no specification on the radius yet you were getting good parts, then one day you got parts that didn't work yet they were manufactured using the same print. Wasn't there a huge uproar that originally blamed the manufacturer for the error since the print had "worked" in the past? The customer I dealt with had used certain vendors for years and when they went through a big cost savings crusade, they had things re-quoted and began to use different vendors. The result was a lot of bad parts made to print. The prints were not very good and the previous vendors had worked their way through the issues over the years and had figured out what the customer had wanted. The first knee jerk reaction was that the new vendors were morons because the prints were yielding good parts before the switch and it took an act of Congress to get them to see that the prints were the problem, not the vendors. The biggest issue was the misuse or non-use of GD&T.

Anyway, I don't mean to hijack the thread, I just wanted to know if the manufacturer originally got the blame for the non-functional parts.

Powerhound, GDTP T-0419
Production Manager
Inventor 2010
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[dgallup]

I use a lot of max radii on turned part inside corners. The tool can never produce a sharp corner but even if it could, zero would be OK (no stress issues). Too much radius from a broken down tool can be a problem. Just using a max dimension makes it easier to inspect. Typically I will model at half the max value.

I use a lot of max values for draft angles too. I don't care if the mold maker uses zero draft if they can get the part out of the mold. Usually, the mold maker will use very nearly all the draft I give them.

You definitely have to think through the consequences of all your dimensioning choices.

 

[ModulusCT]

Thanks everyone... Some valuable info in this thread.

 

[looslib]

Powerhound,
It was all internal to the parent corporation. I worked in the mold shop where we machined the molds for the glass plants to form the product.
We did a lot of fine finish polishing on the molds by hand and these blend radii where part of the hand process.
Once we understood the problem and had inspected the molds, a simple drawing change and instructions to polish guys and the issue was resolved.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[KENAT]

Assuming you work to ASME Y14.5M-1994 look at section 2.5 "SINGLE LIMITS".

It defines the meaning of Max & Min and gives examples of when to use them.

The issue above where MBD gets involved is significant and has come up in other MBD related threads.

I think max/min has been discussed before too.

As to why to use them, it's to maximize the likelihood of “good parts” while ensuring function.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[cadman1964]

We use min and max here and there on our detail prints. I mainly use them on pockets and cut outs. I place the biggest radius permissible and then put max. reasoning for this is, now the machinist can use what ever size of end mill, or what ever, to make the feature.

Solid Edge V20

 

[PeterStock]

On some slots here I have seen the end radius called out like this:

4X R.030 MIN TO 2X FULL R MAX

I was confused at first but I figured it out and plan to use it where appropriate in the future. One more exception to my dislike of MIN and MAX.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net