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First you need to check you have all the right Tools for the job as follows.
Bear in mind most of the Tools you will find in DIY Stores are inferior to proper Tools and will make the job many times more difficult than it need be.
Small enough to cut a Mortice in a Post but large enough to slice end grain if needed.
Expect to pay £10 for a single decent Chisel.
Tenon Saw or preferably a Japanese Hassunme Cross Cut Saw.
The Tenon Saw is mainly used for Cutting the Tenons on the ends of the Handrails and costs around £12 for a half decent type but the Japanese Saw has a replaceable Blade and although costs more to start with it does a far better job.
Electric chop Saw (not a necessity but if you are fitting Oak etc its going to be hard work without it)
They can be purchased pretty cheaply in the DIY Stores but again don’t expect them to be that fantastic for the Money.
4mm and 6mm Drill bits
10mm Flat bit.
50mm Hole Saw
You can get a decent make (Bosch) for just over £5 on ebay.
This is not a necessity but makes the job easier.
6 or 7 mts of Rope or Sash Cord.
(This will be used to loop around the Newel Posts to pull them tight against the Handrails while the Glue is setting).
150mm Cramps (2 should do but 6 is ideal)
25mm Panel Pins
PVA White Glue and Polyurethane five minute Glue.
Building Regulations in England state that a Domestic Handrail needs to be a minimum of 900mm high so the existing square Newel Post needs to be cut off at the correct height to achieve this.
We always start with the Newel Post at the top of the Stairs, cut this post off 200mm above the Floor level.
Then at the front of the Post where the Stair String enters the Post measure down to the top edge of the Stair String, this will be between 190mm and 210mm depending on the angle of the Stairs.
Whatever this measurement is the next Post down the slope will have to be cut off at the same height, (This applies to most situations).
Now you have to drill a 50mm hole, 80mm deep in the top of both of the stub Posts you now have.
To do this insert the 50mm Hole Saw in your electric Drill and place it in the centre of the Post, Hole Saws have a pilot Drill bit in the centre to help guide the bit when drilling.
Start the Drill slowly and push the hole saw about 2mm into the wood.
Now remove the Hole Saw and insert a 6mm standard Drill Bit.
With this bit Drill a series of Holes within the area you marked with the 50mm bit and take out as much of the waste as you can.
Leave some wood in the centre of the Hole as you now have to use the 50mm Hole Saw again to cut a neat Hole, if you cut out the middle section their is nothing for the pilot bit to cut in to.
Hole Saws don’t like to cut end Grain of Wood so you will only be able to cut about 8mm deep at a time as the teeth will need unclogging, be careful as they get very hot.
You should now have a clean Hole in each Post, don’t worry if the hole appears to big or uneven, it does not matter too much.
Now try both New Posts in their respective holes and check each one with a spirit level, if the Post will not go exactly Plumb then a small amount will need to be removed from one side of the hole to make the Post Plumb, again don’t worry if the Post is too loose at this stage. (When using the Level on the Newel Posts, only rest it on the top square section of the Post and don’t try and level down to the Base Post. This is because the existing Base may not be Plumb in itself so you will get a wrong reading on the Level.)
With the two Post stood in the holes the 900mm height of the Handrail should now be marked on to the Blocks at the top of the Posts. The 900mm should be from the front edge of the Stair Treads and measured vertically but to make thing easier you can measure 900mm from the top edge of the Stair String and as the Stair String usually stand around 30mm above the Tread Nosing's this will give you a Handrail height of around 930mm.
This extra 30mm helps allow for any Carpet thickness on the Stair Treads and ensures you are always over the minimum height required.
The original and best way of fixing the Handrails to the Posts is by using a Tenon fixed in to a Mortice.
The first thing is to cut the Mortice at the correct height and then cut the Tenon.
Cutting Tenons on the Sloping Handrail is always the most challenging part of fitting Stair Parts but it can be made easier using the following technique.
