Help with basic technique fail please

I have been having fun turning bowls, but having run out of storage and people to give them to I decided to make some salt and pepper grinders using Crushgrind shaft mechanisms. I had some lovely lace sheoak blanks from Dusteater but thought I would try a practice on some Blackwood first. That was just as well as I chose the wrong web instructions from the US for the first one (it had the instructions the wrong way around - the base was drawn as the shorter section of the grinder!). That caused all sort of problems but, having sorted that I made the first grinder up without any trouble.

Attachment 439990

So, emboldened, I began to rough out the shape for the second grinder with my roughing gouge. Instead of a lovely smooth surface to finish with the skew chisel or with sandpaper the surface became very lumpy and the gouge cut spiral grooves in it! It was very disconcerting.

Attachment 439991Attachment 439992 I'm not sure if you can see them in the photos.

So, I've fixed it now, but could someone please tell me what I did wrong so I can avoid that problem next time? (I'll post some pics of the finished salt grinder when I receive the next mechanism and assemble it.)

Thanks

David

Just a bit of a guess here. It looks as though the chuck jaws are not centrally aligned, this could mean your piece of timber is turning in an oval manner, instead of circular.

The chuck jaws are way too far open, meaning that the timber is only be held on 8 small points.

The tenon for the chuck jaws should be of a size that it is just a little bit bigger than what is needed when the jaws are almost closed. When the chuck jaws are nearly closed, say, around 5mm gap between jaws maximum; the chuck jaws will almost be in a circle. Your tenon would then be gripped by something like 90% of its surface, instead of the "probable" 5% you have as seen on your picture.

The tenon should end with a 90º flat face, "Shoulder" to the top of the jaws and be pushed up hard against the chuck jaws, then you tighten the chuck jaws until your tenon is held firmly.

I don't have a picture, but maybe someone has one showing how your tenon should be held by your chuck jaws.

Or perhaps have a look at this short clip:

https://www.youtube.com/watch?v=7V1BHYqN0Fk


I don't know for certain, but I would think most of your issues could be related to this not quite correct holding procedure.

Mick.

Make sure you have the bevel rubbing on the timber. Often these types of marks are a good indicator that the bevel wasn't in contact with the wood.

Thanks Mick,

That makes sense- the timber is certainly only held at a few points. That may also explain why I sometimes also have problems with concentricity. By that, I mean that the spigot or tenon that I turn to fit the top into the base turns out not quite central so that when I turn the top of the grinder it doesn't stay in line at the outside surface, even though I have a nice close fit between the tenon and mortice.

The first ones I turned I used a spur centre rather than the chuck to hold it, but then had issues removing the marks so tried the chuck hold.

Still learning this - probably will be for the rest of my life!

David

Thanks Brendan,

Yes, I had forgotten about rubbing the bevel with the roughing gouge even though do it as standard with a bowl gouge.

At least I saved the blank, but will try again with some less precious timber to try to improve my technique.

P.S. I like your videos, which I have just found, they are very informative.

David

Brendan is on the money, not rubbing the bevel. Mind you although I am fine with a skew I found the spindle gouge and finishing by shear scraping with a bowl gouge does a better job on Dusty's blanks.

As well as mentioned above speed of travel can also produce spirals

Quote:

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Originally Posted by Xanthorrhoeas

Still learning this - probably will be for the rest of my life!

David

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Won't we all!! life is one big learning curve. but as we get older the parabola tends to flatten somewhat.

Mick, thanks, I will watch for that in my turnings.

[QUOTE=Xanthorrhoeas;

So, I've fixed it now, but could someone please tell me what I did wrong so I can avoid that problem next time? (I'll post some pics of the finished salt grinder when I receive the next mechanism and assemble it.)

Thanks

David[/QUOTE]

A little instruction and about 20 hours in front of the lathe with roughing gouge and skew will fix that. Some years ago I was in despair over the skew and some encouragement from Retired and 20 hours of lathe time brought me to where playing with the skew is entertainment.

I did bowls to start, and still do 95% bowls, so was fairly good with bowl gouge and scraper.

You could find my adventures with skew posts if you search. Key word might be Accursed Skew.

Quote:

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Originally Posted by Fumbler

Won't we all!! life is one big learning curve. but as we get older the parabola tends to flatten somewhat.

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So we keep telling ourselves, anyway.

I suspect a lot of the 'parabola flattening' is simply that we become blasé about our mistakes. I know I certainly still make the occasional stupid ones. A beginner often has scarce resources, wants to show off their work and feels every boo-boo is a hurdle to overcome.

With time, practice and resources it becomes "Oh bugger. Another for the firewood pile," we move on and don't give it a second thought, let alone bring it up in public... :D

Of course, by the same token, with experience one can often recover from mistakes that would stop a beginner in their tracks. :think:

Quote:

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Originally Posted by Skew ChiDAMN!!

Of course, by the same token, with experience one can often recover from mistakes that would stop a beginner in their tracks. :think:

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In my world that is called a design opportunity:lb::lb::lb: