Foundations of Mechanical Accuracy by Wayne R. Moore

[rmcphearson]

I read this recently and had a hard time putting it down. I would like to open a discussion here about some of the quotes and notes I took.
1) "Basic to man's behavior is his ability to determine, modify, and adapt to his environment."
2) "...greatly enhanced the scope of the book. I single out particularly James Bryan, of the Lawrence Radiation Laboratory, University of California, with whom many informative discussions were held."
3) "Milling the gibs caused more machining distortion and somewhat permanent instability until the gibs were stressed relieved. In other words, it is possible to machine-in instability."
4) "Stability of the casting is assured initially by slow cooling in the mold. However, the method of machining may also introduce stresses. Major functional surfaces of machine members, such as the ways, should be single-point planed."
5) "The theory that a cast iron part must be exposed to the weather to rest and 'age' in order to stabilize it is a carry-over from the past."
6) "Awareness of the potential rigidity in this design came from a technical report* on the rigidity of a welded steel surface plate..." *Adolph Kleinsorge, "Welded Surface Plates," Bulletin 60-WA-241, American Society of Mechanical Engineers, New York
7) "The plate was supported on its underside at three points for geometric stability."
8) "4:3 relationship (which is the usual longitudinal to cross-travel relationship in machine travel)."
9) "The type of scraping stroke found most satisfactory is the 'half moon'. The advantage is that the stroke starts from the valley, reaches its greatest intensity directly on the spot (plateau), and again fades to nothing as it passes to the other side. The type of cut used also depends on the purpose for which the surface is to be used. For instance, a surface to be used as a master for bearing should be cut deep for longer life, whereas the cut should be shallow on the ways of a machine where rollers are to be used for smoother rolling action."

Whew...that's all for now. I'll add more later.

-Roland

 

[MCritchley]

5) "The theory that a cast iron part must be exposed to the weather to rest and 'age' in order to stabilize it is a carry-over from the past."

Interesting that people including many on the forum will say that storing castings outside for years stabilizes them. The line above is gospel from the man himself, there have also been numerous papers posted agreeing with Wayne Moore. The line about this misnomer being a carryover from the past is spot on.

Incredible book, we should all be thankful the Moore took the time to publish it.

3) "Milling the gibs caused more machining distortion and somewhat permanent instability until the gibs were stressed relieved. In other words, it is possible to machine-in instability."

After reading this statement i started stress reliving cast iron scraping tooling several times. It does help stabilize the machined surface layer.

 

[rmcphearson]

Incredible book, we should all be thankful the Moore took the time to publish it.

I sure am thankful. "A simultaneous characteristic of the company is it's desire- and rare ability - to communicate the intimate knowledge it has acquired of these specialties to a wide audience."

 

[IceCzar]

Major functional surfaces of machine members, such as the ways, should be single-point planed."

If only my shaper was larger.
I really need to finish that book

 

[Richard King]

If you want an advanced discussion on machine tools construction. Look up and read DR. Alex Slocum of MIT. Midland on here is a friend of his and an MIT grad.

The Moore Book is wonderful and many Machine Tool Builders have it in their libraries. For a rookie who picks it us, it scares them because it is about jig bore scraping and .00005" per 12" accuracy. Once they get a taste of precision it's super. 3 - plates, 3 points, temp control, etc. - great !! The book can still be purchased from Moore Special Tool in Bridgeport CT.

One thing that I get a kick out of, when they picture an Indicator it's a Last Word and electronic indicators. Back when it was written that's all they had. Maybe Federal too.

Matt or Mcritchley could have gone to MIT in my opinion and he has a friend also named Matt ( 1 & 3) who graduated #1 in his MIT class.

 

[jim rozen]

Notable the *exensive* section on achieving close-loop temperature control. Not yet a 'thing' when that book was done.

 

[dgfoster]

For those of you who have been recently been poring over Moore, does he say how much better single point planing is vs common milling. Undoubtedly both will induce stress. Did he detect a quantified difference? If so, how much difference i.e. 20 millionths vs 80 millionths depth of stressed metal. That would be interesting to know given the relative scarcity of planing services vs milling. Then a person could judge how much trouble it is worth to do one vs the other.

I do not recall reading that quantitative difference, but it has been a while…

Denis

 

[TGTool]

For those of you who have been recently been poring over Moore, does he say how much better single point planing is vs common milling. Undoubtedly both will induce stress. Did he detect a quantified difference? If so, how much difference i.e. 20 millionths vs 80 millionths depth of stressed metal. That would be interesting to know given the relative scarcity of planing services vs milling. Then a person could judge how much trouble it is worth to do one vs the other.