If fitting between two Posts, stand the two Posts in their respective Holes in the Base Posts and level them by holding a spirit level on the square section of the Post.
Hold them level with battens and Cramps. (Battens across the Stairwell from wall to wall can then be cramped to the Post).
Hold the Handrail alongside the Posts making sure the top of the Handrail lines up with the top of the Mortice in the Post, this can either be cramped to the Posts or use a couple of Helpers.
When you are satisfied the Handrail is in the correct place, mark one Shoulder against the Post and the same at the other end of the Handrail.
Remove the Handrail and transfer the lines to the other side of the Handrail.
Now cut the Tenon on one end of the Handrail using a sharp Tenon Saw or preferably the Japanese cross cut Saw . At this stage the Shoulder cut does not have to be perfect. The Japanese Saw is used by pulling towards you rather than away from you with normal Handsaws, because of this the Blade is made very thin which in turn makes the cutting easier.
This action takes a few minutes to get used to, so try a few cuts in some scrap wood before cutting the Handrail.
If you try to push the Saw it will buckle so remember to always pull.
If you are satisfied with the fit in one Mortice then the other Tenon can be cut, but add on about 4mm so the Shoulders will be too long at this stage.
When both Tenons are cut put the Handrail in position, if the Tenons are too tight it will stop the Posts going to the Plumb position so a little loose at this stage is a good thing.
Now loop a piece of Rope around the Ball on the top of the Posts and insert a small piece of Timber or a large Screwdriver in to the Rope and twist it until it is tight enough to pull the Posts tight against the Shoulders of the Tenons.
With the Rope giving the pressure you can now insert your Saw between the Shoulder and the Post and trim the Shoulder to give a perfect joint, if the Handrail is too long just cut again until you lose the 4mm that was added on previously.
If you put a piece of Masking Tape one one side of the Saw teeth it will stop the Teeth scratching the Post.
(As long as you are cutting straight, the Japanese Saw makes such a fine cut it rarely scratches the Post.)
Now that you know everything fits, remove the Posts and Handrail.
You now have to Drill a 10mm hole through both Mortice's for the Dowel that will pin the Tenon in position.
The centre of the hole needs to be approx 15mm from the face of the Post.
Using the 10mm flat bit Drill through until the point just appears on the other side and then drill the rest of the hole from the other side, this avoids any splitting.
Alternatively you can cramp a scrap piece of Wood on the other side of the Post and drill straight through in to the scrap which stops any tear out.
Now put the first Tenon in its Mortice and place the 10mm bit in the hole and press in so that the point of the bit marks the Tenon.
You now have to withdraw the Tenon and drill the 10mm hole through it but NOT in the place that you have just marked.
Mark a new point 3mm closer to the Shoulder and Drill the hole in this position, this slight offset will help the Handrail pull in tight when the Dowel peg is driven in. Now do the same with the other Tenon.
You should be now ready to Glue everything together.
When fitting Posts it is best to fit them both at the same time as fixing one Post first can make it awkward fitting the Handrail.
The Glue to use will be the Polyurethane five minute Glue, their is two types of this Glue, Rapid set and normal set.
It is not always easy to know how long the Glue will take to set as it varies by make but as a general rule the quick setting Glue in a tube used in a sealant Gun will start to set after about five minutes whereas the Polyurethane Glue in liquid form from a bottle will start to set after about twenty minutes.
Both types will start to foam and expand as it sets which makes a really strong joint and fills up any gaps if the 50mm hole in the Base Post has been made too big.
The Glue when expanding will squeeze out a lot but don’t be tempted to wipe it off, let it set and it will peel of easier when dry.
Before you put the Glue in the Holes of the Base Posts Drill a 10mm hole about 10mm deep in one side of the Base Post about 25mm from the top, this hole is for a Wooden Pellet to cover the Screw that you will put through the Base Post and in to the Spigot because as the Glue expands it will tend to lift the Newel Post out of the Hole.
