Opinions for tolerance required on a "REAM" Callout?

[litlerob1]

I used to be a drafter. We did remove 'processes' from older prints, unless there was a reason for that particular process. The main reason is cost. If a supplier could produce a part to specs, ie size, surface finish etc. then why limit them. Also, if they had certain types of machines that gave a different finish, say Blanchard ground.
Now on the reverse of that, I was in an interview and mentioned this. One of the interviewers had an example of parts cracking, due to it being ground vs milling.
I also worried about how a part was dimensioned. I tired to dimension (GD&T), to the design intent of the part. I do remember on supplier wanting the part dimensions in a particular way. It was obvious to me that it suited their equipment and would be costlier to other to produce.
I think in the OP situation, it would be basically a 0.500 slip fit hole. IE 0.501 +/-0.0005

First I would like to say that a simple .5005" is not really a slip fit for .5. When we get down to .0005" interference, then it comes into Cylindricity, Straightness and Roundness not really hole size.

Meanwhile back at the Ranch, I can't even tell what you are talking about. You had an interview and......what? It was Ground but it cracked and it was obvious and you designed the intent of the Machine, and the interviewer was like waaaa, and GD&T and costlier??

 

[litlerob1]

Solution....get to reaming. This is not the last time you will ever need to do it.

Unfortunately this is probably true (even for a person who loathes Reamers).

 

[mhajicek]

An interpolated hole is never "round" or circular. How far out is expensive to measure.

A reamed hole is never "round" either. No physical object has perfect geometric precision. That's why we use tolerances. In this case the tolerance was not specified.

I would bet there are folks on here who use machines that can interpolate a hole with better cylindricity than a typical reamer will produce.

 

[litlerob1]

A reamed hole is never "round" either. No physical object has perfect geometric precision. That's why we use tolerances. In this case the tolerance was not specified.

I would bet there are folks on here who use machines that can interpolate a hole with better cylindricity than a typical reamer will produce.

;

 

[Johnny SolidWorks]

What's block tolerance for three places on the print? That's technically what they're asking for. Anything better than that's a freebie.

Good thought, but there's no tolerance block on the drawing.

 

[Johnny SolidWorks]

You asked for opinions....
If I was making the part I would throw a .5007 carbide reamer in (we have those on hand where I work) and let it buck. Probably around 45 SFM and .006/.008 per rev (steel numbers) and let it go. I would expect the hole to end up a snug .501 fit but I would assume the customer wants a semi precision .500 shaft or pin to slide through the hole.
I am not intending to be a dick.......but your problem is more about your fear of reaming and less about what is a crappy callout on a print.
Solution....get to reaming. This is not the last time you will ever need to do it.

It's not so much a fear of reaming as it is super inconvenient on my machine, and the inconvenience of the process itself.

That said, one of the reasons I'm looking for a rule of thumb tolerance is because I have a handful of 501 reamers (even some shorties) but at what point do I call them 'worn out' and toss them in the bucket?

If I'm running a brand new .501 reamer and getting a hole that's consistently .501+/-.0002, do I swap the tool when I start dropping a tenth? two? five?

I'm good with following an industry standard 'best practice' even if I don't understand it fully - I'm just not crazy about it.

Maybe a decent question: following manufacturer's specs for SFM and % of material left to remove, what kind of life should I expect out of a .501 reamer in mild steel?

Thanks for the input all!

 

[litlerob1]

It's not so much a fear of reaming as it is super inconvenient on my machine, and the inconvenience of the process itself.

That said, one of the reasons I'm looking for a rule of thumb tolerance is because I have a handful of 501 reamers (even some shorties) but at what point do I call them 'worn out' and toss them in the bucket?

If I'm running a brand new .501 reamer and getting a hole that's consistently .501+/-.0002, do I swap the tool when I start dropping a tenth? two? five?

I'm good with following an industry standard 'best practice' even if I don't understand it fully - I'm just not crazy about it.

Maybe a decent question: following manufacturer's specs for SFM and % of material left to remove, what kind of life should I expect out of a .501 reamer in mild steel?

Thanks for the input all!

This is a link to the PDF of the ISO standard H value for fits and tolerances;;

https://www.google.com/url?sa=t&rct...Ch6.8wGO.pdf&usg=AOvVaw1GkRvhu_IUGCJZSsjKlGEV

 

[Guest]

If I had to make an assumption on tolerance I would agree with the slip fit on a .500 dowel pin crowd. No way am I holding +/-.0002 unless it is clearly stated. Even most 4 place decimals are +/-.0005.

 

[kenton]

It's not so much a fear of reaming as it is super inconvenient on my machine, and the inconvenience of the process itself.

That said, one of the reasons I'm looking for a rule of thumb tolerance is because I have a handful of 501 reamers (even some shorties) but at what point do I call them 'worn out' and toss them in the bucket?

If I'm running a brand new .501 reamer and getting a hole that's consistently .501+/-.0002, do I swap the tool when I start dropping a tenth? two? five?

I'm good with following an industry standard 'best practice' even if I don't understand it fully - I'm just not crazy about it.

Maybe a decent question: following manufacturer's specs for SFM and % of material left to remove, what kind of life should I expect out of a .501 reamer in mild steel?

Thanks for the input all!

As far as I know the only rule of thumb for when to dispose of a reamer is when it no longer make a hole that is in tolerance. Or when you are tired of pulling it out of the drawer, reaming a hole, finding it is cutting undersized, trying to make it cut larger by slowing down the feed rate, then putting it back and getting another until you find one that cuts on size (standard practice at a former employer).

Since their is no tolerance I would guess that their was either an internal standard that was lost or you are not privy to. Or they expected that as long as a 1/2 dowel pin fit it would be fine.

