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turnerted
2nd May 2011, 06:08 PM
G'day
Here are my latest two disc lamps.The first is Iron bark. The disc is 270 mm and the overall height is 490mm .The second and third are either side of a Coolabah burl lamp 270mm diam by 480 mm high .
The finish is DO on both .
This was the hardest bit of coolabah ,or anything else, that I've ever turned .I even had difficulty just getting the blank trued up . Supprisingly the first face was not that difficult to turn but when I turned it over that's when the real problems started . At one stage I was sharpening three gouges at a time and using each one for a few seconds untill it went blunt then sharpen them again . I thought the problem may have been grain orientation related so I tried running the lathe in reverse and turning from the other side of the lathe, but it made no difference.
As I got closer to the outside perimeter of the disc , where the radious of the curve is smaller I could get virtually nothing but dust off . In desperation, I decided to attack the wood with an angle grinder , starting with P24 grit , it worked quite well and I worked my way through the grits . I was quite happy with the result and I don't think anyone could pick which side I used the grinder on .
I would be interested in any suggestions of a different aproach I could have taken since I still have enough left of this burl slab left to do another lamp .
I do most of my cutting with a pull cut and have the wings on my bowl gouge fairly well swept back .
I also tried a scrapper with no effect .
From the shape of the edge of the burl slab I could determine that the difficult side would have been the side closest to the trunk of the tree which I suppose means that was the oldest side but since the slab was only about 50mm thick , It's hard to see how that could be relevent also this side had just been sawn whereas the easier side had been surfaced .
I look forward to your comments and suggestions.
Ted

Sawdust Maker
2nd May 2011, 10:15 PM
Ted

Nice work on both

that burl looks great even after the trouble you had

powderpost
2nd May 2011, 10:20 PM
They look pretty good Ted. Try slowing the lathe down and see if it cuts better.
Jim

thompy
3rd May 2011, 01:33 AM
Agree with Powderpost, slowing down the lathe RPM on large discs will slow the FPM (foot/feet per minute) down on the outer edges. At 1000RPM 1" out from the centre you'll have roughly 523 FPM sliding past the tool, at 6" out same speed you'll have about 3140 FPM.

Quite a difference in the ammount of work the tool has to do or wood to cut or have it being ground away by the wood in the one minute (if your metric then its the distance of 150m vs almost 1klm).

Dropping the lathe speed to say 400RPM will give you 1250 FPM (almost 400m) 6" out from centre. I havent't bothered with exact math but shows what i mean i hope.

Neal.

PS: inspiring work, they look fantastic, and the centre roses, have me fascinated, i'm guessing round stock indexed and turned just a little bit offcentre in a headstock faceplate jig or chuck jig, then turned around and returned from the back side of it also offcentre and indexed to make the reliefs? given me much food for thought.:2tsup::2tsup:thanks!

artme
3rd May 2011, 07:57 PM
Aye! Noice!!:):):)

The black cord certainly looks good and is well hidden in the front "panel".

Ad de Crom
3rd May 2011, 08:17 PM
These disc lamps are very pretty, playing with different lathe speeds, can make the difference.
Very well done.
Ad :2tsup:

turnerted
4th May 2011, 06:05 PM
Thanks for the comments . I'll try slowing the lathe down next time although this still doesn't explain why one side was more difficult than the other .Or maybe it does .I would have slowed the lathe down to sand the first side and speeded it it up when I turned it over to do the other side and maybe it was then running faster . I can only experiment on the next one .
Thompy The inserts are made by first preparing a blank about 8mm thick and about
10 mm larger diameter than required . Mount on a screw chuck with the screw in the centre and cut the grooves with a parting tool halfway through .Turn over and mount on a similar screw chuck with the screw about 7mm offcentre .Put a small 'lock' screw in the waste wood beyond the required diameter of the insert and cut the grooves through to the previous cuts . Make sure you are going to mis the centre screw and the lock screw , Mount on another screw chuck with a central screw and which is just slightly smaller than the required finished size . Fit a wooden disc , the same size as this screw chuck, on the live centre then bring the tail stock towards the head stock so's the insert is held as a sandwich . Carefully turn down to size .
Best of luck . I had a high failure rate when I first started off . More than 50% .To make these four inserts took five attempts.

Ted

wheelinround
4th May 2011, 06:26 PM
Ted very nice indeed well done :2tsup:

There will be for Sydney siders a lesson on this at the next GTG................by Nick:p

thompy
4th May 2011, 10:37 PM
Hmm Ted, yeap it was offset turning from both sides as i suspected, and after reading you use the screw chuck and had a 50% failure rate i can assume due to either the flex after the piece is reduced in its structural integrity being partially compromised or sandwitching the final and turning to round, my idea might work for you i dont know.

Instead of screw chucking it, prepare a round of MDF of similar on the faceplate, and slot the dia. of your (finished)piece into the mdf by the 7mm or so (sideways for the offset turning) and the 4mm deep. That way you'll be turning against the mdf backing from each side giving it a lot more support. You'd have to turn it as a finished dia. first though i think. i'll see if i can get a simple google sketch up.

There we go, its not accurate just a view of what i mean, dunno if it'll help or not, its just a thought, i'm about a week (i hope) away from being able to try this out myself.

Neal.

thompy
4th May 2011, 10:52 PM
.