Mitre & Bevel Angle Calculator

Printable tables

Every angle, worked out

Mitre saw settings, where 0 is a square crosscut. Both pieces of a corner take the same setting, cut in opposite directions.

Flat trim: skirting, architrave, deck framing

Frames and boxes with equal sides

Coving cut flat on the saw table

Cut nested instead (held in the saw at the angle it hangs) and there is no bevel at all: the mitre is the flat-trim figure from the first table, which is 45° at a square corner.

Checked against the published tables

Mitre / bevel. Small differences are rounding in the published table.

UK coving profiles

Blade for the material

Getting the cut you calculated

• ▸SAFETY, read this before the angles. A mitred offcut is a wedge trapped between the blade and the fence, and it is the classic mitre saw ejection case. Let the blade come to a complete stop before you raise the head, every cut, no exceptions: the manual says always let the blade come to a full stop before raising the arm, and keep your hands in position until the trigger is released and the blade has stopped. Clamp the workpiece rather than hand holding it. Clamp anything that would put a hand within 152mm of the blade, and do not perform any operation freehand, meaning with the piece not supported by both the table and the fence. Keep both hands at least 150mm from the blade and never cross an arm over it. Cut short pieces off a long board against a stop block instead of holding a short piece. The DWS780 manual does not print a minimum workpiece length, so we are not going to invent one, but its own labels say clamp small pieces before cutting, and a coving return or an architrave head is exactly the size it means. Check the lower guard closes freely before each session, make a dry run with the power off before any new setting, and wear eye, hearing and respiratory protection.
• ▸Check the saw is square before you trust any calculated number. The fence arithmetic is this: a fence 1 degree out of square puts 1 degree into each half of the joint, so 2 degrees across the mitre, and 125mm multiplied by tan 2 degrees is about 4mm of open joint. Call it 4mm on 125mm coving and about 5mm on 150mm. You need roughly 170mm of face before a 1 degree fence error reaches 6mm. Either way it is visible from the doorway. Check the blade against the fence and the blade against the table before you start, including on a brand new saw, and run the manufacturer's mitre scale and bevel pointer adjustments. On a saw with crown pawls, also check the bevel pointer reads exactly 22.5 when the head is tilted fully left against that pawl, because that is the reference the crown pawls are set from.
• ▸Check the answer is a setting your saw can actually reach, before you walk to the saw. The compound numbers for sharp corners go a long way past the stops on most machines. A 45 degree wall angle needs a mitre of 56.07 at 38 degree spring, 59.64 at 45 degree spring and 62.27 at 52 degree spring, and bevels of 46.72 and 40.79. A DWS780 reaches 50 degrees mitre left and 60 right, and 49 degrees bevel both ways, and that is a large 305mm machine. Many of the 216mm saws that dominate UK sites are single bevel, tilting to somewhere around 45 to 48 degrees one way and barely at all the other, so check your own rather than assuming. Treat about 45 to 50 left and 57 to 60 right as the mitre ceiling and 45 to 49 as the bevel ceiling unless you have checked. When the answer is out of range, do not force the head past a stop and do not freehand it. The nested fallback does not save you either, because a 45 degree wall angle nested needs 67.5. The real fallbacks are a hand mitre box or a purpose built jig, cutting the corner in two passes, or a corner block.
• ▸Zero on the mitre scale means a square crosscut, and a 45 degree mitre reads 45. DeWalt describes mitre crosscuts as made with the mitre arm at some angle other than zero, settable anywhere from zero to 50 degrees left or 60 degrees right. Wayne Drake names the two scale types: the complement of the face angle scale, which starts at 0 and runs to 45 or more both ways, is what every modern saw uses, while the older face angle scale started at 90 and ran down to about 45. That difference is the whole reason the folk rule, measure the corner and halve it, gives the wrong answer on an out of square corner. On a 0 start scale the setting is (180 minus the wall angle) divided by 2.
• ▸Bevel means the blade tilting out of vertical, mitre means the table rotating, and bevel direction matters when you buy. A single bevel saw tilts one way only, so to cut the opposite hand of a compound joint you have to flip the workpiece end for end, and for coving that means the ceiling edge ends up where the wall edge was, so re-mark it before you cut. A dual bevel saw such as the DWS780, 49 degrees left and right, lets you cut both hands without flipping, which is the main reason people buy them for crown work. None of this matters for plaster coving, which is cut nested with the bevel at 0 all day.
