Dimensional Quandry?

[Peter Warcholyk]

Hello Folks,

Came across this on a print for a Japanese part.
I'm not sure how to interpret it.

I'd appreciate your input.

Dimension on print is as follows; 6.5mm -0.05mm -0.15mm. There are quite a few dimensions like this on the print. The one that I have indicated is across the parts thickness in one area.

How do you interpret this?? I can't recall seeing a "double", "one-sided" dimension.

Thanks in advance for your assistance.

Blessings,
ZydecoPete

[craiger_ny]

I remember this and every time it comes up I forget what the heck it is. I want to say your limits are 6.35 to 6.45. I don't know why I keep forgetting the application for this.

I think J knows.

[Jan d.]

They made it easy for you: per ISO tolerance system for shafts, they could have put on the print 6.5 mm g6. This is a standard tolerance per the ISO standard. They were nice to you and decided to convert it to something that you don't need an encyclopedia to translate.

It seems to me that the Japanese engineers realized that their parts would be made in the US, and therefore refrained from using the ISO tolerance limit scheme. And in that scheme it is VERY common to see the "double one-sided" tolerance limits. Batteries of profs and PhD's have spent rainforests in trees arguing that this is the right thing to do. They came up with certain applications where you need exact clearances. And for every applications, they define what call needs to be used on the print. So for what the Japanese engineer tried to do, they probably specified that g6 was giving the right limits.

So they are probably right... That's what the Japanese engineer must have thought...


Jan.

[Matthew D. Hoedeman]

I have seen it before myself on sheet metal parts. The cad is to a perfect design assembly, but they want (need) clearance so that the components go together without using hammers, so they use the double negative (or positive) tolerance so that the final part is in a sense, NOT to cad data, but to assembly requirements.

[Perry Fisher]

What Matt says.

When I worked in a T&D shop we had some catalogs from Misumi, a Japanese die component supplier, that had tables of all the shaft and bore tolerances Jan references.

[Lawrence Hardtacke]

Follow up question:
If it were say an "X" axis tolerance
The Tolerance band would be entered as -0.05 & 0.15
How do you set up the "T" Tolerance band? Wouldn't this depend on whether you make contact before or after the Nominal?

[Matthew D. Hoedeman]

Yep. that is something you would have to figure out, it will depend on which side you measure from. And yes, the POS tol value woudl be the smaller negative tolerace, entered AS a negative. Normally you neter the tolerance values as the ABSOLUTE value (ie, you don't use a negative sign when entering the negative tolerance value, it ASSUMES it is negative).

[Peter Warcholyk]

Many thanks to the answers thus far !!

Lawrence, I'm not following what you're saying. The tolerance is not a "minus" and then a "plus", it specifically is a "dimension" followed by "minus tol", and another "minus tol".

Best Regards,
ZydecoPete

[Lawrence Hardtacke]

Yes but in order for PC-DMIS to understand you must enter a (-) minus in front of the positive tolerance band. Remember two negatives make a positive and a plus and minus become negative.

[djayne]

We have this on almost every print in house (Japanese Company). It really messes with these engineers when I leave it like this on the CMM printout! Especially when the axis is a negative and I have a plus plus tolerance. Some new engineer is always coming in here full of himself thinking he's found an error in the way we've been measuring a part for years. It was annoying at first but now it's fun stuff!

[djayne]

Oh yeah - sometimes on a diameter, it has something to do with a press fit as well ????

[craiger_ny]

What Matt says.

When I worked in a T&D shop we had some catalogs from Misumi, a Japanese die component supplier, that had tables of all the shaft and bore tolerances Jan references.

Shafts dammit that is where I have seen it on shafts and couplings for fit up like Matt said.

[Peter Warcholyk]

Thanks to All !!

Sorry about the delay in the follow up.

Blessings,
ZydecoPete

[emkay4597]

I'm thinking of it as X - Y - Z where X is the nominal and the first - is a minus sign and the second is to be read as "through", would this be right? so X minus (Y through Z) so X minus any value between Y and Z would be acceptable?

[Ken379128]

Had the same thing on the 1 print we have from japan