Thread: Recess Cut

Lots of info to digest.

I thought every one knew that all woodturners are some what wankers.

The forstner bit recess does work well, and I have done thousands of bowls that way (turning time is way down now ever since Arthur (itis) stopped in for a visit, and didn't leave. If you are nervous about a forstner bit recess, you can use the tailstock which will make sure the bowl blank doesn't leave the chuck, and then remove it when it is time to make a tenon or recess for the bottom of the bowl. Like any recess or tenon, you do not want the bowl to bottom out on the face of the chuck. Recess diameter holds best if it is within 1/8 inch or so of the chuck jaw diameter (for a 2 inch closed jaw measure, you want 2 1/8 inch diameter recess). You can get away with a bit more, but not for heavy roughing or coring cuts.

robo hippy

I don't use a Forstner bit to cut my recess - I don't have one.

I use a parting tool and a scraper or skew.

Hi DIY Dan,

Just read the first post from Artme and forget the rest. I think it is OK however to cut the recess up to two or three mm greater in dia. than the fully contracted dia. of the scroll chuck.

Cheers Old Pete

Originally Posted by artme

I don't use a Forstner bit to cut my recess - I don't have one.

I use a prting tool and a scraper or skew.

Art ,
do you use a steel hammer or a wooden mallet with your chisels when you carve out the recess ?


Seriously , my take on the query in the opening post is that it is regarding the initial mounting of a blank on lathe, and therefore a drill and bit , either in a press or handheld would be used to cut the recess.

, fair 'nuff.

He's a low user of the forum (178 posts in 4 years).

Assuming he accepted the default forum settings he may have read Woodhacker's post (a good one IMO), felt it didn't address his concern and not tuned into the thread.

Or he may have gone on holiday after posting his query.

He's not on my ignore list.

....

As for creating a recess in the bowl bottom with a saw-tooth bit, it's not my cuppa tea.

My 2" bit has a point 6mm higher than the rim.

So assuming a recess depth of 4mm, if I wanted to turn that point mark away and leave some thickness at the bottom of the bowl there'd have to be at least half an inch between the bowl bottom and base which with my kind of bowls would be fugly.

Originally Posted by Manuka Jock

Art ,
do you use a steel hammer or a wooden mallet with your chisels when you carve out the recess ?


Seriously , my take on the query in the opening post is that it is regarding the initial mounting of a blank on lathe, and therefore a drill and bit , either in a press or handheld would be used to cut the recess.

Steam hammer and cold chisel MJ. Just love the hiss of steam!

Take your point mate, but my post was in relation to Skew's post.

Seems this will forever be a "point of discussion" amongst turners.

For anyone with the stamina left to explore the issues about bowl bottom expansion mounting, here's the earlier thread. Click

Originally Posted by rsser

, fair 'nuff.

He's a low user of the forum (178 posts in 4 years).

Assuming he accepted the default forum settings he may have read Woodhacker's post (a good one IMO), felt it didn't address his concern and not tuned into the thread.

Or he may have gone on holiday after posting his query.

He's not on my ignore list.

....
Quite right rsser. I've been away for a couple of days. Didn't expect 36 replies though. I've gone through them all and learned a bit, (despite the jargon).
I'm not an experienced turner, but have done quite a bit of it, although still got a long way to go. Being up in Blackheath it's hard to get all the latest gadgets for turning, so I'll probably have more questions in the future.
Thanks to everyone for the info.

DIY DAN

G'day all,

Thought I would weigh into this one belatedly.
Not going to belabour the eternal arguments regarding expansion/contraction dovetail vs parallel etc, but just some bits, which seem not to have been cleared up.

Most of the modern chucks, (Nova, Vicmark, and the various clones) have their "perfect circle" diameter, roughly in the middle of the opening range, BOTH FOR EXPANSION AND CONTRACTION. eg, old time original Nova has expansion 50-60mm, as I recall, with perfect circle 55mm. Figures for contraction are ~45mm - 55mm, PC 50mm.
Obviously targeting PC for most secure hold in either mode.

