X-Carvers are survivalists, and innovators. Long after I angrily gave up on that pathetic 24v stock spindle, others found very clever and resourceful ways to make amazing things happen. Even in aluminum. I could not and would not have persisted to achieve their results. .01" DOC with 20 IPM feed rates? But the results speak for themselves.

Tool Loading This is a topic I don’t know very much about and would like if someone with experience could chime in. This is typically measured as Cubic Inches per Minute. And has to do with the physical amount of material displaced. It is mainly calculated when milling and especially when doing aggressive high speed milling. (Not typically calculated for flat sheet cutting and mild pocketing).

Example: We will use a single cutting edge tool that requires a .005” chip load. And we are running a spindle at 16,000 RPM.

I am no professor, I have just broken a lot of bits and damaged a lot of material. Just think of me as the kid that has flunked the class so many times, I just can’t help but to finally absorb the lecture.

If you are finding your parts are equally inaccurate in both the X and the Y then your tool should be the first thing measured. The kicker is you need to measure the cutting diameter not the shank. The shank will be groud to a cutting edge resulting in it being slightly smaller. To take your spindles runnout in consideration you can cut a slot in a clean cutting material and measure the width of the slot and use this as an accurate tool diameter for your CAM generated offset toolpaths.

Single edge tooling is good for machines with faster spindles (Like a X-Carve with a trim router). You are cutting once per revolution, giving the tool time to take a larger chip out of the material.

Thank you for sharing @RichardShannon! I am just getting started with my X-carve and this knowledge you shared about feeds and speeds probably saved me numerous broken bits and hours of frustration!

First I want to say hello to everyone, this is my first post on this forum. I wanted to write a topic that I hope will contribute to helping people who are new to machining by providing a better understanding of how a tool works in relation to the material.

Plunging When you are moving a tool downward in the Z axis into a material it is commonly called a Plunge Rate. Please keep in mind that while most flat endmills are designed to be able to plunge downward, they are still a poor design and inefficient when compared to say a drill bit that is only designed to move down and never side to side. All tools behave different in plunging based on their tip design. I have never used a formula (I am sure someone has one out there) for plunging but I typically start somewhere about 1/10 of my linear Feed Rate and see how that goes as a starting point. You will know if you are doing it right as you will get a nice continuous coil of material (if cutting plastic or aluminum) that is being removed from the hole. If you are going too fast you will get a horrible chattering sound and moaning sound. If you are going too slow it will burn or melt the material you are cutting into.

Taps are cutting tools used to create screw threads inside a hole, while drill bits are used to create the initial hole before tapping. This chart provides guidance on the correct tap and drill bit sizes to use for different thread sizes, ensuring that the threads are of the correct size and pitch and that they will fit the intended screw or bolt.

5/8tap drill size

Welcome to the forum. What a great way to start. Having a concise all together primer to feeds and speeds on this forum is a much welcome addition. Thanks!

Assuming you’re cutting an outside profile, a too-small diameter results in a too-large part. One can preview this sort of thing in a vector drawing program by off-setting paths by half the ideal diameter, then assigning a stroke equal to the actual diameter.

5/8-11tap drill size

Here are the three possible ways to calculate chip load. You will need to know any two variables to solve the third (chip load, feed, and rpm). Typically you will know chip load and also know a RPM or a Feed that you wish to run out, and solve for the other.

I have learned the hard way that tools are rarely the diameter they claim to be. A .25” endmill can easily be .245” in diameter and result in parts that are larger than expected.

Great post, very informative and much appreciated. This should help out a LOT of users who are unfamiliar with cut settings.

4 40 rolltap drill size

Single Edge Tool ……80 IPM / (16,000 RPM x 1 Edge) = .005” Chip Load Three Edge Tool ……80 IPM / (5,333 RPM x 3 Edge) = .005” Chip Load

This is a very well-written post! Once you get into x-carve and other home made CNC machines another variable (actually about 1,000 other variables) are introduced. Not the least of which… in fact the MOST of which is machine rigidity. These machines are not as structurally sound as commercial machines. And most, immediately after assembly require hours and hours of modification, squaring, flattening spoil boards, etc. So, most x-carve users will never really experience optimum chip loads or that beautiful “sweet spot” sound. Most will subject the first .05" of their tool to overuse, dulling that section while the rest of the razor sharp flutes remain unused. The DIY CNC world is one of aspiring to commercial standards but compromising within the context of EACH individual machine. Because they are all very, very different and have very different capabilities. Once bits 1/8" and smaller are connected to a DIY machine ANYTHING can happen. The only optimum is what your machine on THAT day, in THAT material are capable of handling.

