<%@LANGUAGE="VBSCRIPT" CODEPAGE="1252"%> CNC Frequently Asked Questions

CNC Systems and Applications

If you do not find the answer to your question below, try our Reference Library or write to support@PreciseBits.com

Can I use solid carbide end mills on any machine?

I am new to CNC. what do you recommend?

What should I know about routers?

Can I use a Dremel® or compatible device with PreciseBits tools?

Can I use a RotoZip® Rebel on my CNC router?


Can I use PreciseBits solid carbide end mills on any milling machine?

Carbide grade have improved substantially during that past decade.  Higher transverse rupture strengths, more resistance to shattering and a greater understanding of the role of each chemical component in the mix have resulted in the introduction of solid carbide tools in applications that once demanded high speed steel with exotic surface treatments. Nonetheless, the stability of your machine and the way your have it set up are very important.  Consider the following items (in order of importance):

  1. Spindle Runout (TIR) - should be less than or equal to 2% of the tool's diameter (absolute maximum).
  2. Spindle axis to table orthogonality- should be at 90° with no more than .1° variance.
  3. Spindle Peak RPM  - most of our tools require a minimum of 15,000 RPM under maximum anticipated load.
  4. Collet Retention Force - the collet must not let the largest diameter tool you will use slip under maximum anticipated load.
  5. Appropriate Feed Rates - motor drivers should be capable of moving the bit (or the workpiece) fast enough to prevent burning and tool overheating.
  6. 0 (Zero)  Slip - 0 (Zero) backlash in x and y axes.
  7. Proper hold down of work piece.

The above notwithstanding, a number of VERY skilled cuemakers successfully use our 0.010" tools on manual pantographs operating at 8,000 - 12,000 RPM.  From their experience it is apparent that even our smallest diameter cutters are compatible with manual equipment if the the skill of the operator is sufficiently high.

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I am new to CNC woodworking.  What do you recommend?

Talk about a question that needs a entire book to answer. In lieu of a complete, useful answer, we can only offer a few pearls of advice.

First. Go slowly.  Give yourself time to learn the equipment and to become familiar with the vagaries of cutting wood before investing a lot of money in precision tools.  Start with cutting a reasonably uniform wood like maple.  It doesn't cost much, cuts beautifully and can be used to test every aspect of most CNC systems. Start with larger sized bits (0.0469" and above). They are cheaper and harder to break than the smaller bits. Once you get the hang of it (count on a month or so) get some smaller bits as needed.  Some of our 1/32 in. bits are relatively cheap and are a popular size for new CNC users.

Second. Take time to understand how the parameters that you set with your controller configuration affect bit life, cutting time and overall system performance.  There are subtleties (like feeds, speed and acceleration ramps) that you need to master in order to be effective with your new equipment.

Third. Take time to talk to the vendor that you anticipate buying your machine from.  If they do not have time to help educate you now, it is unlikely that they will be very helpful after you have left you money with them. Shop around.  There is a lot of new equipment out there, some of it very good, some of it not so good.  Price is definitely not the final determinant of quality.  A number of modestly priced systems appear to work as well as much more expensive equipment. The most important issue is to size the system to your needs.  If you are going to be making pool cues, you do not need a US$50,000 CNC router with an 8 HP Colombo router and a 4' X 10' X 1' machining envelope.

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 What should I know about routers?

Compact CNC systems are often mounted with a low-cost shop router instead of a more expensive variable speed spindle.  In spite of being quite noisy, a router can give years of reliable service in operations requiring modest cutting power and minimal speed control. There are two types of routers commonly in use on CNC machines:  plunge routers and laminate trimmers. Plunge routers are designed for continuous use and are equipped with adequate cooling to prevent excessive heat build up.  The shafts are typically mounted in high-quality, sealed ball (or roller) bearings and backed up with a thrust bearing to allow drilling and ramp milling. Typical units cost between US$90 and US$350.  Laminate trimmers are much more compact and generally  much cheaper (US$45 to US$100). They are intended for intermittent duty, but, with light loading, can provide reasonable service in a CNC environment. 

Spindle speed (RPM) is very important when you are cutting with microtools. If you are fitting a shop router to your CNC, we recommend that you use a variable speed plunge-style router.  Plunge routers typically operate in the 25,000 to 30,000 RPM range, as opposed to 18,000 to 22,000 RPM for the single speed laminate trimmers.  More importantly, they are usually built around a so-called universal AC/DC motors that, with external controllers, can be operated from a few hundred RPM up to 120% of the rated maximum. One disadvantage of plunge routers is that most of them vent all of the cooling air through the bottom.  Unless you redirect this blast of air, it will render any vacuum removal of debris totally useless and your shop will slowly be buried in sawdust.

No matter what type of router that you decide on, go out an buy a dial test indicator with 0.0001" (0.0025 mm) resolution.  You will use this gage to periodically measure the runout of your "spindle" to determine when the bearings need to be replaced. Excessive spindle runout caused by worn out shaft bearings or a damaged collet adapter is one of the major causes of breakage with small rotary cutters. PreciseBits currently offers precision collets for a limited number of low-cost router / laminate trimmers. 

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Can I use a Dremel® or compatible device with PreciseBits Tools?

Are you using a Dremel mounted on a CNC stage or intending to use it by hand?

If the unit will be mounted to a CNC system you should not use any tool with a diameter smaller than 1/32" (0.0313", 0.80mm mm) cutting diameter. We have found the runout (TIR) of most handheld, pencil-style grinders to be too high to accommodate microtools. High TIR almost always translates to poor cut quality and broken bits.  

CAUTION:  We have measured a number of Dremel grinders and have yet to find a unit with less than 0.006 in. ( 0.15mm) TIR.  If you plan to use bits smaller than 0.0469 in. (1.20mm) you will need to replace the collet adapter with a more precise component.

If the Dremel will not be mounted to a CNC system,  we highly recommend the use of one of their attachments:  cutting kits, router attachment, shaper/router table or a drill press attachment. If you will be using the tool by hand, stick to the larger tools (0.0625" to 0.1250", 1.59 mm to 3.18 mm) to minimize breakage.  

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Can I use a RotoZip® Rebel on my CNC router?

I just recently purchased a CNC machine which utilizes a Rotozip Rebel.  I'm going for the smallest diameter cut possible for very fine cutting/engraving into oak.  The Rotozip tool utilizes 1/4 and 1/8 bits.  Could any of the bits on the PreciseBits site be utilized for the Rotozip?

The challenge with the Rotozip is that the runout (TIR) of the spindle increases rather rapidly with wear.  We are not familiar with the Rebel model so the problem may have been fixed.  In any case, if you are new to CNC woodworking, start with relatively large, robust cutters (0.0469" and above) to gain experience and to get a feel for the material that you are cutting.  After you have made some sawdust and feel adventurous, move on to more detail oriented tools (0.03125" and below).  You will find that clear maple (a medium density hardwood) cuts beautifully, with little fraying, accurate sidewalls, and no splintering to speak of. Assuming that your CNC is up to the task, tolerances of +/-0.002" are routinely achievable.

No matter what type of spindle or router that you are using, go out an buy a dial test indicator with 0.0001" (0.0025 mm) resolution.  You will use this gage to periodically measure the runout of your "spindle" to determine when the bearings need to be replaced. Excessive spindle runout caused by worn out shaft bearings is one of the major causes of breakage in small rotary cutters.

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