• ▸Detents, also called positive stops or latch points, are the spring loaded notches at common angles. The DWS780 has mitre detents at 0, 15, 22.5, 31.6, 45 and 60 degrees and bevel stops at 0, 22.5, 33.86, 45 and 49. The 31.6 mitre and 33.86 bevel detents exist for one job only, cutting American 52/38 crown lying flat. The bevel pawl is reversible: flip it so the 30 degree text faces up and the saw stops at 30 for 45/45 crown instead, which is a manufacturer level confirmation that 45 degree spring crown at a square corner needs a bevel of exactly 30.00. For UK work those factory detents are mostly decoration. Plaster cove is cut nested at mitre 45, bevel 0, where the 45 detent is the only one you touch. The 35.26 and 30.00 pair is for 45/45 TIMBER crown lying flat, and 35.26 has no detent on any saw, so it has to be set by eye between the 35 and 36 marks.
• ▸Compound versus sliding compound. A compound mitre saw rotates for the mitre and tilts for the bevel, but the head only drops, so crosscut width is limited to roughly the blade diameter. A slider adds rails so the head pulls out and pushes through, which is what buys the width: a 305mm DeWalt slide manages 112mm high by 231mm wide, or 349mm wide at 76mm high. For trim work the width almost never decides it. What decides it for coving is how far the piece stands up the fence, which is the next note.
• ▸Nested coving capacity is set by how far the coving stands up the fence and out across the table, not by crosscut width. A cove sits at 45 degrees, so it occupies its nominal size divided by root 2 in each direction: about 71mm for Gyproc Cove 100 and about 90mm for Cove 127, plus whatever packer you put behind it. Check that against your saw's rated vertical capacity before you start, because on many 216mm machines, which are the common UK size, neither cove will clear it, and the job belongs in a coving mitre box or on a larger saw. The DWS780 is separately rated to hold 171mm of moulding vertically against the fence at a 45 degree mitre, so a 305mm machine takes either cove without thinking about it. Capacity also falls the moment you angle the saw, which is why the DWS780 goes from 112 x 231mm at 0 degrees mitre to 112 x 147mm at 45. You only move to a flat compound cut when the moulding is too wide to sit nested, and it is the wrong move for plaster coving in any case, since cove has no flat back to lie on.
• ▸Kerf allowance when cutting to a pencil line. A 216mm or 254mm blade runs roughly 2.6mm kerf thin and about 3mm standard, and the kerf is printed on the blade itself, so read it rather than guessing. Always cut on the waste side of the line, so the whole kerf sits outside your mark rather than straddling it. DeWalt's technique for hitting a line exactly is to match the angle as close as you can, cut deliberately a little long, then measure from the pencil line to the cut edge to work out which way to nudge the mitre before recutting. For coving there is a trap: the waste side flips between the internal and the external cut of the same corner, so work out which piece you are keeping first and then decide which side of the line to cut. With a 3mm kerf on a 71mm drop, one cut on the wrong side of the line is most of a visible gap. Cut the first piece of any new corner at least 25mm long.
• ▸Saw scales are in whole or half degrees and compound answers are not, so a calculator has to say how to set them. Wayne Drake's guidance is to interpolate by eye: if the answer is 32.8 degrees set the pointer about 80 percent of the way between 32 and 33, and do the same for the bevel. He publishes to one decimal rather than rounding, because rounding makes a 93 degree corner and a 94 degree corner look identical, both 30 mitre and 33 bevel, when they are genuinely different settings. Print the fraction next to the number rather than making the user work it out: 33.86 sits 86 percent of the way from 33 to 34, 35.26 sits about a quarter of the way from 35 to 36. Then cut a test piece, because the pointer is only as honest as the last time you checked it.
• ▸Reflex and external corners. An external corner can be entered as its reflex angle and the arithmetic still works: 267 degrees gives a mitre setting of 43.5, because 360 minus 267 is 93 and (180 minus 93) divided by 2 is 43.5. The sbebuilders tables pair every corner with its reflex partner in the same row, which is the right model here: a 90 degree and a 270 degree corner take identical mitre and bevel settings and differ only in which side of the cut you keep. Say that out loud in the output, because keeping the wrong side of the cut is a more common error than getting the angle wrong. For 45/45 timber crown cut flat, the external 90 degree case, reflex 270, is mitre 35.26 and bevel 30.00, the same as the internal, and external 135, reflex 225, is 59.64 and 40.79, which is past the mitre range of most saws.
• ▸Coving mitre boxes are a fixed 45 degree tool and that is a feature. Because a nested cut at a square corner is 45 degrees regardless of spring angle, one box handles Gyproc Cove 100, Cove 127 and every foam profile in the sheds, and it does it without dust, without a blade change and without a power lead across the floor. The corollary is that a plain box cannot handle an out of square corner at all, which is exactly where a mitre saw or this calculator earns its keep. For bays and splayed corners you need a box with the 135 degree slot in it as well as the 45, or a saw.

