Which router cutter for stair strings.

[tomba26]

I have a set of stairs to make for a customer and she wants oak strings but mdf treads and plywood risers as it's going to be carpeted.
In the past I have used jigs that I knocked up in the shop but recently purchased a Unika stair jig. It suggests using a 16mm or 22mm dovetail cutter for routing the strings....I've never used a dovetail cutter before for this, only straights. Anyone used them before....any pros/cons or should I just stick a straight cutter in and be done?
Any problems with the dovetail tapering smaller and the strings being hardwood (oak)?
Thanks.

 

[JoinerySolutions]

The idea behind useing a dovetail cutter is so that when wedged up the treads and risers crush the strings wood fibres thus making a gap free joint between said treads/riseres and string.

For MDF treads I would not use less than 25mm thickness.
Check out the Trend catalogue for their stair housing bit, and their instructions download for the way to set up/depth of housing etc.

An accurately made jig and a straight bit will do the job just as well, after all they never dovetailed the housings in the days when all was hand cut.
This stair I made last week, 25mm mdf treads 9mm ply risers and softwood strings, using mdf jig and 1/2" straight cutter.

Rob.

 

[tomba26]

Thanks Rob, I need some new cutters so I'll try some of the 16mm dovetails then. Looks like 16mm will work with my jig for up to 25mm mdf, then it's the bigger (more expensive no doubt) 22mm.

Stairs look good.
Do you always use 9mm ply for the risers (for carpeted/covered stairs) or do you also use 12.5mm?

 

[JonnyD]

I used to use expensive cutters but moved on to these http://www.axminster.co.uk/axcaliber-do ... rod808970/ They seem to last as long as an expensive one and are really cheap.

cheers

jon

 

[JoinerySolutions]

Thanks Rob, I need some new cutters so I'll try some of the 16mm dovetails then. Looks like 16mm will work with my jig for up to 25mm mdf, then it's the bigger (more expensive no doubt) 22mm.

Stairs look good.
Do you always use 9mm ply for the risers (for carpeted/covered stairs) or do you also use 12.5mm?

Depends on what gets specified by the architect. I have used 12mm or 1/2" ply and 9mm and 12mm mdf. Sometimes its all solid timber then its 18mm risers (no point in planing more of a 1" sawn board than neccessary)

Keep in mind when using the dovetailed cutters that they must be plunged fully to required depth before starting your cut and to let the cutter stop spinning before removing from the string or newel otherwise a gouge out of the top face will occur.
My Trend stair jig is over 20yrs old, but I rarely use it due to the sub base not fitting my latest router, I really should get off my backside and make a sub base to fit!
It also bears a scar when I got in a rush and dovetailed a slot out of it, two pack woodfiller fixed that.

 

[tomba26]

Keep in mind when using the dovetailed cutters that they must be plunged fully to required depth before starting your cut and to let the cutter stop spinning before removing from the string or newel otherwise a gouge out of the top face will occur.

That's the bit I'm a little worried about, the strings are solid oak and with a straight cutter I could do it in 2 or even 3 plunges if the cutter was struggling. I would think the dovetail cutter would struggle at full depth with one plunge and routering the strings?

 

[JoinerySolutions]

What size/make router are you using?

 

[GazPal]

That's the bit I'm a little worried about, the strings are solid oak and with a straight cutter I could do it in 2 or even 3 plunges if the cutter was struggling. I would think the dovetail cutter would struggle at full depth with one plunge and routering the strings?

Route to full depth using a straight bit before dovetailing. Both bits should be bearing guided and capable of working to the same template. :wink:

 

[tomba26]

Using a Makita 3612cx 1/2 router, 1850w power. I'm just dubious as to whether it will do full plunge routering on solid oak strings.

 

[bench_monkey]

in our shop we have always used trend 1/2" straights, im not too keen on the idea of dove tails, as long as its sharp a straight would give a flat edge for the tread/rise to sit on. it would also give me more confidence with wedging to, especially with the quality of oaks of late!

 

[JoinerySolutions]

Using a Makita 3612cx 1/2 router, 1850w power. I'm just dubious as to whether it will do full plunge routering on solid oak strings.

Router is man enough. I made loads of stairs with the trend jig and their cutters using Elu177e routers.
I wore out the adjustable nosing piece of the sub base so had a new one made from Duralium :lol:

Route the riser trench first and work around to the tread, check it is all done prior to moving the jig along, they are almost impossible to get located exactly where they came from.
On the strings start at the bottom of the string that would be on your left as you climb the stair and at the top end on the right hand string.
This will reduce the risk of breakout at the corners where tread meets riser.

Rob.

