Widening turntable hole in 6mm ply

[spikey]

I need to increase the diameter of the turntable hole in my 6mm ply baseboard by getting on for 2cm.  I can mark out the new hole accurately but how best to cut it?  Using my router's out on the grounds of too much surrounding landscape destruction if nothing else.  They don't seem to make the rounded blade for a standard Surform file any more, so it's looking more and more like a job for the Dremel. 

 

However, the only Dremel cutters I have are either the ones I use for fine work, which are way too small for this job, or some queerthings that came with the tool that look like twistdrills with weird flutes, which I think are intended for routing holes in plasterboard or something.  I've tried one of those on the edge of a bit of 6mm ply and it's hardly controllable.  Anybody know which cutter would be my best bet?

[Happy Hippo]

Have you thought of using the router from underneath the baseboard?

 

Other than that it's the good old fashioned coping saw.

[Gordon A]

Or possible a jig saw. Either way you are going to make a mess of dust and small bits.

[doilum]

Old school. A 3mm drill and chain drill the new perimeter. This is the safest way to minimise collateral damage. 40 grade grit paper glued to a bit of broom handle or similar round scrap makes a cheap rasp. Make a coffee, choose some music and accept this might take 20 minutes to complete.

[AdamsRadial]

Make up a small jig with a piece of dowel on a screw to act as a bearing to run around the inside of the existing hole, ideally use a piece of wood slightly longer than the diameter of the hole and put a similar piece of dowel on the other side, so you have a bar that runs around inside the existing hole, and on one side extends just beyond where the new hole perimeter will be.

 

Make a hole in this piece of wood outside the roller bearing to take your Dremel at the appropriate new diameter. This way you don't have to keep struggling to control the Dremel for precise position, you just have to control it against the forces that the cutters that look like twist drills with weird flutes will be introducing.

 

Depending on their type they may either wish to burrow down into the plywood or else try to thrust upwards.

 

Be warned, those cutters might be solid carbide and therefore will snap like a carrot if you put too much sideways force on them. I bought a Parkside mini-router a couple of years back that was absolutely perfect for doing things like this, cutting out parts of ply baseboards in-situ, but I broke the cutters before learning to always used an outline or location jig and go very very gently. Annoyingly, they are unobtainable and I ended up getting a range of carbide cutters for Dremels and making a collet reducer to fit them to the Parkside.

Edited October 11, 2020 by AdamsRadial

[Enterprisingwestern]

 

Blank off the turntable hole from the underside, identify the centre, make a trammel/radius arm to mount the router on but high enough not to damage surrounding scenery and use a deep worktop cutter to enlarge the hole.

 

Mike.

[boxbrownie]

10 minutes ago, Enterprisingwestern said:

 

Blank off the turntable hole from the underside, identify the centre, make a trammel/radius arm to mount the router on but high enough not to damage surrounding scenery and use a deep worktop cutter to enlarge the hole.

 

Mike.

This......blank off with a temporary sheet of ply under the board, recentre and maybe just use a hole saw bit,  what diameter is the hole you need?

Edited October 11, 2020 by boxbrownie

[spikey]

Thanks gents.  The hole needs to be 11.00" and the existing one's a bit over 10".  It hadn't occurred to me to blank it off and work from a new centre, but that's a good idea if I end up using the Dremel.  Similarly, the penny hadn't dropped that given the diameter of the existing hole, I should be able to get the coping saw in there.

 

I didn't mention that access to the area is more than a bit awkward, but given enough cushions for support, I reckon I should be able to wriggle under it on my back and work from underneath.  Marking it out on the underside of the baseboard might be interesting, but I think I can do it: blank off existing hole on top, drill new centre, pass bolt through hole and use that to locate 11" card disc underneath to mark round ...

[Ray Von]

59 minutes ago, Enterprisingwestern said:

 

Blank off the turntable hole from the underside, identify the centre, make a trammel/radius arm to mount the router on but high enough not to damage surrounding scenery and use a deep worktop cutter to enlarge the hole.

 

Mike.

That's the way I would do it, plus I'm lucky that I have this Dremel attachment and router bits. 

It's pretty straightforward, the spike goes into the centre hole, you can then adjust the arm to the required radius.  The Dremel goes in the other end with the router bit attached (a hole needs to be drilled at your starting point on the circles circumference.) Then off you go!

It's also got a fitting for cutting parallel straight edges.

Here endeth the advertisement (!) Seriously though, it is a handy bit of kit.

