Saturday, 6 October 2012

Hollow Form WIP

pic 1
 Thought I'd show you how I go about making hollow forms (well a lidded form in this case), from the start of the process to having a finished form ready to be decorated.
pic 2
 I of course start off with a blank mounted between centres(pic1). This one is Sycamore that I have already cut on the bandsaw into a 4x4" square section, I think it started off about 8" long(but I didn't measure the length!).
 Once the blank is mounted centrally I rough turn it into a cylinder using my trustly 1/2" bowl gouge that is kept for this purpose, which I have sharpened into a long grind profile. I could use a roughing gouge here but I am just very comfortable with a bowl gouge in my hands LOL!
pic 3
 Once it is turned into a rough cylinder I square up the ends and cut in a dovetail for chucking(pic 2). To do this I simply use a diamond parting tool from the outside and dovetail the produced spigot using my super handy point tool (I only got one of these about a year ago and how I ever managed without it I just don't know...LOL).

pic 4

 As the blank was a little long for what I wanted I also parted in with a straight cut at the other end, made another dovetail on the produced piece so that it can be mounted in a chuck and the lid made from it(pic 3). The parting tool plunged in does tear the end grain a bit(at least when used as aggressively as I do..) but there was plenty of wood spare and the torn grain will be turned away in forming the shape anyway.

This cut stops leaving an inch or so of timber which is cut through using a saw.
  Pic 4 shows the blank reversed  and mounted in the chuck jaws with the removed end piece that will have the lid turned from it. I always use the tailstock for support while turning the outside of the form, it just ensures everything stays put!

pic 5

  The outside of the form is shaped using a 3/8" deep flute bowl gouge with a  long grind. Its quite important to leave enough 'meat' at what will become the base to give the required strength and stability during the hollowing process, as obviously you don't want it to break off or vibrate when you are trying to hollow. To be honest I have got a bit carried away with this one and should have really left it a bit thicker to avoid the chance of vibration.                                                                                                                          
pic 6

pic 7
  I start the hollowing process by first drilling down through the piece using a 20mm auger bit mounted in a Jacobs chuck in the tailstock. The dimple left by the point on the revolving centre gets the drill started off nice and centrally (without the dimple the long auger bit can try to drift when the screw end first hits the wood).     The lathe is run on a low speed for the auger. The depth to drill is measured and marked on the bit by a piece of tape so I know where to stop (crude but effective).

Pic 7 shows my home made captured bar style hollowing rig, its basically a few bits of old box section welded together with a cheap ebay laser pointer. It takes my Kelton hollowers and really takes the hassle out of hollowing. Although I can hollow with hand held tools I would much rather use this as I get to stand upright 'driving' it with my fingers and best of all the wall thickness is entirely visual by way of the laser, thus removing the need to constantly check and measure!!                                                     

pic 8
After opening up the augered  hole  a bit I cut a step inside(pic 8), this step is where the lid will sit. It is necessary as I like to have a flush fitting top on my lidded forms.
 At this point I remove the piece still mounted in the chuck and mount the small piece for the lid in a second chuck and turn the what will become the lid to the correct diameter. This is drilled (the hole can be seen in pic 9 and is where the finial/topper will be attached) and parted off, leaving it a couple of millimetres thicker than needed. I use a second chuck as I find it near impossible to get a piece to line back up perfectly true in a chuck after taking it out.

pic 9

 With the form and its chuck returned to the lathe the piece for the lid fitted (it must be a very snug/tight fit) I shape the lid and make any final adjustments to the top of the form. The hole in the lid can be used to wind a screw into for easy removal. With the lid removed I hollow out the rest of the vessel to the desired thickness ( with this piece its all about 5mm thick with the base about 15mm to give a bit of stability to the finished piece) Thickness isn't really an issue with wood as dry as this and as I intend to decorate it with the pyrography pen I don't want to go too thin
pic 10
as I don't want to get distortion from the heat.

  After hollowing I replace the lid and finish sand the top and sides of the form, I tend to go through the grits with 320 being the finishing grade.
 At this point I also cut in any markings to be made on the form before removing it from the chuck. You can see in pic 10 I have made a band on the lid for texturing. This is cut in again with the ever useful point tool.                        
pic 11

After removing the form from the chuck a cone shaped piece of timber is placed in the chuck and with a small piece of anti-slip matting to give it grip. The open end of the form is then placed over this cone and the tailstock is brought up with the revolving centre locating in the original dimple from the first between centres mounting that lines it all up perfectly. I then turn the the foot and remainder of the sides. I  leave a fairly wide piece attached to the bottom at this point while I sand the sides to a finish. The reason for this is if you haven't sanded the sides to the final grade and the form starts to break free, you have a real problem(well more work/hassle) to get the piece finished.
 After the sides are done I thin the piece in the tailstock right down as far as I dare  making sure to leave the base slightly concave (ensures it doesn't wobble). Its then a case of cutting off the last bit with a sharp wood chisel and finish sanding the tiny bit of base by hand.

 And that's pretty much it! A hollow/lidded form ready for decorating. Others probably do some parts different from me and this just represents how I do things......

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