Questions about a Casting Drawings 3

[popm]

A call-out note for two holes on a casting drawing say:


?.468 Drill
?.500 Reground E.M.
?0.5025 Reamer
2X?.5025+/-0.010 THRU

questions:
1. what's E.M. represent?

2. Reground is supposed to have a higher accuracy than "Reamer", why is the "reground" before "Reamer"?

3. Is "Reground" same as "ground"? why "RE-"?

thanks!

 

[ctopher]

Machining steps called out on a drawing is a recipe for trouble and errors. Call out the hole as the final dimension with tolerances and leave it up to the machinist which reamer/etc to use.

Chris
SolidWorks 10 SP4.0
ctopher's home
SolidWorks Legion

 

[KENAT]

What Chris says is pretty much correct per ASME Y14.5 section 1.4. Only exception is where the process has an impact on the performance.

So arguably the important part is the final dimension 2X?.5025+/-0.010 THRU.

I suppose if the EM means Electron_beam_machining then maybe it imparts properties to the material which are significant.

Posting guidelines faq731-376

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

 

[HGMorgan]

I agree with ctopher, but will explain the process anyway.
E.M = End Mill
Reground means they want to make sure the End Mill is sharp and to size.

We do this process a lot on holes that have a tight location tolerance.
1. Center Drill hole
2. Undersize Drill hole
3. Use EM in a drill cycle and bore down, say .2 deep
(This squares up and fine tune locates the hole for the reamer. A basic peck drill cycle can wonder off center, and a reamer would follow that, so the EM drill cycle brings it back to center.)
4. Ream hole

 

[KENAT]

End Mill, doh! Of course, that makes more sense. I've seen similar process done.

Posting guidelines faq731-376

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

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

 

[rhythmmagic]

Reground E.M in this application would probably stand for a reground endmill. In machining a casting, the end mill will straighten the hole on location from the drilling operation.

 

[juergenwt]

Why would you specify .5025 +/- 0.010?
Why not just .500 +/- 0.008?
Center drill, drill 3/8, drill 31/64, drill 1/2 should do it unless there is a requirement for a specific finish.

 

[MechEng2005]

Probably because the assembly is designed for a hole .5025 +/- 0.010.