drilling big holes

[marcros]

I need to cut some holes with flat bottoms. Some at 75mm and some at 58mm. They need to be pretty accurate and pretty tidy (they are for clock inserts, that would be removed to replace batteries. I havent measured the depth, but IRO 40mm.

I dont have enough holes to do to warrant even cheap forstner bits, at £30+ each, and cannot find a 58mm one.

Option 1 is to buy a cheap set of holesaws- Screwfix do a set for downlights which contains a 60mm and a 75mm for a tenner. Cut a template, add a bit of something to reduce the hole by 2mm diameter and use a template router bit on the workpiece. I could use a forstner bit to drill out the centre to depth if necessary, I have one at 50mm i think.

Option 2 is to use an expansive drill bit. Never used one, dont know if they are any good or not.

I can drill slowly and controlled on my hand cranked bench drill. i cant go fast though, if that is required.

Any thoughts?

 

[woodfarmer]

Do you have access to a lathe ?

 

[Chrispy]

This sounds familiar, you could mark on a piece of 6 or 9mm MDF with a pair of dividers set to the right size cut out with a coping saw and file to a good fit then use this as a template for your router.Chris

 

[woodpig]

This sounds familiar, you could mark on a piece of 6 or 9mm MDF with a pair of dividers set to the right size cut out with a coping saw and file to a good fit then use this as a template for your router.Chris

That's a good idea.

 

[Baldhead]

This sounds familiar, you could mark on a piece of 6 or 9mm MDF with a pair of dividers set to the right size cut out with a coping saw and file to a good fit then use this as a template for your router.Chris

+1

Baldhead

 

[marcros]

Do you have access to a lathe ?

Not set up ready for use. Making a bench for it is a winter project I think.

 

[marcros]

This sounds familiar, you could mark on a piece of 6 or 9mm MDF with a pair of dividers set to the right size cut out with a coping saw and file to a good fit then use this as a template for your router.Chris

Thanks Chris, I will go with that idea. I dont think that there is a huge margin of error with these clock inserts, so making the template will allow me to check it.

 

[The Bear]

I'd cut the template (or even the hole itself) with a small circle router jig, much easier to get a perfect circle first time. If you havent got one, i'm talking something like in this thread
http://www.audioheritage.org/vbulletin/ ... 44-project

Mark

 

[Stu_2]

I use one of these. Works well.

 

[AndyT]

The hand drill methods can work, but the 75mm requirement may be a bit much, depending on the wood and the size of your arms.

Richard Maguire drills a lot of big holes when making his benches and has these good words to say about expansive bits:

http://www.theenglishwoodworker.com/?p=2242

I'd just add that they are pretty common and cheap on ebay, so may be worth a go.

You might also like to look at this video, (drawn to our attention by CheshireChappie at https://www.ukworkshop.co.uk/forums/in-praise-of-the-centre-bit-t84482.html) - http://www.renaissancewoodworker.com/center-bits/ - which demos old style centre bits needing surprisingly little effort.

You might be able to find a 2 1/4 inch one for your 58mm and a 3" for the 75mm, but frankly the expansive bit is easier to get if you want to try a non-powered option. I've only used old ones so have no idea if the current offerings from Toolstation etc would work - I doubt they'd be as good as the proper old Sheffield ones.

 

[Cheshirechappie]

I've never had much luck with expansive bits, especially at larger sizes. Having played with some centre bits, which will drill quite large holes, I now think the problem is one of feed rate. With the centre bits, there's no leadscrew, so feedrate depends on how much you're prepared to lean on the brace - more diameter, slower feed sort of happens automatically, or you just can't turn the thing; with the expansive bits, it's dictated by the pitch of the leadscrew, so you have no choice but to take out a fair slice per revolution, often more than you can turn.

Centre bits were made up to quite large sizes - 3" or so. They do crop up secondhand from time to time, but not with the regularity of the ones from about 1/4" to about 1 1/2". Finding a biggie of a definite size when you need one in a hurry may not be easy, and almost certainly won't be cheap.

For the holes in question, if I were forced to use hand methods, I think I'd mark out, then drill away the bulk of the waste inside the line to depth with a smaller centre bit; say 3/4" or so, which will cut fast and easy in almost any wood. Then I'd chop away the rest of the waste with bench chisels, finishing the periphery with a paring gouge. The base could be cleaned up with a hand router, though 40mm depth is getting a bit deep for them; a chisel bevel down might make a quicker and easier job of it. I think once you'd got into a rhythm, that could be quite quick - maybe five minutes a hole finished, irrespective of size.

If an electric router is to hand, that may well be quicker once the circle jig is set up, and give a cleaner finish to the bottom of the holes, especially if the batch is reasonably large. Noisy and dusty, though.

 

[Terry - Somerset]

Mark out diameter. Cut roughly to size with a scroll saw, drill out adjacent holes in the perimeter or similar.

Then use sanding drum in a drill - preferably a pillar drill as this will ensure sides are square (I have done it). Although not intended for sideways loads, I have used these for occasional work with no lasting problems/damage.

You can even make a box to sit on the drill table with a hole cut for the sanding drum and another for connection to dust extraction. Axminster sell these with 25mm and 50mm diameter and it is easy to get a smooth curve to the marked line.

Terry

Just re-read the thread - this only works well for holes through the wood not with flat bottom!!

 

[nanscombe]

... but that wouldn't stop the addition of a baseplate in similar, or contrasting, material.

 

[Sheffield Tony]

If you were going for a holesaw approach, can't you just make the hole directly rather than a router template ? You might have to stop a few times to chisel out the waste, and might need to remove the centre drill for the last step to avoid an unwanted hole.

On the other hand, you might not do many this way with a £10 hole saw set ! In fact, if my experience of cheap S******x forstner bit sets is anything to go by, if the wood is in any way hard you might struggle to finish one !

 

[marcros]

The 75mm one may work ok like that tony but the nearest holesaw to 58mm is 60mm in that set. I hear what you are saying about the 10 pound holesaw set although I have found the screwfix forstners to be fine (they were the more expensive of their 2 sets). It is all relative though- I have not used them every day.

I am tempted to pick up an expansive bit for my brace from eBay, to give it a try and probably make an mdf template with a fret saw too. That way, total outlay will be about a tenner and the expansive bit will get used at some point anyway.

 

[nanscombe]

I notice that the inserts have to removed to replace the batteries.

If you used a holesaw you could enlarge, and smooth, the hole left by the centre bit enough to be able to poke something through to push the insert out.

 

[MusicMan]

I also like the expansive auger bits, they work very well. Lubricate with beeswax or candle wax to reduce the effort a lot.

Keith