Clarke Super 7R Edger: Specs, Disc Sizes, Variable Speed

The Clarke Super 7R uses 7-inch edger discs. Most have a 7/8-inch center hole; some older 7Rs take 5/16-inch. PSA stick-on discs are the rental-shop standard. Match the edger grit to the drum grit at every stage. Use the variable-speed dial — slow RPM for coarse grits, fast RPM for fine grits, opposite to what feels intuitive. Budget 4 to 6 discs per grit for a 200 sq ft room. This guide covers center-hole sizing, the variable-speed technique most operators miss, rental counter inspection, and per-grit shopping lists.

Three pre-rental checks

Same as for any floor sanding rental:

1. Engineered vs solid? Check.
2. Pre-1978 house? Lead test first. Why.
3. Two circuits available? Sander + HEPA vac on different breakers. Setup.

Clarke Super 7R specifications

Specification	Value
Disc diameter	7 inches
Center hole	7/8 inch OR 5/16 inch (check your machine)
Motor	1.5 HP
RPM	175–2500 (variable speed)
Working width	~5 inches along wall
Weight	~35 lbs
Best for	Edging 300–800 sq ft floors; pair with drum sander

Two center hole sizes — confirm before you buy

This trips up most DIYers. The Super 7R ships in two spindle configurations:

7/8-inch center hole

• Most common on newer Clarke 7R models
• Standard on generic 7-inch edger discs
• The hole looks like a thick bolt thread when you look at the spindle

5/16-inch center hole

• Found on some older Clarke models
• Less common; harder to find discs
• The hole looks like a thin rod

Confirm before you order. Measure the spindle (or just ask the rental shop staff). Wrong hole size = wasted trip to the supplier.

Why the 7R has variable speed (and how to use it)

The 7R’s 175–2500 RPM dial is the feature that separates it from a single-speed edger. Most operators never touch the dial and run at one speed all day. That’s a 50% reduction in finish quality for no reason.

What changes with RPM:

• Low RPM (175–800): maximum torque. The disc cuts aggressively but with low surface speed — less heat, lower burn risk. Use this for the first pass through old polyurethane or stain.
• Mid RPM (800–1500): workhorse setting for 60 and 80 grit on bare wood. Balanced cut speed and control.
• High RPM (1500–2500): smooth, fine cuts with minimal aggression. Use for fine grits (100/120) only and only on bare wood. Running 80 grit at 2500 RPM glazes the disc fast and burns the wood in soft species.

The rule

Grit	RPM range
36	175–800
60	800–1200
80	1200–1500
100/120	1500–2500

Slower RPM with coarser grit, faster RPM with finer grit. Inverse to what feels intuitive (most operators think faster = more aggressive). Speed and cut aggression are opposite levers.

7R rental counter inspection — 60 seconds

• Pad condition. Look at the rubber backing pad through the disc hole, or peel a corner. Worn flat to the metal = swap the machine. The pad has to give slightly under disc pressure or you’ll bog the motor.
• Center spindle size. Confirm 7/8” or 5/16” and match to the discs you’re buying.
• Variable-speed dial. Sweep from low to high with the motor off. Should turn smoothly and click into detents. Sticky dial = you’ll burn the floor at the wrong speed.
• Power cord end-to-end for nicks.
• Dust port hose connection tight.

Worn pad is the most common failure. If the rental shop doesn’t have a fresh pad to install, find a different shop.

PSA vs hook-and-loop discs

PSA (pressure-sensitive adhesive)

• Sticky backing adheres directly to the metal backing plate
• Slightly cheaper per disc (~$2–4)
• Cannot be repositioned during installation
• Disc changes take 5–10 minutes (clean adhesive, install new, wait for set)
• Industry standard at rental shops — most rental 7Rs come PSA-configured

Hook-and-loop (Velcro-style)

• Velcro-like backing grabs a hook-and-loop pad on the sander
• Slightly more expensive per disc (~$3–5)
• Plus the machine needs hook-and-loop pad installed (~$10–20 one-time)
• Disc changes take 30 seconds
• Industry standard for professional contractors who change grits multiple times per job

Which should you choose?

If your rental 7R has the PSA plate installed — run PSA. That’s how most rental machines come configured, it’s what rental shops stock, and it’s what we link in the Pro Pick above. The 5–10 minute disc changes cost you maybe half an hour across a full grit sequence — annoying, not job-killing.

