Problems with measuring offset of cut - Router Forums
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post #1 of 11 (permalink) Old 08-21-2014, 10:46 AM Thread Starter
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Default Problems with measuring offset of cut

I'm building some bookcases and am at a stage where I need to make three quarter inch square cuts at the ends of the top of the case so it will fit down over the sides of the cases.
I'm using a Craftsman router that I haven't worked with for a while. The offset from the right side of where I want the cut to be is three and a half inches. I've calculated it three or four different ways.
I make a mark three and a half inches from the end of the board and clamp a square securely flush with the edge of the board to use as a guide.
When I make the cut it winds up being off anywhere from one quarter to one eighth to the left of where I want it to be. I cannot get the same result two times in a row.

Any suggestions?
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post #2 of 11 (permalink) Old 08-21-2014, 11:51 AM
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Art,

From your description it sounds like you are intending to use the outside of the router base along a clamped board as a guide. The distance from the center of the bit to the outside of the router is 1/2 of the diameter of the router. So if you are figuring this to be 3-1/2" this would mean your router base is 7" across on its diameter (7 divided by 2 = 3.5). If your router base has a different diameter than 7 inches, then the offset to the center of your bit will be different.

When calculating the offset to the edge of the bit you need to subtract 1/2 of the bit diameter form the offset to the center of the bit. Example: If you are using a 3/4" bit, 1/2 of the diameter of this bit is 3/8". So the offset would be 3-1/2" - 3/8" = 3-1/8" from edge of router to near edge of bit.

Another consideration is how thick of stock is the wooden guide you are clamping to your work piece. Some Craftsman routers have a casting that sweeps out to the handles. If your stock is too thick (greater than 1/4") then this outward sweep of the casting will push our router away from your guide if your handles move toward the guide.
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post #3 of 11 (permalink) Old 08-21-2014, 12:11 PM
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Welcome to the forum Art. You are able to post pictures and diagrams if needed as long as they are in the hard drive of your computer. You would click on the Go Advanced button and then click on Browse Files where you will go to find the file you want to upload.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #4 of 11 (permalink) Old 08-21-2014, 12:57 PM
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Stop.
No matter what router, routing, using the subbase, will be ambiguous. Don't use it. The subbase, unless a square or rectangle, cannot be counted on to locate a cutter position.
A collar system is a better choice but only if that collar can be centered to the cutter.
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post #5 of 11 (permalink) Old 08-21-2014, 01:50 PM
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Quote:
Originally Posted by Art Hackett View Post
I'm building some bookcases and am at a stage where I need to make three quarter inch square cuts at the ends of the top of the case so it will fit down over the sides of the cases.
I'm using a Craftsman router that I haven't worked with for a while. The offset from the right side of where I want the cut to be is three and a half inches. I've calculated it three or four different ways.
I make a mark three and a half inches from the end of the board and clamp a square securely flush with the edge of the board to use as a guide.
When I make the cut it winds up being off anywhere from one quarter to one eighth to the left of where I want it to be. I cannot get the same result two times in a row.

Any suggestions?
If you are using the base of the router it may not be concentric with the bit. If the base is square, one edge may be shorter/longer than the other. If base is round it may not be centered on the bit. If you might be using a different part of the base as you pick up and use the router each time it could account for inconsistent cuts with the same router.

If this is the case, center the base if round or use the same edge if square base.

Good luck...Nick

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post #6 of 11 (permalink) Old 08-22-2014, 07:11 AM
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I agree with Pat. As said ,just make sure the collar is exactly centered.
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post #7 of 11 (permalink) Old 08-23-2014, 12:08 AM
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Hi Art, All of these are good suggestions, but not the easy way. My way is to take a piece of scrap and clamp a strait edge to it and make a cut. Then measure the distance from the strait edge to the edge of the dado you just cut in the scrap. From that point on all you need to do is mark one edge of the cut plus that measurement, and clamp your strait edge in place. You do need to make sure you always keep the router base turned the exact same way toward strait edge. Just mark the router with a Sharpie, and write the measurement down to remind yourself.

Dick

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post #8 of 11 (permalink) Old 08-23-2014, 04:08 AM
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Welcome to the forum Art.

Ross,
Rockhampton, Queensland, Australia


Enjoy the knowledge of others that can be found within.

‘Members are requested to add a first name in their profile as we are a very friendly bunch here'.
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post #9 of 11 (permalink) Old 08-23-2014, 09:07 PM
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Quote:
Originally Posted by Willway View Post
Hi Art, All of these are good suggestions, but not the easy way. My way is to take a piece of scrap and clamp a strait edge to it and make a cut. Then measure the distance from the strait edge to the edge of the dado you just cut in the scrap. From that point on all you need to do is mark one edge of the cut plus that measurement, and clamp your strait edge in place. You do need to make sure you always keep the router base turned the exact same way toward strait edge. Just mark the router with a Sharpie, and write the measurement down to remind yourself.

Dick
+1 for a quick and easy way to make the cut without having to make a jig.

Saw this method also on youtube, but can't seem to find it....


Maybe this will explain better.

http://shar.es/1nSAjG

The first part applies in your case.

James
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Last edited by jw2170; 08-23-2014 at 09:39 PM. Reason: aadd link
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post #10 of 11 (permalink) Old 08-24-2014, 08:26 AM
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Quote:
Originally Posted by Willway View Post
Hi Art, All of these are good suggestions, but not the easy way. My way is to take a piece of scrap and clamp a strait edge to it and make a cut. Then measure the distance from the strait edge to the edge of the dado you just cut in the scrap. From that point on all you need to do is mark one edge of the cut plus that measurement, and clamp your strait edge in place. You do need to make sure you always keep the router base turned the exact same way toward strait edge. Just mark the router with a Sharpie, and write the measurement down to remind yourself.

Dick
I agree. I have templates I have made for the different diameter bits I use. Keep that in mind.


Just remember what my father always said, " Half the people in this world are below average!", and everything in life will make a hellova lot more sense.
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