Designed for heavy-duty use in industry and repair workshops the 8.5" centre height by 30, 40, 60 or 80 inches between-centres Mondiale Celtic "17" owed little other than general design parameters to the smaller machines in the range. Intended it was not offered with the option of production turrets or slides and was mounted on two heavy cast-iron plinths spanned by a deep slide-out chip tray; unfortunately there was no form of storage, not even an open shelf, for either tools or accessories.
Unlike the smaller Gallic lathes with their compartmentalised headstock casting that of the Model 17 was a double-walled and internally braced box. It still had a centre section however (sealed against the ingress of oil from the speed-reduction and changewheel-drive gearing) that held a 5-step V-pulley running in its own roller bearings to isolate the effects of belt pull. Following a less-than-desirable Mondiale tradition the 1.625" the bore of the Timken taper roller bearing headstock spindle was rather small for the capacity of the lathe and the nose fitting a similarly under-sized American long taper L0 - in comparison the equivalent Colchester Mascot had a 3-inch spindle bore and, with an L2 fitting, a nose fitting two steps larger that was able to carry much heavier chucks.
Drive to the headstock came from a 4-speed gearbox mounted inside the left-hand cabinet plinth with its operating lever, a large chrome-plated rod, on the font of the stand. The box was oil-splash lubricated and held induction-hardened gears running on ball-bearing supported, hardened and splined shafts. Bolted behind the gearbox was a push-button controlled electric motor with 2 speeds as standard; for the faster of the two spindle-speed ranges this was a 6.5 - 4 HP unit and for the slower a 5 - 3 HP. When combined with the single-lever-operated headstock reduction gears - which on the Celtic 17 were more like a conventional backgear assembly and quite different to the dog-engaged gears on both smaller and larger models - the drive gave a total of 16 speeds from 22 to 1000 rpm on the standard lathe and 30 to 1350 rpm on the high-speed version. Although many contemporary competitor machines offered either a spindle brake or clutch (and sometimes both) no such option was available for the Celtic 17, a situation that must have frustrated many operators as they watched their bonus-payment seconds slip away because a 100 lb lump would not stop rotating quickly enough.
Fitted with V and flat ways, the bed could be had with, or without, a detachable gap piece that, if specified, allowed material up to 25" inches in diameter and approximately 7" in thickness on the faceplate to be swung. The V-ways were of a design similar to that first used on the beautiful American Wade No. 7 precision bench lathe where the (asymmetric) front V was both laid back at a shallower angle than normal and made especially wide; the rear surface was narrower and, in order to better absorb tool thrust, set at a steeper angle. Although not hardened (a process restricted to the extensive options' list) the bed was of robust construction and very deep in relation to the machine's centre height.
With every thread or feed selection made by rotary levers (and a consequent absence of sliding controls) the oil-bath lubricated screwcutting and feeds box, with its hardened gears, could be completely sealed against the ingress of dirt and swarf. By using just the ordinary set of changewheels the box was able to generate 54 English pitches (from 48 to 13/16 t.p.i.) and 27 metric (from 0.45 to 20mm pitch) - a range superior to the 45 English and 12 metric of the Colchester Mascot. The sliding and surfacing feeds totalled 54 from 0.0028" to 0.090" per revolution of the spindle on longitudinal travel and from 0.0014" to 0.09" on the cross feed. With different changewheel set on the quadrant arm a complete range of diametral and module pitches could be produced and the 5-segment screwcutting chart included these thread sets in its layout. The leadscrew (which was disengaged when not in use) could be had with an inch or mm pitch ground thread and its bronze engagement clasp nuts were adjustable for backlash; power feeds were taken to the apron by a separate keyed shaft below and parallel to the leadscrew.
With its double-wall construction, oil-bath lubrication and ingenious mechanical design the all-helical-geared apron was well engineered for its task - and of a type used throughout the Celtic range. The drive shaft from the gearbox transmitted its power through a worm and wheel to a shaft that passed vertically though the centre line of the casting; at the top of the shaft a double-sided dog clutch that moved up or down to select power surfacing and sliding feeds respectively. The 17 was the only Celtic model to have the selection of power sliding and surfacing feeds operated by other than a quadrant lever on the face of the headstock - in this case a lever that protruded horizontally from the centre of the apron's lower edge. Although the apron was a robust and reliable piece of engineering its feeds engagement mechanism suffered from the usual drawback of all lever-operated systems working through a horizontal arc: the rotary motion, even against some sort of positive stop, could not compare with the more certain movement of a snap-action lever working vertically between fixed positions. The right-hand face of the apron provided a pivoting point for a lever that operated, via a long control rod, an electrical switch to reverse the spindle - a useful safety feature, especially on longer-bed versions.
Entirely conventional (though without T-slots in its wings) the saddle carried a compound slide rest with proper taper gibs that were adjustable, with the usual sensitivity, by a push screw at the front and a stop screw at the rear. Two cross slides were available, both with a travel of 9.25": a plain-top standard version version - unfortunately shorter than the slide that it ran on and with a cast extension cover at the rear to protect the feed screw - and a full-length one able to accommodate a rear-mounted toolpost, its support block and other accessories. The top slide could be rotated only 45 degrees in either direction but came complete with an indexing (though 8-positions) 4-way toolpost.
The tailstock was, perhaps the weakest point in the lathe's specification for, although the (unhardened) 2.187"-diameter No. 4 Morse taper barrel was "microfinished" its travel was short at 5.125" (Colchester Mascot 8.5") and the two bed clamp nuts required a loose spanner to operate - the latter gambit may have saved the makers money but was guaranteed to waste time in the customer's workshop when the spanner was inevitably "borrowed" for some other task. The top section could be offset in the usual way for taper turning and had a maximum movement of 5/8". The weight of the lathe varied with the between-centres capacity as follows: 30" 2860 lbs; 40" 2970 lbs; 60" 3140 lbs; 80" 3600 lbs..