 

[tomba26]

Thanks for the reply Rob/Bench monkey.
With regards the straight cutters, I have loads of 12.5mm kitchen worktop cutters, and I like the idea of using them as I found out yesterday the dovetails are not a stock item at either of my suppliers where I have accounts. I would have to order them and would be looking at wednesday realistically. Ideally I'd like to crack on mon/tues.
So....if I chose to use the 12.5mm straights, would this throw out the jig/sub base/bush combo or can I offset it in a way that would allow these to be used?
It is the Unika stair jig if it helps.....here.....http://www.itslondon.co.uk/pd_UNISTAIRJ ... airJig.htm

Thanks again fellas, the info is very much appreciated.

 

[bench_monkey]

Now, we use one of those! You obviously got the pack with the router base and multiple guide bushes? ie - screw the base to the router and screw the guide bush to that base and follow the shape on the jig? that will be fine. As Rob also said, as long as you go left to right (and turn the jig over when you swap strings ) it will be good enough. A new or sharp cutter is a must with oak however.

Currently have one of the chaps making two flights of solid oak (string/tread+rise) open ended stairs, wall side is a normal string, room side the tread/rise sits on blocks glued/screwed to a 6x3 s/w string with 1" oak glued to it, so you can imgine the fun we are having!!

Tom

 

[JoinerySolutions]

If in doubt do a test run on some scrap or mdf offcut, the critical point is the noseing over hang which needs to be a snug fit. Otherwise no worries just crack on and get that stair done, take some pics as you go for reference and to show future clients and post some here, we love pics. :lol:

Tom sounds like a fun project you got on. These were good fun too!

Have fun!
Rob.

 

[katellwood]

One issue i've always considered with dovetailed router bits for stair trenching is the glue surface, surely if the edge of the trench is tapered and the tread/riser square then the only direct glue contact is where the tread meets the outermost part of the trench, similar with the wedge on the underside. now i appreciate that in softwood strings there will be an element of compression to enhance the glueline however with oak strings this will not be the case.

In essence the wedge and the endgrain of the tread will be holding the stair together

I use a 7/8 dia router cutter and use a separate jig for the tread and riser (this eliminates a 1/4 radius in the internal corner where the tread meets the riser) I then thickness my treads for a a tight fit for the nosing.

I route in two passes utilising the depth stop on my elu 177e

My last staircase

 

[JoinerySolutions]

Nice stair Katellwood. \/

With the Trend sub-base system the gap is not produced, it occurrs when using guide bushes but can be resolved by using a pair of inserts to assist in letting the guide bush make a smooth straight run, no need for two jigs.
While I understand your concern re: dovetailed shoulders in tough woods like oak it really does not pose a problem. In the workshop pics posted above those stairs are dry assembled with lightly wedged treads and risers and one or two screws on the cut string side, no glue! I walked up them as I was assembling them, no issues.
What really holds these stairs together is the wedges, in all honesty there is little need to apply glue to the trenching, the bond strength between tread and riser and the trenched string is minimal, the main bond strength comes from glueing the wedges, it is a much larger surface area.
The frictional bond from a well wedged up tread or riser is extremely secure as you would know from trying to disassemble a stair over enthusiastically wedged up by an apprentice, many stairs I have made have to go to site as "flat packs" to get them in the building. :lol:

So while square edged trenchings are absolutely fine so are dovetailed ones, the bits are not a 1:6 or 1:7 or 1:8 as per a drawer dovetail but a more shear 95/5° (1:6 being 171/9°) depending on where you measure the angle. So on a housing depth of 12mm as suggested by most literature, the gap between the tread and widest point of the dovetailed trench would be 1.05 mm before wedging up and most modern glues would be "gap filling" enough for that if we were really that concerned about it. Anyway thats all a bit technical and put people to sleep so what ever works for you...do. But enjoy it, else it's not worth doing. :wink:
Rob, now going for a Sunday beer! :lol:

 

[katellwood]

Thanks for the comments Rob

I think the most important issue on any solid string stair is to get the taper of the wedge exactly right

 

[JoinerySolutions]

Thanks for the comments Rob

I think the most important issue on any solid string stair is to get the taper of the wedge exactly right

Absolutely! They don't last as long as some I've taken out otherwise. :lol: :lol:

All jokes aside, the interwebby thing chucks up a lot of poor advice, so we need to keep to facts and try to lose some of the misconceptions that we all, at some point, take on board as fact. Wickipeadia is a prime source by the way.
On another forum I wrote about mortice and tenon joints, due to a number of mis-informed posts on the subject and an ex-pat brit quoted Wicki basically calling me a liar! Is he a professional woodworker? No! But believes what he reads first to be gospel. Well, hell the world is definately flat then! :lol:
I loved my Elu routers and was saddened when one 'died' and later the other broke making the newel caps in the pics above. Glad to hear yours are still going strong, great tools.

 

[tomba26]

Fantastic advise folks and some stunning staircases.
Thanks again and I'll post pics when I'm done.

 

[tomba26]

Bench Monkey am I correct in thinking there must be an adjustment made with either the jig/base combo or when marking out the strings if I use a 12.5mm straight cutter? The suggested cutter is 16mm dovetail and I am wanting to use a 12.5mm straight....this gives a 3.5mm difference?