Why the Drill Chart on Your Shop Wall Is Lying to You
Most shop SFM charts were accurate once, for a drill nobody sells new anymore, and running 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 is wrong because it was accurate, decades ago, for a drill that has not been sold new in years. Many shops still running uncoated 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 could safely run three to five times faster. 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 insulate the cutting edge and tolerate several hundred degrees more heat than bare HSS before losing hardness. 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
Solid carbide and cobalt-HSS blends hold 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
FA 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 | Modern Coated Carbide SFM | Approx. Multiplier |
| Aluminum (6061/7075) | 200 to 300 | 800 to 1,200 | ~4x |
| Mild Steel (1018) | 80 to 110 | 350 to 550 | ~4 to 5x |
| Alloy Steel (4140) | 60 to 90 | 250 to 400 | ~4x |
| Stainless (304/316) | 30 to 50 | 150 to 300 | ~5x |
| Stainless (17-4 PH) | 25 to 40 | 150 to 250 | ~6x |
| Titanium (Ti-6Al-4V) | 30 to 40 | 100 to 180 | ~4x |
The modern column comes straight from Chapman’s SFM, RPM, and chip load guide, the same reference used across the rest of this blog cluster. 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.
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 four 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. Straw to light blue chips mean normal heat. Dark blue, purple, or visibly discolored chips mean the cut is already past the material’s real limit, 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.
Chapman’s SFM, RPM, and chip load guide is built to be the living reference instead of a single laminated number per material, because it accounts for tool substrate and coating rather than assuming HSS by default. 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.