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Author Topic: Level the Table Top  (Read 6437 times)

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Offline kolias

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Level the Table Top
« on: October 15, 2012, 10:45:50 AM »
I have attached a dial indicator to my spindle and trying to level the table top which is a 5/8” MDF piece about 28”x40” (cutting area about 24”x36”)

It looks like that the dial indicator has its own mind because as I move it slowly over the table I always get different readings and I wonder if it is appropriate to use a dial indicator for this job or my dial is not good.

I bought the indicator with a magnetic base from eBay and I only paid $35.00 so perhaps its not one of the best?
Nicolas
Re: Level the Table Top
« Reply #1 on: October 15, 2012, 11:15:10 AM »
I would be as much inclined to say that the MDF is not flat as much as anything else.  I don't believe that MDF manufacturers have that great a tolerance on flatness.  Ideally, you need to machine the table so that it is flat.
Re: Level the Table Top
« Reply #2 on: October 15, 2012, 01:23:52 PM »


It looks like that the dial indicator has its own mind because as I move it slowly over the table I always get different readings 


Hi Nicolas,
  You might be careful not to move the x/y axis with the indicator down on the material.
Instead, move up, over then down again to the same z value to eliminate any side load on the indicator.

Might be more reliable.
Russ

Offline kolias

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Re: Level the Table Top
« Reply #3 on: October 15, 2012, 01:51:07 PM »
Now it works much better Russ, thanks. Before I only had it touching by 2 thou but as you mentioned I did not count for the side loads.

EJ I had the impression that MDF was perfect flat but you may be right. I was thinking to machine the table top but this will create a “pocket” and if later I want to work at the center of a long piece it will not sit flat on the table.
Nicolas
Re: Level the Table Top
« Reply #4 on: October 15, 2012, 04:18:08 PM »
An indicator *should* be able to cope with the method you described.  My day job is as a machinist, and I set some pretty rough flamecuts with my dti's.  I do agree that it may be a source of an error.  When I'm setting up a new machine, you must be careful to reverse the axis before taking the reading at one end, and then continue in one direction only and do not reverse before taking the reading at the other end - its quite surprising how much error will show up.  To be fair though, I am usually dealing with traveling column machines where the column can weigh in at over 10t, but its still evident on smaller machines if your dti can measure it.

I have to ask the question, what is 'perfectly flat'.  Father used to work in a hardboard mill so I know a bit about the manufacturing process, although I don't know the tolerances.  You have to consider though, it isn't an 'engineering' material.  It would be interesting to know what you get when you're happy that your setup is good and your clock is good.

Offline budman68

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Re: Level the Table Top
« Reply #5 on: October 15, 2012, 05:45:26 PM »
Now it works much better Russ, thanks. Before I only had it touching by 2 thou but as you mentioned I did not count for the side loads.

EJ I had the impression that MDF was perfect flat but you may be right. I was thinking to machine the table top but this will create a “pocket” and if later I want to work at the center of a long piece it will not sit flat on the table.


You really should surface or I truly believe you will not be happy with the outcome of your work.

Cut the mdf so that it will fit within the envelope of your cutting area and that way you won't have to worry about it being a pocketed area.

Dave
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Offline ger21

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Re: Level the Table Top
« Reply #6 on: October 15, 2012, 08:57:02 PM »
A clean, new sheet of MDF is probably uniform in thickness to about .005" or so. But you can't rely on it being flat, as it can warp in different directions simply by moving it around your shop. If it's securely fastened to the machine, then any unevenness should probably be due to the machine frame itself, as MDF is quite flexible and should easily conform to whatever it's mounted too.

Rather than checking how flat the table is, I'd be more concerned with how flat, parallel, and square the linear rails are. If they are flat, then you surface the table and it'll be flat. If the rails aren't parallel to the the table, then it's possible that the table won't be flat, even though your indicator may tell you it is.


It sounds like your MDF table is larger than your machine can reach. If so, you should mount a secondary piece of MDF that the machine can reach completely, and machine that flat.
Gerry

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Offline kolias

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Re: Level the Table Top
« Reply #7 on: October 15, 2012, 09:58:41 PM »
Looks like that the best way is to machine the top. I will complete my leveling and if the results are not good then I will machine the top.

As for squaring the machine, I did a 10"x10" square and the last leg of the square did not hit the starting point by about 1/8". I adjust the home switches on the Y&A axes a few times and finally I got a perfect square (but the depth of cut was not equal). So as far as I know this proves that the Y&X axes are square, unless I'm wrong
Nicolas
Re: Level the Table Top
« Reply #8 on: October 30, 2012, 09:18:33 PM »
Looks like that the best way is to machine the top. I will complete my leveling and if the results are not good then I will machine the top.

As for squaring the machine, I did a 10"x10" square and the last leg of the square did not hit the starting point by about 1/8". I adjust the home switches on the Y&A axes a few times and finally I got a perfect square (but the depth of cut was not equal). So as far as I know this proves that the Y&X axes are square, unless I'm wrong
Now REPEAT the cut, and set the Z axis a little deeper. Does the machine EXACTLY follow the first cut? This is the true test of the machine's accuracy, the ability to return to an exact point each and every time. There are many factors at work in "leveling the table", if the Z axis travel is not perpendicular to the table, in both the X and Y directions, then even machining the table top will not make it truly flat. Also the router's actual mounting block or clamp can effect this. Because the cutter will cut deeper into the MDF along one side of it's path, creating a "Shingled" set of tool paths. Actually, this will occur without the need to machine a whole table top, only to discover that the Z travel is not at 90 degrees with the table's surface. By simply cutting a pocket into a smaller piece, fastened to the table top. Only when you are able to do this, (with NO Shingled paths, but a smooth, flat surface as a result), should you consider machining the table top to make it flat. Even then, you are talking wood. It changes with the weather. It all depends on what you want to use your machine for. I recently tried mounting an electric engraving tool onto my machine, to engrave some plexiglass. And learned that the table "flatness" which had worked so well for my wood carving projects, was FAR from being "flat" enough to achieve the consistency needed for the engraver's micro-strokes. Some areas, the tool would plunge so deep into the plexiglass, that the tool could not even complete it's strokes! While other areas, the tool would not even contact the surface with the tip of the tool. I actually obtained a granite counter top slab, to use for calibrating my table top. With intentions of using dual dial indicators mounted in the router spindle to set the table as close to perfect as possible. But perfection is simply a target to aim at, never actually hitting. The best anyone can hope for, is to get it as close as possible. The best results I have achieved for things which require a very tight tolerance, invloves cutting a pocket into a larger piece of stock mounted on the table, and (while still bolted down to the table), attaching the workpiece to that! (As long as I am ready to start cutting right away). Even this method does not work very well, if the planed stock has been left bolted down overnight.  Wood never truly dies..... it is constantly squirming!
Re: Level the Table Top
« Reply #9 on: November 07, 2012, 05:17:07 PM »
Now it works much better Russ, thanks. Before I only had it touching by 2 thou but as you mentioned I did not count for the side loads.

EJ I had the impression that MDF was perfect flat but you may be right. I was thinking to machine the table top but this will create a “pocket” and if later I want to work at the center of a long piece it will not sit flat on the table.


Hi Kolias
It really doesn't matter if you create a pocket when machining the table flat as you would almost certainly be using a spoil board of at least 3mm thickness, and this would raise the table surface again so that any long pieces would actually be above the actual table surface.

Bob Willson