Deep drilling on a milling machine? In tempered stainless steel?

We first made contact back in 2018. 

Three years later, we received the request described above: in addition to normal milling, the company wanted to use the same machine to perform deep drilling down to 1,500 mm. Not in field, forest or meadow steel, but in X37CrMoV5-1 stainless steel with a tensile strength of 1,200 N/mm² and a hardness of 38 HRC! It was immediately clear to us that this was not something we could do off the cuff! 

First test: promising! 

After intensive preliminary discussions, including with the drill manufacturer Botek Präzisionsbohrtechnik, we got down to business. We installed an additional pump on a customer's machine – an RT 3000 without a V-axis – which delivers up to 220 litres/min to the drilling point. This is because with a drilling diameter of 80 mm, the volume is crucial and not so much the pressure. The "throw line" was connected to the rotary feed through the drill, the pilot hole was pre-milled, and off we went. Due to the machine capacities, we were "only" able to use a 650 mm drill bit, but this was perfectly adequate for an initial test. And the test was extremely positive, although the main spindle motor of the test machine reached its performance limit. Conclusion: We can do it, but the machine we want for our deep drilling project needs a few additional options.

What must our ideal machine be capable of? 

The test run revealed additional requirements for the machine when drilling really deep holes: Ideally, an RT milling machine with a 2000 mm V-axis for long drill bits up to 1800 mm in length; a cooling lubricant pump with a capacity of 250 litres/min; a cooling lubricant preparation tank that can also filter the volume; and finally, a more powerful main spindle motor. The successful test also convinced our prospective customer of the quality of this concept, and we were awarded the contract to design a suitable machine. Now, around 18 months later, this machine is in operation at the customer's premises. We carried out the final drilling test last week with highly satisfactory results across the board. 

Deep drilling on our RT milling machine – the most important data 

For those interested in the technical details, we have summarised everything you need to know: 

• • Drill diameter 80 mm
• • Drilling depth 1,500 mm
• • Drill length with rotary feed for cooling lubricant = 1,800 mm
• • Drill weight approx. 50 kg
• • Mounting SK 50
• • Cutting speed vc = 60
• • Feed per tooth = 0.17
• • Speed 1/min = 239
• • Feed vf mm/min = 41 

The accuracy achieved was exceptionally high. The deviation between the entry and exit openings was only 0.08 mm (in X) and 0.4 mm (in Y). This cannot be achieved easily even with a deep-hole drilling machine! According to Botek Präzisionsbohrtechnik, these are excellent values, especially since the hole is then honed. Once again: we are talking about a milling machine, not a specialised deep-hole drilling machine with support legs.

The experiment was worth it. 

For everyone. We were curious to see how well our milling machine would perform in unfamiliar territory. The success confirms the concept: deep drilling on a modified MTE is possible, and with excellent results. However, the main focus is on the benefits for our customer, who now has everything under control when it comes to deep drilling. No more searching for external suppliers with capacity on a deep drilling machine. Full control of all processes, including quality. Better scheduling, lower costs and added value remain in-house. The project has paid off for everyone! 

MTE RT-3000-V (modified) specifications 

• • X = 3000 mm (length)
• • Y = 1500 mm (width)
• • Z = 150 0mm (vertical)
• • V = 2000 mm (transverse 2--> machine stand)
• • Rotary table 2000 x 2000 mm
• • Milling head diagonal design with 0.01°x0.01° and 6000 rpm
• • Main spindle with 65 kW and 2020 Nm
• • IKZ 50 bar
• • Additional connection with quick coupling for drill rotation feedthrough with 250 L/min and 12 bar
• • Full cabin + extraction and much more.