On Mk. 1 machines a Brown & Sharp 00 "dead-length", nose-clamping "spring" collet was used (a modern alternative is a Crawford CC18) and, on the Mk. 2 and Mk. 3, a Newhall-Balas "Type C6" that, whilst still pushed in on its nose was tapered for its full length and had to be removed with a special extractor. In the manual for the Mk. 2 a specific instruction was given for including a needle-roller thrust bearing and washer in the collet nosepiece assembly, although this was omitted from the edition supplied with Mk. 3 machines. The original Brown & Sharp collets were supplied in a 16-piece set from 1/16" to ?quot;, in steps of 1/32" (including one with No. 1 Morse taper) whilst later machines arrived with just 6 collets capable of holding cutters with of 1/4", 3/8", 1/2", 5/8" and 3/4" shanks - and one collet as a No. 1 Morse taper adaptor. As an alternative, metric collets could also be supplied in a set of 6, 10, 12, 16 and 20 mm. The collets were stored in a rack on the inside of a stand door that gave access to a rather inadequate storage space fitted, at least on the Mk. 1, with a small slide-out tray. Two hardened spanners were provided: one to hold the spindle still, the other to lock and unlock the hardened nosepiece nut - the last, as an interesting detail, having its spanner flats hardened but the threads left soft to protect those inside the (expensive) spindle from careless handling. The maximum distance between the spindle nose and table was 9.5" (240 mm).
Made from hardened steel the 16" x 7" (406 mm x 178 mm) table had generous movements of 12" (300 mm) longitudinally and 7.5" (190 mm) laterally; however, some tables on the Mk. 1 have been measured at 17" x 7". Very large-diameter, satin-chrome, vernier engraved micrometer dials were fitted with a direct reading scale of 0.001" (0.02 mm) and vernier marks that allowed movements as little as 0.0001" (0.002 mm) to be easily read. The feed screws were manufactured from nitride-hardened steel with the 0.100" (2.5 mm) pitch Acme threads precision ground. The end thrust of the screws was taken against pairs of miniature radial needle-roller bearings and each feed nut was adjustable to reduced backlash between it and the screw. The table ways were hardened and ground and the top surface given special attention with a ultra-careful finish grind; as a final touch the side faces of the three T slots were ground parallel with the guideways, so allowing workpieces to be adjusted against them - and so quickly but accurately set. Each axis of the table's movement was also fitted with a finely engraved, full-length ruler that had an adjustable zero setting on its stop.
Optional extras included a boxed table-clamp set, centre-edge finder, hardened 4-inch precision vice, 6-inch rotary table, keyless drill chuck and two sizes of Boring head: the Model OZ with a body 1.25" in diameter and an offset of 0.5" and the 2" diameter Model 1Z with a maximum offset of 0.5". If the machine was used for conventional milling rather than boring it was advisable to employ a special set of 3 collets (listed only for the Mk. 3 ) that were threaded internally to accept standard 1/4", 3/8" and 1/2" screwed shank cutters ; if you have one of these jig borers (of any year) and intend to mill with it contact Crawford Collets to see if they can supply the correct collets - possibly as Brown & Sharpe 00 or 00A, catalogue numbers 4996 and 5071.
Working from the light of practical experience a professional user of the machine has suggested the following small but worthwhile alterations and additions:
- the Metabo-Futuro drill chuck (supplied with a MT shank for fitting in the supplied No. 1 Morse taper collet) can be replaced by a Jacobs type, of similar capacity, but with a 5/8 parallel shank (a standard listed item); this has the dual advantage of increasing the available height by about 50 mm whilst obviating the need for a collet change when mounting the boring head
- a feature not really required (and all too easily engaged when operating the head locking lever) is the power up feed; this function can be disabled by the addition of a spacer within the feed box
- a stop added to the quill clamping lever will prevent its interference with the feed-depth stop.
- a magnetic strip, calibrated over 100 mm in 5 mm increments and mounted on the right-hand side of the column adjoining the feed head is helpful when repeatedly using drills of different lengths
- an 'O' ring added to the bottom of the head-feed screw will help to minimise the impact of the quill at the end of its travel
- by purchasing the entire range of the Balas collets any fitting with diameter of up to 20 mm can be accommodated with an additional increase in vertical capacity for longer drills.
- a dial-test Indicator holder, with controlled adjustment in two planes and mounted on the collet retaining nut, will be found a great convenience.
Always a relatively expensive machine the following prices from mid 1960s (when a good wage was ?0 per week) give a clue as to the exclusivity of the machine: basic Mini Borer: ?25: 6-inch rotary table ?2: Model 0Z boring head ?3 10s: 0d screwed shank end mill collets ?0 each: Keyless drill chuck ?: Model 13 boring head ?7 10s 0d and single-phase electrics ? 16s 0d extra
Tipping the scales at 880 lbs (340 kg) the Downham-Elliott was, considering its compact dimensions, a very heavy machine and there can be few others like it that offer the keener home-enthusiast, small professional tool-making or instrument workshop a dual-purpose machine capable of jig-boring, co-ordinate drilling and light but very accurate vertical milling.
One most unusual version of the machine was an example of the early Excel version, this having a rotating head with, so far, only two examples have come to light.