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Adjustable reamer 23.75-27 NRZe
1263
€32.37 tax inc.
Net price: €26.32
Description
Adjustable reamer 23.75-27 mm – reamer adjustable to 25 mm
Technical data – HSS blades, shank with square drive for a tap wrench
| Technical data | |
|---|---|
| Adjustment range | 23.75–27 mm |
| Designation | NRZe to PN |
| Blades | HSS, in inclined grooves |
| Diameter adjustment | two nuts |
| Shank diameter | 15.5 mm |
| Shank square | 12.2 mm |
| Overall length | 210 mm |
| Blade length | 70 mm |
| Drive | tap wrench |
Adjustable reamer 23.75-27 mm NRZe finishes holes from 23.75 to 27 mm, including the whole-millimeter sizes 24, 25, and 26 mm. The diameter is set using two nuts that move the high-speed steel (HSS) blades along inclined grooves in the body. The shank square measures 12.2 mm, almost the same as on M20 hand taps. For a 25 mm hole, use an 24.75 mm drill bit with Morse taper MT3. The tool is operated by hand using a tap wrench fitted to the shank square.
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: 23.75-27 mm and adjacent sizes
Holes from 23.75 to 24.5 mm are also covered by the 21-24 mm and 21.5-24.5 mm reamers. They have smaller squares, 11 and 10.5 mm, and are operated with a No. 3 tap wrench. From 27 mm, the range is covered by the 27-30 mm reamer with a 14 mm square, which can be operated with the same No. 4 tap wrench.
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 3.25 mm, from 23.75 to 27 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
Use a 24.75 mm drill bit for a 25.0 mm hole. Remove the 0.25 mm allowance in two passes.
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: from 0.05 to 0.15 mm on the diameter in one pass. A smaller allowance produces a smoother wall. Too little allowance is detrimental, as the blades rub against the wall instead of cutting and become dull faster.
Calculation: 25 mm hole after drilling with a 24.75 mm drill bit
Diametral allowance = finished hole diameter 25.0 mm − drill bit diameter 24.75 mm = 0.25 mm. This exceeds the 0.15 mm that the blades remove in one pass. Set the first pass to 24.9 mm – it will remove 0.15 mm. Set the second to 25.0 mm – it will remove the remaining 0.1 mm.
| Finished hole [mm] | Drill bit [mm] | Diametral allowance [mm] | Layer thickness at the wall [mm] | Passes |
|---|---|---|---|---|
| 24.0 | 23.75 | 0.25 | 0.125 | 2: set to 23.9, then 24.0 |
| 25.0 | 24.75 | 0.25 | 0.125 | 2: set to 24.9, then 25.0 |
| 26.0 | 25.75 | 0.25 | 0.125 | 2: set to 25.9, then 26.0 |
| 27.0 | 26.75 | 0.25 | 0.125 | 2: set to 26.9, then 27.0 |
All these drill bits in the range have a Morse taper MT3 and diameters in 0.25 mm increments. Each leaves a 0.25 mm allowance. The first pass removes 0.15 mm, and the second, finishing pass removes 0.1 mm.
Tap wrench and lubrication – what to prepare
Tap wrench for a 12.2 mm square and oil suited to the material
Tap wrench No. 4
The shank square measures 12.2 mm, almost the same as M20 hand taps with a 12 mm square. The same tap wrench therefore fits. Select an adjustable tap wrench to DIN 1814, size No. 4. It accommodates squares from 5.5 to 16 mm and fits M9–M27 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 23.75-27 mm NRZe covers the whole-millimeter sizes 24, 25, and 26 mm. The reamer is 210 mm long, and its blades are 70 mm long. For each of these holes, use a drill bit 0.25 mm smaller, with Morse taper MT3. Ream in two passes, with the last pass bringing the hole to final size. The 12.2 mm square fits a No. 4 tap wrench.
Questions about drill bits, size selection, and operation
Frequently asked questions about hand reaming
Drill it with a 24.75 mm drill bit with Morse taper MT3. Remove the 0.25 mm allowance in two passes: to 24.9 and 25.0 mm.
A 27 mm hole is at the upper limit of this reamer and the lower limit of the 27-30 mm reamer. This reamer will finish it after drilling with a 26.75 mm drill bit, in two passes: to 26.9 and 27.0 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.
Product accessories
Metal drill bit 26 NWKc HSS DIN 345 Baildon
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