Powermatic 66 fence problem

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...just thought I'd throw this into the mix: I have encountered an accuracy problem having to do with the fence, I think?! Before I go on, it's lined up fine...fence is perfectly parallel with the blade and blade is at 90 degrees. When I adjust the scale, the machine cuts perfectly up to maybe 10 inches...then my final measurement creeps up to about a 32nd at 36 inches or so. Huh? This has been a poser for a while and I've learned to check fence to blade to compensate, but what the heck is going on?
Charlie Groh
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On Sat, 1 May 2004 22:35:48 -0700, "Charlie Groh"

Either the tape on the scale, or the tape your using to measure the cut part, or both, are off
Barry.
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Charlie Groh wrote:

Are you saying your scale (the measuring tape thingy) on the front rail is off?
If so, how do you know this? What I'm getting at is, are you cutting using the scale from the saw and then checking with a hand held tape? If so it could be your tape or it could be the scale on the saw. You need to determine which is correct.
UA100
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Unisaw A100 wrote:

He said that once he sets it up, it cuts fine on shorter pieces - up to 10 inces, but wanders on longer pieces. At least that's what I get from his description. In that case, I can't see anything but a fence that is not holding well and is creeping at the front as the pressure from longer pieces is applied to it. I'd take a hard look at the lock down on the fence.
--

-Mike-
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On Sun, 02 May 2004 11:56:33 GMT, "Mike Marlow"

Could be, but you've never seen an inaccurate tape?
Barry
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B space a space r space r space y

Which begs the question, how do you know you have an accurate measuring device?
UA100
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wrote:
*B space a space r space r space y *>Could be, but you've never seen an inaccurate tape?* * * *Which begs the question, how do you know you have an *accurate measuring device? * *UA100
...good thought. My brother is a machinist and our conversations about tolerances are, ah, interesting! He thinks in "tenths" (ten-thousanths of an inch) and I get to 128th on a good day. So, once upon a time, he gave me a state of the art set of calipers. Since then, I've made a few mdf and some ply patterns representing "perfect" measurements. When I need to tune the saw, or any given measuring device I use, I use these patterns as my bench mark. Works well, for an old framer anyhow! :O)
Charlie Groh
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wrote:

Some sort of standard.
My standard is my ts fence rail, as it's the hardest measuring device in the shop to change. <G> I have a few tapes that agree with it, but stick with one throughout a project. My favorite is a 16' "center finding" tape I bought from Lee Valley.
I have no idea if any of them are truly accurate beyond my needs.
Barry
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"B a r r y" wrote in message

I don't think I've ever seen an "accurate" one .. just ones that don't read _precisely_ the same. :)
I do have two Stanley ten footers that _agree_ with my table saw fence to less than a 64th over 50", as best as I can actually _see_.
I wouldn't trade either for all the Starret's in the world that don't.
--
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On Sun, 02 May 2004 12:33:55 GMT, B a r r y
*On Sun, 02 May 2004 11:56:33 GMT, "Mike Marlow"
*>He said that once he sets it up, it cuts fine on shorter pieces - upto 10 *>inces, but wanders on longer pieces. At least that's what I getfrom his *>description. In that case, I can't see anything but a fence that isnot *>holding well and is creeping at the front as the pressure fromlonger pieces *>is applied to it. I'd take a hard look at the lock down on thefence. * *Could be, but you've never seen an inaccurate tape? * *Barry
...these are good replys, you guys. The info I gave does allow for your hypothesis, Barry, although I've had the saw for 10 years and this problem has cropped-up in the last year or so...the tape is fine, as is the tape I make my final measurements with. I think you have a good idea, Mike, and I'll really check out the fence. Thanks for the help, gentlemen! cg
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snipped-for-privacy@groundhogday.yeah wrote:
If I had a problem resembling this on a band saw I would blame the blade or the tension. Is there any possibility that your blade has some damage that causes it to "pull" to one side? You might test this idea with a different blade -- assuming that the problem is reproducable.
Dick

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"Mike Marlow" wrote in message

