Table saw tolerance on flatness
Brett Austin
disappointed to find out that the central cast iron table was not flat.
I measured the table with my Starrett straight edge and a set of feeler
gauges and found that it was very flat parallel to the miter slots but
perpendicular to the slots the table was dished out so that the center
was 0.008 inches lower than the outter edges. I contacted both
Powermatic and the dealer I bought the saw from and they both had the
same answer, "Powermatic specs the table flatness to 0.010 or less".
Therefore, they both concluded that my saw had no defect.
I checked out a floor model at the dealer where I bought my saw and it
did have a few localized areas which showed small gaps under the
straight edge but they were very small and restricted to a small area.
My table on the other hand shows the 0.008 inch depression over the
entire table top front to back. It seems to me that this systematic
error in the flatness of the table is somewhat different than small
localized depressions. Am I being too picky here? I assumed that when
I upgraded from my 10 year old Jet saw to the Powermatic 66 that I was
buying a quality and precise tool. Would any of you professionals out
there be satisfied with this much error in the flatness of your saw
tables? I would really appreciate the groups thoughts on this issue.
Brett Austin
gw
"Brett Austin" <Brett....@unh.edu> wrote in message
news:3B4B3DF3...@unh.edu...
> I just bought a new Powermatic 66 table saw last friday and was
> disappointed to find out that the central cast iron table was not flat.
<snipped>
Mark
Brett Austin wrote:
>
> I just bought a new Powermatic 66 table saw last friday and was
> disappointed to find out that the central cast iron table was not flat.
> I measured the table with my Starrett straight edge and a set of feeler
> gauges and found that it was very flat parallel to the miter slots but
> perpendicular to the slots the table was dished out so that the center
> was 0.008 inches lower than the outter edges. I contacted both
> Powermatic and the dealer I bought the saw from and they both had the
> same answer, "Powermatic specs the table flatness to 0.010 or less".
> Therefore, they both concluded that my saw had no defect.
<snip>
Your saw is within spec. Functionally, I can't see a total deviation of
1/128" having any effect on the operation of the saw, i.e. cosmetic
only. If you don't like the appearance of the saw, I expect that you
can return it.
FWIW, the nature of the depression (pun intended) suggests that it was
caused by the tightening of the trunnion bolts 'bending' the sawtable
down. You might try backing off the tabletop bolts a bit (if you can
avoid screwing up the alignment) & seeing if the top springs back.
-Mark
-Mark
Brett Austin
requirement for all lengths of material.
gw
blade and trunnion adjustments, I would think you have a case for
replacement. Otherwise, if it's within their mfg. specs, it can't really be
considered defective, so you'll have a hard time getting them to do anything
about it.
Bottom line, and what I meant to say originally: Does it cut wood to
tolerances within the mfg. specs of the saw, or are you just upset that the
one you got does not measure perfectly flat? I would think that 1/128th of
an inch is within tolerance even in this class of saw. If it cuts within
spec, I personally wouldn't worry about the numbers.
"Brett Austin" <Brett....@unh.edu> wrote in message
news:3B4B5132...@unh.edu...
Phil Anderson
I, too, was surprised when I got my Unisaw and checked for table flatness.
It's not. I just used my eyes and my Starrett staight edge. I could see
light under the Starrett, but didn't check with feeler gauges. At the
time, there were other posters here saying the same thing. Now, I've had
the saw for about three years. I've never noticed it to be a problem. My
advice: Get used to it. Nothing is like it used to be. Enjoy your new
saw!
Phil
--
mad...@foxinternet.net
Visit My Web Site
www.madrona.bizhosting.com
Brett Austin <Brett....@unh.edu> wrote in article
<3B4B3DF3...@unh.edu>...
> I just bought a new Powermatic 66 table saw last friday and was
> disappointed to find out that the central cast iron table was not flat.
> I measured the table with my Starrett straight edge and a set of feeler
> gauges and found that it was very flat parallel to the miter slots but
> perpendicular to the slots the table was dished out so that the center
> was 0.008 inches lower than the outter edges. <snip>
Mark C
tighter than 0.008 you may as well tack on an extra $100.00 per .001 that
you want to hold. Someone in this group must have some grinding experience
that could elaborate on this, but I can tell you from my experience with
the NuCraft router tables that holding anything at 0.007 or less which this
table is spec'd at, is expensive. At this tolerance, a piece of wood can
change more in size overnight!
Mark
http://www.sawdustsales.com Home of the monthly woodworking giveaway!!
http://www.tablesawguards.com
Steve Strickland
<Brett....@unh.edu> wrote:
This depends on the type of work you do. If you're making 3D mechanical
wooden puzzles a table top curvature of 0.008" is a total disaster. If you
are making furniture then don't worry about it.
First, I'd check and make sure that the support frame is not warping the
table. Once you are satisfied with this then the only cure I can think of
is to remove the top and take it to a machine shop and have it surface
ground. I seriously doubt that the manufacturer either could or would
improve the flatness.
