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Adjustable reamer 7-8 mm NRZe
2743
€22.66 tax inc.
Net price: €18.42
Description
Adjustable reamer 7-8 mm – reamer adjustable to 8 mm
Technical data – HSS blades, shank with square drive for a tap wrench
| Technical data | |
|---|---|
| Adjustment range | 7–8 mm |
| Designation | NRZe to PN |
| Blades | HSS, in inclined grooves |
| Diameter adjustment | two nuts |
| Shank diameter | 3.7 mm |
| Shank square | 2.8 mm |
| Overall length | 90 mm |
| Blade length | 33 mm |
| Drive | tap wrench |
Adjustable reamer 7-8 mm NRZe finishes holes from 7 to 8 mm. This is the smallest NRZe reamer in the range. Set the diameter with two nuts that move the high-speed steel (HSS) blades in the inclined slots in the body. For a 8 mm hole, use a 7.9 mm straight shank drill; for a 7.5 mm hole, use a 7.4 mm drill. Both leave an allowance for one pass. Operate it by hand with a tap wrench fitted to the square on the shank.
Manufacturers design adjustable blade reamers for repair and assembly work. They are useful wherever a hole needs to be fitted to the part at hand. The diameter is then set to the size of the part, rather than to the standard size series of fixed reamers.
Which size to choose: 7-8 or 8-8.7 mm
Two reamers cover a hole of exactly 8.0 mm: 7-8 mm and 8-8.7 mm. The 7-8 mm reamer has a 2.8 mm square and is 90 mm long. The 8-8.7 mm reamer has an 3.7 mm square and is 106 mm long. Both can be turned with a No. 0 tap wrench, designed for squares from 2 to 5 mm.
How diameter adjustment works – blades and two nuts
NRZe reamer construction and measuring the diameter setting
The body has inclined grooves around its circumference, each holding an HSS blade. Two nuts, front and rear, retain the blades at both ends. Moving the blades along the grooves moves their cutting edges away from or toward the axis. This changes the cutting diameter over a range of 1 mm, from 7 to 8 mm. This is why the tool is also called an adjustable reamer.
Adjustment in three steps
First, loosen one nut. Then tighten the other — the blades will move to the new diameter. Finally, lock the blades by tightening the first nut. The rear nut, on the shank side, provides the main clamping force; the front nut is only snugged up. Tighten carefully. Excessive force bows the blades outward and causes the reamer to catch in the hole.
How to measure the set diameter
With an even number of blades, measure the diameter across two opposite blades using a micrometer. With an odd number, a groove lies opposite each blade, so the micrometer will read too low. In this case, use a setting ring or a hole of known diameter. Insert the reamer and expand the blades until they contact the hole wall.
How to ream step by step – tap wrench and clockwise rotation
Guidelines for using an adjustable hand reamer
Insert the reamer into the hole and apply light pressure so the blades engage the wall immediately. The tap wrench must fit the square closely to ensure smooth rotation without jerking. Align the reamer axis with the hole axis. For a longer hole, check the alignment with a square.
Hand reaming in six steps
1
Drill a hole
0.05–0.15 mm smaller than the finished hole, e.g., 7.4 mm for 7.5 mm.
2
Set the diameter
Loosen one nut, move the blades with the other, then lock the first nut.
3
Fit the tap wrench
Fit it to the square and align the reamer with the hole axis.
4
Turn clockwise
Turn smoothly with light, even pressure.
5
Withdraw the reamer
Keep turning clockwise, including as the blades leave the hole.
✓
Check the hole
Too tight? Set a larger diameter and make a second pass.
Guidelines based on adjustable reamer manufacturers' instructions.
As the blades emerge from the far end of the hole, resistance drops suddenly. Reduce pressure at this point, but maintain the same turning speed. Otherwise, the reamer will jump through the end of the hole and leave it uneven.
▲
Never turn counterclockwise
Turning counterclockwise in the hole dulls the blades and may chip them. It can also loosen a nut and change the setting. Turn clockwise when withdrawing the tool as well; otherwise, you will scratch the hole wall.
How much material one pass removes
Reaming allowance and drill bit selection
This tool finishes a hole rather than drilling it. It removes a thin layer: 0.05 to 0.15 mm on diameter in one pass. A smaller allowance produces a smoother hole wall. Too little allowance is detrimental because the blades rub against the wall instead of cutting and dull faster. The drawing shows a 7.5 mm hole after a 7.4 mm drill.
Calculation: 8 mm hole after drilling with a 7.9 mm drill bit
Allowance on diameter = finished hole diameter 8.0 mm − drill diameter 7.9 mm = 0.1 mm. Half of this, or 0.05 mm, is on each wall. This layer is thinner than a sheet of paper. A reamer set to 8.0 mm will remove it in one pass.
| Finished hole [mm] | Drill bit [mm] | Diametral allowance [mm] | Layer thickness at the wall [mm] | Passes |
|---|---|---|---|---|
| 7.0 | 6.9 | 0.1 | 0.05 | 1 |
| 7.5 | 7.4 | 0.1 | 0.05 | 1 |
| 8.0 | 7.9 | 0.1 | 0.05 | 1 |
| 8.0 | 7.8 | 0.2 | 0.1 | 2: set to 7.9, then 8.0 |
A 7.8 mm drill leaves a 0.2 mm allowance for a 8 mm hole. Remove it in two passes: set the first to 7.9 mm and the second to 8.0 mm. Two passes, preliminary and finishing, also produce the smoothest hole wall.
Tap wrench and lubrication – what to prepare
Tap wrench for a 2.8 mm square and oil suited to the material
Tap wrench No. 0
The shank square measures 2.8 mm, almost the same as M3 hand taps with a 2.7 mm square. The same tap wrench therefore fits. Select an adjustable tap wrench to DIN 1814, size No. 0. It accommodates squares from 2 to 5 mm and fits M1–M8 taps.
With oil or dry
| Workpiece material | Lubrication |
|---|---|
| Steel and cast steel | cutting oil or emulsion |
| Aluminum alloys | cutting oil or emulsion |
| Gray and malleable cast iron | dry |
| Bronze and brass | dry |
Remove chips from the reamer after use. Before adjusting the blades, also clean the body grooves so the blades move evenly.
Adjustable reamer 7-8 mm NRZe is the smallest size in the series, with a 3.7 mm shank and a 2.8 mm square. The square is almost the same size as on M3 hand taps, so the same No. 0 tap wrench fits. Prepare a 8 mm hole with a 7.9 mm drill for one reaming pass. Always turn the reamer clockwise.
Questions about drill bits, size selection, and operation
Frequently asked questions about hand reaming
A 7.9 mm straight shank drill to DIN 338. It leaves a 0.1 mm allowance on diameter, so a reamer set to 8.0 mm will remove it in one pass.
Either can produce a 8.0 mm hole: it is the upper limit of the 7-8 mm range and the lower limit of the 8-8.7 mm range. The 7-8 mm reamer also covers smaller holes, from 7 mm. The 8-8.7 mm reamer covers larger holes, up to 8.7 mm.
Clockwise, just as when reaming. Clockwise rotation protects the blades and the hole wall. It also keeps the nuts in place, so the setting does not change.
Yes, at very low speed and with plenty of oil. At high speed, the hole may end up larger than the setting. Using a tap wrench provides the best control.
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Shipping
All orders are delivered by courier company GLS. For orders exceeding 369 PLN gross shipping is FREE
| Courier GLS | Przelew24 / Prepayment | 14,76 zł gross | Delivery time 1 working day |
| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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