Galloway Woodturners

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Aluminium Stemmed Goblet – Rick Dobney

 

 

Cutting list, finishes and materials

Sycamore – 6” x 3” x 3”/ 150 x 75 x 75mm

Aluminium bar 18 to 22mm diameter 6063 T6. 6063 being the aluminium alloy type, T6 being the tempering level. This is readily available on eBay for a modest sum.

Molyslip MCC cutting compound to lubricate the tools whilst turning

Autosol metal polish or similar for final finishing

Wood finish of your choice, using Melamine will water or indeed wine proof your goblet should you wish to use it.

 

General Notes

A goblet is typically turned from a spindle blank, initially between centres for roughing down to a cylinder before being held in a scroll chuck for turning. Initially the bowl is shaped and hollowed before moving on to the stem, then the foot before finally parting off from the chuck and reversing and finishing the base.

This particular project requires a complete rethink of process and steps due to the need to turn the component parts separately while ensuring that that individual components flow and work together.

I typically turn the aluminium stem first then use the stem as a visual guide for turning the bowl and foot of the goblet. There are no hard and fast rules governing this but if you want the two elements to flow into one another you should find this approach easier.

As an alternative to working the aluminium, you can adopt the same method but substitute a contrasting timber for the stem; from a turning point of view you can turn or at least finish turn the stem and bowl/foot as one, similarly final sanding and finishing can be done as one just take care not contaminate a pale wood with dust from a contrasting dark wood if for example you use ebony or blackwood for the stem and a pale timber such as sycamore or holly for the bowl and foot.

 

Turning Process – Aluminium stem

  • All turning tools used in this process should be regularly lubricated using Molyslip MCC or similar cutting compound. Standard HSS turning tools will be sufficient to work 6063T6 grade aluminium.
  • Note it is critical that the ‘kiss test’ is done and any adjustments made before turning to ensure accurate alignment and fit of the work
  • Ideally the aluminium bar should be held in O’Donnell chuck jaws which provide a strong centralised hold on the bar stock, alternatively pin jaws could suffice.
  • Note it is worth having a play on a bit of scrap material initially to get a feel for the way the aluminium cuts before starting on the goblet stem, also tools must be kept sharp at all times to cut effectively
  • Using a ¼” spindle gouge, true up the sawn end of the bar, take small cuts to avoid chatter.
  • Using an engineer’s centre bit held in Jacobs chuck, drill a 2mm deep register in the end of the blank.
  • Turn a tenon on the end of the bar precisely 7mm in diameter, the tenon should also be around 7 or 8mm long. Measure using a Vernier gauge to ensure accuracy.
  • Reverse the stem and repeat the above drilling another 2mm register and turning an identical 7mm tenon.
  • The blank can now be held between centres at the headstock end either
    • in a collect chuck, or
    • in a piece of hardwood held in chuck jaws and drilled precisely to 7mm diameter
    • and a conical live centre in the tailstock located in the 2mm register
  • The stem can then be turned to your desired profile using a sharp ¼” spindle gouge. Take small cuts to avoid chatter and remember to keep the tool lubricated with Molyslip MCC. If you fail to lubricate the tool, the cutting point will heat and weld itself to the aluminium.
  • Remember the aluminium has no grain so can be cut in any direction, uphill or downhill.
  • Once the desired profile has been achieved, put on a pair of latex surgical gloves to avoid contamination of your skin.
  • Sand using Rhynogrip abrasive, starting initially at 120 grit where you fully remove any tooling marks, then progress through each grit grade 180, 240, 320, 400, 600, 800 then finally 1200 removing the scratches from the previous grit.
  • Finally polish the stem using Autosol Chrome polish (or similar) to bring the stem up to a shine.
  • I do not use a finish on the aluminium as I have not found it necessary.

 

Turning the bowl and foot

  • Mount the sycamore blank between centres and rough down to a cylinder
  • Prepare a tenon on both ends of the blank to suit your scroll chuck
  • Decide which way is up and mount the bowl end of the blank into your scroll chuck
  • Mark a line approx. 3” from the chuck jaws and part through
  • True up the end grain using a spindle gouge.
  • Turn a tenon to suit your scroll chuck. N.B. this end will be the bottom of the goblet bowl where it joins the stem.
  • Use the long point of the skew to mark a register in the centre of the blank then using the 7mm drill bit held in a Jacobs chuck drill a hole to a depth of around 8mm.
  • Test the fit of the goblet stem in the drilled hole, support using the live centre in the tailstock and check that all is running true.
  • Beginning at the chuck end, form the outer shape of the goblet bowl, using the goblet stem as a visual guide, however……. Do not remove the tenon you have just created, you need this for the hollowing process.
  • Reverse the bowl into the chuck, either remove, or optionally incorporate the chucking point into the goblet depending upon the size and dimensions of the goblet bowl intended.
  • Hollow the bowl of the goblet to your preferred wall thickness, ideally 2-3mm
  • Abrade and finish the bowl inside and outside as far as the remaining chucking point; remove from the chuck.
  • Turn a recess jamb chuck to suit an external fit on the goblet bowl, a tenon jamb can be used but this runs the risk of splitting the bowl if the fit is too tight….be warned. Use a layer of paper in the joint to reduce the risk of scorching the bowl if is jamb chuck slips.
  • Fit the stem to the bowl and bring up the live centre for support. Again ensure all is running true – it necessary adjust the jamb fit to correct any imbalance.
  • Turn away the chucking point ensuring the bottom of the bowl and the aluminium stem flow together; leave slightly larger to allow for abrading the bowl.
  • Abrade and finish the bottom of the goblet bowl.

  • Now to turn the foot of the goblet……
  • Mount the remaining blank in the chuck jaws.
    N.B. The foot will actually be from the timber 1” to 2 ½” from the jaws, the 1” of wood adjacent to the chuck is sacrificial allowing for turning the underside of the foot.
  • Using a spindle gouge, trim the end of the blank to true up and remove any end grain tear out as a result of the parting cut, making sure that the face is flat or ever so slightly concaved.
  • Using the long point of a skew, create a small indentation in the centre of the blank, this will act as a centre for the next step.
  • Fit a 7mm HSS drill bit into a Jacobs chuck mounted in the tailstock and drill a hole to a depth of 8mm
  • Now fit the bottom of the aluminium stem into the drilled hole and check for a good fit. Bring up the tailstock live centre into the upper 2mm register and lock everything down.
  • Spin up the lathe and ensure that all is running true.
  • You can now turn the foot with a spindle gouge using the stem as a guide to the final profile. If the foot is to flow into the stem with no steps or features then stop a little shy of the diameter of the stem to allow for abrading and finishing the foot.
  • You should now have sufficient waste wood to allow the underside of the foot to be turned with a spindle gouge rather than parted through; this will result in a cleaner cut minimising the risk of end grain tear out.
  • Before parting off, take the opportunity to sand and finish the foot while driven by the lathe.
  • Part off slightly away from the bottom of the foot to remove the risk of end grain tear out then sand away the remaining stub of timber to a finish using a mandrel mounted in the chuck.

  • Now assemble the goblet sparingly using a two part epoxy adhesive.

 

I hope you enjoy the project and please email photos to me…. rick@rickdobney.uk

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