Large hole boring

[cellist]

Good evening. I've taken on a job to rebuild a piano leg from a grand piano. Yikes. After 2 hours of excavation, I have managed to get the top bit (the part that's bolted to the underside of the piano) separated from the leg itself. The top bit has been badly cracked when some yobbo tried to do something to it....like see if it would fly? :C

I drilled around the tenon and used a mortice chisel to remove the leg. It was held in with two rounded wedges, so I did well to preserve the leg assembly. Now I will make the new top part, which is essentially a rectangular cube with a couple of bandsawn curves on the underside.

Now....the tenon is round. Without the wedges, that tenon is 64.5mm in diameter. The rounded recesses for the wedges will be drilled before the big center tenon on an angle, using a forstner bit. But the hole itself has to be that big and also DEEP.....like 100mm deep. I'm thinking of a single toothed holesaw or even just a bi-metal one, going down the 1.5 inches it can handle, chiselling out the waste and then going in again and again....

But does anyone have a good solution for this kind of a hole? Keep in mind, please that this is hardwood....the original was beech. I'll probably be using jarrah. Thanks!

Michael

[Chipman]

Good evening. I've taken on a job to rebuild a piano leg from a grand piano. Yikes. After 2 hours of excavation, I have managed to get the top bit (the part that's bolted to the underside of the piano) separated from the leg itself. The top bit has been badly cracked when some yobbo tried to do something to it....like see if it would fly? :C

I drilled around the tenon and used a mortice chisel to remove the leg. It was held in with two rounded wedges, so I did well to preserve the leg assembly. Now I will make the new top part, which is essentially a rectangular cube with a couple of bandsawn curves on the underside.

Now....the tenon is round. Without the wedges, that tenon is 64.5mm in diameter. The rounded recesses for the wedges will be drilled before the big center tenon on an angle, using a forstner bit. But the hole itself has to be that big and also DEEP.....like 100mm deep. I'm thinking of a single toothed holesaw or even just a bi-metal one, going down the 1.5 inches it can handle, chiselling out the waste and then going in again and again....

But does anyone have a good solution for this kind of a hole? Keep in mind, please that this is hardwood....the original was beech. I'll probably be using jarrah. Thanks!

Michael

Choices:

Find a suitable forstner bit (if it is slightly too big, you can grind them down a bit)

The bimetal hole saw (good quality)

Use a 50mm straight bit in a router and a template.... would need to cut from both sides (it would be wise to cut the hole as close a possible to size to make it easier on the router)

Mount the piece on the lathe and turn it out.


Hope this helps,

Chipman

[ian]

Michael

I can't tell from your photos whether the tenon is round or oval, but it appears tapered

If I can do the sums, 64.5 mm = 2.5 inches, near as makes no difference, so I suggest a similar sized forstner bit (Lee Valley stock them – I didn't check an aussie retailer's site)
I'd then taper and tweak the hole (assuming it needs tapering and tweaking) using a pattern makers rasp (Nicholson #49 or #50 if you don't have an Aurou)

lastly, if you use jarrah instead of beech, will the repaired piano sound "off"

I've seen a description of a table restoration where the restorer used a router mounted on an angled sled to rout a tapered hole
a similar technique might work for the wedge recesses


ian