Machines with ground cast iron surfaces

Rob Keeble

Member
Messages
12,633
Location
GTA Ontario Canada
Dave Black in his jointer post got into the issue of flatness on the table and fence of his new jointer.

I am in agreement with Dave on his desires, but i would still like to know where does one find the specifications for flatness for these surfaces.

Is there a general industry specification for ground cast iron surfaces like a table saw top or a jointer bed etc. Something that produces a general norm.

I am guessing there has to be something like this in order for a manufacturer to work to a specific flatness tolerance and then another for the go no go acceptance of the product even in batch form at the factory by a vendor such as say Grizzly.

Seems to me without this flatness spec its arbitrary as to whether one has claim on a vendor when one considers the flatness of a particular surface to be out.

Then there is the issue of what to expect for the kind of money we spend for the machine we get. I mean this has been pointed out before that we kinda get a whole lot of machine for very little money if one is realistic about it. But a whole lot of machine is pointless if it cannot do what its intended to do.

So how would a person in either Dave or Grizzlys shoes arbitrate this flatness thing. I am not specifically considering Daves situation which also has unique specifics related to it for his specific intentions of use.

We all get the support when we buy a new machine that says "check it out" or set it up. But check it out to what? I have a straight edge and feeler gauges but that means nothing without a spec. Even the weighs and measures guys have specs for what a standard pound/ kilogram etc are.

Does anyone have any knowledge on this matter that they would care to share to help shed some light on the matter?
 
talk with shiraz from grizzly he has his email address available on his gun sight ..he was once a member here and still is on SMC.. there was a thread here long time back about his gun page and that should give the first step.. he is a avid target shooter.
 
What do guns have to do with table flatness?

Rob - I don't know where to acquire specifications like that except from the manufacturer. It's an interesting question.

That being said, it is incredibly difficult to create an object that is more precise than the tools used to create it. Too often, at the table saw, I find myself working in increments of 'left of' or 'right of' the 32nd mark on the tape. Call them 64ths if you like. Twice as precise is 128ths. 1/128 is .0078125.

So, for me, flatness of better than .0078125 is the minimum. That's not very flat, by the way. I can get a mass produced, 24" straight-edge guaranteed to better than .001 for $40. Today's world is incredibly precise.
 
What do guns have to do with table flatness?

That being said, it is incredibly difficult to create an object that is more precise than the tools used to create it. Too often, at the table saw, I find myself working in increments of 'left of' or 'right of' the 32nd mark on the tape. Call them 64ths if you like. Twice as precise is 128ths. 1/128 is .0078125.

So, for me, flatness of better than .0078125 is the minimum. That's not very flat, by the way. I can get a mass produced, 24" straight-edge guaranteed to better than .001 for $40. Today's world is incredibly precise.

Mr Agnew ,, shiraz is one of the owners of grizzly tools,!! and i was just giving you a place to get in touch with him.. i WAS not trying to promote guns in any way!
 
Anyone here remember Jorgeson Blocks?

Enjoy,
JimB

No, but I do remember Johannson Blocks. We called them Jo-Blocks; They were very precise hardened & ground steel blocks of different thicknesses that could be combined & used for: setting up tooling for Tool & Die Makers and Machinists; for precise comparative measurements; and because they were made to very tight tolerances & very smooth, we would "ring" them together to gang them up for the desired thickness & then had to "ring" them again to separate them.

What were the Jorgeson Blocks?
 
It has been my experience that tool brands each have their own tolerances and the only way I've heard to find out what they are is to call 'em up and ask. I suggest asking prior to giving too many details about what you've measured because I'm cynical and wouldn't be shocked to say "I'm out .024" and hear "Oh our spec is .025" from them. (btw, 25 thou is CRAZY out of flat).

I'm unaware of any published standard toward which all manufacturers work short of the soft "standard" set by the industry/market/competition that pressures them to come in pretty dang flat. Obviously flatness is often associated with quality which is also often associated with cost. Achieving a tight tolerance is more expensive than not so I am willing to bet you'd see a trend of tight to loose as you descend the quality chain of brands.

