Router bit size

[magicalwonders]

Hi,

I am going to be making my own skirting boards and would appreciate some advice regarding the size router bit I need for a cove shape at the top of the board.

To minimise the cost, I will be using 9mm MDF in conjunction with 16mm spacer blocks. This will give me a 25mm skirting. An 18mm moulded rail will go on top, overlapping the 9mm board by 2mm. The picture below (not to scale) gives a side view.

I have a router but have not used it yet, as this will be my first project for it. I would welcome some advice on the size of the cove bit I would need to achieve a curve in the MDF. I need to go to a depth of 7mm.

I need to do around 100 metres, so will need something pretty durable. I have no idea what mileage can be expected from a router bit. I guess it depends on quality. etc.

The cove bits all come in different sizes, but I'm not sure which radius would be best for what I want to achieve?

Any advice would be most welcome.

Myles

 

[The Bear]

I know this is not what you’re asking but my advise is don’t do it. Do it properly in either solid redwood or if you must buy a premoulded mdf skirting.
firstly you’ll need to deal with the fluffy mdf you create with your cove bit. The 2 mm overlap is never going to be even because no ones walls are flat. I also don’t think the 9mm mdf is going to sit flat on spacer blocks it’s too flimsy. I think it will look wavy regardless of the wall. Especially once you paint one side of it
100m done like you suggest is going to take you an age.
sorry
Mark

 

[magicalwonders]

Thanks for the feedback Mark.

My house is an old Victorian property with very high skirting boards. The cost of replacing in pre-moulded skirting is coming in around £2000. My way will be about £300. I'm actually emulating what the original builders did (1890) so I think it will look ok!

Edit. The Victorians filled the join area with plaster. I know I can do the same using silicon if needed, as I tried it on a short stretch last year.

 

[Phil Pascoe]

I'm actually emulating what the original builders did (1890) ...

Not with MDF, you're not. You'll have a nightmare job finishing it.

I replaced a lot of skirting (up to 250mm) in my house (1899) with built up boards from strips of 18mm ply topped with a 75mm ogee architrave. A biscuit jointer kept the face pretty much in line and flat. Perfectly stable and it didn't look at all out of place.

I know that in NZ (for one) skirtings are sold as T&G base boards and mouldings, mix and match.

 

[The Bear]

I doubt the victorians used 9mm mdf. I would be more worried using it if they are tall as it’s more likely to look wavy. Unless you are using the term generically silicon is also not the filler you want. You say you’ve never used your router which suggests you are in experienced, I’m not sure you know how much work you are making for yourself

out of interest, what’s happened to the originals?

mark

 

[The Bear]

Phil’s approach would be way better
Mark

 

[J-G]

If you insist on doing it your way in spite of the excellent advice already given then it basically depends upon what YOU want to achieve. I have to presume that you want a smooth transition between the molded rail and the MDF so the minimum cove bit would be a 14mm dia (7mm radius) but other than that it depends upon how far down the MDF you want the curve to exit.

Here's a drawing (to scale - width at least) :

showing 14, 16,18, 20, 22 & 24mm dia. cove bits and how they would impact the exit height.

To get the smooth transition the centre of the cove bit would have to line up with the top of the MDF no matter what size you decide to use.

@The Bear has raised the fact that silicone is not the filler to use.

I can't understand how - even for a one off 'special' - that a 100m run could come in at £20 per metre - it's likely to be more than £3, but £20!!

 

[magicalwonders]

I doubt the victorians used 9mm mdf. I would be more worried using it if they are tall as it’s more likely to look wavy. Unless you are using the term generically silicon is also not the filler you want. You say you’ve never used your router which suggests you are in experienced, I’m not sure you know how much work you are making for yourself

out of interest, what’s happened to the originals?

mark

Lol. Yes, the Victorian didn't use MDF. I was referring to the manner of construction, using thinner stock on blocks to make the skirting come out from the walls further.

I am doing a complete rewire of the property. Getting the skirting boards off the wall damaged some beyond repair. It will be easier to just replace.

Although I haven't used a router before, I have used about every other tool going, so I am not phased by it. I know MDF is nasty stuff to cut, but I have excellent extraction and respirator gear. So I will survive! Lol.

The painting side of things shouldn't be a problem. There's no end grain to worry about. A good primer and quality paint should get me a very good finish.

I might step this up to 12mm MDF. Does anybody know what size bit I need?

 

[J-G]

I might step this up to 12mm MDF. Does anybody know what size bit I need?

If you do that, and maintain the 16/18mm measurements, then the minimum cove bit would be 20mm dia. - for a 10mm deep cut.

 

[magicalwonders]

If you insist on doing it your way in spite of the excellent advice already given then it basically depends upon what YOU want to achieve. I have to presume that you want a smooth transition between the molded rail and the MDF so the minimum cove bit would be a 14mm dia (7mm radius) but other than that it depends upon how far down the MDF you want the curve to exit.

Here's a drawing (to scale - width at least) :
View attachment 116252

showing 14, 16,18, 20, 22 & 24mm dia. cove bits and how they would impact the exit height.

To get the smooth transition the centre of the cove bit would have to line up with the top of the MDF no matter what size you decide to use.

@The Bear has raised the fact that silicone is not the filler to use.

I can't understand how - even for a one off 'special' - that a 100m run could come in at £20 per metre - it's likely to be more than £3, but £20!!

