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Trimming a Door: Which Saw and Blade Give a Clean, Straight Cut?
The neatest way to trim a door is with a circular saw fitted with a fine, carbide-tipped blade with a high tooth count, run along a guide rail or a clamped straight edge. Take the door off its hinges first, tape the cutting line and lay the door good face down.
If you are trimming a door that is hollow, check how much solid timber there is in the bottom rail before you cut anything.
What will you learn in this article?
- When do you need to trim a door?
- How much should you take off the door?
- Which saw should you use to trim a door?
- Which saw blade should you use for a door?
- How to trim a door, step by step
- Trimming a hollow door: check the bottom rail
- Can you trim a door without taking it off?
- Finishing the cut edge of the door
- Trimming a door safely
- Frequently asked questions about trimming a door
- In short: trimming a door
When do you need to trim a door?
The most common reason is a new floor. A thicker laminate or vinyl floor with underlay, or new carpet, reduces the gap under the door and it starts to drag. A new threshold or the need for a ventilation gap can also be a reason. Leave enough space under internal doors for air to circulate around the house, especially if you have a mechanical ventilation system. The documentation for your ventilation system tells you how much gap it needs.
How much should you take off the door?
Measure the clearance you need at the point where the door has to sit highest above the floor. Floors are rarely completely level. Open and close the door and see where it catches first. Then mark a line on the door parallel to the bottom edge. Take off a few millimetres too little rather than too much: you can always plane or sand a bit more off, but you cannot put it back.
Which saw should you use to trim a door?
| Saw | Suitable? | Why |
|---|---|---|
| Circular saw with guide rail or straight edge | Best choice | Straight, fast, the full width of the door in one cut |
| Plunge saw with guide rail | Very suitable | Splinter-free with the right rail and blade |
| Jigsaw | Only if there is no alternative | The blade wanders easily and the cut is rougher |
| Handsaw | For a single thin strip | Slow and hard to keep straight |
| Mitre saw | Not suitable | Its cutting width is too small for a whole door |
Some guides mention a mitre saw, but the cutting width of a mitre saw, even a sliding model, is too small for a door of standard width. A circular saw is the right machine. A cordless circular saw from the Maxxpack 18V range is handy for this, because you can trim the door on two trestles in the hallway or the room you are working in.
Which saw blade should you use for a door?
Number of teeth
The more teeth, the finer and cleaner the cut. A blade with few teeth cuts fast but tears the paint or veneer away at the edge. For a door, choose a fine blade intended for finishing work or sheet material. The diameter and the right blade type for your saw are given in its manual and on the blade itself.
Tooth material
Choose carbide-tipped teeth. Many doors have a core of chipboard or MDF with glue in it, and carbide stays sharp far longer in that material.
Diameter and bore
The blade must match your circular saw exactly: the same diameter and bore as given in the manual. You can sometimes use a blade with a larger bore with a suitable reducing ring, if the manufacturer allows it. Never fit a blade with a larger diameter than specified.
Slots in the blade
The slots in a saw blade absorb expansion from heat and reduce vibration and noise. A slotted blade stays truer and cuts more smoothly.
How to trim a door, step by step
Take the door off its hinges
Unscrew the hinges from the frame, supporting the door as you go. If the screw heads are clogged with paint, scrape them clean with a knife first. On a door with lift-off or pin hinges, cut the paint around the pin and tap the pin out from below with a screwdriver and hammer.
Lay the door down
Put the door on two trestles with an old blanket or cardboard on top, good face down.
Mark and tape the cutting line
Draw the cutting line and cover it with masking tape. Score the line with a sharp knife along a straight edge so the paint does not tear out.
Set up the guide and depth
Clamp a guide rail or a straight edge in place and set the cutting depth a few millimetres deeper than the thickness of the door.
Make the cut
Cut in one smooth pass. Support the offcut at the end so it does not snap off.
Finish the edge
Take the sharp edge off with abrasive paper and seal the cut edge.
The cut itself is over quickly. Most of the time goes into taking the door down, marking up and finishing. Allow drying time for the paint or varnish on the cut edge before you rehang the door. Our guide on how to hang an interior door covers putting it back.
Trimming a hollow door: check the bottom rail
Many internal doors are hollow: two thin skins with a honeycomb core and a frame of solid timber or chipboard. If you cut off more than the depth of that bottom rail, you are left with an open gap at the bottom and the door loses strength. So measure the depth of the bottom rail first, for example by drilling a small hole where it will not show or by looking at the end grain. If you need to take off more, remove a little of the core, glue the cut-off rail back into the opening and clamp it until the glue has dried.
Can you trim a door without taking it off?
In some situations you can use a multi-tool with a flush-cut blade running along the floor, but the result is rarely straight and you risk damaging the floor. A multi-tool is useful for undercutting door linings and architraves when you lay a new floor. For the door itself, taking it off is almost always the better option.
Finishing the cut edge of the door
A bare cut edge absorbs moisture, which can make the door swell or warp. Sand the edge lightly, remove the dust and seal it with paint or varnish. This matters most for bathroom and kitchen doors and for external doors.
Trimming a door safely
Wear safety glasses, ear defenders and a dust mask. Lay the door down securely so the cutting line hangs clear of the floor. Keep both hands on the saw and wait until the blade has stopped before you lift it. Remove the battery from the saw when you change the blade or set the cutting depth. A heavy door is best carried by two people.
Frequently asked questions about trimming a door
What is the best saw blade for trimming a door?
A carbide-tipped circular saw blade with a high tooth count, made for fine finishing work or sheet material. The diameter and bore must match your circular saw exactly.
Can I trim a door with a jigsaw?
You can, but over the width of a door the blade soon wanders off line and the cut is rougher. If you do, use a wide, fine blade, switch off the pendulum action and guide the saw along a clamped straight edge.
How do you stop a door splintering when you trim it?
Tape the cutting line, score it with a knife and lay the good face down when using a circular saw. Use a sharp blade with plenty of teeth and cut at a steady pace.
What do you do if the bottom of the door is hollow after cutting?
Remove a little of the core, glue the cut-off bottom rail back into the opening and clamp it. That makes the door solid again and lets you finish the bottom edge neatly.
In short: trimming a door
Trim a door with a circular saw or plunge saw fitted with a fine carbide-tipped blade, running along a guide rail. Take the door off its hinges, tape and score the cutting line, lay the good face down and check the bottom rail on a hollow door. Always seal the cut edge against moisture.