Leigh FMT Pro top width

[Jeff Harville]

can someone tell me how wide the Jig top is? Not the router plate. Can you also tell me how far below the bottom of the jig top you can safely lower the factory 1/4 carbide router bit? I want to route mortises into a concave surface and I know the top of that surface will not be up against the bottom of the jig top except for one point on the edge. If I have these two pieces of information I will look at it in CAD and determine my depth at each mortise location.


Thanks

[Charles Lent]

The more I read your post, the more confused I am getting about what you are looking for.
Can you post any sketches or pictures to help me understand what it is that you are looking for?

On an FMT Pro jig you can rout tenons up to about 1 1/2" long, if your router bit and router plunge depth capability is long enough, but you should do it in several passes at increasing depths to prevent overloading and flexing the bit and the router. Mortises should also be cut in multiple depths if they need to be this deep to prevent the bit from flexing. Multiple plunge cuts, followed by a horizontal passes at each depth should be made to clean out the waste. Cutting in multiple depths will also make chips that are short enough to not plug the vacuum port. Any chips that are cut longer than about 3/4 " will bridge the vacuum port and plug it up.

You can cut mortices and tenons that are longer than the top opening of the FMT, if you cut them in several passes, moving the boards horizontally for each pass, but wide M&T joints of more than about 4" will produce problems and splitting when the wood changes size due to moisture content. I prefer making several M&T joints 2-3" long with spaces between them when there is a need to join very wide boards.

I hope I have somehow answered at least part of your questions.

Charley

[Jeff Harville]

See attached sketch. How wide is the top of the jig? How deep can you plunge the 1/4" carbide router bit that is sold by Leigh. An illustration of what I'm wanting to do. Excuse the not so good sketching.
311955

[Charles Lent]

Jeff,

OK, I understand what you need now. I'll be in the shop later today and will get measurements for you. Not sure why you need the measurement for the top of the FMT, but I'll get it anyway.

Charley

[Charles Lent]

Well, I'm back from the shop sooner than I expected. Here are the measurements, plus a few more that you may want, now that I understand your questions.

The top plate is 1/2" thick and 16 1/2" wide. It has a left - right movement capability of 3 1/2" and a position lock for that movement. This movement is normally used when cutting joints longer that the template or when doing multiple M&T joints and there are precision stops that can be set for this.

The router base - the special base used for following the templates is 3/16 thick but it does not sit flat on the top plate,
so the combined thickness of the top plate with the router base on it is 3/4". Your wood part being machined would touch the bottom of this (if it was straight) and your router would be mounted to the top. The distance from the router collet in it's full down position to this router base plus the length of the bit inside the collet will need to be added to this to determine the max depth that the router bit can reach. My 1/4" carbide bit will easily allow for 1" plunge depth below the FMT top plate. You may be able to locate a longer bit than this, as mine is not a Leigh bit. Using a significantly long bit presents several problems depending on it's length. Long bits will bend under load, giving you results that may not be acceptable. They are also much more likely to break, especially if made from solid carbide. A long bit may also not retract fully, depending on the plunge depth of your router, and this might present a significant safety problem. Also, a long bit that is extended to cut tenons, when the cut length will be longer than about 3/4" will produce cuttings that will bridge across the vacuum port and plug the port. If you will be making tenons longer than 1/2", do it in several passes at increasing plunge depths to prevernt this problem. DAMHIKT.

The base of the FMT is 15 1/4" wide and the top plate extends beyond this width, depending on the top plate position. The width of the FMT can be extended by building side wings from wood, so that position marks can be made on these wings when making multiple mortises along a long work piece like you are doing. The FMT comes with metal brackets that fit slots in the base of the FMT so you can easily make and attach these wings. Mine are made from 1/2" Baltic Birch, but almost anything can be used, and the length can be whatever you need. They can also be used with clamps to help support long work pieces.

The FMT base, from the bench to the bottom of the top plate is 7 1/2". Unless you hang the working area of the FMT over the edge of the bench this is the maximum height of the material that it can handle. However, I have mounted my FMT on my bench so the work piece can extend all the way to to the floor, and I once clamped my FMT to my neighbors 2nd story deck railing (with his permission) to tenon some bed rails.


