Why the Drill Chart on Your Shop Wall Is Lying to You
Most shop SFM charts were written for uncoated HSS drills, and running coated or carbide tooling to them quietly gives away cycle time and tool life on every hole
Category: Drilling • Reading Time: ~8 minutes • Audience: Intermediate to Advanced Machinists
The chart taped above the drill press is not wrong because someone got sloppy compiling it. It was written for uncoated HSS drills, and it is still accurate for those drills. It is wrong for the coated and carbide drills most CNC shops now run. Many shops still running HSS-era speeds off a laminated wall chart are not protecting their tools. They are giving away cycle time on every hole, all day, on tooling that can often run roughly two to three times faster on most steels and stainless, depending on drill design and coolant. This is not an argument to ignore published speeds and feeds. It is an argument to check what tool the chart on your wall was actually written for, because for most shops running coated or solid carbide tooling today, it was not written for what is currently in the spindle.
Where the Number on the Wall Actually Came From
Most of the SFM charts still hanging in machine shops trace back to reference tables built for uncoated high-speed steel twist drills, using the metallurgy, coatings, and coolant delivery available when those charts were first printed. HSS tolerates heat poorly compared to what came later, so the numbers were set conservatively, and for the shop floor of that era, conservative was correct.
Nothing about those numbers got updated when the tooling changed underneath them. The chart got laminated, taped to the column, and treated as a fixed reference instead of what it actually was: a snapshot of a specific tool material at a specific point in time.
What Actually Changed Since the Chart Was Printed
Coatings
Modern PVD coatings reduce friction and wear and allow a modest speed increase on HSS. The big jump in speed comes from carbide substrates, whose hot hardness far exceeds HSS. Chapman’s cutting tool coatings guide covers how TiAlN and AlTiN specifically extend the usable temperature range well past what an uncoated edge survives.
Substrate
Cobalt HSS (M35/M42) gives a modest gain over standard HSS, while solid carbide runs considerably faster and holds a cutting edge at speeds and temperatures that would round over a bare HSS edge in seconds. The full breakdown of where each substrate actually wins is in Chapman’s carbide vs. HSS end mill guide, and the same substrate logic applies directly to drills.
Coolant Delivery
Through-spindle coolant on a modern machining center pulls far more heat out of the cut than the flood or hand-applied cutting oil most wall charts assumed. A drill running the same SFM with proper through-coolant delivery runs measurably cooler than the setup the original chart was built around.
Machine Rigidity
A CNC machining center holds tolerance and resists deflection at speeds that would chatter a manual drill press off true. The chart was never written with that rigidity in mind, because most of the machines it was written for did not have it.
Legacy Chart vs. What Modern Tooling Actually Handles
| Material | Legacy HSS Chart SFM | Coated Carbide Drill SFM | Approx. Multiplier |
| Aluminum (6061/7075) | 200 to 300 | 300 to 500 | ~1.5 to 2x |
| Mild Steel (1018) | 80 to 110 | 200 to 290 | ~2.5x |
| Alloy Steel (4140) | 60 to 90 | 170 to 255 | ~3x |
| Stainless (304/316) | 30 to 50 | 75 to 145 | ~3x |
| Stainless (17-4 PH) | 25 to 40 | 60 to 110 | ~2.5x |
| Titanium (Ti-6Al-4V) | 30 to 40 | 50 to 150 | ~3x |
The carbide column is the typical spread of published speed data for general-purpose coated solid carbide drills at roughly 3xD to 5xD with coolant (Garr Tool, Dormer Pramet, Redline, Tru-Edge, Maritool, and Morse Cutting Tools). The HSS column is consistent with published HSS drill speeds from Morse and Redline. Premium high-performance drills can run higher, and speed usually has to come down as depth increases (Redline, for example, advises reducing speed 20 to 30 percent beyond 2xD). The point is not that every shop should immediately run at the top of that range. The point is that a laminated chart from the HSS era cannot tell a shop running coated carbide where its actual ceiling is, because it was never built to. Start at the low end of the range and confirm against the data sheet for your exact drill, coating, and depth.
Don’t Just Multiply the Number
The jump from chart speed to modern speed only holds if the rest of the setup scales with it. A worn spindle, a manual drill press, or a dull edge does not become safe at several times the SFM just because the tool in it is coated carbide. Running that fast on a setup that cannot support it does not fail gently. It just trades “too slow” for “burned edge and short tool life” as the new failure mode.
Reading the Real Ceiling, Not the Chart
Chip color and form tell the truth faster than any chart. Chip color is a relative indicator, and it only applies to steels. With HSS, chips should stay silver to straw. With coated carbide at proper speed, straw to blue chips in steel are normal. Judge by changes in color and form over the tool’s life, plus wear, sound, and spindle load, regardless of what the chart, or a formula, says it should be.
A change in cutting sound, chatter, or resistance is usually the earliest sign that the current combination is past what the machine and tool can actually support. Back off from what you are hearing and seeing, not from the number printed on the wall.
Tool life over a full shift is the real test, not the first hole. Heat accumulation and coolant delivery under sustained cutting show up over hours, not in a single cycle that happened to look clean.
The manufacturer’s data sheet for your exact drill, substrate, and coating is the living reference, not a single laminated number per material. Chapman’s SFM, RPM, and chip load guide shows how to turn any published SFM into RPM and feed. If your shop has moved to coated or carbide tooling as the standard, the old wall chart should come down, or at minimum get relabeled “HSS reference only” so newer tooling does not get accidentally derated to speeds it was never designed to run at.
A Practical Checklist Before You Trust the Chart
- Confirm what the posted chart’s numbers were actually calculated for (HSS, uncoated) before applying them to coated or carbide tooling
- Cross-check chart SFM against the tool manufacturer’s data sheet for the actual substrate and coating currently in the spindle
- Scale up gradually and watch chip color and form, not just the RPM readout, when moving off a legacy number
- Confirm machine rigidity and coolant delivery can actually support the increase before trusting a coated-tool SFM figure
- Update or retire the wall chart once the shop has moved to coated or carbide tooling as the default
Chapman Can Help
Getting the real ceiling right, not the chart’s ceiling, comes down to matching tool material, coating, and machine class to the job in front of you. Chapman stocks coated HSS and solid carbide drills from Dormer Pramet, Mitsubishi Materials, Garr Tool, and Harvey Tool, and our team can help set real speeds and feeds for what is actually in the spindle instead of what is taped to the wall.
Browse our CNC Cutting Tools catalog at shop.wcchapman.com, or call us at 410.686.6860 to talk through your application with a member of our team.