# New Member Leigh FMT question



## Ronny (Jun 15, 2011)

In a "typical male" fashion I am going to dismiss with the formalities of an introduction and go straight to hopefully getting the gratification of someone else having experienced the same problem.

I visitied the Forum a couple of weeks ago when I was haing trouble with an 8mm router bit slipping when attempting dovetails on a Leigh D4R. I had given up in trying to reslove the problem only to find I was no orphan.. I have since ordered an 8mm collett out of the UK to fit my Triton Router.

My current problem is using a Leigh FMT mortice and tenon jig. When trying to cut a 40mm deep mortice in JARRAH using a 12.5mm sprial upcut bit the bit jumps and tears. Has anyone else had a similar problem? 


Cheers


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## CharleyL (Feb 28, 2009)

Ron,

Welcome aboard! I think you will like it here.

Well, Jarrah isn't a wood that I've ever used but, whenever using my FMT on either hard or soft wood I first make a very light climbing cut pass all the way around the part (*to prevent edge splintering*), followed by 1 or more forward cuts around the tenon to remove the bulk of the material. These passes are unguided (not against the guide), going just by the "feel" and sound of the router as I make the cut to remove the bulk of the wood. You should never try to cut more than 1/2 the diameter of the router bit when doing this unless you are going between multiple tenons. When I reach the guide I make an additional complete pass, pressing lightly against the guide, and then I make a final climb cut pass around the tenon while pressing a little bit firmer against the guide, to achieve a precise, clean, and repeatable tenon cut.

I've also found that when making tenon cuts on tenons that are longer than 1" I cut them at two different bit depth settings. I make the first pass at something less than 1" until I reach the guide and then I change the bit depth and repeat the cuts at the final bit depth. In this case, the final climb cut pass isn't done until the final cut at the full depth. Cutting the longer tenons at full depth produces chips that are too long for the vacuum port and they clog the port frequently. Shorter chips don't seem to clog the port. 

I attached a 3/16 X 3 X 6" piece of clear Lexan to the front of my FMT with a strip of velcro along the front edge of the top plate, so that it hangs down in front of the cutting area of the jig. This blocks any stray chips that the vacuum misses from coming forward toward me and it adds a bit of safety to the jig. After having a carbide bit explode on me some years ago (not on the FMT) I have never felt comfortable using a carbide bit in a router in a way where it is exposed so that pieces of it could directly hit me. The bullet proof Lexan material should help protect me if this should ever happen. You should never look through this Lexan while cutting. Always keep your eyes above the jig whenever the router is running.

Charley


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## jw2170 (Jan 24, 2008)

Ronny said:


> In a "typical male" fashion I am going to dismiss with the formalities of an introduction and go straight to hopefully getting the gratification of someone else having experienced the same problem.
> 
> I visitied the Forum a couple of weeks ago when I was haing trouble with an 8mm router bit slipping when attempting dovetails on a Leigh D4R. I had given up in trying to reslove the problem only to find I was no orphan.. I have since ordered an 8mm collett out of the UK to fit my Triton Router.
> 
> ...



G’day Ron

Welcome to the router forum. 

Thank you for joining us


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## Ronny (Jun 15, 2011)

Hi Charley
Thanks for the quick response. Your advice on tenons is well appreciated. I would normally only do one light pass climbing cut pass and haven't tried doing them in several depths. So far tenons have not been a problem. Where I am having trouble is with mortises. I have been in contact with Leigh Jigs and this moring sent them a photo of one mortise. I wont get a response until tomorrow but it may just come down to using progessive depth cuts. When I routed a 1/2" mortise in progressive steps from 15mm to 35mm in 3 increments it worked OK. When I tried to plunge to 35mm in one step I got the chatter again. When I say chatter it is understating the quite severe movenment that occurs. 
I can't understand why progressive depth cuts seems OK and a single cut to 35mm isn't. I am taking things slowly and from my appreciation the router bit is not cutting any more material per rev irrespective of depth. If I sort it out I will let you know.

Cheers

Ron


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## CharleyL (Feb 28, 2009)

Ron,

Trying to cut a mortise to depth by sliding the router from one end of the mortise to the other at full or even partial plunge depth causes problems because you are trying to remove too much material at a time.

You need to make several plunge cuts (like drilling holes with the router bit) to make a mortise. This is covered in the FMT manual. Do a full depth plunge at one end first, followed by a full depth plunge at the opposite end. Then alternate back and forth from these positions and plunge cut the rest of the material out in the same manner. Multiple depths are less important than when making tenons. When you have the entire mortise cut by plunging, then and only then, attempt to trim the mortise to the correct shape and size by first plunging to the desired depth and then following the template. You can make one pass, kind of free hand down the center from one end to the other and then follow the template all the way around to complete the mortise. My final cut here is the same as when making a tenon. I use a climbing cut to leave the sides smooth and trimmed to the correct dimension. The climb cut should only shave the surface and not actually remove any significant amount of material.

I have both a D4R and an FMT Pro jig, so I should be able to help with problems using either jig, although I haven't had any problems using the 8mm bit adapter. I always tighten the router collet using 2 wrenches, even though most of my routers have a shaft lock button, and I use a grommet in the collet hole (behind the collet) to prevent the bits from bottoming out. Maybe this is your problem. The 8mm bits with the adaptor do require the collet to be very tight, or about as tight as I can get them by squeezing the two wrenches together with one hand.

Charley


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