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Stainless steel shotgun is RIMD’s first project

Posted on 02 Oct 2021 and read 935 times
Stainless steel shotgun is RIMD’s first projectThe Hurco VMX42HSi on the shop floor at RIMD, Aylesbury. Christopher Iaciofano is pictured left with machinist Dan Green at the control

Clay shooting is a popular activity as well as being one of the 42 Olympic disciplines and as in any sport, the quality of the equipment is paramount. One enthusiast who is determined to manufacture a range of affordable yet high-quality shotguns to bring them within the financial reach of a wider market is Christopher Iaciofano, who set up RIMD in Fleet Marsden (near Aylesbury) in January 2021.

To produce the metal parts for the guns, he has installed a Hurco five-axis CNC machining centre and a Dean Smith and Grace (DSG) 6.5-tonne manual lathe specially adapted in-house to enable highly accurate deep hole drilling of barrels. The first gun will be marketed as the 'Chiltern' later this year through an established manufacturer of traditional hand-crafted shotguns.

The rationale for establishing the venture was Mr Iaciofano’s identification of a gap in the engineering marketplace for a company capable of undertaking the functions needed to launch a new product — research, innovation, manufacturing and development (RIMD).

HurcoThe company is able to remove some or all of these elements from a customer’s activities and inject a high level of expertise to achieve a superior end product and accelerate time to market. There is a special focus on R&D, which is generally the first area to be neglected in favour of day-to-day activities.

Having gained a BSc in mechanical engineering at Bournemouth University, Mr Iaciofano subsequently worked in the oil and gas sector. He was responsible for designing and manufacturing chemical injection equipment capable of withstanding pressures up to 3,000 bar using a diverse range of exotic materials, which he became expert in machining.

With that knowledge and having an antipathy towards the mild steel parts on his own shotgun rusting, he decided to design and construct a new version from a special blend of PH17-4 hardened stainless steel.

It is particularly difficult to machine, as it is a sticky material requiring very sharp cutters yet has a hardness of 38 HRc and above, which tends to wear them quickly. To make matters worse, small drills are involved in the production as well as milling cutters down to 0.6mm in diameter.

Hurco offers two main styles of integrated five-axis vertical machining centre (VMC), one with a swivelling trunnion supporting a rotary table and the other with a B-axis spindle and a horizontal rotary table. Neither design was suitable for RIMD, as it would have been impossible to mill the outside of the one-piece shotgun barrel from a 76mm diameter, 900mm long billet without buying an excessively large machine.

The answer was to purchase a Hurco VMX42HSi three-axis VMC equipped with a Kitagawa two-axis compound rotary table positioned at the far right hand side of the machining area. The latter enables the 900mm barrel billet, which has already had the two bores roughed and finished on the DSG, to be fixtured by picking up on the bores and rotated.

The entire outside can then be milled along its length using the VMC's one-metre X-axis. In the process, the barrel is reduced to about 1.2mm wall thickness and 1.4kg, just 5% of the original billet weight of 28kg.

HurcoThe machine is equipped with an 18,000rev/min spindle, so very high surface finish is achieved. Linear scales provide ultra-precise feedback of the orthogonal axis positions to the control. The table additionally feeds its rotary positions back to the proprietary Hurco WinMax CNC, which is capable of controlling all five-axis motions simultaneously.

Many such programs are employed in the production of components for the Chiltern gun, all of which come off the Hurco in one operation to within 5µm dimensional accuracy on all critical features.

Most of the remaining cycles are ‘3+2’, with the rotary axes positioned and clamped to present the part to the spindle in convenient orientations to maximise machining efficiency. All programming is carried out using either SolidCAM or GibbsCAM rather than directly at the WinMax control, although the latter conversational software remains a convenient option for future projects.

Mr Iaciofano concluded: “Our immediate business plan is to complete the shotgun venture through to series production and take on another couple of projects. They will be either ‘cradle-to-grave’ development of a new product of our own design, or manufacturing support for a third party’s project to relieve them of some of the work.

“It is also a target to be able to take on smaller projects from individuals with great ideas but without the means to bring them to market, and to offer free development and manufacturing for a share of the company. Our intention is to more than double our factory space to 4,500ft2 by expanding into an adjacent factory unit.”