However - the story doesn't end there! Cast iron moves a good deal over time after being sprung from the mold. Old cast iron is much more stable than new cast iron simply by the passage of time. I forget the exact time frames but it's in the range of months to years that a manufacturer should let their cast iron sit and rest before machining. Given our fast paced race to the bottom, MOST of today's budget-friendly brands don't let their iron rest as long as the premium brands do. Some of the higher end ones will even tell you how long they let them sit before machining.

All this is to say keep in mind that the spec a manufacturer works within is AT the time of machining. Since they might be machining iron that isn't done moving, it's pretty common to have it wiggle out of spec a year after it's been made. Whether the brand honors that eventuality and makes you whole depends on the brand. It seems like a game of odds for them, how many will move far enough out of flat in the hands of a customer who would be willing to take them to task for it. Hobbyists are probably less likely to be that diligent - then again, big pro shops probably don't mess around with stuff that may move on them and pony up for the higher end stuff.

Phew - I thought I was just gonna say a few words and it turned out to be a whole dang thesis! :D
 
As stated, cast iron is aged or cured over time before machining. The push for lower prices or fast turnaround has caused some makers to hasten that process. This would be our equivalent to hurrying logs through the mill and the drying process. Inadequate seasoning leads to a potentially more active product.

As to who allow what and how much, I agree that in all cases I have had to contact the maker / seller. Even then I have had to get past the front-line, queue-card folks in some cases. I had the same saw that Rob has and Orion stated that there should be no more than .006" or .008" (don't recall for sure) difference between any two points on the top. Although Orion could have simply sent me a new top, I bought the saw through Sears and their only recourse was to send me a whole new saw. This actually worked out well as I ended up with a very nice machine that I would probably still be using except for an unexpected opportunity.

The point is that there is probably some number that the 'requester' requires from the 'maker' and these things probably vary depending on who the customer is. Jet may accept a range that Powermatic does not or vice versa. I imagine it also varies with machine model or type. It would certainly be possible to try to find these things out prior to purchase so that you have a ruler to measure by.

It makes you long for the days when you could buy a 'brand' and be pretty well assured of a level of quality, don't it? ;-)
 
i used to pour the stuff, Iron that is, and have been threw the process from sand molds to the machining, and both jason and glenn have got great info.. in my past the castings were at least a year old depending on the applications and others were the next week if needed..to the machining area.
 
Back in the 70's (yes I remember that far back.) There was a company out of Bridgeport Connecticut called Bridgeport machine (well what did you expect). Anyhow they produced a knee type three axis milling machine that was the gold standard of this type of machine. They would age their casting I seem to recall for a year prior to machining. As a result they had a limited production capacity and lead time for their mills (referred to a Bridgeports) ran up 60 weeks. They were also very expensive but every shop around wanted a Bridgeport due to their tolerances which were second to none. Finally in the late 70's several Ti/chi companies entered the market with faster deliveries and lower prices. Although Bridgeport sued they were not successful and these Ti/Chi copies flooded the market. The copies did not have the same QC as the original and they did not age their castings. This only proves one thing my old boss taught me about selling any product, all a company can offer is 3 things. Price, Delivery and quality. The customer only get to pick 2 of the three the company determines the other.
 