Best mitre saws in the UK →

How it is done here

The short answer for UK coving, before anything else

Square corner, any UK cove, any size, any brand: mitre 45 degrees, bevel 0, cut in position in a coving mitre box or nested against the fence of a mitre saw. Out of square corner: mitre (180 minus the measured wall angle) divided by 2, bevel still 0. An 87 degree corner is 46.5, a 93 degree corner is 43.5. The spring angle changes neither number. That is the whole reason one 45 degree coving mitre box handles Gyproc Cove 100, Cove 127 and every foam profile in the sheds as well. Spring angle only matters if you are cutting the coving lying flat on the saw table, and you should not be doing that with plaster cove at all.

Coving goes in the box upside down and backwards

The base of the box or the table of the saw is standing in for the ceiling and the side or the fence is standing in for the wall, so the piece sits inverted and reversed from the way it will hang: ceiling edge down, wall edge up against the fence, decorative face towards you. DeWalt describes exactly the same position for crown on a mitre saw, the bottom of the moulding, the part that goes against the wall, against the fence, with the top of the moulding resting on the table and the angled flats on the back resting squarely on both. Before you cut anything, pencil CEILING on one edge and WALL on the other, and always mark your length on the wall edge. If you pack the piece to stop it rocking, use the same packer for every cut on the job, because a packer that moves changes the angle.

Never cut plaster coving lying flat, and what the flat compound numbers are actually for

Plaster cove is always cut in position, never lying flat. DeWalt's own precondition for the flat compound method is that the moulding lays flat with its broad back surface down on the saw table, and a cove has no broad flat back, only two narrow lands at the edges. Laid face up it rests on two thin lines, rocks under the blade, and cannot be held as the same manual demands: never make any cut unless the material is secured on the table and against the fence. The flat compound figures belong to timber and MDF crown mould, which does have a flat back. For those, at a square corner, 45/45 crown needs mitre 35.26 and bevel 30.00, and American 52/38 crown needs mitre 31.62 and bevel 33.86. If you are cutting timber crown, measure its spring angle first rather than trusting the label.

Which end of the cut to keep, which is a more common mistake than getting the angle wrong

Nested, with the ceiling edge on the table and the wall edge against the fence, DeWalt publishes the whole table. Piece running along the left hand wall: internal corner, mitre right 45, save the right side of the cut. External corner, mitre left 45, save the right side. Piece running along the right hand wall: internal corner, mitre left 45, save the left side. External corner, mitre right 45, save the left side. The pattern is worth memorising: on the left hand wall you always keep the right piece, on the right hand wall you always keep the left piece, whatever kind of corner it is. For timber crown cut flat, 52/38 only: left wall internal is bevel left 33.9 with the mitre table right 31.62, save the left end. Left wall external is bevel right 33.9, mitre left 31.62, save the left end. Right wall internal is bevel right 33.9, mitre left 31.62, save the right end. Right wall external is bevel left 33.9, mitre right 31.62, save the right end.

