so - how would you do this?

[durango dude]

I have a project (shaker style mantle clock) that calls for the following:

3/4" walnut 17" long - cut a 1/4" dado in the center (I'll put a quarter inch piece of maple plywood in the dado cut). (the 3/4" creates a frame)

Seems like a simple task - but I've done it 3 times, now ---- and still don't have the center of the 3/4" (I'm using pine to practice).

I can see that the dado is slightly off ---- but when I measure it - everything seems right (dado ends at 1/2" - and appears to be 1/4" wide).

I re-checked the wood --- yup, it's 3/4". (suspect it's off by 1/16" --- but my tape measure simply isn't that precise).

I'm thinking next project, I use some measuring bars - but there's no time to wait for them to arrive. This is for a project that I'm trying to finish by Christmas - so I need to get a move-on (can't wait for stuff, now).

I'm thinking that as long as I cut the same 1/4" dado cut in the same place throughout the "frame," I'll be fine. (the maple will fit).

With 1/16" error - I suspect I can handle adjustments with the sander.

[cabinetman]

I'm thinking that as long as I cut the same 1/4" dado cut in the same place throughout the "frame," I'll be fine. (the maple will fit).

Yes you should be. Use the same edges for reference.

.

[Daryl]

Set the dado for a little less than a 1/4 inch and then make a cut from each edge, it will be prefectly centered.

[durango dude]

Figured out what was going on.

My tape measure needs to be replaced (talked to Santa about that....)

In any event ---- I finally cut into my walnut - and simply kept the saw set the same for each piece. (off-center by 1/16"). I suspect the dado is slightly less than 1/4" (it's not a wobbler, though - and adding a shim makes it wider 1/4")

I asked Santa for some brass layout blocks and a new tape measure - and we should be a little better off, next time.

The hard part was cutting a tenon that matched my slightly off-center dado.

I figured that out, too. I started shallow, and worked my way up to where the dado matched the tenon. (did anyone know that when you adjust the blade height on the bt3000, you need to check the blade angle, again? - I figured that one out, too)

That said ---- cutting with such tight tolerances (1/16" can really ruin your day) is a new deal for me!

The shaker clock is 75% done as of tonight......

[LCHIEN]

if you're trying to split hairs on 3/4" material, a tape measure is far from the device i'd use to be measuring with.

If you really want it centered, use a flat top blade and set it to cut close the middle. Make another pass after flipping it over. The outer edges of the dado will be perfectly centered.

Use a pair of digital calipers - they are so inexpensive now a pair should be in everyone's box. Measure the width of the dado.

Subtract the width from your perfect .250" - split the difference in half, call it "X".

Move your fence to the right or left (this depends on whether the right or left edge of the blade is at the edge of the dado) by X or a smidge less - a microadjuster is your best friend for this. Make the cut and flip the wood and make another cut.

Measure again and repeat sneaking up on the .250" you want.

[cabinetman]

My tape measure needs to be replaced (talked to Santa about that....)

While tape measures certainly have their place, their markings aren't super accurate as the lines might be too wide for the application. A simple ruler with precision markings like this might be easier to use.

For depth measurements this gage works good for dadoes and rabbets.

I picked up a digital caliper for $9.99, from HF with one of the coupons that came out in several magazines and fliers. It's very accurate, and would help in doing some of those measurements. If you haven't seen the coupon, I have a few left, and would send you one for the asking.

.

[cork58]

The only place I use a tape measure is outside the shop. I have a few of the Lufkin 0x46 extension ruler. They are all the same and I can use one at the saw and another at the project table and have the same results. Tape measures will vary from one to another and are never absolute.

link: http://www.amazon.com/Lufkin-X46-6-F.../dp/B00002N5KI

Just my 2 cents

[Wood_workur]

While tape measures certainly have their place, their markings aren't super accurate as the lines might be too wide for the application. A simple ruler with precision markings like this might be easier to use.

I've got a collection of rules similar to that (probably a half dozen 6" ones and others up to 48"). I've found that they are marked the same as each other (all checked against the longest one with a good magnifying glass), and the engraved markings are very precise and won't disappear like the printed on ones will.

[cabinetman]

Tape measures will vary from one to another and are never absolute.

I have several tapes, and use the same one for a complete project. I do back up that tape with one that reads the same JIC.

.

[LCHIEN]

I published a how to tutorial on using calipers you might find useful.

[geeoh]

When I use a tape to find center, I measure and mark from both ends (not just one end) using either 1/2 the total length or just shy of 1/2 the length. This way you can see where the middle is

[cabinetman]

When I use a tape to find center, I measure and mark from both ends (not just one end) using either 1/2 the total length or just shy of 1/2 the length. This way you can see where the middle is

Here's an idea for finding a quick center.

.

[durango dude]

interesting tape measure!

I'm learning not to trust hook ends, though...... Mine moves around its rivet by about 1/10"

[LCHIEN]

interesting tape measure!

I'm learning not to trust hook ends, though...... Mine moves around its rivet by about 1/10"

They are virtually all designed like that on purpose. The slop allows the end to be used for outside measure (e.g. push the end up against a wall to measure distance from the wall) or to be used for inside measure (catch the hook on the end of a board to measure the board). If the end did not have the slot then one or the other of those measures would be off by the width of the hook. With the play of the slot, both measures will be corrected for the width of the hook.

There's an art to measuring things and not everything is as simple as it looks. Many people don't use the right tool and/or don't use it properly.

see this thread:
http://www.bt3central.com/showthread...e+measure+hook

[LarryG]

I'm learning not to trust hook ends, though...... Mine moves around its rivet by about 1/10"

That is, in concept, normal and by design. The movement is intended to compensate for the thickness of the hook when you take an inside measurement.

If it is literally 1/10", however, that's a bit much ... 1/32" or so would be more typical.