Forstner Bits

[morpheus83uk]

Hello,

I am looking at making a candle holder or two and I am looking at using Forstner bits which everyone seems to suggest are the best for flat bottomed circles. I have noticed they leave a central hole which I presume is for self feeding. How do I get rid of this? can I plug it with something as I think it will ruin the aesthetics of the holder.

Is there something I can do or is there a better way maybe with a router or another drill bit?

Thanks

James

 

[Roger928]

It can be done with a router, guide bush and circle jig easily enough.

 

[KenGMac]

morpheus83uk, good evening.

Can I suggest you look at the central Forstner bit, holes in a different "light?"

If there is a Candle in the holder [as intended] then the hole will not be seen? just a thought?

Or? one of my favoured options, make a feature of the hole? place a "Spike" as a "feature" to locate the candle?

Just trying to shed some light on your concerns?

Ken.

 

[morpheus83uk]

Thank you for your responses.

I can see what your saying about making a feature but I am looking at something more like this.

http://hogislandwood.com/wp-content/uploads/2015/03/Wood-12.jpg

I haven't ever used a Forstner bit so I am unsure how far down it goes.

Roger928 - I am not sure what you mean as I can't see how I could make a jig this small as the hole diameter would need to be around 45mm. I have no idea what a guide bush is even after some googling I am still confused.

Any help would be appreciated in this as I think it should be very simple but I just can't see a way forward.

Thanks

James

 

[Roger928]

30mm guide bush fitted to a plunge router.

Example...
32mm hole jig with an 8mm cutter will give you an accurate 10mm hole.

 

[Roger928]

Or fit the trend router compass to your router..
http://www.trend-uk.com/en/UK/trend...dge&id=15292&tot=&max=15&cur=0&search_value=n

 

[morpheus83uk]

How would I make the jig? and I am not quite sure how the maths is working out. with a 32mm jig yiu get a 10mm circle. Sorry for being dumb.

Would what your suggesting would this do the same as a Forstner bit just without the hole as shown above? or can you get Forstner bits which have removable guide so it can be started with the guide and then removed so I don't have the hole at the bottom?

Thanks

James

 

[Roger928]

30mm guide bush in the router and 8mm cutter.

And a 67 mm hole jig will give you a 45mm hole.

Radius of your 45mm hole is 22.5mm. When you plunge the router center with an 8mm cutter fitted, 4mm of the radius is cut.
You need to cut another 18.5mm.
So 18.5mm plus half the diameter of the guide bush = 67mm for the hole jig.

 

[morpheus83uk]

Just doing some looking around what about a plug cutter drill bit? would that not be easier just take a 45mm plug out of the wood? would this leave a flat bottom?

Thanks

James

 

[Roger928]

One of these mebbe....
http://www.axminster.co.uk/axcaliber-adjustable-tct-boring-bit-501990

 

[Deleted member 174758]

Just doing some looking around what about a plug cutter drill bit? would that not be easier just take a 45mm plug out of the wood? would this leave a flat bottom?

No the plug has to be broken out using a screwdriver so the bottom of the hole would be dog rough

One of these mebbe....
http://www.axminster.co.uk/axcaliber-adjustable-tct-boring-bit-501990

The problem is that the bit you are talking about has both a centre point and spurs at the outsides of the wings which will leave a groove around the outside.

To the OP - if you want to drill this you'll have to accept that drill bits for wood NEED to have a centre point to keep them from wandering off track, which is why even Forstner bits have them, albeit very small ones. Almost all other drill bits will have nickets or wings at the periphery of the cutter which are designed to cleanly slice the fibres to make drilling more accurate and less tiring. So unless you can accept those technical limitations, drilling is out. If you really need to make a perfect hole, then you are going to have to invest in a plunge router, some straight plumge cutters, some guide bushes - and you'll need to invest some time in learning about routers and guide bushes and how to use them.

Examples of how a guide bush works:

The reason we use guide bushes is that they are far less prone to causing damage to a template jig than other methods of routing (especially with less experienced operators), but the guide bush most obviously be larger that the cutter, so the hole in the router template jig must be made bigger, e.g. with a 12mm diameter router cutter and a 30mm guide bush the outside edge of the cutter is inset 9mm from the outside of the guide bush. To cut a 45mm diameter hole, the hole in the router jig will need to be 45 + 18mm = 63mm. A 63mm hole in a plywood template could be made with an appropriate-sized hole saw or using the adjustable boring bit proferred above

 

[morpheus83uk]

Ah right I think I understand now. So if I make a template from a hole saw near enough 63mm. Then using the guide bush at 30mm I guide the plunge router round the template giving a perfect hole?

OK so if I use a 12mm bit put it into a 30mm bit that gives the 9mm inset of the bit as it's 9mm on each side of the bit. This is where the 18mm comes from. So then you take the hole you want to make and add the inset giving you the template size? is that correct? I am thinking so I can make other ones in the future.

Then just clamp the template on the wood and just follow it round to make the desired hole? I presume that the guide bush sits inside the template and rotates inside?

Thank you

James

 

[Deleted member 174758]

Well almost.....

OK so if I use a 12mm bit put it into a 30mm bit that gives the 9mm inset of the bit as it's 9mm on each side of the bit. This is where the 18mm comes from. So then you take the hole you want to make and add the inset giving you the template size? is that correct? I am thinking so I can make other ones in the future.

The 18mm is 2 x the offset from the cutter to the guide bush (inset was my attempt to describe this the other way round....). But fundamentally the idea is to be able to "productionise" the hole making

Then just clamp the template on the wood and just follow it round to make the desired hole? I presume that the guide bush sits inside the template and rotates inside?

Yes, however the guide bush doesn't rotate. It just rubs against the edge of the template jig. Otherwise I think you've got it

 

[Roger928]

How do I get rid of this?

Some wood fillers will get rid of it.

 

[morpheus83uk]

Sorry yes I move the router with guide bush attached around the inside of the template once made is what I had in mind i just didn't state it clearly.

Oh and never thought of wood filler either could you stain wood filler so it matches the rest of the wood?

Thanks

James