Rolltap drill size

Basic Troubleshooting Melted/Burned material or charred endmill - Lower RPM or Increase your feed speed. You are generating too much heat in the tool as a result of not taking large enough chips of material away with each revolution. You need more material to make its way in the flute on the cutter before it gets sliced away by the cutting edge. Either moving the material into the flute faster will increase the chip size or slowing down the revolution to give more time for more material to enter the flute will decrease tool temperature. Remember you should be able to touch your tooling immediately after a cut and it should only be warm and not hot.

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I just re-read my post and I think I have flip flopped conventional and climb cutting. I need to revise it tonight. I have not setup any tooling in nearly 6 months so I need to knock the cobwebs out a little.

If we could slow down time and witness what happens then a spinning tool is moving linear through material we would see that the flute (the void just before the cutting edge of the tool) is where all the magic happens. This flute allows material to be pushed inside of the tool which is then immediately sliced away. This amount of material that is inside the tool to be cut away is the golden key to CNC heaven. The material cut away is called a chip, this chip is not only pushed into the flute after cutting and ejected, the chip also carries the heat of the tool out with it. Yes, the stuff that is making a mess of your shop is the same stuff that is stopping your bits from turning red hot after an hour long job. The thicker the chip that is sliced away the more heat the chip can be carried away from the bit. If you are not letting enough of a chip be created inside of the tool flute you are not removing any heat and you will burn your material and your tooling. You should be making nice uniform “C” shaped chips.

37/64drill bitto mm

Multi edge tooling is good for slower spindles as it allows the machine to act as if it has a much faster spindle and in relation allows for faster feeds and quicker job times. Think of cutting aluminum on a mill that has a 10,000 RPM max spindle, if you put in a three edge tool you have basically increased RPM to 30,000 as you are taking three cuts per revolution.

The tap and drill bit chart lists the next parameters: Number of Threads Per Inch (TPI), Major Diameter, Minor Diameter, Tap Drill size, Clearance Drill size, Decimal Equivalents for Tap drills, Decimal Equivalents for Clearance Drills, Close Fit size, Free Fit size, and the percentage of thread engagement. The pitch diameter is the diameter at which the width of the thread and the width of the groove between threads are equal. The percentage of thread engagement is the percentage of the length of the screw that will be engaged in the threaded hole.

5/8-24 tap drill size

Cutting Depth Note: This is theory based on adequate horsepower and rigidity Most tooling is typically designed to cut at least at a depth of 1 x the diameter of the tool. A 1/8” tool can get optimal heat and chip clearing by cutting at a depth of 1/8”. Tool manufactures typically post their chip load as 1 X D which means 1 x Tool Diameter. Please keep in mind that cut depth is very limited by the rigidity of the machine, if your machine is not rigid it can induce chatter which can easily break a bit (especially expensive solid carbide bits which will not flex like High Speed Steel HSS when things get sloppy)

If you know Feed and RPM………Feed Rate / (RPM x # of cutting edges) = Chip Load If you know RPM and Chip load ………….RPM x # of cutting edges x chip load = Feed Rate (IPM) If you know feed and Chip Load ………Feed Rate / (# of cutting edges x chip load) = Speed (RPM)

Basic Rules of Thumb: Your tool should not be hot Your chips should not be dust, they should be slices Your tool should not sound like Adam Savages “Duck Bomb” - if it sounds bad, there is a good chance it is not cutting optimally.

In short, the best results are achieve via experimentation on your machine. As often defying conventional wisdom as seizing upon an important nugget of wisdom offered by a real pro (@RichardShannon) generous enough to share their hard earned know-how.

1/4 20drill size

Smaller tools are easier to spin and in my experience put less lateral force against your material allowing you to hold down you’re work piece with less force. Their cutting edge is also traveling at a slower speed than an larger tool at the same RPM (remember that the outside of a wheel is traveling faster than its hub). This reduction in speed means that a slower Feed or higher RPM is typically required than that of a larger tool. I have seen that smaller diameter cutters typically leave better edge finish along the top edge of the cut if the material is prone to chipping (think plywood, or a painted surface) as the amount of material being sliced away with each revolution is smaller.

Climb vs Conventional Cutting This basically means are you feeding your tool around the tool path either clockwise or counter clockwise (this has nothing to do with the direction the spindle is spinning it is alway spinning the same). Some materials benefit from Climb cutting and will provide a superior edge finish. Basically when Conventional cutting you are running the tool clockwise around your path and the tool is spinning clockwise at the same time, thus, the tool is pushing its cutting edge toward the rear of the cut path. When Climb cutting the tool is spinning clockwise but is being driven around the path counter clockwise, which means the cutting edge is driving into the material in a forward motion. There is a very simple way to determine if you need to cut Climb or Conventional. Simply cut a line running from the front of the machine to the back that is a few inches long. If the cut is cleaner on the left side of the cut then you should run the material with a Climb and if the cut is cleaner on the Right of the line then cut with a Conventional. When in doubt Conventional cutting is well…conventional.