I do not recall reading that quantitative difference, but it has been a while…

Denis

I'd be curious too how Moore quantified that. And they might have been simply going by experience of how castings responded or how many more scraping cycles it took to get repeatability. It's also possible that their experience was conditioned by tools of the time. If they were using carbide insert cutters in production (reasonable guess) they might have been negative rake geometry to match the carbide grades and what was known about production machining at the time. So the action of negative rake tools might have induced surface stresses they wouldn't have seen with the different cutting action of planers or maybe even HSS positive rake cuts.

 

[Peter from Holland]

I friend of mine makes chasers
The material must be planed If milled the teeth break premature
So there is defenitly a difference between milling and planing Even nowadays
Peter

 

[dgfoster]

I friend of mine makes chasers
The material must be planed If milled the teeth break premature
So there is defenitly a difference between milling and planing Even nowadays
Peter

No one would deny the processes are different and may induce different stress patterns.

The question is how much practical difference do the two processes make on CAST IRON (chasers are made of what tool steel and in what dimensions and what pattern?) in preparation for scraping. Would planing save a scraping pass? Maybe Five passes?Seems very unlikely. But, a.flat statement that one process is better than another leaves open the crucial question of how much better.

Metrology is full of such unquantified statements leading in some cases to wasted effort and expense. See my recent thread on linear expansion of a steel bar where I attempted to quantitate hand contact and thermal expansion for a single specific instance. I did this real-world test as people were making recommendations for heat-related alterations to my angle plate that were likely unnecessary. Incidentally, I am machining a casting today on which I plan to do follow testing to see if those initial findings are borne out in practice.

Pics and results will be posted in a separate thread.

Denis

 

[MCritchley]

Dennis, cutters wear the most on the entry and exit on the cut as that is the least stable part of the cut. What does that mean in planning vs milling stress concentration? Milling will have millions of individual cuts, meaning millions of individual entries and exits. That will also give you millions of individual elastic deformations in front of the milling tooth. I consider each cut to be a collision with the reaction being metal sheared away.

Planning a gib might have like 100 cuts and those entries and exits are on the extreme ends of a gib or table.
This means less induced machining stress on a planned part. This would all be easy to quantify if one had the time. A micro hardness tester would be quite valuable so you could map the hardness and look at the post machining warp.

A good place to look for evidence of this interesting phenomenon would be to compare a carbide lathe insert's working life to that of an indexable milling cutters life. The lathe inserts last longer meaning it stays sharper longer and will induce less stress into the material. Its impressive how much volume of chips one can make with 1 lathe insert vs 5 inserts on a milling cutter.

 

[dgfoster]

Dennis, cutters wear the most on the entry and exit on the cut as that is the least stable part of the cut. What does that mean in planning vs milling stress concentration? Milling will have millions of individual cuts, meaning millions of individual entries and exits. That will also give you millions of individual elastic deformations in front of the milling tooth. I consider each cut to be a collision with the reaction being metal sheared away.

Planning a gib might have like 100 cuts and those entries and exits are on the extreme ends of a gib or table.
This means less induced machining stress on a planned part. This would all be easy to quantify if one had the time. A micro hardness tester would be quite valuable so you could map the hardness and look at the post machining warp.

A good place to look for evidence of this interesting phenomenon would be to compare a carbide lathe insert's working life to that of an indexable milling cutters life. The lathe inserts last longer meaning it stays sharper longer and will induce less stress into the material. Its impressive how much volume of chips one can make with 1 lathe insert vs 5 inserts on a milling cutter.

All above seems true enough and is interesting.

How many scraping passses are saved by planing vs milling?

Denis

 

[Peter from Holland]

All above seems true enough and is interesting.

How many scraping passses are saved by planing vs milling?

Denis

You are going to tell us soon I supose

 

[Peter from Holland]

And then we have grinding to evaluate the surface for

 

[Tyrone Shoelaces]

Dennis, cutters wear the most on the entry and exit on the cut as that is the least stable part of the cut. What does that mean in planning vs milling stress concentration? Milling will have millions of individual cuts, meaning millions of individual entries and exits. That will also give you millions of individual elastic deformations in front of the milling tooth. I consider each cut to be a collision with the reaction being metal sheared away.

Planning a gib might have like 100 cuts and those entries and exits are on the extreme ends of a gib or table.
This means less induced machining stress on a planned part. This would all be easy to quantify if one had the time. A micro hardness tester would be quite valuable so you could map the hardness and look at the post machining warp.

A good place to look for evidence of this interesting phenomenon would be to compare a carbide lathe insert's working life to that of an indexable milling cutters life. The lathe inserts last longer meaning it stays sharper longer and will induce less stress into the material. Its impressive how much volume of chips one can make with 1 lathe insert vs 5 inserts on a milling cutter.

