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Eggnigma #1: Deep hollow turning for the Eggnigma

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Blog entry by Gumnut posted 08-11-2012 07:07 AM 1727 reads 1 time favorited 2 comments Add to Favorites Watch
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My First Deep Hollow Turning for the Eggnigma box
The 09 wood show had me itching to jump in for next years show and the ideas were buzzing through my head, conversations with Gordon Ward (the late) and Jack Devos who are Australian wood turning artists caused me to investigate the process of Deep Hollow Turning.
While at the wood show this gave me the opportunity to purchase some great jarrah burl for the idea of the Eggnigma box. Mr Mcjing, a tooling suplier provided some great cutting tools for the job, and they made their way home from the show and the wife said “more crap” as they do!

A Google search opened a can of worms on the subject of deep hollowing, firstly the rule is not to cut below the centre line or 90 degree point or it will catch and possibly smash to pieces. Secondly a tool was needed to cut deep into the vessel and thirdly the vessel needed to be supported by a lathe steady, this all seemed fairly simple (uhmm NO).
The vessel was shaped on the outside first and then mounted in the drill press with a forstner bit to remove most of the centre waste as possible, the experts tell me that cutting in the centre is a challenge and the drill does this much easier anyway. Then it was remounted in the lathe but turned around to hollow out the internal section.
This is where the fun started, being only held by the chuck it would wobble and smash to pieces and a lathe steady had to be purchased or made up to give the support needed. For what I wanted the prices began at $180 but the larger ones went into the stratosphere with fancy flip top heads so being a tight arse I opted to make the lathe steady.

Grand plans ended up being a very crude but effective frame made from scrap steel lying around the workshop that I welded together. The frame has a choice of two positions on the lathe bed mount for future options and then some bars were bolted to the frame which were held from moving by four individual threaded adjusters and ball roller bearings attached at the ends of the bars to just support the turning wood.
Most of the readily available steadies are three wheel devices but being a mechanic I like to over engineer things, thus four wheels were attached, this also allowed me to get the cutting tool between the rollers easily.
On its first trial the roller bearings were so noisy that it would have woken up the dead. Google taught me that the gurus use soft rubber inline roller skate wheels.
Tight fisted kicked in again and after trying to find a local verge rubbish collection to scrounge up the wheels I found that they had recently finished the clean up in our local areas for the moment (Bugger), the wife being frugal with money as well, suggested asking Chris (our son) if he wanted his heel skates that attach to his shoes, so I begged for the donation and he was happy to get them out of his rubbish tip (bedroom) because they never worked for him anyway.
Onto the frame went the wheels and as it spun into life on the lathe I realised that these were not your average skate wheels, they had self powered LED lights in them and provided a very Christmas like feel in the darkened workshop. This caused a great laugh at the recent woodwork meeting in “show and tell” and my son Chris was laughing his head off as well.

Next was to make the tool for turning, among the many different tools researched was a very simple style that had a solid bar to get into the deep section of the vessel and to prevent torsional twist the bar has another section of bar attached off the side in a “Y” arrangement. These pieces of metal I purchased from the local steel merchant and the steel is called “bright steel”, apparently harder than plain steel.
I cut the lengths and bent one shorter bar with the oxy and welded them together to what I guessed was required. Flattened the end and cut a thread for the tool to attach and then tried it out with the McJing scraper cutting tip purchased at the show, this was OK but it still grabbed a lot and the vibration was incredible, also not to mention was the fact that my elbow was the rear steady to prevent downward force of the cutter so after a while it gave me a sore shoulder.
I gave Gordon Ward a phone call and he suggested two things, keep the tool tip very small and have a look at Rolly Monroe in New Zealand with a Google search, because he has invented and marketed a tool which is a gem to use and doesn’t grab as much.
Rolly Monroe’s tool has a tip that is ¼ square HSS with a rounded end and a lead off section to allow the waste to flow out while cutting. Mounted on the top of this was the key to the success of the tool, a Brass plate to restrict how much cutting tip can dig in at any one time. Luckily I purchase from McJing a HSS ¼ bar and mount that would bolt onto the welded bar and then with the help of an aluminium oxide wheel that came with an old Christmas present never used “Safe T Planer” from Carba Tech, I ground out the tool tip as per the design. A shaped block of brass became the cap and as it dug into the Egg, the wood chips just flowed off in a breeze.
I did say chips and not shavings as it’s supposed to do because the vessel is Jarrah Burl and this is a challenge on its own.

I also used the same concept on the scraper tool, adding a brass plate and this worked a treat as well.

Next I was getting close to the outer surface and to prevent wasting all this effort I stopped and used the idea of a laser pointer to guide me from the outside, added onto the Y frame tool I welded up extra bits of steel to mount up an adjustable overhead bar on the outside of the turning vessel and fixed a laser to the end that came from a cheap electric tile cutter. This laser had a prism to spread the light out into a line so this was removed and a dot was just what the doctor ordered.
I should mention that doctor is the appropriate word needed for such a venture because Deep Hollow Turning is fraught with dangers and warnings were over all the websites.
Anyway the vessel was shaped to within about 5 mm but for what I wanted it had to be sanded and polished on the inside to be as clean as the outside, so I made up some rounded pieces of scrap wood that attached to the tool and clamped different grades of sand paper under a mounting washer for the clean up. A slight modification was needed because the sand paper being only small became burnt very easily, so a piece of sticky foam underneath did the trick to spread the contact area. I think a piece of rubber may be even better with hindsight.
This tool is in the development stage and if any more changes come about I will let you all know, at the time of writing this no parts of the vessel or me are broken and no blood has been released yet.

-- Peter, member of the Fine Woodwork Association http://www.fwwa.org.au/index.htm



2 comments so far

View HalDougherty's profile

HalDougherty

1820 posts in 1992 days


#1 posted 08-11-2012 10:20 AM

Great article! I thought I was impressed with your steady rest, but your chip breaker or depth limiter was even more impressive. I carve gunstocks to pay for my woodworking addiction, and turn scrap wood to relieve stress. When I mess up a gunstock, I spend the rest of the day turning bowls, rolling pins, or goblets. Whenever I have some new turning pieces, the first comment I get is, “Messed up again, didn’t you?” Not, what a beautiful bowl or wow another great looking rolling pin… When I get time I’m going to make a hollowing tool, and yours looks as good or better than the expensive one’s I’ve seen at Woodcraft.

-- Hal, Tennessee http://www.first285.com

View kenn's profile

kenn

788 posts in 2475 days


#2 posted 08-12-2012 04:55 AM

What I really need is some of those light up wheels for my steady rest! Loved the story.

-- Every cloud has a silver lining

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