Unisaw table flatness

[Ron Kellison]

I purchased a 5HP LT Unisaw with a 52" Bies fence a few months back at a price that I couldn't resist. As I haven't gotten around to reworking my shop to install 220V I've taken my time in assembling and adjusting it. It has been an educational experience!

I've learned that the aluminum used in most beer cans is 0.00125 thick and that it's a rough job to move and align extension wings working alone. In the process of aligning the saw, I've discovered that while the wings are absolutely flat the actual top of the table is dished across 0.015, mostly on the right side of the blade. It is also dished 0.008 front to back, mostly near the blade insert.

While I realize that accuracy requirements are really dependent upon the work being done, I would be interested in knowing what tolerances are expected by the other denizens of Sawmill Creek. Do you think my saw will be inaccurate enough to notice?

Regards,

[Mike Marcade]

In my opinion .015" flatness sucks, especially for a saw that demands big money like a Unisaw. My cheap Grizzly jointer tables are flat within .0015". I would expect the big money cabinet saws to have flatness in the ballpark of my jointer. Just my opinion, mind you.

[Rick Lizek]

I know for a fact that Powermatic considers .015" tolerance for the main table of the Model 66. A warm breeze will make your wood move that much. Most woodworking machines don't need the tolerances of metalworking machines. A jointer would be to tighter tolerances. On my older 16" Oliver jointer the old Oliver considered .010" an acceptable flatness for the table. Your saw is fine in my opinion and experience.

Also what are you using for a straight-edge? A level or a real machined straight edge. Companies have to draw the line somewhere on standards. Most saws are pretty flat for the most part.

[Mike Marcade]

I would expect the accuracy of the tool to be an order of magnitude better than the work you are trying to produce.

[glenn bradley]

Steel City and Delta have stated in emails that .01" is within tolerance.

[Ron Kellison]

I'm using a 24" German straight edge acquired from Lee Valley and one of the new 50" Veritas straightedges. I'm also using a set of Mil-spec feeler gauges.

[Bruce Page]

I think we would all love to have dead flat tables. I also think .015 out of flat on a tablesaw is a non-issue. Think about it, what exactly is being affected as you cross-cut or rip?

[Pete Bradley]

In my opinion .015" flatness sucks, especially for a saw that demands big money like a Unisaw. My cheap Grizzly jointer tables are flat within .0015".

What effect do you expect .015 in a table saw to have on the work and why?

Are you saying your griz jointer is good to .0015 over the length?

Pete

[Art Mann]

My guess is if you had never used the straight edge and feeler gauge, you would never have known the difference.

[Cliff Rohrabacher]

I've learned that the aluminum used in most beer cans is 0.00125 thick
I rather suspect that there is one zero too many in there.
It's more like 0.0125" or Twelve Thousandths. The extra zero makes the material lots thinner than aluminum foil.

At any rate I've made the tooling for stamping beer cans.
The material they start with is a flat disk of aluminum. The forming dies are carbide. the upper set drop onto the disk with oodles of force, grab the aluminum and pull it up around the internal die that forms the can shape. It's a fast and hot process. the metal is stretched so that it's lots thicker at the base than the top where the seal is when the can is filled & finished.

[Ron Kellison]

I just remeasured using an electronic caliper and got 0.0020 in my cold shop.. With a 1" micrometer I get 0.0035. Of course, that may be because I cut the these particular shims from an Old Milwaukee can and they may go for the thin stuff to match the quality of their beer!

In any case, I'm inclined to agree that if I didn't have the straight edges and feeler gauges I may not have noticed the dip in the table! After I get power I'll let the quality of the cut determine how happy I am. I'm sure it will be much better than my 30-year old Craftsman!

[Mike Marcade]

What effect do you expect .015 in a table saw to have on the work and why?

Are you saying your griz jointer is good to .0015 over the length?

Pete

I just expect a pretty good flatness on a machine that is quite expensive like a Unisaw. Maybe my expectations are too high.

On my Grizzly jointer, I place a 4 foot precision ground tool steel straight edge along the length of my outfeed or infeed table and can not get a .0015" feeler gauge underneath it anywhere.

[Greg Funk]

I've never put a straightedge on my Unisaw and I don't intend to unless I suspect it is somehow hindering my ability to make straight and square cuts. I don't think it is a critical tolerance.

Greg

[Mike Marcade]

I've never put a straightedge on my Unisaw and I don't intend to unless I suspect it is somehow hindering my ability to make straight and square cuts. I don't think it is a critical tolerance.

Greg

How did you align your wings?

[Gary Keedwell]

How did you align your wings?
Hey....That's what I was thinking...I wish I didn't put a straightedge on my Uni....I lost all respect for it especially after I went to a show and the guy showed me how flat the Steel City TS was.:(:cool:
Gary

[John Thompson]

My first TS in 1972 was not flat. As a matter of fact it was probably not close to flat as plywood won't stay flat long exposed and un-coated with a 15 lb. circular saw hanging underneath in Florida. Kinda the same scenario with the fence, I suppose. A piece of poplar and two C clamps was about the best I could do for a fence at the time.

Completed 4 projects with that saw before up-grading to a very highly machined Sears contractor saws in 1974. Well.. at least it had a cast iron table with aluminum wings. Sort of state of the art at that time. :)

I didn't notice any problems with the origainal saw. Apparently my first wife didn't either as they are still in her current home. If she had noticed any problem... she would have called me and let me know. Trust me... she would call and let me know! ;)

Straight edges and calipers have there place, but I would put them away for the moment and just cut some wood. It will tell you if you have a problem and I doubt seriously you will. Perhaps we put too much emphasis on "dead flat" these days with a machine top? A piece of wood that can move litterally 1/16" over-nite with a humidity change is what's going to cross it's path.

Relax and enjoy your saw...

Sarge..

[Bruce Page]

Hey....That's what I was thinking...I wish I didn't put a straightedge on my Uni....I lost all respect for it especially after I went to a show and the guy showed me how flat the Steel City TS was.:(:cool:
Gary

I wonder how many they had to check before they found the one that they took to the show? :rolleyes:

[Gary Keedwell]

I wonder how many they had to check before they found the one that they took to the show? :rolleyes:
Probably picked one at random since it within their tolerances for their table saws.:rolleyes::rolleyes:
Gary

[Bob Feeser]

How did you align your wings?

I know the question is not directed towards me, but I thought I would input my 2 cents. I have a PM66, and the wings were high on the outer edges. So I took some aluminum foil, folded it over 4 times, giving me an 8 fold thickness, cut about a 1/4" strip, lightly loosened the attaching bolts, slid the aluminum foil shim down into the crack, right above the bolts, then tightened. By tweakiing the number of folds, I was able to get the extensions perfectly flat with the top. And I mean perfectly.
The interesting thing is that it is an all metal repair, and the seam for the extensions did not open up at all. I can take a razor blade, and try to shove the sharp corner into the crack and it doesn't go anywhere. It is as if the crack does not exist.
When I first hit upon this, I was so pleased, I wanted to tell the world, but of course, a lot of people already realized it. Some used beer can metal instead of foil. I like the foil for it's fine tune ability.

[Bruce Page]

Probably picked one at random since it within their tolerances for their table saws.:rolleyes::rolleyes:
Gary
Yeah, I'm sure that is the case...;)

[Gary Keedwell]

I would expect the accuracy of the tool to be an order of magnitude better than the work you are trying to produce.
My sentiments exactly. What people have to remember is that part of the process of making a table saw, or for that matter, any piece of machinery, is all the parts they make have tolerances. They have to grind the top anyways, so why not take the time to grind it right and make the darn thing flat!!!!
A long time ago I worked for Williams and Hussey. They make quality machinery for the woodworking industry. As a nite shift machinist, I was moved around where I was needed. For two weeks I worked on a huge blanchard grinder that was grinding planer tops when I was over there. I can tell you that that grinder worked within tenths of an inch.
If your machinery is not groung smooth and flat, it is because they rushed it through the process and quality was not a priority.
I was wet behind my ears when I bought my Uni without even looking at the table. I bought it on reputation alone. Any manufacturer that goes that extra step to make things right is what gets my respect.
Gary

[Art Mann]

Do you guys who are worried about 0.015" out of flatness know how ridiculous that is? Do a little trigonometry from your high school math class and calculate how much of a difference that will make on your saw cut. Suppose you have a saw that slopes as off by 0.015" from the blade to the edge of the saw 12" away. Now suppose you are ripping a very wide piece of 8/4 material. How much of an error will that 0.015" produce?

2 * (0.015/12) = 0.0025"! Are you really worried about an error less than half the thickness of a sheet of paper ripping a 2 X 12? Inconsistencies in your rip fence or material feeding technique will produce more error than that.

[Phil Thien]

I'm not saying .015" (1/64") is out of line.

But, I've noticed that almost any piece of machinery I purchase can be tweaked to near perfection if I'm just patient and spend some time contemplating the problem and possible solutions.

Before doing anything I'd examine everything I had done so far (like adding fence rails and extensions) to make sure I hadn't inadvertantly tweaked it.

Then I'd examine the problem for possible solutions (like shimming between the cabinet and the top). Mind you, I wouldn't just jump in there and start making changes. Think about the ramifications of changes you'd make. 1/64" won't prevent you from using your saw in the mean time. But I'd just let it sit in the back of my head and stare at the saw some and a solution (if one is required, not saying one is) would perhaps eventually make itself obvious.

[John Thompson]

A note of clarification...

It was suggested earlier that the Steel City TS that was shown to Gary in Mass. at a show was flat as it was hand-picked by Steel City before the show.

Steel City.. or very few of the other manufacturers takes stock to a show from their warehouses. They let the local distributor take one from their floor to the show along with other machines to avoid trucking all over the country. Then they fly in and work the show.

The TS Gary probably saw likely came from Woodcraft in W. Springfield if the show was in Mass. I bet if you call Woodcraft there you will find that distributors don't have a 100 TS's to chose from. Maybe 3... if that many!

Sarge..

[Mike Marcade]

To Art's point ... I am not worried that the flatness descrepancy will affect the accuracy of my work so much, it is mostly a principal thing with me. Paying that kind of money for a Unisaw I expect it to be ground to a decent flatness. Hell, my 5 year old Delta contractor saw is flat within .005", I expect a Unisaw that cost at least 4 times as much to be manufactured to a higher standard.

[Gary Keedwell]

A note of clarification...

It was suggested earlier that the Steel City TS that was shown to Gary in Mass. at a show was flat as it was hand-picked by Steel City before the show.

Steel City.. or very few of the other manufacturers takes stock to a show from their warehouses. They let the local distributor take one from their floor to the show along with other machines to avoid trucking all over the country. Then they fly in and work the show.

The TS Gary probably saw likely came from Woodcraft in W. Springfield if the show was in Mass. I bet if you call Woodcraft there you will find that distributors don't have a 100 TS's to chose from. Maybe 3... if that many!

Sarge..
Thanks for the clarification John.....Also, let me add to my previous post by saying that the flatness of a table top is but ONE specification when the top is ground. When working with blueprints flatness, perpendicurity, parallelism and other criteria is involved for assembly and proper operation for the consumer. After the top is ground it is then probably sent to the to drilling and milling departments for further machining.Locations of holes, threads, welds etc. are probably located from the top of the table.
Experience tells me that the more exact the finish ground is the more exact locations of further machining will be and that will show up at assembly and ultimately at your shop.
Also, I am writing this with no book or other references in front of me. It is just things that I picked up from being in manufacturing.:o:)

Gary

[Phil Thien]

To Art's point ... I am not worried that the flatness descrepancy will affect the accuracy of my work so much, it is mostly a principal thing with me. Paying that kind of money for a Unisaw I expect it to be ground to a decent flatness. Hell, my 5 year old Delta contractor saw is flat within .005", I expect a Unisaw that cost at least 4 times as much to be manufactured to a higher standard.

I don't know what kind of surface grinder they use on a Unisaw top, but I don't know of any surface grinders that are +/- .015" over 20-30", either.

I think the likelyhood is that it was originally ground flat, but as the CI ages and it gets moved and assembled to a base (is the base flat?) there is a chance to introduce problems.

I see your point re: price vs. performance, but I've read too many similar complaints that if I someday spring for a cabinet saw I'm going to make sure that it is at least to within manufacturer's specifications and then move forward from there to optimize it.

[Gary Keedwell]

I don't know what kind of surface grinder they use on a Unisaw top, but I don't know of any surface grinders that are +/- .015" over 20-30", either.

I think the likelyhood is that it was originally ground flat, but as the CI ages and it gets moved and assembled to a base (is the base flat?) there is a chance to introduce problems.

I see your point re: price vs. performance, but I've read too many similar complaints that if I someday spring for a cabinet saw I'm going to make sure that it is at least to within manufacturer's specifications and then move forward from there to optimize it.
That's a good point Phil. Cast iron has to be aged and grinding out of sequence or grinding before it is ready should affect the outcome. Sometimes it could be things like how they hold it down while they grind it. They could be putting stress on the hold-downs and after it is ground it could spring....just like wood.
Gary

[John Thompson]

It might be added also that cast iron can wrap on it's own as stress doesn't always show it's ugly head from the on-set. It's a tedious process from start to finish that has to be quality controlled through all stages. Even then there is no gaurantee that that batch of iron won't warp as sometimes the stars don't align properly and the carbon and other ingredients are not evenly distributed through-out the mix, etc.

