What am I doing wrong ???

[govarney]

Hello,

I hope someone can offer me some advice. I'd like to blame my equipment but I know it must be me :;

When turning a bowl, (current example 30cm diameter, 15cm depth) I start by screwing it to a face plate and then turning the outside to finish. I then make a rebate for my Vicmarc chuck in the base. I then attach the chuck by expanding the jaws. I push the jaws hard against the base when expanding the jaws.

I then take the bowl off the lathe, turn it around and mount it using the chuck and then remove the face plate.

When I turn the lathe on there is ALWAYS a wobble. Obviously, the larger the bowl the more pronounced the wobble. (On the 30cm x 15cm approx 3-4mm movement)

What am I doing wroing ? (Can I blame by equipment ? :doh:)

[Gil Jones]

I have similar problems when I turn green wood, probably due to the wood changing shape (warping) as it dries. Some species are more apt to move as they dry than others, but your trouble is not an unusual one.

[artme]

I've had a similar problem on some pieces. On each occasion I put it down to the factbthat different parts of the blank had different densities due to things such as hidden holes or knots.

[Pat]

Let's see . . . warping in the seconds it takes to turn it around, phase of the moon, differing densities, the rebate just not being perfect by 1/2mm, the chuck not seated properly on the spindle, the planets not aligning, the jaws not seated properly, your dog did it :U

For me, I will try to take my time when seating the blank, then give it a manual turn to check. If I am certain that I have got it right and it develops a wobble, I trim it up. I try not to finish the outside until I have completed the bowl section . . . :doh:

[NCPaladin]

You probably know this but..
Make sure only the outer surface of the jaws is contacting the bowl. The tendon cannot be long enough (or a recess deep enough) for the wood to touch the chuck body.
I would remove the faceplate first. Install the chuck, not loose but slightly movable, and return to the lathe. Bring the tail stock up and apply pressure to the bowl to press it securely to the chuck. Tighten the chuck. I do this because my chuck uses tommy bars and I just cannot hold it securely and use the two bars at the same time.
If you are drying it in the meantime, you will have to re-turn the recess or tendon. A reason to leave the original point from the tail stock while drying.
Mike

[hughie]

When turning a bowl, (current example 30cm diameter, 15cm depth) I start by screwing it to a face plate and then turning the outside to finish. I then make a rebate for my Vicmarc chuck in the base. I then attach the chuck by expanding the jaws.

Are you clamping the bolw by contracting the jaws on to the bowl? or other wise?

I push the jaws hard against the base when expanding the jaws.


What I do with suspect timber here is to coat the spigot with CA and always use in contraction mode. Then reverse the bowl to remove the spigot and finish the base on something like a donut chuck etc

[oldiephred]

My evaluation of this problem, and I have had it a lot, is that the faceplate surface and the chucking surface are not exactly parallel so when the work is turned around I was setting against a surface that was not parallel to the original. I found that on critical pieces an extra step works well. By the way I use the chuck for both sides rather than using the faceplate to start.
!/ Use a forstner bit to bore a recess for the chuck jaws on the "faceplate" (top) side.
2/ Chuck the piece and flatten the bottom then make a chuck recess.
3/ Turn the piece and work on the "faceplate" side recess so the bottom of the bore will be parallel to the bottom bore.
4/ Turn the piece again making sure it is well seated against the jaws then finish the bottom as usual.
You may sometimes find a small amount of wobble this way but with care it will be quite small.

Good luck

[Calm]

There have been many threads/posts on wobbling bowls/chucks.

Does the chuck jaws wobble (even slightly) with nothing on them.

You say you "push it hard against the base" check that the taper on the jaws is not going "too far" inside the recess. (recess too deep)

When the jaws are holding the bowl for the jaws to be a "perfect circle" there should be about a 2-3 mm gap between each jaw - this means they contact the wood on the biggest possible area. (recess too big diameter)

Apart from that most bowls do this and a lot of turners dont finish the outside until they have turned it and mounted it in the chuck. - Talking to KenW the other day he said he mounts it by the base on the faceplate - finishes the whole bowl then mounts in donut chuck or whatever and removes the faceplate, screw holes and cleans up that little bit. So he mounts it once and finishes all except the faceplate area. Where you dont have enough material to waste screw holes on the bottom of a bowl glue on a waste block with hot melt glue gun first.

Hope that helps

Added - just realised you are in Ballarat (sunny part of Vic) send a PM with phone number and come around i will show you what i mean.

Cheers

[thefixer]

There have been many threads/posts on wobbling bowls/chucks.



Added - just realised you are in Ballarat (sunny part of Vic) send a PM with phone number and come around i will show you what i mean.

Cheers


Hmmmmm. Used to live in Hamilton. whenever we went to Melbourne we drove real fast through Ballarat so the engine wouldn't freeze up:D:D

Cheers
Shorty

[KenW]

Hello,

I hope someone can offer me some advice. I'd like to blame my equipment but I know it must be me :;

When turning a bowl, (current example 30cm diameter, 15cm depth) I start by screwing it to a face plate and then turning the outside to finish. I then make a rebate for my Vicmarc chuck in the base. I then attach the chuck by expanding the jaws. I push the jaws hard against the base when expanding the jaws.

I then take the bowl off the lathe, turn it around and mount it using the chuck and then remove the face plate.

