duncanh
Established Member
After I posted a spiral piece in this thread I was asked how I did it so I made another piece and photographed the steps.
click images for a larger versions
Turn a cylinder and put a dovetail at one end. Mount this in the chuck.
Hollow a cup at one end as you would for a goblet. This one is wide and deep enough to hold a night light. This is then sanded and finished.
Turn the rough outline that you want for the spiral. Aim to shape the top shoulder so that when the spiral is shaped it flows smoothly into opposite side of the cup.
Similarly for where the spiral meets the base.
Using whichever indexing system you prefer put 8 equally spaced marks along the length of the spiral. (if the piece is of greater diameter you may want to use more marks).
Put a matching number of dividing marks perpendicular to the first marks. (here I used 8 )
I started in the middle and marked the intersection point of 2 lines. Then move one line sideways, one line down and mark the next intersection. Continue until you reach the top. Move back to the centre, move one line sideways, one line up and mark the intersection.
Join up these marks and you've got one edge of the spiral. I joined these with a rough pencil line but if you want to be exact (you don't really need to be!) then one tip is to use tape to join each pair of intersection points and then draw along the edge of the tape.
Repeat the above process using the intersection points one step to the right.
You now have the outline of the complete spiral. Shade all the wood that falls outside the spiral edges - this wood has to be removed. This can either be done using a small angle grinder with suitable blade or by hand. I don't have a grinder so resorted to the hand method.
Saw by hand just outside the edges of the spiral. You can saw with one hand a rotate the piece by hand in the lathe with the other. Depth of cut is approx 1cm.
Once the outline is defined put close perpendicular saw cuts from one side of the spiral to the other. Once you have several of these use a chisel to prise the wood out. I used this method for my first spiral but found the sawing to be very monotonous so for this one I built a jig to hold the piece on the bandsaw.
If you use the hand cutting and chisel method do the top of the spiral first and then move towards the bottom because as you remove wood the structure will become weaker.
Cutting on the bandsaw is a lot faster but ensure that the piece is held securely so that it can't rotate under the blade. It's very easy to cut too far into the parts of the spiral that you can't see so be careful and err on the side of cutting less than you need. (see the final image for an example of overcutting :-( )
Mount the piece back on the lathe and start the sculpting process. For this one I used various sizes of drum sanders held in a flexible drill shaft. Put some form of protection on the cup at the top in case you get careless with the sanding.
Progress on to smaller sanding drums to get into the tight curves.
Here I'm trying to blend the curve of the spiral into the curve of the cup. A cup with a more vertical curve would have been much easier here.
You need to blend the bottom of the spiral into the base as you did at the top.
Once you've got the shape it's time to start final sanding. My hands started to ache keeping a tight grip on the abrasive so I made this sanding frame. It's 2 pieces of plywood held together with hex bolts and lock nuts. Just loosen the nuts at the sanding end, slip in new abrasive and then tighten.
I used flexible cloth backed abrasive here.
Go back to hand-held abrasive for final sanding of the curve - this method helps get a more rounded profile.
Finally, part off the base. Use only enough headstock pressure to hold the cup - the spiral will be quite springy and if you over tighten and switch the lathe on it might cause problems. Finish the bottom
This is the finished piece. Just above the base on the left you can see where I cut too far with the bandsaw :-(
That's it. Good luck
Duncan
click images for a larger versions
Turn a cylinder and put a dovetail at one end. Mount this in the chuck.
Hollow a cup at one end as you would for a goblet. This one is wide and deep enough to hold a night light. This is then sanded and finished.
Turn the rough outline that you want for the spiral. Aim to shape the top shoulder so that when the spiral is shaped it flows smoothly into opposite side of the cup.
Similarly for where the spiral meets the base.
Using whichever indexing system you prefer put 8 equally spaced marks along the length of the spiral. (if the piece is of greater diameter you may want to use more marks).
Put a matching number of dividing marks perpendicular to the first marks. (here I used 8 )
I started in the middle and marked the intersection point of 2 lines. Then move one line sideways, one line down and mark the next intersection. Continue until you reach the top. Move back to the centre, move one line sideways, one line up and mark the intersection.
Join up these marks and you've got one edge of the spiral. I joined these with a rough pencil line but if you want to be exact (you don't really need to be!) then one tip is to use tape to join each pair of intersection points and then draw along the edge of the tape.
Repeat the above process using the intersection points one step to the right.
You now have the outline of the complete spiral. Shade all the wood that falls outside the spiral edges - this wood has to be removed. This can either be done using a small angle grinder with suitable blade or by hand. I don't have a grinder so resorted to the hand method.
Saw by hand just outside the edges of the spiral. You can saw with one hand a rotate the piece by hand in the lathe with the other. Depth of cut is approx 1cm.
Once the outline is defined put close perpendicular saw cuts from one side of the spiral to the other. Once you have several of these use a chisel to prise the wood out. I used this method for my first spiral but found the sawing to be very monotonous so for this one I built a jig to hold the piece on the bandsaw.
If you use the hand cutting and chisel method do the top of the spiral first and then move towards the bottom because as you remove wood the structure will become weaker.
Cutting on the bandsaw is a lot faster but ensure that the piece is held securely so that it can't rotate under the blade. It's very easy to cut too far into the parts of the spiral that you can't see so be careful and err on the side of cutting less than you need. (see the final image for an example of overcutting :-( )
Mount the piece back on the lathe and start the sculpting process. For this one I used various sizes of drum sanders held in a flexible drill shaft. Put some form of protection on the cup at the top in case you get careless with the sanding.
Progress on to smaller sanding drums to get into the tight curves.
Here I'm trying to blend the curve of the spiral into the curve of the cup. A cup with a more vertical curve would have been much easier here.
You need to blend the bottom of the spiral into the base as you did at the top.
Once you've got the shape it's time to start final sanding. My hands started to ache keeping a tight grip on the abrasive so I made this sanding frame. It's 2 pieces of plywood held together with hex bolts and lock nuts. Just loosen the nuts at the sanding end, slip in new abrasive and then tighten.
I used flexible cloth backed abrasive here.
Go back to hand-held abrasive for final sanding of the curve - this method helps get a more rounded profile.
Finally, part off the base. Use only enough headstock pressure to hold the cup - the spiral will be quite springy and if you over tighten and switch the lathe on it might cause problems. Finish the bottom
This is the finished piece. Just above the base on the left you can see where I cut too far with the bandsaw :-(
That's it. Good luck
Duncan