Internal and external coving corners, which edge runs long

At an internal corner the ceiling edge is the shorter one, so the cut leaves the ceiling edge short and the wall edge long, and you reverse the cut direction for the other side of the same corner. At an external corner it is the other way round and the wall edge is short. Said as a measuring rule rather than a cutting one: measure internal corners to the long point, which is the wall edge, and measure external corners to the short point. On Gyproc Cove 100 the ceiling edge finishes about 71mm short of the wall edge at an internal corner, which is also how far out your guide line will be if you strike it at 100mm instead of 71mm.

Where to strike the guide line on the wall, and why cove is different

The instinct is to mark the wall a distance from the ceiling equal to the size of the coving. That is right for a flat or stepped profile and wrong for cove, because cove runs on the diagonal and drops its nominal size divided by root 2. Gyproc Cove 100 drops about 71mm and Cove 127 about 90mm. Strike a 127 line at 127mm and you are 37mm out, the coving will not reach it, and you will have chased the line round the room before you notice. The safest method on any profile is to hold an offcut into the corner, mark where the bottom edge actually lands, and use that.

Out of square corners, and the folk rule that gets it backwards

Measure the actual corner with a digital angle finder or a sliding bevel, do not assume 90. Then on any modern mitre saw the setting is (180 minus the wall angle) divided by 2. An 87 degree corner needs 46.5 on each piece, a 93 degree corner needs 43.5. This is the single most common arithmetic mistake in trim work, because the folk rule everyone repeats, measure the corner and halve it, is only correct on the older style of saw whose scale starts at 90 and counts down. Every saw sold today has a scale that starts at 0 and runs both ways, so you subtract from 180 first and then halve. Wayne Drake's worked example is an inside 93 degree corner giving 43.5, not 46.5. This rule is for nested or upright cutting only; timber crown lying flat needs the full compound calculation. The low tech version for site work is to stand an offcut in the corner, note the real angle, and split the cuts unevenly, say 43 and 47 rather than 45 and 45.

Walls that lean, which is a different problem from walls that are out of square

Everything above assumes the corner is square in the vertical plane as well as in plan. In older UK stock, Victorian and Edwardian terraces in particular, and in anything with lath and plaster over uneven studwork, walls lean. A wall out of plumb changes the effective spring angle along the run, and an external corner that is out of plumb will open a flat 45 degree skirting mitre at the top even when the plan angle is a perfect 90. Two things follow. Check the corner with a level before you cut, and check it at the height the moulding is going, at coving height for coving and at the floor for skirting, not at whatever height is comfortable. If the corner leans, an external skirting mitre becomes a compound cut: keep the mitre at (180 minus the plan angle) divided by 2 and tilt the bevel by the lean angle. At the very least, when a plan-perfect mitre still gaps at one end, this is what you are looking at.

Measuring a corner when you do not own an angle finder

Hold two offcuts into the corner so each one beds against its own wall, scribe along both onto the floor or onto a piece of card, and bisect the marked angle. Or set a sliding bevel into the corner, lock it, and lay it on a printed protractor. Either way you end up with the real wall angle, which is the number the calculator wants. Do the bisect at coving or skirting height, not at whatever height is comfortable, and remember the point above: the answer is (180 minus that angle) divided by 2, not half of it.

Bay windows and splayed corners, which the UK has more of than anywhere

The canted bay of a Victorian or Edwardian terrace is normally set out on a 45 degree splay, which gives a 135 degree internal wall angle and a 22.5 degree mitre on each meeting piece of skirting or architrave. The other two common splays are 30 degrees, giving a 150 degree wall and 15 degree mitres, and 60 degrees, giving a 120 degree wall and 30 degree mitres. For coving in the same bay, cut in position, it is the same arithmetic: (180 minus 135) divided by 2 is 22.5, bevel 0. A plain coving mitre box only cuts 45, so a bay needs either a box with the 135 degree slot in it or a mitre saw. Cut the short bay returns last and leave them at least 25mm long, because a short piece that is short is scrap.

