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Discussion Starter · #1 ·
The other day I made up a little jig to flatten on one side of a rectangular blank. All it was was a base with two pieces of wood fixed down to run the router along with the blank fixed in between so nothing complicated. When I'd finished I had a nice finish on both sides of the blank which I was happy with but I noticed that one end of the blank was about 0.4mm thicker than the other even though the jig was good for about 0.1mm over about a 100mm length.

I realise that there are many factors that can affect the outcome and in this in this instance it's not an issue but, not having much experience at all with routers, I was just curious as to what sort of tolerances to expect when doing something like that.
 

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Not sure how you cut the piece. If on a tale saw, using a miter gauge, it could just be that your not set at an exact 90, or your saw's not tuned properly with a fence not parallel with the blade or miter slot. Or the fence wasn't tightened up and crept slightly. Did you cut this on the table saw?

That isn't much of an error over 4 inches, but it's a little more than I would like. We could use more information and a picture when you get a chance.
 

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at about 1/64'' over 4''...
that's good..
1/64'' tolerance is very good... it's wood...

are your resting/holding blocks of uniform thickness...
sawdust got under something somewhere... the block or the rests...
the surface the block rested on had a bump on it...
raised grain will give you that much...

did you face both sides of the block???
what held the milled block down???
 

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Discussion Starter · #7 ·
Here's a couple of pics of what I did. As you can see it's just a bit of MDF for the base with a bit of scrap I cut in two and which isn't as rough as it looks in these pics and is actually more level than I had expected. They're screwed down and the blank was stuck down in between using the masking tape/CA glue method.

The blank is one I acquired many moons ago and I have no idea how it was cut. One side was pretty clean so I just cleaned it up on the sander and stuck that face down to clean up the other side with the router.

Thinking about it last night, it's entirely possible that the masking tape and glue wasn't totally flat, even a small wrinkle in the tape would account for what I found.

Like I say, in this case it isn't a problem and was just something I was curious.

I also fully realise that you're probably all looking at the pics and thinking "What the &$"#? are you doing it that way for??!!??" :lol::lol: I'm all ears to other methods :grin:
 

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Did you measure the guide strips to see if they are the same height from one end to the other? it looks ,from the grain that the cut ends are on the same end of the jig, and if the long stick before you cut it had thicker ends than the middle it would cause the guide pieces to be tapered from one end to the other by 1/64".

Herb
 

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Discussion Starter · #11 ·
Did you measure the guide strips to see if they are the same height from one end to the other? it looks ,from the grain that the cut ends are on the same end of the jig, and if the long stick before you cut it had thicker ends than the middle it would cause the guide pieces to be tapered from one end to the other by 1/64".

Herb
When I checked them they were flat to within 0.1 to 0.2mm over the length. I'm thinking more it was the tape I used to hold the blank down. Next time I'll probably spend a little bit more time setting it up just as a challenge to see how accurate I can get it although I know from past experience that that sort of thing can become an obsession very quickly :grin:
 
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