We talk to Straitline's Dennis Paulson, who, besides being a part-owner, has over twenty three years of experience on the machine shop floor. Much of that time has been spent running CNC machines, as well as on product development. Besides manufacturing their own pedals, stems, chain guides, and other components, Straitline also uses their CNC machining skills to fabricate products for both the aerospace and surveillance industries. It's fair to say that they know a thing or two about CNC machines. First off, what is a CNC machine and how do they work?
CNC is short for Computer Numerical Control. CNC machines are used primarily in metal component
manufacturing, however they are also used in many other industries such as textiles, and food and
beverage manufacturing. In a nutshell, a computer controls a very sophisticated electric motor, called a
servo motor, that then turns a ball screw (similar to a conventional screw, but the threads are half
round instead of 'V' shaped, and are filled with ball bearings that allow for lower friction and to eliminate
backlash) that is attached to the machine frame. This screw drives the controlled axis back and
forth as needed. The computer can also control a rotary axis that allows the part or cutting tool to rotate.
Almost any shape can be created when two or more axis are combined.
The machine on the left is a nine axis MTM (Multi-Tasking Machine) that employs an upper five axis head intended for complex drilling and milling jobs. The lower turret can both turn and mill, but it is mainly used for boring and drilling operations. The machine on the right is a six axis Turn Mill Machine. It is similar to the MTM, but does not have the five axis milling head. It can still perform both turning and milling operations, but is more limited in the complexity of the milling. What are the advantages to CNC machining over casting or forging?
The two main advantages of CNC machining over castings and forgings are flexibility and precision. Are there different types of CNC machines?
While forging and castings don’t typically replace CNC machined parts, they do reduce the time needed
in a CNC or conventional machine. Surface finishes on a CNC machined part will typically be near perfect
and appear very consistent and precise, whereas cast or forged parts will be a little rougher, usually
requiring polishing or tumbling in an abrasive media to achieve a better surface finish
There are many different types of CNC machines in the manufacturing world and we are fortunate
enough to have and use virtually all of them, but I'll leave out the more specialized machines and focus on
universal equipment. Typically the most basic CNC’s are two axis lathes, then we move up to three axis
Vertical Machining Centers (VMC`s for short). We can add a fourth, rotating axis to a VMC to make
it a four axis VMC. Next step up from the four axis VMC would be the four axis HMC (Horizontal machining
center). These machines typically have two or more work piece pallets that can be changed automatically
for increased production. As we carry on up the food chain we start to get into five axis, Turn Mill and Multi
Tasking Machines. Five axis machines can be either VMC's or HMC's, and have one other additional rotary axis
on either the cutting tool head or work piece pallet, allowing more sides of the work piece to be completed in
a single operation to allow very complex work pieces to be manufactured. Turn Mill machines are lathes
that also combine some milling to produce parts that are primarily round, with some milled features. These
machines are typically five or six axis machines. MTM's are the latest and greatest pieces of equipment in
the manufacturing world. They typically have seven to nine axes, and can be used to machine almost anything.
They combine the advantages of a full five axis machine with full turning capabilities as well. Most parts
machined on this type of machine will have a lot of milling and turning, and all will be completed in one process
cycle. As far as cost goes on CNC machines, industrial quality two axis lathes go from $40,000 - $100,000,
and the sky is the limit from there. CNC machines now reach into the millions! Almost all machines used in
advanced manufacturing also have the means to automatically change tools and remove metal chips or
shavings from the work area.
Straitline's Defacto pedals are machined in a four axis HMC with a rotating axis that runs vertically. This allows the pallet to rotate so that machining can be performed on multiple parts and multiple faces of each part. This photo was taken as the machine was performing a tool check to verify that the cutting tool was not broken before performing the next machining operation. What sort of parts can be made by a CNC machine?
Almost anything can be made on a CNC machine, such as stems, pedals, sprockets, brake levers etc.An AMP pedal body nears completion in a four axis VMC. The machine component holding the pedal body is free to rotate around the axis for the length of the table to allow Straitline to machine all sides of the pedal in single operation. On the left you can see the cutting tool at the top, and at the bottom you can see a laser tool setter that is used to set tool lengths and check for broken tools in the process. CNC machines are certainly impressive, but they must have some limitations?
We use CNC for almost every part in our product range, with the exception of screws. Screws can be produced
on CNC's, but cold heading (which is similar to forging) is much more cost effective. Even the plastic parts
we produce are made in a CNC injection molding machine, and the mold used to produce
them are cut in house on our CNC metal cutting machines.
There are certain limitations to CNC, for instance you cannot easily machine sharp internal corners, Stay tuned for upcoming To The Point articles where we'll explain the ins and outs of your bike.www.straitlinecomponents.com
as rotating tools will always leave a radius in the corner being cut. Also, production of irregular shapes that
do not require extreme precision can be made much quicker with forgings and castings. These parts are
usually CNC'd after forging or casting to produce any size critical features. Almost any material can be
machined in some way or orther, and we typically machine aluminum, steel, titanium, and plastic, each of
which have hundreds or thousands of different alloys or polymers.