Regular polygons, planters and frames, including the 22.5 degree octagon

For a regular shape with equal sides the setting is 180 divided by the number of sides. Three sides 60, four sides 45, five sides 36, six sides 30, seven sides 25.7, eight sides 22.5, nine sides 20, ten sides 18, twelve sides 15. DeWalt prints this table and adds the caveat that decides whether your planter closes up or not: 180 divided by n is the MITRE if the material is cut standing vertically against the fence, and the BEVEL if it is cut lying flat. Get that the wrong way round and an octagon comes out as a very neat pile of firewood. Two 22.5 degree cuts make the 45 degree turn and close the 135 degree internal corner, which is why the octagon number and the bay window number are the same. For setting out, side length from the internal across-flats width W is W multiplied by tan(180/n): 0.7265 x W for a pentagon, 0.5774 x W for a hexagon, 0.4142 x W for an octagon. Allow 10 per cent waste and cut one test joint first.

Scribing internal corners on skirting instead of mitring them

Scribing is the professional standard for internal corners on skirting, and it matters more in the UK than almost anywhere, because the walls of an older terrace are rarely square and rarely flat. A scribed joint will not open as the timber moves and it copes with a corner that is not 90 degrees without any adjustment at all. The method: run the first board square into the corner. On the second board swing the MITRE TABLE to about 43 degrees with the blade vertical, bevel 0, and cut across the face to reveal the profile line. Cut it as an internal mitre, so the back of the board stays long and the face is the short point; if the face came out longer than the back you have cut the wrong hand and the revealed line is useless. Pencil the line where the mitre face meets the skirting face. Back cut the flat section at mitre 90 with about 5 degrees of tilt to undercut it, then cope the curved part with a coping saw held angled backwards. Test fit and take the high spots off with a half round file. Working left to right, clockwise from the door opening, the scribe always lands on the left hand end of the board. Note the wording trap: the 43 degrees is the table, not the tilt.

External corners on skirting, architrave corners, and return ends

External corners on skirting are mitred, not scribed: 45 degrees on both pieces, PVA on the mitre faces, then cross nail or pin through the joint so it cannot open. Architraves are mitred at every corner. A door gives you two legs and a head: the bottom of each leg is cut square where it meets the floor or the skirting, the top is a 45 degree mitre. Measure between the corner quirk points, which is the short length of the mitre, and add 5mm. Run a consistent quirk, normally 5mm, and a consistent quirk matters more than a perfect mitre, because the eye follows the quirk line and not the joint. Windows take four pieces, worked anticlockwise from the right hand side. Glue every architrave mitre. Where skirting or architrave stops in mid air, at an opening or a hearth, close the end with a mitred return: cut the run at 45, then cut the small triangle off the same board's 45 and glue it on, so the profile wraps round instead of showing raw end grain or bare MDF core. Cut that triangle off a long board with a stop block, never as a loose offcut held by hand.

UK skirting board heights, thicknesses and profiles

UK skirting is sold in a standard ladder of heights: 44, 58, 68, 94, 119, 144 or 145, 168 or 169, 194 and 219mm. If you have to pick one without measuring, 144 or 145mm is the default in most UK homes and the safest single answer. 94 to 119mm reads as modern or new build, and 194 to 219mm belongs to period property, barn conversions and high end work. Standard thicknesses are 15, 18 and 25mm, and standard lengths 2.4, 3.0, 4.4 and 5.4m. The profiles you will actually meet are torus and ogee, with chamfered, bullnose, pencil round and square edge behind them; B&Q, Wickes and Screwfix carry torus, ogee, chamfered and bullnose in MDF at 119mm and 144 or 145mm. Match the architrave profile to the skirting profile so the two meet cleanly at the bottom of the door lining.

