FAQ Products

CNC Notes & Product Selection Information

>Which one to choose - Router or Spindle?
>Conventional vs Universal Vacuum Hold-Down
>What's the difference between 2.5D and 3D?
>3-Axis CNC Tools vs 5-Axis Tools (and ShopBot's Rotary Indexer, a 4-Axis Tool)
>Doing 3D without 3D Design Software
 

Which one to choose - Router or High-Frequency Spindle?

NOTE ShopBot Tools recommends and sells Porter Cable 3.25hp routers, Model 75182 (Model 7519 for international sales), for our CNC systems in which a spindle is not installed.  Mounting brackets and electrical connections are designed for this model router.  Other models may not fit or function correctly in this bracket and may thus be unsafe.

ShopBots can be fitted with a variety of tools/heads for cutting and machining. The most common tools are either a standard woodworking router or a high-frequency industrial spindle. These tools are similar in principle, basically a motor for turning a cutting bit at high speeds. A router (we recommend and sell a Porter Cable 3 1/4hp router) provides the affordable solution for a CNC tool. We also sell several high-frequency spindles that are the industrial grade solution for a CNC tool. Power (usually 3-phase) for a spindle is routed through an inverter that converts it to a higher frequency for powering the spindle/motor. Spindles have the advantage of being more powerful (note that hp ratings between routers and spindles are not comparable) and will maintain their full torque down to much lower RPMs than a router. Spindles have precision bearings, which means less run-out and thus smoother and more accurate cutting. These bearings also stand up to continuous use better than those of a router. Bearings in a heavily used router might need to be replaced every 3-4 months, while a similarly used spindle should be good for a year or two between bearing replacements. A high-frequency spindle is also much quieter in operation than a router.

For many shops, the cost and power requirements of a high-frequency spindle will be prohibitive. ShopBot's will certainly cut fine with a standard router. It is also possible to get started in CNC with a router, and then fit your ShopBot with a spindle at a later date. If you don't need a heavy cut and noise is not an issue then a router is a safe choice. For heavy production situations, we recommend a spindle. In addition, the full performance capabilities of a PRSalpha are only realized with a spindle because a router will bog down in heavy cutting at higher cutting speeds.

Conventional vs Universal Vacuum Hold-Down

There are two general strategies for the use of vacuum in holding parts for cutting or machining with a CNC router. You can either create seals around specific areas to be vacuum clamped in a “Conventional” manner, or you can draw air through a broad area of a permeable bleeder board to create a more “Universal” vacuum.

Conventional:  The conventional solution is usually less expensive. It makes use of high vacuum (20-29”Hg) with a low flow volume. It works well for machining parts that are not cut out with through-cuts. It works well if you are cutting repetitive parts for which it is practical to first cut a vacuum template that maintains the vacuum seal, even when the part is through-cut. With conventional vacuum systems, small leaks will cause a large drop in vacuum, which is why the vacuum seal is so important to holding your parts securely. When using conventional techniques it is often adequate to use: a shop-vac, compressed air venturi vacuum, small blower, or rotary vane blower to produce the vacuum. Conventional vacuum solutions tend to be specific to the application or production process and are usually devised by each shop. The plenum system, described below, could be used in conjunction with vacuum templates in a conventional system, even though it is designed for universal vacuum and bleeder board. ShopBotters have experimented with a variety of conventional systems and with a number of accessories for improving holding. You can find information on the Talk ShopBot Forum. There are also links for vacuum accessories in the ShopBot CNC Resource List.

Universal:  In contrast to conventional vacuum holding, universal systems have the advantage that you do not need specific sealed vacuum fixtures or templates. You can just put a piece of material down on your table, apply the vacuum and cut, assuming there is enough surface area to the parts for the vacuum to hold the material while the parts are cut. The universal system does not usually require a vacuum template. Material can be placed directly on a bleeder board and sufficient vacuum can be maintained as long as the required airflow does not exceed the specifications of the particular blower. The universal solution requires a lot of airflow and depends on relatively powerful and expensive industrial blowers/pumps (either displacement or regenerative type) that typically require 3-phase power. The displacement type blowers are the most powerful and robust, but they are also very noisy, usually requiring some sort of sound isolation. They are the best vacuum for the price, but a regenerative blower is frequently a more practical compromise. We sell several different types of universal vacuum holddown systems. Each includes all the necessary plumbing to set up a multi-zone system for your tool.

What's the difference between 2.5D and 3D?

[Click here to view our 3D introduction with answers to this and other 3D questions.]

3-Axis CNC Tools vs 5-Axis Tools (and ShopBot's Rotary Indexer, a 4-Axis Tool)

[Click here to view our 3D introduction with answers to this and other 3D questions.]

Doing 3D without 3D Design Software

[Click here to view our 3D introduction with answers to this and other 3D questions.]