Thread: Reverse mounting bowls

Not quite sure what the problem is here. I have several SN2 chucks with a variety of jaws and have found I can just about have it running true each time I reverse it. True, that is only a small amount of run out discern able to the eye.

Ok, heres what I do, I turn my spigot/tenon marginally above the closed dimension of the jaws being used. In fact its standard for me to completely finish the outside right down to a primary coat of finish before reversing.
Whats marginal for me? Well if the jaws have a closed dimension of say 64 mm then I will turn the foot to 65 mm. This amount is also in consideration to the species I am turning and lately its hardwood, so 1 mm is just fine.

If for any reason I fear the worst or the timber appears to be a bit soft. I may wrap a couple of layers of lecky tape around the foot before remounting the bowl and tighten it right up.

Failing all that, you might be not taking enough fine finishing cuts to true it up after roughing it out. Here, I endeavour to have it running dead true after the final finishing cut.

i normally only rough the outside and finish the whole thing once I have it in the chuck.

As hughie has said, but a couple questions.

Are you making the spigot too long? It should register on the face of the jaws not the bottom. This surface should be flat.

Is it wet or dry wood? Wet wood can sometimes compress in the long grain and throw it off a bit as one side tightens more than the other.

Originally Posted by

i normally only rough the outside and finish the whole thing once I have it in the chuck.

As hughie has said, but a couple questions.

Are you making the spigot too long? It should register on the face of the jaws not the bottom. This surface should be flat.

Is it wet or dry wood? Wet wood can sometimes compress in the long grain and throw it off a bit as one side tightens more than the other.

,
thanks again for helping
The spigot is not touching the bottom of the jaws (I do at least know that much ).
Actually, nearly all of the wood I have used is only semi-dry at the most so that may be some of my problem.
I also suspect that I am not getting the bottom of the bowl at a perfect 90 degrees to the lathe axis and that possibly my spigot is not truly parallel to the axis so am not gripping / supporting the full surface area.
Next bowl I do like this, I will test it before removing the faceplate. I will also make the spigot closer to the fully contracted jaw size (from Hughie) for better grip.
Your comments are always very much appreciated
cheers
Mick

Next bowl I do like this, I will test it before removing the faceplate. I will also make the spigot closer to the fully contracted jaw size (from Hughie) for better grip.

It pays to do that all the time to make sure it fits.

Hello Mick,
I notice that you are at French's Forest. Could I suggest that you join a men's shed that does turning, so that
you are up to speed on the fundamentals or take some lessons. I apologise if I am out of order here - only a suggestion.
There is a men's shed at St.Ives Showground (Ku-ring-gai) but I dont know their arrangements for access. If you would
like to contact me at the Hornsby Men's Shed (after 15/1 when we return from the break), I could perhaps help you with
some aspects, including sharpening. We are open on Tuesdays, Fridays (9.30 - 2 pm) and Saturday afternoons, (12 noon to 4 pm).
We use Nova lathes and have the full kit. Needless to say, we are always on the lookout for good members, altho I appreciate that
it is some distance for you and that you may be still working. There is also a Peninsula Woodturners Group - see details NSW woodturning guild
website. Only other thing I would mention is that the jaws of the chuck are (normally) dovetailed - so you should cut your spigot with a dovetail with
the depth of the jaws about 10mm from memory. This gives a good anchored fit. Easy enough to measure that depth. Again I would not generally use a faceplate for this - but a screw
chuck for the purpose of making the spigot. The screw hole should then give you a centre when you reverse chuck to hollow out the inside. Hope
that makes some sense. I am not however saying that you should not use a faceplate. That depends on the piece - bulk, out of balance etc. (John Markham - 94894651).

Only other thing I would mention is that the jaws of the chuck are (normally) dovetailed

Depends on a number of things.

Compression or expansion mode and brand of chuck.

This is with standard jaws that the chuck comes with:

Teknatool have parallel jaws in compression but a dovetail in expansion.

Vicmark and most of the others have a dovetail for both compression and expansion.

thanks all

John - unfortunately I am still working full time but hope to change that in the not too distant future. Last time I looked at men's sheds around my way, they were only opened during working hours but might do another look. At the moment, I am using books, DVDs, YouTube and this forum.

cheers

Mick

I may be completely wrong.....but could it be where your chuck is registering on the lathe when you screw the chuck on to the head of the lathe?

I built my lathe and that was a problem I had until I took my drive shaft to an engineer who welded/brazed a collar on to the shaft to form a shoulder to register accessories on then he remachined the OD thread on the shaft.

As I said I may be completely wrong.

Originally Posted by chambezio

I may be completely wrong.....but could it be where your chuck is registering on the lathe when you screw the chuck on to the head of the lathe?

Are you saying the chuck may not be parallel to the lathe bed? Is there a way of determining this without trying to measure? If I can true up a piece while in the chuck (even with the tailstock in place) does this show it is parallel?

cheers

Mick

Are you saying its out of round - or not centered correctly?

If you are saying its out of round then that is a natural process as timber attempts to stabilise itself after the cutting process through end and side grain relieves tensions within the timber. The amount of out of round will depend upon the type of timber, how it was dried, if it is wet or dry turned, and how long an interval there is between turning one side then reversing it to do the other side and also upon your techniques in mounting & hollowing out the bowl.