UK architrave sizes

69 x 18mm is the UK standard architrave, with 95 x 18mm as the wider option for taller rooms or heavier doors. Thicknesses run 15, 18, 19 and 25mm and lengths 2.2, 2.4, 4.4 and 5.4m, which means one 4.4m length usually covers both legs of a standard door and a 2.2m length does one leg with very little waste. The profile names are the same set as skirting, ogee, torus, chamfered, bullnose, pencil round and square edge, so that architrave and skirting match where they meet. Order the head from the same pack as the legs: a head cut from a different batch of primed MDF can sit a fraction proud and the mitre will show it.

UK timber sizes, CLS against regularised

CLS is the UK's standard stud material, machined smooth with radiused corners, and comes as 38 x 63mm (sold as 3x2), 38 x 89mm (4x2) and 38 x 140mm (6x2). Regularised or sawn carcassing is the square-edged alternative, sized nominal 47 x 100mm finishing at about 45 x 95mm, plus 47 x 75, 47 x 150, 47 x 175, 47 x 200 and 47 x 225mm. Planed timber, PSE or PAR, loses about 3mm per planed face from the sawn size, which is why a 4x2 never measures 100 x 50. Do not mix CLS and regularised in the same wall: the sections are different depths and the rounded corners on CLS leave a line at every plasterboard joint. When you are cutting a stud wall to length on a mitre saw, cut off a long board against a stop block rather than measuring each piece, and check the saw is square first, because an out of square stud twists the whole wall.

Out of square door linings, which is not the same as an out of square wall

Check the lining with a square and note the real angle, then adjust the architrave mitres to suit, 43 and 47 rather than 45 and 45. The two pieces have to add up to the real angle but they do not have to be equal halves, and it is usually better to split the error unevenly so the quirk stays constant down both legs. A consistent 5mm quirk reads as a straight line from across the room. A joint that is half a degree off does not.

Long point, short point, and how much length a mitre adds

On any mitred end the long point sits past the short point by the material thickness multiplied by tan(mitre). On 18mm skirting at a 45 degree external corner that is 18mm. In a bay at 22.5 degrees it is only 7.5mm. That is the number you need whenever a source says measure to the long point and does not say how much longer that is. For coving, measure to the wall edge at an internal corner and to the ceiling edge at an external one, and cut the first piece of every new corner at least 25mm long, because a mitre that is 1mm short at the ceiling cannot be recovered and a mitre that is long can.

Period plaster cornice, which you do not mitre at all

An ornate Victorian or Edwardian cornice, run in situ or cast in fibrous plaster, is a different job from coving out of a shed. You do not mitre it and expect it to line up: the enrichment, the dentils, the egg and dart, will not meet across a mitre however accurately the angle is cut. The traditional answer is to cut the plain grounds square, form the corner with a prefabricated corner piece or a hand-mitred and modelled joint, and make good with plaster rather than filler. If you are matching an existing run, take a profile off it with a contour gauge before you order anything, because sections vary house by house and even room by room. NOT SOURCED: this is general conservation practice rather than a manufacturer instruction, and a specialist fibrous plaster supplier should be the one to confirm a profile and a corner detail.

Raked and cathedral ceilings, which this calculator does not cover

On a rake the coving sits on the ceiling exactly as it would if the ceiling were flat, so the discrepancy shows up on the wall and not on the ceiling, which means a bigger gap to fill at the bottom of the run than at the top. Here is the part that matters and that most write-ups leave out: the profiles genuinely do not match at a rake. A stock cove run up the rake cannot mitre cleanly into the same stock cove on the level run. Either the level run has to be rolled or tipped out of position, which distorts it, or a second profile has to be developed for the raking piece. That is why the usual site fix is what it is, a 45 degree cut with the gap filled in finishing compound, or the raking coving fitted first and the bottom of the lower run kicked out with about 5mm left to fill. It is not a bad habit, it is what a stock profile allows. A rake corner is also a horizontal turn and a vertical turn at the same corner, so it is not one angle, and this calculator does not handle it. Work from a ceiling slope table or order a raking profile. If your pitch is given as a ratio, degrees equals atan(rise divided by run), so 1 in 20 is 2.9 degrees and 1 in 10 is 5.7 degrees.

