Routing a slot in MFT-style top?

[promark747]

I'm in the process of making a larger custom top (3' x 6'), and decided to make it approx 1.25 inches thick (3/4" + 1/2" MDF, laminated on both sides).  I'm currently laying out where I want the 20mm holes, along with an opening for a router plate.  The holes should work great for the clamping elements and my Parf Dogs, but as you know, the Festool clamps will not fit through a 20mm hole that is 1.25" deep.  Originally I was going to simply make some larger holes to accommodate the clamps, but then I thought it might be better to rout a 20mm slot between two (or even three) holes.  That way I can slip the clamp in parallel to the slot and then have the whole slot's length to position the clamp.

What would be the best way to rout the slot?  Accuracy is not of paramount importance as the slots will preclude the use of Parf dogs for guide rail alignment, but I would like them to at least look precise.

 

[Svar]

Not answering your question, however, why not chamfer the holes on the bottom side. You'l be able to use both bench dogs and clamps.
Cutting a bunch of slots will defeat the purpose of thick top, which is rigidity I imagine.
If you proceed with slots, then a plywood template with a slot and router with guide bushing would be my choice.

 

[Corwin]

Not answering your question, however, why not chamfer the holes on the bottom side. You'l be able to use both bench dogs and clamps.
Cutting a bunch of slots will defeat the purpose of thick top, which is rigidity I imagine.

This would be my answer too.

 

[Klemm]

I'm in the process of making a larger custom top (3' x 6'), and decided to make it approx 1.25 inches thick (3/4" + 1/2" MDF, laminated on both sides).  I'm currently laying out where I want the 20mm holes, along with an opening for a router plate.  The holes should work great for the clamping elements and my Parf Dogs, but as you know, the Festool clamps will not fit through a 20mm hole that is 1.25" deep.  Originally I was going to simply make some larger holes to accommodate the clamps, but then I thought it might be better to rout a 20mm slot between two (or even three) holes.  That way I can slip the clamp in parallel to the slot and then have the whole slot's length to position the clamp.

What would be the best way to rout the slot?  Accuracy is not of paramount importance as the slots will preclude the use of Parf dogs for guide rail alignment, but I would like them to at least look precise.

you leave us wondering what you are trying to accomplish with such a thick top. ? - if greater stiffness is your aim, have you considered  a simple vertical stiffening rib or two? - they could have semicircular cutouts next to the top so you can still hook the clamps
Hans

 

[promark747]

Not answering your question, however, why not chamfer the holes on the bottom side. You'l be able to use both bench dogs and clamps.
Cutting a bunch of slots will defeat the purpose of thick top, which is rigidity I imagine.
If you proceed with slots, then a plywood template with a slot and router with guide bushing would be my choice.

Thanks, I had thought about chamfering the bottom.

The reason I went with a thicker top was for rigidity for the router plate.  Most commercially available router tables seem to be this thickness.  I knew going in that it would present a couple of limitations but I think it will work for me.

 

[Bohdan]

I found that after mounting a router in the middle of my MFT1080 that the top sank down in the middle. I just used a section of RHS under the MDF with a couple of bolts directly to the router mounting plate to lift it back up.

I find the even this small obstruction is a PITA when using clamps as invariably one of them will hit the support brace.

 

[tjbnwi]

If you have a Domino use it to plunge slots where you want them. Don't connect the holes. Use the back edge of a guide rail as your guide.

Tom

 

[Roseland]

I made a top out of two thicknesses of 3/4" ply.  I routed slots the width of the clamp legs (less than 20mm) across the shorter dimension of the top.  It worked well but was quite a lot of work.

If I was doing it again I'd probably glue strips of ply on, rather than cover the whole bottom and then rout away material; it would certainly be quicker.

Andrew

 

[Stone Message]

Hi [member=7714]promark747[/member]

There are some good answers above and TSO is right to question your need for an extra thick top. However...

I am not sure what the limiting thickness is for a Festool clamp in a 20 mm hole; I suspect it is a little over 22 mm. However...

For accurate work Parf Dogs should be secured from below. They only need about 19 mm of top thickness to get an accurate fix as long as the diameter of the hole is not excessive. I am not sure how you are making your 20 mm holes but one of the best cutters for size is the Axminster one that comes with the Parf Guide System. You can now buy this as a single item and the latest ones have a Centrotec end on them.

Here is a link to the straight shafted 20 mm cutter:http://www.axminster.co.uk/ujk-technology-20mm-cutter-for-parf-guide-system-101841

and this is the new one:http://www.axminster.co.uk/ujk-technology-d-g-20mm-cutter-for-parf-guide-system-102481

Good luck.

Peter

 

[promark747]

If you have a Domino use it to plunge slots where you want them. Don't connect the holes. Use the back edge of a guide rail as your guide.

Tom

Interesting...hadn't thought about using my Domino.  Thanks!

Peter,

Thanks for the advice on the cutter.  Right now I am planning to use a pattern bit and an old MFT 1080 top as a template, though I think there's a chance the holes I rout may end up being a bit too tight, depending on the tolerances of the bit.  I need to do a test hole or two.  If that doesn't work out, I will probably go with the bit you suggested.

I forgot to mention that another reason I went with the thicker top is that I plan to add a miter track for the router (leaning towards the Woodpeckers combo track, which has a miter slot and a clamp track which fits the Festool clamps).  I felt that adding the track to a 3/4" piece of plywood or MDF might compromise the top.

 

[Svar]

I am planning to use a pattern bit and an old MFT 1080 top as a template

By far the most efficient way, clean, no burns, no blowout on the underside. I prefer using bit with bearing on the end. You need to roughly predrill holes using the same template, for example 1/2", to allow the bit through. Then template on the bottom and workpiece on top. This way there is no chance you can accidentally cut into the template. With bearing by the shank bit you can do it in one step, but need to pay extreme attention to every plunge.

 

[J0hn]

I am planning to use a pattern bit and an old MFT 1080 top as a template

I think you will find that with most pattern bits - the bit is very slightly undersized in relation to the bearing to prevent the 'pattern' from being cut up.  (bearing and cutter needs to be the exact same diameter).  The result will be the holes will be just a little too tight.  If you are having problems finding one - I would suggest you give Whiteside a call.  Very good customer service, their shop foreman went out on the floor and found me one with the exact dimensions I needed
http://www.whitesiderouterbits.com/

Also, I bought a 'drill bushing from McMaster Carr (625" ID, 3/4" OD) that helped center up the holes and protected the template (mft top) when drillinghttps://www.mcmaster.com/#catalog/122/2603/=15nztfg

And for me, it was easier to just use a foot pedal with my router and not try to 'plunge' the hole.

 

[Sean KS]

Promark, I'm using a thicker top as well. I decided to file the Festool clamps so I could take them apart and slip them through the dog holes. 3 or 4 file strokes sounds easier than milling those slots.