After drilling the Pellet hole continue on through with a 4mm bit.
Now it is just a case of putting Glue in both Base Post Holes and both Handrail Mortice's with a small amount on the Shoulders of the Handrail. If this is your first attempt at fitting Posts and Handrails you should definitely use the Liquid form of Polyurethane as it will give you more time to work with it.
The amount of Glue to use is hard to explain if you haven’t used Polyurethane before use no more than you would with ordinary Glue.
With the Glue applied and your helper holding one Post and you holding the other put the Posts on to the ends of the Handrails and then lower both Posts in to the Holes of the Base Posts.
Put the Rope back on to the Posts and tighten as before.
The 10mm Dowel Pins can now be hammered in to the Blocks and through the Tenons, the Dowels need to be cut around 18mm shorter than the thickness of your Newel Post, this is so that the Dowel can be knocked below the surface using another piece of Dowel and leave room to insert a Wooden Pellet. (glued in , but don’t clean it off until the Glue is set.)
With all that done all that remains is to Plumb the Posts, both ways using temporary battens and cramps.
We will usually cut a piece of batten from Wall to Wall and just cramp the Posts to the Batten.
Ideally this should be left overnight but if you have used the Polyurethane Glue, you should be able to remove the Battens after one Hour.
The Baserail can now be cut between the Base Posts and fixed with 50mm Screws to the Stair String, make sure it is positioned in the centre of the Base Post.
If you have a Chop Saw it is fairly easy to cut the Baserail to length always allow an extra 5mm on the length, you can always trim it again if it is too long.
Fitting the Spindles
First cut one Spindle to length, this is best done by cutting the angle on the bottom and sit it on the Baserail tight up against a Newel Post and then mark the angle under the Handrail. Don’t forget the mark is not allowing for the Grooves in the Baserail and Handrail so add on around 30mm to the length.
Stand the Spindle in position at one end and trim it until it fits.
Now try the Spindle at the other end, if you haven’t quite got the Handrail the same height each end the Spindles can be cut to suit. You should keep this Spindle as your Template for cutting the rest.
Fit a temporary Spindle in the centre of the Handrail as most Handrails will dip slightly in the middle, so look down the Handrail to check their is no sag but also don’t make the temporary Spindle too long or the Handrail will curve up in the middle.
The spacing of the Spindles have to be close enough so that a 100mm sphere cannot pass through them, the perfect gap between the square sections of the Spindles is normally no more than 78mm horizontally and this will normally give you a fillet length of around 100mm but this only works if everything is fairly standard.
The first gap against the Post should be smaller (around 55mm) as the deeper contour of the Posts means a larger gap.
The following is the way we work out our Spindle spacing's.
Horizontal measurement between Posts, say
Deduct 110mm (this is the 55mm first gap each end against the Post)
Deduct the thickness of one Spindle, say 45mm
Divide by 123mm (this is the ideal gap of 78mm and the thickness of the Spindle)
This shows you need 19.87 Spindles (20) (not including the one you knocked off earlier)
So the calculation to give you the correct horizontal gap will be,
2445mm divided x 20 = 122.25mm minus 45mm which is the thickness of the Spindle
All that remains now is to fit all of the Spindles in position.
The spacing fillets and the ends of the Spindles should be Glued with ordinary White Glue.
The Fillets can be Pinned but we always use cramps for around 15 minutes which is usually long enough for the Glue to grab the Wood and the cramp can then be moved along.
This is easy on the Handrail but on the Baserail the cramp would need to be a lot longer.
To overcome this we put the cramp over the fillet and tighten the cramp on to the String, a small wooden wedge can then be inserted under the cramp and pressed on to the fillet.
Doing it this way means their are no Pin holes to fill, especially good if you are not painting the Timber and a better looking job.
Fitting of Stair Parts, especially Handrails is one of the most challenging of jobs for the DIYer but can be easy if time is taken and the job is not rushed.