Reamer Feed and Speed Calculator
Estimate spindle speed, feed per minute, cutting time, stock allowance, and finish risk for machine reaming in common shop materials.
Calculation Breakdown
| Material | HSS Reamer SFM | Carbide Reamer SFM | Starting Feed per Rev |
|---|---|---|---|
| Aluminum 6061 | 100–180 | 250–450 | 0.004–0.012 in/rev |
| Mild Steel 1018 | 45–80 | 140–220 | 0.002–0.008 in/rev |
| Stainless Steel 304 | 25–45 | 80–140 | 0.001–0.005 in/rev |
| Free-Cutting Brass | 80–140 | 180–320 | 0.003–0.010 in/rev |
| Bearing Bronze | 60–110 | 150–260 | 0.002–0.008 in/rev |
| Gray Cast Iron | 50–90 | 150–260 | 0.002–0.007 in/rev |
| Prehard Tool Steel | 18–35 | 60–110 | 0.001–0.004 in/rev |
| Acetal / Nylon Plastic | 80–160 | 180–350 | 0.004–0.014 in/rev |
| Finished Diameter | Typical Total Stock | Stock per Side | Use When |
|---|---|---|---|
| Under 1/4 in | 0.003–0.006 in | 0.0015–0.003 in | Small dowel and screw clearance holes |
| 1/4 to 1/2 in | 0.006–0.015 in | 0.003–0.0075 in | Common chucking reamer work |
| 1/2 to 1 in | 0.010–0.025 in | 0.005–0.0125 in | Bushings, sleeves, and bearing fits |
| Over 1 in | 1%–3% of diameter | 0.5%–1.5% per side | Large shell, adjustable, or CNC reamers |
| Reamer Type | Common Flutes | Best Fit | Setup Note |
|---|---|---|---|
| Straight-Flute HSS | 4–8 | General shop holes, brass, cast iron | Use rigid alignment and steady feed |
| Spiral-Flute HSS | 4–8 | Blind holes and ductile chips | Prefer coolant flow out of blind holes |
| Solid Carbide | 4–6 | Production holes and abrasive materials | Needs rigid holder and low runout |
| Expansion Reamer | 6–10 | Fine size correction | Adjust in tiny increments only |
| Hand Reamer | 6–10 | Manual sizing and repair work | Use cutting oil and avoid reverse cutting |
| Symptom | Likely Cause | Feed / Speed Move | Setup Check |
|---|---|---|---|
| Chatter marks | Too fast, too little stock, or poor rigidity | Reduce RPM 15%–30%; keep feed positive | Check holder runout and pilot straightness |
| Bell-mouthed entry | Misalignment or hand pressure | Use steadier feed and floating holder | Chamfer lightly before reaming |
| Oversize hole | Runout, built-up edge, or wrong stock | Slow surface speed and improve lubrication | Indicate reamer and inspect cutting edges |
| Torn finish | Dull tool or chips trapped in flutes | Increase lubrication; avoid dwelling | Clear blind holes before final pass |
You can tell the reamer is making a clean cut because it make a dull rumble rather than a high-pitched screech or grind, which ends most shop floor arguments. At this point you’ve got the hole drilled, put the reamer in the spindle, and now you’re guessing at how fast to go. That’s where the tool and material values goes into calculator (above) and let you do the math. You won’t have to guess at conversions or coefficients anymore. But knowing how numbers work will keep holes round and the tool sharp.
Reaming gets mistaken as drilling by machinists. The idea seems to be that if they go faster they’ll get there work done quicker. That’s not true for reaming, which is a finishing operation. You are taking a small amount of material off the inside wall of a hole. The multiple flutes shares the cut; there are a lot of cutting edges involved. Each one takes very little material away. Go too fast and you will create too much heat which then expand and destroys your tolerance before you extract your tool. This explains the large differences in speeds (table at the bottom of the page) between carbide and high speed steel. Because carbide can handle heat better, you can push it further but only if your machine have the rigidity to back it up. Even a slight bit of wavering in your spindle becomes vibration with the added speed.
Tips for Better Reaming
There are hidden variables. One of those is stock allowance. In order for tool to have something to bite into, you can’t run the reamer through and then polish the hole to size; you should of drill it out to somewhere close enough so the tool has some material to remove. If there isn’t enough stock, say only one thousandth of an inch left on each side of the diameter, the flutes will simply rub without cutting. That creates heat and wears down finish. On the other hand, too much stock overwhelms the small cutting edge which deflects or chips. The calculator compares your initial pilot hole diameter to the final desired size to show the risk regarding this balance. Does it tell you that you’re asking the tool to do more work than its capable of doing in one go? Most shop reamers prefer to take off three to six thousandths total. If you take off any more then that, you are likely better off boring the hole first to avoid bell-mouthed holes. Otherwise, the tool will break.
Feed rate is where intuition matter less. Positive and steady is what you want. Do not linger at the end of a blind hole. Dwell is defined as when the cutting edges aren’t advancing while they’re still spinning. So they become grinding stones on the unmoving metal. That tears up the finish and works hardens surface. The calculator figures your desired feed per revolution into an IPM rate that your CNC controller can make sense of. But in the real world it’s just this: keep it moving down there. Feel resistance? Slow down the RPM but don’t quit feeding. If you feed the material while the spindle stops spinning, you will ruin edge quality of stainless steel or any other gummy material.
Choosing a coolant is more complex than it seems. Standard flood coolant will do fine, but air-oil mist can be effective on harder alloys such as hardened steels and Inconel. Because of its low viscosity, it has an easier time getting through the tight confines of the flutes different than a heavier flood does at times. Brass and aluminum can be dry reamed carefuly, although buildup is likely sooner in those materials. The tool simply gums up.
If troubleshooting, check shape of the chips. Do they appear long and stringy? Then your feed rate may not be fast enough for the cutting speed and you’re allowing the tool to drag instead of shear. Ideally, short broken chips leave cleanly from the hole before the next pass pushes them back down the flute. That’s when you want to ream. Respecting the physics of a small cut will get those parameters correct. It doesn’t want to dwell; it wants to move forward. And it doesn’t want to rub; it wants to cut. Tune the RPM and feed until you hear that hum settle into the background and you’ll know you’ve hit the sweet spot. The holes will turn out round, the finish will be smooth, and the tools will last way longer than usual. A good part of the quality control check in the shop is that steady sound.
