How to drill a tapered hole

davros

How would you go about drilling a tapered hole in wood? Not tapered down to nothing, though. It would be, say, 25mm at the bottom, 30mm at the top, and 25mm deep.

I've been googling for drill bits but haven't found anything suitable. Would you drill a straight hole and then grind away the sides in some fashion? How would I do that neatly?

I'd appreciate any tips.

FarmerGreen

There is a gadget called a 'cone cut' , used for enlarging holes in sheet metal.
Looks like it may do the job.

davros

But how would I rotate the bit around the hole (or the hole around the bit)? I think that would require computer control.

FarmerGreen

Nah, just put it in a tap wrench and turn it by hand.
If its a one off, turn a dowel to the taper and glue on one turn of glass paper.

davros

OK, that's something to try for the first few anyway. Thank you for the tips!

Fingalian

I use ones like these for boring holes for chair legs. You can usually pick 'em up cheap on ebay, Vintage Tool Section.

http://www.fine-tools.com/G303710.htm

davros

It looks like I'm going to have to make tapered through-holes, if I'm to have any hope of doing this quickly and repeatedly. I'm considering how I'll adapt my design accordingly.

I'll get a tapered drill bit or some kind of reamer, as suggested, and experiment.

Thanks for the help, guys. It has been very useful!

JoeB-

A small palm router with a tiltable base may help. You could tilt a straight bit, and use it to produce the taper. Not absolutely perfect, but it should be quick and relatively repeatable.

If they're through holes it should be easier, as you'd be able to taper the entire hole, using a bearing guided straight bit... this'd be trickier if the holes are blind, although still possible with a little ingenuity, and if you don't need the blind bottom of the hole to be flat... but you would need some equipment.

ennisa

does it need to be smoothly tapered or can it be stepped? If it can be stepped then you could use 2 bits, the smaller one first to the depth you want and the the larger into the smaller to the depth you want. Need to be careful centering the larger bit on the smaller hole though. Especially if the smaller hole is not too far from the size of the larger.


Hope this helps.

davros

I've seen stepped drill bits too, online. Up to now I've been experimenting with a hand-held drill so I can't do anything precise. I have a drill-stand but I'm waiting for an opportunity to visit the folks to set it up in their back garden. I've already ruined my apartment :-)

I also tried straight-sided holes. Not as elegant but something has to give. With a 30mm flat bit I was able to drill a (fairly) blind hole. It's not quite flat at the bottom and it has a smaller through-hole in the centre.

What would be the right way to drill a 30mm, perfectly square (in profile) blind hole in a piece of wood?

Alun

Those stepped drill bits (like these) are meant for cutting progressively bigger holes in sheet material like metal or plastic, just like the conical bits mentioned above.

Personally, if you're going to be doing lots of these, I'd be looking at first drilling a straight 25mm diameter hole using a forstner or saw bit to the required depth, and then getting something a bit like the spoon bit Fingalian mentioned made to your specs. You could maybe start off with a 30mm flat spade bit, grind the point off and then get the rest ground to a 5mm taper.

If you keep the piece firmly clamped to the pillar drill's base between changing bits you should have no problem with centering.

You'll still have a small indentation in the centre of the bottom of the hole from the tip of the saw /forstner bit, but less than you would from a flat bit .. is that a problem?

ennisa

What are you making?

davros

I've been kind of vague about what I'm making. Apologies for that. I'm trying to prototype a small wooden "craft" product, just to see if it works as well in reality as it does in my head.

If the prototype comes out nicely, and it can be made at a reasonable cost, I'll look into using a proper workshop to reproduce the thing.

The holes are a main feature and the item needs to look well and feel good to the touch. Imagine a tealight holder that holds several candles, say. That scale and finish.

It's probably obvious that I'm not much of a woodworker I'm trying to get away from my PC, to do something with my hands. I'm looking at doing a woodturning class this autumn, and I have some nice oak to do something with.

A forstner bit... that looks very promising. I think I'd be happy with a 30mm version, and lose the tapering.

Alun

All the tealights I have (I'm a woodturner and make quite a lot of single tealight holders of various designs) are about 38-39mm diameter. On the lathe I usually drill a 35mm hole with a saw bit in the tailstock and then enlarge and tidy it up by hand as the finish from the saw bit alone isn't really up to scratch IMO. I also have a 40mm bit, but once I've tidied it up and sanded it it's a bit too sloppy, size wise. I do tend to put a very, very slight taper on the hole and round the edge off a little just to make removing the used tealight a little easier but it's not really necessary as long as the hole isn't too tight.

Given that you're doing multiple holes, and aren't too bothered about the taper, I'd reconsider the router approach. That way you could have one or two ready made templates with the holes laid out in the correct pattern for each of your designs and use a large-ish diameter straight cutter to make the holes.