Thread: Recess Cut

Not sure Dan but I would imagine that the are referring to cutting the recess and then holding the blank on a scroll chuck in expansion mode.

cheers
WH

Originally Posted by wood hacker

Not sure Dan but I would imagine that the are referring to cutting the recess and then holding the blank on a scroll chuck in expansion mode.

I sincerely hope not!

A recess should be slightly dovetailed to match the jaws when used in expansion mode, to maximise the grip. (This diagram will sorta show what I mean.)

The hole from a forstner bit really ain't suitable for this! However, with a deeper hole you can use a doover like the one I've used in this thread: https://www.woodworkforums.com/f8/i-w...61/#post364246

I find that if the jaw faces are pressed against the bottom of the recess, the forstner bit hole will suffice on most projects. Some chuck jaws have serrated edges rather than tapered so a hole with parallel sides is very acceptable for them. Softer woods allow the dovetail jaws to grip the sides of parallel holes quite well.

Originally Posted by Skew ChiDAMN!!

However, with a deeper hole you can use a doover like the one I've used in this thread: https://www.woodworkforums.com/f8/i-w...61/#post364246

They are now made and sold by Pops Shed as the Con Chuck.


Peter.

Hello!! The old chestnut.!!

I always do my bowls using the chuck in expansion mode in a VERTICAL sided recess.

Properly done with absolutely vertical walls, an absolutely flat bottom and a decidedly clean and square corner you should have no trouble. The other proviso is that the diametre of th recess must be within a cigarette paper's thickness of the diametre of the closed chuck jaws.

I have a friend with an eneneering background who taught me this method. I have had one failure only and this was due to carelessness on my part.

I mount mine on a tennon in compression mode then clean up the base when I'm finished

The other proviso is that the diametre of th recess must be within a cigarette paper's thickness of the diametre of the closed chuck jaws.

Not sure why this is important. IMHO the recess dia should be as close as possible to a chuck opening dia. that will result in max. chuck.workpiece contact. This might be fully closed or some other setting depending on the chuck?

Yes, I'm with Sturdee; the only app I'd use a Forstner bit for is as per the Conchuck, ie. top of a natural edge bowl and expand Shark or Spigot jaws into the hole in order first to work the outside.

Originally Posted by oldiephred

The other proviso is that the diametre of th recess must be within a cigarette paper's thickness of the diametre of the closed chuck jaws.

Not sure why this is important. IMHO the recess dia should be as close as possible to a chuck opening dia. that will result in max. chuck.workpiece contact. This might be fully closed or some other setting depending on the chuck?

Not so Oldie. The only time any chuck I have used have a close to perfect circle is when the jaws are closed. It there fore makes sense to set your recessto the size of the closed chuck jaws.

Originally Posted by rsser

Yes, I'm with Sturdee; the only app I'd use a Forstner bit for is as per the Conchuck, ie. top of a natural edge bowl and expand Shark or Spigot jaws into the hole in order first to work the outside.

Yep , and bring up the tailstock just for good measure .

The expansion chuck by Bruce Leadbetter works with a shallow recess and comes with its own cutter. I use it more than the nova as it is so easy to do the recess. It is also a shallower recess than required for the nova jaws so saves a bit of wood also. I think Record lathes used to have something similar.
Regards
John

FWIW I'm not a fan of Nova jaws in general; most are rounded over slightly on the outside of the face and the Spigot jaws are chamfered on the outside, so for expansion purposes you're losing contact area.

This issue has been thoroughly thrashed out in an earlier thread, and folk have made chuck expansion mounts work for them in a variety of ways.

IMO still the best way is to use quality dovetail jaws, match the recess angle to the dovetail angle and so you have a keyed fit, not a plain pressure fit.

...

MJ, we tested the Conchuck not so long ago on a hefty lump of Elm, unsupported by the tailstock (cost it overhung the bed on the swivel head) and it held well. So Con (and Skew) are on the ball with this. That said, it has limitations with a nat edge bowl, as do shark jaws cos you can't reposition the lump the align the high points or the low points.

Please think about it for a second or two. The hole can't be the same as the fully compressed jaws, or it would be impossible to insert into the hole. AFAICT, the "normal" way of making jaws is to turn round, and then slit into four parts. The width of the cutter establishes the "perfect" diameter, and enables further compression for insertion. I suppose that could be the thickness of a cigarette paper at the periphery, but not the gap in the jaws - more like 1-2 mm for the slitter. Measure your jaws with dial or vernier calipers, across opposing corners and across opposing middles, and adjust the opening until both measurements are the same, to find the correct setting for complete contact; which may or may not be 48mm - YMMV.

And I think it's generally better to seat the workpiece at the shoulders instead of the tips of the jaws, because the shoulders are larger. If the hole is slightly deeper, the tips can more easily (and gently) penetrate the wood.

Aside from all that, I'm with artme.

Cheers,
Joe

I used the Forstner bit method for many years. It works quite well. More recently I've swung back to using faceplates and rings, not because the Forstner method wasn't working for me, I just find screwing a faceplate or ring on and off quicker.

Robo Hippy, who probably turns more bowls in a year than anyone else on this forum, uses and prefers the Forstner bit method. See his comments in this thread.
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