Routing a housing..

[drillbit]

If I want to rout a housing for something which is 10mm thick, then how wide should I make the housing? 10mm? Or should I give it clearance, and if so, how much would be advisable?

Reason for asking, I'm making a simple hinged blackboard, which is basically a wooden frame around a piece of 10mm MDF. I tried routing a 10mm groove using a 6mm bit, but having a lot of trouble putting it all together....I have a 12mm router bit which would make things a lot easier than having to keep adjusting the router fence and do multiple passes, but not sure if that will make things too sloppy...

 

[blackrodd]

You may hear better ways than mine, I carefully put a piece of insulation tape on the fence and after the housing is finished, I take the tape off and cut again.
It may be only a "smidge" but it does help in fitting together.
Should you need glue all around the housing you can use two or 3 pieces
HTH Regards Rodders

 

[Phil Pascoe]

It doesn't work easily at 10mm, but sometimes you can float between metric and imperial - a 1" cutter will give clearance on 25mm, a 3/4" clearance on 19mm and so on. A 10mm would give clearance on 3/8" (but that doesn't help you any!)

 

[MMUK]

If you're routing to a depth of 10mm, you'll need to make at least two if not three passes anyway. Personally I'd use the 12mm bit set to cut a width of 11mm and make two passes, 6mm depth and 11mm depth. The extra 1mm depth of cut will allow for any glue. Cut your board to size and allow 1-2mm clearance, ie; if your 'opening' is 1200mm x 1200mm, cut your board 1198mm x 1198mm.

 

[drillbit]

Sorry for the confusion MMUK - I meant I am routing the width of the housing 10mm, not the depth (which is 3mm all round)

The problem I have is the 10mm housing is such a tight fit for the board going into it..that there is no 'give' and I'm having trouble putting it all together... I'm wondering if maybe a mm either side of the board (ie. 12mm width housing) would help, or make it loose and sloppy.

 

[MMUK]

Ah I see. I'd still go with the 12mm bit and set the fence up to cut 11mm. That will give you 1mm all the way round which you can fill with glue.

 

[Jacob]

if there is a back side out of sight you could either go over size and tighten up with little wedges all round, or under size but taper the edges of the board in the old fashioned way.

 

[Richard S]

How do you make a 12mm cutter route an 11mm groove?

Drill bit, a 12mm groove will be really sloppy, try as Blackrodd says or you could try easing the leading edges of the panel.

 

[wellywood]

Have you got a smaller bit than the 12mm? If so and assuming your rebate is on the centre line of the stock, you could set your fence up to cut one side of the rebate then rotate the stock and cut the other side. In other words, 'sneak up' on (say) a 11mm wide rebate.

 

[Mar_mite]

Does your router fence have a micro adjuster? You'll just have to move the fence slightly until you get a nice fit. Trial and error. 12mm will be too slack. Your panel will rattle around.

 

[MickCheese]

I'm with Jacob on this one.

Taper the board at the edges.

Mick

 

[custard]

Drillbit, is the board that you're fitting man made, like ply or MDF? If so then it's very unlikely to be the same thickness as its stated nominal size. I've seen 18mm ply be anywhere from 16.5mm to 18.2mm thick, and it can even vary within the same 8x4 sheet. So the first thing to do is be absolutely sure about the thickness of the piece you're trying to fit into a housing. Vernier callipers aren't expensive but they are a very useful tool.

As a rough rule of thumb about 0.2 to 0.4mm is a decent allowance for a gap. So the previous tip about a strip of masking tape would put you in that range.

 

[CHJ]

May be overkill for current project but is this principle of any use:-

https://www.ukworkshop.co.uk/videos/adju ... t-jig.html

 

[MMUK]

How do you make a 12mm cutter route an 11mm groove?

Using a fence on the router set to 11mm :?

 

[wellywood]

How do you make a 12mm cutter route an 11mm groove?

Using a fence on the router set to 11mm :?

I think the OP is trying to rout a groove on the centreline of the frame stock edge. So it would be impossible to get an 11mm wide groove with a 12mm dia cutter.
He might be better off routing the groove at (say) 11mm on the rear edge of the frame stock, inserting the blackboard into the frame and then panelling the back with a sheet of thin MDF as long as he only wants one blackboard face. This way he could use a 12mm cutter as suggested above to get an 11mm groove.
Apologies if I've misinterpreted.

 

[MMUK]

Ah I see. Sorry I was assuming he was rear mounting into a picture frame.

In that case, rout a 10mm slot and rebate the board thickness to 9.5mm around the edges where the frame fits over it.

 

[andersonec]

Have you got a smaller bit than the 12mm? If so and assuming your rebate is on the centre line of the stock, you could set your fence up to cut one side of the rebate then rotate the stock and cut the other side. In other words, 'sneak up' on (say) a 11mm wide rebate.

My way too, using a 6mm / 9mm bit, that way your groove is exactly central without any measuring and you can sneak up on the last fractions with tape on the fence, just make sure (after the first cut) you are cutting on the side of the groove nearest to you otherwise you will be making a climb cut and we all know where that leads.

Andy

 

[drillbit]

Many thanks for all the replies. Glad I didn't try a 12mm bit - a mill either side doesn't sound much, but it does make it sloppy.

In the end I decided to invest in a 10mm straight cutter today, which made it a lot easier to go over the housing I'd already cut. Used the tape method and everything ended up nice and snug.

It's good to know the ideal allowance of 0.2 to 0.4mm. The tip about easing the edges of the board is very useful as well.

@mar-mite...my table is a couple of bits of melamine chipboard clamped to an old workmate. The pencil line down the middle is my reference for center, and I make other pencil marks to line up the fence and then erase them. The only microadjuster is me loosening the clamps and nudging it..

 

[drillbit]

just make sure (after the first cut) you are cutting on the side of the groove nearest to you otherwise you will be making a climb cut and we all know where that leads.

Hi Andy - I don't get about the climb cut. If you rout the workpiece right to left...then turn it round and rout it right to left again...wouldn't that always be ok?

 

[bugbear]

The only microadjuster is me loosening the clamps and nudging it..

Engineers and tool makers use small hammers and tap for position. This is surprisingly precise if the thing being moved is heavy relative to the hammer (the maths of momentum). It easy to adjust the force of the blow, which is then "geared down" by the mass ratios, giving very fine adjustment.

This is, of course, how planes without screw adjustment are adjusted.

A softfaced hammer (e.g. rubber, nylon, hide etc) can be used if the victim is delicate.

BugBear