If you are cutting a square that is 10"x10" your CAM software will generate an offset tool path that places the tool outside of the 10"x10" part. This is done so that the kerf of the cut (the material removed by the tool) is outside of your part. If you tell your CAM software that your tool is .250" in diameter it will place the centerline of the square tool path .125" outside of the part (called tool offset). If you then cut this toolpath with a tool that is .245" diameter and it is riding on the same .125" offset toolpath you are now leaving .0025" extra material along your toolpath as the centerline of the tool is .125" way from your part instead of the correct .1225". Because we are cutting a closed shape and not just an open line our part is being cut on all sides which means this increase is happening on all sides. Your final part is now 10.005"x10.005".

Number of Cutting Edges The number of cutting edges you have is basically multiplying the RPM of the spindle. If you have one cutting edge then your tool is only slicing one chip away per revolution. If you have three cutting edges then our tool is slicing three chips away per revolution. This means if I we spun the three edge cutting tool at 1/3 the RPM as the single edge cutting tool we would get the same size chip and theoretically the same quality of cut.

5/8-24die

Excellent post, the only thing I can add is that if someone is using the Dewalt 611 router the available RPM range is pretty high. The lowest setting is about 16,200 RPM which is pretty fast for most multi flute tooling. So as a general rule of thumb I have found that the Delwalt works much better when the setting is kept at 3 or below. Higher settings can cause the bit to overheat.

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Machine Screw Size Number of Threads Per Inch (TPI) Major Diameter Minor Diameter Tap drills Clearance Drill 75% Thread for Aluminum, Brass, & Plastics 50% Thread for Steel, Stainless, & Iron Close Fit Free Fit Drill Size Decimal Equiv. Drill Size Decimal Equiv. Drill Size Decimal Equiv. Drill Size Decimal Equiv. 0 80 .0600 .0447 3/64 .0469 55 .0520 52 .0635 50 .0700 1 64 .0730 .0538 53 .0595 1/16 .0625 48 .0760 46 .0810 72 .0560 53 .0595 52 .0635         2 56 .0860 .0641 50 .0700 49 .0730 43 .0890 41 .0960 64 .0668 50 .0700 48 .0760         3 48 .0900 .0734 47 .0785 44 .0860 37 .1040 35 .1100 56 .0771 45 .0820 43 .0890         4 40 1120 .0813 43 .0890 41 .0960 32 .1160 30 .1285 48 .0864 42 .0935 40 .0980         5 40 1250 .0943 38 .1015 7/64 .1094 30 .1285 29 .1360 44 .0971 37 .1040 35 .1100         6 32 .1380 .0997 36 .1065 32 .1160 27 .1440 25 .1495 40 .1073 33 .1130 31 .1200         8 32 .1640 .1257 29 .1360 27 .1440 18 .1695 16 .1770 36 .1299 29 .1360 26 .1470         10 24 1900 .1389 25 .1495 20 .1610 9 .1960 7 .2010 32 .1517 21 .1590 18 .1695         12 24 0.216 .1649 16 .1770 12 .1890 2 .2210 1 .2280 28 .1722 14 .1820 10 .1935 32 .1777 13 .1850 9 .1960 1/4 20 0.2500 .1887 7 .2010 7/32 .2188 F .2570 H .2260 28 .2062 3 .2130 1 .2280 32 .2117 7/32 .2188 1 .2280 5/16 18 0.313 .2443 F .2570 J .2770 P .3230 Q .3320 24 .2614 I .2720 9/32 .2812 32 .2742 9/32 .2812 L .2900 3/8 16 .3750 .2983 5/16 .3125 Q .3320 W .3860 X .3970 24 .3239 Q .3320 S 3480 32 .3367 11/32 .3438 T .3580 7/16 14 0.438 .3499 U .3680 25/64 .3906 29/64 .4531 15/32 .4687 20 .3762 25/64 .3906 13/32 .4062 28 .3937 Y .4040 Z .4130 1/2 13 0.500 .4056 27/64 .4219 29/64 .4531 33/64 .5156 17/32 .5312 20 .4387 29/64 .4531 15/32 .4688 28 .4562 15/32 .4688 15/32 .4688 9/16 12 .5625 .4603 31/64 .4844 33/64 .5156 37/64 .5781 19/32 .5938 18 .4943 33/64 .5156 17/32 .5312 24 .5514 33/64 .5156 17/32 .5312 5/8 11 0.625 .5135 17/32 .5312 9/16 .5625 41/64 .6406 21/32 .6562 18 .5568 37/64 .5781 19/32 .5938 24 .5739 37/64 .5781 19/32 .5938 11/16 24 .5875 .6364 41/64 .6406 21/32 .6562 45/64 .7031 23/32 .7188 3/4 10 0.75 .6273 21/32 .6562 11/16 .6875 49/64 .7656 25/32 .7812 16 .6733 11/16 .6875 45/64 .7031 20 .6887 45/64 .7031 23/32 .7188 13/16 20 .8125 .7512 49/64 .7656 25/32 .7812 53/64 .8281 27/32 .8438 7/8 9 0.875 .7387 49/64 .7656 51/64 .7969 57/64 .8906 29/32 .9062 14 .7874 13/16 .8125 53/64 .8281 20 .8137 53/64 .8281 27/32 .8438 15/16 20 .9375 .8762 57/64 .8906 29/32 .9062 61/64 .9531 31/32 .9688 1 8 1 .8466 7/8 .8750 59/64 .9219 1-1/64 1.0156 1-1/32 1.0313 12 .8978 15/16 .9375 61/64 .9531 20 .9387 61/64 .9531 31/32 .9688 1-1/16 18 1.0625 .9943 1.000 1.000 1-1/64 1.1056 1-5/64 1.0781 1-3/32 1.0938 1-1/8 7 1.125 .9497 63/64 .9844 1-1/32 1.0313 1-9/64 1.1406 1-5/32 1.1562 12 1.0228 1-3/64 1.0469 1-5/64 1.0781 18 1.0568 1-1/16 1.0625 1-5/64 1.0781 1-3/16 18 1.1875 1.1193 1-1/8 1.1250 1-9/64 1.1406 1-13/64 1.2031 1-7/32 1.2188