Hook-and-loop is the upgrade when the machine already has a hook pad installed, or you own the machine and can add one for $10–20. Thirty-second changes, and partially-worn discs reuse at the next grit. We don’t have a verified VA hook-and-loop listing yet — search 7-inch hook-and-loop edger discs and match your center-hole size before ordering.

Pro tip: ask the rental company if the machine comes with a hook-and-loop pad installed. Many do now. If not, ask them to install one for a small fee.

Disc recommendations by grit

For cross-brand comparison (VA vs Norton vs 3M, with honest links to all three), see our 7-inch edger disc guide. Quick summary:

• Virginia Abrasives 36/60/80 grit: the cut grits. Semi-closed coat resists loading on old finishes. Affiliate link, our recommendation.
• Norton 100/120 grit closed-coat: finishing grits where scratch consistency matters under water-based finish or stain. Same commission either way — it’s just the right call.
• 3M: middle option if VA or Norton isn’t in stock.

How many discs do you need?

Room size	36 grit	60 grit	80 grit	100 grit
250 sq ft	2–3	2–3	2–3	1–2
400 sq ft	3–4	3–4	3–4	2–3
600 sq ft	5–6	5–6	5–6	3–4

Edger discs wear faster than drum sander sheets — the 7R operates at high pressure and RPM, and the smaller disc traces every corner. Budget generously. You can reuse hook-and-loop discs at the next-grit level if they’re not completely worn.

VA’s 36- and 60-grit Amazon listings are 50-disc boxes — far more than the table says you need, but per-disc cost beats loose retail several times over and spares carry to the next job; the 100-grit sells as single discs (~$2 each): 36 grit · 60 grit · 100 grit.

For the full sheet calculator with species multipliers, see our sheet calculator.

7R edging technique

Setting up

1. Install the disc (clean adhesive on PSA, peel-and-press on hook-and-loop). Wait 5 minutes on PSA before operating.
2. Connect HEPA vacuum to dust port.
3. Set variable speed for your starting grit (see table above).
4. Test motion without disc on floor to verify vacuum and oscillation.

The pass

• Hold steady with both hands. Don’t let the machine tip or lean — the disc should kiss the floor flat.
• Keep the disc flat. Tilting creates swirl marks.
• Move steadily. Don’t linger; constant slow walking pace.
• Light pressure. Don’t jam the machine into the wall. Light, consistent pressure lets the disc do the work.
• Overlap your passes 2–3 inches.

Corners and tight spots

• Inside corners: the 7-inch disc can’t reach a 90° angle. After the edger pass, hand-sand corners with matching grit on a sanding block.
• Around door frames: edge carefully; the disc edge stops short of trim.
• Under radiators and obstacles: reach in safely; hand-sand spots the machine can’t reach.

Avoiding swirl marks

• Don’t tilt the disc (most important)
• Move in consistent lines parallel to walls
• No circular motions or pivoting
• Light-to-medium pressure
• Overlapping passes in the same direction, not crisscrossing

Troubleshooting

Disc slips or spins without cutting

• PSA: adhesive weak. Peel off, reinstall, ensure no air bubbles. If still slipping, the pad is dirty.
• Hook-and-loop: pad worn. Ask rental to replace.
• Either: disc glazed (shiny, not cutting). Lower RPM or change disc.

Disc tears or chunks come out

• Too much pressure — lighten up.
• Disc hit an obstacle (nail, staple, wood splinter) — inspect the floor.
• Disc was defective — replace.

Uneven sanding (dips or missed spots)

• Not overlapping passes enough — make longer, more overlapped passes.
• Tilting the disc inconsistently — keep angle steady.
• Moving too fast — slow down.

Hand-sanding to complete the corners

Even with the edger, some spots remain unreachable: very tight corners, under baseboards, around door hinges. Hand-sand with 80–120 grit to blend.

• Sanding block for control
• Sand with the grain
• Light pressure matching the edger results
• This final detail work separates pro-looking floors from amateur ones

Current prices

Prices pulled from Amazon at publish; verify before ordering. Amazon Associate disclosure: we earn from qualifying purchases.

Center hole first, RPM second, technique third. The 7R is a precision tool when you respect the dial.

Matt.