Choosing a machine
The pillar drilling machine or drill press is accepted as the most widely used machine tool in the world. It is also the machine tool chosen with the least consideration and, when in use, is the most abused machine with little or no care being given to its maintenance. With well over one hundred variations in machine specification there are a great number of factors which should be considered before investing in a drilling machine. This essential guide is designed to help with the evaluation process, if any further information is required then contact Meddings Machine Tools for their considered opinion.
The essential guide to drilling machine selection
Basic Types of Drilling Machines
Belt drive (stepped pulley)
Belt drive (variable speed pulleys)
Electronic variable speed control
Hybrid machines are also available. i.e. belt drive with gearbox, geared head with 2 speed motors, etc Machines are available as bench or floor models, in various sizes (larger machines are normally floor only) with or without power feed options
Sizes of Drilling Machines
Drilling machines are normally designated by their drilling capacity, maximum capability to drill holes in mild steel (50/60 Kg Steel) using a standard HSS drill i.e. 13mm (1/2”) machine should have the capability to drill a 13mm (1/2”) diameter hole in mild steel
Maximum distance from the edge of component to the twist drill centre line
Spindle nose to table
Maximum height of component
Spindle nose to base
If the base is machined, it can be used for large or heavy components
Main column size
Should be sufficient to maintain rigidity
Should be finished / toleranced for strength and to minimize play
Spindle travel (stroke)
Determines maximum depth of hole
Size or Sizes of Hole
Loosely there are four main categories for drilling sizes:
1. Heavy drilling Holes larger than 16mm (5/8”) diameter
2. Light drilling Holes between 2.5 & 16mm (3/32” & 5/8”) diameter
3. Small hole drilling Holes between 0.25 & 3mm (.010” & 1/8”) diameter
4. Micro drilling Holes between 0.05 & 0.5mm (0.002” & 0.020”) (These require specialist consideration)
Speeds and /or Feeds
The maximum spindle speed available on a drilling machine is normally determined by the maximum drilling capacity. The larger the machine the slower the top spindle speed. If holes to be drilled are both very small and large it may be necessary to have two machines or a wide speed range machine. Note: - For steel the normal maximum speed required will not exceed 8000rpm for drills around 1mm diameter. Below 1.0mm diameter recommended drilling speeds start to slow down
Quality of hole to be drilled
It is just not possible to drill high quality holes on a low quality machine. If the machine is for casual use in the corner of a home workshop and accuracy or reliability are not important, a lower cost machine is probably all that is required.
A good machine must have
A robust quality cast head with an accurately bored and preferably honed quill bore that is square to the machining table
Belt drive machines require balanced pulleys and quality Vee belts
Gear driven machines require precision manufactured gears
All machines should be accurately made with quality bearings, etc
The quill / spindle should be concentric and precision ground
Light or occasional use
The possibility to purchase a lower cost belt drive machine, unless accuracy or deep holes are required
Tool room use
Accuracy is paramount, a quality machine is required, and normally manual feed will suffice for drilling hole sizes up to 20mm. Tool room operators are skilled, appreciate the ability to feel the drill through the work piece and would not be drilling holes all day.
Buy the best machine that can be afforded. It will last longer and produce better quality holes and give longer drill life. Belt drive machines are the best option if the holes to be drilled are of the same or similar size. Belt drive machines are efficient, quieter running and they have less moving parts with potentially less possibility of breakdown. If hole sizes vary and are over 16mm diameter, either an all geared head or a variable belt drive machine should be considered for ease of speed change. Machines for use on large batch production for drilling anything but very small holes should, if possible, always have some form of power feed, as it considerably lessens operator fatigue.
Chuck / Morse Taper
Whilst most machines have a Morse Taper some are supplied with a chuck fitted semi-permanently to the spindle end. A Morse Taper spindle adds little to the cost and provides greater flexibility.
Machines sold in Europe should be CE marked with a Certificate of Conformity. Belt drives should be suitably guarded with an incorporated micro switch to isolate the machine should the guard be lifted. Chuck guards appropriate for the machine should be used at all times.
Points for Consideration when Choosing a Machine
1. Maximum and minimum hole diameters to be drilled Consider the sizes of holes to be drilled; this will determine the basic size of machine required
2. Maximum and minimum drilling speeds required Bearing in mind the material to be drilled, and hole size, check that the required speeds are available.
3. Maximum size of component Be sure the throat depth is sufficient, check the clearance spindle nose to table and that the quill travel is sufficient
4. Maximum weight of component Be sure the component weight can be carried on the machine’s table. If it is a very heavy component consider using the base of the machine (if suitably machined)
5. Accuracy required For accuracy always choose a quality machine
6. Casual or production use For a casual low quality requirement, a lower cost machine should suffice. For high volume production work a model with power feed should be considered
7. Amount of variation in speed required If hole sizes and hence speeds vary, consider a geared head or a variable belt drive machine on larger hole sizes. Electronic variable speed control on smaller (> 13mm) hole sizes
8. Intermediate table For machines with an intermediate table, if work size varies greatly, it is an advantage to have height adjustment by rack and pinion; on larger machines it is essential, due to the weight of the table
9. Chuck or Morse Taper A chuck fitted directly to the spindle is the simplest form of tool holder. Morse Taper spindles give greater flexibility of use, but introduce an unnecessary joint if only smaller size drilling is required. Larger machines normally have Morse Taper spindles
10. Spindle rotation Normally drilling machines are set to rotate for right hand drilling, if for any reason left hand rotation is required (i.e. for tapping) make sure the machine has a reversing switch
11. Single or three phase Always specify a three-phase model if a suitable power supply is available. Single phase motors can introduce unnecessary vibration into the machine, whilst three phase motors are generally more reliable and smoother running.