Adjustable Dado jig - setup problems

[rovenm]

Hi,

I just got my new router a week ago and decided to build an adjustable dado jig as my first woodworking project.

I replaced the router base with a 7 inch base (the router came with a 6" base) and built my jig as per the instructions provided. When I tried to do a trial dado cut on a piece of scrap, I noticed that the 1/4 inch straigh bit did not align perfectly with one of the sides of the jib. There was a gap of approx. 1/8" resulting in the dado being smaller than the planned size.

What seems to be the problem here? Is it because the bit is not centered perfectly with the new router base? when the two boards (fixed and adjustable) are butted together, the 7" base fits in perfectly but the dado is off by 1/8".

Any suggestions are highly appreciated.

thanks

Roven

[niki]

Welcome to the forum Roven

I don't know which dado jig you are talking about (a picture would be helpful) but, it looks to me that your bit is not siting at the center of the router base...

I'm marking the side that I used for the jig and always work with the marked side facing the jig fence.

Regards
niki

Attachment 117158Attachment 117159

[rovenm]

Hi Niki,

thanks for the reply. I made my own jig which is similar to the pic posted on this link: http://www.routerforums.com/jigs-fix...-dado-jig.html. The jib has one fixed side and one adjustable side. The problem as you have pointed out could be caused due to the centering of the router base. Is there a way to find out if the bit is dead center. I was just eyeballing the bit to determine if it was centered.

[rovenm]

Thanks Niki. I will mark the side that try out one more time. The jig that I made was per the instructions that I got from this site: www.woodsmithshop.com/download/204/adjustabledadojig.pdf

[Afro Boy]

Is there a way to find out if the bit is dead center. I was just eyeballing the bit to determine if it was centered.

Not sure if this would work but it sounds logical ... Cut one dado with the router then measure the width with some accurate calipers. Then rotate the router 180 degrees and cut into the same dado. Measure again.

If the second cut is wider then your bit is off centre (or your jig moved!)

This won't tell you which side it is closer to but will let you know that you need to be careful using the same side to the fence each time.

Cheers,
Af.

[rovenm]

Thanks AF. Will do this test.

[Afro Boy]

Something else I just read ... If you have a guide bushing, you can put that in with a dovetail bit that is larger/wide than the bushing itself. Then release the plunge until the bit just barely touches the inside edge of the bushing. Rotate the bit by hand and you should be able to see if it is close to any one side than the other.

Af.

[Stevenp]

G'day Roven, I have made a couple of these jigs over the years and found them to be excellent.
When making one of these the base needs to be a bit wider than necessary so that the router bit trims the base to size with the first cut. The jig will only work with the bit that was used to trim it, so make a note of which bit was used.
Once the jig is trimmed the first time it is simply a matter of using a piece of the material that is to fit in the dadoe, as a "sizer" and away you go.
I have found these to be a great asset in my shed, I hope you work this one out.
Cheers Steven.

[rovenm]

Thanks Steven.

[mailee]

I too use one of these jigs for cutting dados. I use the same cutter that I used to trim the jig as has been suggested and it works fine. You will find however that even the router base is not concentric across it's base. No matter how good the tooling is that made the machine there will be discrepencies albeit of just a few thou or so but it will be there. I always reference the same side of the router to the jig face to ensure the cut is central and this works fine for me. If however you do change the cutter it will effect the dado size and you will have to account for this. HTH.

[rovenm]

I have got the jig to work and have done a few dados. Thanks for all the suggestions received.