New bowl and some help with a problem?

[Alie Barnes]

Hello

Well i finished my Elm bowl, finished in Danish oil.





Now for the problem, i mounted the log on a faceplate and rounded and trued it all up, shaped the base and put in a tenon for the chuck.

when i turned the piece round and put the chuck on it was slightly out of centre, why is this? it means that i cant sand a piece becuase ill have to true it up again when i reverse it?

Any ideas on whats causing it? i dont think its vibration because i thought it could be so placeda cup of tea on the bench while making it and there was no movement whatsoever. could it be the tenon itself? not quite flat?

I just cant work out why its not staying true when turning it around.

thanks for help.

Alie

 

[Jenx]

'Typically' because of not quite seating correctly in the chuck jaws...
Not 'guaranteeed' as the problem Alie, but that is the usual type of fault...

Did you grip a tenon in compression or a dovetailed expansion hold ?

I do the same 'personalised turning' sometimes ! :lol: :lol:
Usually attributable to not being quite perfect in the jaws in my case, I think.

Assuming that you haven't got any 'float' in your headstock spindle, of course ( Worn headstock bearings etc ).

HTH 8)

 

[Alie Barnes]

dovetailed expansion, So many terms that i dont fully know!!!!

I made a ring in the base of the bowl, placed the chuck in that and expanded the chuck.

 

[stevebuk]

dovetailed expansion, So many terms that i dont fully know!!!!

I made a ring in the base of the bowl, placed the chuck in that and expanded the chuck.

in expansion then :lol:
i had the same experience last time i tried too, it was as Alun said, the wood was not in the jaws corectly.

 

[TEP]

Trouble is that most folks really tighten up the chuck when reverse chucking, and end up crushing the mounting point. Timber not being a material of consistent density it moves of centre as you crush the fibres. Also don't forget that wood WILL move as you turn it as you relieve any stresses in the wood.

If you are careful re-chucking and the bowl walls are of a reasonable thickness you can get away with it, as long as the movement is only small.

If you are making a thin wall bowl best to rough out the external shape, reverse chuck then finish off the outside, and sand in that position. Then take out the inside, that way you get a perfect wall thickness.

 

[Jenx]

Thats the one ! ... I do most of mine the same way.. and experience the same problems sometimes too.

If i take my time and pay attention to making the dovetail recess 'right', then the problem 'goes away'.
if i rush it ( impetuous impatient over-eager novice that I am.. :wink: ). then a similar disaster befalls !

Try to get the 'seating' of the expanded jaws as close to a proper 'circle' ( the further out they go, the less of a true circle they 'contact' the wood at ).. and ensure clean, debris-free surfaces, which will give the bowl a fighting chance of running concentrically, when reversed.

As I know only too well, its very easy to get this wrong !

See if payiong particularly close attention to this part of the procedure helps... Probably like most novices, I was a bit guilty of trying to make huge recesses, both in diameter and depth, and compounding the problems... they don't need to be 'much', just 'right'.
( Still dont get it 100% right.. but I'll learn :wink: :lol: )

That sounds a 'likely' explanation.

Your headstock spindle is 'true', I guess ? ...
as the bearings wear through use.. eventually it'll start to run-out a little bit... unless your're in the realms of the top-notch phosphor bronze bearings for example.. ( Machines like the VB36 etc ... the 'thousands of pounds' machines, rather than 'more lower end' machines like I have )
Even when it eventaully happens, its 'repairable' without breaking the bank too much ! 8) :lol:

 

[Bodrighy]

When you are making a recess, make it marginally larger than the outside diameter of the chuck fully closed. You need to have some depth but probably a lot less than you think. Also tighten the chuck gently until you start to feel resistance. It is surprising just how much grip it has. As Tam says, tighten too much and not only do you mark the wood you end up off centre. Doing it in compression, (on a tenon) the problem is even worse, especially with softer wood.

Pete

 

[robo hippy]

Another few points on chuck mounts. I have found that the final cut on a recess or tenon needs to be like a finish cut on the bowl, very dainty. There is always a bit of run out when turning, the tools simply cut differently in end grain and side grain, so there is always a little bump. By holding your tool (I use a specialized dove tail tool, others use a skew or a spindle gouge works) to the wood so that it just barely touches, you can remove some of the run out/bump. Also, any dust/shaving/wood particles in the recess or on the jaws of your chuck can throw things off kilter. Some times you can rotate the bowl 90 or 180 degrees on your chuck, and this can help as well.
robo hippy

 

[Alie Barnes]

gonna try out some of your good suggestions in the next few days and will see if it helps.

thanks