I have a factory re-conditioned Uni-saw that the table is very flat. But... It was re-ground at the factory before it was put back on the market for sale. May have been really un-flat.. may not have been that bad. I will never know as I inspected it before the purchase and the top had already been re-ground.

Scott Box from Steel City told me that one of the reasons they were excited about using Black Granite is to eliminate the gamble that you take with every batch of cast iron mixed. Again.. even with tight quality control, there are no guarantees and if you issue a 5 Year Warranty.. you back it up for 5 Years.

Sarge..

[Greg Funk]

How did you align your wings?
I didn't since there was no need. They look close to flat and even if they were .010 or .020 out it doesn't affect anything. The only wood that would normally make contact with the wings is plywood and a minor offset in the wings isn't going to affect the cut. I use a sled for any precision crosscuts and the cuts I get are square.

Greg

[David Weaver]

This is just my opinion, and only that, but I think that's terrible. If they season the cast, I don't see how it could be out that far.

I don't know what Steel City uses as a flatness spec, but I recall reading something a while ago that said that they season tops for 6 or 8 months before they finish them off. Maybe I have them confused with someone else - who knows.

But one thing is for sure - you can't use any 0.015" tablesaw top to lap handplane soles.

My delta hybrid is just north of 0.008" hollow from front to back, and I wasn't pleased with that.

It's just a sign of the times, I guess - do it quickly and cheaply.

[Art Mann]

There is a reason surface plates are made of granite rather than cast iron. There is a reason the specifications for premium tablesaws are +/- 15 thousandths. I doubt it is due to sloppy grinding. We are all accustomed to wood being unstable, changing dimensions, twisting and warping. Why is it so hard to understand that cast iron will do the same thing on a tiny scale? It would be an interesting study to survey a bunch of the old Unisaws and PM66s to see how flat they are.

[Bruce Page]

The bottom line is - it makes no difference to the piece you are cutting if the table is out .015 or is dead flat perfect. Why do we want the manufactures to expend the time & effort to give us perfect when it is only going to cost us more money? I’d be willing to bet that even the legendary Northfield table saws are not perfectly flat. It just ain’t necessary.

[Gary Keedwell]

The bottom line is - it makes no difference to the piece you are cutting if the table is out .015 or is dead flat perfect. Why do we want the manufactures to expend the time & effort to give us perfect when it is only going to cost us more money? I’d be willing to bet that even the legendary Northfield table saws are not perfectly flat. It just ain’t necessary.
Yea, that's the ticket....Lets tell all the manufacturers to LOWER the standards so we can get it cheaper. Opssss To late...Taiwan is now making most of them.:rolleyes::cool:
Gary

[Bruce Page]

Yea, that's the ticket....Lets tell all the manufacturers to LOWER the standards so we can get it cheaper. Opssss To late...Taiwan is now making most of them.:rolleyes::cool:
Gary
Not suggesting that they lower standards. I’m suggesting that .015 is perfectly adequate. Everything manufactured today is manufactured to a tolerance. You should know with your background that the tighter the tolerance the more it costs to machine. I work in aerospace, where a component failure can cost millions, yet every component, every nut, bolt & washer was made to a tolerance. There’s no such thing as perfect, you can get close but you’re going to pay for it.

[Richard Wagner]

Well, I came here with a question about my Shopsmith Mark V Saw Table and I am now feeling pretty darn good. I was concerned about a .005"-.007" dip in the table in the area around the table insert. Without even discussing my Shopsmith, I now know that I have nothing to be concerned about. Many of you with expensive iron have the same problem or maybe even worse. Thank you. You have made my day.

[Bill White]

Just as a point of reference, I'm not usin' my TS top to lap a plane sole. That's for which granite or glass is used.
The very idea.......Water and lapping on a TS top? Come on!

Bill

[jim gossage]

Most of the time it will not matter but there are occasions where it might. I was once miter ripping 5 x 5" pieces of wood on my table saw to build mitered boxes. I had the same problem with a 0.012 inch dip around the blade. Since the pieces were fairly small, they would follow the dip and this would impart a slight curve to the miter cut. It was impossible to close the miters with this set up. I had to build a sled to correct this problem