[doilum]

54 minutes ago, Enterprisingwestern said:

 

Blank off the turntable hole from the underside, identify the centre, make a trammel/radius arm to mount the router on but high enough not to damage surrounding scenery and use a deep worktop cutter to enlarge the hole.

 

Mike.

Forty years ago a complicated hi tech solution would have been my first choice method. Funny it has taken so long to appreciate the low tech solution. By the time jigs have been made, cutters adjusted and measurements triple checked the guy with the drill is starting to join up the dots......

Maybe it is a result of retirement when time doesn't really matter but I have come to embrace the slower boring ( bad pun) approach and find it is usually quicker. I have every type of power saw available but, for the first time in my life really enjoy using a ten quid jack saw.

Just a thought for Sunday morning!

[Andymsa]

I would use a multi tool with a small blade

[tomparryharry]

Plug the hole with a solid bung to match your existing hole, then you can centre to whatever diameter you wish to cut. Like others have suggested, a coping saw is the business, and 6mm is actually quite thin, so the more time & relaxation, the less  collateral damage you might inflict.

 

Hope this helps,

Ian.

[boxbrownie]

Didn’t realise you needed that size hole  as above I’d use a new/existing centre and make a radius arm with a hole for a saw/router etc.

[spikey]

1 hour ago, Andymsa said:

I would use a multi tool with a small blade

 

I probably would if I had one.

 

Having considered all the worthy suggestions above, the winner is ... the coping saw.  Which of course I only have the one blade for, and that's blunt.  But Ebay to the rescue for £3.69 delivered, and I have plenty of other fish to fry meanwhile.

 

Thank you gentlemen.

[tomparryharry]

2 hours ago, doilum said:

Forty years ago a complicated hi tech solution would have been my first choice method. Funny it has taken so long to appreciate the low tech solution. By the time jigs have been made, cutters adjusted and measurements triple checked the guy with the drill is starting to join up the dots......

Maybe it is a result of retirement when time doesn't really matter but I have come to embrace the slower boring ( bad pun) approach and find it is usually quicker. I have every type of power saw available but, for the first time in my life really enjoy using a ten quid jack saw.

Just a thought for Sunday morning!

 

I don't know if the current Jack Saw is any good, but it used to be a contractors disposable saw. very good for what it's meant to be. Once it's lost its kerf, chuck it away. I've seen craftsmen re-sharpen a saw, and I really ought to learn how its done. I've got 6-7 saws in the garage, and I haven't the heart to chuck them out.  You can buy an electricians hole saw, which do come in various depths & diameters. Remember however, that using one of these will require re-centreing with a secure bung,  as discussed earlier. Otherwise, it's all over the place, and tears before bedtime.  A variation on the theme is a keyhole saw, sometimes called a padsaw. 

[doilum]

13 minutes ago, tomparryharry said:

 

I don't know if the current Jack Saw is any good, but it used to be a contractors disposable saw. very good for what it's meant to be. Once it's lost its kerf, chuck it away. I've seen craftsmen re-sharpen a saw, and I really ought to learn how its done. I've got 6-7 saws in the garage, and I haven't the heart to chuck them out.  You can buy an electricians hole saw, which do come in various depths & diameters. Remember however, that using one of these will require re-centreing with a secure bung,  as discussed earlier. Otherwise, it's all over the place, and tears before bedtime.  A variation on the theme is a keyhole saw, sometimes called a padsaw. J

Disposable teflon coated and less than a tenner!

[tomparryharry]

1 minute ago, doilum said:

Disposable teflon coated and less than a tenner!

 

Lifebouy soap, if you please! Either that, or Wrights Coal tar soap. 

[boxbrownie]

2 hours ago, tomparryharry said:

 

Lifebouy soap, if you please! Either that, or Wrights Coal tar soap. 

Just rub a candle on the blade surely, that’s what my Grandad taught me to use to stop a saw picking up.......

[tomparryharry]

19 minutes ago, boxbrownie said:

Just rub a candle on the blade surely, that’s what my Grandad taught me to use to stop a saw picking up.......

If I can refer to the honourable gentleman, 2 posts previously.....

You can use soap, candle, trefolex, cutting compound, or any selection of cutting aids. I used Lucozade once, but I had a cold....

[The Johnster]

It's all that outdoor work on the shed, Ian.  Wrap up warm and take a lot of rum and blackcurrant juice.  Won't cure your cold but after about half a dozen or so of these toddies, you won't care...