I'm with you on this Mike. If he is indeed describing, as it certainly appears, a "tapered cut", that problem is generally caused by a misalignment, most likely blade and fence, or a fence that is flexing/moving.
The first thing that I would check, despite what was said about being "perfectly parallel with the blade", is to see if the back of the fence is not toed out too far away from the blade.
--
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Check the set screws that set the fence to blade parallelism. Mine went south a few weeks ago and the fence would go out of parallel. I used locktite 241 to keep them in place. You can break the screw out of the 241 if necessary in the future. The factory screws are nyloks and won't last forever.
Ed Angell

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Charlie,
Barry and Keith are likely correct, a while ago I had a problem with a tape that had a slight logarithmic progression on it. It drove me nuts until I discovered the error. Check the tape.
--
Greg

"Charlie Groh" < snipped-for-privacy@groundhogday.yeah> wrote in message
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On Sat, 1 May 2004 22:35:48 -0700, "Charlie Groh"

back of the fence... BUT I have no problem sawing a 8 foot 1x6 down to a 1x 3 and having both ends of the finished piece measure 3 inches...
I keep the workpiece firmly against the fence at a point just if front of the blade itself..I could care less how far the work piece is away from the fence at the rear.. if everything is dead on parralel like you say then I think you are not feeding the stock correctly...
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"Bob G." wrote in message

Just a case in point.
I recently bought a Unit-T-Fence to go on my UniFence. Since it is supposedly a slide-on replacement, I didn't bother to initially check the alignment when I "slid" it on.
When I did, I found the toe-out at the bottom rear of this fence replacement to be almost 3/32" ... that's about five times the recommended 1/64th toe-out for those who subscribe to the theory.
Hell of it is, the cuts are, like yours, absolutely dead-on consistent from one end to the other.
While I am aware of the obvious departure from normal, I have chosen to ignore it since I firmly believe that whatever gets the results you want is obviously correct for that particular situation.
(One of the reasons I am not too worried about it is that the strip of UHMW could well be worn at that particular spot, or is inconsistent in thickness throughout the length of the fence ... it's not like I am dealing with metal.)
--
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My first guess, like the other replies, is a tape measure problem.
But, let's say that doesn't turn out to be the problem. Second guess would be to check the front rail on your fence. If it has a bow it will affect accuracy and squareness as you slide the fence along said rail.
-- Bill Pounds http://www.billpounds.com/woodshop

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straight down on the cursor when you set the fence? 1/32" seems like about the right amount of error for it to be from parallax.
Bob S
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On 02 May 2004 16:24:04 EDT, snipped-for-privacy@yahoo.com (Bob Summers) wrote:
*On Sat, 1 May 2004 22:35:48 -0700, "Charlie Groh"
*>...just thought I'd throw this into the mix: I have encountered anaccuracy *>problem having to do with the fence, I think?! Before I go on, it'slined *>up fine...fence is perfectly parallel with the blade and blade is at90 *>degrees. When I adjust the scale, the machine cuts perfectly up tomaybe 10 *>inches...then my final measurement creeps up to about a 32nd at 36inches or *>so. Huh? This has been a poser for a while and I've learned tocheck fence *>to blade to compensate, but what the heck is going on?*> *>Charlie Groh*> *> *One possibility that hasn't been mentioned yet is parallax; are you looking *straight down on the cursor when you set the fence? 1/32" seems like about *the right amount of error for it to be from parallax. * *Bob S
...true, but I've messed around with that alot since learning about the "cheek weld" in army marksman training; in order to hit the target the same every time, you need for your eye to be in the same place relative to the sights every time. See? Same goes for anything re. accuracy vis-a-vis the position of your eyeball. A toughy for sure when looking down at a hair line and a scale. So, yeah, I've taken this factor into account. Another friend of mine mentioned the rail, but that's out also, as I'm the only person to operate my machine and would know about all the knocks and stuff. But in that discussion the nylon "keepers" attached to the fence were mentioned (this guy runs the cabinet shop for Universal Studios, the park, out here and they have great equipment...but he deals with a lot of others using it...you get the idea, heh.) so *that* got me to thinkin'...like I said, the machine is 10 years old and I haven't been so easy on it, either. I'll go through it this week and give you guys an update. cg
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Could it be the way the blade is shrpened ? Does it do that with other blades. Maybe the blade is pulling the piece away from the fence ?

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