Chip Chad
The most common question on hobby CNC forums is "what speeds and feeds should I run?" The honest answer is: it doesn't matter until the machine is tight. A well-tuned $600 router cutting clean tells you more than a sloppy $3,000 machine drowning in chatter.
Tune the machine first. Then tune the numbers.
Why the machine comes before the numbers
Feeds and speeds are a system: tool, material, machine, and setup all interact. A rigidity problem looks like a chip load problem. A tramming problem looks like a finish problem. A loose V-wheel looks like chatter at a specific RPM. If you keep adjusting the numbers without fixing the machine, you're chasing ghosts.
The diagnostic question is simple: does the problem move when you change the setup, or does it stay constant? Constant problems across different tools and materials are almost always machine problems.
Tighten everything
Work through the machine systematically before cutting anything:
V-wheels and eccentric nuts — these are the most common source of slop on gantry routers. Finger-tighten a wheel, then back off 1/8 turn. You should feel slight resistance when rotating by hand, not free spin and not locked up. Check all of them; one loose wheel ruins the whole axis.
Belts — a belt that you can deflect more than 1/4" (6 mm) mid-span is too loose. A belt you can't deflect is too tight and will wear bearings fast. Most hobby routers are designed to run around 3–5 lb (13–22 N) deflection force.
Couplers — the flexible coupler between stepper and leadscrew should have zero play. It will develop play over time. Tighten the set screws and replace if the insert is visibly worn.
Collet and router base — a collet that isn't fully seated is the number one cause of unexpected tool breakage and terrible surface finish. Clean the taper, clean the collet, and make sure you're using the correct collet size for the shank. A 1/4" (6 mm) collet should not hold a 6mm shank.
Check tramming
Tramming is squaring the spindle to the table surface. Even 0.002" (0.051 mm) of tram error over a 4" (100 mm) face mill width will leave witness marks that no amount of feed-rate tuning will fix.
The simple test: put a dial indicator in the collet, swing it in a circle, and note the difference between the highest and lowest readings. Less than 0.002" (0.051 mm) over a 4" (100 mm) radius is good for most hobby work. Less than 0.001" (0.025 mm) for precision work.
Backlash
Some hobby machines have measurable backlash in the lead screw or rack-and-pinion system. The test: command 1" (25.4 mm) of travel, reverse 1" (25.4 mm), and measure where you ended up. Any discrepancy over 0.003" (0.076 mm) is backlash worth addressing. On leadscrews, anti-backlash nuts help. On rack and pinion, the pinion tension adjustment affects this.
The cut implication: climb milling amplifies backlash by pulling the table in the direction of cut. On a backlash-heavy machine, conventional milling on the finish pass may give better results.
Speeds and feeds for low-rigidity machines
With the machine tight, start conservative. Hobby machines flex under cutting load in ways that rigid VMCs don't, which means you're working with a lower effective stiffness than the tool manufacturer assumed when writing their chip load tables.
Starting point for a hobby router:
- Use 50–70% of published chip loads for the tool and material
- WOC 40–50% for roughing, 5–10% for finishing
- DOC 0.5–1× tool diameter for roughing in aluminum, less in wood with grain issues
- Conventional milling until you've verified the machine handles climb reliably
Once you've dialed in cuts that sound clean and consistent, you can push toward published values. But there's no benefit to starting there.
Reading the cut
The cut tells you more than any chart. Listen and look:
- Consistent hum, good-looking chips — you're in the right range
- High-pitched squeal — usually too light a chip load; increase feed rate
- Rhythmic chatter — too aggressive or loose setup; slow down and check for slop
- Dust instead of chips — cutting too slow in wood or plastic; increase chip load
- Spiral chips in aluminum — correct, this is what you want
- Blue or discolored chips — too much heat; check chip load (often too light) and coolant
If the cut sounds different from one pass to the next at identical settings, something is physically changing — material is moving, a clamp is loose, or the tool is dulling. Don't change the numbers; find the mechanical problem.
The 3× diameter rule
Stick-out matters more than most hobby machinists realize. Every time you double the stick-out, deflection increases eightfold for the same cutting force. The rule of thumb is to keep stick-out at or below 3× the tool diameter for general milling. If you need more reach, you need lower DOC and slower feed to compensate.
Chip Chad shows deflection estimates in the Results tab when you enter stick-out and shank diameter. If the deflection estimate looks high, extend the reach in small steps rather than all at once.