When I turn the lathe on there is ALWAYS a wobble. Obviously, the larger the bowl the more pronounced the wobble. (On the 30cm x 15cm approx 3-4mm movement)

What am I doing wroing ? (Can I blame by equipment ? :doh:)
Using you chuck in expansion mode is the quickest way to get hurt, also makes finishing the bottom of the bowl harder. It is much safer to use you chuck in compression mode.
Having said that, I never use a chuck to make a bowl, not accurate enough.
Glue a scrap of ply to the bottom of the bowl blank, when glue is dry screw a small faceplate to ply. Mount blank in lathe, turn outside and inside of bowl from this mounting. Reverse bowl onto a wooden faceplate to turn away ply and shape foot.

[tea lady]

Hello,

I hope someone can offer me some advice. I'd like to blame my equipment but I know it must be me :;

When I turn the lathe on there is ALWAYS a wobble. Obviously, the larger the bowl the more pronounced the wobble. (On the 30cm x 15cm approx 3-4mm movement)

What am I doing wrong ? (Can I blame by equipment ? :doh:) Its prolly what they call "runout" on the lathe. the head stock is maybe just a poofteenth (a well known technical term.:D) off perfectly horizontal and/or square. :shrug: It runs straight in one orientation, but when you turn it round the off centeredness is in a opposite spot, si is twice as "out" as before. So you CAN blame the equipement. :cool: How to mitigate it? :think: What they said. :whattheysaid: Or, if you want to continue doing what you are doing, you could try spinning the bowl around in the chuck. Try spinning it round 180°. If the wobble is still too much try 90° either way etc until its close to ok. :shrug:

[orraloon]

Not being the perfect turner I find most times I reverse a turning it does not run 100% true. I can get close but it is now just habit to adjust as required after reversing onto the chuck. I have long suspected most others have this problem too. I figure that the jaws deform the wood slightly in either mode so a bit of a fiddle is nearly always required. The base of the blank has to sit on the jaw rim as near to flush as possible for minimum runout but usually there is some. I also do a quick spin to check and if it wobbles a lot I loosen the chuck turn the wood about 10* or so and nip up and check again. Keep doing this to find the position of least wobble. Another trick is to spin on slow and mark the rim with a pencil to find the high spot. The chuck being just mildly tight. Then with the lathe stopped tap the high spot with a mallet or wood block then check all over again. with a few tries like this you can get close to true. Then some times you just have to take a skim off the outside to true up when the thing will not play the game. Turning wood is not an exact science but about finding what works.
Regards
John

[govarney]

Thanks for all you advice guys. Excellent.



Gil Jones
I have similar problems when I turn green wood, probably due to the wood changing shape (warping) as it dries.


I haven't yet tried turning green. All bowls so far have been well seasoned.



Pat
Let's see . . . warping in the seconds it takes to turn it around, phase of the moon, differing densities, the rebate just not being perfect by 1/2mm, the chuck not seated properly on the spindle, the planets not aligning, the jaws not seated properly, your dog did it :U

You mean there could be more than one thing I'm doing wrong :D



NCPaladin
The tendon cannot be long enough (or a recess deep enough) for the wood to touch the chuck body.

Must go and have a look. I thought is was OK. but maybe not.



hughie
Are you clamping the bolw by contracting the jaws on to the bowl? or other wise?

KenW
Using you chuck in expansion mode is the quickest way to get hurt,.....



The very first time I used the chuck I used compression, got a catch and the bowl ripped straight off the lathe. Scared the s**t out of me. Been doing expansion ever since.:no:



oldiephred
!/ Use a forstner bit to bore a recess for the chuck jaws on the "faceplate" (top) side.
2/ Chuck the piece and flatten the bottom then make a chuck recess.
3/ Turn the piece and work on the "faceplate" side recess so the bottom of the bore will be parallel to the bottom bore.
4/ Turn the piece again making sure it is well seated against the jaws then finish the bottom as usual.



Thanks. I'll try this next time.



thefixer
whenever we went to Melbourne we drove real fast through Ballarat so the engine wouldn't freeze up

I used to think Ballarat was cold too until I started working with a bloke in Canada who told me about there -40C winters (without the chill factor). Now whenever I talk to people from the northern hemisphere I never complain about the weather. :D

[govarney]

.....So you CAN blame the equipement. :cool: ......

I like the Lady. :2tsup::D

[Paul39]

Govarney,

You may be doing nothing wrong. It is the nature of woodturning to be a little loose.

Lots of good advice above. Just keep turning and you will find ways to get rid of little wobbles or fix pieces that don't sit right.

Relax and keep turning, the catches will happen less and less, The pieces will look better and better, the time to make something will get remarkably shorter.

Just keep playing, it will all come in time.

[Texian]

Another detail- When chucking a face grain piece, align the grain with the centerline gap between chuck jaws, or with centerline through centers of opposite jaws. It's a small thing, but helps the wood respond equally in all four directions from pressure of the jaws. Actually has more to do with centering than wobble. Never mind.

[NeilS]

Cut the largest circle of flat MDF that your lathe will swing (inboard or out). Mark centre.

Clamp your screw centre into the chuck.

Drill centre of MD disk to take screw.

Attach disk firmly to chuck with screw.

Rotate disk by hand using headstock hand wheel while holding a pencil or similar to the face of the disk closest to the edge. Steady pencil on toolrest.

If the disk does not run close to true the problem is somewhere in your equipment, most likely with your chuck and/or thread insert. If so, there are many postings on the forum about this problem.
.