Regarding depth, in expansion, the face of the jaws MUST register on the bottom of the recess. In fact recess should never be deeper than jaws for proper registration, and should be dovetailed. Can be much shallower, see below.

In contraction onto a tenon, tenon should be parallel, and as long as poss, but not so as to "bottom out". Jaws should register against a shoulder on the tenon. This gives wider diameter registration, and hence a longer "lever" for stability. I don't doubt that apart from accurate registration, the differences are small, and probably only really matter when you are using regular jaws to do a job more suited to power or shark jaws, which I am often guilty of!

Most of this from chuck specs, with a bit of personal exp thrown in.

Regarding Forstner recesses, I find that in all but 1 instance, they hold no advantage, and several disadvantages:
Multiple operations, whether on tailstock, or drillpress.
Slightly less secure hold, unless you get deformation in soft timber.
Bottom of recess has dimple, and requires futher work anyway, unless you intend to turn it off.
Exception is green turnings, after drying, when the recess "ovals" out., and you can't get the jaws to fit in. In general, I just make the original recess oversize, and grip well enough in the oval recess, to allow me to remount and reverse for returning.

Regarding depth of recess, I am one who uses them as a feature of the base. As such, I make them as shallow as possible, and finish to the same standard as the piece.
In sound timber, I will seldom exceed a 2-3mm recess, up to maybe 10", and rarely get up to 5mm, even for pieces up to 24". I have had major problems only twice, both on heavily spalted timber. I have occaionally had pieces let go, but only after disastrous digins, which trashed the piece anyway. Solution is to pay attention when turning!

Finally a pearl of wisdom I have found out the hard way........

If you are using the old style Nova in compression, and doing interrupted turning, (eg rounding down irregular blanks on Glaser screw, winged bowls, natural edge, etc), be aware that the tap-tapping of the interrupted cut acts like a rattle gun, and loosens the scroll, when in compression. Frequently, when I find I'm making a mess of shaping the outside of a bowl, I stop the lathe to find the Glaser screw has sneakily become loose in the jaws, and the blank is no longer running true.

In expansion of course, it only serves to tighten the grip.

regards

Originally Posted by Alastair

Bottom of recess has dimple, and requires further work anyway, unless you intend to turn it off.

Alastair, most of us who have used the Forstner method have applied it to the top of the blank (the side that is hollowed out) and not the foot.
.

Good post Alastair!!

Thanks Alastair; good info.

FWIW, the getting close to a circle in either expansion or clamp mode has never been a priority for me but can see if you didn't want to remount after clamping then it's useful.

With my small and medium VM100 Shark Jaws the ID appears to be closest to a circle just a bit wider than fully closed.

So presumably they were machined first as a collar/flange unit and then cut into quarters.

Another tip that may be useful to newbies is to check tightness as you go with any green or soft woods, esp in clamp mode. Cos fibre compression can increase as you turn, then you wonder whether you've lost any skill that you ever had, then the piece gets levered out of the chuck and your confidence takes a dive.

I would not use the forstner bit for the bottom of the bowl recess. Just not accurate enough. On a drill press, especially if the bit is getting a bit dull, it will tend to drift a bit. If you are using a freshly sharpened bit, in a jacobs chuck (tailstock mount) at slow speeds, you could be fairly accurate, but you would have to mount the blank on a face plate or some thing, which would defeat the whole purpose of saving time.

I have also found over the years that grain alignment on your chuck, in flat grain/bowl orientation makes a difference. You want the grain to be at a 45 degree angle to the chuck jaws. You do not want one set of jaws to be on the end grain, and the other to be on the side grain. Very little compression on the end grain, and a lot on the side grain, especially if the wood is green. Of course, as said before, if the wood is really wet, it doesn't hurt to check your grip as you turn, and tighten up again as needed.

robo hippy

Originally Posted by NeilS

Alastair, most of us who have used the Forstner method have applied it to the top of the blank (the side that is hollowed out) and not the foot.
.

Makes sense now, Neil

Didn't think of that, since I have always used Glaser screw for primary mount For NE, mount between centres @ slow speed, adjust orientation, and turn a small flat surface, before removing and drilling hole for Glaser.

regards.