Charley

[Jeff Harville]

Charlie

I appreciate the reply. With that width top it will put the bit 8.25 inches from either edge when it's centered in a mortise. If the bit is only an inch or so below the bottom of the top plate when it's fully extended it probably won't engage my wood by very little. I was afraid this wouldn't work especially with a quarter inch bit. I'm afraid if I get an extended length bit, it will vibrate like you said and either break or not give a satisfactory mortise. I ordered a 6mm bit for my domino 500. It came in today so I'm going to see how deep it will penetrate while I jig it to stay perpendicular to the long straight edge. I will use it to make a wide mortise if it works. I tried the 5mm bit on a straight edge piece and thought it would work until I realized my grizzly planer would only plane down to around 5.5mm. So no 5mm thick slip tenons without some rigging the planer.
I used to have the fmt pro until I got the domino machines. I just don't remember any of the dimensions. I thought if it would work I would get another one.

Thanks.

[Charles Lent]

How about making a mortising jig with a curved bottom and clamp it into position on your curved stock. Then use a small diameter, small base plunge router like a DeWalt DW611 with a 3/8 bushing to guide the router to do the mortise cutting. You might need to make several jigs, one for each lower mortise, to the center point of the curve, but then you could reverse the jigs to do the other half of the positions, starting from the opposite end. The small jigs and small diameter router base would let you get the router much closer to the work and keep the need for long bits to a minimum.

Just a thought...take it for what it's worth, even if it only helps you get to the final method.

PM me for a phone number if you want to try to talk it through to a solution. I'm available most any time (retired).

Charley

[Jeff Harville]

Charley,
I appreciate the suggestions on the custom made mortising jigs. I may think through that a little. I don't currently have any small diameter routers. The small diameter would get me as close as possible to my curved surface. I tried my domino 500 yesterday afternoon. It worked pretty well but I wasn't completely satisfied with the results. The small router and wooden jigs may be my best solution. I did see some pretty long carbide end mills on McMasters website last night but I am afraid I will get some unwanted vibration. I won't get back to this project until Saturday afternoon so I will think through your idea.
Thanks
Jeff

[Mike Berrevoets]

How thick is the piece? I made a bunch of mortises on a headboard rail that was 1.5" thick. It was basically face glueing the two 3/4 pieces together after routing groves in the faces with the board edges clamped together. The grove was half the mortise width thickness on each board. I had a board on the top to cover up the groves. But you could stop the groves before exiting the edge of each board. It would be easier to cut the arch after the boards are sandwiched together.

A picture would help. If it sounds like the idea might work for your application I'll sketch something up.

Wasn't my idea, It was in the woodsmith plan. Plansnow - classic cherry bed.

[Jeff Harville]

Mike,

The plan you have is the same plan I have. I was a knot head and decided I could do it better after the glue up and arc cut. I had also thought about tossing the work I've done and do it like the author of the plans said do it. I think its one of those "I told you so" things but I didn't listen. It's a beautiful bed. Can't wait to get it finished. I've got most of my pieces cut already including headboard and foot board slats cut a little short since I was not going to insert them in the upper and lower rail. I also though about using my hollow chisel mortiser to cut the mortises in the upper rail (arc) and the domino to cut the mortises in the lower rail.

[James Zhu]

It would be a lot easier to cut the mortise first, then cut the arch. Check the following video.

https://www.youtube.com/watch?v=sYrsYFuC2iQ

[Mike Berrevoets]

Mike,

The plan you have is the same plan I have. I was a knot head and decided I could do it better after the glue up and arc cut. I had also thought about tossing the work I've done and do it like the author of the plans said do it. I think its one of those "I told you so" things but I didn't listen. It's a beautiful bed. Can't wait to get it finished. I've got most of my pieces cut already including headboard and foot board slats cut a little short since I was not going to insert them in the upper and lower rail. I also though about using my hollow chisel mortiser to cut the mortises in the upper rail (arc) and the domino to cut the mortises in the lower rail.

That bed was the first project I ever made. I chickened out and didn't cut the arc. All I had was a router, cheap table saw, small drill press and a few hand tools. Its not my best work but I made it for the new bride 16 years ago and she won't let me rebuild it now. I thought it was great at the time but with more experience I now see all the mismatched grain, sloppy polyurethane finish, rounded off over sanded edges and bunch of other things I'm smart enough to not do anymore. Of course I'll probably say the same thing 20 years from now on the things i finished last week. :)

Always learning, that's what makes it fun.