If there is a common standard I'm unaware of I would love to learn about it, I come here to learn. Though I'm not sure what ISO H values have to do with either reamers or an old print with inch dimensions and no H value specified.

 

[Jim7511]

I have a saying for times like this. "Unless otherwise specified you get what I give you."

I see prints like that often and they can call them out multiple ways. Just helix a slip fit for a 1/2 dowel pin.

No need to over think it. Whoever drafted the print didn't.

I agree with this 100% slip fit for 1/2" dowel. I see this callout for Ø.501 holes and generally understood as slip fit.

 

[toolsteel]

If I had to make an assumption on tolerance I would agree with the slip fit on a .500 dowel pin crowd. No way am I holding +/-.0002 unless it is clearly stated. Even most 4 place decimals are +/-.0005.

I agree...

If someone wants .0002" they better at least have the courtesy to ask for it.

 

[anonimasu]

I ran into a problem myself once with the same kind of reasoning by assuming that the general shaft tolerances applied.

Long story short.
My customer supplied no tolerance for a run of parts and when asked for the tolerance the customer replied that the tolerance was nothing critical.

After a few days I got a bag back of 400 plastic “spacers” as my customer called them when handing me the undimensioned print without any tolerance specified with a marking on each do the bags saying they were off by -0.005/-0.002 from nominal all parts were comfortably within the limits of iso h7 for a 20mm shaft.
I would have passed up the job or made a short trial run of parts to be measured/verified by my customer if they properly had called them motor shafts.

My pet peeve with the issue is that it is impossible to deliver parts to a customer that meets their expectations unless they communicate them or provide any means to infer them.(I prefer not to rent a psychic and hope my assumption is correct).

 

[Mechanola]

What comes out from this thread is that people did communicate in earlier times, verbal, orally, they made knowledge common. One has to imagine a talk such as We want a dowel pin to slip in here.—Alright, clear. Today’s prevailing egocentrism takes everything back to What the heck is that? But don’t worry, counterpart times will be back in 2097.

 

[Mike1974]

First I would like to say that a simple .5005" is not really a slip fit for .5. When we get down to .0005" interference, then it comes into Cylindricity, Straightness and Roundness not really hole size.

Meanwhile back at the Ranch, I can't even tell what you are talking about. You had an interview and......what? It was Ground but it cracked and it was obvious and you designed the intent of the Machine, and the interviewer was like waaaa, and GD&T and costlier??

Thank you! Used to argue with a guy about this. He insisted that he would wireburn his dowels .0005" oversize and it was great. A standard(?) dowel is .0002" oversize, then you get into location/position tolerances, and whaddya know, damn thing doesn't fit OR you have to beat it together.

 

[Bobw]

What comes out from this thread is that people did communicate in earlier times, verbal, orally, they made knowledge common. One has to imagine a talk such as We want a dowel pin to slip in here.—Alright, clear. Today’s prevailing egocentrism takes everything back to What the heck is that? But don’t worry, counterpart times will be back in 2097.

I'm lucky enough to have a customer like that... Over the years I've made 100's of unique parts for his
contraptions, and only one single time did I get more than a quick sketch.. And that one time was a full
size 'print' that was actually drawn on a drafting table (he has 3 of them, and actually uses them occasionally).
No computers, no internet access, no Cad, No Cam, a flip phone... And he does have a CNC machine that he finger
bangs. His son who also works there does have a smart phone.

I usually get a handful of parts and instructions to make 'This' fit in 'That'...

Great customer... He even buys the material, and cuts it up, and pays COD(his choice).
He gets the "Good" pricing and the quick turn arounds...

This isn't some fly by night place making luggage racks and brush guards.. He makes all kinds of crazy
complicated machinery.. Making some repair parts right now for a machine he put into service
over 30 years ago.

That "ream .501" would have been a circle on a ripped piece of dirty note book paper, and it
would have been labeled 1/2", and there would have been a greasy part with it and verbal instructions
that 'this' has to fit in 'there'...

 

[Mechanola]

What the goold old times were about

 

[litlerob1]

I'm sorry you guys that are reminiscing about the good old days. Indecipherable drawings on Beer coasters, note paper, a shitty dirty old part, Bearing fits where the Bearings were blown out the side!!! Oh yeah I miss that. Some hack with a pencil scribbled out the old and re-wrote new notes. Let alone realizing they made a mistake and scribbled out the new ones and re-wrote the old ones. Coffee mug ring on it. I don't miss that shit at all. I get what you're saying, but lets remember the past for what it is.

CAD files have no ketchup stains on them. They NEVER been dropped on the floor and walked on. I like working from a paper Drawing/Print. Just not the ones drawn with a Quill and Ink.

R

 

[triumph406]

I bet if a print said

"ream for slip fit with 1/2" pin"

75% of machinists wouldn't have a clue what that meant and how to go about achieving a slip fit, or even choosing the right diameter reamer to begin with.

Asking for a "light press fit would probably cause a complete melt down for most machinists"

 

[triumph406]

What's block tolerance for three places on the print? That's technically what they're asking for. Anything better than that's a freebie.

So if the block tolerance for .xxx is +/-.005, you think the tolerance on the hole will be .501 +/-.005?

if it says REAM .501 you'd expect that a typical .xxx wouldn't apply. although I guess you could argue otherwise

 

[Mike1974]

I bet if a print said

"ream for slip fit with 1/2" pin"

75% of machinists wouldn't have a clue what that meant and how to go about achieving a slip fit, or even choosing the right diameter reamer to begin with.

Asking for a "light press fit would probably cause a complete melt down for most machinists"

What kind of machinists do you work with??
Although if I saw the first note about 1/2" pin I would ask them (someone) to clarify what type of "pin" they are talking about.