Leigh SFMT Jig.....using 12mm twist bits

**chopper** · 19th September 2011, 05:45 PM

Hi,
I bought one of these Leigh SFMT jigs[metric] and am just teaching myself how it goes. I found that using a Leigh 1/4" twist bit, the tenon thats created using the plastic template is quite a nice snug fit for the 1/4" mortice slot.

However I wanted to get a decent width of tenon so I bought a 12mm twist bit, the tenon that is cut is always a few mm thinner than the 12mm mortice slot it [also] cuts. I've tried adjusting the front brass pin that follows the plastic tenon guide, so that its down as close to the template sides as possible....but the tenon still ends up with at least 2-3mm play, ie when sitting inside the mortice.

Is this a know problem with this jig? Any other tricks to it?

**chopper** · 19th September 2011, 06:10 PM

I forgot to mention, for the larger tenon I'm using the 12mm Leigh template set, bought seperate from Carbatec Brisbane......so it all should all match up okay.

**ian** · 19th September 2011, 08:52 PM

the first place I'd look is the template and bit
are they both 12mm or is one 12.7mm ie. 1/2 in?

**Superbunny** · 19th September 2011, 09:36 PM

Most upcut bits are 12.7mm ie 1/2 inch but if you are using a 12mm guide this will make a difference. I have the FMT in imperial for this reason as there are few 12mm upcut bits available in all sizes. I know Liegh can supply them.

SB

**chopper** · 25th September 2011, 05:54 PM

Though I bought the "metric" Leigh jig, they supply it with
a 5/16"[7.9375mm] spiral up cut bit,
the templates are 8mm.

I've then bought a 1/2" [12.7mm bit] that I'm mistakenly been trying to use with the 12mm templates.
Hence the skinny tenons and wide mortices.

Obviously I need to find a 12mm Up cut bit as suggested by SB, and then we should be cooking with gas.

.

Thanks for the responses.

**Superbunny** · 25th September 2011, 09:46 PM

Chopper, I notice in my copy of the Carba-tec Catalogue page 101, they sell 12mm upcut spiral bits for $99 along with the other bits in mm.

SB

**ian** · 28th September 2011, 01:26 AM

Originally Posted by chopper

Though I bought the "metric" Leigh jig, they supply it with
a 5/16"[7.9375mm] spiral up cut bit,
the templates are 8mm.

I've then bought a 1/2" [12.7mm bit] that I'm mistakenly been trying to use with the 12mm templates.
Hence the skinny tenons and wide mortices.

Obviously I need to find a 12mm Up cut bit as suggested by SB, and then we should be cooking with gas.

.

Thanks for the responses.

there's only 2 thousands of an inch between 5/16" and 8mm slightly more than the difference between 3/4" and 19mm.
As far as I know, 5/16" and 8mm are considered interchangeable

**martink** · 1st October 2011, 03:44 PM

Originally Posted by chopper

Though I bought the "metric" Leigh jig, they supply it with
a 5/16"[7.9375mm] spiral up cut bit,
the templates are 8mm.

I've then bought a 1/2" [12.7mm bit] that I'm mistakenly been trying to use with the 12mm templates.
Hence the skinny tenons and wide mortices.

Obviously I need to find a 12mm Up cut bit as suggested by SB, and then we should be cooking with gas.

.

Thanks for the responses.

There is another option, get your hands on the 1/2 inch inserts. That's what I ended up doing for my FMT (the cast alloy one) which is the 'metric' model and it worked a treat.

M.

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