Reaming Speed and Feed Calculator
Calculate finish reaming RPM, feed rate, cycle time, chip load, and stock allowance from real machining inputs.
Reaming setup results
| Material | Typical SFM | Feed per rev | Stock on diameter | Coolant note |
|---|---|---|---|---|
| Low carbon steel 1018/1020 | 60-100 | .004-.010 in/rev | .003-.008 in | Flood coolant improves size repeatability |
| Alloy steel 4140 prehard | 45-75 | .003-.008 in/rev | .0025-.007 in | Use steady feed and rigid holding |
| Stainless steel 304/316 | 30-55 | .002-.006 in/rev | .002-.006 in | Keep tool engaged to avoid rubbing |
| Aluminum 6061-T6 | 150-220 | .006-.012 in/rev | .004-.010 in | Use coolant or mist to prevent pickup |
| Free-machining brass | 120-200 | .005-.012 in/rev | .003-.009 in | Often runs well with light oil |
| Gray cast iron | 55-90 | .004-.010 in/rev | .004-.010 in | Dry or air blast is common |
| Bearing bronze | 70-110 | .004-.009 in/rev | .003-.008 in | Oil helps finish and chip control |
| Acetal / Delrin plastic | 180-260 | .006-.014 in/rev | .004-.012 in | Air blast controls heat and chips |
| Titanium Grade 5 | 25-45 | .0015-.004 in/rev | .0015-.005 in | Flood coolant and reduced speed |
| Tool steel annealed | 30-55 | .002-.006 in/rev | .002-.006 in | Use sharp reamer and slow entry |
| Reamer diameter | Common flutes | Starting feed | Best use | Watch point |
|---|---|---|---|---|
| 1/8-1/4 in | 4 or 6 | .0015-.004 in/rev | Small dowel and pin holes | Runout changes size quickly |
| 1/4-1/2 in | 6 | .003-.008 in/rev | General machine reaming | Leave enough stock for cleanup |
| 1/2-1 in | 6 or 8 | .006-.014 in/rev | Bushings and fixture bores | Check horsepower and chip flow |
| 1-2 in | 8 or 10 | .010-.020 in/rev | Large guided bores | Use rigid holder or floating holder |
| Metric 3-6 mm | 4 or 6 | 0.04-0.12 mm/rev | Precision small holes | Avoid dwelling at bottom |
| Metric 6-12 mm | 6 | 0.08-0.20 mm/rev | Dowel holes and slip fits | Keep feed consistent |
| Metric 12-25 mm | 6 or 8 | 0.15-0.35 mm/rev | Bearing and sleeve bores | Confirm pilot hole straightness |
| Tolerance class | Speed factor | Feed factor | Typical intent | Setup note |
|---|---|---|---|---|
| H6 / very close finish | 0.85 | 0.85 | Gage-critical hole | Measure warm-up and tool runout |
| H7 / precision dowel fit | 0.92 | 0.95 | Dowel and location holes | Good default for accurate reaming |
| H8 / normal reamed fit | 1.00 | 1.00 | General precision bore | Normal shop finish target |
| Slip fit / running clearance | 0.95 | 1.05 | Pin or shaft clearance | Check mating part allowance |
| Utility cleanup ream | 1.05 | 1.10 | Improve roundness or size | Finish may be less controlled |
| Finished diameter | Light stock | Normal stock | Heavy stock | When to use |
|---|---|---|---|---|
| Under 1/4 in | .001-.002 in | .002-.004 in | .005-.006 in | Small holes need careful runout control |
| 1/4-1/2 in | .002-.003 in | .003-.006 in | .007-.010 in | Most common machine reaming range |
| 1/2-1 in | .003-.005 in | .005-.010 in | .011-.015 in | Use boring if drilled hole is not straight |
| 1-2 in | .005-.008 in | .008-.014 in | .015-.025 in | Guided tools and rigid machines preferred |
| Metric 3-6 mm | 0.025-0.05 mm | 0.05-0.10 mm | 0.12-0.15 mm | Use sharp tools and steady feed |
| Metric 6-12 mm | 0.05-0.08 mm | 0.08-0.15 mm | 0.18-0.25 mm | Common dowel-hole allowance |
| Metric 12-25 mm | 0.08-0.13 mm | 0.13-0.25 mm | 0.28-0.38 mm | Confirm boring accuracy before reaming |
Finishing operations such as reaming may appear easy but in reality they can make difference between good parts and scrap. First, you drill near your final dimension; secondly, you push a reamer through this hole. Doing this will create your final dimensions including diameter, straightness and surface finish.
Now if you don’t have the right feed and speed, you’ll either tear up the surface or rub the reamer on part. In one case, the hole won’t maintain tolerance; in another, mouth of the hole will flare out. Knowing how these variables work together can make difference.
How to Get Good Reaming Results
Let’s begin with the reamer itself. The bigger the diameter, the more material that has to be removed and the slower it can go. For example, a quarter-inch reamer spinning at the same surface feet per minute as a half-inch one would spin half as fast. This result in a different amount of heat and chip load. Skilled machinists never rely on just remembering a number; they adjust their settings based off the actual tool size each time.
The size of tools is important but so is the material they are cut from. Because aluminum conducts heat easy, it will try to run fast; however, it smears when not supplied with sufficient coolant. Stainless steel resist by immediately work hardening whenever you slow down the feed. And cast iron may be able to withstand dry running in some shops but rewards flood coolant with longer tool life and better size control. This is why the same reamer may have recommended speeds that differ by a factor of six depending on what it is cutting.
The other variable few consider is stock allowance. You never want to have too small an amount. The reamer will not cut; instead, it will burnish sides of hole and result in an oversize hole. But if you go too large with stock, you can experience chatter/difficulties which ruin roundness and cause deflections. For holes less than one inch, the optimal allowance is typically between 3-10 thousandths on diameter. However, if you are chasing an H6 tolerance or your previous drill wasn’t dead accurate, then this range gets tighter. Most issues is avoidable with a simple measurement of actual hole diameter.
The chip thickness of each flute is controlled by feed per revolution. Too light a feed and you will polish instead of shear the material. This cause the bore to glaze and increases wear. Too heavy a feed and the chips pack in the flutes, particularly in blind holes with no place to go but up. Once you know how many flute your reamer has, the calculator will convert feed per revolution to inches per minute, allowing you to consider if that’s an appropriate chip load based on your set-up rigidity and available coolant flow.
Another truth emerges from cycle time calculations. What appears to be a fast feed rate on a short hole is painfully slow on a deep bore. When you add in the overtravel and approach distance, the numbers becomes honest. Then those seconds begin to count as your parts run for two shifts. All of a sudden, that theoretical feed rate doesn’t look so attractive.
Across the shop, people make similar mistakes. Why does my finish look smeared? Oh, I slowed down because it was safer. Oops, I forgot about increased slipperiness of through-tool coolant. We need a tight tolerance, so we slow everything down. We didn’t improve the preceding bore quality. One problem for another. Tackling it as a system is always the best bet.
Normally, getting the right RPM down to decimal point doesn’t compare to having the right coolant, enough feed pressure with a solid + direction, a good cutting tool and correct amount of stock. Running the numbers against actual material facts removes the guesswork, protects your tools, and saves time on the machine. All this leads to the final proof, which is that quiet reamed hole. If you get all the numbers lined up and the tool slips into place with no drama, your bore will be straight, round and the correct size, right the first time. Just take a few minutes to work the numbers correctly to get that smooth bore. You should of used more care to ensure accuracy. You’ll recieve better results if you follow these steps. Actualy, it is moddern technology.