Shadow gap and stop bead junctions have nothing to mitre

Where the wall meets the ceiling in a shadow gap, a plaster stop bead or a shadowline detail there is no sprung coving, no spring angle and no compound mitre. The corner is formed with a metal or PVC bead and finished in plaster, not cut on a saw, and the same is true of a plain square set junction where the board simply runs into the ceiling and the joint is taped. Do not look for an angle here, and be careful of any calculator that hands you one: feed a 0 degree spring angle into the compound formulas and they return a confident mitre of 0.0 and a bevel of 45.0, which is a real-looking answer to a question that does not exist.

Bowed and wavy walls, uneven floors, and bowed timber

A flat wall and a level floor are rare in any UK house and unheard of in an older one. Ranked fixes for a wavy wall: scribe the skirting to the wall profile with a compass or a scribing tool, fill with grab adhesive for minor undulation up to about 3mm, pack low spots with timber shims, or use flexible skirting for a genuinely curved wall. For a gap under the skirting where the floor is not level: scribe to the floor, which is best on solid floors, fit scotia or quadrant over it, or caulk variation up to about 3mm. There is a specific plasterboard problem worth naming, skirting dip, where the board tips inward at the bottom because it sits in the tapered edge of the sheet. Drive screws into the studs at skirting height so the heads sit flush with the main wall surface, then let the skirting bear on the screw heads instead of sinking into the recess. On brick and masonry, mark the fixings by driving a nail through the skirting face, drill the holes, plug them flush, and use grab adhesive plus screws, with softwood rather than MDF because MDF does not hold fixings as well. On dot-and-dab plasterboard, fix through to the blockwork or to a batten rather than to the board. Separately, the timber itself: a bowed board must go on the saw so the bow cannot close on the blade near the end of the cut. DeWalt prints a right way and a wrong way for this. Set it up wrong and the cut pinches the blade and the piece kicks.

Test cut on scrap, every time, before the real length

Both the manufacturer manual and the compound mitre reference say this in capitals. DeWalt: the angles for crown moulding are very precise and difficult to set exactly, they shift easily, and very few rooms have exactly square corners, so pretest with scrap. The same goes for coving with one extra reason: coving adhesive has a limited working life once it is mixed or opened, so cut and check every piece for fit before you start sticking anything. Once the adhesive is going off you will accept a joint you would have recut ten minutes earlier.

Fitting the last piece and springing the mitres in

Install the shorter lengths of coving first, then fit the longer lengths by bowing them out slightly to spring the mitres into place. Butter all mitres and butt joints with coving adhesive before pushing them home and clean the excess off straight away with a filling knife and a damp brush, because set adhesive comes off with a chisel and takes the paper facing with it. Temporary nails or pins along the top and bottom edges hold the run while it sets. Follow the setting and support times printed on the adhesive you are actually using rather than a figure from somewhere else, because ready-mixed and powder coving adhesives behave differently.

Measure every corner, and measure the moulding too

Do not trust the label on the moulding. Wayne Drake documents stock labelled 52/38, which implies a 38 degree spring angle, that was actually 45/45, and warns that some crown labelled 38 or 45 is undercut at the factory by up to 3 degrees, giving a real spring angle of 35 or 42. Three degrees of spring angle error moves the mitre and the bevel by 1.5 to 1.8 degrees each, and on a 125mm face that is a visible gap at the ceiling. He also makes a point that trips people up, that a moulding has two spring angles depending on which edge you decide is the bottom, so measure it the way the piece will actually hang. Method: hold the bottom edge of the moulding flat against a straight edge standing in for the wall and measure from the back of the moulding to that straight edge, or measure the angle at the back of the piece and subtract from 180. None of this applies to plaster cove, which is cut nested where the spring angle drops out of the sum entirely.