Milling leaves a slightly glazed skin on cast iron. You need to get under that with your scraper. With a planed surface you don’t get that glaze and you can get right at it. The difference isn’t that problematic in the great scheme of things but it is an issue. Grinding is worse still.

Your explanation of why this happens is pretty credible to me.

Regards Tyrone.

 

[dgfoster]

I probably will not be evaluating myself. I really was hoping someone like Moore would have done so. Otherwise, we seemed to be nudged toward choices for "good" reasons, but with unknown benefit. So, then you are left wondering if "it is worth it" to go out of your way and how far out of your way to follow certain advice. Quantifying it in some way makes the decision more reason-based. Maybe it simply boils down to Tyrone's observations above making the difference noticeable but not a big deal. I have tended to think of it that way myself but could really not defend that prejudice beyond very limited personal observation and hearing what others have said.

Denis

 

[MCritchley]

Grinding induces quite a bit of stress into material, it's quite a bit different from milling or planning.
I had a stress relived plate that i scrapped both sides that was 6 x 12 inches that made up a test coupon for surface grinder evaluation. The first time I ground the surface the plate warped .001"! This was with a open coarse wheel meant for cast iron. Again, if you do a micro hardness test you will notice that a ground surface is quite a bit harder than one of a milled surface.

It's also much harder to push a scraper through a ground finish then that of a milled finish.

 

[lucky7]

^^^ certainly my experience as well.

 

[wildo]

For those of you who have been recently been poring over Moore, does he say how much better single point planing is vs common milling. Undoubtedly both will induce stress. Did he detect a quantified difference? If so, how much difference i.e. 20 millionths vs 80 millionths depth of stressed metal. That would be interesting to know given the relative scarcity of planing services vs milling. Then a person could judge how much trouble it is worth to do one vs the other.

I do not recall reading that quantitative difference, but it has been a while…

Denis

I was told when I was an apprentice, and I believe it now, that metal 'enjoys' being cut on a shaper due to the stress relieving effect.

I have been really surprised using my shaper how little distortion there is. Cutting full 16" length and over depth keyway through 4140 and a 24" continuous grey cast straight edge both with very minor distortion. Both of these would've pulled pretty good if they'd been milled I'm sure.
My uneducated opinion I would say that there is very little/no stress induced, and any distortion would be attributed to stress relieving effect that is naturally going to happen removing mill scale/manufactured stresses etc.

 

[dgfoster]

I was told when I was an apprentice, and I believe it now, that metal 'enjoys' being cut on a shaper due to the stress relieving effect.

I have been really surprised using my shaper how little distortion there is. Cutting full 16" length and over depth keyway through 4140 and a 24" continuous grey cast straight edge both with very minor distortion. Both of these would've pulled pretty good if they'd been milled I'm sure.
My uneducated opinion I would say that there is very little/no stress induced, and any distortion would be attributed to stress relieving effect that is naturally going to happen removing mill scale/manufactured stresses etc.

My milling experience has been quite different. Of course, your and my technique and tooling may be also be very different. But over the past few years I have milled probably on the order of a hundred straight edges of my own design and manufacture. The majority have been of a prism design and that type of straight edge would immediately reveal any mill-induced warping that might occur as there are three planes intersecting that are milled in succession. My routine is, using carbide-inserted face mills, to first mill the sole, then I mill the 45 degree face and finally the top rail. Of course, these casting are properly thermally stress-relieved prior to milling (or sale) in my oven by me. So, their condition is known.

After milling one face, I often check it for flatness and then go on to the next and then check all three faces when milling is completed. In almost all cases each face checks within 1 thou of flatness after machining on the prism is complete. If the casting were warping them due to either relieved internal stress or induction of new stress through milling, one would expect that perhaps the last surface milled might be straight, but the second face would be warped and the first warped even more. But that is not the case.

Is it possible to induce stress and warping of a casting by milling it? I suspect it is. For instance, I have also noted that milling with high RPM or dull cutters can cause surface glazing and smoking hot blue chips as well as a very very hot part. So, I am careful to avoid those traps. With good inserts and moderately slow SFPM I get a dull grey cross-hatched pattern and I make a light (.005") finish pass after allowing the casting to cool uniformly and to near room temperature. (I have previously written up the methods I use to support the casting to minimize fixturing strain.)

And another but anecdotal report really struck me. I had a guy pretty new to scraping buy an 18 from me a while back. He gave me some updates on his progress (I really do like that) and reported he first mille and then scraped the sole of his 18. THEN he milled and scraped the 45 degree face. I was stunned to hear that his first face blued up essentially the same after milling the second face as it did prior.

For those unfamiliar with my 18" prism design here is a photo.

And here is a 26" prism of similar design that I also have machined numerous times (not this one obviously) with similar results.


Denis