As to where the specs are for what is considered flat by a given manufacturer I haven't came across any that I can remember. I looked in the manual and spec sheet for my jointer and didn't see any there. My common sense says that if its far enough out to cause problems with the intended purpose of the machine then thats too far out. In my specific case, whats the job of a jointer, to give you 2 flat and straight surfaces 90˚ to each other. Well the fence is cupped enough that if the board I'm edge jointing is shorter than the fence I no longer get surfaces that are 90˚. I have 2 other tools that I bought new, my sawstop 3hp cabinet saw and my delta 17-959l drill press, all of the ground surfaces on those machines are dead flat as far as I can tell. I also have a slightly older mortiser that I recently got used, Its a bridgewood, I think 12 years old and Grizzly also sold the same machine. While the machining on the table of the mortiser is a little rough, its overall flat and square to the fence. I have other old tools and aside from being slightly out of flat from 50 or more years of use the surfaces on them are also basically flat. So what is flat and who determines it, I don't know but all the other manufacturers that are represented in my shop seem to have the answer. Right now the answer I seem to be getting from grizzly is analogous to this. I just buy a new car and drive it home, on the way home I am holding the wheel straight as I drive down a straight road and the car swerves back forth from my lane into the other lane. I call the dealer and say there's something wrong with the car it swerves all over the road and their response is, yeah, but does it swerve OFF the road. I say no, but it swerves into oncoming traffic, they say well as long as it doesn't swerve OFF the road we consider that in spec. Well I'm going to wait a few days and call grizz and see whats up. If they can't or won't get me a better fence I'll fix it my self, I'm fairly confident that I could grind it much flatter on my HOMEMADE edge sander.
 
I myself have to wonder when it is your checking. When ever I setup up a new tool be it a table saw or a jointer or what ever else it is I do the basic checks and then use it. If it does what it's supposed to do then I look no further and just start using the machine. I could not tell you how flat my table saw top is or the beds or fence on my jointer. All I know is when I run a board on the jointer it comes out flat and when I rip one on the saw it comes out straight and square.

Unless there is a problem with the finished product coming off the machine does it really matter? After all we are working with wood and not making something that requires a precision piston type fit that can only be accomplished on a metal working machine.
 
I myself have to wonder when it is your checking. When ever I setup up a new tool be it a table saw or a jointer or what ever else it is I do the basic checks and then use it. If it does what it's supposed to do then I look no further and just start using the machine. I could not tell you how flat my table saw top is or the beds or fence on my jointer. All I know is when I run a board on the jointer it comes out flat and when I rip one on the saw it comes out straight and square.

Unless there is a problem with the finished product coming off the machine does it really matter? After all we are working with wood and not making something that requires a precision piston type fit that can only be accomplished on a metal working machine.

I agree with you, I noticed this problem when I was squaring the fence to the table when assembling the machine. I was holding the square on the table and trying to adjust the fence, I couldn't seem to get the edge of the square to sit on the fence right. I thought I was overshooting the adjustment, then I realized that there was a quite visible gap in the middle of the fence. Its not a problem if I am face jointing or edge jointing pieces that are taller than the fence. If they are shorter than the top of the fence then the top edge of the board references off the cupped part of the fence which means it doesn't produce a square edge. I tried it with a few different boards and confirmed this. While I am not in the habit off walking around with with a straight edge and feeler gauges while drinking my morning Mt Dew I do use them when I get a machine and set it up if thats what is called for, or if I notice problems with wood coming off machines. I couldn't tell you exactly how flat my table saw is only that it didn't throw any flags while assembling it and adjusting the wings with a 4' level, The only reason I know my planer bed is slightly wore is that I used a dial gauge to set the blades, I used a magnetic holder that sat on the table with the gauge upside down so I could set the knives to the head. I moved it back and forth to each end of the head and noticed a slight variation in the middle meaning the table was slightly out, its not much and doesn't effect what I do with it. I don't have to have dead perfect machines but when I make a purchase like I just did, I expect it to perform the job it was designed to do, .008" is not enormous but over a 5" span( really a 2.5" span because it goes .008" out then back to 0 at the top of the fence) and on referencing surface I think is way too much.

Thats my humble $.02
 
Dave i empathize with your dilemma. It seems to me there are many cases in the machine or tool business where this kind of important information is left in the gray territory to be arbitrated on the basis of he who makes the most noise. Its the same for the HP spec. The brand owners would certainly like to keep this aspect out of the limelight given its not published by any of them. There are only a few ordinary squares where you see the spec published on just how square the square is.