Thanks for the drawing. Much appreciated! The price I was getting on skirting boards was off-the-shelf. After getting a quote last year for some custom picture rail, it seemed like a very expensive way to go.

Anyway, I have managed to obtain some rail from Travis Perkins cheap as chips. It's end of line for them but I was able to get 24 x 4.4-metre lengths at 75% off.

The silicon I mentioned is just decorators caulk. I repaired a stretch of skirting board some time ago, which is when I discovered that the skirting was actually two-part! I replaced the plaster filler with the decorator caulk, overpainted and it looked great!

 

[magicalwonders]

If you do that, and maintain the 16/18mm measurements, then the minimum cove bit would be 20mm dia. - for a 10mm deep cut.

Cool, thanks!

 

[Doug71]

I'm doing something similar at the moment but using 22mm MRMDF which will fit back to the wall, for what you are doing I wouldn't go any thinner than 15mm. Make sure you get Moisture Resistant MDF as it machines and paints much better.

If you can put a "quirk" where the two parts meet, if you try to finish them flush it will never be flush and the joint will probably crack anyway.

This is a rough sketch of what I am making, finishes about 9" high, mine fits back to some panelling so no problems keeping the top and bottom in line.

 

[J-G]

If you do increase the thickness to 12mm then you would be well advised to consider using redwood rather than MDF. The finish would be vastly superior.

Any decent wood-yard (not the 'sheds' - or even builders merchants) should be able to supply 12mm finished by 35 - 60mm wide stock (I don't know how high you need). You still have the potential problems of the joint but as @Doug71 has said a 'quirk' would be a good answer.

 

[magicalwonders]

If you do that, and maintain the 16/18mm measurements, then the minimum cove bit would be 20mm dia. - for a 10mm deep cut.

No, if I go with 12mm MDF I would reduce the thickness of the spacer blocks to 13mm so as I still only come out 25mm from the wall. The rail which is 18mm at its thickest point will go flat against the wall. If I come out further than 25mm the rail will be set too far back and look a bit weird.

I'm puzzled why some folk think that wood will give a better finish. MDF is a fantastic substrate for paint. Providing you do it right of course! But then the same can be said of wood!

 

[The Bear]

IMO the problem with painted mdf is that it looks like mdf, which I wouldn’t want in a Victorian house that I’m trying to preserve the original features in. You also have the problem of the curve you are routing, fluffy edges don’t paint well without effort and prep and you have 100 metres to do
I’ve got nothing against mdf got plenty in my house but wouldn’t use it like this
Good luck with the project

mark

 

[Spectric]

Having just done some lengths of mouldings for a bathroom I can recomend the cutters from Infinity, C17 & C19 ranges. I made drawings of their profiles in a 2d cad package and this allowed me to try various combinations, rotate etc etc to see what works before buying the cutters and running it through my router table.

IMO the problem with painted mdf is that it looks like mdf,

Yes not everyones cup of tee, as mentioned try and use good redwood at least, I used Sapelle for all my bathroom paneling.

 

[magicalwonders]

IMO the problem with painted mdf is that it looks like mdf, which I wouldn’t want in a Victorian house that I’m trying to preserve the original features in. You also have the problem of the curve you are routing, fluffy edges don’t paint well without effort and prep and you have 100 metres to do
I’ve got nothing against mdf got plenty in my house but wouldn’t use it like this
Good luck with the project

mark

I think I know what you mean. A bit too perfect? I could always put a few dings and chips in to make it look like what I've got now! (I'm joking!)

Although I'm trying to retain some period features, the cost of renovation is an issue. So I am having to compromise on some things.

This look is very acceptable to me - and a fraction of the price.

Myles

 

[magicalwonders]

Having just done some lengths of mouldings for a bathroom I can recomend the cutters from Infinity, C17 & C19 ranges. I made drawings of their profiles in a 2d cad package and this allowed me to try various combinations, rotate etc etc to see what works before buying the cutters and running it through my router table.


Yes not everyones cup of tee, as mentioned try and use good redwood at least, I used Sapelle for all my bathroom paneling.

Cheers Roy,

I've previously looked at Infinity. The bits are expensive, but I guess they are really good quality?

My skirting will be 25cm high before adding a rail, so wood is not within my budget. I already have moulded rail, so only need a cove bit for the 25cm boards. The Infinity UK site doesn't really give any info on sizes, so I'll need to reach out to them.

Before routing, I'm going to bevel the edge of my boards, which will leave a lot less wood for the router to cope with. I appreciate I will be left with a fuzzy area from the cut. However, I understand that applying a sealer, followed by sanding, smooths this out very well, so it shouldn't be much of an issue.

 

[clogs]

I had similar issues with Oak skirting and architraves in France for my 17th cent water mill resto.....
in the end I said to the wife I need a WADKIN EQ spindle moulder and power feed....hahaha.....
within a month I had one.....pre Brexit of cource.....
can u say that word now moderators...? hahaha.
sure miss it.....
also did a lot of it for others.....
would it pay u to get a small spindle like a Kitty etc and use real wood....? just asking....

 

[Spectric]

I can not only recomend the infinity cutters, not cheap but really good quality but a good book, yes it is american and they call skirting boards base boards but it gets the brain working and feeds in ideas, called finish carpentry by Tauton's. Shows how they use horizontal "furring strips" on which the base board is attached and then caped off with one, two or three mouldings. This gives a substantial solid look but without using a lot of wood.