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Forum topic by Silverline posted 02-23-2019 02:12 AM 468 views 0 times favorited 12 replies Add to Favorites Watch
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Silverline

11 posts in 32 days


02-23-2019 02:12 AM

Can’t figure this one out and it’s driving me crazy. So I have a cabinet project and I have to make a lot of dado’s. I want to make a straight edge jig so I don’t have to measure the offset from my dado to my straight edge every time.

So I made this zero clearance jig. The bottom piece is 1/2” MDF and was wider than the offset from the outer edge of my router base to my bit. The top piece is 3/4” MDF for the straight edge. Once I had everything put together I ran the router along the top straight edge to create the zero clearance edge on the bottom.

I clamped up the jig on a test piece and cut a dado. I was surprised after the cut to the the dado was about 1/32” away from the zero clearance guide. And it’s not in just one spot, it’s perfectly square and +1/32” along the entire line.

I set the router back on the jig against the straight edge and looked under the base and saw the bit was about 1/32” away from the zero clearance edge. How is that possible if I followed the straight edge on on the top.

I even made another jig and have the exact same condition.

 photo IMG-0246_zpsscskwz9h.jpg


12 replies so far

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Andybb

1797 posts in 901 days


#1 posted 02-23-2019 03:10 AM

Send us a picture of the bit and router on the jig and your router base. Is there a bushing on your router base?? Some bases aren’t perfectly round. Make sure you keep the same section of the base along the top board that you used to measure it.

I use this jig.

Here are others.

Here is one that looks just like yours.

-- Andy - Seattle USA

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Lazyman

3098 posts in 1685 days


#2 posted 02-23-2019 03:19 AM

Is it possible that your router base is not centered? If not then turning the router so that a different point is against the jig’s fence when you make it versus when you make the cut, you’ll get a discrepancy. My router came with a special cone that is for centering the base. Look to see if your base is adjustable.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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Silverline

11 posts in 32 days


#3 posted 02-23-2019 03:24 AM

Here is a pic of my router with bit.

 photo IMG-0253_zpslugy2ekd.jpg

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Andybb

1797 posts in 901 days


#4 posted 02-23-2019 03:27 AM

+1 Lazyman. You worded that better than I did.

Ok. So no bushing.

The other thing to make sure of is that you make the bottom piece wider than the distance to your bit and then cut it off so that the bit is making the measurement for the bottom piece, if that makes sense.

My first thought though is that you are not using the same part of the base against the fence like we’ve both said. Use a reference point like the handle. Put the handle against the fence when you cut the jig, then put THE SAME handle against the fence when you cut your dado so you know you’re using the same section of the router base. Again, let the router cut the bottom piece, then you don’t need to measure.

-- Andy - Seattle USA

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Woodknack

12640 posts in 2678 days


#5 posted 02-23-2019 03:29 AM



Is it possible that your router base is not centered?
- Lazyman

+1
Bingo!

This is why some routers have a flat side on the base, and why some people make bases with a flat side, just so they don’t have to worry about getting the base perfectly centered.

-- Rick M, http://thewoodknack.blogspot.com/

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Silverline

11 posts in 32 days


#6 posted 02-23-2019 03:43 AM

Interesting. I just assumed the bit is centered and with the base being round it didn’t matter what part of the base you use against the straight edge.

And you are correct, I did start with the bottom piece wider so that my first cut with the jig was to zero the base do no measuring would be needed. That’s why I was so surprised when it was off.


+1 Lazyman. You worded that better than I did.

Ok. So no bushing.

The other thing to make sure of is that you make the bottom piece wider than the distance to your bit and then cut it off so that the bit is making the measurement for the bottom piece, if that makes sense.

My first thought though is that you are not using the same part of the base against the fence like we ve both said. Use a reference point like the handle. Put the handle against the fence when you cut the jig, then put THE SAME handle against the fence when you cut your dado so you know you re using the same section of the router base. Again, let the router cut the bottom piece, then you don t need to measure.

- Andybb


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Silverline

11 posts in 32 days


#7 posted 02-23-2019 12:55 PM

Upon further review the baseplate was not centered. Didn’t even now that was possible since the holes on the plat and the threaded holes on the router base are all in a fixed position. But I took it off and reseated the base plate and screwed it back down. Measurement from the edge of the plate to the center of the bit was consistent from 4 different spots on the base plate.

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Silverline

11 posts in 32 days


#8 posted 02-23-2019 03:51 PM

UPDATE: Life is good. Made a new jig with the now centered router base. Cut a test piece and the edge of the joint ran perfectly even along the zero clearance edge. Thanks for the guidance. Time to cut some rabbets and dado’s!
 photo IMG-0264_zpsisvncdy5.jpg

View Robert's profile

Robert

3316 posts in 1779 days


#9 posted 02-23-2019 04:22 PM

I recommend dado jigs with guides runners on both sides of the plate.

You’ll thank me the first time the bit drifts.

-- Everything is a prototype thats why its one of a kind!!

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Andybb

1797 posts in 901 days


#10 posted 02-23-2019 04:26 PM

+1 on the guides on both sides. If you’re making multiple cabinets as rwe said, Murphy’s Law will make that bit drift at some point.

Take a look at the jig I linked to.

Glad you figured it out.

-- Andy - Seattle USA

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John_

197 posts in 2004 days


#11 posted 02-23-2019 07:54 PM



I recommend dado jigs with guides runners on both sides of the plate.

You ll thank me the first time the bit drifts.

- rwe2156

+1

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Andybb

1797 posts in 901 days


#12 posted 02-23-2019 08:20 PM

Definitely agree with John. The jig I linked to uses the same principle as the Woodpeckers tool he linked to and can be made for pennies on the dollar and can then be used for any width dado you want to cut. Also, what’s most important is that the dado will be cut to the exact width of your stock every time and the bit can’t drift. 3/4” stock isn’t always exactly 3/4”. 3/4” MDF and 3/4” plywood are not the same thickness, but your 3/4” bit IS 3/4”.

It might set you back a day or two to gather the parts and build but is worth the effort IMO. No drift and versatility. Plus, I enjoy building my own jigs, and the bushings are $25 and are good to have for other router work.

-- Andy - Seattle USA

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