# Help with guide for using a jig



## LoriWD (Apr 11, 2016)

I'm trying to produce some general /generic guides to using a router and accessories etc. To help beginners, like me, and student users. 

If anyone can help and review my information I'd be very grateful for some expert help and corrections you can provide.

This is what I have in regards to offset:

'The offset is the difference between the edge of any jig or template and where the cut will actually be made in the material when using a guide bush. Most jigs need to be used with a guide bush, but some, more basic, templates may just require a guided cutter, which would not have any offset and will produce a cut which is the same size as the template. The offset depends on the combination of guide bush and cutter being used. 

CALCULATING THE OFFSET

Take the diameter of the guide bush's collar, subtract the diameter of the cutter (which is the distance between the outside of the cutting edges, rather than the diameter of the cutter's shaft) and half this.
(Guide bush collar diameter - cutter diameter) ÷ 2 = Offset
This is how far away from the edge of the template the cut will be made. When routing out holes or other openings, following the inside edge of a template, this is how much smaller the hole will be compared to the template outline. When routing out shapes, following the outside edge of a template, this figure is how much larger the cut out shape will be compared to the template.'

Thank you in advance :laugh2:


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## Cherryville Chuck (Sep 28, 2010)

Welcome Lori. I think you have it worded very well.


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## LoriWD (Apr 11, 2016)

Thank you very much, and thanks for taking the time to read it


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## cocobolo1 (Dec 31, 2015)

Welcome to the forum Lori. 

I'm not sure that you need too much help from us old codgers...speaking for myself that is. More likely that you can teach us a thing or two! :smile:


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## LoriWD (Apr 11, 2016)

I appreciate the faith you have in me but I'm a total novice  And experience beats youth everytime!


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## furboo (Oct 12, 2015)

Lori, you've worded it well. A picture might help...maybe something like this from Lee Valley:

Lee Valley Tools - Woodworking Newsletter Vol. 1, Issue 4

See their next page in the article, too.


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## gjackson52 (Jul 4, 2015)

Welcome to the forum !



Gary


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## Mike (Nov 22, 2004)

Lori, bearing guided bits can have different offsets by changing the bearing size. 2nd and 3rd up from the bottom right you will see two stacks of different sized bearings sold for this purpose. Notice I drilled a small hole next to them for storing the Allen wrench to keep it handy.

I also attached the guide bushing cheat sheets from the Router Workshop(Oak Park) and Trend. Knowing the formula is great but having the sheet by your router table can save time.


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## old55 (Aug 11, 2013)

Welcome to the forum Lori.


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## Quillman (Aug 16, 2010)

"If anyone can help and review my information I'd be very grateful for some expert help and corrections you can provide.*
**************************************************************************
In my view, it boils down to measurement. Just how accurate can you measure? There are so many variables in routing, a well measured calibration cut (on scrap) is essential. Some of the variables include the cutter diameter, the centricity of collar to cutter, the location and design of the templet, and what tools you use to measure the result and how well can you do that?

Is it a direct or transfer measurement, can you hold the measuring tool for the most accurate measurement, is it (the measuring tool) calibrated and so on. 

Edge guides, base plates, circle makers, shank bearings, collar guides, router table fences, if made well, can work with precision. But not necessarily on the first shot. Your material prep is just as important.
If your stock is misshapen or poorly prepared then you'll have more variability from stick to stick. 

Woodworking/routing, compared to metal work, is still in the dark ages.
It's getting better, but if you want reputability, precision, predictability, and accuracy you have to make that calibration cut first.
There's more to this story, but knowing how to calculate the cutter target (as Lori has done) for one guide system is just the starting point.


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