If it is not centred then that is a process in which you will have to systematically eliminate the possible errors causing it. Headstock - tailstock alignment both in the vert & horiz axes; tennon size, shape & match for jaw profile; jaw design; chuck registration on the headstock spindle and also on the tailstock reversing adaptor etc. Simple things like well cut tennons which match your jaw sets profile and actually register on the front face of the jaws will make a big difference in centering as Hughie says. Poorly cut missmatched tennons which do not register on the faces of jaws sets and that also rely upon the 8 corners of the jaws to hold are perhaps the single biggest cause of bowl turning problems and sheared tennons. Its basically pot luck with a poorly cut tennon!

The surveying profession realised long ago that there is never perfection in the centering of a circle, hence the accuracy of theodolites etc, so all you can do is adopt techniques which eliminate or reduce the error. Same goes for reversing a bowl.

Have a squiz at these clips by extraordinary Irish bowl turner Glen Lucas, you won't go far wrong following his techniques. Yes like all DVD's etc the clips don't always show him wearing safety gear forgive that because he is a very talented and safe turner. His turning technique is very refined from being a large volume production bowl turner.

Glenn Lucas - YouTube
Glenn Lucas - Step 6 chucks - woodturning a bowl - YouTube

Originally Posted by mick59wests

If I can true up a piece while in the chuck (even with the tailstock in place) does this show it is parallel?

No. Your chuck can be out of true, but you can still turn a blank true (parallel) to the centreline of the headstock spindle.

However, when you remount the piece by the foot in the 'out of true chuck' it will throw the piece askew.

Had that problem caused by a chuck insert that I used for outboard turning on my old Woodfast. 'Runout' (ie wobble) in the insert is the most common cause of that problem, other than the seating issue that pointed to.

Quickest way to check for this problem is to borrow a chuck that is known to run true. There was a bad batch of Nova inserts that hit the market some time ago that was covered in an earlier thread on the forum (here). It had info on how to diagnose the problem.

Originally Posted by mick59wests

Hi all - back again for some more help

it seems that whenever I reverse a bowl onto my chuck I am around 1 to 2mm out of round.

Mick

If I got that close when I reversed a bowl I would immediately die and be assumed to heaven.

I am pleased if my bowls are only flopping 6 mm. Almost all to my timber is found, fresh cut, or lying on the ground dry on top - partially rotted and wet on the bottom.

The fresh cut is blocked, split down the middle a bit longer than the diameter, more or less centered flatish side to a faceplate with some course grit sandpaper on the face, and held there with a live center screwed up tight with the tailstock.

I run the slowest I can get and be sure it will not jump out and take enough off to make a spigot or recess leaving a long spigot extending to the center. I take it off the lathe and cut off the long spigot with a hammer and chisel and remount with the chuck grabbing the bottom.

I run up the center nice and tight and rough the outside and as much as I can of the inside leaving a long spigot to the center as long as possible. Then I pull back the tailstock and turn off or break off the long spigot and rough out the inside. I make the bowl thickness about 10% of the diameter.

I use any or all of bowl gouge, Bedan, Easy Finisher, for roughing, I do not bother about finish at this point. I then soak the ones prone to splitting in 1/2 water 1/2 hand dish washing detergent for a week or two or three, then drain and let dry a day and then wrap in 3 - 5 layers of newspaper and let dry for several months.

I inspect every once in a while and when the bowl has turned nice and oval I use a center finder and make a series of lines on the spigot or recess to more or less find a center.

I put the top against the sandpapered faceplate and scoot it around so that a cup center with a sharp point in the center goes into the center of the oval spigot.

I turn the spigot round and establish a flat face for the tops of the jaws to touch. I put a pencil line on the spigot that goes under the center of the #1 jaw. Any time the bowl is removed it goes back in the same position.

I then mount the bowl by the spigot or occasionally a recess and turn it round inside and out and refine the rim. I usually leave it on the lathe overnight at this point, and the next day check to see if it has gone oval or if any cracks are developing. If it has gone oval I set it aside for a while. If it is cracking I apply CA glue, wrap in newspaper and let it sit for a week, weeks, or month.

I then remount and make round, sand, finish, and let dry several days or a week. I then put the rim of the bowl against a padded face plate and using the mark left by the point of the cup center hold it against the faceplate with the same center. I either turn off the spigot or refine it into a foot, sanding and finishing, leaving a little nub to the center. I then take the bowl off the lathe and chisel off the nub, sand and finish.

I have a series of 6 inch disks with a recess for the chuck that have sandpaper on them. I use that to make the bottom slightly concave and and then scoot the bowl over a piece of sandpaper glued to a flat surface to get a flat area at the rim of the foot of the bowl.

For bottom finishing I have also made a jam chuck with medium density fiberboard and taped the bowl to it. I have also used jumbo jaws with buttons to hold the bowl in place but find the bowl does not run as true as with a jam chuck with a groove for the rim.

Dryer pieces of timber start somewhere in the middle of the above.

Paul,

thanks very much for the details of what you do. Two things I did not quite understand:
1. When you remount your 'to be' bowl after rough turning and drying, how do you do this to get the spigot or recess round again?
2. How did you get the spigot to be concave?

thanks

Mick