Where did I go wrong?

[Mr Finch]

It is fast becoming obvious to me that I have still have lots to learn, far more than I first thought!

I turned this bowl from a spalted (hardly) white elm blank that was given to me.

From tooling the surfaces were smooth and ready for sanding. Starting at 120 grit I went through to 600 and by the time I had finished the rim had disintegrated and I had to re-tool it.

As you can see from the above photos I still managed to get some dropout in the rim at one point and the tearout in the bowl in the second photo.

So, can anyone please advise what I did wrong ( or didn't do at all) that causing this pitting?

TIA

Collin

 

[Random Orbital Bob]

Hi Collin

Are you 100% certain the tearout in the bowl (not the rim) was introduced by the sanding and not already there after tooling? In my experience, the tearout in the photo can be removed by:

1/ Very sharp gouge. Always re-sharpen your gouge just before the last one or two or three cuts
2/ Experiment with going up or downhill (despite) the "rules" because often little patches of grain haven't read the "rules"
3/ If grain is particularly punky you can try firming it up with a fast acting CA glue...let it dry...refinish with sharp gouge

I've never found tearout like that to happen when sanding...more really annoying scratches. To remove those I just go back a grit. Also have you tried power sanding?

 

[chipmunk]

Hi Collin,
I agree with Bob that it isn't likely to be sanding it must have been there from the tool. It could be one of several things.

Are you hollowing with a bowl gouge or a scraper?

A sharp gouge with the bevel rubbing wouldn't have resulted in tear-out like that unless the wood is badly spalted which doesn't look the case - I would suggest that either the gouge was blunt or the bevel wasn't rubbing. http://www.turningtools.co.uk/wtintro/cleancut/cleancut.html

Another possibility is that you should be hollowing (at least the finishing cuts) from the outside of the bowl into the middle on a cross-grained bowl. If you cut the other way then you're going against the grain and it will lift and tear out.
http://www.youtube.com/watch?v=Vbhs-lhpBZ8

If you used a scraper to refine the inside then it almost certainly wasn't sharp enough.

HTH
Jon

 

[Mr Finch]

Hi Bob

I can't be 100%, probably 95%. I saw it happen on the outside and was much more careful on the inside.

I think it's technique rather than tools, but my sharpening skills are a little lacking at the moment so that may contribute.

I think it's really rather rude of the wood not to read the rules!

The wood being pinky may also be an issue, especially as it was sold as spalted. How the only visible spalting was a very small patch on the corner of the blank which I took off during turning. I fear that I would have had to use CA on the whole bowl and that would just be pointless in my mind.

I will be trying the shape again, but in a different wood. I will try the white elm again at some point in the future to see if I can turn it without this result.

Many thanks for your help!

Collin

 

[Mr Finch]

Jon

Nails and heads I think. Yes, I used a scraper in the inside after the bowl gouge and yes, outside to in.

So, a bit of technique and a bit of bad sharpening on the scraper ( which is an old file that my dad had turned into a scraper.

I think new tools are required and then practice practice practice!

Would I be ok re-chucking the bowl and trying it do you reckon? Although I put a finish on, I didn't remove the tenon from the bottom yet.

Thank you!

 

[chipmunk]

Collin,
The trouble with a scraper, especially one made from a file, is that it'll only remain truly sharp for a few seconds of use.

The other issue is that using a scraper from an old file is that it can be dangerous if you get a catch. Unless they've been tempered, and then the edge will not last as long, they can shatter and you may find yourself impaled on the bits.

Are you a member of HWA? http://hants-woodturners-hwa.co.uk/

HTH
Jon

 

[Random Orbital Bob]

Re-chucking should be OK. Just watch the speed at the start as it will likely have gone out of true. Retrue it and then go through the process again. Unless it was particularly green it wont have gone far out of true.

I think the sharpening issue is a big one though. As I've learned a little about turning, the more I turn, the more I realise that sharpening is critically linked to decent surface finishes. The difference is really staggering. I have my sharpening station right next door to my lathe so I just turn through 90 degrees and my grinders are right there ready for use. You simply wont get a good finish off the tools until you handle the sharpening thing. I now consider sharpening as important as the lathe and the tools in respect of its position in turning.

You'll also be really pleased when you sharpen and take that final cut down the inside of a bowl. Its very satisfying when you can start at 320 grit paper because the tooling left such a good surface best of luck.

 

[Mr Finch]

Thanks Jon.

I do have proper bowl gouges, I bought a couple second hand (both HSS) at a show a couple of months ago.

The scrapers I have will be going in the bin when I get home!

I will look at the shop and see what I can do, money is tight at the mo (as it is with everyone no doubt!)

I will watch the vid you linked when I get home too.

Thanks again

Coll

 

[Mr Finch]

I am not a member of HWA yet, I have spoken to a couple of members though and both say they really like the club. I will be joining when funds allow!

