Basics - accurate centre marking

[woof]

Happy New Year everyone. I have a very basic question to ask. When I use my Leigh FMT to make mortice and tenons, I find absolute centre marking with squares almost impossible to achieve - 1mm is the closest. Although this does not matter with the FMT provided you use the same sides, it would be nice to be spot on for accuracy.

What marking/measuring tools do you use to be spot on in dividing a rail or style end (thus works on end grain and long) and provide the most accurate centre point?

Thanks in advance, Mark

 

[Chris Knight]

I use precision Tee squares/rulers from Incra for a lot of my measuring tasks ( http://www.rockler.com/product.cfm?page=2091 ) and these are very good indeed. However, I don't think any measuring system is a substitute for using a reference face in most operations requiring a precise fit.

There are centre finding rules (with a zero in the middle) and I had one once but hardly used it, it's easy enough to use any ruler for the same purpose if you swing it at an angle to give you an easy to divide (by 2) number from edge to edge of the workpiece.

 

[joiner_sim]

Using a marking guage is the most accurate for centre points in my opinion.

 

[Digit]

Marking gauge, as JS states. But never having used the Leigh I am surprised that marking out is necessary, it isn't on my home brewed jigs.

Roy.

 

[OLD]

Use one of these for better accuracy.
http://www.axminster.co.uk/product.asp?pf_id=21755&name=center+rule&user_search=1&sfile=1&jump=44

 

[Oryxdesign]

work out the centre line and adjust your guage, now mark the line from both sides and you will see the inaccuracy of your settings.

 

[Shultzy]

If you want the centre of the end of a rail, join the corners up with knife.

If you want to find the centre of a board or its edge, make a jig.

Take a strip of 1/4" ply about 1" wide
Drill three holes on the centreline equi-distance from each other
The centre hole is just large enough to put a fine point in
The other two drill out for dowels
The distance between the dowels should be about 2" larger than the board / edge
Lay the jig on the board / edge, twist and hold the dowels against the wood and mark the centre

You might have to make a few to cover your needs.

 

[AndyT]

The most basic simple method is to set your marking gauge to something nearly right, mark a dot from one face, then from the other, then split the difference.
(To make tiny adjustments, gently tighten, then tap the end of the stem on the bench to nudge the body just a tad.)
When the pin falls in the same spot from either face, that's the middle.

 

[woof]

Seems a marking guage is a good starter so thats my excuse to complete my Axminster basket

The tinyT sounds rather nifty too although either from the US or maybe Roger at woodworkers workshop might have some?

Many thanks all

 

[Mike Wingate]

For wide boards, I do what Shultzy does. I have a centre finder for my Incra jig that is easy and accurate, and essential for equalized ends on boxes. At home and school I use my fingers and a pencil, scribing from 2 or more sides. This is good for finding the centres of circular pieces. For repetitive work I use a marking gauge.

 

[Jeremys]

I use 2 jigs on the same principle...one homemade and one over-engineered toy...

Home made version is described here...

http://www.diynetwork.com/how-to/viewer-jig-board-center-finder/index.html

This one is beautifully made and I love it, but not essential even in my warped judgement...

http://www.bridgecitytools.com/Products/Layout+Tools/CS-2+Centerscribe


Jeremy

 

[woodbloke]

Alternativley, if you have a very nice Sectet Santa...

...you could use one of these :wink: - Rob

 

[ondablade]

I have the Incra T too, but have always used the measure from both sides move. You can do it pretty effectively with a vernier callipers and a marking knife too.

How's about a tuned up version of a vernier calliper????? Fit a face guide block aligned on the edge of one jaw (like on a trad marking gauge), and an arrangement to hold a marking knife or point centered on the other.

This is another take on centre marking - the Lee Valley combination of the dowel tool, and the Incra T's through hole marking: http://www.leevalley.com/wood/page.aspx ... 3513,51657

That Bridge City tool you linked Mike is pricey, but very nice. Especially with the mortice marking attachment added: http://www.bridgecitytools.com/Products ... +Accessory

When you really get down to it though it's hard to avoid the need for something like the centre gear arrangement it uses if you are to 100% reliably find and mark a centre - all the rule based items are subject to error. The dowel variety work fine, but can't go to the end of a board, or mark the end grain surface.

:wink: Better make sure your pencil (if you are using one, and not a marking point) is sharpened with the point on the centre axis though in the case of their item.

I'm surprised nobody has come up with a more reasonably priced version. Or have they???

ian

 

[jlawrence]

from reference face, 2 lines at 90deg distance between them doesn't matter. then corner to corner using the lines and set the marking gauge to that point.

 

[Mooeee]

Woodbloke
Did you make this tool or is it available to buy??????

HAVE A HAPPY NEW YEAR

 

[Chris Knight]

With all the concentration on marking the centre, I think there is a danger of losing sight of what is important. It very rarely matters where the centre of a piece of wood involved in a M&T joint is (which was the subject of the OP's question) but what does matter is where the face(s) of the components are located. Quite often they will be required to be flush and in such a case any variation in component thickness can lead to a mismatch if a reference face was not used consistently during machining.

 

[woodbloke]

Woodbloke
Did you make this tool or is it available to buy??????

HAVE A HAPPY NEW YEAR

Not one of mine, nor is it available to buy...but if you speak to Tiddles very nicely :wink: - Rob

 

[TheTiddles]

The design is based on one my dad has which was his Grandfather's, I have not seen one like it before or since, furthermore, I didn't make one for myself either! Sounds like I need to make one and do a WIP

Aidan