Mortise Measuring - Router Forums
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post #1 of 16 (permalink) Old 03-30-2009, 08:55 PM Thread Starter
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Default Mortise Measuring

I’m practising on a scrap 1/2” MDF to make my 1st mortise

I bought from Lee Valley a length of 3/8”x 2” tenon and checking with my micrometer it reads 3/8” (0.37”)

I chuck up a 1/2” shank 3/8” bit on the router

I route the mortise to 1/4” depth in 2 passes but the tenon fits loose on the 3/8" dimension, about 1/32”

I measure the mortise and it is 0.38” to 0.39”

Am I doing something wrong?

Thank you
Nicolas
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post #2 of 16 (permalink) Old 03-30-2009, 09:08 PM
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You need room for the glue. If it was a tight fit the glue would get scrubbed off when you put the pieces together.
Did you measure the bit width?

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post #3 of 16 (permalink) Old 03-30-2009, 10:30 PM Thread Starter
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Hello Mike

I measured the bit with micrometer and it's 3/8" (0.375")

Never done a mortise before and so I know nothing about it. I just have seen some videos and have noticed that they push the tenon into the mortise; it looks like a tight fit and mine it's not. I'm almost sure it's not correct what I did.

I know about the spacing required for the glue. The sides of the tenon I bought are covered with grooves to easy off the glue.

Perhaps you don't use a 3/8" bit to do a 3/8" mortise. May be you use a 1/4" bit and make a few passes until you get a hair line before the 3/8"?

Nicolas
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post #4 of 16 (permalink) Old 03-31-2009, 07:25 AM
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Those were just some thoughts of mine. I have yet to use the router for the job, having a mortiser for the drill press. I'm waiting for someone to bail you out so I'll learn something too.

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post #5 of 16 (permalink) Old 03-31-2009, 09:37 AM
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Using a .375 bit to cut a .375 mortise assumes that there is no variation in the mechanics of the jig nor with the operator. It's difficult to maintain tolerances that tight under the best of circumstances with hand operations. You might be better off using a 5/16" bit, pressing it to one side of the template in one direction, and then the other side in the opposite direction. Them, lightly trim the loose tenon to fit as desired.

In hand work (non-router), the tenon is usually cut a smidgen over-sized, and then trimmed to fit with a shoulder plane, rabbet plane or float (specialized file).

Once glue is applied, the fit should be tight enough to require light to moderate pressure to seat the pieces. If it needs to be hammered into place, it's probably too tight.

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post #6 of 16 (permalink) Old 03-31-2009, 11:00 AM
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Nicolas
It sounds like you are trying for some very tight tolerances. I cut all my mortises first then I cut the tenons to fit them. I cut them to fit tight and then loosen them up enough for the glue with a rasp and sandpaper or a hand plane. It sounds to me you are trying to make it more dificult then it realy is.
Good luck
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post #7 of 16 (permalink) Old 03-31-2009, 12:19 PM Thread Starter
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Ralph, I like your idea with the 5/16" bit, perhaps that's the way to go.

However I found what my problem was

The first bit I used was a 1/2” shank 3/8” bit. This time I used a 1/4” shank 3/8” bit and the results was the same. Then I turned the router base to have the long face ride against the fence and presto the mortise came out perfect, the tenon now fits like a glove, just a slight pressure and she goes in snug.

This phenolic 3/8” thick 9”x 12” base I bought it a couple of months back and had no holes pre drilled and I used the base of my router as a template to drill the holes. But it seems that I’m out by about 1/32” on this base alignment to the center of the bit. Although I used the drill press I guess somehow did not work perfect.

But I still don’t understand this. Since now I know which side of the base is the good one, I chuck up again the same 1/2” shank 3/8” bit and did a now mortise and this one became loose again like the first one.

Have to scratch my head again for more ideas....

Nicolas
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post #8 of 16 (permalink) Old 03-31-2009, 02:30 PM
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Hi Nicolas,

The distance between the bearings need to be same from the center of the bit. This will give a true cutting. Pending on if you're pushing or pulling the router, also depends on which side each bearing rides on. You still need to have a certain amount of room for glue up. You make the mortises first, then the tenons. The tenons are made to fit. Check your measurements from bearing to bit. If these aren't the same, your mortises will be off.

I have the OP 7" x 7" plate and the bearings are dead on. Makes mortises quite easily.

Ken

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post #9 of 16 (permalink) Old 03-31-2009, 11:42 PM Thread Starter
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Thank you Ken

I had a look at the OP 7"x7" plate and the bearings and they look good. I may go for them

Nicolas
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post #10 of 16 (permalink) Old 03-31-2009, 11:52 PM
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HI Nicolas

Here's a shot of the plate and a jig you can make very easy.

http://www.routerforums.com/jigs-fix...ge-router.html

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Quote:
Originally Posted by kolias View Post
Thank you Ken

I had a look at the OP 7"x7" plate and the bearings and they look good. I may go for them

Nicolas



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