My bet is that some of this originates from the fact that they probably take on the warranty liability on their purchases. Then they probably do a batch inspection of machines based on a sampling method. Which means although their factory runs on ISO logic of continuous improvements and real time error correction, they know that the batch has potential to have some less than perfect machines in it purely on the basis of yield from castings and the spread. If they published the specs i guess many would be returning parts then just because they out of spec rather than as in your case a real issue being out of spec for your application.
Doing it on an as and when individual case turns out to be the most economical solution when they the ones picking up the warranty tab. This can work but only if they have the ethics to honor the customers needs.
Seems to me to date Grizzly is attending to you and trying to accommodate your needs. Given the boss man is a woodworker and makes guitars you always have him to appeal to in the event of them not totally satisfying you.

I share Glenn's concern about going it alone and trying to flatten it. Would if it came to that rather use a shop with a surface grinder where they have jigging to set it up and reference its mounting point properly to get true flat surface that's in the correct plane for when you re-install it.
Hopefully the power of the forum discussion on these matters out in the open helps with leverage for your case. best of luck. Another thought is they might find when they open the stock on hand up that there is a batch issue where the castings all had this problem.
 
I am a 40 year veteran manufacturing engineer with a fair amount of design experience as well as manufacturing experience in metal cutting and CNC.

I am currently employed at a gage manufacturer and we make - "gages". We DO in fact grind things to a flatness spec but to "gage" specs.

BTW - BRIDGEPORT knee mills are currently still being made by Hardinge in Elmira New York. I have been there and seen them being made.

The company I work for, and the processes I oversee - are all in the single millionths to 10's of millionths. To me working to .0001 tenths is pretty with open and working to thousandths is like working with a hatchet.

Generally speaking - the tolerances applied to a gage of jig or fixture is about 10% of that being measured, of fixtured for. So - if I were to design a gage to measure something with a +/- .005 tolerance, which is very popular in industry, I would use a "rule of thumb" of 10% and tolerance the gage to +/-.0005.

So on a table saw - which by the way is NOT a precision instrument - I would not expect flatness to be much better that errr - .005 That five thousandths is a pretty precise number --- for a table saw. Yes, Cast Iron does move around and getting something made of cast iron that size to be REALLY flat is near impossible.

On my Grizzly 18" band saw, I was not happy with the flatness of the top - so I disassembled the table and brought it to work and had the top ground to within .0002. That is a TON flatter that anything else in my shop. It was out .017 when we started.

Another time, I bartered some work on my CNC machine electronics and I got an old Cast Iron Surface plate ground to .0001 flatness. It will not stay, but due to the thickness and age, it will remain within .0005

Flatness - is an EXPENSIVE process. It takes a LARGE surface grinder. Just by nature of the process - grinding - is one of the MOST expensive processes in any manufacturing process. In the cost of, say a Grizzly table saw the cost is a HUGE consideration. On a VERY expensive saw, say like a saw stop, the flatness may - MIGHT - be a TAD better.

Looking at the grind marks will give a clue to the process. If the lines are straight - it is surface ground. If the lines are curved, it is Blanchard ground. Surface grinding is a more expensive process.

Getting to the high precision is where the money is. Getting that flatness to .0002 - is going to be VERY expensive. The sales price of the Grizzly 1023 is not going to support a process like that.

Smaller items like jointer tables can be surface ground at a somewhat reasonable cost. Again - the higher the precision - the higher the cost.

Then there is the question of HOW to measure Flatness - and NO it is NOT to lay a "supposedly" straight edge and use a feeler gage under it. I would challenge the claim is straightness on those supposed straight edges. I may buy one some day and measure it. We have a NIST certified measure center - the straight edge manufacturer most likely does not.

There are industry instructions to measure flatness.

There is always going to be a trade off, Cost vs Value vs Sales price

I sent off a request for the flatness spec to Grizzly --- They MIGHT give an answer

My GUESS is that it will be about .005 or so.
 
The new fence arrived today, much better than the others. According to the "straight" edge and feeler gauge method it is cupped .004" in the center and less than that moving towards each end. I assume this is the best one they could find in stock so I think I will call it a day on this matter. As Rob mentioned it would be nice for manufacturers to publish their specs for the machines so there's no questions of what is good enough.
 
Well Dave they saw you right best they could and you better off than in the begining.
So how does it work for your drum parts thats what matters. Tested that part yet??

sent from s4
 
Top