While you're at it, check the straightness of the miter grooves. If they
are like the top then you might want to have these machined also.
For small, local depressions in the top you can drill a bunch of small
holes and fill in the area with Liquid Steel or JB Weld epoxy. Sand the
epoxy down flat checking it with your straight edge. The patch looks ugly
but it works remarkably well and is permanent.
--
Steve Strickland, Puzzlecraft
st...@puzzlecraft.com
www.puzzlecraft.com
CW
in fact, many, if not most, tablesaw tops are that close after grinding.
There are many factors that contribute to an un flat top. As cast, a piece
of cast iron has built in stresses, internal and surface. If one side only
is machined, the stress on that side will be relieved, causing the stress on
the other side the pull it out of flat. Even if it machined all over,
internal stresses will eventually relieve themselves and cause a warp. The
problem is usually not the grinding, it is the manufacturer not dealing with
these stresses adequately. Years ago, it was common machine shop practice to
rough machine a casting well oversize then store it out back of the shop for
a couple of years. The heating and cooling it was subjected to by normal
weather would cause the part to stress relieve. They would then machine it
to size and be confident that it would hold it's shape. The modern method of
doing this involves heating and cooling in a furnace. Either method ads cost
to the part and would likely not be done or not be done adequately for
something like a tablesaw.
To the original poster. Powermatic holds their tolerances to .010 or less
for a reason. It is not that they are lazy. It is because they know that
flater than that would make no difference in the performance of the saw. I
agree with them.
Of course, you could always through it out back for a couple of years then
have it ground :)
--
CW
KC7NOD
"Mark C" <stkb...@earthlink.net> wrote in message
news:3B4B9534...@earthlink.net...
CW
"Steve Strickland" <st...@puzzlecraft.com> wrote in message
news:steve-10070...@as-5-176-tyl.cox-internet.com...
Lawrence Wasserman
of an inch. I can't see what kind of problem that would cause. Enjoy
your new saw.
--
Larry Wasserman Baltimore, Maryland
lwas...@charm.net
Brett Austin
the top to the cabinet were causing any of the problem and it appears
that that was a contributing factor. Powermatic uses 3 bolts to hold
its tables to the saw cabinet, 2 on the front corners and one in the
middle of the back. I loosened all of the bolts and rechecked the top
for flatness. The back measured much flatter (around 0.002 inches but
the front was still the same 0.008. I suspect that maybe I should have
removed the fence rail too.
Anyway, I appreciate all of your comments. I think I am just going to
finish setting up and get back to work. If it does present a problem
later I guess I can allways find a local machine shop with a big enough
Blanchard grinder to flatten the surface.
As an aside. I checked out an old Delta unisaw which is in the machine
shop at my work and it was absolutely dead flat.
Thanks,
Brett
Steve Wilson
.008 is OK depending where it is. How is the table around the throat
(especially in front) and how sweeping is the dip. If it's .008
evenly spread from wing to wing then you'll likely be ok. If it's
diping .008 within 4 inches (left to right) and it's doing that right
near the saw's opening then you might have a problem. Tell the dealer
that you'll try the saw out and if your not satisfied with the cut
then return it. Be forcefull, and if you paid with a credit card you
might want to hold up the charge (dispute it) if your dealer doesn't
believe in helping you. More than likely this won't be a problem, but
I could see a case, depending on where the dip is, where this could
lead to problems making square cuts with the fence, or in accurately
cutting dato's (depth migh vary), etc.
Steve
Jeff LaCoss
Brett Austin wrote:
>
> I just bought a new Powermatic 66 table saw last friday and was
[...]
> perpendicular to the slots the table was dished out so that the center
> was 0.008 inches lower than the outter edges. I contacted both
> Powermatic and the dealer I bought the saw from and they both had the
> same answer, "Powermatic specs the table flatness to 0.010 or less".
> Therefore, they both concluded that my saw had no defect.
> Am I being too picky here?
Yep.
Consider that the base of the saw is made of sheet metal. If
you get a bent ear or a flange to within 4-5 thousandths of it's
nominal location, you're doing well.
Now, heave a non-solid (webbed) cast iron plate onto a box
made of sheet metal, and gronk it down with substantial bolts.
The plate won't be flat any more.
Hang a couple hundred pounds of iron and copper from the center
of the top, and I guarantee the things gonna sag some in the
middle.
Is this ia problem? I don't think so. Seasonal movement of wood
will create bigger changes than the out of flatness of your saw
table. Now it MIGHT make a very slight difference when cutting
miters, but I don't see that as a show-stopper: you have to be
systematic about cutting wood so that angular inaccuracies cancel
out, even on dead-flat tables.
I was talking with Frank Klausz about how flat a workbench top
should be. I mentioned that people in this NG have talked about
trying for 0.001". Frank thought that was pretty amusing - he
planes down the top of his when it gets really mauled, but said
his shifts through the year enough so that hand-planing is plenty
good enough for the work he does.
I mean, hell, we're just working with wood, not plutonium.
Jeff
Richard Chaney
Richard