RPM and Feed relationship If you play with the formulas enough you will notice that you can get the same Chip Load with different Feed or RPM numbers. We are still using a Single Cutting edge tool.

This technical reference document provides information on the appropriate tap and drill bit sizes to use when creating threaded holes in various materials such as Stainless Steel, Steel, Iron, Brass, Aluminum, and Plastics.

Why is correct chip load important? It results in the three best things we as CNC operators can ask for. Longest tool life, cleanest cut, and fastest possible job time. Remember though that Chip Load recommendations are just that - recommendations. They are the best place to start and then troubleshoot to refine from there.

Disclaimer: Please understand that my experiences and theories are based on personal experience with large commercial CNC routers and not with the X-Carve; however, tooling interacts with the material being cut the same regardless of the machine size. I have spent the better part of a decade using CNC routes to cut flat sheet materials, mainly plastics. While I have been factory trained and have industry experience I will not claim to be an expert in the field of CNC routing (or grammar). If you don’t agree or see errors in my thinking please feel free to speak up, we are all hear to learn.

I have learned the hard way that tools are rarely the diameter they claim to be. A .25” endmill can easily be .245” in diameter and result in parts that are larger than expected. If you are working with something that needs to be + - .01” tolerance and you start off with a tool that is .005” different in size than what you tell your CAM software you are already halfway to having you part out of spec. So always measure you tool.

Chattering - Slow down your feed rate or increase RPM. This means there is too much lateral force against the tool and it is beginning to bend and deflect its cutting edges away from the proper cut path. Most likely you are trying to put more material into the flute per revolution than there is room for (you are basically gagging the tool by shoving too much material down its throat). When you are getting chattering and deflection you are dangerously close to breaking you tooling which can cost you money and is very dangerous. I have personally had a bit break and fly across the room passing between me and a coworker about two feet next to me and bury itself in a wall (wear your safety glasses). While I have typically only used solid carbide tooling (I was spending other peoples money on tools not my own) HSS or High Speed Steel has more flex to it and can tolerate more chatter and more force against it unlike Carbide which has superior long term sharpness but is very brittle.

Ah, I didn’t consider the outside profile. In the case of an inside profile or a pocket, this would result in under-sizing though correct?

Chip load is simply a measurement of the amount of material that is shaved off with each pass a cutting edge of the bit. This is not some mythical number, you can literally take the chips that are being cleared out of the cut and measure their thickness with calipers and it should match your calculations. Any reputable router bit manufacturer should be able to provide the Chip Load for a specific bit in a particular category of material (i.e. “Hard Plastics” or “Hard Woods”)