Bob - thanks! My grinder is one step to the left of my lathe and I have a Sorby jig so I think it's just practice with sharpening and remembering to touch the edge up regularly. I really need to change the wheel in it though, that is on my shopping list for tonight so I can fit and play at the weekend.



Coll

 

[paulm]

Its very satisfying when you can start at 320 grit paper because the tooling left such a good surface best of luck.

I'm looking forwards to that one day :lol:

Cellulose sanding sealer, or a bit of danish oil or similar on the uncooperative areas can also help if you don't have any superglue to hand. Toolstation are great for superglue by the way, dead cheap compared to most places !

Cheers, Paul

 

[Mr Finch]

Its very satisfying when you can start at 320 grit paper because the tooling left such a good surface best of luck.

I'm looking forwards to that one day :lol:

Cellulose sanding sealer, or a bit of danish oil or similar on the uncooperative areas can also help if you don't have any superglue to hand. Toolstation are great for superglue by the way, dead cheap compared to most places !

Cheers, Paul

Awesome, thanks Paul. I will have to check out Tool Station.

 

[Random Orbital Bob]

mm....I confess 320 only really works on very fine grain and dense woods (apple springs to mind) but a 220 starting point is really do-able. But only after a decent sharpening literally before you take the last cut.

 

[paulm]

I'll hide the 40 grit next time you come round Rob :lol:

Cheers, Paul

 

[Random Orbital Bob]

If you own any 40 grit Paul I'll eat my lathe

 

[chipmunk]

Starting at 320 grit on a cross-grain bowl from the tool is an interesting claim...

I'd just like to point out that the late great Bert Marsh used to start with 80 grit despite having a great finish off the tool.

Jon

 

[KimG]

If I have a good finish off the tool I will start with the finest I can get away with, it's rare that that is less that 180 grit, for small fine items like finials then 240, but as the main purpose of sanding is to remove any tool marks or small tears then 80 or 120 make better sense as a starting point as they will remove the material quickly with a minimum of heat build up, once the initial finish has been achieved, work down through the grits to finish, but don't move away from the coarse grits while a flaw or blemish you are not willing to leave remains because it will be even harder to remove as you step down through the finer grits.

 

[Random Orbital Bob]

well...I'm quite surprised at that.

I did confess 320 was pushing a bit but 220 on many woods is perfectly within reach. I guess on average I would range from 120 to 320 depending on the species, punkyness etc but I very rarely use 80 when I'm powersanding. I am a bit fanatical about sharpening mind. I have a Tormek and a regular grinder setup permanently next to the lathe and I always sharpen directly before the finishing cuts. I must say, with that approach, I don't see the problem?

Here's an oak burr bowl that commenced power sanding at 220. Yes....Burr

 

[Random Orbital Bob]

Sorry Kim...we crossed in the ether. This response was from the previous poster. But Im in violent agreement that one starts sanding at an appropriate grit for the project. Naturally I don't want to be slogging away trying to 220 out a whopping great piece of tearout. Were there to be tearout, of course I'll start with 80 and work up. I'm not claiming to be a magician. I just find that perhaps because I'm so looney with my sharpening, I must get a better than average finish off the tools. I must say this thread has rather surprised me. I kind of figured everyone did that??

I think...to be honest...I hate sanding....so I go to some length to avoid it. That means spending more time on the tools. I'll give an example. If the gouge doesn't seem to polish the grain enough or its a bit naughty etc, I'll sharpen a round nose scraper and sheer scrape the finish. I leave the grinder running and do one sharpening pass before every single pass on the bowl. It takes literally 3 -4 seconds since the toolrest is all setup. The amount of pounding the edge of even a HSS turning tool edge gets is phenominal and that little touch up is definitely noticeable on the work. It's fine but it's there and that maybe one whole grits worth of a jump in sandpaper.

 

[chipmunk]

Bob,
Skipping a few grits if the finish off the tool is good is obviously normal and to be expected but what I was reacting to was the suggestion that somehow a starting grit of 240/320 on a bowl was what was reasonable all of the time and anything else was a sign of incompetence.

I was just redressing the balance - Bert Marsh was probably a little extreme in the other direction but if you check his book he says that he always started with 80-grit because he claimed it cut quicker and generated less heat. I was lucky enough to see him in action and indeed I can confirm that is what he did.

Jon

 

[Spindle]

Hi

Whilst all of the advice above regarding the tooling is valid I'm not so sure that that is your problem in this case. The voids do not seem to follow the path of the tool as would be expected.

I think these faults are the result of the spalting or some other condition of the blank. Try prodding the damaged areas with a knitting needle or something of that profile, are they makedly softer than their surroundings?

Elm has a pretty random and interlocking type of grain and therefore it is not the easiest of woods for a beginner to get an acceptable finish on, try something a little easier to turn, sycamore would be my suggestion.

Above all don't give up, it will 'click' sooner than you think.

Regards Mick