Advice on how best to make this back panel

[Ronan James]

Hi and good morning to you all,
I am looking for some advice from our more experienced members on how best to create this back panel for a project I am building either with my table saw or router. The panel is 18mm mdf and the grooves or dados actually need to be 6mm wide to accommodate 6mm mdf strips. I wonder is there some sort of jig I could make to ensure accuracy and repeatability. I appreciate any advise
Reagrds
Ronan j

 

[novocaine]

router on a track alla festool.
2 L shaped bits of wood the long side of which is 55mm (because the cm is a unit of measurement designed for primary school and word files). use these to line up the track.
first cut has the short side of the block hang over the edge, the rest have it sit in the previous groove.

 

[Cabinetman]

Hi Ronan, on your drawing it says 5.6 mm you ask for 6 mm a quick look at router cutters shows a popular size is 6.3 mm.I think a router is the right way to go. But don’t use a fence that uses the last cut as a reference point or by the time you get to the other side side it will be way out. How accurate does it need to be? Ian

 

[spb]

A router on a guide rail adapter is the most obvious answer - if your router doesn't have that attachment, or you don't have a tracksaw and rails already then an ad-hoc guide jig shouldn't be hard to fashion.

I'd be looking at two straight edges held parallel, with the gap in between being the width of your router's base plate. Then you just need some 6mm guide blocks on the bottom to lock it into the previous groove and make sure the spacing is accurate and everything's parallel.

 

[Cabinetman]

That was my first thought too but the trouble is SPB, if his straight edge is even marginally not parallel by the time he gets across to the other side he could be 5 mm out and it would look like a fan instead of railway tracks.
Also you don’t need to parallel guides the width of your baseplate it will naturally pull over to the left-hand one due to the direction of cut. Ian

 

[Felix]

How about making a guide rail thus:

Make a guide that has a tongue rebated on the underside that is parallel to the edge of the guide rail and the same width as your chosen panel rebate width. Using that tongue as a straight edge mark the centre line of your 1st rebate which will be the distance from the edge of the panel to the edge of the rebate (furthest from the edge of the panel) MINUS half the size of the router bit you use. It looks like 52.5mm - assuming your rebates are 5mm wide

Route a slot that accepts a guide bush that is larger than your chosen bit size and install the chosen guide bush and bit.

Place the edge of the tongue against the edge of your panel and route the first slot - then place the tongue in the slot you've just routed and route the next one .... and so on. Since you used the tongue as a register to route the guide bush slot - your rebates should be parallel.

You can make the guide rail as wide as you like to support the router - but the critical distance is the edge of your router to the outside edge of your router bit. Once the guide is made you can use it on as many panels as you have. I think that'll work

Cheers
Dean

 

[Cabinetman]

Bowmaster, as I was saying in the post before yours, if the guide isn’t exactly parallel it won’t work, half a millimetre narrower at one end over 15 cuts is 7 1/2 mm, the lines would not be parallel they would be splayed.
Accurate marking and just pushing the guide on the marks is the safest way I think. Ian

 

[Felix]

? If you use a router with an edge guide to route the rebate for the tongue and then use the tongue as a reference for the guide bush slot and then use the routed rebate as a reference for the next one - how can they not be parallel?

Also, the error you're talking about is accumulative - where every rebate is out by some value, but if you're first measurement is out by 1mm and all the others are parallel then you will be out by 1mm after x number of cuts

 

[Cabinetman]

We are obviously talking at cross purposes. I was suggesting that if the guide is narrower at one end than the other the error will as you say be cumulative if you use the previous cut as you reference each time.
By the way, they are grooves not rebates.

 

[Felix]

We are obviously talking at cross purposes. I was suggesting that if the guide is narrower at one end than the other the error will as you say be cumulative if you use the previous cut as you reference each time.
By the way, they are grooves not rebates.

Whether the guide is narrower at one end is irrelevant. What matters is that the tongue is parallel to one good edge (preferably factory). You are not using the opposite edge for anything at all (other than to define the width of the guide)....and I agree it's not a rebate, but it could be a housing - depends whether you are with or across the grain

 

[Ronan James]

Hi Ronan, on your drawing it says 5.6 mm you ask for 6 mm a quick look at router cutters shows a popular size is 6.3 mm.I think a router is the right way to go. But don’t use a fence that uses the last cut as a reference point or by the time you get to the other side side it will be way out. How accurate does it need to be? Ian

Hi Ian, thanks for your advice and apologies for my delay in responding. It needs to be bang on accurate, very little room for error

 

[MikeK]

This appears to be an ideal task for a CNC machine. I'm not suggesting buying one for this project, but if this is a one-time project, I would look for a shop that could do this.

 

[Ronan James]

This appears to be an ideal task for a CNC machine. I'm not suggesting buying one for this project, but if this is a one-time project, I would look for a shop that could do this.

Thanks Mike, that would be cost prohibitive. I'm trying to come up with a very accurate method that I can do myself on an ongoing basis

 

[peter-harrison]

Whether the guide is narrower at one end is irrelevant. What matters is that the tongue is parallel to one good edge (preferably factory). You are not using the opposite edge for anything at all (other than to define the width of the guide)....and I agree it's not a rebate, but it could be a housing - depends whether you are with or across the grain

Totes agree, Bowmaster. That's just how I'd do it. If I was feeling keen I'd make on that would do different spacings!