Report 25 September 2024
Report by: Kieran FitzGerald
Warning: graphic descriptions and metal working references.
This report contains references to metals and metal devices, and may be harmful to some woodworkers. If you are affected by this report, you may obtain help at South Auckland Woodturners Guild Inc. | Turning Tomorrow’s Treasures (sawg.org.nz).
The demonstrator this week is Jon Pearse. Jon was introduced as our resident inventor, and it is noted that in addition to his skills as a metal working machinist, Jon has completed all his the required courses and obtained his National Certificate in Woodturning in less than 2 years.
Check out Jon’s YouTube channel where he posts regular videos, including a number where he makes jigs for the wood lathe. The Hobby Machinist NZ – YouTube.
In this report you will see how Jon successfully blends his metal engineering abilities with his woodturning talent.
Jon began by welcoming the audience in German, a language he has been studying for a while. He went on to discuss in simple terms how a rose engine works, and showed us a couple of bowls which have recently been embellished by club members on the SAWG rose engine (there is an “ornamental group” within SAWG which meets every fourth Monday night of the month; newcomers are welcome, contact John Whitmore).
The stumbling block for the common turner, of course, is the outrageous price of a rose engine – commonly upwards of USD$100,000, out of reach for most of us. This set Jon to thinking about how he could replicate some of the functions of the rose engine with a jig that could be used on the wood lathe and developed within the ranges of a manageable budget for your average Joe Turner.
The components of Jon’s jig are a mixture of steel fabrications made in his workshop and pieces purchased cheaply from Chinese sources on the internet. He described the construction in a relatively simple manner and logical order.
First up is a 1 ½ inch boring head, typically used in a milling machine for boring holes. Jon will attach a variety of cutters to the boring head and drive it using the headstock spindle of the lathe. The cutters are secured with grub screws. The boring head is inserted in to the spindle via a number 2 morse taper, but it also requires a tie back rod to prevent accidental self ejection. Jon made the necessary modifications in his metal workshop.
The body of the jig is fitted on the bed way of the lathe. It is made up of:
A metal base plate and spacer block which tightens on to the bed and can be slid to the appropriate position. The purpose of the spacer block is effectively to elevate the jig to the required cutting height, which is in line with the centre height of the spindle. While Jon built his base plate and spacer block out of steel, it could potentially be constructed from wood or other materials.
Next Jon attached a cross slide table to the spacer block. The cross slide table is a positioning mechanism with two planes – one which moves laterally across the bed, and one which moves parallel to the bed. Fine positioning is achieved with hand wheels on each axis (just like advancing the tailstock quill on your wood lathe).
Sitting on top of the cross slide table is a 4” rotary table mounted vertically. This can be precisely turned from 0° to 360°. Affixed to the front of the rotary table with bolts is an adapter with a 1 ¼” x 8 tpi thread which the chuck from the wood lathe can be screwed on.
When a wooden bowl or lidded box is held stationery in the chuck (with tenon still on obviously), it can be manually presented to the cutter(s) to produce an infinite variety of patterns and decorations.
The components bought on the internet (boring head, cross slide and rotary table) cost in total about $230 NZD.
Jon made a number of cutters from HSS 8mm drill bits and centre drills in his workshop, but Holm advised cutters can be purchased on the internet from the USA.
Jon demonstrated how the jig operates, firstly on the side of a lidded box. He laterally inserted a pointed 90° cutter in to the boring head. After securing the base of the lidded box in the chuck, he adjusted the jig so the box was adjacent to the cutter and parallel to the side of the bed.
With the lathe running at 2000 rpm, he turned the hand wheel to move the cross slide table in which engaged the cutter. After making one cut, he advanced the rotary table by 20° to make the next cut. Rinse and repeat. Jon made 4 cuts then moved the cross slide 4.5mm so that more cuts can be made further along the side of the box. For this second row of cuts he also phased the angle on the rotary table by 10°. This offsets the second row of cuts to produce a brick wall type pattern. He explained that it would take too long to complete all the cuts around box with multiple rings of cuts spaced apart, so he handed around finished pieces which demonstrated the nature of the cuts he was making. The pieces included patterns made with a flat bottom cutter. While some samples showed cuts were sharp and clean, others, particularly those made with the flat bottom cutter, had visible signs of tear out. Jon put this down to the type of wood used (which was soft), along with the flat bottom cutter.
The flat bottom cutter should only be used with dense tight grain hard woods.
Next Jon used a 45° detail cutter to decorate the top of a lid. The detail cutter is mounted in the front of the boring head. This cutter is used to make barley corn designs, about 1/4mm deep. The top of the lid needs to be flat, and the jig positioned squarely on the bed to achieve a consistent depth of cut. Using the cross slide table, the jig is adjusted so the cutter tip rotates between a picture frame line on the outside of the lid and the centre of the lid. The lid is then advanced gently in to the cut. After starting with the rotary table set at 0°, it is turned to 10° to make the next cut. This process is repeated over and over until the pattern circumscribes the whole lid.
With some slight adjustments to the cutter and the jig, and also using the ‘bump’ and ‘half-moon’ cutters, Jon demonstrated different patterns on the sloped outer perimeter of the lid. As before, he did not complete a pattern because of time constraints, but the finished examples he passed around were stunning in their precision, detail and finish quality. This is amazing considering the whole set up and operation of the jig is manually performed: Jon described it as using his eyecrometer. If you remember using a sprirograph, the patterns achieved with the jig are exactly the same as those that astounded us as kids.
To cap it off, Jon showed that the jig could also be used to make patterns on other materials and he demonstrated cuts within aluminium.
Jon has made a YouTube video on this jig. If you want to watch it here is the link: Ornamental Turning Device (youtube.com).
Thanks Jon, for an absorbing demonstration. The cleverness of the jig aside, your commentary and presentation is totally enjoyable. You’d better start thinking about what you are going to do for your next SAWG demo.