Powermatic 66 fence problem

...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

Reply to
Charlie Groh
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Either the tape on the scale, or the tape your using to measure the cut part, or both, are off

Barry.

Reply to
B a r r y

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

Reply to
Unisaw A100

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.

Reply to
Greg Millen

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.

Reply to
Mike Marlow

Could be, but you've never seen an inaccurate tape?

Barry

Reply to
B a r r y

B space a space r space r space y

Which begs the question, how do you know you have an accurate measuring device?

UA100

Reply to
Unisaw A100

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.

Reply to
Swingman

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.

Reply to
Swingman

================ First of all MY fence is set up with about 1/32 inch offset at the 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...

Reply to
Bob G.

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.)

Reply to
Swingman
** *>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. * *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

Reply to
Charlie Groh
*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

Reply to
Charlie Groh

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.

Reply to
Pounds on Wood

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

Reply to
Richard Cline

Some sort of standard.

My standard is my ts fence rail, as it's the hardest measuring device in the shop to change. 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

Reply to
B a r r y

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

Reply to
Bob Summers
** *>...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 *> *> *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

Reply to
Charlie Groh

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 ?

Reply to
Charlie Campney

I'd bet you've got the most likely suggestion Charlie. It can't be his tape or paralax as others have suggested or he would never have gotten accurate cuts on shorter pieces. If I understand him correctly, he's seeing a run on longer pieces and a blade that is too thin (thin kerf) or one improperly sharpened seem like they could well be the culprit. This has captured my interest - have to mark this thread as one to follow.

Reply to
Mike Marlow

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